Change search
Refine search result
12 1 - 50 of 68
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Arjmand, Mehdi
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Energy Saving in Crude Oil Atmospheric Distillation Columns by Modifying the Vapor Feed Inlet Tray2011In: Chemical Engineering & Technology, ISSN 0930-7516, E-ISSN 1521-4125, Vol. 34, no 8, p. 1359-1367Article in journal (Refereed)
    Abstract [en]

    Optimization of a typical crude oil atmospheric distillation unit and reduction of energy conservation were carried out through modifying the implementation and change in the flash zone of the tower. A conventional procedure in such units involves the combination of liquid and vapor product of the prefractionation train surge drum upon introduction to the tower. However, it is theoretically illustrated and represented by simulation means that introducing the vapor feed into the upper stages of the distillation column separately can lead to an energy saving of 12.6% in the condenser duty, an increased liquid-to-gas flow (L/G) at certain points of the column, and hence to a reduction in diameter and investment costs of new tower designs of approximately US$ 0.7 million a(-1). The proposal can be put into practice without the need of additional equipments or additional cost of difficult rerouting the streams. An industrial case study of a steadystate crude oil distillation unit is given by simulation provision of AspenHysys (TM).

  • 2.
    Arjmand, Mehdi
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Optimization for energy conservation of crude oil atmospheric distillation columns by modifying vapour feed inlet tray from pre-fractionation train2010In: 2010 AIChE Annual Meeting, 2010Conference paper (Refereed)
    Abstract [en]

    Optimization of a typical crude oil atmospheric distillation unit and reduction of energy conservation were carried out through modifying the implementation and change in the flash zone of the tower. Conventional procedure in such units involves combination of liquid and vapour product of the pre-fractionation train surge drum upon insertion to the tower. However it is theoretically illustrated and represented by simulation means that introducing the vapour feed into the upper stages of the distillation column separately can lead to an energy saving of 12.6% in the condenser duty, increased liquid to gas flow (L/G) at certain points of the column and hence a reduction in diameter and investment costs of new tower designs of approximately 0.7 × 10 6 $/y. The proposal can be put into practice without the need of additional equipments or additional cost of difficult re-routing the streams. An industrial case study of a steady-state crude oil distillation unit is given by simulation provision of AspenHysys™.

  • 3.
    Benavente, Martha
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. National University of Engineering (UNI), Nicaragua.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Martinez, Joaquin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Sorption of heavy metals from gold mining wastewater using chitosan2011In: Journal of the Taiwan Institute of Chemical Engineers / Elsevier, ISSN 1876-1070, E-ISSN 1876-1089, Vol. 42, no 6, p. 976-988Article in journal (Refereed)
    Abstract [en]

    This study is concerned with the use of chitosan produced from shrimp shell waste for the removal of Cu(II), Hg(II), Pb(II) and Zn(II) from gold ore tailing solutions containing cyanide. This work involved the study of equilibrium and kinetic adsorption, the physicochemical characterization of mining effluents and desorption using different regenerating solutions. The experimental results showed that the adsorption capacity of chitosan is a function of the solution pH and that the optimum pH for these metallic ions is 6, except for Hg (pH 4). The equilibrium data were described using the Langmuir, Freundlich, Redlich-Peterson and SIPS isotherm models. The Langmuir equation was used to find the maximum adsorption capacity for Cu (79.94 mg/g), Hg (109.55 mg/g), Pb (58.71 mg)g) and Zn (47.15 mg/g). To determine the rate-controlling mechanism for metallic ion adsorption, pseudo-first-order, pseudo-second-order and the Elovich equation kinetic models were tested with experimental adsorption kinetic data. Tests conducted with gold ore tailing solutions indicated that chitosan is effective to remove these metallic ions above 70%. Desorption studies revealed that the regeneration of chitosan saturated with these metallic ions depends on the type and concentration of the regenerating solution ((NH(4))(2)SO(4), H(2)SO(4), HCl, NaOH and NaCl).

  • 4.
    Benavente, Martha
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Adsorption Kinetic of Copper and Zinc from Binary Solutions using Chitosan2010In: Hydro Process 2010: Proceedings of the 3rd International Workshop on Process Hydrometallurgy / [ed] Marcelo Jo, Juan Patricio Ibáñez, Jesús Casas, Santiago, Chile: GECAMIN, 2010, p. 22-23Conference paper (Refereed)
  • 5.
    Benavente, Martha
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Biosorption of Lead using Chitosan2009In: Advances in Chitin Science, Volumen XI: EUCHIS 2009 / [ed] Franco Rustichelli, Carla Caramella, Sevda Senel, Kjell M. Vaarum, Venice, Italy, 2009, p. 487-492Conference paper (Refereed)
  • 6.
    Benavente, Martha
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Production of Glucosamine Hydrochloride from Crustacean Shell2011In: Advances in Chitin Science, Volume XIII: EUCHIS 2011 / [ed] Valery Varlamov, Svetlana Bratskaya, Irina Yakovleva, Sevda Senel, SAINT-PETERSBURG, RUSSIA, 2011, p. 29-35Conference paper (Refereed)
  • 7.
    Benavente, Martha
    et al.
    National University of Engineering, Nicaragua.
    Sjörén, Anna
    KTH, School of Chemical Science and Engineering (CHE).
    Westergren, Robin
    KTH, School of Chemical Science and Engineering (CHE).
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Martinez, Joaquin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Biosorption of Heavy Metals on Chitosan2007In: Hydro Copper 2007 / [ed] Jorge M. Menacho and Jesús M. Casas de Prada, Santiago, Chile: GECAMIN Ltda. , 2007, p. 283-290Conference paper (Refereed)
  • 8.
    Benavente, Martha
    et al.
    National University of Engineering, Nicaragua.
    Álvarez, Erick
    National University of Engineering, Nicaragua.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Martinez, Joaquin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Removal of Copper and Zinc from Gold Ore Tailings Solutions using Chitosan2008In: Hydro Process 2008 / [ed] Jorge M. Menacho and Jesús M. Casas de Prada, Santiago, Chile: GECAMIN Ltda. , 2008, p. 139-152Conference paper (Refereed)
  • 9. Bozkurt, S.
    et al.
    Lucisano, M.
    Moreno, Luis
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Neretnieks, Ivars
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Peat as a potential analogue for the long-term evolution in landfills2001In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 53, no 02-jan, p. 95-147Article, review/survey (Refereed)
    Abstract [en]

