Remediation Of Heavy Metal Contaminated Soil By Magnetic Carboxyl-Rich Biochar

Carboxyl group has a high ability to capture heavy metals,and additional magnetism can solve the recovery of carboxyl compounds and prevent secondary pollution.Besides,using corn straw as raw material to prepare biochar can also realize the reuse of resources.So the magnetic carboxyl-rich biochar was prepared by one step hydrothermal synthesis method with citric acid and FeCl₃ as modifiers.And the functional group composition,structure composition,specific surface change and zero charge point change of biochar before and after modification were analyzed in this study.Then,the adsorption,removal and fixation of heavy metals in soil by magnetic carboxy-rich biochar were investigated.The results is as follows:?1?Biochar and magnetic carboxyl-rich biochar contain more oxygen-containing functional groups and aromatic structures.The FTIR spectrum of the magnetic carboxyl-rich biochar appears a new carboxyl absorption peak at 1709cm^-1,indicating that the citric acid is successfully modified.And the magnetic substance is determined to be Fe₃O₄particles by FTIR and XRD.The specific surface area of modified biochar increases greatly and the average pore diameter decreases as well as the Zeta potential.?2?The adsorption process can be well described by the pseudo-second-order model,which suggests that the whole process is dominated by the chemical adsorption.Besides,the isothermal adsorption characteristics of Cu²⁺,Zn²⁺,Pb²⁺,Cd²⁺on magnetic carboxyl-rich biochar can be well fitted by Langmuir and Freundlich isothermal models.And the adsorption of Cu²⁺,Zn²⁺,Pb²⁺,Cd²⁺on magnetic carboxyl-rich biochar is mainly a monolayer adsorption on the surface.With temperature increasing,it is conducive to the progress of the adsorption reaction.Thermaldynamics parameters indicated that the Cu²⁺,Zn²⁺,Pb²⁺,Cd²⁺adsorption on magnetic biochar was a non-spontaneous,endothermic and entropy-increasing process.?3?The removal rate of heavy metals increases with the increase of dosage and p H,and then,the equilibration time is 16h after contact.When the dosage is 5%,pH is 10,the removal rates of Cu,Zn,Pb,and Cd in soil by magnetic carboxyl-rich biochar is 58.21%,37.99%,62.20%and 78.99%,respectively.Magnetic carboxyl-rich biochar can reduce the content of weak acid extracted and reducible state of heavy metals in soil,reduce the content of Cu,Pb,Cd oxidizable state and Cu residue state,and increase the content of Pb,Cd residue state,Zn oxidizable state and residue state,which indicating that magnetic carboxyl-rich biochar can achieve fixation by reducing the content of heavy metal form and has the ability to promote the mutual transformation of heavy metal forms.The effective content and leaching concentration of heavy metals are decreased,and the leaching concentration is lower than the industry standard,indicating that the immobilization of magnetic carboxyl-rich biochar can reduce the biological toxicity of heavy metals and it has low potential environmental risk,so it can be used for heavy metal remediation in soil.