Method for the recovery of valuable metals and arsenic from a solution

• US 20090022639A1
• Filed: 04/25/2006
• Published: 01/22/2009
• Est. Priority Date: 05/03/2005
• Status: Active Grant

• Current Assignee: Metso Outotec Finland OY (Metso Outotec Oyj)
• Original Assignee: Outotec Oyj (Metso Outotec Oyj)
• Inventors: Poijarvi, Jaakko, Nupponen, Raimo, Makinen, Tuula, Romppanen, Jaana
• Granted Patent: US 7,615,199 B2
• Time in Patent Office: Days
• US Class Current: 423/24
• CPC Class Codes: C22B 15/0054 Slag, slime, speiss, or dross treating
• CPC Class Codes: C22B 3/08 Sulfuric acid , other sulfurated acids or salts thereof
• CPC Class Codes: C22B 3/44 by chemical processes treatment or purification of solutions by liquid-liquid extraction C22B3/26, by ion-exchange extraction C22B3/42
• CPC Class Codes: C22B 30/04 Obtaining arsenic extraction of metal compounds by leaching in organic solutions C22B3/16; treatment or purification of solutions by adsorption on solids C22B3/24, by liquid-liquid extraction C22B3/26, by ion-exchange extraction C22B3/42
• CPC Class Codes: C22B 7/007 by acid leaching
• CPC Class Codes: C22B 7/02 Working-up flue dust
• CPC Class Codes: Y02P 10/20 Recycling

Abstract

The invention relates to a method for the treatment of material containing at least one valuable metal and arsenic to form a valuable metal-depleted scorodite sediment and a pure aqueous solution to be discharged from the process. According to the method, the valuable metals are first removed from the material to be treated and then arsenic precipitation from the solution is performed in two stages. By means of the method, the aim is to obtain as low a valuable metal content as possible in the scorodite sediment that will be formed. Likewise, the arsenic and valuable metal content of the aqueous solution that is formed during arsenic precipitation also remains so low that the water can be released into the environment.

Claims

1. A method for treating a material containing at least one valuable metal and arsenic to form a valuable metal-depleted scorodite sediment and a pure aqueous solution to be discharged from the process, wherein a dilute acidic solution of the material containing the valuable metal and arsenic is formed, whereby at least one valuable metal is first removed from the solution by means of liquid-liquid extraction and/or precipitation, after which the valuable metal-depleted solution is routed to two-stage arsenic removal, where in the first stage arsenic is precipitated as scorodite FeAsO₄.2H₂O, which is suitable for storing, and the solution exiting precipitation is routed to the second precipitation stage, where the remainder of the arsenic is precipitated as amorphous ferric arsenate FeAsO₄, which is recycled to the first precipitation stage and the arsenic concentration of the aqueous solution exiting the second precipitation stage is around 0.01-0.2 mg/l.

2. A method according to claim 1, wherein the material to be treated is fly ash generated in a pyrometallurgical fabrication of non-ferrous metals.

3. A method according to claim 1, wherein the material to be treated is a calcine generated in a pyrometallurgical fabrication of non-ferrous metals.

4. A method according to claim 1, wherein at least some of the dilute acid used for leaching material containing a valuable metal and arsenic is an arsenic-containing dilute acid generated in the treatment of arsenic-containing gases.

5. A method according to claim 1, wherein the acid is sulphuric acid, with a concentration of 10-200 g/l.

6. A method according to claim 1, wherein the valuable metal is copper.

7. A method according to claim 1, wherein after liquid-liquid extraction, the remainder of the valuable metal is recovered from the valuable metal-depleted aqueous solution, or raffinate, by sulphide precipitation.

8. A method according to claim 1, wherein the Fe/As mole ratio in the first arsenic precipitation stage is adjusted to be around 1-1.1 and that an oxidant is routed to the stage to oxidise the arsenic to pentavalent and the iron to trivalent, the pH value of the stage is adjusted to the range 1-2 and the temperature to between 85-135°

C. to precipitate the arsenic as scorodite.

9. A method according to claim 8, wherein the Fe/As mole ratio is adjusted by means of arsenic analysis and/or by adjusting the ratio of the solution streams.

10. A method according to claim 8, wherein the pH adjustment of the first precipitation stage is carried out by means of limestone or lime.

11. A method according to claim 8, wherein the underflow of the first precipitation stage thickening is recycled to the front end of the precipitation stage.

12. A method according to claim 1, wherein the overflow from the first stage thickening is routed to the second precipitation stage, where the Fe/As mole ratio is adjusted to be over three, the pH value between 4-7 and the temperature between 40-60°

C. to precipitate the arsenic as ferric arsenate.

13. A method according to claim 12, wherein the Fe/As mole ratio is adjusted by adding divalent and/or trivalent iron to the precipitation stage.

14. A method according to claim 12, wherein the pH adjustment is carried out by means of lime.