Process for preparing iron free zinc oxide

Abstract

The present invention provides a process for the separation and removal of iron ions from a basic zinc solution. The process involves: treating an aqueous basic zinc solution with a solid ion exchange resin containing an insoluble cross-linked polymer which contains at least one pendant phosphonate group, at a pH of from about 8 to about 12, and a temperature of from about 10° C. to about 90° C., for a time period sufficient to form solid phase-bound iron ions and a liquid phase containing the aqueous basic zinc solution having an iron ion concentration that is substantially reduced; separating the solid phase-bound iron ions and the liquid phase; and treating the solid phase-bound iron ions with an aqueous acidic solution under conditions sufficient to regenerate the solid ion exchange resin. The present invention also provides a process for preparing zinc oxide that is substantially free of iron ions. This process involves: (a) treating ammonium carbonate and zinc oxide to form a mixture containing a zinc ammonia carbonate complex and metal impurities such as iron, lead, and cadmium, and optionally sulfur; (b) optionally filtering the mixture from (a) to produce a residue containing mostly sulfur and a filtrate containing mostly the zinc ammonium carbonate complex and metal impurities containing iron, lead and cadmium; (c) treating the filtrate from (b), or the mixture from (a) with zinc(0) to remove the lead and cadmium and to form a cementation product, and filtering the cementation product to form a cementation residue containing mostly lead and cadmium and a cementation filtrate containing mostly zinc and iron ions; (d) treating the cementation filtrate from (c) with the above mentioned ion exchange resin, for a time period sufficient to form solid phase-bound iron ions and a liquid phase containing the cementation filtrate having an iron ion concentration that is substantially reduced; (e) heating the liquid phase from (d) to remove ammonia and to precipitate zinc ions in solution as mostly zinc carbonate; and (f) calcining the zinc carbonate precipitate of step (e) at a temperature of from about 200° C. to about 1100° C. to convert the zinc carbonate to zinc oxide.

1 . A process for the separation and removal of iron ions from a basic zinc solution comprising said iron ions, said process comprising the steps of: 
 (a) contacting an aqueous basic zinc solution that comprises said iron ions with a solid ion exchange resin comprising an insoluble cross-linked polymer, said polymer comprising at least one pendant phosphonate group;    (b) maintaining said contact at a pH of from about 8 to about 12, and a temperature of from about 10° C. to about 90° C., for a time period sufficient to form solid phase-bound iron ions and a liquid phase containing the aqueous basic zinc solution having an iron ion concentration that is substantially reduced compared to the solution from (a);    (c) separating the solid phase-bound iron ions and the liquid phase; and    (d) contacting the solid phase-bound iron ions with an aqueous acidic solution under conditions sufficient to regenerate the solid ion exchange resin.    
     
     
         2 . The process of  claim 1 , wherein the iron ions comprise iron(ill) (Fe 3+ ) ions.  
     
     
         4 . The process of  claim 1 , wherein the aqueous basic zinc solution comprises a zinc ammonia carbonate complex.  
     
     
         5 . The process of  claim 1 , wherein the aqueous basic zinc solution comprises at least one member selected from the group consisting of ammonium hydroxide and sodium hydroxide.  
     
     
         6 . The process of  claim 4 , wherein the zinc ammonia carbonate complex is derived from zinc oxide and ammonium carbonate.  
     
     
         7 . The process of  claim 4 , wherein the ammonium carbonate is derived from ammonia and carbon dioxide.  
     
     
         8 . The process of  claim 6 , wherein the ammonium carbonate is an ammoniacal ammonium carbonate solution.  
     
     
         9 . The process of  claim 1 , wherein in step (b), the pH is about 8-9.  
     
     
         10 . The process of  claim 1 , wherein in step (b), the pH ranges from about 9 to about 12.  
     
     
         9 . The process of  claim 1 , wherein the temperature is from about 30° C. to about 70° C.  
     
     
         10 . The process of  claim 1 , wherein the pendant phosphonate group is a monophosphonate group represented by the formula  
       
         
           
           
               
               
           
         
       
       or a geminal diphosphonate group represented by the formula —CH(PO 3 R 2 ) 2  or >C(PO 3 R 2 ) 2  wherein R is hydrogen, a monovalent cation or the two R groups together are a divalent cation.  
     
     
         11 . The process of  claim 10 , wherein the monovalent cation is an ammonium ion (NH 4   + ), a C 1 -C 4  mono, di-, tri- or tetra-alkyl ammonium ion, or an alkali metal cation.  
     
     
         12 . The process of  claim 10 , wherein the divalent cation is an alkaline earth metal cation.  
     
     
         13 . The process of  claim 1 , wherein the polymer further comprises at least one pendant sulfonic acid group.  
     
     
         14 . The process of  claim 13 , wherein the sulfonic acid group is a benzenesulfonic acid group.  
     
     
         15 . The process of  claim 1 , wherein the polymer further comprises at least one carboxylic acid group.  
     
     
         16 . The process of  claim 1 , wherein the solid ion exchange resin has a mesh size of about 15 to about 50 mesh.  
     
     
         17 . The process of  claim 1 , wherein in step (b), the ion exchange resin is in the form of particles that are contained in one or more columns, and wherein in step (c), the solid and liquid phase separation is effected by elution.  
     
