Iron Precipitation Strategies from Nickel Laterite Ore Sulfuric Acid Leach Liquor

A two-step closed circuit, operated at 90-95oC, was found suitable for practical iron removal from real sulfuric acid leach liquors, resulting in low losses of nickel and cobalt to the solid phase. In the first step, NH4OH was used as a reagent to treat iron-rich liquors (1.8 g.L-1< [Fe](total)<8.7 g.L-1) with an initial pH of 1.6 +/- 0.1, and nickel and cobalt concentrations of 1.59 +/- 0.05 g.L(-1)and 108 +/- 6 mg.L-1, respectively. Metal losses are greatly affected by the liquor's pH, which increased when liquors with respective higher initial [Ni]/[Fe] and [Co]/[Fe] concentration ratios were treated. Losses were mostly associated with adsorption reactions on the surface of the precipitate, identified mainly as jarosite and goethite phases. Iron removal higher than 99% was obtained at pH 2.5-3.3, with metal losses of up to 1.8%. In the second step, milk of lime (1.5 CaO g/100 mL) was used as a reagent. A final solution containing only 2.1 mg.L(-1)of iron, with nickel and cobalt losses below 1.6%, was achieved at pH 3.7-3.8; the precipitate was identified as bassanite. The precipitates presented rapid sedimentation and good filterability, which were observed visually. Filtration operation should be carried out at temperatures above 80 degrees C. A brief review of the literature is also presented.

Automated summary

A two-step closed circuit system was developed for practical iron removal from sulfuric acid leach liquors. The system effectively reduced nickel and cobalt losses while achieving high iron removal rates. By treating the iron-rich liquors in two separate steps with different reagents, metal losses were minimized. The experimental results showed that controlling the pH of the leach liquor and using suitable reagents can significantly reduce metal losses and increase iron removal efficiency.