Abstract
Zinc sulphide is currently produced by reacting hydrogen sulphide gas with the end solution leaving the nickel hydrogen reduction circuit at Sherritt’s nickel and cobalt refinery located in Fort Saskatchewan, Alberta. While effective in removing zinc from this solution, hydrogen sulphide is a safety hazard and represents a significant reagent cost. In addition, some nickel and cobalt are co-precipitated with the zinc byproduct resulting in unrecoverable losses. These impurities in the zinc sulphide also reduce its marketability, often leading to additional costs for storage and disposal of this material.
Precipitation of the zinc as zinc struvite (ZnNH4PO4) has been tested at Sherritt Technologies, a division of Sherritt, as a potential option to replace the current precipitation process using hydrogen sulphide. Batch and piloting test work indicated that dissolved zinc may be precipitated as anhydrous zinc struvite from hydrogen reduction end solution with the addition of diammonium phosphate (DAP) and ammonia. The implementation of this process may reduce nickel and cobalt losses, reduce hydrogen sulphide consumption on site, and eliminate storage and disposal costs associated with the current zinc sulphide material. Furthermore, the zinc struvite produced may be heated to convert it to zinc pyrophosphate, an alternative byproduct.