WO1994008057B1

WO1994008057B1 - Method for the enhanced recovery of zinc oxide

Info

Publication number: WO1994008057B1
Application number: PCT/US1993/008497
Authority: WO
Filing date: 1993-09-07
Publication date: 1994-04-28
Anticipated expiration: 1995-03-29

Abstract

A method for the recovery of zinc oxide from industrial waste materials of various components, including zinc, lead, iron and cadmium, by roasting the waste material at an elevated temperature, treating the waste material with an ammonium chloride solution maintained at an elevated temperature, separating the undissolved components from the solution, treating the solution with zinc metal to displace undesired metal ions from the solution, cooling the solution to precipitate therefrom zinc compounds, washing the precipitated zinc compounds to remove unwanted compounds such as diamino zinc dichloride, and drying the remaining zinc compound which is essentially hydrated zinc oxide, resulting in essentially pure zinc oxide.

Claims

AMENDED CLAIMS

[received by the International Bureau on 15 February 1994 (15.02.94); original claims 1, 15, 26 and 31 amended; remaining claims unchanged (6 pages)]

1. A continuous method for the recovery of zinc oxide from waste material streams which comprise zinc compounds, comprising the steps of: a. roasting said waste material at an elevated temperature and in a reducing atmosphere; b. treating said waste material with an ammonium chloride solution at an elevated temperature to form a product solution which comprises dissolved zinc and dissolved zinc oxide whereby any iron oxide in said waste material will not go into solution; c. separating said product solution from any undissolved materials present in said product solution including any of said iron oxide; d. adding zinc metal and a dispersant to said product solution whereby any lead and copper ions contained within said product solution are displaced by said zinc metal and precipitate out of said product solution as lead and cadmium metals and said dispersant is selected from the group consisting of dispersants which will prevent the aggregation of said zinc metal; e. separating said product solution from the lead and cadmium metals; f. lowering the temperature of said product solution thereby precipitating the zinc component as a mixture of crystallized zinc compounds; g. separating said precipitated zinc compounds from said product solution; h. washing said zinc compounds solids with a wash water thereby solubilizing certain of said zinc compounds; i. separating the remaining zinc compounds solids from said solution; and then j. drying said remaining zinc compounds solids at a temperature of between about 100°C and 200°C whereby said resulting product is zinc oxide of 99% or greater purity.

2. The method as described in Claim 1, wherein said product solution of step d is maintained at a temperature of at least 90°C.

AMENDED SHEEHAWi E W 13. The method as described in Claim 12, wherein said dispersant is selected from the group consisting of water soluble polymers.

14. The method as described in Claim 13, wherein said dispersant is selected from the group consisting of maleic based acrylic oligmers, lignosulfonates, polyphosphates, polyacrylates, polymethacrylates, maleic anhydride copolymers, polymaleic anhydride, phosphate esters, and phosphonates.

15. A continuous method for the recovery of zinc oxide from waste material streams which comprise zinc compounds, comprising the steps of: a. treating said waste material a first time with an ammonium chloride solution at an elevated temperature to form a first product solution which comprises dissolved zinc and dissolved zinc oxide whereby any iron oxide in said waste material will not go into.solution; b. separating said first product solution from the undissolved waste material compounds present in said first product solution including any of said iron oxide; c. roasting said undissolved waste material compounds at an elevated temperature and in a reducing atmosphere; d. treating said roasted undissolved waste material compounds a second time with said ammonium chloride solution at an elevated temperature to form a second product solution which comprises dissolved zinc and dissolved zinc oxide whereby any iron oxide remaining in said roasted undissolved waste material compounds will not go into solution; e. combining said first and second product solutions to form a combined product solution and adding zinc metal and a dispersant to said combined product solution whereby any lead and copper ions contained within said combined product solution are displaced by said zinc metal and precipitate out of said combined product solution as lead and cadmium metals and said dispersant is selected from the group consisting of dispersants which will prevent the aggregation of said zinc metal; 21. The method as described in Claim 20, wherein the lowering of the temperature of said combined product solution is accomplished using a reverse natural cooling profile.

22. The method as described in Claim 15, wherein said wash water has a termperature of between about 25°C and 100°C.

23. The method as described in Claim 15, further comprising the step of recycling said solution after the zinc component is precipitated therefrom in step g to be reemployed in steps a and d.

24. The method as described in Claim 15, further comprising the step of recycling said wash water after said zinc oxide is separated therefrom to be reemployed in step h.

