Iron Removal as Goethite from Synthetic Laterite Leach Solutions

The aim of this study was to precipitate goethite from high-iron(II)-bearing atmospheric and heap leach solutions of lateritic nickel ore generated either by reductive leaching of the ore or by reducing Fe(III) of the leach solution to Fe(II) using a suitable reducing agent and to understand the Ni and Co losses during the iron precipitation. Removal of Fe was carried out using an oxidative hydrolysis technique targeting goethite precipitation from a synthetic laterite leach solution containing Fe as ferrous (Fe(II)), Al, Mg, Ni, Co, Cr, Mn, Cu, and Zn using limestone as the neutralizing agent and air as an oxidant. The behavior of goethite precipitation and the losses of Ni and Co were examined under various conditions of pH, temperature, and Fe concentration. The precipitation of Fe increased with increasing pH, temperature, and feed Fe(II) concentration. Precipitation at pH ∼4.0-4.1 (measured at ambient temperature) and 90 °C resulted in ∼96-97% Fe removal from a feed solution containing more than 50 g/L Fe(II), giving ∼1 g/L Fe in the final liquor. Goethite formation was confirmed as a result of the Fe precipitation, and it appeared to take place via ferrihydrite/schwertmannite intermediate phases. The crystallinity of the goethite increased with time, temperature, and feed Fe(II) concentration. The goethite precipitate was found to be associated with an alunite phase. Losses of Ni and Co during Fe precipitation increased with pH, temperature, and feed Fe(II) concentration. The losses were significant above pH 4 and found to be ∼7-22% Ni and 4-19% Co in the pH range 4.1-5. The test results indicate that efficient Fe removal via goethite precipitation can be achieved from reduced atmospheric and heap leach solutions of laterite ore; however, careful pH control is required to minimize the loss of Ni and Co during this precipitation.