Study On The Transport Properties And Mechanism Of Heavy Metals In The Soil Around The Dismantling Area Of Waste Electrical And Electronic Equipment

Following after the waste from chemical industry,metallurgy,paper manufacturing,printing and dyeing in the industrial era,waste electrical and electronic equipment?WEEE?is a new type of solid waste.The rapid development of global economy and information products promotes the amount and categories of WEEE entering into a dramatic growth period.As a result of that,lots of adverse impacts are imposed on the environment,especially the dismantling and recycling of WEEE by adopting chemical methods,which may cause a series of environmental issues.This study focuses on the dismantling area of WEEE and investigates the contamination and transport characteristics of heavy metals?Cd,Ni,Cu,Cr,Zn,Hg,As,Pb?in soil around the dismantling area.The influence factors of heavy metals transport pathways are obtained according to the physicochemical properties of detailed soil profile,and the transport mechanism is discussed.The main conclusions are as follows:?1?The contamination of heavy metals in dismantling area and the surrounding surface soil?0-20 cm?is mainly caused by human activities.Except for Cr and Ni,the high concentrations of heavy metals are all detected in the downstream region of dismantling area,and the contamination level is affected greatly by it.The dismantling area and the surrounding surface soil?0-20 cm?are characteristics of acidity and evenly distribution of organic matter.?2?The concentrations of Cr,Ni,Zn,Cu,Pb and Cd in transverse soil profile are all higher than the background values.There is an obvious influence of human factors on the pollution of Cu?Cd and Hg,and the composite or homologous contamination is speculated between Cd,Zn,Cu and Pb.Different transport pathways of heavy metals are identified in transverse soil profile deeper than 60 cm?the fourth layer?.The transport rates of the 8heavy metals are in the following order:Cd?Pb?Cu?Cr?Ni?Zn?As?Hg.?3?The contamination of heavy metals in detailed soil profile is more serious in the surface layer.The concentrations of Cd,Ni,Cu and Hg in surface soil are higher than others and the lowest one is As.Similar contamination and transport properties are found between Cr and Ni.There is a decrease tendency of Cd,Cu,Hg,Pb and Zn in soil along with the increase of depth.The results of principal component analysis suggests that the contamination of Ni and Cr is affected by natural factors while the others are influenced by human factors.?4?The detailed soil profile is characteristics of acidity and a positive correlation between pH and depth.CEC varies with the profile surface,and there is an incremental impact of depth on it.Different variation rules of pH_zpc in two profiles are revealed,and the soil in the FJ04 profile at the depth of 0-10 cm and 20-30 cm are found with positive charge.The dominant mineral component is quartz and a certain amount of plagioclase and potassium feldspar.Illite and chlorite are less in it.SiO₂ is the major ingredient in silicate,followed by Al₂O₃ and Fe₂O₃.More organic matter,dominated by humin,is found in surface layer and declines with depth.The main composition of soil in the two profiles is silt with the particle diameter between 0.075-0.005 mm.There is a positive correlation between depth and the content of clay with 0.005 mm particle diameter.?5?The stepwise regression analysis method is adopted to identify the influence factors of heavy metal contamination in the detailed soil profile.As the results suggest,the influence factors in FJ04 profile are less than those in FJ04'profile,and the impact of human factors on the contamination in FJ04 profile is more notable.?6?The effect of soil in the dismantling area on the transport of heavy metal includes the specific absorption,electrical absorption and complexation.Among them,the specific absorption and complexation are two primary processes influencing the contamination of heavy metal,in which the oxide,phyllosilicate mineral and organic matter play a major role.The intrinsic properties of heavy metals also impact the absorption by soil.