Process for the concurrent recovery of acid and metal values from spent pickle acid containing the same

Claim 2

The process of claim 2 where in addition to iron, the spent pickle acid contains one or more metals in the form of a salt or salts of the waste pickle acid, said metal selected to be copper, beryllium, nickel, chromium, cobalt or zinc.

Claim 3

The process of claim 1 wherein excess sulfuric acid is added at step (a) and the distillation step (b) is carriEd out well under the fuming temperature of sulfuric acid.

Claim 4

The process of claim 1 wherein the oxidizing step is carried out with air, hydrogen peroxide or nitric acid as the oxidizing agent.

Claim 5

The process of claim 1 wherein the pH adjustment of step (g) is carried out with sulfuric acid or lime.

Claim 6

A process for the concurrent recovery of acid and metal values from spent pickle acid containing the same which comprises: a. adding a quantity of sulfuric acid to a spent pickle acid stream other than a spent sulfuric acid stream to convert the soluble metal salt or salts to soluble metal sulfates and at the same time, regenerate the pickle acid; b. recovering the pickle acid by distillation; c. adding to the distillation residue of (b) which comprises a solution of soluble metal sulfates; at least one member of the group consisting of an iron-containing mill scale, mill sludge, grinding dust and baghouse dust reacted with strong sulfuric acid, and insoluble metal hydroxide including iron hydroxide sludge; d. digesting the insoluble metal hydroxides with sulfuric acid to form soluble metal sulfates; e. oxidizing the soluble metal sulfates to insoluble metal hydroxides; f. neutralizing excess sulfuric acid present in the medium of step (e) with lime to adjust the pH from about 3 to 7 and to form metal hydroxides and calcium sulfate; g. adding a quantity of sulfuric acid to the medium resulting from step (f) to lower the pH to about 3.0 to 3.5 to redissolve all of the insoluble metal hydroxides except iron hydroxide; h. removing the insoluble calcium sulfate and iron hydroxide by filtration to provide a filtrate containing iron-free soluble metal sulfates. i. adjusting the pH and the concentration of metal salts in the filtrate to that suitable for an electroplating solution; and j. recovering the metal values from the solution of step (i) by electroplating.

Claim 7

The process of claim 7 wherein the spent pickle acid is nitric acid, nitric-hydrofluoric acid or hydrochloric acid.

Claim 8

The process of claim 8 wherein the spent pickle acid contains one or more metals in the form of a salt or salts of the waste pickle acid, said metal selected to be copper, beryllium, iron, nickel, chromium, cobalt or zinc, further provided, that when the metal is iron, at least one other of the aforementioned metals is also present.

Claim 9

The process of claim 7 wherein excess sulfuric acid is added at step (a) and the distillation step (b) is carried out well under the fuming temperature of sulfuric acid.

Claim 10

The process of claim 7 wherein the oxidizing step is carried out with air, hydrogen peroxide or nitric acid as the oxidizing agent.

Claim 11

The process of claim 7, wherein the insoluble metal hydroxide added in step (e) is iron hydroxide or a mixture of iron hydroxide and at least one other hydroxide of nickel, cobalt, manganese, zinc or chromium.

Claim 12

The process of claim 7 wherein the pH adjustment of step (h) is carried out with sulfuric acid or lime.