Method for recovering nickel from sulfuric acid aqueous solution

1. A method for recovering nickel from a sulfuric acid aqueous solution containing nickel and cobalt, and impurity elements including iron, aluminum, manganese, characterized by comprising the following steps (1) to (5);

step (1): by adding calcium carbonate into the sulfuric acid aqueous solution, under blowing mixed gas composed of sulfurous acid gas and air or oxygen gas, to subject the solution to oxidation neutralization treatment, and to remove a precipitate (a) containing iron and aluminum generated;

step (2): by adding calcium hydroxide to the solution after the oxidation neutralization treatment obtained in the step (1), to subject the solution to neutralization treatment, and to separate and recover mixed hydroxides containing nickel and cobalt;

step (3): by subjecting the mixed hydroxides obtained in the step (2) to dissolution treatment in a sulfuric acid solution having a concentration of equal to or higher than 50% by mass, to remove a precipitate (b) containing manganese and gypsum generated, and to obtain a concentrated solution of nickel and cobalt;

step (4): by subjecting the concentrated solution obtained in the step (3) to solvent extraction treatment, using a phosphate ester-based acidic extraction agent, to obtain an extraction residual liquid containing nickel and a back extraction liquid containing cobalt;

step (5): by adding a neutralizing agent to the extraction residual liquid obtained in the step (4), to subject the solution to the neutralization treatment, and to separate and recover nickel hydroxide generated.

2. The method for recovering nickel from an sulfuric acid aqueous solution according to claim 1 , characterized by further comprising the following step (6) subsequent to the step (3);

step (6): by adding a neutralizing agent into the concentrated solution of nickel and cobalt obtained in the step (3), under blowing mixed gas composed of sulfurous acid gas and air or oxygen gas, to subject the solution to the oxidation neutralization treatment, to remove a precipitate (c) containing manganese and cobalt generated, and to transfer the resultant solution after the oxidation neutralization treatment to the step (4).

3. The method for recovering nickel from an aqueous sulfuric acid solution according to claim 1 , characterized by further comprising the following step (7) or step (8);

step (7): by adding a neutralizing agent to the back extraction liquid obtained in the step (4), to subject the solution to the neutralization treatment, and to separate and recover cobalt hydroxide generated;

step (8): by adding hydrogen sulfide gas or alkali sulfide to the back extraction liquid obtained in the step (4), to subject the solution to sulfurization treatment, and to separate and recover cobalt sulfide generated.

4. The method for recovering nickel from a sulfuric acid aqueous solution according to claim 1 , characterized in that the oxidation neutralization treatment in the step (1) satisfies the following requisites (i) to (iii);

(i) content ratio of sulfurous acid gas in the mixed gas is 1 to 10% by volume relative to air or oxygen gas of dilution gas;

(ii) oxidation-reduction potential (based on a silver/silver chloride electrode) is 400 to 600 mV; and

(iii) pH is 4.0 to 4.5.

5. The method for recovering nickel from a sulfuric acid aqueous solution according to claim 1 , characterized in that the neutralization treatment in the step (2) satisfies the following requisite (iv);

(iv) pH is 7.5 to 7.7.

6. The method for recovering nickel from a sulfuric acid aqueous solution according to claim 1 , characterized in that the dissolution treatment in the step (3) satisfies the following requisites (v) and (vi);

(v) the mixed hydroxides are mixed with the sulfuric acid solution to form a slurry, wherein the slurry concentration is 30 to 40% by mass;

(vi) pH at completion of dissolution of the mixed hydroxides is 1.5 to 2.2.

7. The method for recovering nickel from a sulfuric acid aqueous solution according to claim 1 , characterized by comprising transferring the precipitate (b) to the step (1), in the step (3).

8. The method for recovering nickel from an aqueous sulfuric acid solution according to claim 1 , characterized in that the neutralization treatment in the step (5) satisfies the following requisites (vii) to (ix;

(vii) pH is 7.5 to 8.0;

(viii) the neutralizing agent is magnesium hydroxide;

(ix) reaction temperature is a temperature of 80° C. to boiling temperature.

9. The method for recovering nickel from a sulfuric acid aqueous solution according to claim 2 , characterized in that the oxidation neutralization treatment in the step (6) satisfies the following requisites (x) to (xiii);

(x) content ratio of sulfurous acid gas in the mixed gas is 1 to 10% by volume relative to air or oxygen gas;

(xi) oxidation-reduction potential (based on a silver/silver chloride electrode) is 500 to 600 mV;

(xii) pH is 5.0 to 6.0;

(xiii) the neutralizing agent is sodium hydroxide.

10. The method for recovering nickel from an sulfuric acid aqueous solution according to claim 1 , characterized in that the sulfuric acid aqueous solution is a leach solution produced from the step to leach under high temperature and high pressure, by adding a sulfuric acid solution to slurry of a nickel laterite ore.