    A survey of the existing studies on peat and its decomposition processes is presented with the aim to characterise the long-term behaviour of peat accumulating systems. The chemical and physical characteristics of peat together with its accumulation and decay processes have been analysed. Peat is an acidic mixture of dead and decomposed. mainly vegetable, matter formed in boggy areas; it is the youngest and least altered component of the combustible rocks and is characterised by the lowest content of fixed carbon and the highest content of volatile constituents. Peat is formed by degeneration processes under exclusion of atmospheric oxygen by the action of water; the speed of formation depends upon the climatic and environmental conditions. In most peatlands two layers can be characterised: the aerobic acrotelm and the anaerobic catotelm, their relative importance being controlled mainly by the position of the water table. In the acrotelm the aerobic processes are responsible for the loss of up to 90% of the original mass, Degeneration in the acidic and anaerobic catotelm is still imperfectly characterised even though the catotelm is the real site of peat accumulation. Most of the recent literature considers peat as composed of easily degradable compounds, e.g. polysaccharides. and recalcitrant matter (lignin and complex aromatics). The lone-term destiny of peat has not been sufficiently characterised: although in a large majority of cases it seems probable that peat decomposes completely (even though slowly) provided that it is given a sufficiently long residence rime in the catotelm, some cases can still be interpreted as examples of simple accumulation. The rates of influx of oxygen and hence the degradation of organic matter into both saturated and partially saturated peat have been estimated. The depletion rate is about 4500 g m(-1) year(-1) for partially saturated peat. The average depletion rate of the peat for this case will then be such that it will take on the order of 5 to 50 years to degrade half of the organics in a 10 cm partially saturated layer. For the water-saturated case the depletion rate varies between 8 and 12 g m(-2) year(-1), which is considerably lower than in the partially saturated region. The models used to analyse the field and laboratory data on generation, diffusion and emission of methane and carbon dioxide indicate that laboratory data and field observations agree reasonably well. It is suggested that peat-accumulating ecosystems may be valuable natural analogues for the study of the long-term destiny of industrial and municipal solid wastes. Accurate studies of active mires together with an ad hoc review of the existing literature give valuable insights in this problem. Peatlands might then be considered as organic waste deposition experiments lasting up to several thousands years.

  • 10. Bozkurt, S.
    et al.
    Moreno, Luis
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Neretnieks, Ivars
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Long-term processes in waste deposits2000In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 250, no 03-jan, p. 101-121Article in journal (Refereed)
    Abstract [en]

    A conceptual model, which is a unitary and continuous description of the overall processes in waste deposits, has been developed. In the model the most important processes governing the long-term fate of organic matter in landfills and the transport and retention of toxic metals are included. With the model as a base, a number of scenarios with different levels of complexity have been defined and studied in order to carry out long-term assessments of the chemical evolution in waste deposits for industrial and municipal solid waste containing much organic matter and the leaching of toxic metals. The focus of the modelling has been to quantify the important processes occurring after the methane production phase has ceased, i.e. during the humic phase. The scenarios include the main mechanisms based on various transport processes as well as different landfill constructions, e.g. binding capacities of sulfides and humic substances. They also include transport mechanisms by which the reactant oxygen can intrude into a deposit, sorption capacities of hydrous ferric oxides, and pH-buffering reactions, etc. Scoping calculations have shown that the binding capacity of humic substances is sufficient to bind all toxic metals (Cd, Cr, Pb, Zn and Hg). In addition, the humics could also bind a smaller part of Ca, Fe and Al, provided much of the organic waste remain as humic substances. Sulfides on the other hand can bind approximately twice the amount of all toxic metals. The binding capacity of hydrous ferric oxides, which can be formed by oxidation reactions during the humic phase, is estimated to be three times the total content of metals that can sorb on hydrous ferric oxides. In the studied landfill the pi-I-buffering capacity, primarily represented by calcite, is estimated to be 1 mol/kg dry waste. Quantifications indicate that the alkalinity of the wastes is high enough to buffer the acidity produced by the oxidation of sulfides and by the degradation of organic matter, as well as that added by acid precipitation. Therefore, the main conclusion is that higher remobilisation rates of heavy metals due to lowering of pH are not expected for many thousands of years.

  • 11. Bozkurt, S.
    et al.
    Sifvert, M.
    Moreno, Luis
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Neretnieks, Ivars
    KTH, Superseded Departments, Chemical Engineering and Technology.
    The long-term evolution of and transport processes in a self-sustained final cover on waste deposits2001In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 271, no 03-jan, p. 145-168Article in journal (Refereed)
    Abstract [en]

    A new principle for confinement of waste based on a self-sustained seal is presented. The top cover is considered to consist of two main layers; an organic carbon rich surface layer that is able to support vegetation and an inorganic layer beneath it. The function of the cover is to mitigate oxidation and acidification of landfilled waste and hence the release of toxic metals. It is suggested that forest soil formation and soil development could prove to be valuable information sources for the study of the long-term behaviour of a final cover on waste deposits. Since the cover is expected to develop in northern temperate climate the focus is on Spodosol soil. A number of simulations of the long-term behaviour of the final self-sustained landfill cover are made, including the rates of influx of oxygen into the cover. A cover having a large portion of organic matter compared with a cover with no organics can considerably decrease the oxygen concentration and thus the influx of oxygen into a landfill. The calculated oxygen intrusion rate for the former case is of the order of 0.05 kg m(-2) year(-1). Degradation of the organics produces acids. Our simulations indicate that the pH-buffering capacity of the mineral layer, represented by calcite and primary rock minerals, will last for many thousands of years.

  • 12. Crawford, J.
    et al.
    Moreno, Luis
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Neretnieks, Ivars
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Determination of the flow-wetted surface in fractured media2003In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 61, no 04-jan, p. 361-369Article in journal (Refereed)
    Abstract [en]

    Diffusion and sorption in the rock matrix are important retardation mechanisms for radionuclide transport in fractured media. For the conditions existing in a deep repository in crystalline rock, interaction with the rock matrix is controlled by the water flowrate in the fractures and the surface area in contact with the flowing water (the so-called flow-wetted surface (FWS)). The flow-wetted surface may be determined from the frequency of open fractures intersecting a borehole. The choice of packer distance used in these hydraulic measurements is crucial, however, since several open fractures may be found in one packer interval. The use of a packer distance that is too large may result in a considerable underestimation of the flow-wetted surface. This is especially important in zones with a high frequency of open fractures (fracture zones) where a small packer distance is a fundamental requirement. A large volume of hydraulic data has been compiled in Sweden from measurements using quite small packer distances. Over the last decade, the most common packer distance used for the hydraulic tests has been 3 m, although some new measurements using a shorter packer distance have also been performed. In several cases, the resolution of these measurements has been less than 0.5 m. All these data have been analysed in detail. From these data, the flow-wetted surface has been calculated and compared with the flow-wetted surface estimated in earlier studies. The results show the importance of using a small packer distance for carrying out borehole transmissivity measurements.

