Integrated diffusion dialysis precipitation - Cementation for selective recovery of leaching chemicals and metal values from electroplating sludge

The hydrometallurgical valorisation of electroplating metal hydroxides sludge was investigated here. It proposes a complete solution. The hazardous solid waste is both an environmental and an economic global issue. It is considered as a challenging scientific topic. This work aims to recover selectively the leaching acid excess and metal values. Fast and complete sludge dissolution is a necessary first step that needs a large excess of concentrated leaching chemical (acid, base, complex...). This constitutes a serious drawback of hydrometallurgical processes because this excess is generally lost and constitutes a supplementary pollutant. The combination chemical leaching diffusion dialysis (DD) cementation precipitation was the main hypothesis of this research. The acid excess was recovered and reused by DD. This constitutes this research novelty. Finally the DD de acidified retentate, loaded with dissolved metals, was successfully processed by various separation operations: selective precipitation and cementation. DD is a well established membrane process for pickling acid recovery, however this sludge specific and efficient application is quite novel. Promising results have been obtained; more than 95% of the acid excess was recovered. Copper was successfully cemented (100%). Selective metals precipitation by phosphate was the final recovery step. The studied problem dealt with an important Algerian tap manufacturing plant. It shows very excellent results (100% of zinc, 99% of nickel, 98, 11% for Lead, 84, 6% Iron and 78, 46% of chromium).