Thermodynamic study of Lake Katwe Natural brine.

Abstract

From literature, Uganda has good salt deposits which if well utilized could provide approximately 40,000 tones/year for over thirty years. [1] Despite the fact that it has these deposits, there has been a gap in the salt processing methods in the Ugandan salt industry, since currently impure salt is being produced. This work involves the thermodynamics study of Lake Katwe concentrated natural brine. This study was aimed at development of the concentrated brine process schemes, perform their simulation and provide their cost evaluation. In order to enhance the extraction of pure sodium chloride (Halite) and also other salts such as gypsum, anhydrite and many others which if not extracted would be impurities. The previous thermodynamic studies on natural brine, together with literature concerning Lake Katwe composition have been documented. A thermodynamic study has been carried out with the aid of the geothermal simulation software called PHREEQC. The Pitzer database which is one of the PHREEQC databases was opted for this particular study because concentrated brine (salt) was being dealt with. Before development of the schemes and their simulations, the Pitzer database was updated to include the salts that were missing such as soda ash (Na2CO3). With this software, three brine processing schemes have been developed and studied to detail. These schemes were produced based on different properties. That is to say; the first scheme uses change in pH and temperature variation, the second scheme was based on isothermal temperatures and the third on temperature variation where a big range of temperatures was considered with respect to their saturation indices. Then the cost evaluation was also done. From the results, simulations revealed that process scheme one produces large quantities of Halite (NaCl) compared to the other two process schemes and also it produces a more pure product since there are only two salts present at the end of the scheme. Also results reveal that there was Halite in large quantities compared to the rest of the salts in all the three process schemes. These simulations provided an approximate output of 70%, 50% and 30% Halite as per schemes respectively that is to from process scheme one to three. The cost evaluation results also revealed that all the three process schemes had a payback period around four years. It also revealed that all the three process schemes were viable for commercialization, given the fact that each process scheme provided Net present value (NPV) > 0, Profitability index (PI) > 1 and internal rate of return (IRR) > 10%. Though process scheme one was found to be more profitable as revealed by the cost evaluation of the three schemes. Generally the current work provides better technology and information for Lake Katwe natural brine processing and extraction.