  • 13.
    Crawford, James
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Moreno, Luis
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Neretnieks, Ivars
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Harmonisation of site characterisation and performance assessment modelling - The relative importance of surface sorption and matrix interaction phenomena2004In: Scientific Basis For Nuclear Waste Management XXVII / [ed] Oversby, VM; Werme, LO, 2004, Vol. 807, p. 551-556Conference paper (Refereed)
    Abstract [en]

    In the context of geological repositories for nuclear waste disposal, the goal of site characterisation (SC) is to obtain input data that can later be used as a basis for performance assessment calculations (PA). Performance assessment is required to give an indication as to whether the repository will behave as intended over the geological timescales relevant for risk analysis. Processes that may be important in a PA setting for constraining radionuclide transport may not necessarily be dominating, or indeed may not even be observable during SC investigations. In this paper it is shown that the migration of sorbing tracers is governed largely by surface sorption phenomena in typical SC-type field experiments whereas in a PA scenario, matrix interaction instead can be expected to play an overwhelmingly important role. This study uses data and settings that are representative for fractured rocks in Sweden, but the method used and the conclusions may have more general applicability.

  • 14. Galvez, Edelmira D.
    et al.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Mellado, Mario E.
    Ordonez, Javier I.
    Cisternas, Luis A.
    Heap leaching of caliche minerals: Phenomenological and analytical models - Some comparisons2012In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 33, p. 46-53Article in journal (Refereed)
    Abstract [en]

    Antofagasta, Chile, has one of the most important deposits of saltpetre in the world, which is called caliche. These deposits are mainly composed of nitrate, halite, sodium anorthite, and quartz. Minor species include anhydrite, glauberite, loeweite, calcite, polyhalite, probertite, and gypsum. Recently, several operations began to use heap leaching for the extraction of saltpetre. Modelling the heap leaching of caliche is not straightforward because of the many minerals and their different dissolution rates. Moreover, caliche may have a large fraction of soluble minerals, approximately 40%, which causes the heap to slump. In this work, we present two models. The first, which is a phenomenological model, is an extension of the model published by Valencia et al. (2008). The system is modelled as a column comprised of N small columns, and in each of these small columns, the height of the solids varies with time when the soluble minerals are dissolved. The liquid in each small column has the same composition (well-stirred reactor). The second model, which is an analytical model, is an extension of that published by Mellado et al. (2009) for low-grade minerals, such as copper and gold, which considers that the leaching phenomenon occurs on different scales of size and time. However, in this work, the time scale at the particle level is based on the Bruner and Tolloczko dissolution model. The objective of this work is to test the suitability of the analytical model as a tool for use in optimisation, for which the model needs to be solved many times. The phenomenological model was used to generate simulated experimental data. The results show that the analytical model may be a useful tool in optimisation.

  • 15. Garca, I.
    et al.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Removal of natural organic matter by conventional and enhanced coagulation in Nicaragua2007In: Water Resources Management IV, WIT Press, 2007, Vol. 103, p. 399-409Conference paper (Refereed)
    Abstract [en]

    Enhanced coagulation was applied to raw water from a drinking water plant in Nicaragua through bench scale jar test in order to reduce the presence of natural organic matter (NOM) and decrease the trihalomethanes (THMs) formation which has been linked to carcinogenic diseases. Due to the lack of information about the presence of chlorination by-products (CBPs) like trihalomethanes, a study of their formation by varying pH, contact time, temperature and chlorine dose was also performed; following conventional or enhanced coagulation treatment. The results show that enhanced coagulation decreases considerably the formation of THMs because it reduces strongly the presence of organic matter due to the fact that higher alum doses were used in comparison with conventional coagulation utilized at the facility. The removal of dissolved organic carbon (DOC) was improved from 44 at the facility to 67 with enhanced coagulation. Trihalomethanes concentration increases drastically when extreme conditions of the four parameters evaluated were applied exceeding the maximum contaminant levels of USEPA (80 g/L) but not the Nicaraguan target value (460 g/L) for both coagulation types.

  • 16.
    Garcia, Indiana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Benavente, Martha
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Sorption kinetics of fulvic and humic acid onto chitosan of different molecular weightsArticle in journal (Other academic)
  • 17.
    Garcia, Indiana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Benavente, Martha
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Use of chitosan as coagulant in the removal of natural organic matter from four different raw waters2011In: Proceedings of the 10th International Conference of the European Chitin Society (EUCHIS 2011), 2011, p. 106-110Conference paper (Other academic)
  • 18.
    Garcia, Indiana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Removal of humic acid by coagulation and flocculation with chitosan2010Article in journal (Other academic)
  • 19.
    Garcia, Indiana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Removal of natural organic matter from water in Nicaragua to reduce the total exposure cancer riskArticle in journal (Other academic)
  • 20.
    Garcia, Indiana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Removal of nitrogen and carbon organic matter by chitosan and aluminium sulphate2012In: Water Science and Technology: Water Supply, ISSN 1606-9749, E-ISSN 1607-0798, Vol. 12, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    River and lake waters were separated into four fractions to study the removal of nitrogen and carbon organic matter using chitosan (CH) and aluminium sulphate (AS). The fractions were very hydrophobic acid, slightly hydrophobic acid, charged hydrophilic acid and neutral hydrophilic. The results showed that the whole and fractionated water from both sources have a markedly hydrophobic character. However, lake water had a lower NOM concentration than river water. The ratio of dissolved organic carbon and dissolved organic nitrogen (DOC/DON) and dissolved inorganic nitrogen to total dissolved nitrogen (DIN/TDN) were higher in the hydrophobic fraction from both sources. Similarly DOC, colour and ultraviolet absorbance at 254 nm (UV254) also presented higher values in the same fraction. Chitosan achieved the better results in the removal of NOM from Boaco water, whole and fractionated, whereas aluminium sulphate achieved better removal from Juigalpa water. DON and DIN were removed by aluminium to about 30%. The DOC/DON and DIN/TDN ratios decreased with both coagulants in whole waters from both sources. The hydrophobic fraction contributed most to the formation of trihalomethanes, slightly hydrophobic acid being the biggest contributor. Lake water led to less THM formation than river water.

