Method for a treatment for wastewater containing aluminum, magnesium, and manganese

A wastewater treatment method for obtaining demanganized wastewater from sulfuric acid acidified wastewater obtained by processing nickel oxide ore and containing aluminum, magnesium, and manganese, comprising:

• adjusting the pH of the sulfuric acid acidified wastewater to not less than 4.0 and not more than 5.0 by adding an acid or alkali;
• precipitating aluminum;
• preventing coprecipitation of magnesium with aluminum;
• and then
• separating the pH adjusted sulfuric acid acidified wastewater into a dealuminized solution that includes magnesium and manganese and has an aluminum concentration of not more than 0.1 g/L, and an aluminum hydroxide precipitate that includes adhering water and is represented as [Al(OH)3];
• admixing water and the aluminum hydroxide precipitate to form an aluminum slurry;
• adjusting a pH of this aluminum slurry to not less than 9.0 and not more than 9.5;
• thereby
• forming a pH-adjusted aluminum precipitate slurry including a stabilized aluminum hydroxide precipitate that does not form a precipitate with magnesium;
• and then
• separating the pH-adjusted aluminum precipitate slurry into the stabilized aluminum hydroxide precipitate and a filtrate including manganese;
• adjusting a pH of the dealuminized solution to a range of not less than 8.0 and not more than 9.0,
• adding an oxidizing agent to the dealuminized solution;
• forming an oxidized and neutralized slurry that includes a trivalent manganese;
• and then
• solid-liquid separating the oxidized and neutralized slurry into a trivalent manganese precipitate and demanganized wastewater,
• wherein the stabilized aluminum hydroxide precipitate, the filtrate including manganese, and the demanganized wastewater are usable as an alkali used for adjustment of the pH of the sulfuric acid acidified wastewater.