Purification of Cr(VI)-containing wastewater by chemical precipitation: test results of an experimental-industrial installation

Abstract

We present the main results of experimental and industrial study of the developed process and pilot plant for purification of the Cr(VI)-containing rinse water by chemical precipitation. This technique implies full or partial return of treated water to rinse workpieces after chromium plating and prepare working solutions (precipitators). We characterize the manufacturing scheme of the pilot plant and the mode of its performance. Saturated aqueous solutions of Са(ОH)2 and Ва(ОH)2 were used as precipitating reagents. The tests confirmed the possibility of automatic dosing the reagents with due regard for the pH value of a medium, which can be used in both continuous and periodic rinsing. The operating conditions of rinsing the workpieces after electrochemical chromium plating were justified. We derived the equation for the calculation of the total salt content in the rinse water after its purification. We determined the duration of the rinsing without the need to renew the bath volume. The performed calculations substantiated the possibility of reducing the consumption of fresh water supplied for rinsing by the recycling of wastewater without deteriorating the quality of the rinsed workpieces. The reduction of water consumption by 35% was observed as compared with that stated by the regulations.