Method for preparing magnesium hydroxide and co-producing silica powder by using copper-nickel sulfide ore tailings

The invention relates to a method for preparing magnesium hydroxide and co-producing silica powder by using copper-nickel sulfide ore tailings. The method comprises the following steps: S1, mixing the copper-nickel sulfide ore tailings and sodium hydroxide/sodium carbonate according to the ratio of 1:(0.6-1.5), and grinding to 200-300 meshes to obtain a mixed raw material; s2, roasting the mixed raw material to obtain active clinker, and collecting roasting furnace gas at the same time; s3, making the active clinker leached with water to obtain water leaching residues and water leaching liquid; s4, introducing carbon dioxide into the water extract for carbonation decomposition, and performing solid-liquid separation to obtain silica gel and a sodium carbonate solution; s5, sufficiently combusting the furnace gas, collecting with water to obtain a sulfuric acid solution, adjusting the sulfuric acid solution to 2-5mol/L, and performing acid leaching on the water leaching residues to obtain filter residues and f