Process for recovering zinc and/or zinc oxide II
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.
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 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.
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.