New Insights into the Penetration Depth of Sulfuric Acid and Leaching Effect in the Sulfuric Acid Curing-Leaching Process of Vanadium-Bearing Stone Coal

In the process of sulfuric acid curing-leaching vanadium-bearing stone coal, the curing effect is very important. The main purpose of this study is to capture the difference in the curing effect between coarse and fine stone coal, with a V 2 O 5 content of 0.88%. In this work, the effects of various factors such as sulfuric acid concentration, curing time, curing temperature, and different agents for curing on the leaching efficiency of vanadium were investigated by the comparison of the two size fractions. The results showed that the leaching efficiency of vanadium was 87.65% under the optimum curing conditions of 25 wt % sulfuric acid, curing time of 8 h, and curing temperature of 130 °C. It was clearly found that, under the same curing condition, the curing effect of fine stone coal was better than that of coarse stone coal. The penetration part of stone coal particles by sulfuric acid was loose, while the non-penetration part was dense after acid curing. Moreover, the penetration depth of sulfuric acid into the particles was mainly 0.5-0.7 mm on average. There was more sericite/illite in coarse leaching residues, which were mostly dense and hard carbonaceous siliceous slate. Thus, sulfuric acid was difficult to penetrate into and reach the interior of the particle, which resulted in that the leaching efficiency of coarse vanadium-bearing stone coal ore was lower than that of fine vanadium-bearing stone coal ore.