Study On Preparation And Mechanism Of Adsorption Materials From Red Mud/lignin Co-Pyrolysis

In recent years,biochar has attracted attention at home and abroad in controlling heavy metal pollution in water due to its high specific surface area,rich pore structure and easy preparation;Therefore,it is of great significance to develop green and efficient heavy metal adsorbents for industrial and agricultural wastewater treatment.In this paper,a new type of iron-loaded biochar adsorption material was prepared by coupling red mud and lignin by carbothermal reduction method for the directional removal of lead ions in wastewater,and it was activated and modified by acid leaching and alkali melting to improve the adsorption performance.The main research results and conclusions are as follows:（1）A new type of iron-based biochar was prepared by coupling red mud and lignin by carbothermal reduction,and its reduction mechanism and products were systematically investigated.The results show that in the process of carbothermal reduction,lignin is used as a carbon source to reduce Fe³⁺in red mud,which is called Fe²⁺or converted into Fe⁰.At the same time,elements such as Fe and Al in red mud can promote the development of lignin carbon structure,increase the specific surface area of composite materials,form more holes,and improve its adsorption performance.（2）Based on the preparation of composite adsorption materials,lead ion adsorption experiments were carried out,and their adsorption characteristics and adsorption mechanism were systematically explored.The results showed that the adsorption capacity of the composite adsorption material prepared by co-pyrolysis of red mud and lignin to lead ion in water reached 211.97mg/g,and did not cause secondary pollution.The adsorption mechanism of the composite material prepared by the co-pyrolysis of red mud lignin on lead ion mainly shows that the metal cations such as K⁺,Ca²⁺,Na⁺,Mg²⁺in the red mud exchange with Pb²⁺in the water.The zero-valent iron generated in the carbothermal reduction process improves the existing form of lead in the solution,which is conducive to the further removal of lead.In the process of co-pyrolysis,the form of Si O₂ in red mud changes,and Si O₃^2-is formed,which combines with lead ions in water to form Pb Si O₃ precipitation and can be removed.（3）In order to improve the adsorption performance,red mud was activated by acid leaching and alkali melting.The results show that the activated red mud undergoes a phase change,and the water-insoluble aluminosilicate is converted into water-soluble sodium silicate and sodium aluminate,providing more adsorption sites for the removal of lead ions.Through the analysis of the results of lead ion adsorption,the adsorption amount of lead ion on activated co-pyrolysis carbon reached 328.34mg/g.Langmuir and Fredlich fitting curves show that the adsorption process is mainly chemical adsorption and monolayer adsorption.XRD,XPS and SEM-EDS are used to characterize the co-pyrolysis carbon before and after adsorption,and the main adsorption mechanism is coprecipitation and ion exchange.This study provides a practical basis for the preparation of novel iron based biochar by coupling red mud and lignin through carbothermal reduction.At the same time,it provides theoretical support and technical guidance for the removal of heavy metals from water bodies.Realize the resource utilization of red mud and lignin through the energy conversion concept of"treating waste with waste".