Washing Efficiency Of Plant Materials For Co-contaminated Soil With Lead,Zinc And Cadmium

It is important to find a high-efficiency,low-cost and eco-friendly soil heavy metal remediation technology due to the concealed and highly toxic of metal pollution in soil.In this study,we used water eluants that extracted from Colocasis esculenta(L.)Schott and Achyranthes bidentata Blume to wash metals lead,zinc and cadmium in industrial soil(soil 1)and mining soil(soil 2).Removal efficiency of heavy metals under different eluent concentrations,washing time,pH,temperature and frequency were investigated.Meanwhile,the absorption efficiency of Pb2+,Zn2+ and Cd2+ in wastewater and soil quality after washing were studied.The main conclusions are as followed:(1)The metals removal ability of Colocasis esculenta(L)Schott and Achyranthes bidentata Blume was verified.Compared with mining soil,the heavy metals in industry soil was easier to remove.And the removal efficiency of metal Zn was higher than Cd and Pb.Eluent concentrations,washing time,pH and frequency have made significant influences on the soil washing,and we finally set 50 g/L,60 min,pH 3 and 25? as the best washing parameters.(2)The adsorption efficiency of Pb2+,Zn2+ and Cd2+ in wastewater used the waste residue extracted from the two kinds of plant materials was increased with its increasing concentrations.(3)The fractions of heavy metals have changed after soil washing.For industry soil,the carbonate-bound fraction,organio-bound fraction and residual fraction concentrations of Pb were decreased;the all fractions of Zn were decreased;the exchangeable fraction of Cd was decreased.For mining soil,the exchangeable fraction of Pb was decreased with Achyranthes bidentata Blume washing,while the other fractions were decreased with Colocasis esculenta(L.)Schott washing;exchangeable fraction of Zn was decreased;and the exchangeable fraction and carbonate-bound fraction of Cd was decreased.(4)Soil washing can partly affect the soil quality.In our study,concentrations of soil organic matter,total nitrogen and available nitrogen were increased after washing with plant materials.Total phosphorus concentration was increased in soil 2,and available phosphorus were decreased in both soils after washing.Meanwhile,available potassium concentration were increased and the total potassium have no change.As for enzyme activities in soils,the activity of catalase and sucrase were increased while urease was decreased.(5)Results of spectral analysis showed that the chemical functional groups contained in the two plant materials are basically same.The main reaction groups during washing are including carboxylic acid,alcohol,fat,amine and phenol.Images of scanning electron microscope showed that the Achyranthes bidentata Blume have a more stable microstructure than Colocasis esculenta(L.)Schott.Otherwise,process of washing can slightly affect the physical structure of industry soil and mining soil.