Method of precipitation of iron from leach solutions

Abstract

We propose a method of removing iron from leach solutions, obtained by leaching of metal bearing materials with acids, in the form of hydroxide and/or oxide by precipitation. The advantages with the method according to the invention include that the method can be performed at atmospheric pressure and at temperatures from ambient to boiling temperatures and that no gases are emitted. Another important advantage is, by prevention of gel formation of the iron precipitate, that solid/liquid separation becomes much easier and loss of valuable metals is minimized.

1 . A method of removing iron from a metal bearing material, the method comprising:
 leaching the metal bearing material with an acid, wherein the iron is removed in the form of a hydroxide, an oxide or a combination thereof, thereby forming an iron bearing leach solution;   precipitating the iron from the iron bearing leach solution by adding the iron bearing leach solution with a first acidic pH to an emulsion of lime, limestone or a combination thereof with a pH of over  10 , wherein adding the iron bearing leach solution to the emulsion raises the first acidic pH to a second acidic pH.   
     
     
         2 . The method according to the  claim 1 , wherein the first acidic pH of the iron bearing leach solution is ≧0.1. 
     
     
         3 . (canceled) 
     
     
         4 . The method according to  claim 1 , wherein iron and aluminum remaining in the iron bearing leach solution with the second acidic pH are completely precipitated out of the iron bearing leach solution by initially increasing the iron bearing leach solution pH to around 4.5 with lime, limestone or a combination thereof, then lowering the iron bearing leach solution pH to between 3.25-3.5 with dilute hydrogen peroxide, and then increasing the iron bearing leach solution pH back to around 4.5 with lime, limestone or a combination thereof. 
     
     
         5 . The method according to  claim 1 , performed at essentially atmospheric pressure. 
     
     
         6 . The method according to  claim 1 , wherein a temperature is anywhere between an ambient temperature and a boiling temperature. 
     
     
         7 . The method according to  claim 1 , wherein the iron bearing leach solution is a ferric leach solution which comprises dissolved metals such as nickel, cobalt, zinc, copper, similar other similar metals that are normally soluble in a relevant acid or a combination thereof. 
     
     
         8 . The method according to  claim 1 , wherein the method is used in continuous mode, in a batch mode or a combination thereof. 
     
     
         9 . The method according to  claim 1 , wherein a shock pH increase of the iron bearing leach solution is achieved with alkalines selected from the group consisting of soda ash, magnesium oxide, magnesium hydroxide, magnesium carbonate, caustic and ammonia to prevent formation of a gel of the iron oxide/iron hydroxide precipitate thus enabling easy filtration and minimizing loss of any other metallic values. 
     
     
         10 . The method according to  claim 1 , wherein the first acidic pH is preferably essentially as low as 0.1. 
     
     
         11 . The method according to  claim 1 , wherein the first acidic pH is more preferably 0.1. 
     
     
         12 . The method according to  claim 1 , wherein the second acidic pH is between 2.8 and 3.0. 
     
     
         13 . The method according to  claim 1 , wherein the emulsion is preferably prepared separately. 
     
     
         14 . The method of  claim 9 , wherein the shock pH increase is performed instead of or in addition to raising the first acidic pH of the iron bearing leach solution to the second acidic pH. 
     
     
         15 . A method of removing iron from an iron bearing leach solution, the method comprising:
 precipitating iron, which is present in the form of iron oxide, iron hydroxide or a combination thereof, from the iron bearing leach solution by adding the iron bearing leach solution with a first acidic pH to an emulsion of lime, limestone or a combination thereof with a pH of over 10, wherein adding the iron bearing leach solution to the emulsion raises the first acidic pH to a second acidic pH.   
     
     
         16 . The method according to  claim 15 , wherein the first acidic pH is about 0.1 and the second acidic pH is between 2.8 and 3.0. 
     
     
         17 . The method according to  claim 15 , wherein iron and aluminum remaining in the iron bearing leach solution with the second acidic pH are completely precipitated out of the iron bearing leach solution by initially increasing the iron bearing leach solution pH to around 4.5 with lime, limestone or a combination thereof, then lowering the iron bearing leach solution pH to between 3.25-3.5 with dilute hydrogen peroxide, and then increasing the iron bearing leach solution pH back to around 4.5 with lime, limestone or a combination thereof. 
     
     
         18 . The method according to  claim 15 , wherein the iron bearing leach solution is a ferric leach solution which comprises dissolved metals such as nickel, cobalt, zinc, copper, other similar metals that are normally soluble in a relevant acid or a combination thereof. 
     
     
         19 . The method according to  claim 15 , wherein a shock pH increase of the iron bearing leach solution is achieved with alkalines selected from the group consisting of soda ash, magnesium oxide, magnesium hydroxide, magnesium carbonate, caustic and ammonia to prevent formation of a gel of the iron oxide/iron hydroxide precipitate thus enabling easy filtration and minimizing loss of any other metallic values, and wherein the shock pH increase is performed instead of or in addition to raising the first acidic pH of the iron bearing leach solution to the second acidic pH.