Treatment of electroplating wastewater using the freezing method

Wastewater produced from washing can be concentrated and reused in an electroplating bath to produce a cleaner product. Predominant methods of concentrating wastewater from electroplating washing include reverse osmosis and evaporation concentration. However, reverse osmosis cannot treat strongly acidic (pH < 2) or strongly alkaline (pH > 12) wastewaters, and the scope of its application is narrow, while evaporation uses high quantities of energy and is costly. In contrast, freezing electroplating washing wastewater incurs low cost and can be used for treating washing wastewater from various electroplating processes. In this study, supercooled water dynamic ice making (SWDIM) technology was applied for the first time to freeze and crystalize electroplating washing wastewater, followed by centrifugal separation to separate solid and liquid phases. Freezing treatment was performed on the washing water from the acid copper process (pH = 1.15), nickel plating process (pH = 5.1), and zincate zinc plating process (pH = 13.2). The results show that after primary freezing and centrifugal dehydration, the solute removal rate of ice melt water exceeded 90%, which can meet the requirements of the primary washing tank to supplement the washing water. After secondary freezing and centrifugal dehydration, the concentrated wastewater (approximately 0.14 vol of the original wastewater) can be produced, further evaporated and concentrated 2.8 times, and reused for the electroplating bath.