Releasing Characteristics Of Colloids From Contaminated-soil And Their Effect On Transportation Of Heavy Metals

There are a large number of mobile colloids underground,which can form colloidal heavy metals through a variety of physical and chemical adsorption action because of its huge specific surface area and electric charge.Colloid and colloidal heavy metals will release into the underground environment under the change of physical and chemical condition,which cause underground pollution and pose a potential threat to human health.Therefore,heavy metal contaminated soil sample was collected from farmland surrounding a zinc refinery plant in Liaoning province to investigate the releasing characteristics of colloids from the soil and their effect on transportation of heavy metals in soil by leaching experiments in soil column under the condition of different environmental factors(pH,ionic strengths,flow velocity).Results showed that 98.87% soil particles in leaching solution were less than 10 ?m,the release value of colloids from soil tended to increase in the early of the leaching experiments and reached a peak,then lowered gradually,and kept a stable value at last.pH,ionic strength and leaching flow velocity have obvious influence on the release of soil colloid.Under the condition of weak acidic solution(pH = 6),the release of colloids from the soil was the most heavily.The release was weakest in leaching solution with strong acidic condition(pH = 4).When pH = 7 or pH = 9,the release value was between the two values above.The releasing capacity of soil colloids decreased with the increase of the ionic strength and increased obviously in the early and then kept no change with the increase of the flow velocity.Because there existed a leaching velocity threshold,which was 1.67 ml/min.The releasing law of Zn,colloidal Zn and Cd,colloidal Cd were the same as soil colloid in the soil under different influence factors(pH,IS,leaching velocity).Weak acidic solution(pH = 6)was the best release condition of Zn and Pb from the soil while pH=7 was the best release of Cd.The migration ability of Zn and Cd were decreased with the increase of ionic strength while migration ability of Pb had no obvious change.The migration ability of Zn,Cd and Pb were increased with the increase of leaching velocity,the degree of change order: Zn > Pb > Cd.There were 70% to100% of zinc,Cd,Pb as the form of colloidal heavy metal in the leachate.Correlation coefficient r between the concentration of colloids and total heavy metal in leachates were calculated by SPSS software.Results showed that the concentration of soil colloidand total Zn,Cd had strong a highly significant correlation,while the concentration of soil colloid and total Pb had no correlation.The transportation of Zn and Cd in soil was mainly dominated by the release of the colloids,while the transportation of Pb was not dominated by the release of the colloids.