الفهرس 
Abu Zeneima gibbsite ore materialOnly 14 pages are availabe for public view
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Abstract
Gibbsite beds of Talet Seleim locality of East Abu Zeneima are among the sedimentary rock sequence of Um-Bogma Formation which belongs to the Caboniferrous age. This ore material is considered as non- conventional resource of REEs in Egypt because its relative high content of REEs that reached up to 1.18% beside its main component of Al as well as the considerable levels of Zn and Mn.
The aim of the present work is to investigate the leaching cahacteristics and recovery studies of REEs and the associated economic metal values; namely Zn and Al. For this purpose, a technological representative sample of Abu Zeneima gibbsite ore material was properly collected from Talet Seleim locality. The chemical analysis of this sample revealed the presence 0.43% REEs, 1.25% Zn besides 10.79% Al. The mineralogical analysis of this sample by XRD technique revealed that it contains about 31.0% gibbsite mineral, 23.18% silica, 12.2% goethite, 5.43 % chalchophanite as well as 21.9% dolomite. There are no identified minerals for REEs and this may be due to their adsorption on the clayey ore material.
Different leaching methods were performed to determine the optimum conditions that realize highest dissolution efficiencies for all the interesting metals. For H2SO4 acid agitation leaching route, it was possible to achieve dissolution of REEs, Zn and Al with efficiencies of 90.3, 91.1 and 97.6% respectively. This was achieved by using 30% H2SO4 acid in a S/L ratio of 1/3 with stirring time for 5 hrs at room temperature. On the other hand, for salt roasting rout, the dissolution efficiencies attained about 91.3, % for REEs, 82.4% for Zn and complete Al dissolution. This was achieved at 1/3 ore/ (NH4)2SO4 ratio, 3 hrs roasting time at 600 oC as roasting temperature. However, H2SO4 agitation leaching is preferred and convient to prepare sulfate leach liquor suitable for the recovery of the valuable metals. The prepared leach liquor assays in g/l: 0.77 REEs, 2.28 Zn and 21.1 Al.
Direct precipitation techniques were applied upon the prepared Abu Zeneima sulfate leach liquor for the recovery of the metals of interest. First, Zn was selectively precipitated as ZnS by 2% Na2S at low pH value of 2. The precipitate was found to contain elemental sulfur which is due to the reduction of Fe 3+ to Fe 2+ and oxidation of S 2- to elemental sulfur (S). Therefore, purification of the impure ZnS was carried out by its dissolving in 4% HCl where a concentrated solution of ZnCl2 was obtained leaving behind a bright yellow sulfur precipitate. This followed by re- precipitation of Zn from chloride solution as Zn(OH)2 using 20% NaOH at pH 8.6, the latter was ignited to ZnO.
After zinc precipitation, the filtrate was then subjected to an oxidation step using H2O2 prior to the REEs precipitation to oxidize Fe2+ (which produced during ZnS precipitation and would be co-precipitated with RE-oxalate) to Fe3+. The REEs were selectively precipitated by using 30% oxalic acid (after raising the pH value to 2.9) where almost complete precipitation of REEs was carried out at pH 1to obtain RE2O3 cake.
Soda precipitation of Al as Al(OH)3 was carried out by using 20%NaOH at pH 5.6 accompanied with Fe(OH)3 that can be separated by dissolving their cake in excess NaOH to obtain soluble NaAlO2 leaving Fe(OH)3 un-dissolved behind.
The obtained RE2O3 cake was then dissolved in HCl to get rid of any impurities and the highly pure RE cake was then treated to separate its individual components. The individual separation of REEs is started with separation of Ce (about15.0% of the total RE concentrate) through oxidation process at pH 3.4 for 3hrs at 130 0C in the form of CeO2.nH2O to realize almost complete separation of Ce (IV). The remaining almost Ce-free RE concentrate has been subjected to individual REEs separation using cationic exchange resin (Dowex 50-X8, 150 mesh size) in its hydrogen form by applying successive complexing agents with EDTA solution at pH 8.50 to increase the separation factor between REEs. In other words, the loaded column in hydrogen form (17ml w.s.r) is coupled with a second column packed with the same resin but in the Cu (II) form (retaining column, twice of the loaded column and of the same diameter). The applied conditions include the contact time of 20 min. with flow rate of 1ml/min. Separation of highly pure concentrate of Sm Nd and La were achieved. In addition, the resin column technique improved the purity of Pr up to 73%.
The failure to attain individual separation of the HRREs may be due to their lower concentration in the input sample as well as the smallest stability constants of these elements with EDTA. Finally, a technological flowsheet for processing of Abu Zeneima gibbsite ore material was designed.