Separation and recovery of reusable heavy metal hydroxides from metal finishing wastewaters
OwnerJames M. Frankard, Orville V. Brochinventors
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Abstract
A method is disclosed for the elimination of hazardous metal wastewater and sludges by recovering the non-ferrous metals zinc, nickel, copper (II), cadmium or chromium (III) present in an aqueous sludge comprising mixed metal hydroxides by selectively precipitating the ferrous metal ions present while maintaining the non-ferrous metal ions in solution, isolating the precipitate and then precipitating the non-ferrous metal ions from solution.
Claims29
A method for treating wastewaters and sludges from a plating process to facilitate reuse of metal values by the recovery of non-ferrous metal hydroxide, said method comprising the following steps (a) through (f) in the order presented:
- (a) lowering the pH of an aqueous slurry obtained from a plating process from an alkaline pH to an acid pH, said slurry comprising solid ferrous hydroxide and a solid non-ferrous metal hydroxide wherein the non-ferrous metal is selected from the group consisting of zinc, nickel, copper (ii) cadmium, and chromium (III) to dissolve the non-ferrous metal hydroxide;
- (b) converting the ferrous hydroxide to solid ferric hydroxide by aeration of the aqueous acidic slurry;
- (c) isolating the solid ferric hydroxide from the slurry leaving a solution comprising non-ferrous metals;
- (d) raising the pH of the solution of step (c) to precipitate non-ferrous metal hydroxide;
- (e) recovering the precipitated non-ferrous metal hydroxide;
- and
- (f) introducing said non-ferrous metal hydroxide into the plating process.
A method for treating wastewaters and sludges from a plating process to facilitate reuse of metal values by the recovery of zinc hydroxide, said method comprising the following steps (a) through (f) in the order presented:
- (a) lowering the pH of an aqueous slurry obtained from a plating prodess from an alkaline pH to an acid pH, said slurry comprising solid ferrous hydroxide and solid zinc hydroxide, to dissolve the zonc hydroxide;
- (b) converting the ferrous hydroxide to solid ferric hydroxide by aeration of the aqueous acidic slurry;
- (c) isolating the solid ferric hydroxide from the slurry leaving a solution comprising zinc;
- (d) raising the pH of the solution of step (c) to precipitate zinc hydroxide;
- (e) recovering the precipitated zinc hydroxide;
- and
- (f) introducing said zonc hydroxide into the plating process.
Dependencies are inferred from the claim text.