Method for the removal of calcium from a zinc process sulfate solution

Abstract

The invention relates to a method for removing calcium from a sulfate solution in the zinc production process. Calcium is removed as an anhydrate from the raw solution coming from concentrate or ore leaching before the solution purification stages.

1 . A method for the removal of calcium from a sulfate solution in a zinc production process, whereby an iron-containing zinc raw material such as zinc concentrate, ore or calcine is leached into a sulfuric acid solution in order to obtain a raw solution, where said solution is routed to electrolysis after solution purification stages, and the iron is precipitated out from the process, characterized in that the calcium is precipitated from the raw solution as anhydrite in the presence of anhydrite crystals at a temperature between 75-100° C.  
     
     
         2 . A method according to  claim 1 , characterized in that the calcium is precipitated from the raw solution before going to solution purification.  
     
     
         3 . A method according to  claim 1 , characterized in that the anhydrite crystals formed in calcium precipitation are separated from the raw solution and that part of the solid-containing slurry including the crystals, is circulated back to the calcium precipitation stage.  
     
     
         4 . A method according to  claim 3 , characterized in that the anhydrite crystals are ground before their return to the calcium precipitation stage.  
     
     
         5 . A method according to  claim 3 , characterized in that part of the solid-containing slurry including anhydrite crystals is routed to calcine or concentrate leaching.  
     
     
         6 . A method according to  claim 5 , characterized in that the anhydrite is removed from the leaching cycle in conjunction with the iron precipitation.