Isıl Önişlemin Bir Çinko Karbonat Cevherinin Hidrometalurjik Olarak İşlenmesi Üzerine Etkileri
Özet
In the first step of this study, the leaching behaviour of a zinc carbonate (smithsonite, ZnCO3) ore sample (24.22% ZnO) from Yahyalı (Kayseri, Turkey) region was investigated comprehensively in sodium hydroxide solutions under different experimental conditions using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS), thermal (TG/DTA) and chemical analyses methods. It was observed that the leaching ratio value of zinc continuously increased with the increase of concentration of sodium hydroxide solution from 1 M to 4 M, and the highest zinc leaching ratio values of 70.7% and 66.5% were reached after leaching for 60 minutes in 4 M NaOH solutions at 25°C and 90°C, respectively. On the other hand, the leaching ratio value of zinc increased from 40.0% to 67.2% with the increase of leaching time from 15 minutes to 60 minutes, respectively, but the extension of the time to 240 minutes decreased the leaching ratio of zinc to 63.0%. The XRD, FT-IR, TG/DTA and chemical analyses of the ore sample and the residues obtained after leaching showed that the smithsonite phase in the ore sample dissolved selectively against gangue minerals and the reductions in the zinc leaching ratio values observed at higher temperature (90°C) and longer leaching time (240 minutes) resulted from the formation of zinc oxide and calcium zincate phases, respectively, in the leaching solutions.
In the second step of the study, the structural changes occured in the ore sample following thermal pretreatments applied at different temperatures (250, 400, 450, 550, 650, 750 and 900°C), which were selected according to the DTA curve of the ore sample, were revealed by using XRD, FT-IR and TG/DTA analyses. Then, the effects of thermal pretreatments applied at different temperatures on sodium hydroxide leaching of zinc were showed comparatively by determining the leaching ratio values of zinc in the thermally pretreated ore samples. While the thermal pretreatment at 250°C did not cause any structural change in the ore sample, the thermal pretreatment applied at 450°C completely converted the smithsonite in the ore sample to zinc oxide. The phases such as ZnFe2O4 and Zn2SiO4, which have higher dissolution resistance in sodium hydroxide solutions, formed after thermal pretreatments at higher temperatures, and as a result of this, the leaching ratio value of zinc, 70.7%, in the ore sample in 4 M NaOH solution decreased to 62.0% and 31.3% following thermal pretreatments applied at 450°C and 900°C, respectively. In addition to zinc, the changes caused by thermal pretreatments on the leaching ratio values of lead and cadmium in the ore sample were also presented within the scope of this thesis.
In the last step, the comparative experimental studies were performed on the possibilities of obtainment of zinc by precipitation from the pregnant solutions formed after leaching of the original sample and the sample thermally pretreated at 450°C in 4 M NaOH solutions, and it was found that the zinc in the pregnant solutions could be precipitated by addition of concentrated sulfuric acid as zinc oxide solids, having different morphologies and crystallite sizes, at efficiencies of 96.0% and 84.1%, respectively.
