Recovery of metals

Abstract

A method for recovering metal from electronic waste contacting electronic waste with a recovery solution to dissolve metals from the electronic waste into the recovery solution, wherein the recovery solution comprises nitric acid and ferric nitrate; and raising the pH of the recovery solution to precipitate at least some of said metals therefrom.

1 . A method for recovering metal from electronic waste, the method comprising;
 contacting electronic waste with a recovery solution to dissolve metals from the electronic waste into the recovery solution, wherein the recovery solution comprises nitric acid and ferric nitrate; and   raising the pH of the recovery solution to precipitate at least some of said metals therefrom.   
     
     
         2 . The method of  claim 1 , wherein the recovery solution comprises from 0.5 to 12 wt % ferric nitrate. 
     
     
         3 . The method of  claim 1 , wherein the recovery solution comprises from 10 to 60 wt % nitric acid, preferably from 15 to 40 wt %. 
     
     
         4 . The method of  claim 1 , wherein the recovery solution comprises chloride ions. 
     
     
         5 . The method of  claim 1 , wherein the recovery solution further comprises sulphamate ions. 
     
     
         6 . The method of  claim 1 , wherein the recovery solution further comprises a copper corrosion inhibitor. 
     
     
         7 . The method of  claim 1 , further comprising subjecting the recovery solution and electronic waste to agitation with an oxygen-containing gas. 
     
     
         8 . The method according to  claim 1 , wherein the electronic waste is immersed for at least 30 minutes in the recovery solution. 
     
     
         9 . The method of  claim 1 , further comprising adding chloride ions to the recovery solution prior to raising the pH. 
     
     
         10 . The method of  claim 1 , wherein the raising the pH of the recovery solution comprises raising the pH to from 3 to 6. 
     
     
         11 . The method of  claim 1 , further comprising:
 (i) raising the pH to from 3 to 6;   (ii) raising the pH to greater than 6; and   (iii) lowering the pH to from 3 to 6,   
       wherein precipitate formed by steps (i), (ii) and (iii) is recovered from the recovery solution before the next step. 
     
     
         12 . The method of  claim 1 , wherein contacting the electronic waste with the recovery solution is carried out in a revolving drum. 
     
     
         13 . The method of  claim 1 , further comprising continuous filtration of the recovery solution. 
     
     
         14 . The method of  claim 1 , wherein method is a batch process and the recovery solution is regenerated with nitric acid between batches. 
     
     
         15 . The method according to  claim 1 , wherein the electronic waste comprises circuit-board waste. 
     
     
         16 . The method according to any  claim 1 , wherein the electronic waste is contacted with a recovery solution having a pH of less than 1. 
     
     
         17 . The method according to  claim 1 , the method further comprising removing any electronic waste residue from the recovery solution before raising the pH. 
     
     
         18 . The method according to  claim 1 , wherein the electronic waste is not provided in the form of a powder. 
     
     
         19 . The method according to  claim 1 , wherein the step of raising the pH is conducted stepwise to allow for the separate precipitation and recovery of different metals. 
     
     
         20 . The method according to  claim 1 , wherein the metals recovered comprise one or more of lead, silver, iron, copper, gold, zinc and tin. 
     
     
         21 . The method of  claim 1 , further comprising recovering the precipitated metals from the recovery solution. 
     
     
         22 . The method according to  claim 1 , the method further comprising subjecting the precipitated metals to further treatment to recover one or more substantially pure metals. 
     
     
         23 . The method according to  claim 1 , wherein the method comprises additionally recovering and sorting electronic components separated from the electronic waste by the dissolution of metal from the electronic waste. 
     
     
         24 . The method of  claim 1 , wherein:
 the metals recovered comprise tin;   the recovery solution and electronic waste are subjected to air agitation;   the pH is raised to from 3 to 6; and   the recovery solution comprises:
 from 1 to 3.5 wt % ferric nitrate; 
 from 15 to 40 wt % nitric acid; 
 from 0.5 to 2 wt % chloride ions; 
 from 1 to 10 wt % ammonium sulphamate; and 
 from 0.01 to 0.5 wt % benzotriazole.