Recovery Process of Mixed Electroplating Wastewater

Many Chinese small electroplating enterprises usually discharge mixed electroplating wastewater which contains CN^-, Cr(VI), Cu²⁺, Zn²⁺ and other toxic heavy metals. It is hard for efficiently treating this mixed wastewate. At present, conventional chemical methods could usually meet discharge standard, but may not meet recycling need. In this paper, a combined treatment process include O₃ oxidation, FeSO₄ reduction, heavy metal ions precipitation, nanofiltration and reverse osmosis was studied by experiment. The results showed that the removal rates of total cyanide was above 99% when pH was 9, O₃:CN^- was 5:1(mass ratio) and oxidation time was about 45 minutes; the reduction rates of Cr(VI) was above 99% when pH was 9~10, FeSO₄ : Cr(VI) was 10:1 (mass ratio) and reduction time was about 15 minutes, and main pollutants such as Cr, Cu, Zn in the end treated water by nanofiltration and reverse osmosis closed to zero, the conductivity less than 50us/cm, which was superior to tap water and could be recycled for rinsing water.