Chemo-physical concentration of a Low-grade nickel laterite ore

Abstract

• A novel method for the beneficiation of limonitic Ni laterites . • Long-term oxalic acid leaching of a low-grade Ni laterite ore from Iran. • A dissolution-precipitation behavior for Ni in contrast to leachability of Fe. • Fast dissolution for Ni and Fe but delayed precipitation for Ni at high temperature. • Collection of nickel oxalate particles in the fine fraction of the leach residue. Extraction of nickel from laterites is a challenging task due to the lack of an efficient nickel concentration method. Current efforts on the beneficiation of nickel laterites–especially low-grade ones– are mainly focused on atmospheric leaching methods using mineral acids, organic acids, or a mixture of them. The aim of the present paper is developing a novel hydrometallurgical approach to concentrate nickel from laterites based on a long-term oxalic acid leaching followed by size separation of the leach residue. A limonitic laterite sample from Sarchahan deposit (Fars province, Iran) containing 0.8% Ni and 27.3% Fe was used for the experiment and dissolution behavior of nickel and iron during the course of long time leaching runs (52 h) was studied under the influence of temperature (60–90 °C) and oxalic acid concentration (0.75–1.25 M). The results show that nickel initially dissolves, but subsequently precipitates with the presence of oxalate ions as NiC 2 O 4 ·2H 2 O. In addition, iron steadily dissolves as ferric oxalate and maintained in solution so long as light-protected. However, it tends to precipitate as FeC 2 O 4 ·2H 2 O at higher temperatures and long retention times. The leach residue was separated into a fine and a coarse fraction via wet classification using a cut point of 44 μm. Phase and chemical analysis confirmed accumulation of nickel in the fine fraction yielding a Ni concentrate as an intermediate product. The concentrate obtained at 60 °C and 1.25 M oxalic acid concentration contained 3.2% Ni (∼10% NiC 2 O 4 ·2H 2 O) and 3.5% Fe with a corresponding concentration ratio of 4.05, enrichment ratio of 3.44 and nickel recovery of 84%. The proposed method appears to provide a promising prospect for exploiting low-grade nickel laterites, as the obtained concentrate could be a suitable feedstock for both pyro- and hydrometallurgical processing to yield a marketable Ni product.