     
         18 . The process of  claim 1 , wherein prior to contacting the zinc solution with the solid ion exchange resin in step (a), the ion exchange resin is conditioned by passing a solution of potassium or sodium hydroxide through the ion exchange resin.  
     
     
         19 . The process of  claim 1  wherein in step (d), the conditions sufficient to regenerate the solid ion exchange resin comprise performing the steps below in the following order: 
 (i) optionally backwashing the column with water;  
 (ii) passing an aqueous acid solution through the column;  
 (iii) passing water through the column;  
 (iv) optionally backwashing the column with water until the liquid eluting off the column has a neutral pH;  
 (v) passing a solution of sodium or potassium hydroxide through the column; and  
 (vi) optionally passing water through the column.  
 
     
     
         20 . The process of  claim 19 , wherein in step (ii), the aqueous acid solution is an aqueous hydrochloric solution having a concentration of about 3N to about 12N.  
     
     
         21 . The process of  claim 19 , wherein in step (v), a 1N sodium hydroxide solution is passed through the column.  
     
     
         22 . A process for preparing zinc oxide that is substantially free of iron ions, said process comprising the steps of: 
 (a) contacting ammonium carbonate and zinc oxide to form a mixture comprising a zinc ammonia carbonate complex and metal impurities comprising iron, lead, and cadmium, and optionally sulfur compounds;    (b) optionally filtering the mixture from step (a) to produce a residue comprising mostly sulfur compounds and a filtrate comprising mostly the zinc ammonium carbonate complex and metal impurities comprising iron, lead and cadmium;    (c) treating the filtrate from step (b), or the mixture from step (a) with zinc(0) to remove the lead and cadmium and to form a cementation product, and filtering the cementation product to form a cementation residue comprising mostly zinc, lead and cadmium and a cementation filtrate comprising mostly zinc and iron ions;    (d) contacting the cementation filtrate from step (c) with an ion exchange resin comprising an insoluble cross-linked polymer, said polymer comprising at least one pendant phosphonate group, and maintaining said contact for a time period sufficient to form solid phase-bound iron ions and a liquid phase containing the cementation filtrate having an iron ion concentration that is substantially reduced compared to the concentration of iron ions in the cementation filtrate in step (c);    (e) heating the liquid phase from step (d) to remove ammonia and to precipitate zinc ions in solution as mostly zinc carbonate;    (f) calcining the zinc carbonate precipitate of step (e) at a temperature of from about 200° C. to about 1100° C. to convert the zinc carbonate to zinc oxide.    
     
     
         23 . The process of  claim 22 , wherein in step (f), the calcining is carried out at a temperature of about 250° C. to about 700° C.  
     
     
         24 . The process of  claim 23 , wherein the calcining is carried out at a temperature of from about 400° C. to about 600° C.  
     
     
         25 . The process of  claim 22 , wherein the iron ions comprise iron (III) (Fe 3+ ) ions.  
     
     
         26 . The process of  claim 22 , wherein in step (d), the contacting of the cementation filtrate with the ion-exchange resin takes place at a pH of from about 8 to about 12, and a temperature of from about 10° C. to about 90° C.  
     
     
         27 . The process of  claim 26 , wherein the pH is about 8-9.  
     
     
         28 . The process of  claim 26 , wherein the pH ranges from about 9 to about 12.  
     
     
         29 . The process of  claim 26 , wherein the temperature is from about 30° C. to about 70° C.  
     
     
         30 . The process of  claim 22 , wherein the pendant phosphonate group is a monophosphonate group represented by the formula  
                         
or a geminal diphosphonate group represented by the formula —CH(PO 3 R 2 ) 2  or >C(PO 3 R 2 ) 2  wherein R hydrogen, a monovalent cation or the two R groups together are a divalent cation.  
     
     
         31 . The process of  claim 30 , wherein the monovalent cation is an ammonium ion (NH 4   + ), a C 1 -C 4  mono, di-, tri- or tetra-alkyl ammonium ion, or an alkali metal cation.  
     
     
         32 . The process of  claim 31 , wherein the divalent cation is an alkaline earth metal cation.  
     
     
         33 . The process of  claim 22 , wherein the polymer further comprises at least one pendant sulfonic acid group.  
     
     
         34 . The process of  claim 33 , wherein the sulfonic acid group is a benzenesulfonic acid group.  
     
     
         35 . The process of  claim 22 , wherein the polymer further comprises at least one carboxylic acid group.  
     
     
         36 . The process of  claim 22 , wherein the solid ion exchange resin has a mesh size of about 15 to about 50 mesh.  
     
     
         37 . The process of  claim 22 , wherein in step (d), the ion exchange resin is in the form of particles that are contained in one or more columns, and wherein the contacting of the cementation filtrate with the ion exchange resin comprises passing the cementation filtrate through said one or more columns.  
     
     
         38 . The process of  claim 22 , wherein in step (f) the zinc oxide has an iron ion concentration of 5 ppm or less.  
     
     
         39 . The process of  claim 22 , wherein the liquid phase containing the cementation filtrate has an iron ion concentration of 0.3 ppm or less.