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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.

2

Characterization and treatment of clayey waste using a sulfuric acid roasting-water leaching process for the extraction of lithium

Obut Abdullah, Aktosun Zeynep, Girgin İsmail, Deveci Hacı, Yörükoğlu Abdulkerim

Physicochemical Problems of Mineral Processing

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2022

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Vol. 58, iss. 4

art. no. 149635

EN

In this study, a detailed characterization of the clayey waste of the Kırka boron plant was undertaken before the development of a sulfuric acid roasting-water leaching process for the extraction of lithium from this waste. The effects of roasting temperature (650-800°C) and sulfuric acid/waste ratio (90-260 kg H2SO4/1000 kg waste on a dry basis) on the extraction of lithium were investigated. By roasting the waste sample, which contained 0.37% Li2O with dolomite, smectite and borax as the main phases, at temperatures between 650°C and 800°C in the absence of sulfuric acid as the additive, CaMgSiO4 was found to form as the dominant phase after the decomposition of dolomite and smectite present in the sample. On the other hand, the X-ray diffraction analyses of the waste sample subjected to sulfuric acid treatment without roasting showed the in-situ formation of various hydrated calcium sulfate phases for all sulfuric acid/waste ratios tested. Besides, at the highest acid/waste ratio of 260, a hydrated magnesium sulfate phase was also identified in the sample. The application of the sulfuric acid roasting-water leaching process under the optimum roasting temperature of 750°C and the acid/waste ratio of 180 was found to lead to a lithium extraction of 85.7%. The applied sulfuric acid roasting-water leaching process appeared to be an attractive process with its attributes including low roasting temperature, high extraction percentage and no requirement for gypsum as the external sulfation agent.

3

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.

4

Effect of heating on structure and leaching characteristics of a zinc carbonate ore

Kumas Cavit, Obut Abdullah

Physicochemical Problems of Mineral Processing

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2021

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Vol. 57, iss. 5

23--32

EN

In this work, the structural changes occurred in a zinc carbonate (smithsonite) ore sample following heating at temperatures between 523 K and 1173 K were investigated in detail using X-ray diffraction (XRD), thermal (TG/DTA) and Fourier-transform infrared (FT-IR) spectroscopy analyses. Afterwards, the leaching characteristics of zinc from the ore sample and the heated ore samples in sodium hydroxide solutions were determined. While heating at 523 K did not cause any structural change in the ore sample, heating at 723 K completely converted smithsonite (ZnCO3) in the ore sample to zinc oxide (ZnO), which resulted lower zinc leaching efficiencies of 40.6% and 62.0% for 3 and 4 mol/dm3 NaOH concentrations, respectively, in comparison to zinc leaching efficiencies (67.2% and 70.7%) obtained for the unheated ore sample. On the other hand, due to neoformation of dissolution resistant ZnFe2O4, Ca2ZnSi2O7 and Zn2SiO4 phases during heating and formation of CaZn2(OH)6∙2H2O phase during leaching, the leaching efficiency of zinc further decreased to 22.2% and 31.3%, respectively, in 3 and 4 mol/dm3 NaOH solutions for the ore sample heated at 1173 K. The formation of zinc-containing dissolution resistant phases by high-temperature heating was observed to be the only reason for the reduction in the zinc leaching efficiency (49.4% at 1173 K) at the highest NaOH concentration (8 mol/dm3) studied. In this work, the comparative precipitation studies were also conducted and crystalline zinc oxides with different morphologies could be precipitated at considerably high efficiencies from the selected pregnant solutions obtained following leaching.

5

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.