Sülfürlü Olmayan Bir Çinko Cevherinin Amonyak Liçiyle Değerlendirilmesi
Özet
In this study, following characterization, the dissolution behaviour of a non-sulfide zinc (smithsonite) ore (DDM) from Yahyalı (Kayseri, Turkey) region in aqueous ammonia solutions was investigated in detail (together with another smithsonite ore (KM) with different chemical and mineralogical compositions from the same region) and the conditions for obtaining various zinc compounds by precipitation (and/or calcination) from the pregnant solutions formed after dissolution under different experimental conditions were revealed.
The chemical, X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) analyses showed that DDM (28.70% ZnO) and KM (23.73% ZnO) samples used in the experimental studies were non-sulfide type smithsonite (ZnCO3) ore samples and their main carbonate gangue minerals were calcite (CaCO3) and dolomite (CaMg(CO3)2), respectively.
Following leaching of the ore samples at room temperature in aqueous ammonia solutions under different conditions (NH3 concentration: 1-13.3 M, stirring time: 15-120 minutes, solid/liquid ratio: 0.075-0.50 g dry solid/mL solution) according to ZnCO3 + 4NH3 → Zn(NH3)42+ + CO32- general reaction, 76.2% of Zn (80.4% of Cd) in DDM sample and 50.8% of Zn (45.4% of Cd) in KM sample could be dissolved under the selected optimum condition (4 M NH3 concentration (initial NH3/Zn mole ratio: 7.52), 90 minutes stirring time, and 0.15 g/mL solid/liquid ratio). The highest dissolution ratio values of 79.7% Zn (87.6% Cd) and 65.3% Zn (61.7% Cd) for DDM and KM samples, respectively, were reached at the maximum workable ammonia concentration of 13.3 M (NH3/Zn mole ratio: 25.08). The chemical, XRD and FT-IR analyses performed on the undissolved solids (the leaching residues) obtained after leaching experiments showed that the aqueous ammonia solution could selectively dissolve zinc ore mineral, smithsonite, into the solution phase against the main carbonate gangue minerals. Within the scope of this thesis, beside the ammonia concentration, the effects of stirring time and solid/liquid ratio have also been studied in detail.
Because of the higher zinc (and cadmium) dissolution ratio values obtained for DDM sample under all of studied experimental conditions, the pregnant solutions formed after dissolution of DDM sample were used in the precipitation experiments. The precipitation experiments were performed on the pregnant solutions, named as ʻʻN60ʼʼ (pregnant solution obtained after dissolution in 4 M NH3 solution at 0.15 g/mL solid/liquid ratio), ʻʻN120ʼʼ (pregnant solution obtained after dissolution in 8 M NH3 solution at 0.30 g/mL solid/liquid ratio) and ʻʻN200ʼʼ (pregnant solution obtained after dissolution in 13.3 M NH3 solution at 0.50 g/mL solid/liquid ratio), obtained after dissolution of DDM sample at increasing solid/liquid ratio values (in order to obtain higher amounts of zinc-containing solids) under constant 7.52 NH3/Zn mole ratio. Precipitation processes were performed by separate heating of each pregnant solution to complete dryness at different temperatures in the range of 50°C-150°C, and by complete drying of all three pregnant solutions at 50°C, quite pure zinc ammine carbonate (Zn(NH3)(CO3)) precipitate containing very low amounts of hydrozincite were obtained. By complete drying at 150°C, pure hydrozincite (Zn5(CO3)2(OH)6)), quite pure hydrozincite containing very low amounts of zinc ammine carbonate, and hydrozincite containing considerable amounts of zinc ammine carbonate were obtained from N60, N120 and N200 solutions, respectively. Different zinc containing precipitates were obtained after precipitation under the same experimental conditions probably due to the differences in the amounts of ammonia, carbonate and zinc contents of the used pregnant solutions. On the other hand, single-phase zinc oxide solids having crystallite sizes of 27, 28 and 34 nm, respectively, could be obtained by calcination (at 450°C) of the zinc-containing precipitates obtained after complete drying of N60, N120 and N200 solutions at 50°C. Finally, in this study, considering all the obtained experimental findings, a flowsheet is proposed for the preparation of different zinc compounds by hydro(/pyro)metallurgical methods from smithsonite ores, which have considerable reserves in our country.
