Effects of removing heavy metals from suspensions separated by soil washing with four flocculants
淋洗过程预分离细颗粒悬液重金属去除的研究

In order to determine the optimal flocculants and the corresponding dosage, the effects of four flocculants (including aluminum sulfate, polyaluminium chloride, ferrous sulfate and calcium oxide) were studied for removing cadmium, lead, zinc from the suspension containing fine soil particles separated by soil washing process. The concentrations of cadmium, lead and zinc in the suspension were decreased firstly and then increased with the increasing dosage of aluminum sulfate. The concentrations of these three heavy metals were rapidly decreased with the increasing dosage of polyaluminium chloride and calcium oxide. However, when the dosage of ferrous sulfate increased, the concentrations of lead and zinc were decreased, and the concentrations of cadmium rapidly were decreased and then slightly increased. By comparison, the best flocculation dosage of these four flocculants for the flocculation and precipitation of the particles in the suspension were 0.25, 0.04, 1.0 and 0.3 g/L, respectively. When the suspensions treated with the optimal dosage of each flocculants, the concentrations of these three heavy metals were all below the irrigation water quality standards of China. Using the optimal dosage, the cost of flocculant for treating the same volume of suspensions were ferrous sulfate > aluminum sulfate > polyaluminium chloride > calcium oxide. In conclusion, calcium oxide was the optimal flocculants for treating the suspension containing fine particles, and the corresponding optimal pH range was 10 to 11.