A characteristic feature of serpentine oxidized nickel ores (ONO) of the Serov deposit (≈ 1 wt.% Ni) is the increased content of iron and magnesium. The main nickel-containing phases are lizardite, antigorite, clinochlore and iron oxides with the nickel content varying from 1.6 to 9.2 wt.%.
Heap (percolation) leaching with aqueous H2SO4 solutions was used for processing. During a pilot study, 89% of nickel, 99% of cobalt, and 78.4% of iron were extracted from the oxidized nickel ores during 440 days of leaching at an acid consumption rate of 475.1 kg per ton of ore. The high iron content of the product solutions did not allow for high-quality extraction of nickel and cobalt. The dependences of the nickel, cobalt, and iron extraction on the irrigation pauses, initial size of the ore fragments, and specific consumption of the leaching solution were studied. A solution was found on how to reduce the sulfuric acid consumption and considerably decrease the iron content of the product solutions by increasing a pause between irrigations at the initial stage of or leaching and redirecting the leaching solutions to treat fresh ore. In this case, iron is hydrolyzed in the form of insoluble hydroxides within the ore body. The optimal process conditions of heap leaching of such ores are as follows: initial size of ore fragments – 50 mm; concentration of H2SO4 solutions – decreasing from 20 to 5 g/dm3 during the leaching process; irrigation density – 140 dm3 per ton of ore; combination of the irrigation pauses from 4 days during the initial stages to 1 day during the subsequent stages. Given the average rate of H2SO4 consumption of 221 kg per 1 ton of ore and leaching duration of 408 days, these conditions make it possible to extract up to 62% of nickel and 66.7% of cobalt, as well as significantly reduce the percentage of iron leached from the ore to obtain iron-free product solutions suitable for extraction of nickel and cobalt.