Influence Mechanism Of Dissolved Organic Matter(DOM)on Adsorption Of Heavy Metals By Different Minerals

In recent years,environmental pollution by heavy metals has become increasingly prominent.As a simple and efficient treatment method,the adsorption method is widely used in the pollution removal of heavy metals.Among many adsorbent materials,natural minerals（such as calcite and halloysite）are cheap and rich in resources,and they have certain application potential as heavy metal pollution remediation materials.Soil dissolved organic matter（DOM）is widely present in the soil environment in South China.The interaction between DOM and minerals may affect its adsorption behavior of heavy metals.Therefore,this paper selects Cd（II）and Cu（II）as the target pollutants to study the effect of DOM addition of calcite and halloysite on the adsorption of two heavy metals,and explore its internal impact mechanism.The main research conclusions of this paper are as follows:（1）According to the adsorption isotherm and kinetic fitting results,in the presence of dissolved organic matter in farmland soil（DOM concentration of 5mg/L,10mg/L and 20mg/L）,the adsorption equilibrium time of calcite to Cd（II）Increasing from 400 min to 1200 min,the corresponding adsorption capacity decreased from 48.94 mg/g to 44.14 mg/g,28.11 mg/g and22.30 mg/g,respectively.The effect of p H on the adsorption process is more obvious.Calcite shows a strong adsorption capacity for Cd（II）at p H=6.0.SEM and XPS analysis showed that Cd（II）was adsorbed on the surface of calcite in the form of Cd CO_3.Two-dimensional and three-dimensional fluorescence analysis（2D-COS,3D-EEM）results show that DOM can form a Cd（II）-DOM complex with Cd（II）.The results of mass spectrometry showed that DOM would undergo fractionation on calcite,which changed the structural characteristics of DOM and enhanced the mobility of the metal-DOM complex.The Cd（II）-DOM complex is soluble in water,but not adsorbed on calcite,which in turn reduces the adsorption capacity of calcite to Cd（II）.（2）In the presence of soluble organic matter（DOM concentration of 15mg/L and 30 mg/L）in forest soil,the adsorption equilibrium time（200min）of halloysite on Cu（II）remains unchanged,while the corresponding adsorption The capacity increased from11.95 mg/g to 15.56 mg/g and 23.14 mg/g.SEM spectra,Zeta potential and XPS analysis results show that Cu（II）is not in the form of precipitates,but is adsorbed on the surface of the material through electrostatic attraction.The results of 2D-COS and 3D-EEM show that Cu（II）can also form Cu（II）-DOM complexes with DOM.Experimental observations and organic carbon analysis（TOC）results show that the complex is a solid precipitate,so dissolved organic matter reduces the migration of heavy metal Cu（II）,and the adsorption effect is enhanced.