ISIL ÖNİŞLEMİN LATERİTİK BİR NİKEL CEVHERİNİN ASİT LİÇİ DAVRANIMI ÜZERİNE OLAN ETKİSİNİN İNCELENMESİ

Abstract

In this thesis, the leaching behavior of Gördes (Manisa/Turkey) lateritic nickel ore in citric acid solutions following thermal pre-treatments at different temperatures was investigated. Initially, the ore sample was chemically and mineralogically characterized, and it was determined that the ore under study is a low-grade lateritic nickel ore containing 0.633% Ni, 0.034% Co, 15.46% Fe, 7.24% Ca, and 4.51% Mg. The ore sample was found to be composed of six main minerals as; quartz, dolomite, goethite, hematite, smectite, and calcite, along with smaller amounts of serpentine and asbolane minerals. It was also identified that the nickel in the sample is associated with goethite, smectite, and asbolane. Based on TG/DTA analysis, thermal pre-treatment temperatures of 350°C and 900°C were chosen to be applied before leaching of the ore sample.

Following agitated citric acid leaching experiments performed under atmospheric conditions at constant 60-minute leaching time and 10% solids ratio, using different citric acid concentrations (0.25 M, 0.5 M, 1 M, 2 M, 4 M) at different leaching temperatures (25°C, 45°C, 65°C, 85°C), the dissolution ratios and leaching behaviors of nickel, cobalt, iron, calcium, and magnesium in the compositions of the unheated (original) ore sample, the sample thermally pre-treated at 350°C, and the sample thermally pre-treated at 900°C were determined through chemical analyses and XRD analyses. It was observed that the dissolution ratios of nickel in the unheated samples and samples thermally pre-treated at 350°C and 900°C generally increased with increasing citric acid concentration and leaching temperature. Compared to the unheated sample and the sample thermally pre-treated at 900°C, the highest nickel dissolution rate was achieved after leaching the sample pre-treated at 350°C. The maximum nickel dissolution rate of 47.4% was obtained by leaching the sample pre-treated at 350°C, under the conditions of 85°C leaching temperature, 4 M citric acid concentration, 60 minutes leaching duration, and 10% solid ratio. The dissolution behaviors of nickel and cobalt were found to be quite similar, with the highest cobalt dissolution rate (67.6%) also being achieved under the conditions of 85°C leaching temperature, 4 M citric acid concentration, 60 minutes leaching duration, and 10% solid ratio for the sample pre-treated at 350°C.

The dissolution ratios of Fe, the main component in the ore sample, remained considerably lower compared with those of Ni and Co, indicating that citric acid selectively dissolved Ni and Co over Fe. On the other hand, the obtained dissolution ratios revealed that thermal pre-treatment negatively affected the dissolution selectivity. The dissolution behaviors of Ca and Mg present in the sample composition, primarily originating from dolomite and calcite that are easily soluble in citric acid solutions, were similar. >90% Ca and >70% Mg dissolution ratios were achieved at citric acid concentrations of 1 M and higher, at leaching temperatures of 45°C and above.

Finally, a pre-test was conducted to recover nickel from a selected pregnant leach solution and recommendations were provided regarding the utilization of citric acid leaching in the processing of Gördes lateritic nickel ore.