Insights Into The Heavy Metals Adsorption/Desorption And Binding Mechanisms Onto Several Typical Soils In Shandong Province

In recent years,the rapid development of industrialization and urbanization have brought some benefits.However,many human activities,including industrial production,mining,agriculture and so on,have brought a series of serious environmental problems.Heavy metal pollution has become one of the most widespread and most serious environmental problems in the world because of its wide range of pollution,long duration,pollution concealment,great harm and uneasy degradation.Therefore,the study of the adsorption and desorption of heavy metals in the soil and the mechanisms of their migration and transformation will play an important theoretical guiding role in preventing environmental pollution and soil remediation.This study mainly studied the adsorption,desorption and binding mechnisms of mercury onto the cinnamon soil(CS),bro'wn soil(BS),fluvo-aquic soil(FS),and saline soil(SS)in Shandong Province.It also studied the adsorption and desorption of seven kinds of heavy metals(copper,zinc,lead,chromium,cadmium,nickel and mecury)onto typical saline soil in the Yellow River Delta.The five sampling points of the Yellow River delta mainly included the dongying district(DY),hekou district(HK),kenli county(KL)in Dongying city,and two points in Binzhou city(BZ1 and BZ2).We drew the following conclusions:1.Insight into the mecury adsorption,desorption and binding mechanisms onto four typical soils in Shandong ProvinceThe maximum potential adsorption capacities of the four soils to Hg(?)followed this order:CS>>BS>FS>SS.And the adsorption capacity increased with the increasing of soil organic matter,cation exchange capacity,free iron and aluminum oxide,clay content and specific surface area,but decreased with the increasing of pH.Four soils on Hg(?)desorption increased with increasing of adsorption.Meanwhile,the combination of various techniques had revealed the combination mechanisms of soil and Hg(?)better from a qualitative and quantitative perspective.The specific adsorption of Hg(?)on four soil surfaces was confirmed by X-ray photoelectron spectroscopy(XPS)owing to the change of elemental bonding energy after adsorption.Fourier Transform Infrared Spectroscopy(FTIR)demonstrated that multiple oxygen-containing functional groups(C=O,C-O,and O-H)were involved in the Hg(?)adsorption,and the content of oxygen functional groups determined the adsorption capacity of soil.Meanwhile,scanning electron microscopy combined with X-ray energy dispersive spectrometer(SEM-EDS)more intuitive revealed the binding of mercury to organic matter,metal oxides,and clay minerals in soils,and fundamentally confirmed the results of XPS and FTIR to further elucidate adsorptive phenomena.The complexation with oxygen-containing functional groups and the precipitation with minerals were likely the primary mechanisms for Hg(?)adsorption on several-typical soils.2.Insight into the adsorption and desorption of seven heavy metals onto typical saline soil in the Yellow River Delta.The order of adsorption of seven heavy metals,including Cu2+,Zn2+,Pb2+,Ni2+,Cr6+,Cd2+ and Hg2+,onto five typical saline soils in the the Yellow River Delta region were DY>BZ1>HK>BZ2>KL.And the maximum adsorption amount of the five soils to seven heavy metals were Zn2+>Cu2+>Pb2+>Ni2+>Cr6+>Cd2+ ? Hg2+.RDA analysis suggested that the adsorption capacities of saline soil to heavy metals were consistent with the content of SOM,CEC,clay,Fe2O3 and C elements,but not related to pH value.Meanwhile,the results also showed that the adsorption capacities of saline soil to heavy metals were opposite to the electrical conductivity,which indicated that the adsorption capacities of saline soil to heavy metals decreased with the increasing of salinization degree.The adsorption amount and desorption amount of saline soil to heavy metal showed a linear correlation and polynomial correlation,and the desorption amount increased with increasing of adsorption amount.The order of desorption rate of different heavy metals in soils were Hg2+>Cd2+>Cr6+>Ni2+>Pb2+>Cu2+>Zn2+,which was opposite to the order of adsorption of heavy metals by soil.The results showed that the smaller the adsorption,the greater the amount of desorption quantity,and the combination of soil and heavy metals were more stable.Fourier transform infrared spectroscopy(FTIR)demonstrated that the position of the functional group that occurred in the adsorption reaction was consistent with the desorption reaction,and the combination of soil and heavy metal(Cu,Zn,Pb,Ni,Cr,Cd,Hg)occurred mainly on the multiple functional groups(O-H,N-H,C=O and COO-).Although the combination of different heavy metals and functional groups was different,the order of the sum of relative absorbance of the functional groups in the adsorption of soils to different heavy metals were in accordance with the order of the adsorption capacity.The results also suggested that the complexation of heavy metals and surface functional groups was an important combination mechanism of heavy metals and soil.The results of this study can well elucidate the structural characteristics of different types of soils,and have important theoretical significance for assessing the environmental capacity and environmental effects of different types of soil for different heavy metals.These results also provides data reference and theoretical support for evaluating the risk of heavy metal pollution,forecasting and taking prevention as well as control measures in time at the field and regional scale.