Application of the Pulsed Column Technology in Uranium Recovery from Gattar Uranium Ore Concentrate, Eastern Desert, Egypt

Abstract

The Gattar mini pilot plant was constructed in Gabel Gattar area situated in the northern Eastern Desert in the year 2000 for the experimental treatment of the promising uranium occurrence that is mainly associated with the younger granites and El-Hamamat sediments. Due to the relatively low grade of the uranium in the collected ore material, the mini pilot plant flow sheet involves heap leaching with 20=50g/l sulfuric acid solution followed by uranium adsorption from the obtained leach liquor upon the Chinese anion exchange resin(D263B).The adsorbed uranium was then eluted by acidified 1M NaCl solution and the obtained eluate was subjected to alkali precipitation using NaOH to obtain the uranium concentrate that is commercially known as yellow cake (sodium diuranate).However , the latter was of low grade besides including several impurities; a matter which is due to the highly impure eluate which depends in turn on the ore composition that affects both the adsorption and elution. Therefore, to obtain a uranium concentrate of high purity, it was found necessary to subject the obtained eluate to a solvent extraction step prior to uranium precipitation i.e. an Eluex procedure. However, according to the chemical composition of the eluate, which only assays 7gU/l, presence of 1.25gFe/l and up to 32 gCl-/l are greatly deleterious for either the Amex or the Dapex process. This is due to the fact that in case of the Amex procedure, both Cl-and FeCl4- would be co-extracted by the applied tertiary amine. In the meantime, in the Dapex procedure, presence of iron would largely compete with the UO22+. Accordingly, it was decided to apply the mixed solvents procedure i.e. a mixed Amex composed of 3% TOA and 2% D2EHPA in kerosene and a mixed Dapex composed of 3%D2EHPA and 3% TBP in kerosene for uranium upgrading in the Gattar mini pilot plant eluate. In both systems, the present work involved the characteristics of the batch equilibrium procedure to first determine the optimum conditions for uranium upgrading, followed by application of the obtained results in a continuous system using the pulsed perforated plate column. To realize the objectives of this thesis, an introduction was presented explaining the characteristics of the uranium occurrence in G-Gattar in the North eastern Desert of Egypt as well as a brief discussion of the purpose of the present work .This was followed by Chapter-I including an overview of the different hydrometallurgical techniques used for uranium ore processing besides a brief description of the concerned literature. Besides acid and alkaline leaching procedures of uranium from its ores, this chapter includes the different procedures for the uranium recovery from its leach liquors in order to be concentrated and purified. The latter involved mainly both the ion exchange resins and organic solvents. This was followed by a brief description of the different recovery equipment that is mainly used for this purpose and which mainly include the characteristics and design aspects of the pulsed perforated column. This chapter has finally included the different procedures for uranium precipitation from its upgrading and purified solutions. Chapter II describes the chemicals and reagents used as well as the chemical composition of both the heap leach liquor and the working eluate solution of Gattar mini pilot plant. Also included is a brief description of the equilibrium batch experiments that would determine the optimum conditions. The latter have then been applied upon the continuous recovery experiments using the pulsed perforated plate column. In addition, the geometrical characteristics of the pulsed perforated plate column that has been constructed in the present work are briefly discussed. Chapter III includes all the obtained results together with a detailed discussion of all these results. Thus, it has been found that the optimum extraction conditions of the mixed Amex batch procedure for treating Gattar eluate involved an O/A ratio of 1.8/1that has been obtained from the McCabe-Thiele extraction diagram. In addition, these conditions involved working at a pH of 1 at room temperature and for a constant time of 1.5 minutes and that the studied mixed solvent ratio indicated the optimum values of 3%TOA and 2%D2EHPA in kerosene. On the other hand, the studied optimum conditions for the mixed Dapex batch equilibrium involved a solvent ratio of 3%D2EHPA together with 3%TBP in addition to a pH of 1.8 at room temperature for 3 minutes contact time. In this system an O/A ratio of 1.72 has been obtained from the corresponding McCabe-Thiele diagram. After having determined the optimum extraction conditions of the two study systems through the batch equilibrium experiments, two uranium-loaded mixed solvent samples were then prepared for studying their stripping characteristics. In the loaded mixed Amex solvent (3%TOA/2%D2EHPA) the uranium assay attained 3.9gU/l while in the loaded mixed Dapex solvent (3%D2EHPA/3%TBP), the uranium assay attained 4.15gU/l. However, prior to study the stripping conditions, it was found necessary to subject both loaded mixed solvents to a scrubbing test using 0.1 and 0.5M sulfuric acid solutions respectively in a manner to eliminate as much as possible any co-extracted metal impurities .