PHYSICAL AND CHEMICAL STUDIES ON THE URANIFEROUS MINERALIZATION OF EL- SELLA AREA FOR ITS LEACHING AND RECOVERY PROCESSES

Abstract

The present work is concerned with the recovery of uranium and rare earth elements from their mineralization in the shear zone of El-Sella highly altered granite. The raw collected material composite sample under study was found to assay 0.11% RE2O3 and 0.05 % U3O8. El-Sella mineralization is located at Halayeb environ at about 30 km west of Abu Ramad City Southeastern Desert, Egypt. To realize the objectives of this work, the hydrometallurgical characteristics of both uranium and REEs ores have been adequately summarized. Thus, uranium ores are generally subjected to an acid or alkaline leaching step. Choice between the two leaching reagents have is generally depends on many factors that have been summarized in the literature review. From the above discussion and in the light of the working El-Sella ore material, the present work have been formulated in studying simultaneous the acid leaching of metal values. For this purpose sulfuric acid was used as leaching agent and the optimum factors thereof has been determined. Sulfuric acid was used as a conventional leaching agent for uranium and rare earths; thereafter it has required to study the factors that affect the leaching of uranium and rare earths. These factors include sulfuric acid concentration, solid/liquid ratio, leaching temperature and leaching time. Studies shown that the optimum conditions to obtain a leaching efficiency of 99 and 95% for uranium and rare earth respectively from El-Sella mineralization with the minimum gangue dissolution would include: Summary and conclusion - 140 - Acid concentration 5% (v/v) with a S/L ratio 1/2 at temperature 90 0C for 4 hrs. To receive the leached uranium and REEs metal values from their combined sulfate leach liquor, it was found convenient to apply two successive solvent extraction procedures. After obtaining the leach liquor that was found to assay 160 ppm U, 330 ppm REEs and about 12 g/l Fe2O3, it was directed to a solvent extraction technique for extraction of uranium then REEs. Two successive circuits have been studied for uranium and REES that have been leached by acid agitation leaching of El-Sella mineralization. The tertiary amine, trioctylamine (TOA) was applied for prior uranium extraction while the REEs left behind would be subsequently recovered by using the di (2-ethylhexyl) phosphoric acid (DEHPA). For uranium extraction by trioctyl amine, the extraction factors have been studied that include pH of aqueous phase, shaking time, solvent concentration, and O/A phase ratio. The optimum results was found to be: pH of the aqueous phase is 1 for 5 min shaking time with 0.088M solvent concentration and at room temperature. A/O phase ratio has been studied and its results has been used to construct the McCabe-Thiele extraction diagram to determine the number of theoretical stages that would be required to almost completely extract the uranium from the acid leach liquor feed of El Sella mineralization composite sample and an operating line having a slope equivalent to a flow rate A/O ratio of about 7 was properly fitted to the obtained equilibrium isotherm. Accordingly, in a continuous countercurrent extraction system, 3 stages were found required to almost completely extract the uranium from the acid leach liquor. The Summary and conclusion - 141 - maximum obtained uranium saturation level was found to be about 1.2 g/l in the organic phase. To study uranium stripping factors, a loaded solvent sample was first prepared by repeated contacts of a suitable volume of the working TOA/benzene (0.088M) with fresh acid leach liquor samples till almost saturation. Uranium concentration in the prepared loaded TOA/ benzene solvent sample attained about 1.2 g/l. Two stripping agents have been used; namely, sulfuric acid and sodium carbonate. In case of stripping by sulfuric acid the optimum stripping factors to strip more than 98% of the loaded uranium were found to be 15% acid concentration (v/v) for 20 min contact time at room temperature. On the other hand, from the McCabe-Thiele stripping diagram it was clearly evident that, 4 stripping stages in the counter current at an O/A phase ratio of 0.32 would require to strip most of the uranium. Under these conditions, 4 stripping stages would result in a stripping solution assay more than 3 g U/l. On the other hand, when using sodium carbonate as a stripping gent the optimum conditions were using 5% sodium carbonate concentration for 20 min. s at a phase ratio of 1/1 A/O at room temperature. The obtained equilibrium data at different A/O phase ratio has been used to construct the equilibrium isotherm (McCabe_Thiele Diagram). To the latter, a proper operating line with a slope about 0.3has been lilted to show that the required stages in the counter current system would be about 3 while the O/A ratio would be 0.3 (A/O=3.3)