  • 21.
    García, Indiana
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Moreno, Luis
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Drinking Water Treatment Plants in Nicaragua: a short review2003In: Proceeding of the IWA Asia Pacific Regional Conference, 2003Conference paper (Refereed)
  • 22.
    García, Indiana
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Moreno, Luis
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Influence of Enhanced Coagulation in the removal of Natural Organic Matter to avoid formation of Trihalomethane in a drinking water plant in Nicaragua2004Conference paper (Refereed)
  • 23.
    García, Indiana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Presence of trihalomethanes in drinking water plants in Nicaragua2006In: Journal of Water Supply: Research and Technology - Aqua, ISSN 0003-7214, E-ISSN 1365-2087, Vol. 55, no 3, p. 221-231Article in journal (Refereed)
    Abstract [en]

    The impact of enhanced coagulation on the formation of trihalomethanes (THMS) from drinking water was studied in four treatment plants in Nicaragua. Enhanced and conventional coagulation techniques were compared with regard to the removal of natural organic matter (NOM), which was measured by surrogate paramametres. The enhanced coagulation process showed a better removal of NOM, and as a consequence the THM formation was up to 50% lower than with conventional coagulation. The influences of chlorine dosage, temperature, PH and contact time on the THM formation in water treated by enhanced and conventional coagulation were also studied.

  • 24.
    García, Indiana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Use of GAC after enhanced coagulation for the removal of natural organic matter from water for purification2009In: Water Science and Technology: Water Supply, ISSN 1606-9749, E-ISSN 1607-0798, Vol. 9, no 2, p. 173-180Article in journal (Refereed)
    Abstract [en]

    Filtration with granular activated carbon (GAC) after an enhanced coagulation (EC) process was evaluated in order to determine the effectiveness of GAC in the reduction of natural organic matter (NOM), which should result in much lower formation of trihalomethane in the disinfection step. The results show that a combination of EC and GAC considerably reduces the organic matter content, which is mainly fulvic acid. This type of organic matter is removed with high coagulant dosages which neutralize their high anionic charge. A further reduction of NOM is achieved due the adsorption of NOM by GAC. As a result, the average trihalomethane (THM) concentration was only 14.5±5 mg L-1. Enhanced coagulation alone decreased the NOM concentration by 50%, but the remaining NOM reacted in the chlorination step and a higher average THM concentration was found (38±23 mg L-1). An average THM concentration of 73.8±41.2 mg L-1 was found at the drinking water plant of Boaco when conventional treatment was used. This THM concentration sometimes exceeds the maximum contaminant level of 80 mg L-1 established by the United States Environmental Protection Agency (USEPA), but not the Nicaraguan threshold of 460 mg L-1.

  • 25.
    García, Indiana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Use of pH, contact time, chlorine dose, temperature on the formation of trihalomethane and some empirical models for predicting trihalomethane formation2006In: WIT Transactions on Ecology and the Environment, 2006, p. 411-421Conference paper (Refereed)
    Abstract [en]

    An empirical model for predicting trihalomethane (THMs) formation, using linear and nonlinear regression, was carried out using a database built when the influence of enhanced coagulation on the formation of THMs was studied. These experiments were done under different conditions of pH, temperature, chlorine dosages and contact time; and two types of coagulation (enhanced and conventional). This database was first used to compare the formation of trihalomethane obtained in these experiments with some existing predictive models. Because the values measured experimentally did not agree enough with the values from the predictive models for both coagulation types, new ones were developed using the results of enhanced coagulation experiments. In order to test the predictive capacity of the models, both linear and non-linear models, were used to predict the formation of THMs using the database obtained from the conventional coagulation experiments. The nonlinear model gave best results in comparison with the linear model. The results were statistically validated by analysis of variance and other statistics parameters.

  • 26.
    García, Indiana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Use of two different coagulants for the removal of organic matter from a drinking water.2005Conference paper (Refereed)
  • 27.
    Korsak, Larisa
    et al.
    National University of Engineering, Managua, Nicaragua.
    Cabezas, Andrés
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    A Model of kinetics and mass transfer in an UASB reactor2008In: Environmental Science and Technology 2008: vol. 1, 2008, p. 426-433Conference paper (Other academic)
  • 28.
    Korsak, Larisa
    et al.
    Department of Chemical Engineering, National University of Engineering, Managua, Nicaragua.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Alternatives of Sludge Use in Nicaragua2005In: Proceedings of the 27th Annual HWEA Conference "New Technical Knowledge for Clean Water", 2005Conference paper (Other academic)
  • 29.
    Korsak, Larisa
    et al.
    Department of Chemical Engineering, National University of Engineering, Managua, Nicaragua.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Evaluation of anaerobic sludge activity in wastewater treatment plants in Nicaragua2006In: Water Pollution VIII: Modelling, Monitoring and Management / [ed] Carlos Alberto Brebbia; J. S. Antunes do Carmo, 2006, p. 571-579Conference paper (Refereed)
    Abstract [en]

    Sludge of three municipal anaerobic wastewater treatment plants was evaluated. This study was initiated due to the low activity observed in the anaerobic wastewater treatment plants in Nicaragua. An additional goal to select one of them, if possible, as an inoculum for the brewery treatment plant was proposed. Two of these plants work with an Imhoff tank and one with a Septic tank followed by an anaerobic upflow filter. The study consisted in the characterization of biomass in terms of Specific Methanogenic Activity (SMA), Volatile Suspended Solids (VSS), density, pH, and redox potential (RP). The treated waters were also analysed for nutrients, heavy metals and the organic load. The substrate used in the experiments for determining the methanogenic activity was acetic acid. NaHCO3 was added to maintain pH in the normal range of operation. The tests were carried out at a sludge load of 1.5 g VSS/l. The results indicate that treated wastewater does not have any impediment to proper development of microorganisms; no presence of toxic substances and enough essential nutrients were detected. The specific methanogenic activity of sludge (SMA) in the Imhoff tanks is relatively close and oscillates between 0.16-0.28 g CH4-COD/g VSS/day, and in the septic tank is 0.09 g CH4-COD/g VSS/day. These values agree with the methanogenic activity found in the literature for septic tanks (0.02-0.1 g CH4-COD/gVSS/day). The highest methanogenic activity measured during the test was 0.28g CH4-COD/g VSS/day in the sludge of the Imhoff tank in The Viejo city, so this sludge could be proposed as a seed for the brewery treatment plant.

