Waste-free technology of hydrometallurgical processing of sludges from the acid decomposition of serpentinites

We develop a technology for the production of iron oxide-pigment and nickel concentrate from the sludges of acid decomposition of serpentinite. We study the chemical and phase compositions of the polymetallic sludge obtained as a result of cleaning of the magnesium-chloride solution performed after the acid decomposition of serpentinite from the Bazhenov deposit. It is shown that the predominant element in the composition of sludge is Fe, and its weight fraction recalculated to iron (III) oxide is 53–56%. The weight fraction of Ni in the polymetallic sludge attains 1.3%. It is experimentally demonstrated that the procedure of selective leaching seems to be the most acceptable method for separating elements in the polymetallic sludge. The maximum degree of nickel (II) extraction equal to 96–99% is observed for pH = 1.4–1.5 at a temperature of 80 °C and a concentration of the HCl solution equal to 20 wt%, while the degree of extraction of iron (III) into the solution does not exceed 7%. A technological scheme of processing of polymetallic sludges is developed. The degree of nickel (II) extraction into the solution is 98%. The obtained iron-oxide pigment contains 93 wt% Fe₂O₃. The remaining qualitative characteristics of the pigment are comparable with the characteristics of the YIPIN S130 (China) pigment.