Reduction of chloride emission by thickening of metallurgical wastewater

Institute for Chemical Processing of Coal, ul. Zamkowa 1, 41-803 Zabrze, Poland

^* Corresponding author: kslowik@ichpw.pl

Abstract

Purification and thickening tests of metallurgical industrial wastewater from sintering dust dechlorination unit were carried out. Raw wastewater of pH 6.95 consisted primarily of Zn²⁺, Pb²⁺, Cd²⁺, Tl⁺, Cl^-, SO4^-2, at concentrations of approx. 3,200; 60; 11,500; 100; 40,100 and 5,300 mg/dm³ respectively. The heavy metals removal consisted in chemical precipitation and sedimentation, firstly by sodium hydroxide, and secondly by sodium sulphide solutions resulting in average removal to levels below 1mg/dm³. Moreover, the experimental studies of evaporation process confirmed the possibility of chloride ions reducing, the distillate yield was approx. 80% of the initial effluent stream. The solid product obtained by two-stage evaporation was characterized by satisfactory purity. The results indicate maturity of the applied processes for wastewater treatment, allowing conditions close to zero-liquid-discharge to be achieved.