  • 30.
    Korsak, Larisa
    et al.
    Department of Chemical Engineering, National University of Engineering, Managua, Nicaragua.
    Moreno, Luis
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Wastewater treatment in Nicaragua2003In: Proceedings of the 9th Annual IWA Specialised Conference "Design, Operation and Economics of Large Wasewater Treatment Plants", 2003Conference paper (Other academic)
  • 31. Lara, G. A.
    et al.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Ramírez, Y.
    Cisternas, L. A.
    Modeling an airlift reactor for the growing of microalgae2018In: Open Chemical Engineering Journal, ISSN 1874-1231, Vol. 12, no 1, p. 80-94Article in journal (Refereed)
    Abstract [en]

    Objective: The flow dynamics of an airlift reactor for the growing of microalgae is modeled using Computational Fluid Dynamics (CFD). The model is applied to the operation and optimization of the reactor, giving a valuable picture of the liquid movement and carbon dioxide trajectory at different air injection flow rates. Methods: A novel aspect of the model is that air and carbon dioxide are injected at separated locations. Air is injected at the bottom of the reactor and CO 2 injection takes place in the downcomer region of the reactor to obtain longer CO 2 paths, improving its transference. Results: The results show modeling is a useful tool in the control of the reactor operation; for example, in avoiding the sedimentation of microalgae or for detecting the existence of zones with extremely low CO 2 concentrations.

  • 32.
    Liu, Longcheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    A Dynamic Force Balance Model for Colloidal Expansion and Its DLVO-Based Application2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 2, p. 679-687Article in journal (Refereed)
    Abstract [en]

    A force balance model that describes the dynamic expansion of colloidal bentonite gels/sols is presented. The colloidal particles are assumed to consist of one or several thin sheets with the other dimensions much larger than their thickness. The forces considered include van der Waals force, diffuse double layer force, thermal force giving rise to Brownian motion, gravity, as well as friction force. The model results in an expression resembling the instationary diffusion equation but with an immensely variable diffusivity. This diffusivity is strongly influenced by the concentration of counterions as well as by the particle concentration in the colloid gel/sol. The properties of the model are explored and discussed, exemplified by the upward expansion of an originally highly compacted bentonite tablet in a test tube. Examples are presented for a number of cases with ionic concentrations varying between very dilute waters up to several molar of counterions. The volume fraction of particles ranges from 40% to very dilute sols.

  • 33.
    Liu, Longcheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    A Novel Approach to Determine the Critical Coagulation Concentration of a Colloidal Dispersion with Plate-like Particles2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 2, p. 688-697Article in journal (Refereed)
    Abstract [en]

    The critical coagulation concentration (ccc) of counterions is commonly described by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory on the basis of a static force balance. It can, however, also be estimated from a kinetic point of view by studying the process of colloidal coagulation, or from a dynamic point of view by considering colloidal transport in nonequilibrium systems where other processes such as diffusion and the influence of gravity come into play. In particular, in a test tube where colloidal expansion takes place, the ccc can be interpreted as the electrolyte concentration below which expansion of colloids would always lead to full access to the entire volume of the test tube and above which a sharp boundary is established between a colloidal gel and pure water. On the basis of this perception and the dynamic force balance model that we developed to describe colloidal expansion in a test tube, accounting for the effects of particle diffusion and gravity in contrast to the DLVO theory, we propose an alternative way to assess the ccc of counterions. We also derive an approximate expression for the case of homointeraction at constant charge for montmorillonite. The estimated ccc values agree quite well with those observed experimentally for both Na+ and Ca2+ counterions for montmorillonite dispersions, at pH similar to 6.5. This is in contrast to the DLVO theory, which overpredicts the ccc by about 2 orders of magnitude. In addition, the detailed analyses suggest that the ccc of counterions decreases with increasing surface area and with the thickness of the particles. For montmorillonite, the ccc is nearly independent of the surface charge density of the particles for the range of typical charge densities.

  • 34.
    Mahiques, Joan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Modelling of Leaching of Copper Oxides in Dumps and In-Situ2006In: Hydro Process 2006 / [ed] Esteban M. Domic & Jesús M. Casas de Prada, Santiago, Chile: GECAMIN Ltda. , 2006, p. 429-441Conference paper (Other academic)
  • 35.
    Mahmoudzadeh, Batoul
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Evolution of fracture aperture mediated by dissolution in a coupled flow channel–rock matrix–stagnant zone systemManuscript (preprint) (Other academic)
    Abstract [en]

    Fracture aperture is an important entity controlling fluid flow in natural fractures in rocks. The aperture of fractures in crystalline rocks may decrease or increase by different mechanical and chemical mechanisms. A model to describe the evolution of fracture aperture mediated by dissolution and precipitation is presented in this study. It includes advective flow in the fracture that can carry in or away dissolved minerals. The model also accounts for the fact that dissolved minerals in the fracture plane, in both flow channel and stagnant water zone, can diffuse into the adjacent porous rock matrix. The analytical solution obtained in the Laplace space is then used to study evolution of the fracture aperture under combined influence of stress and flow, in a pseudo-steady-state procedure. The simulation results give insights into the most important processes and mechanisms that dominate the fracture closure or opening under different circumstances. It is found that the times involved for any changes in fracture aperture are very much larger than the times needed for concentrations of dissolved minerals to reach steady state in the rock matrix, the stagnant water zone and the flow channel. This suggests that the steady state model can be used to assess the evolution of concentration of dissolved minerals in the rock fracture. Moreover, it is shown that diffusion into the rock matrix, which acts as a strong sink or source for dissolved minerals, clearly dominates the rate of concentration change and consequently the rate of evolution of the fracture aperture.

