Applied Basic Research On The New Process For The Selective Leaching Of Ni And Co From Laterite Ore By Leaching-hydrolysis Coupling Reactions

Hydrochloride acid leaching-hydrolysis process was proposed by our research group to treat laterite ore. The advantages of this process are:limonitic laterite and saprolitic laterite can be treated in one process, hydrochloride acid can be fully utilized, Ni and Co are selectively leached in a high efficiency at mild leaching conditions. The main points are listed as follows:1) Saprolitic laterite ore contains 1.37 wt.% Ni, and 18.80 wt.% Fe. The main mineral phases of this ore are saprolite, goethite, and quartz. Ni is deposited in saprolite and goethite as Ni(OH)2. The concentrations of Fe(Ⅲ) and HCl are high and the concentration of Ni is 1.98 g/L in the limonitic laterite hydrochloride acid leaching solution. Fe(Ⅲ) exits in the solution as FeCl4- and Fe(H2O)63+.2) Thermodynamics research for hydrolysis of chlorides indicates that FeCl3 is hydrolyzed at high temperature. NiCl2, CoCl2, and MnCl2 are stable under 200℃. Thermodynamics research indicates that saprolite and metal hydroxides can be leached by HCl and FeCl3. E-pH diagrams indicate that the pH value of Fe hydrolysis is lower than that of Ni, Co, and Mn; therefore, Ni, Co, and Mn can be selectively leached from laterite ores by controling the pH value.3) Leaching of saprolitic laterite ore by FeCl3 solution was studied. Under the optimal leaching conditions, the leaching of Ni and Co were 82.8% and 88.1%, respectively; the precipitation of Fe was 87.4%. The mechanism of the leaching of saprolite and goethite by FeCl3 solution indicates that FeCl4- and Fe(H2O)63+ being hydrolyzed to α-FeOOH (GG) and H+, with the H+ produced then reacting with Mg3Si2O5(OH)4 and α-FeOOH (OG) to produce Mg2+, mSiO2·nH2O, FeCl4-, and Fe(H2O)63+. The FeCl4- and Fe(H2O)63+ generated are then hydrolyzed to α-FeOOH (GG) or α-Fe2O3, with α-FeOOH (GG) finally transforming to a-Fe2O3.4) Leaching of saprolitic laterite ore by HCl was studied. Under the optimal leaching conditions, the leaching of Ni, Co, and Fe were 89.4%,97.3%, and 8.7%. The mechanism of selective leaching of laterite ore by hydrochloride acid was studied. Laterite is leached by HCl, FeCl4- and Fe(H2O)63+ generated are then hydrolyzed seeded by a-FeOOH (OG). The a-FeOOH (GG) generated during hydrolysis process then losts H2O and generates α-Fe2O3. The HCl generated during hydrolysis process leaches laterite ore.5) The mechanism of the reaction between HCl and saprolite/goethite was studied by DFT. HCl was absorbed on the crystal surface of saprolite and goethite, HCl reacted with saprolite and goethite, then, the generated H2O was desorbed from the crystal surface of saprolite and goethite.6) The conditions of hydrochloride acid leaching-hydrolysis process were studied. Under the optimal conditions, the leaching of Ni and Co were 75.0% and 82.5%, respectively; and the precipitation of Fe was 67.9%. The mechanism of this process was coordinated with the conclusion obtained in chapter 4.