METHOD OF REGENERATION OF ACID FOR THE ETCHING PROCESS

Claims

1. A method for treating waste acid containing from 0.5 to 18 mass percent hydrochloric acid and from 60 to 350 g / l of iron, in which the following steps are carried out: i) mixing the said spent acid with an aqueous solution of sulfuric acid to carry out reaction (1): reaction (1) FeCl2+ H2SO4+ nH2O ≈ FeSO4.nH2O + 2HCl, to obtain a reaction mixture containing from 5 to 40 mass percent sulfuric acid, ii) distilling said reaction mixture to obtain a distillate containing HCl with a weight content of 10 to 40% and a concentrate containing essentially hydrated forms of iron (II) sulfate, iii) mixing said concentrate with water in such a way that the mass ratio between the concentrate and water is from 0.1 to 10, to obtain an aqueous solution containing hydrated forms of iron sulfates, iv) bringing the temperature of said aqueous solution to between -10 and 50°C to obtain a liquid phase containing metal chlorides and sulfates, metal salts and acids, and a solid phase containing mainly hydrated forms of iron sulfate, v) separating said liquid phase and said solid phase obtained in step iv).

2. The method according to claim 1, wherein the distillation in step ii) is carried out using membrane distillation.

3. The method according to claim 1, wherein the distillation in step ii) is carried out using a column distillation.

4. The method according to claim 1, wherein the distillation in step ii) is carried out using a rotary evaporator.

5. The method according to any one of claims 1 to 4, wherein the distillation in step ii) is carried out at a temperature of from 60 to 95°C.

6. The method according to claim 5, wherein the distillation in step ii) is carried out at a temperature of from 75 to 85°C.

7. The method according to any one of claims 1 to 6, wherein the distillation in step ii) is carried out at a pressure of from 0.0001 to 50 kPa (from 0.01 to 500 mbar).

8. The method according to claim 7, wherein the distillation in step ii) is carried out at a pressure of from 3 to 20 kPa (from 30 to 200 mbar).

9. The method according to any one of claims 1 to 8, wherein the distillation is carried out to obtain a distillate containing essentially HCl with a weight content of from 15 to 20 percent.

10. The method according to any one of claims 1 to 9, wherein in step iv) said aqueous solution is brought to a temperature of from -5 to 10°C.

11. The method according to any one of claims 1 to 10, wherein in step v) the separation is carried out by centrifugation.

12. The method according to any one of claims 1-10, wherein in step v) the separation is carried out by filtration.

13. The method according to any one of paragraphs 1-12, which includes the following steps: vi) mixing the solid phase with water such that the mass ratio between the solid phase and water is from 0.1 to 10 to obtain a second aqueous solution containing hydrated forms of iron sulfate, vii) adjusting the temperature of said aqueous solution to a temperature of from -10 to 40°C to obtain a liquid phase containing chlorides and a solid phase containing hydrated forms of iron sulfate, viii) separating said liquid phase and said solid phase obtained in step iv).