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Extraction of Metal Values: Thermodynamics of Electrolyte Solutions and Molten Salts Extraction Process
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science. (Materialens processvetenskap)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Over the past centuries, a number of process routes for extraction of metal values from an ore or other resources have been developed. These can generally be classifiedinto pyrometallurgical, hydrometallurgical or electrometallurgical routes. In the caseof the latter two processes, the reaction medium consists of liquid phase electrolytesthat can be aqueous, non-aqueous as well as molten salts. The present dissertationpresents the work carried out with two aspects of the above-mentioned electrolytes.First part is about the electrolyte solutions, which can be used in solvent extractionrelevant to many hydrometallurgical or chemical engineering processes; the secondpart is about the molten salts, which is often used in the electrometallurgical processesfor production of a variety of many kinds of metals or alloys, especially those that arehighly reactive.In the first part of this thesis, the focus is given to the thermodynamics ofelectrolyte solutions. Since the non-ideality of high concentration solution is not wellsolved, a modified three-characteristic-parameter correlation model is proposed,which can calculate the thermodynamic properties of high concentration electrolytesolutions accurately. Model parameters for hundreds of systems are obtained foraqueous as well as non-aqueous solutions. Moreover, a new predictive method tocalculate the freezing point depression, boiling point elevation and vaporizationenthalpy of electrolyte solutions is also proposed. This method has been shown to be agood first approximation for the prediction of these properties.In the second part, a process towards the extraction of metal values from slags,low-grade ores and other oxidic materials such as spent refractories using molten saltsis presented. Firstly, this process is developed for the recovery of Cr, Fe values fromEAF slag as well as chromite ore by using NaCl-KCl salt mixtures in the laboratoryscale. The slags were allowed to react with molten salt mixtures. This extraction stepwas found to be very encouraging in the case of Cr and Fe present in the slags. Byelectrolysis of the molten salt phase, Fe-Cr alloy was found to be deposited on thecathode surface. The method is expected to be applicable even in the case of V, Mnand Mo in the waste slags.Secondly, this process was extended to the extraction of copper/iron from copperore including oxidic and sulfide ores under controlled oxygen partial pressures.Copper or Cu/Fe mixtures could be found on the cathode surface along with theemission of elemental sulphur that was condensed in the cooler regions of the reactor.Thus, the new process offers a potential environmentally friendly process routereducing SO2 emissions.Furthermore, the cyclic voltammetric studies of metal ions(Cr, Fe, Cu, Mg, Mn)in (CaCl2-)NaCl-KCl salt melt were performed to understand the mechanisms, such asthe deposition potential, electrode reactions and diffusion coefficients, etc. In addition,another method using a direct electro-deoxidation concept(FFC Cambridge method),was also investigated for the electrolysis of copper sulfide. Sintered solid porouspellets of copper sulfide Cu2S and Cu2S/FeS were electrolyzed to elemental Cu, S andCu, Fe, S respectively in molten CaCl2-NaCl at 800oC under the protection of Argongas. This direct electrolysis of the sulfide to copper with the emission of elementalsulfur also offers an attractive green process route for the treatment of copper ore.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , viii, 77 p.
Series
ISRN KTH/MSE, 2009 : 21
Keyword [en]
Electrolyte solutions, activity coefficient, osmotic coefficient, freezing point depression, boiling point elevation
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-10638ISBN: 978-91-7415-346-0 (print)OAI: oai:DiVA.org:kth-10638DiVA: diva2:222424
Public defence
2009-06-12, Salongen KTHB, Osquars Backe 31, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100714Available from: 2009-06-09 Created: 2009-06-08 Last updated: 2010-07-15Bibliographically approved
List of papers
1. Correlation and prediction of activity and osmotic coefficients of aqueous electrolytes at 298.15 K by the modified TCPC model
Open this publication in new window or tab >>Correlation and prediction of activity and osmotic coefficients of aqueous electrolytes at 298.15 K by the modified TCPC model
2007 (English)In: Journal of Chemical and Engineering Data, ISSN 0021-9568, E-ISSN 1520-5134, Vol. 52, no 2, 538-547 p.Article in journal (Refereed) Published
Abstract [en]

The modification and extension of a three-characteristic-parameter correlation model for calculating the thermodynamic properties including osmotic and mean activity coefficients of aqueous electrolytes at 298.15 K have been presented in this paper. The model can be reduced with two parameters: b, the approaching parameter, and S, the solvation parameter. Although the model adequately describes the thermodynamics with these two parameters, the third parameter, n, which is related to the distance between an ion and a solvent molecule, also can be regarded as an adjustable parameter. The two sets of parameters for 283 single salts in aqueous solutions up to saturation have been obtained from the regression of experimental values. Mean activity or osmotic coefficients of RbNO2, MgCl2, Sm(ClO4)(3), and ZnSO4, with these two sets of parameters, have been compared with the smoothed experimental data, which show good agreement. When the model with three parameters is employed, it gives a more accurate result, especially in case of high concentration. The comparison with Pitzer and the original TCPC model also illustrates the excellent performance of this modified model.

