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Towards the Improvement of Salt Extraction from Lake Katwe Raw Materials in Uganda
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Uganda is well endowed with economic quantities of mineral salts present in the interstitial brines and evaporite deposits of Lake Katwe, a closed (endorheic) saline lake located in the western branch of the great East African rift valley. Currently, rudimentally and artisanal methods continue to be used for salt extraction from the lake raw materials. These have proved to be risky and unsustainable to the salt miners and the environment and they have a low productivity and poor product quality. This work involves the investigation of the salt raw materials that naturally occur in the brines and evaporites of Lake Katwe. The purpose is to propose strategies for the extraction of improved salt products for the domestic and commercial industry in Uganda.

The literature concerning the occurrence of salt and the most common available technologies for salt extraction was documented. Also, field investigations were undertaken to characterize the salt lake deposits and to assess the salt processing methods and practices. The mineral salt raw materials (brines and evaporites) were characterized to assess their quality in terms of the physical, chemical, mineralogical, and morphological composition through field and laboratory analyses. An evaluation of the potential of future sustainable salt extraction from the lake deposits was done through field, experimental, and modeling methods. Moreover, the mineral solubilities in the lake brine systems and dissolution kinetics aspects were investigated.

The results reveal that the salt lake raw materials contain substantial amounts of salt, which can be commercialized to enable an 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. Also, the evaporation-crystallization is the main mechanism controlling the lake brine chemistry. These evaporites are composed of halite mixed with other salts such as hanksite, burkeite, trona etc, but with a composition that varies considerably within the same grades. The laboratory isothermal extraction experiments indicate that various types of economic salts such as thenardite, anhydrite, mirabilite, burkeite, hanksite, gypsum, trona, halite, nahcolite, soda ash, and thermonatrite exist in the brine of Lake Katwe. In addition, the salts were found to crystallize in the following the sequence: sulfates, chlorides, and carbonates.

A combination of results from the Pitzer’s ion-interaction model in PHREEQC and experimental data provided a valuable insight into the thermodynamic conditions of the brine and the sequence of salt precipitation during an isothermal evaporation. A good agreement between the theoretical and experimental results of the mineral solubilities in the lake brine systems was observed with an average deviation ranging between 8-28%. The understanding of the mineral solubility and sequence of salt precipitation from the brine helps to control its evolution during concentration. Hence, it will lead to an improved operating design scheme of the current extraction processes. The dissolution rate of the salt raw materials was found to increase with an increased temperature, agitation speed and to decrease with an increased particle size and solid-to-liquid ratio. Moreover, the Avrami model provided the best agreement with the obtained experimental data (R2 = 0.9127-0.9731). In addition, the dissolution process was found to be controlled by a diffusion mechanism, with an activation energy of 33.3 kJ/mol.

Under natural field conditions, the evaporative-crystallization process at Lake Katwe is influenced by in-situ weather conditions. Especially, the depth of the brine layer in the salt pans and the temperature play a significant role on the brine evaporation rates. With the optimal use of solar energy, it was established that the brine evaporation flux can be speeded up in the salt pans, which could increase the production rates. Moreover, recrystallization can be a viable technique to improve the salt product purity. Overall, it is believed that the current work provides useful information on how to exploit the mineral salts from the salt lake resources in the future.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , ix, 69 p.
Keyword [en]
Lake Katwe, salt extraction, brine, evaporites, saltpan, characterization, evaporation - crystallization, solubility, Pitzer ’s ion - interaction model, PHREEQC software, dissolution kinetics, Avrami model.
National Category
Chemical Process Engineering
Identifiers
URN: urn:nbn:se:kth:diva-179445OAI: oai:DiVA.org:kth-179445DiVA: diva2:883186
Public defence
2016-01-20, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20151217

Available from: 2015-12-17 Created: 2015-12-16 Last updated: 2015-12-18Bibliographically 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
5. Phase developments during natural evaporation simulation of Lake Katwe brine based on Pitzer's model
Open this publication in new window or tab >>Phase developments during natural evaporation simulation of Lake Katwe brine based on Pitzer's model
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2014 (English)Conference paper, Published paper (Refereed)
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-179309 (URN)
Conference
9th Sida Regional Collaboration Conference, July 20-23, 2014, Entebbe, Uganda
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20151215

Available from: 2015-12-15 Created: 2015-12-15 Last updated: 2016-12-05Bibliographically approved
6. Optimization of Solar Energy for Salt Extraction from Lake Katwe, Uganda
Open this publication in new window or tab >>Optimization of Solar Energy for Salt Extraction from Lake Katwe, Uganda
2014 (English)In: Global NEST. International Journal, ISSN 1108-4006, Vol. 16, no 6, 1152-1168 p.Article in journal, Editorial material (Refereed) Published
Place, publisher, year, edition, pages
Global NEST, 2014
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-179313 (URN)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20151215

Available from: 2015-12-15 Created: 2015-12-15 Last updated: 2017-12-01Bibliographically approved
7. Determination and thermodynamic modeling of mineral solubilities in aqueous ternary systems at 303 K
Open this publication in new window or tab >>Determination and thermodynamic modeling of mineral solubilities in aqueous ternary systems at 303 K
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-179317 (URN)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QS 2015

Available from: 2015-12-15 Created: 2015-12-15 Last updated: 2015-12-17Bibliographically approved
8. Dissolution kinetics of natural halite from Lake Katwe (Uganda) in aqueous salt solutions
Open this publication in new window or tab >>Dissolution kinetics of natural halite from Lake Katwe (Uganda) in aqueous salt solutions
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(English)Manuscript (preprint) (Other academic)
National Category
Other Chemical Engineering Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-179320 (URN)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QS 2015

Available from: 2015-12-15 Created: 2015-12-15 Last updated: 2015-12-17Bibliographically approved

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Citation style
  • apa
  • ieee
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  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf