Effect Of Anion Concentrations Of Lake’s Overlying Water On Asenic Mobilization In Sediments

Sediment of lake which is polluted by arsenic is the sink of pollutants. Usually, the arsenic is combined with metal salt in the form of arsenate, arsenite and other anion forms, and it is immobilized in sediments. The stability and mobilization rules of arsenic in sediments have been closely watched by scholars. Researching the rules of arsenic adsorption/desorption in sediment-water interface is the core link to understand the fate of arsenic. If the stability of combination which is combined by metal salt and arsenate or arsenite is affected by other anions’ concentration changes? What is the mechanism? These questions are not clear now. This research is under the condition of enhancing SO42-、PO43-、HCO3- concentrations, investigating the stability of arsenic and metal salt in sediments, then researching the effect of these anions concentrations changes on rules of arsenic adsorption/desorption in sediment-water interface, main conclusions are as follows:(1) After enhancing SO42- concentrations in overlying water, arsenic which released from sediments can be explained for two aspects:on one hand, SO42- directly competed with arsenic and exchange a part of arsenic. On the other hand, SO42-stimulated microbial activity, and microbial activity indirectly promoted further release of arsenic. Therefore, the increase of SO42- concentration in overlying water increased the release of arsenic, which increased arsenic endogenous pollution risk in lake.(2) After enhancing PO43- concentrations in overlying water, PO43- mainly through competed with arsenic sites in surface sediments, then forming FePO4·2H2O, resulting in arsenic in the sediments was released into the water, increasing the risk of arsenic endogenous pollution in water. However, effect of microorganism in this process was small.(3) When the concentration of HCO3- in overlying water was ranging from 101 mg/L to 236 mg/L, with the increasing of HCO3-, the competition of arsenic and HCO3- was not significant. However, it has slight simulation to microbial activity. This made small part of arsenic release to overlying water, but strength of microbial activity was not big. Hence, the changes of HCO3- concentration have little effect on migration of arsenic in sediments.(4) The arsenic released from sediments was mainly in the form of As(Ⅲ). The secondary reason of arsenic release was reductive dissolution of ferric-hydroxide under anaerobic conditions, at the beginning of the experiment iron and arsenic dissolved and released into overlying water at the same time.