Enrichment and recycling of Zn from electroplating wastewater as zinc phosphate via coupled coagulation and hydrothermal route

Electroplating is a common process of converting zinc ion in electrolyte as a micro level zinc layer on electroplating pieces. After electroplating, the remaining electrolyte on the surface of the pieces is washed with water, and accordingly, Zn-containing electroplating wastewater is generated. Hazardous Zn-containing wastewater is generated during the washing of electroplating pieces and plating tank. Herein, Zn was enriched from wastewater by commercial flocculant and then recycled as highly purified zinc phosphate via coupled acid extraction and hydrothermal treatment. Firstly, 98.4% Zn was recovered as sludge from wastewater by adding 0.2 g/L of flocculant. Then, the sludge was dissolved into an acid solution to produce a leachate with 31.2/10.8/19.3 g/L of Fe/Al/Zn and then hydrothermally treated to remove Fe/Al. The Fe removal rate was only 54.2% without phosphate and glucose but was increased to 98.6% after the addition of 0.5 g of glucose with Al/Zn loss