Efficiency Evaluation Of Birnesstte And Its Modified Materials For Stabilization Of Cadmium

Cadmium（Cd）is one of the main pollutants of farmland pollution in China.Excessive Cd concentration in the soil will cause harm to the surrounding environment and human health.How to effectively control soil Cd pollution has become a current hot research topic.This article is based on a pollution investigation and risk assessment of a Cd-contaminated farmland in Hebei Province,the birnessite and the birnessite loaded biochar prepared from the birnessite and waste rice husks in farmland are used as stabilized restoration materials and carried out research on the stabilization effect of materials on Cd under water and soil media conditions.The structural properties of the material were analyzed by XRD,TEM,BET,FTIR.The main results and understandings are as follows:1.Investigation of farmland soil in the study area found excessive Cd concentration in soil.Cd is mainly concentrated in the cultivated layer in the farmland soil of the study area.As the depth of the soil layer increases,the Cd content in the soil gradually decreases.The risk assessment results show that some soils in the study area have high ecological risks.2.Birnessite has a good adsorption effect on Cd²⁺,the maximum saturated adsorption capacity is 185.15 mg/g and adsorption is a monolayer adsorption of Cd²⁺onto minerals.The adsorption effect of birnessite on Cd²⁺increases with the increase of pH.At the same time,with the increase of manganese average oxidationstate,the adsorption effect of birnessite on Cd²⁺will decrease.The adsorption mechanism of birnessite to Cd²⁺is mainly accomplished by forming an inner circle complex with Cd²⁺.The adsorption mechanism of birnessite to Cd²⁺is mainly accomplished by forming an inner ring complex with Cd²⁺above or below the[MnO₆]octahedral vacancy.3.Adsorption between birnessite loaded biochar and Cd²⁺is a monolayer adsorption of Cd²⁺and the maximum saturated adsorption capacity is 57.80 mg/g.During the synthesis of birnessite-loaded biochar,the pore structure of rice husk biochar becomes more abundant due to the strong alkaline environment and the addition of potassium permanganate and more different kinds of functional groups are exposed on the surface of biochar.These characteristic changes are very conducive to improving the adsorption capacity of Cd²⁺.4.The adsorption mechanism of birnessite loaded biochar on Cd²⁺In addition to forming complexes with birnessite,biochar also contributes to adsorption.Cd²⁺will form a complex with the oxygen-containing functional groups on the surface of the biochar.5.One week after adding birnessite loaded biochar material to the soil,the proportion of available Cd in the soil was significantly reduced,and the proportion of residual Cd was significantly increased,indicating that the addition of this material promoted the conversion of Cd to a stable form.The stabilization effect is best when the dosing ratio is 2%.