  • 36.
    Mahmoudzadeh, Batoul
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Rock fracture closing moderated by pressure solution2015In: Future Communication Technology and Engineering - Proceedings of the 2014 International Conference on Future Communication Technology and Engineering, FCTE 2014, CRC Press/Balkema , 2015, p. 269-275Conference paper (Refereed)
    Abstract [en]

    Fracture apertures may decrease or increase by different mechanical and chemical mechanisms when the fractures are subject to stress. A model is presented to describe fracture closure/opening that accommodates pressure dissolution at contacting asperities as well as free-face dissolution/precipitation at free faces of the fracture and of the rock matrix. The derived analytical model accounts for the fact that dissolved minerals carried by flowing water along the fracture can not only diffuse into and out of the adjacent rock matrix but also at first diffuse into the stagnant water zone existing in part of the fracture plane and then from there into and out of the rock matrix adjacent to it. The analytical solution is used to study fracture closure/opening rate in a pseudo steady state, PSS, procedure. This simple model allows us to gain some insights into which processes and mechanisms have the larger impact on the fracture aperture under different circumstances.

  • 37.
    Mahmoudzadeh, Batoul
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Solute transport in a single fracture involving an arbitrary length decay chain with rock matrix comprising different geological layers2014In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 164, p. 59-71Article in journal (Refereed)
    Abstract [en]

    A model is developed to describe solute transport and retention in fractured rocks. It accounts for advection along the fracture, molecular diffusion from the fracture to the rock matrix composed of several geological layers, adsorption on the fracture surface, adsorption in the rock matrix layers and radioactive decay-chains. The analytical solution, obtained for the Laplace-transformed concentration at the outlet of the flowing channel, can conveniently be transformed back to the time domain by the use of the de Hoog algorithm. This allows one to readily include it into a fracture network model or a channel network model to predict nuclide transport through channels in heterogeneous fractured media consisting of an arbitrary number of rock units with piecewise constant properties. More importantly, the simulations made in this study recommend that it is necessary to account for decay-chains and also rock matrix comprising at least two different geological layers, if justified, in safety and performance assessment of the repositories for spent nuclear fuel.

  • 38.
    Mahmoudzadeh, Batoul
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Solute transport in fractured rocks with stagnant water zone and rock matrix composed of different geological layers-Model development and simulations2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 3, p. 1709-1727Article in journal (Refereed)
    Abstract [en]

    A model is developed to describe solute transport and retention in fractured rocks. It accounts for the fact that solutes can not only diffuse directly from the flowing channel into the adjacent rock matrix composed of different geological layers but also at first diffuse into the stagnant water zone occupied in part of the fracture and then from there into the rock matrix adjacent to it. In spite of the complexities of the system, it is shown that the analytical solution to the Laplace-transformed concentration at the outlet of the flowing channel is a product of two exponential functions, and it can be easily extended to describe solute transport through channels in heterogeneous fractured media consisting of an arbitrary number of rock units with piecewise constant geological properties. More importantly, by numerical inversion of the Laplace-transformed solution, the simulations made in this study help to gain insights into the relative significance and the different contributions of the rock matrix and the stagnant water zone in retarding solute transport in fractured rocks. It is found that, in addition to the intact wall rock adjacent to the flowing channel, the stagnant water zone and the rock matrix adjacent to it may also lead to a considerable retardation of solute in cases with a narrow channel.

  • 39.
    Mahmoudzadeh, Batoul
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Solute transport through fractured rock: Radial diffusion into the rock matrix with several geological layers for an arbitrary length decay chain2016In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 536, p. 133-146Article in journal (Refereed)
    Abstract [sv]

    The paper presents a model development to derive a semi-analytical solution to describe reactive solute transport through a single channel in a fracture with cylindrical geometry. The model accounts for advection through the channel, radial diffusion into the adjacent heterogeneous rock matrix comprising different geological layers, adsorption on both the channel surface, and the geological layers of the rock matrix and radioactive decay chain. Not only an arbitrary-length decay chain, but also as many number of the rock matrix layers with different properties as observed in the field can be handled. The solution, which is analytical in the Laplace domain, is transformed back to the time domain numerically e.g. by use of de Hoog algorithm. The solution is verified against experimental data and analytical solutions of limiting cases of solute transport through porous media. More importantly, the relative importance and contribution of different processes on solute transport retardation in fractured rocks are investigated by simulating several cases of varying complexity. The simulation results are compared with those obtained from rectangular model with linear matrix diffusion. It is found that the impact of channel geometry on breakthrough curves increases markedly as the transport distance along the flow channel and away into the rock matrix increase. The effect of geometry is more pronounced for transport of a decay chain when the rock matrix consists of a porous altered layer.

  • 40.
    Meng, Shuo
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Liu, Longcheng
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Mahmoudzadeh, Batoul
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Moreno, Luis
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Solute transport along a single fracture with a finite extent of matrix: A new simple solution and temporal moment analysis2018In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 562, p. 290-304Article in journal (Refereed)
    Abstract [en]

    A new simple and robust solution, based on uniform steady-state flow velocity, is developed for the problem of solute transport in a fracture-matrix system with a finite penetration depth of a radioactive contaminant into the rock matrix. The solution is an extension of Liu et al. (2017) to finite penetration depth and an alternative solution strategy to the problem solved by Sudicky et al. (1982). The solution takes the form of a convolution of two functions. The first function describes the probability density function of the residence time distribution of a conservative solute resulting merely from advection and Fickian dispersion. The second function is actually the impulse response of the fracture-matrix system in the case of a plug flow without any hydrodynamic dispersion. As a result, the effects of Fickian dispersion and matrix diffusion on solute transport are decoupled, and thus the resulting breakthrough curve can be analyzed in terms of those two functions. In addition to this, the derived Péclet numbers of those two functions, based on temporal moments, are also found to be associated with the derived Péclet number of the resulting breakthrough curve. By comparing the Péclet numbers of those two functions, the contribution of Fickian dispersion and matrix diffusion to solute spreading is determined in a straightforward way. This can aid to find out the dominating mechanism on solute transport, and therefore the performance of breakthrough curve.

  • 41.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Modelling of contaminant release from mining waste deposits2007In: Biohydrometallurgy: From The Single Cell To The Environment / [ed] Schippers, A; Sand, W; Glombitza, F; Willscher, S, 2007, Vol. 20-21, p. 189-192Conference paper (Refereed)
    Abstract [en]

    The release of contaminants from mining wastes containing sulphide minerals is addressed. The paper shows the application of a methodology, Performance Assessment (PA), to the long-term behaviour of waste deposits. The aim of the paper is to address the different processes that occur in deposits for mining waste. These processes are applied to one study case; drainage water from a waste rock dump at the Aitik mine in northern Sweden.