25. The method as described in Claim 15, further comprising the step of adding a dispersant to said combined product solution concurrently while adding zinc metal to said combined product solution in step e.

26. A continuoμs method for the recovery of zinc oxide from waste materials which comprise compounds of zinc, iron, lead and cadmium, comprising the steps of: a. roasting said waste material at a temperature of at least 500°C and in a reducing atmosphere; b. treating said waste material with an ammonium chloride solution maintained at a temperature of at least 90°C to form a product solution which comprises compounds of zinc, lead and cadmium whereby any iron oxide in said waste material will not go into solution; c. separating said product solution from the undissolved compounds of iron and any other undissolved materials present in said product solution including any of said iron oxide; d. adding zinc metal and a dispersant to said product solution whereby the lead and cadmium ions contained within said product solution and displaced by said zinc metal and precipitate out of said product solution as lead and cadmium metals and said dispersant is selected from the group consisting of dispersants which will prevent the aggregation of said zinc metal;

AMENDED SHEET (,*«« * e. separating said product solution from the lead and cadmium metals; f. lowering the temperature of said product solution in a controlled fashion over a predetermined period of time to a temperature of between about 20°C and 60°C thereby precipitating out said compounds of zinc, including diamino zinc dichloride and hydrated zinc oxide; g. separating said precipitated zinc compounds from said product solution; h. washing said zinc compounds with a wash water at a temperature of between about 25°C and 100°C thereby solubilizing the diamino zinc chloride component; i. separating the remaining zinc compound solids from said product solution; and j . drying said remaining zinc compound solids at a temperature of between about

100°C and 200°C resulting in zinc oxide of 99% or greater purity.

27. The method as described in Claim 26, wherein said zinc metal is in powdered form.

28. The method as described in Claim 26, further comprising the step of recycling said product solution after said zinc compounds are precipitated therefrom in step d to be employed in step b.

29. The method as described in Claim 26, further comprising the step of recycling said wash water after said zinc oxide is separated therefrom to be employed in step h.

30. The method as described in Claim 26, further comprising the step of adding a dispersant to said product solution concurrently while adding zinc metal to said product solution in step d.

31. A continuous method for the recovery of zinc oxide from waste materials which comprise compounds of zinc, iron, lead and cadmium, comprising the steps of:

AMENDED SHEET (WπCLE ~> a. treating said waste materials a first time with an ammonium chloride solution maintained at a temperature of at least 90°C to form a first product solution which comprises dissolved compounds of zinc, lead and cadmium whereby any iron oxide in said waste materials will not go into solution; b. separating said first product solution from the undissolved compounds of iron and any other undissolved waste materials present in said first product solution including any of said iron oxide; c. roasting said undissolved waste materials at a temperature of at least 500°C and in a reducing atmosphere; d. treating said roasted undissolved waste materials a second time with said ammonium chloride solution maintained at a temperature of at least 90°C to form a second product solution which comprises dissolved compounds of zinc, lead and cadmium whereby any iron oxide remaining in said roasted undissolved waste materials will not go into solution; e. combining said first and second product solutions to form a combined product solution and adding zinc metal and a dispersant to said combined product solution whereby the lead and cadmium ions contained within said combined product solution are displaced by said zinc metal and precipitate out of said combined product solution as lead and cadmium metals and said dispersant is selected from the group consisting of dispersants which will prevent the aggregation of said zinc metal; f. separating said combined product solution from the lead and cadmium metals; g. lowering the temperature of said combined product solution in a controlled fashion over a predetermined period of time to a temperature of between about 20°C and 60°C thereby precipitating out said compounds of zinc, including diamino zinc dichloride and hydrated zinc oxide; h. separating said precipitated zinc compounds from said combined product solution; i. washing said zinc compounds with a wash water at a temperature of between about 25°C and 100°C thereby solubilizing the diamino zinc chloride component;

. j. separating the remaining zinc compound solids from said combined product solution; and k. drying said remaining zinc compound solids at a temperature of between about

100°C and 200°C resulting in zinc oxide of 99% or greater purity.

32. The method as described in Claim 31 , wherein said zinc metal is in powdered form.

33. The method as described in Claim 31, further comprising the step of recycling said combined product solution after said zinc compounds are precipitated therefrom in step e to be employed in steps a and d.

34. The method as described in Claim 31, further comprising the step of recycling said wash water after said zinc oxide is separated therefrom to be employed in step i.

35. The method as described in Claim 31 , further comprising the step of adding a dispersant to said combined product solution concurrently while adding zinc metal to said combined product solution in step e.