Separation of zinc from steel mils sludge

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We are working on the dewatering of the general sludge , at a steel mill...
We want to separate the zinc from the sludge , before dewatering process ....The reason is; the remaining sludge will again go to the sinterizing process where zinc isn't allowed ....
Is there any on who can advise me how to separate the zinc from a sludge ...??
Sludge has DS% of 3-5 .....
Thanks in advance ......

Osman Sandikcioglu
FILTRATION AND WATER SYSTEMS - ANKARA, TURKEY