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

1. 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.

2. The wastewater treatment method according to claim 1 , wherein the pH of the sulfuric acid acidified wastewater is adjusted by the addition of an alkali selected from the group consisting of the aluminum hydroxide precipitate, the filtrate, the demanganized wastewater, calcium carbonate, calcium hydroxide, calcium oxide, slaked lime, sodium hydroxide, potassium hydroxide, and a mixture thereof.

3. The wastewater treatment method according to claim 1 , wherein the oxidized and neutralized slurry is admixed with the pH-adjusted aluminum precipitate slurry or the aluminum slurry; and then solid-liquid separating this admixture into the trivalent manganese precipitate and the demanganized wastewater.

4. The wastewater treatment method according to claim 1 , wherein the oxidizing agent is selected from the group consisting of air, ozone gas, a hydrogen peroxide solution, sulfur dioxide gas, oxygen, and a mixture thereof.

5. The wastewater treatment method according to claim 1 , wherein an oxidizing agent is admixed with the dealuminized solution and this admixture is stored in a pressure vessel.

6. The wastewater treatment method according to claim 1 , wherein the sulfuric acid acidified wastewater is obtained in such a manner that nickel and cobalt, each contained in a nickel oxide ore, are leached with sulfuric acid by high-pressure acid leaching, and a thus obtained sulfuric acid acidified solution is neutralized to separate impurities, and then is sulfurized to separate nickel and cobalt as a sulfide precipitate.

7. The wastewater treatment method according to claim 1 , wherein the pH of the sulfuric acid acidified wastewater, the aluminum slurry, and/or the dealuminized solution is adjusted by addition of the filtrate.

8. The wastewater treatment method according to claim 1 , wherein the method forms demanganized wastewater without precipitating magnesium.

9. The wastewater treatment method according to claim 1 , wherein the alkali used for adjustment of the pH of the sulfuric acid acidified wastewater is the stabilized aluminum hydroxide precipitate, the filtrate including manganese, and/or the demanganized wastewater.