Removal Of Heavy Metal Ions By Biochar And Competitive Adsorption Mechanism

Since various human activities?such as waste discharge,mining activities and wastewater irrigation,etc.?will cause pollution of heavy metals in soil and water,environmental ecological protection and pollution remediation have attracted people's attention.How to repair contaminated soil and water effectively is urgently needed to be solved.Biochar is a carbon-rich material which is prepared by high-temperature oxygen-limited thermal cracking using biomass raw materials.It has high surface area and high porosity.Its raw materials are convenient and easy to obtain.It is especially suitable for developing low-cost and economical adsorbents to remove heavy metal pollutants.Therefore,it can be widely used to deal with heavy metal pollution in various water and soil.Due to that the reported researches mostly focused on the removal of single heavy metal contaminant,the competitive adsorption and associated mechanisms were not fully elucidated.Therefore,in the present study,the competitive adsorption of coexisting heavy metals was emphasized.In this thesis,agricultural waste corn stalks were used as raw materials which is made into biochar under the pyrolysis temperature of 350?and 500?.The typical heavy metal pollutant Pb²⁺were used as an example to study the adsorption effect of biochar on Pb²⁺and the influence of the initial p H value of the aqueous solution on the adsorption.We also compare the adsorption capacity of biochar prepared at different pyrolysis temperatures.At the same time,the adsorption characteristics of the single elements Cu²⁺,Pb²⁺and Cr?VI?of biochar were comparatively studied.In order to improve the adsorption capacity of biochar for Cr?VI?,modified magnetic biochar was prepared by iron salt pretreatment and the study on the adsorption and desorption of Cr?VI?was carried out.The paper focuses on the competitive adsorption of two types of bimetallic coexisting systems of Cu²⁺coexist with Pb²⁺and Cr?VI?coexist with Pb²⁺.We revealed the adsorption mechanism of Cu²⁺and Cr?VI?competing for Pb²⁺.In the study,Considering the wide distribution of natural organic matter?humic acid?in the natural environment,the effect of biochar on the adsorption of monometallic and bimetallic systems was studied and discussed.The main conclusions drawn from the study are as follows:?1?Biochar with high pyrolysis temperature?CSBC500?has stronger adsorption capacity for heavy metals?larger adsorption capacity?and the maximum adsorption capacity of CSBC500 for Pb²⁺can reach 348.92?mol/g;?2?Both physical adsorption and chemical adsorption are involved in the process of adsorption of Pb²⁺by corn stalk biochar,such as precipitation and ion exchange processes which also involve electron sharing and electron transfer;?3?In the adsorption experiment of single metal,humic acid inhibit the adsorption of Pb²⁺and Cu²⁺by biochar but promote the adsorption of Cr?VI?;?4?Fourier infrared spectroscopy FTIR characterization results further show that when Cu²⁺/Cr?VI?coexist with Pb²⁺at a concentration of 0.1m M,Cu²⁺/Cr?VI?can promote the adsorption of Pb²⁺by biochar and the effect of Cu²⁺is more obvious.In the case of high concentration?5m M?of coexisting Cu²⁺/Cr?VI?,it has an inhibitory effect on the adsorption of Pb²⁺by biochar;?5?The magnetic biochar was prepared by pretreatment of biomass with different concentrations of Fe?III?solution.We found that increasing the pyrolysis temperature is an effective method to improve the adsorption capacity of magnetic carbon.