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Characterization of Raw Materials for Salt Extraction from Lake Katwe, Uganda
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Uganda is well endowed with economic quantities of salt evident in the interstitial brines and evaporite deposits of Lake Katwe, a closed saline lake located in the western branch of the great East African rift valley. Currently, rudimentally methods of salt mining based on solar evaporation of brine continue to be used for salt extraction at the lake. These have proved to be hazardous and unsustainable to the salt miners and the environment. In this work, literature concerning the occurrence of salt and the most common available technologies for salt extraction is documented. Field studies were undertaken to characterize the salt lake deposit and to devise strategies of improving salt mining and extraction from the salt lake raw materials. The mineral salt raw materials (brines and evaporites) were characterized to determine their physical, chemical, mineralogical, and morphological composition through field and laboratory analyses. In addition, laboratory extraction techniques were undertaken to evaluate possibilities of future sustainable salt extraction from the lake deposit. Also, PHREEQC simulations using Pitzer models were carried out to determine the present saturation state of the lake brine and to estimate which salts and the order in which they precipitate from the brine upon concentration by evaporation.

Results reveal that the raw materials from the salt lake contain substantial amounts of salt which can be commercialized for optimum production. The brines are highly alkaline and rich in Na+, K+, Cl-, SO42-, CO32-, and HCO3-. Moreover, they contain trace amounts of Mg2+, Ca2+, Br-, and F-. The lake is hydro-chemically of a carbonate type with the brines showing an intermediate transition between Na-Cl and Na-HCO3 water types. The evaporites are composed of halite mixed with other salts such as hanksite, burkeite, trona etc, with their composition varying considerably within the same grades. The laboratory extraction experiments indicate that various types of economic salts such as thenardite, anhydrite, mirabilite, burkeite, hanksite, gypsum, trona, halite, nahcolite, soda ash, and thermonatrite precipitate from the brine of Lake Katwe. The salts crystallize in the order following the sequence starting with sulfates, followed by chlorides and carbonates, respectively. Moreover, thermodynamic modeling in PHREEQC accurately predicted the solubility and sequence of the salt precipitation from the lake brine. Understanding the sequence of salt precipitation from the brine helps to control its evolution during concentration and hence, will lead to an improved operating design scheme of the current extraction processes. The work providesinformation towards future mineral salt exploitation from the salt lake.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , vi, 35 p.
Keyword [en]
Lake Katwe, salt extraction, brine, evaporites, characterization, PHREEQC
National Category
Chemical Process Engineering
Identifiers
URN: urn:nbn:se:kth:diva-134708ISBN: 978-91-7501-767-9 (print)OAI: oai:DiVA.org:kth-134708DiVA: diva2:667784
Presentation
2013-12-13, Sal Kuben, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency, Phase III Uganda
Note

QC 20131129

Available from: 2013-11-29 Created: 2013-11-27 Last updated: 2013-11-29Bibliographically approved
List of papers
1. A State of the Art Paper on Improving Salt Extraction from Lake Katwe Raw Materials In Uganda
Open this publication in new window or tab >>A State of the Art Paper on Improving Salt Extraction from Lake Katwe Raw Materials In Uganda
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2012 (English)Report (Other academic)
Abstract [en]

The characteristics of Katwe salt lake are briefly discussed. The lake is the largest of the eight saline lakes in the Katwe-Kikorongo volcanic field and is a major source of salt production in Uganda. Today, salt production at the lake is carried out using traditional and artisanal mining methods. Attempts to mechanize the production of domestic and commercial grade salt at the lake were unsuccessful due to the use of a wrong technology. In this paper, the most common available technologies for salt extraction from brine are described. These are divided into four broad categories, namely thermal, membrane, chemical and hybrid processes. A review of the state of the art, previous research and developments in these technologies is presented. A detailed analysis of the processes used was done based on studies reported in the literature. From the analysis, it was observed that thermal salt production processes, especially distillation and solar evaporation have the highest share in installed capacities worldwide. Membrane technologies such as Electro-dialysis, Reverse Osmosis and chemical technologies have not found wide application in the commercial salt industry. Electro-dialysis and Reverse Osmosis have been used mainly as pre-concentration processes for subsequent thermal processes. Prospects for application of hybrid systems for salt production through integration of thermal desalting processes should be investigated for better performance efficiencies and recoveries at the salt lake.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2012. 28 p.
Keyword
Lake Katwe, salt, salt recovery and purification, separation processes
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-103348 (URN)
Projects
Improving Salt Extraction at Lake Katwe, Uganda
Note

QC 20121010

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2015-12-17Bibliographically approved
2. Towards the improvement of salt extraction at Lake Katwe, Uganda
Open this publication in new window or tab >>Towards the improvement of salt extraction at Lake Katwe, Uganda
2013 (English)In: International Journal of Scientific and Technology Research, ISSN 2277-8616, Vol. 2, no 1, 76-81 p.Article in journal (Refereed) Published
Abstract [en]

