[Experimental studies on stability of flocs from cadmium pollution emergency treatment]

Taking the flocs from cadmium pollution emergency treatment of Longjiang River in Guangxi province as the research object, the stability of the flocs in the simulated static reservoirs and acidic floods was investigated based on the effects of disturbance and pH on the stability of the flocs. The results indicated that disturbance and pH had great effects on the stability of the flocs, and the concentrations of Cd2+ followed the order of pH 5.0 >> pH 6.0 > pH 7. 0 approximately pH 8.0 > pH 9.0 with the original pH of water. When the original pH of water was 5.0, the concentrations of Cd2+ in samples were 19-58 times higher than the national standard limit, and when the original pH of water were 6.0, 7.0, 8.0 and 9.0, respectively, the concentrations of Cd2+ in samples varied from below to 11 times higher than the national standard limit. The release of cadmium from the flocs was higher in the disturbed water, with the concentrations of Cd2+ in most samples higher than 5.0 microg x L(-1), and the highest was double of the national standard limit. In contrast, there was little release in the simulated static reservoirs, with the concentrations of Cd2+ in all samples below 5.0 microg x L(-1), which was lower than the national standard limit. Therefore, the flocs had good stability in the simulated static reservoirs. But it had poor stability in the simulated acidic floods, with higher release of cadmium, and the concentrations of Cd2+ in samples were 14-25 times higher than the national standard limit. Therefore, the monitoring of cadmium concentrations in the floods should be strengthened in the post project analysis for eco-environmental impact of Longjiang River.