Recovery of metals from Cuban nickel tailings by leaching with organic acids followed by precipitation and magnetic separation

Abstract

The percolation leaching of the Cuban nickel tailings containing 0.34% Ni, 0.08% Co and 44.2% Fe was investigated by using tartaric and oxalic acids at different concentrations. About 70% Ni, 80% Co and 30% Fe were extracted after 5 days of leaching with the mixture of 0.15 mol/L tartaric acid and 0.05 mol/L oxalic acid at ambient temperature and normal pressure. Nickel and cobalt extraction of 80% as well as iron extraction of 50% were achieved from the pregnant solution by means of precipitation at 80 °C for 2 h. The precipitation at ambient temperature led to a similar result after 16 days. Cobalt, nickel and iron oxalates were found in the precipitate by using the X-ray diffraction method. The regeneration of acids during the precipitation step made possible the reuse of the raffinate at the leaching step. Heating of the precipitate at 200 °C increased the metal concentration to 1.22% Ni and 0.33% Co, which can be fed in the existing nickel plant in Moa, Cuba. The magnetic processing of the leaching residues led to a non-magnetic product containing less than 20% Fe and a magnetic product containing more than 50% Fe.

Introduction

Nickel and cobalt are being extracted from the Cuban laterite ores containing more than 1% Ni and 0.15% Co at three hydrometallurgical plants. Two plants are using the Ammoniacal Carbonate Technology (Caron Process) and one plant is using the Acid Pressure Technology. In both technologies only 80–85% Ni and 20–30% Co can be extracted. About 100 million tonnes of the leaching residues containing less than 0.5% Ni and 0.1% Co have been produced in the last 50 years. Due to the serious environmental problem caused by these tailings, several investigations looking for simple operation conditions and low cost technologies are being carried out.

Several authors have investigated the leaching of low-grade nickeliferous laterites using synthetic organic acids or acids obtained during the metabolism of microorganisms [1], [2], [3], [4], [5], [6]. Tzeferis [7] extracted 70–72% of nickel by hot leaching at 95 °C of low grade hematitic laterite from Greece with a solution obtained from the cultivation of fungi at 30 °C. In comparison to several organic acids, Tzeferis and Agatzini [8] found that citric acid was the most effective solvent for nickel. Lactic, formic, acetic and salicylic acids were relatively ineffective. Oxalic acid extracted more iron but no nickel. Mckenzie et al. [9] used citric, tartaric and pyruvic acids for the leaching of Indonesian and West Australian laterites at pH 2.3 and at a temperature of 28 °C. Despite having different leachabilities, the authors found chelated nickel complexes in the leaching solution from both samples. Recently, Stamboliadis et al. [10] found that the magnetic processing of the leaching residue of nickeliferous laterites from Greece could lead to an iron concentrate. From the above publication, it is clearly seen that the metal extraction from laterite ores from different origins depends on the mineralogical composition and the geneses of the ore-body. However, the industrial application of bioleaching of such oxidised ores containing low metal amounts can be achieved only by production of organic acids at low cost.

The aim of this study is to focus on the recirculated precipitate amenable to leaching with the existing process. The percolation leaching with tartaric acid as well as a mixture of tartaric and oxalic acids was attempted. In addition, extraction of metals from the pregnant solution by precipitation, thermal decomposition of the precipitate and upgrading of iron from the residues of percolation leaching were also carried out.