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In this study, the leaching behaviour of lithium, together with cesium and rubidium, from a clay sample of Kırka borate deposit in sulfuric acid solutions was investigated with chemical, XRD, FTIR, DTA analyses methods and specific surface area measurements. It was observed that the leaching behaviours of lithium, cesium and rubidium were quite similar in character in that their extent of leaching tended to improve with increasing sulfuric acid concentration, especially in the range of 0.1 to 2 mol•dm-3 , at the highest leaching temperature of 363 K. Further increase of the acid concentration to 4 mol•dm-3 H 2 SO 4 appeared to have a limited improvement in their extent of leaching. Under the optimum conditions, 2 mol•dm-3 H 2 SO 4 concentration and 363 K leaching temperature, the leaching ratios reached for lithium (Li), cesium (Cs) and rubidium (Rb) were 97.2%, 83.7% and 65.2%, respectively. The results of XRD, FTIR and DTA analyses applied to the clay sample and the leaching residue obtained after leaching of the clay sample under the optimum conditions collectively showed that almost complete destruction of crystalline smectite structure(s) in the clay sample caused by acid leaching resulted in the formation of amorphous silica phase in the leaching residue. During this transformation, as expected, the specific surface area of the clay sample increased, from 59 to 406 m 2 /g. The results obtained in this preliminary study may be exploited for the treatment of very high tonnages of clay containing processing waste of Kırka boron plant as potential Li (Cs and/or Rb) resource.

In this study, firstly, the effects of ammonia concentration, leaching time and solid/liquid ratio on the leaching behaviour of zinc from a smithsonite (ZnCO3) ore sample in aqueous ammonia solutions were investigated at room temperature by chemical, X-ray diffraction (XRD) and Fouriertransform infrared (FT-IR) spectroscopy analyses. It was found that leaching ratio of zinc steeply increased from 30.1 to 76.2% with increasing ammonia concentration from 1.0 to 4.0 M and maximum zinc leaching ratio of 79.7% was reached after leaching in 13.3 M NH3 solution. The XRD pattern of the residue obtained after leaching in 4.0 M NH3 solution for 90 min at solid/liquid ratio of 0.15 g/mL, the optimum condition, showed that smithsonite phase in the ore sample almost completely dissolved whereas the gangue minerals goethite and calcite remained unaffected, confirming the selectivity of ammonia solution for zinc dissolution. Together with zinc, leaching ratios of cadmium were also determined. In second part of the study, precipitation tests (by complete drying at different temperatures) were conducted on dissolved zinc, carbonate and ammonia containing pregnant solutions obtained after selected leaching experiments. By complete drying of the pregnant solutions at low temperatures, i.e. 50°C, relatively pure solid zinc ammine carbonate (Zn(NH3)CO3) precipitates and at higher temperatures, i.e. 150°C, quite pure solid zinc carbonate hydroxide (Zn5(CO3)2(OH)6) precipitates could be prepared. High-temperature heating of Zn(NH3)CO3 and Zn5(CO3)2(OH)6 precipitates at 450°C yielded single-phase zinc oxide (ZnO). The chemical compositions, FT-IR spectra and scanning electron microscope (SEM) photographs of some of the precipitates were also presented.

In this study, the direct conversion behaviors of different alkaline earth metal solids (the hydroxides and the sulfates of alkaline earth metals Ca, Sr, Ba and Mg) to their corresponding carbonates in dissolved carbonate-containing pregnant solutions obtained by direct leaching of a smithsonite (ZnCO3) ore sample in aqueous ammonia solutions having different concentrations (4 M, 8 M and 13.3 M NH3) were investigated by using X-ray diffraction analyses at alkaline earth metal to dissolved carbonate mole ratios of 1:1 and 1:2, for revealing the conversion possibilities of dissolved carbonate in the pregnant solutions to solid carbonate by-products. The results of direct conversion experiments showed that Ca(OH)2, CaSO4•2H2O, Sr(OH)2•8H2O and Ba(OH)2•8H2O converted to their corresponding carbonates, SrSO4 partially converted to SrCO3 as observed by the presence of unreacted SrSO4 peaks in X-ray diffraction patterns of the converted solids, and BaSO4 did not convert to BaCO3 because of its lower solubility with respect to BaCO3. On the other hand, it was observed that Mg(OH)2 did not convert to MgCO3, but MgSO4•7H2O converted dominantly to an uncommon phase, which was tentatively identified as Mg5Zn3(CO3)2(OH)12•H2O. In the study, a complete discussion on the conversion behaviors of alkaline earth metal solids to their corresponding carbonates was given considering the differences between their solubility product constants and the changes in the free energies of the theoretical conversion reactions. In addition, infrared spectra and scanning electron microscope images of some of the converted solids were also presented for characterization purposes.

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