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The processing of El-Fayoum montmorillonite-type clay deposits is attained through leaching with commercial sulfuric acid using a ball-mill-type autoclave. This process yields lithium sulfate, which can be used either for the production of lithium carbonate or to produce lithium metal. The effects of temperature, grain size, and sulfuric acid concentration and leaching on lithium recovery as well as the kinetics of the leaching process have been studied.
INTRODUCTION
Attempts to utilize Egyptian montmorillonite clays are mainly restricted to the improvement of their rheological and surface properties through acidic and alkaline activation.1-3 Only a few studies have been attempted on the occurrence and chemistry of lithium in some Egyptian clays.4,5 Attempts carried out by the U.S. Bureau of Mines relied on the extraction of lithium from montmorillonite-type clay by selective chlorination6 and roast-leach process.7-9 The research included extensive laboratory studies on a lime-gypsum roasting process that converts the lithium in the clay to a water-soluble product. The development of the process to recover lithium from such clay deposits is very important in Egypt for future economic and strategic needs due to the absence of natural spodumene deposits (principal lithium-bearing mineral).
Lithium is one of the essential elements used in aluminum pot lines and in aluminum cells, with lithium carbonate added to reduce electricity consumption and fluorine emissions. The ceramics, air conditioning, synthetic rubber, and pharmaceutical industries also use various lithium chemicals. Recently, lithium has gained importance in areas such as low-density aluminum-lithium aircraft alloys.10,11 Due to high energy consumption required in the roasting process, high reagent consumption, and utility and depreciation costs, efforts have been focused on establishing an alternative hydrometallurgical route for lithium extraction.
This investigation deals with direct sulfuric acid leaching of montmorillenitic-type clay to provide a new applicable technique for producing lithium sulfate in only one step. Calcinations or a roasting process are not required before the leaching stage. The kinetics of the leaching process was also studied.
MATERIALS AND APPARATUS
Bentonite clays are present in Egypt in reserves at El-Fayoum and Cairo-Alexandria Desert. These deposits are a medium-grade ore with 40-60% montmorillonite and 20-30% kaolinite. The representative sample of El-Fayoum bentonites, with a chemical composition (in weight percent) of 54.7 SiO^sub 2^-12.4 MgO-5.2 Al^sub 2^0^sub 3^-5.2 K^sub 2^O-4.3 Fe^sub 2^O^sub 2^-4.2...