Process for recovering zinc and/or zinc oxide II

Abstract

A process for recovering zinc from a zinc containing material, the process including the steps of: leaching the zinc containing material with an alkaline lixiviant comprising an aqueous mixture of NH 3 and NH 4 Cl, or ionic equivalent, having a NH 4 Cl concentration of between about 10 g/L and about 150 g/L H 2 O and a NH 3 concentration of between 20 g/l H 2 O and 250 g/L H 2 O, to produce a zinc containing leachate; stripping ammonia from the leachate to produce a stripped liquor which includes a zinc containing precipitate, the stripped liquor having a NH 3 concentration of between 7 and 30 g/L H 2 O; and recovering the zinc from the stripped liquor.

The invention claimed is: 
     
       1. A process for recovering zinc from a zinc containing material, the process including the steps of:
 leaching the zinc containing material with an alkaline lixiviant comprising an aqueous mixture of NH 3  and NH 4 Cl, or ionic equivalent, having a NH 4 Cl concentration of between about 10 g/L and about 150 g/L H 2 O and a NH 3  concentration of between 20 g/l H 2 O and 250 g/L H 2 O, to produce a zinc containing leachate precipitate in the form of at least one of zinc hydroxide (Zn(OH) 2 ), zinc hydroxy chloride (Zn 5 (OH) 8 Cl 2 .H 2 O), zinc oxide (ZnO) or combination thereof; 
 stripping ammonia from the zinc containing leachate to produce a stripped liquor which includes a zinc containing precipitate, a precipitate containing zinc in the form of at least one of zinc hydroxide (Zn(OH) 2 ), zinc hydroxy chloride (Zn 5 (OH) 8 Cl 2 .H 2 O), zinc oxide (ZnO) or combination thereof, the stripped liquor having a NH 3  concentration of between 7 and 30 g/L H 2 O; and 
 recovering the zinc from the stripped liquor. 
 
     
     
       2. A process according to  claim 1 , wherein the lixiviant has a NH 4 Cl concentration of between 20 g/L H 2 O and 100 g/L H 2 O. 
     
     
       3. A process according to  claim 2 , wherein the concentration of NH 3  in the lixiviant is between 20 and 150 g/L H 2 O. 
     
     
       4. A process according to  claim 3 , wherein the NH 3  concentration after stripping is about 10 g/L H 2 O. 
     
     
       5. A process according to  claim 1 , wherein the stripped liquor has a pH greater than 7. 
     
     
       6. A process according to  claim 1 , wherein the stripping step includes an air stripping process step. 
     
     
       7. A process according to  claim 6 , wherein the air stripping process step includes at least two stripping process stages, the air stream and zinc containing leachate to flowing through the stripping process stages in a counter current flow, and wherein the zinc containing leachate is continually heated in at least one of the strip process stages. 
     
     
       8. A process according to  claim 1 , wherein the major component of the zinc precipitated in the stripped liquor is zinc oxide or zinc hydroxy chloride. 
     
     
       9. A process according to  claim 1 , wherein the step of recovering the zinc produces a zinc depleted liquor which is directly recycled back to at least one of the leaching step or the ammonia strip step. 
     
     
       10. A process according to  claim 1 , wherein the step of recovering the zinc include the steps of:
 separating the zinc containing precipitate from the stripped liquor. 
 
     
     
       11. A process according to  claim 10 , wherein the step of recovering the zinc further includes at least one of the steps of:
 roasting the zinc containing precipitate to a temperature of between 600 to 900° C.; or 
 hydrolysis of the zinc containing precipitate in water having a temperature of between 80 and 200° C. 
 
     
     
       12. A process according to  claim 10 , wherein the step of recovering the zinc includes the steps of:
 hydrolysis of the zinc containing precipitate in water having a temperature of between 80 and 200° C.; and 
 drying the zinc precipitate at a temperature below 200° C. 
 
     
     
       13. A process according to  claim 12 , wherein the step of recovering the zinc further includes the steps of:
 recovering at least a portion of the water from the hydrolysis step; and 
 concentrating this water to produce a concentrated liquor and recycling the concentrate to the leach step. 
 
     
     
       14. A process according to  claim 13 , further including the step of:
 treating the concentrated liquor with sodium hydroxide to precipitate any zinc content for recycle into the process. 
 
     
     
       15. A process according to  claim 10 , wherein the step of recovering the zinc further includes the steps of:
 a first roasting step in which the zinc containing precipitate is roasted at a temperature of between 300 to 500° C.; and 
 a second roasting step in which the roasted solids are further roasted between 300 to 900° C. 
 
     
     
       16. A process according to  claim 10 , wherein the step of recovering the zinc further includes the step of:
 roasting the zinc containing precipitate in a steam atmosphere at a temperature of between 350 to 500° C. 
 
     
     
       17. A process according to  claim 15 , where the zinc containing precipitate is volatised in at least one of the roasting steps and further including at least one of the following:
 condensing the zinc containing precipitate and separating for sale as anhydrous ZnCl 2 ; or 
 capturing the zinc containing precipitate into an aqueous liquor and recycling this liquor to a preceding process step. 
 
     
     
       18. A process according to  claim 15 , wherein after the first roasting step, the roasted zinc containing precipitate undergoes a leaching step with water to produce a leached solid. 
     
     
       19. A process according to  claim 12 , wherein the step of recovering the zinc further includes the steps of:
 roasting the hydrolysed zinc containing precipitate at a temperature of between 300 to 900° C.