沉积物中重金属铅的释放动力学模拟

Dynamic simulation of the release of Pb from sediments

采用扩散通量模型(DIFS)模拟了沉积物中Pb从固相向液相释放的动力学过程.模拟结果表明,对于扩散梯度膜(DGT)测定的Pb浓度CDGT与孔隙水Pb浓度比值(R)接近1的S1样品,靠近DGT的液相Pb被消耗后,固相吸附态Pb迅速补给消耗;其解吸速率常数k-1较大,而且非稳态Pb含量较大,在放置时间(t)内,DGT表面孔隙水Pb浓度一直维持在初始浓度.而对于R接近0的S2样品(无补给情况),靠近DGT孔隙水Pb被消耗后,固相的补给很少,反映在相关参数上便是非稳态Pb含量较低,而且解吸速率常数k-1很小,DGT表面处孔隙水Pb浓度随放置时间的增加而降低.对于R值等于0.39的S3样品(部分补给情况),非稳态Pb含量和解吸速率常数k-1介于S1和S2样品之间,固相的补给能力介于S1和S2之间.由以上模拟结果可知,沉积物中重金属释放动力学过程受到非稳态Pb含量和释放动力学参数共同影响.

A DIFS model was used to investigate the kinetics of release of Pb from sediments.The simulation results show that in a sustained case（sample S1,R→1）,when the dissolved Pb adjacent to DGT（diffusive gradient in thin films） was depleted,the re-supply from the sediment was sufficiently fast to maintain the Pb concentration in the pore water to its initial level as the labile content of Pb and the desorption coefficient,k-1 were high.For sample S2（R→0,a non-sustained case）,the re-supply from sediment was very low,as the labile content of Pb was low and Pb concentration in the pore water adjacent to the DGT device was progressively depleted.For sample S3（a partial sustained case,R=0.39）,the re-supply from sediment was between S1 and S2,as the intermediate labile Pb content and k-1.As a result,the release of Pb from the sediments was influenced by the pool of labile Pb and the kinetic parameters of the release.