.cu / Pb / Zn / Cd Migration Law In Porous Media And Its Simulation Forecast

Traditionally, heavy metal in soil was assumed to be stationary because of its strongly sorbing properties associated with the solid phase. However, it is, unfortunately, also very widely detected in groundwater. Therefore the study of transport was of utmost importance for the evaluation of environmental risks. The mainly objectives of the present study were to evaluate the transport of four heavy metals (Cu, Pb, Zn, Cd) in quartz sand based on miscible displacement experiments under different physical and chemical conditions and CXTFIT2.1 package was used to determine model parameters and predict the outflow dynamics. The conclusions had been drawn as followed:The adsorbed amounts of copper, lead, zinc and cadmium in quartz sand increased with its increasing initial concentration. The sequence of the capacity of the four heavy metals adsorption by the soils was Pb＞Cu, Cd＞Zn according to the distribution coefficient K_d. The Langmuir and Freundlich isothermal adsorption can accurately describe adsorption behavior of four heavy metals.The BTCs of heavy metals from transport experiment were exceedingly asymmetric. The pore water velocity, pH value and ionic strength of solution can obviously influence the shape and peak values of the BTCs of heavy metals in quartz sand column. It was found that the pore water velocity and ionic strength of solution were positively correlated with the transport of heavy metals and pH value was in inverse proportion to the transport of heavy metals.The BTCs of heavy metals in quartz sand column under different conditions can all be fitted by two-site model with high goodness of fit(r²ï¼ž0.9, MSE＜0.003) except that the pore water velocity was lower and the pH value of solution is 7. By these model parameters acquired by the two-site model, we can predict the BTCs of heavy metals at different depth of quartz sand column. As the depth of quartz sand column increased from 5cm to 15cm, the response of relative concentration of heavy metals to pore volumes occurred hysteresis.In the competitive experiment, the resident concentration of heavy metals was higher than that in the single system. The sequence of the capacity of the four heavy metals adsorption by the soils was Pb＞Cu＞Zn＞Cd, which was inconsistence with the BTCs of single transport experiment. It can be explained by the hydrolysis capacity: pK_pb(7.8)＜pK_Cu(8.0)＜pK_Zn(9.0)＜pK_Cd(10.1). There was obviously influence on the decrease of lead and copper adsorption by changing the pH value of solution in competitive system because of the different adsorption sites in corresponding pH value.