  • 42.
    Moreno, Luis
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Crawford, James
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Can we use tracer tests to obtain data for performance assessment of repositories for nuclear waste?2009In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 17, no 5, p. 1067-1080Article in journal (Refereed)
    Abstract [en]

    With regard to the long-term safety of repositories for spent nuclear fuel, tracer tests have commonly been used in site characterisation (SC) for finding information that can be later used for performance assessment (PA). The question arises as to whether data obtained in tracer tests performed over a time scale of weeks or months are relevant for PA calculations. As part of a study overseen by the A"spo Task Force, the mechanisms that determine the radionuclide residence time under SC and PA conditions are addressed, given that they influence the validity of data transference from SC to PA. The results show that radionuclide transport in SC and PA, although governed by the same retardation mechanisms, are dominated by different sub-processes. In a practical sense this means that the parameter values (typically fracture apertures and "in situ" apparent retention data) determined in tracer tests, performed as a part of the SC program, should not be used directly for making PA predictions. The emphasis in SC should focus more on the determination of other parameters of relevance at PA timescales. The PA-specific flow rate, flow connectivity, and flow-wetted surface to flow ratio are given here as examples.

  • 43.
    Moreno, Luis
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Crawford, James
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Neretnieks, Ivars
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Modelling of solute transport under flow conditions varying in time, using the channel network model2004In: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII / [ed] Oversby, VM; Werme, LO, 2004, Vol. 807, p. 797-802Conference paper (Refereed)
    Abstract [en]

    Transport of radionuclides from a repository to the biosphere is calculated in the presence of varying boundary conditions. This may occur in Sweden, for example, during post-glacial rebound. To calculate the transport of radionuclides, the flow field has to be calculated at each time step. An alternative approach is to determine the flow field at certain time intervals; i.e., modelling the dynamic flow system as a sequence of punctuated steady states. This can be done in a rather simple way by using the Channel Network model (CNM), in which radionuclide transport is calculated by particle tracking. Intuitively one would expect such a simple procedure to be permissible and lead to small errors if the time intervals are so short that only small changes in flow rates and flow directions take place. In this paper, the technique is applied to a study case. This describes a repository located at a sub sea level location outside the coastline; where, owing to the land lift that is taking place in Scandinavia the coastline is advancing towards the repository. An important issue to be determined is the minimum number of time intervals that need to be used in order to obtain a reliable solution to radionuclide transport. It is found that the number of time intervals needed is strongly dependent on the variation in the boundary conditions. For the changing conditions used in the example tested, a number on the order of 5-9 time intervals allows a sufficiently good representation of the transport.

  • 44.
    Moreno, Luis
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Crawford, James
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Modelling radionuclide transport for time varying flow in a channel network2006In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 86, no 3-4, p. 215-238Article in journal (Refereed)
    Abstract [en]

    Water flowrates and flow directions may change over time in the subsurface for a number of reasons. In fractured rocks flow takes place in channels within fractures. Solutes are carried by the advective flow. In addition, solutes may diffuse in and out of stagnant waters in the rock matrix and other stagnant water regions. Sorbing species may sorb on fracture surfaces and on the micropore surfaces in the rock matrix. We present a method by which solute particles can be traced in flowing water undergoing changes in flowrate and direction in a complex channel network where the solutes can also interact with the rock by diffusion in the rock matrix. The novelty of this paper is handling of diffusion in the rock matrix under transient flow conditions. The diffusive processes are stochastic and it is not possible to follow a particle deterministically. The method therefore utilises the properties of a probability distribution function for a tracer moving in a fracture where matrix diffusion is active. The method is incorporated in a three dimensional channel network model. Particle tracking is used to trace out a multitude of flowpaths, each of which consists of a large number of channels within fractures. Along each channel the aperture and velocity as well as the matrix sorption properties can vary. An efficient method is presented whereby a particle can be followed along the variable property flowpath. For stationary flow conditions and a network of channels with advective flow and matrix diffusion, a simple analytical solution for the residence time distribution along each pathway can be used. Only two parameter groups need to be integrated along each path. For transient flow conditions, a time stepping procedure that incorporates a stochastic Monte-Carlo like method to follow the particles along the paths when flow conditions change is used. The method is fast and an example is used for illustrative purposes. It is exemplified by a case where land rises due to glacial rebound. It is shown that the effects of changing flowrates and directions can be considerable and that the diffusive migration in the matrix can have a dominating effect on the results.

  • 45.
    Moreno, Luis
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Crawford, James
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Neretnieks, Ivars
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Solute transport in fractured rock. Testing a new and simple aapproach2004In: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII / [ed] Oversby, VM; Werme, LO, 2004, Vol. 807, p. 791-796Conference paper (Refereed)
    Abstract [en]

    A new and simple approach for modelling solute transport in fractured rock is presented, based on our previously used Channel Network Model (CNM). In our underlying concept, solute transport in fractured rocks takes place through undulating flat channels in the rock fractures. The channels form a 3-dimensional network. For non-interacting solutes the volume of the channels determines the residence time of a stream of water. For sorbing radionuclides the residence time is mainly determined by the ratio between the Flow Wetted Surface (FWS) and the flow rate in the channel (Q), in addition to the parameters that determine the interaction between the rock and the radionuclides. The main question explored in this paper is whether it is necessary to solve the flow problem for each studied case. From previous investigations, we have found that the flow rates in the channels where the solutes travel are closely related to the transmissivities of the channels. Simulations are presented in which streams of water are allowed to randomly select channels and trace out the paths where the path volume and its FWS can be assessed. The results obtained in this manner for the RTD (Residence Time Distribution) show rather good agreement with those obtained by solving the full flow problem and tracing particles in the network.