Keyword
VAPOR-LIQUID-EQUILIBRIA; BI-UNIVALENT COMPOUNDS; 3-CHARACTERISTIC-PARAMETER CORRELATION MODEL; ION INTERACTION PARAMETERS; RARE-EARTH PERCHLORATES; LOCAL COMPOSITION MODEL; EXCESS GIBBS ENERGY; ISOPIESTIC DETERMINATION; THERMODYNAMIC PROPERTIES; EVALUATED ACTIVITY
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-14112 (URN)10.1021/je060451k (DOI)000244734600036 ()2-s2.0-33947610111 (Scopus ID)
Note
QC 20100714Available from: 2010-07-14 Created: 2010-07-14 Last updated: 2017-12-12Bibliographically approved
2. Correlation and prediction of thermodynamic properties of nonaqueous electrolytes by the modified TCPC model
Open this publication in new window or tab >>Correlation and prediction of thermodynamic properties of nonaqueous electrolytes by the modified TCPC model
2008 (English)In: Journal of Chemical and Engineering Data, ISSN 0021-9568, E-ISSN 1520-5134, Vol. 53, no 1, 149-159 p.Article in journal (Refereed) Published
Abstract [en]

In this work, the modified three-characteristic-parameter correlation model was introduced to correlate and predict the thermodynamic properties, such as the mean activity coefficient, the osmotic coefficient, and the solvent activity, of different kinds of nonaqueous electrolyte solutions. Two sets of parameters, (b, S) and (b, S, n), for 46 single salts in. methanol, ethanol, and 2-propanol, etc., were regressed from literature data at 298.15 K. Results of standard deviations showed the good applicability of our model. The calculated results of the mean activity coefficient by our model and the Pitzer model have been compared with each other with good agreement. Smoothed experimental data of osmotic coefficients and solvent activities were calculated with the present model with three or two parameters, and the one with three parameters showed a better performance. We also extended this model for some nonaqueous systems at elevated temperatures, and we also found good consistency between the results calculated from our model and experimental data. Moreover, we further developed this model for calculating those in the mixed-solvent electrolyte systems. The results showed our modified model could adequately describe these complicated electrolyte solutions.

Keyword
WATER SOLVENT MIXTURES; ACETONITRILE PLUS WATER; VAPOR-PRESSURE MEASUREMENTS; ELECTROMOTIVE-FORCE MEASUREMENTS; ION INTERACTION PARAMETERS; LOCAL COMPOSITION MODEL; EXCESS GIBBS ENERGY; ACTIVITY-COEFFICIENTS; 298.15 K; OSMOTIC COEFFICIENTS
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-14113 (URN)10.1021/je700446q (DOI)000252292600026 ()
Note
QC 20100714Available from: 2010-07-14 Created: 2010-07-14 Last updated: 2017-12-12Bibliographically approved
3. Calculations of Freezing Point Depression, Boiling Point Elevation, Vapor Pressure and Enthalpies of Vaporization of Electrolyte Solutions by a Modified Three-Characteristic Parameter Correlation Model
Open this publication in new window or tab >>Calculations of Freezing Point Depression, Boiling Point Elevation, Vapor Pressure and Enthalpies of Vaporization of Electrolyte Solutions by a Modified Three-Characteristic Parameter Correlation Model
2009 (English)In: Journal of Solution Chemistry, ISSN 0095-9782, E-ISSN 1572-8927, Vol. 38, no 9, 1097-1117 p.Article in journal (Refereed) Published
Abstract [en]

A method was proposed for calculating the thermodynamic properties, freezing point depression, boiling point elevation, vapor pressure and enthalpy of vaporization for single solute electrolyte solutions, including aqueous and nonaqueous solutions, based on a modified three-characteristic-parameter correlation model. When compared with the corresponding literature values, the calculated results show that this method gives a very good approximation, especially for 1-1 electrolytes. Although the method is not very suitable for some solutions with very high ionic strength, it is still a very useful technique when experimental data is scarce.

Keyword
Electrolyte solutions, Freezing point, Boiling point, Enthalpy of vaporization
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-14114 (URN)10.1007/s10953-009-9433-0 (DOI)000268583800001 ()2-s2.0-68749118107 (Scopus ID)
Note

QC 20100714. Correction Vol 42 no. 4 2013 doi: 10.1007/s10953-013-9993-x, ISI 000318791600014, ScopusID: 2-s2.0-84877763957

Available from: 2010-07-14 Created: 2010-07-14 Last updated: 2017-12-12Bibliographically approved
4. The salt extraction process: A novel route for metal extraction part 1 - Cr, Fe recovery from EAF slags and low grade chromite ores
Open this publication in new window or tab >>The salt extraction process: A novel route for metal extraction part 1 - Cr, Fe recovery from EAF slags and low grade chromite ores
2010 (English)In: Transactions of the Institution of Mining and Metallurgy Section C - Mineral Processing and Extractive Metallurgy, ISSN 0371-9553, E-ISSN 1743-2855, ISSN 0371-9553, Vol. 119, no 1, 27-32 p.Article in journal (Refereed) Published
Abstract [en]

