Counter-Current Leaching of Low-Grade Laterites with Hydrochloric Acid and Proposed Purification Options of Pregnant Solution

Abstract

A hydrochloric acid hydrometallurgical process was evaluated for Ni and Co extraction from a low-grade saprolitic laterite. The main characteristics of the process were (i) the application of a counter-current mode of operation as the main leaching step (CCL), and (ii) the treatment of pregnant leach solution (PLS) with a series of simple precipitation steps. It was found that, during CCL, co-dissolution of Fe was maintained at very low levels, i.e., about 0.6%, which improved the effectiveness of the subsequent PLS purification step. The treatment of PLS involved an initial precipitation step for the removal of trivalent metals, Fe, Al, and Cr, using Mg(OH)2. The process steps that followed aimed at separating Ni and Co from Mn and the alkaline earths Mg and Ca, by a combination of repetitive oxidative precipitation and dissolution steps. Magnesium and calcium remained in the aqueous phase, Mn was removed as a solid residue of Mn(III)–Mn(IV) oxides, while Ni and Co were recovered as a separate aqueous stream. It was found that the overall Ni and Co recoveries were 40% and 38%, respectively. About 45% of Ni and 37% of Co remained in the leach residue, while 15% Ni and 20% Co were lost in the Mn oxides.

Reduction of Ferric Iron in Hydrometallurgical Solutions Using Zero-Valent Iron

“…Microscale elemental iron (H 2 Omet 86) was supplied by Rio Tinto Metal Powders Ltd. H 2 Omet 86 is a high-density fine granular zero-valent iron (ZVI), >99% Fe, with a bulk density equal to 3.28 g/cm 3 and a particle size of less than 250 µm. H 2 Omet 86 was mainly designed for injection in field-scale remediation applications and as a filler for permeable reactive barriers.…”

“…Hydrometallurgical treatment of ores and concentrates to dissolve the valuable metals is commonly carried out using sulphuric or hydrochloric acid solutions. However, this treatment results in the co-dissolution of iron minerals and the generation of high Fe(III) levels in the pregnant leaching solution (PLS) [1][2][3]. Iron is commonly removed from leaching liquors by adding a base (NaOH, CaCO 3 ), which increases the solution pH and causes the precipitation of iron in the form of amorphous hydroxides.…”

Iron Control in Atmospheric Acid Laterite Leaching

“…Their column leaching test for a lower grade Agios Ioannis ore (0.58% Ni) resulted in Ni/Fe ratios varying between 0.15 and 0.24. Mystrioti et al [23] applied a counter-current mode of operation for HCl leaching of a similar ore which suppressed iron dissolution to 0.6%. However, they found out that the operation had a negative effect on Ni and Co extraction, which was limited to 55% and 63%, respectively.…”

Separation of nickel and cobalt from nitrate leaching solutions of laterite ore by solvent extraction using trihexyltetradecylphosphonium bis (2,4,4-trimethyl pentyl) phosphinate

“…Laterite ore processing often uses pyrometallurgical, hydrometallurgical, or both processes [7]. The hydrometallurgical process is used for the recovery of high-purity laterite nickel [8], producing a leach solution (PLS) containing nickel and cobalt along with impurities such as Fe, Al, Cr, and Mn [9]. Precipitation is carried out to remove impurities from PLS so that a mixed precipitate of nickel and cobalt is obtained [10], [11].…”

“…Therefore, this process is favored for separating high-purity nickel and cobalt [7]. Solvent extraction involves mixing the leach solution with an extractant to extract the desired metals to the organic phase and leave the unwanted metals behind [8].…”