Adsorption Of Bimetallic Pb²⁺ And Cd²⁺ In Soil By Biochar

In recent years,soil heavy metal problems have caused widespread concern.According to surveys of soil pollution in the country,soil heavy metal pollution has been found in multiple target areas across the country,and heavy metal pollution in local areas has been severe.research have confirmed that heavy metals such as lead,cadmium,and mercury can easily accumulate and accumulate in the soil,they cannot be degraded by microorganisms and are extremely difficult to control.They pose a major threat to the global environment and human health.Biochar is a kind of carbon-rich porous material produced by thermal anoxic thermal conversion.It has the characteristics of large specific surface area,abundant surface functional groups,high carbon content,strong carbon fixation ability,and great stability,and It can effectively adsorb and fix heavy metals such as lead,cadmium,etc.in the soil and gradually become a new type of soil remediation material,which has attracted widespread attention of scholars.In this paper,biochar was prepared from three different biomass materials:Salix psammophila,rice straw,and corn stover.The physicochemical properties of three kinds of biochars were characterized;the adsorption characteristics of lead,cadmium bimetallics on straw stalks,rice straw biochars,and corn stover biochars were studied;The adsorption and fixation of lead and cadmium bimetallics by rice straw biochar was explored using a simulated column penetration leaching experiment.The main findings are as follows:（1）Sorghum straw biochar（SSB）,straw straw biochar（RSB）and corn straw biochar（MSB）were prepared by pyrolysis at 500°C under anoxic conditions,and the three biochars were characterized.The results show that the three types of biochar have low carbon content and low degree of carbonization,and they are both alkaline.SSB has the strongest alkalinity and the largest specific surface area;The H/C（molar ratio）of MSB,RSB,and SSB are 0.46,0.48,and 0.46,respectively,and they have relatively moderate aromaticity;Scanning electron microscopy analysis of biochar shows that the surface pores of MSB and SSB are more abundant,so the specific surface area is larger,and the skeleton structure of RSB surface is more complete.Therefore,it is determined that biochar has good physical and chemical properties and can be used as an adsorbent material.（2）The sorption kinetics and adsorption isotherms of Pb²⁺ and Cd²⁺ bimetallics were studied for RSB,SSB and MSB biochars,The results showed that the adsorption reached equilibrium within 24 h,and the adsorption kinetics of the three biochars on Pb²⁺ and Cd²⁺ bimetals were more consistent with the pseudo-second-order kinetics equation;The sorption isotherm of biochar on Pb²⁺ is more consistent with the Langmuir isotherm model,the adsorption isotherm of Cd²⁺ is well simulated by the Langmuir and Freundlich adsorption models,indicating that the adsorption of biochar on Pb2+is similar to monolayer adsorption.When the concentration is high,the adsorption of Cd²⁺ by biochar has multi-layer adsorption.（3）Changes in experimental conditions such as ionic strength（IS）,pH,and the initial amount of biochar can affect the adsorption of Pb²⁺ and Cd²⁺ bimetallics by RSB,SSB,and MSB biochars.The results showed that with the increase of pH value,the adsorption rates of three biochars to Pb²⁺ and Cd²⁺ increased significantly.Under the same pH conditions,the removal rate of Pb²⁺ was:SSB>RSB>MSB,and Cd²⁺ was:RSB>MSB>SSB;The adsorption rate of Cd²⁺ in the three biochars except for SSB increases with the increase of ionic strength（IS）.In other cases,the adsorption of biochar on Pb²⁺ and Cd²⁺ was negatively correlated with IS;with the increase of biochar feed,the adsorption rate of biochar on Pb²⁺ and Cd²⁺ bimetallics increased significantly.（4）In the simulated soil column leaching leaching experiment,the adsorption and fixation effect of biochar on Pb²⁺ and Cd²⁺ bimetallics increased with the increase of pH,initial addition of biochar and IS.In the presence of Pb²⁺ and Cd²⁺ bimetals simultaneously,when pH=6,IS=10,and M biochar/M yellow sand=0.5%,biochar has the best adsorption and fixation effect on Pb²⁺ and Cd²⁺ in soil column,and the retention rate is respectively 66.3%and 45.3%.In summary,the paper systematically studied the adsorption characteristics of biochar on Pb²⁺ and Cd²⁺ bimetallics and the effect of biochar on the adsorption and fixation of Pb²⁺ and Cd²⁺ in soil,which provided a basis for the practical application of biochar.