The occurrence of Lake Katwe salt deposit in Western Uganda is well-known through the East African region. Production of salt from this saline lake has been practiced for decades following traditional methods; however the quality and yield of the products are poor. There are also risks of burns, as the workers get into direct contact with the brine. Detail assessment and evaluation of the mine has been done through field studies, raw sample materials analysis. Results indicate that the raw brine from the lake is rich in sodium, chloride, potassium, carbonates, sulphate ions with traces of calcium, magnesium, and bicarbonate ions. This motivates the aspiration to properly extract salts from such a rich source. The lake brines contain impurities such as organic matter and suspended solids. With increasing demand for usage of sustainable technologies for saltextraction, the present study calls for the improvement of salt extraction at Lake Katwe through optimizing the use of the current solar evaporation technique while integrating it with a mechanized chemical separation process. This would ensure better recovery and process efficiencies, low costs and simple brine pre-treatment procedures.

Keyword
Lake Katwe, Brine, salt extraction, Evaporate, Uganda, solar ponds, rock salt
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-134778 (URN)
Funder
Sida - Swedish International Development Cooperation Agency, Phase III Uganda
Note

QC 20131129

Available from: 2013-11-28 Created: 2013-11-28 Last updated: 2017-03-03Bibliographically approved
3. Characterization of brines and evaporites of Lake Katwe, Uganda
Open this publication in new window or tab >>Characterization of brines and evaporites of Lake Katwe, Uganda
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2014 (English)In: Journal of African Earth Sciences, ISSN 0899-5362, Vol. 91, 55-65 p.Article in journal (Refereed) Published
Abstract [en]

Lake Katwe brines and evaporites were investigated to determine their chemical, mineralogical and morphological composition. 30 brine samples and 3 solid salt samples (evaporites) were collected from different locations of the lake deposit. Several analytical techniques were used to determine the chemical composition of the samples including Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), Inductively Coupled Plasma-Sector Field Mass Spectrometry (ICP-SFMS), ion chromatography, and potentiometric titration. The mineralogical composition and morphology of the evaporites was determined using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Physical parameters of the lake brines such as density, electrical conductivity, pH, and salinity were also studied. The results show that the lake brines are highly alkaline and rich in Na+, Cl-, CO32-, SO42-, and HCO3- with lesser amounts of K+, Mg2+, Ca2+, Br-, and F- ions. The brines show an intermediate transition between Na-Cl and Na-HCO3 water types. Among the trace metals, the lake brines were found to be enriched in B, I, Sr, Fe, Mo, Ba, and Mn. The solid salts are composed of halite mixed with other salts such as hanksite, burkeite and trona. It was also observed that the composition of the salts varies considerably even within the same grades.

Keyword
Lake Katwe, brines, evaporites, characterization
National Category
Geochemistry
Identifiers
urn:nbn:se:kth:diva-134779 (URN)10.1016/j.jafrearsci.2013.12.004 (DOI)000331676900005 ()2-s2.0-84891650256 (Scopus ID)
Funder
Sida - Swedish International Development Cooperation Agency, Phase III Uganda
Note

QC 20140203. Updated from submitted to published.

Available from: 2013-11-28 Created: 2013-11-28 Last updated: 2017-12-06Bibliographically approved
4. Mineral recovery from Lake Katwe brines using isothermal evaporation
Open this publication in new window or tab >>Mineral recovery from Lake Katwe brines using isothermal evaporation
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2013 (English)In: International Mine Water Association Annual Conference 2013: Reliable Mine Water Technology / [ed] Adrian Brown, Linda Figueroa, Christian Wolkersdorfer, IMWA International Mine Water Association , 2013, 855-860 p.Conference paper, Published paper (Refereed)
Abstract [en]

Lake Katwe is a saline lake within the East African Rift system in Western Uganda, with a rich source of mineral salts. The present work aims at evaluating possibilities of future salt extraction from the lake deposit. An isothermal evaporation experiment was conducted on the lake brines. The precipitated salts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. Various economic salts such as thenardite, gypsum, mirabilite, burkeite, hanksite, anhydrite, trona, halite, nahcolite, thermonatrite, and soda ash precipitate from the lake brines. The experiments also reveal the sequence of mineral salt precipitation in the order sulfates→chlorides→carbonates.

Place, publisher, year, edition, pages
IMWA International Mine Water Association, 2013
Keyword
Lake Katwe, Brine, Isothermal Evaporation, Sulfate salts, Chloride salts, Carbonate salts, XRD, SEM
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-132376 (URN)978-0-615-79385-6 (ISBN)
Conference
IMWA2013 International Mine Water Association - Reliable Mine Water Technology, Golden, Colorado, USA, 4-9 August 2013
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20131028

Available from: 2013-10-28 Created: 2013-10-28 Last updated: 2015-12-17Bibliographically approved

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