Study On Process And Mechanism Of Selectively Leaching Of Vanadium From Roasted Stone Coal By Pressure Acid Leaching

In China,the gross reserve of vanadium in stone coal is 118 million tons in the terms of V₂O₅.The vast amount of these deposits has made stone coal of considerable interest as a vanadium source.However,there are still some defects like the low leaching rate and the low leaching selectivity in the the acid leaching process for vanadium from stone coal which has been a widely used processing in this region.For solving these problems,the blank roasting-pressure acid leaching process was studied,and then the leaching behaviors of V,Al,P and Fe during the non-circulating pressure acid leaching process and the circulation pressure acid leaching process were investigated,and the selectively leaching process of vanadium from roasted stone coal through dilute sulfuric acid dephosphorization-two stages pressure acid leaching process was proposed on this basis.Result showed under the optimal operation conditions as followed: the kettle pressure was 1.0 MPa,concentration of sulfuric acid was 15%,ratio of L/S was 1.5 mL·g-1,leaching temperature was 150 ℃ and leaching time was 120 min,the vanadium leaching rate could reach 80.51%.The effect for vanadium extraction and impurities decreasing of circulating pressure acid leaching is better than that of non-circulating pressure acid leaching.Under these conditions which are liquid/solid ratio of 1.5 mL/g,leaching time of 120 min,pressure of 1.0 MPa,sulfuric acid concentration of 12.5%（v/v）,the first stage leaching temperature of 180 ℃,the second stage leaching temperature of 150 ℃,the leaching efficiency of V,Al,P,Fe is 84.56%,32.74%,60.69%,5.83%,respectively.Compared with the non-circulating pressure acid leaching which the conditions were as follows: the sulfuric acid concentration of 15%（v/v）,the leaching temperature of 180 °C and the other conditions were as same as the former,the concentration of Fe,Al,P has decreased 45.87%,27.05%,70.79%,respectively,and the dosage of sulfuric acid has decreased 16.67%.The optimum dilute sulfuric acid dephosphorization（DSAD）conditions were showed to be temperature of 20 ℃,sulfuric acid concentration of 3.0%（v/v）,liquid/solid ratio of 1.5 mL/g and time of 120 min.Under these DSAD conditions the dephosphorization rate could reach 98.75% while the vanadium loss rate was just 3.52%.After the DSAD,the effective separation of V from P was achieved.Then the dephosphorization sample was treated by two stages pressure acid leaching with these conditions which were liquid/solid ratio of 1.5 mL/g,leaching time of 120 min,leaching pressure of 1.0 MPa,the first stage sulfuric acid concentration of 3.75%（v/v）,the first stage leaching temperature of 180 ℃,the second stage sulfuric acid concentration of 15%（v/v）,the second stage leaching temperature of 150 ℃.The leaching efficiency of V,Al,P,Fe were 80.46%,12.24%,0.67%,3.12%,respectively.Compared with the non-circulating pressure acid leaching,the leaching efficiency of V has increased 2.95%,the concentration of Al,P,Fe has decreased 83.51%,84.45%,99.32%,respectively.The selectively leaching of vanadium from roasted stone coal has been achieved.