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Direct conversion of alkaline earth metal hydroxides and sulfates to carbonates in ammonia solutions

Ehsani Ilhan, Ehsani Arman, Ucyildiz Ayse, Obut Abdullah

Physicochemical Problems of Mineral Processing

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2022

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Vol. 58, iss. 1

169--180

EN

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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Preparation of different zinc compounds from a smithsonite ore through ammonia leaching and subsequent heat treatment

Ehsani Arman, Ehsani Ilhan, Obut Abdullah

Physicochemical Problems of Mineral Processing

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2021

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Vol. 57, iss. 4

96--106

EN

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 Fourier-transform 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.

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Leaching behaviour of zinc from a smithsonite ore in sodium hydroxide solutions

Ehsani Ilhan, Ucyildiz Ayse, Obut Abdullah

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 2

407--416

EN

In this study, the leaching behaviour of zinc from a smithsonite ore sample (23.43% Zn) having goethite and calcite as main gangue minerals was investigated in sodium hydroxide solutions using Xray diffraction and chemical analyses. Within the studied NaOH concentration range (1-4 mole/dm3), higher leaching ratio values for Zn were obtained by leaching at 298 K because of the decreased stability of soluble zincate species in solution at higher temperatures. When the concentration of NaOH solution was increased from 1 to 3 mole/dm3 at 298 K, leaching ratio value of Zn increased from 3.8 to 70.1%. At 4 mole/dm3 NaOH concentration, Zn leaching ratio value (70.9%) levelled off due to the formation of solid hydrated calcium zincate phase in leaching solution. On the other hand, very low leaching ratio values of Zn were obtained by leaching in 1 mole/dm3 NaOH solution at 298 K (3.8%) and 363 K (1.4%) due to the formation of solid zinc hydroxide and solid zinc oxide phases, respectively. It was observed that increasing leaching time from 1800 to 14400 s at 3 mole/dm3 NaOH concentration, favoured the formation of hydrated calcium zincate phase and so decreased the leaching ratio of Zn to a lower value (60.6%). The effect of solid/liquid ratio was also investigated and it was found that when solid/liquid ratio was decreased, Zn leaching ratio values decreased at constant OH/Zn mole ratio and increased at constant NaOH concentration conditions. Besides, for some of the experiments, leaching ratio values of lead were also given.