The present work is part of an investigation towards the development of a process route for the extraction of metal values from slag, low grade ores and other oxidic materials such as spent refractories using molten salts in the temperature range 800-950uC. The present paper focuses on the recovery of metal values, primarily Cr and Fe, from electric arc furnace slag and chromite ore. The impact of different factors to the dissolution of slag, such as temperature, holding time, flux content and weight ratio of flux/slag was studied. Based on the optimised experimental factors, the salt bath containing metal values extracted from the slag/ore was electrolysed under an applied voltage of 2·8 V. The cathode deposit was subjected to SEM/EDS and XRD analyses, which confirmed the formation of CrFe alloy. The process was also extended towards the production of CrFe alloy directly from chromite ore. The results show that the molten salt extraction process offers a promising route towards the recovery of metal values from slags and low grade ores.

Keyword
Chromite, EAF slag, Metal extraction, Molten salt electrowinning, Recovery
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-14115 (URN)10.1179/037195509X12585446038726 (DOI)2-s2.0-77951482886 (Scopus ID)
Note

QC 20100714

Available from: 2010-07-14 Created: 2010-07-14 Last updated: 2017-12-12Bibliographically approved
5. The salt extraction process - A novel route for metal extraction Part 2 - Cu/Fe extraction from copper oxide and sulphides
Open this publication in new window or tab >>The salt extraction process - A novel route for metal extraction Part 2 - Cu/Fe extraction from copper oxide and sulphides
2010 (English)In: Transactions of the Institution of Mining and Metallurgy Section C - Mineral Processing and Extractive Metallurgy, ISSN 0371-9553, E-ISSN 1743-2855, ISSN 0371-9553, Vol. 119, no 2, 93-100 p.Article in journal (Refereed) Published
Abstract [en]

The present work is Part 2 of a novel salt extraction process towards the extraction of metal values from slag, low grade ores, etc. The authors describe the extraction of copper/iron from CuO, Cu 2S and CuFeS 2, which provides a green process route to treat the copper ore including both oxides and sulphides. The dissolution properties were investigated with respect to process parameters such as weight ratio of flux/copper ore and temperature. The highest extraction ratio is found at 92% in dissolution of Cu 2S, and residue of salt melt was confirmed to be mainly Al 2O 3. A cell voltage between 1·6 and 2·2 V is introduced for electrolysis, and the cathode products are proved to be pure Cu for electrolysis of CuO/Cu 2S, and Cu/Fe mixture for CuFeS 2 by X-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy analysis. Some sulphur and iron chloride were found to volatilise and were deposited in the low temperature zone. Yield of copper has been estimated to be 52·3% during electrolysis of Cu 2S.

Keyword
Copper oxide, Copper sulphides, Electrolysis, Molten salts
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-14116 (URN)10.1179/174328510X498116 (DOI)2-s2.0-77953804744 (Scopus ID)
Note

QC 20100714

Available from: 2010-07-14 Created: 2010-07-14 Last updated: 2017-12-12Bibliographically approved
6. The salt extraction process-A novel route for metal extraction. Part III: Electrochemical behaviors of the metal ions(Cr, Cu, Fe, Mg, Mn) in molten (CaCl2-)NaCl-KCl salt system
Open this publication in new window or tab >>The salt extraction process-A novel route for metal extraction. Part III: Electrochemical behaviors of the metal ions(Cr, Cu, Fe, Mg, Mn) in molten (CaCl2-)NaCl-KCl salt system
(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-14117 (URN)
Note
QC 20100714Available from: 2010-07-14 Created: 2010-07-14 Last updated: 2010-07-15Bibliographically approved
7. Copper extraction from copper ore by electro-reduction in molten CaCl2-NaCl
Open this publication in new window or tab >>Copper extraction from copper ore by electro-reduction in molten CaCl2-NaCl
2009 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 54, no 18, 4397-4402 p.Article in journal (Refereed) Published
Abstract [en]

Sintered solid porous pellets of copper sulfide (Cu2S) and Cu2S/FeS were electrolysed at a cell voltage of 2.2-2.8 V to elemental Cu, S and Cu, Fe, S, respectively in molten CaCl2-NaCl at 800 degrees C under the protection of argon gas. The process parameters for optimal electrolysis are presented. The electrolysis products are characterized by microscopic techniques and XRD. The product characteristics are linked to the process parameters. The direct electrolysis of the sulfide to copper with the emission of elemental sulphur offers an attractive green process route for the treatment of copper ore.

Keyword
Copper extraction, Electro-reduction, Molten salts, Green process, SO2 emission
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-14118 (URN)10.1016/j.electacta.2009.03.015 (DOI)000266826200019 ()2-s2.0-65549112158 (Scopus ID)
Note
QC 20100714Available from: 2010-07-14 Created: 2010-07-14 Last updated: 2017-12-12Bibliographically approved

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