  • 46.
    Moreno, Luis
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Erosion of sodium bentonite by flow and colloid diffusion2011In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 36, no 17-18, p. 1600-1606Article in journal (Refereed)
    Abstract [en]

    Smectite gel formed at the outer part of a bentonite buffer in granitic rock could expand into rock fractures with seeping water. Such a gel can release colloids into low ionic strength waters. In addition the gel/sol can itself slowly flow downstream when it has reached a low particle concentration sufficient to decrease the viscosity to allow flow. The erosion due to the combined effects of particle diffusion and gel/sol flow is modelled for a thin fracture into which the gel expands influenced by various forces between and on particles. Some of the forces such as the electrical double layer force and viscous force are strongly influenced by the ionic strength of the pore water. Changes in the ionic strength due to diffusion and dilution of ions in the expanding clay are modelled simultaneously with the gel expansion, flow of gel and colloid release to the seeping water. The model includes description of flow of the seeping fluid, which gradually turns from pure water to sol to more dense gel as the smectite source is approached. The model also describes expansion of the gel/sol and colloid release and flow and diffusion of ions in the system. The coupled models are solved using a numerical code. The results show that the gel will flow with a non-negligible flowrate when its volume fraction is below 1%, but that the erosion and loss of smectite is not much influenced by the concentration of sodium in the clay or in the approaching seeping water, if they are kept below the Critical Coagulation Concentration, CCC.

  • 47.
    Moreno, Luis
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Long-term environmental impact of tailings deposits2006In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 83, no 1-4, p. 176-183Article in journal (Refereed)
    Abstract [en]

    This paper, within the MiMi project, explains the models and the modelling used in the performance assessment (long-term) calculations for the remediation of sulphidic mine tailings. The long-term impact of tailing deposits on the environment is addressed for two types of cover: soil and water covers. Oxygen intrusion is the process that determines the sulphide oxidation and the generation of acid mine drainage containing toxic metals. The primary acidity generated in the tailings from the sulphide oxidation is to a large extent neutralised by the buffering minerals in the deposit. However, when the water leaves the deposit, more acidity is generated due to the oxidation of mainly the ferrous iron (latent acidity). For soil covers, the generated acidity and dissolved metals flow downward with the infiltrating water. However, in a water cover, the reaction products formed may diffuse upwards into the water covering the deposit. Therefore, the acidity is not neutralised in the interior of the deposit. The behaviour of metals/metalloids such as Cu, Pb, Cd and As are also studied. They may be sorbed on the mineral surfaces of the minerals and retained in the deposit for a long time. Some of them may dissolve the more soluble sulphides (e.g., pyrrhotite) and precipitates as secondary sulphides. The data were selected based on experience from primarily Kristineberg (northern Sweden) but also from other sites.

  • 48.
    Moreno, Luis
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Ordonez, Javier I.
    Cisternas, Luis A.
    Dissolution Model of Multiple Species: Leaching of Highly Soluble Minerals2017In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, no 3, p. 1817-1826Article in journal (Refereed)
    Abstract [en]

    Dissolution of multi-species from a solid matrix is widely extended in different processes such as leaching of minerals; however, its modeling is often focused on a single species. A model for the simultaneous dissolution of soluble species was developed, which considers different solubilities and dissolution rates and considers that particle collapses when the rapidly soluble species is depleted. The collapsed matter is formed by inert material and a fraction of the soluble species with lower dissolution rate that has not dissolved yet. The model is applied to the leaching of a water-soluble mineral (caliche) with two soluble species dissolving simultaneously with different rates. Measured outlet concentrations of nitrate and magnesium were used to validate the model. Results showed that the model reproduced adequately the leaching of species with rapid and intermediate dissolution rate. Effect of the operating and kinetic parameters on the leaching process is also shown using the actual conditions of heap leaching for caliche mineral.

  • 49.
    Neretnieks, Ivars
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Moreno, Luis
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Prediction of some in situ tracer tests with sorbing tracers using independent data2003In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 61, no 04-jan, p. 351-360Article in journal (Refereed)
    Abstract [en]

    Some recent converging tracer tests with sorbing tracers at the Aspo Hard Rock Laboratory in Sweden, the TRUE tests, have been predicted using only laboratory data and hydraulic data from borehole measurements. No model parameters were adjusted to obtain a better fit with the experiments. The independent data were fracture frequency and transmissivity data obtained in the field and laboratory data on sorption and matrix diffusion. Transmissivity measurements in five boreholes in the rock volume containing the region surrounding the injection and collection points show that there is a high frequency of water conducting fractures. Of 162 packed off sections with 0.5 m packer distances, 112 were found to have a transmissivity above the detection limit. The specific flow-wetted surface (FWS) of the rock mass could be estimated from these data. The transmissivities were found to be reasonably well described by a lognormal distribution. Laboratory data on diffusion and sorption properties together with the hydraulic data were used to predict the residence time distribution (RTD) of the sorbing tracers. The results were compared with the experimental breakthrough curves. In these experiments, the water residence time is very small compared to the residence time of the sorbing tracers due to their diffusion and sorption within the rock matrix. We thus could neglect the influence of the water residence time in our predictions. Therefore, no information on water residence times or on dispersion was needed. The dispersion of the sorbing tracers is caused by the different sorbing tracer residence times in different pathways. The sorbing tracer residence time is determined by the ratio of flowrate to the flow-wetted surface in the different pathways and not by the water residence time. Assuming a three-dimensional flow pattern and using the observed fracture frequency and flowrate distribution, breakthrough curves for three strongly sorbing tracers were predicted. Only the laboratory data, the transmissivity measurements and the pumping flowrate were used in the predictions. No information on the water residence time as obtained by the nonsorbing tracers was used. The predictions were surprisingly accurate.

  • 50. Ordonez, Javier I.
    et al.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Mellado, Mario E.
    Cisternas, Luis A.
    Modeling validation of caliche ore leaching using seawater2014In: International Journal of Mineral Processing, ISSN 0301-7516, E-ISSN 1879-3525, Vol. 126, p. 10-17Article in journal (Refereed)
    Abstract [en]

    Leaching column experiments of caliche were performed using seawater as the leaching agent because the caliche deposits are located in Northern Chile where water resources are scarce. The use of seawater without desalination is an attractive alternative for mining operations. The experimental recoveries of different ions were modeled using a hybrid model, which uses empirical information and fundamental principles. The following ions were considered: nitrate, iodine, sulfate, chloride, sodium, potassium and magnesium. The model explicitly considers different column heights, irrigation rates, and leaching agents. A sensitivity analysis showed that parameters associated with the particle level predominantly determined the calculated recoveries. The predictive capability was also tested, and the results were generally good, except for the sulfate ion, the dissolution of which was controlled by the presence of other ions.

12 1 - 50 of 68
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf