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Abstract
Lake Quaroun is considered as a tropical and inland closed basin. It lies in an arid region occupying the deepest part of El-Fayoum Depression in the Western Desert of Egypt about 90 Km SW Cairo. It is fed only by drainage water arising from the cultivated land in the El-Fayoum Depression area where wastewaters are collected in the Lake Quaroun. These wastewaters carrying considerable amounts of salts. Under progressive evaporation the dissolved salts become more concentrated. Accordingly, the salinity of Lake Quaroun tends to undergo a progressive increase with time where it was fresh water about 150 years ago. The continuous increasing of Lake Quaroun salinity will harm bio-diversity and fishing productivity of this lake. Accordingly, Egyptian Salts and Minerals Company (EMISAL) conducted on salt extraction from Lake Quaroun as an environmental protection project. On the other hand, the project is considered as an industrial complex with multi-stages developing program for salt extraction on economic basis. EMISAL is working on; “how to solve an environmental problem and use the solution as an economic tool”. The first stage of EMISAL industrial complex started production by 1993. Now, its production is 100.000 t/y of high quality anhydrous sodium sulphate (99.2% thenardite) and 120.000 t/y of high grade sodium chloride (99.8% halite). This more than sufficient for local demands, and almost half the annual production is exported to Middle East and European Countries. All of EMISAL projects aim to extract the previously mentioned salts and also to return the remaining water into the lake that is essentially free of salts. As such it is an environmental re-balancing project to prevent further deterioration of the Lake Quaroun water and eliminate the consequent socio-economic problems (e.g., collapsed fishing productivity and dislocated population). This can not be achieved unless the residual brine after NaCl extraction have been recycled for further economic proceedings. For this purpose, EMISAL take the decision to utilize the residual brine as a raw material for magnesium sulphate (epsom salt) production. The production of epsom salt representing the last stage of EMISAL designed projects till now. The plant for epsom salt production from residual brine is under construction, the estimated production of this plant according to EMISAL studies is about 40.000 t/y of Epsom salt with 5000 t/y of sylvite.
The present work was conducted on the studing of mineralogy, geochemistry and economic beneficiation of the residual brines, EMISAL storage ponds, Fayoum, Egypt. In EMISAL, four ponds were constructed to concentrate the brine almost 10 folds at the outlet to the Na2SO4 factory. The flow-path removes carbonates and calcium sulphate before brine reaching saturation levels with respect to Na2SO4 (thenardite) and NaCl (halite). The Na2SO4 is extracted industrially in the thenardite plant. The left-over brines (mother liquor) are stored in storage pond (crystallizer) until they evaporate to precipitate NaCl. The residual brines still as small patches in between the halite precipitates. This crystallizer pond named pond 2/2, this pond represents the case study of the present work. In this pond, the residual brine evolution was traced to determine the suitable conditions at which the residual brine should be drained out from pond 2/2 before coprecipitation of magnesium sulphate as contaminations with halite. The study was performed by regular sampling of brines and salts from the studied pond in the period from June to October 2004. This period was characterized by hot arid.