Sulfidation treatment of metal compounds involved in plating sludges

The present study is concerned with the sulfidation treatment of metal reagents of Cu(OH)2, ZnO or Ni(OH)2 as a means of metal resources recovery. The sulfidation was conducted separately for each reagent by contacting the reagent with Na2S solution (S2− to Me2+ molar ratio of 1.5) for 1 h to 7 d. The solid to liquid (S:L) ratio was varied from 1:250 to 1:25. In the case of ZnO and Ni(OH)2, the conversion was determined based on thermogravimetric analyses of the sulfidation products, while XRD analysis was used as the main evaluation parameter for the conversion of Cu(OH)2 to copper sulfide. As a result, it was found that Cu(OH)2 was completely converted to copper sulfide within 1 h at all S:L ratios. In the case of ZnO, a two stage phenomenon was observed. A high conversion rate was observed within the first 12 h at all S:L ratios followed by a lower conversion rate from 12 h to 7 d. The maximum conversion of ZnO to ZnS was 60.3%, which was obtained after 7 d at S:L ratio of 1:25. Meanwhile, the maximum conversion of Ni(OH)2 was only 32.4% after 7 d at the S:L ratio of 1:25.