龙江河突发环境事件河流镉污染化学形态模拟

重金属污染突发水环境事件的应急处置和造成的环境损害与污染物的化学形态及其环境行为密切相关.以2012年初发生在我国广西的龙江河镉污染事件为例,采用Minteq软件尝试计算3种情景下河流水环境溶解态Cd的化学形态.结果表明,在天然背景条件下龙江河Cd浓度约为5μg/L时,水环境中Cd以Cd2+为主,并主要受DOC含量的影响.镉污染事件发生后若无应急处置措施,天然水体对Cd的络合缓冲能力极其有限,以Cd2+形式存在的Cd占75%以上,呈现严重的急性生态毒性.投加聚合氯化铝和碱性物质可以有效控制河流溶解态Cd含量,当p H值超过9.0时,以Cd2+存在的Cd迅速降低.Cd2+含量对河流p H值的参数敏感性最高,DOC其次,水温影响最小.事件处置结束后应密切关注絮凝体中Cd的再释放规律以及水体p H值及DOC对Cd形态的影响.

Modeling of cadmium speciation in Longjiang River during an emergent environmental incident

Chemical speciation of metals and their environmental behaviors are of great importance for the emergency responses and damage assessments of emergent environmental incidents caused by industrial releases. Based on the Longjiang river cadmium pollution accident occurred in year 2012 in Guangxi, China, the dissolved Cd speciation in the river for 3 different scenarios were calculated using Visual Minteq 3.1. It was showed that Cd2+ was the dominant Cd specie with a low concentration (0.005mg/L), and it was strongly influenced by DOC content at the background situation. If there were no immediate responding activities in the river after the release of Cd, Cd2+ would cover more than 75% of the total dissolved Cd with a high concentration (0.4mg/L) because of the little buffer ability of the natural aquatic system, which would present serious ecological emergency toxicities. Adding polymeric aluminum and alkali to the river in a proper way could reduce Cd content in the river efficiently and the ratio of Cd2+ also reduced rapidly when pH raise to 9.0 or higher. Cd2+ was sensitive mostly to pH, and secondly DOC, and was not sensitive to temperature. It was suggested that we should pay attention to the re-release of Cd in inorganic polymer flocculation bodies and the influences of pH and DOC.