Leaching of valuable metals from nickel pyrrhotite by ammonium sulfate roasting method

Nickel pyrrhotite blended with ammonium sulfate was roasted at elevated temperature.The effects of amount of ammonium sulfate,leaching temperature,leaching time and pH value of sulfuric acid leaching solution on leaching rates of metal elements in roasted products were investigated.The roasted products were also leached with a mixed solution containing ammonia and ammonium sulfate.The results show that the leaching rates of Ni and Cu are higher,and the leaching rates of Mg and Fe are lower under different conditions.The ammonia solution is beneficial to leaching Ni and Cu.When the total ammonia concentration is 7 mol/L,the leaching rates of Ni and Cu are 89.56% and 79.35%,respectively.The sulfuric acid solution with low pH value is beneficial to leaching Mg and Fe.When the pH value is 0.5,the leaching rates of Mg and Fe are 61.39% and 62.56%,respectively.The SEM-EDS and XRD analysis shows that most of Ni and Cu are leached out.The leaching rates of Mg and Fe are lower because of undissolved magnesium silicate and calcium ferrite in the roasted products.