Mechanisms Of Adsorption Of Cu(Ⅱ) And As(Ⅴ) From AMD By Goethite Modified Biochar Materials

Cu（Ⅱ）and As（Ⅴ）are typical heavy metal pollution elements in acid mine drainage（AMD）,and untreated discharge of AMD can cause serious harm to human body and environment.In this study,waste crop corn straw was selected as raw material to prepare biochar,and goethite modified biochar composite was prepared by coprecipitation method,and static adsorption experiments were carried out to explore the effects of different adsorption conditions on its adsorption properties.The adsorption mechanism of Cu（Ⅱ）and As（Ⅴ）was analyzed by kinetic,isothermal adsorption,thermodynamic model and various characterization methods（SEM-EDS,BET,FTIR,XPS,XRD）.In addition,to facilitate the recycling of this material and also to examine the value of practical applications,the powdered composites were granulated and the effects of p H and various interfering ions on the adsorption properties of the granular materials were investigated by static experiments,and dynamic continuous flow column experiments were carried out to evaluate the potential of the granular materials for practical applications.The main research results are as follows:（1）Biochar was prepared at different pyrolysis temperatures（400°C,550°C and700°C）,and BC-550 was selected based on the results of static experiments and the economic cost was taken into consideration.BC-550 was subsequently modified with different iron concentrations（0.5,1 and 2）,and the experimental results and characterization results showed that 1 M iron concentration had the best modification effect,and activation by KOH before co-precipitation could better improve the biochar’s pore size and specific.The results of SEM-EDS,FITR,XPS and other characterization results confirmed that the goethite had been successfully loaded onto the biochar.（2）The results of static adsorption experiments show that the adsorption of Cu（Ⅱ）and As（Ⅴ）by modified materials is affected by the dosage of material,different initial p H,initial concentration of adsorbed material and coexisting ions.The adsorption of Cu（Ⅱ）is the best when the dosage is 1g/L and p H=5（±0.1）.The adsorption of Cu（Ⅱ）was significantly influenced by the coexistence of cations,and the influence was greater with increasing concentration,while the order of influence was Cl^->NO₃^->SO₄^2-in the coexistence of anions.For the adsorption of As（Ⅴ）by the material,the removal rate and adsorption amount of As（Ⅴ）could reach 89.05%and 17.86 mg/g when the dosage was1 g/L,p H=4（±0.1）,and the initial concentration of As（Ⅴ）was 20 mg/L.the adsorption of As（Ⅴ）by the material was not significantly inhibited when multiple anions and cations coexisted.In addition,the adsorption of Cu（Ⅱ）and As（Ⅴ）had good regeneration performance,and the adsorption capacity of Cu（Ⅱ）and As（Ⅴ）were still maintained at29.55 mg/g and 13.81 mg/g after five cycles of use.（3）The adsorption processes of Cu（Ⅱ）and As（Ⅴ）were more in accordance with the proposed secondary kinetic model,both of which were dominated by chemisorption,while the intraparticle diffusion model could well describe the variation of the adsorption rates.The isothermal processes of Cu（Ⅱ）were in accordance with the Langmuir isothermal model,while those of As（Ⅴ）were in accordance with the Freundlich model,which the maximum adsorption amounts of 51.23 mg/g and 37.37mg/g,respectively.The thermodynamic results showed that the greater the confusion with increasing temperature,the more favorable the spontaneous adsorption,and the negative values ofΔG indicated that the process was heat-absorbing.The analysis of the composites before and after the adsorption of Cu（Ⅱ）and As（Ⅴ）using XRD,FITR and XPS,it is shown that the adsorption mechanism is composed of oxygen-containing functional group complexation,surface precipitation and electrostatic attraction.（4）The experimental results of the continuous flow dynamic adsorption column showed that the depletion times（C_t/C₀>0.9）in the adsorption columns of the single systems of Cu（Ⅱ）and As（Ⅴ）were 8880 min and 10680 min,respectively,and their Thomas model calculated the maximum adsorption amounts of 117.68 mg/g and 21.73mg/g,respectively.However,when the two coexisted,the adsorption depletion time points of both Cu（Ⅱ）and As（Ⅴ）were delayed,and the Thomas model fitted the experimental data of the adsorption column well（R²=0.94 and R²=0.84）with the maximum adsorption amounts of 171.19 mg/g and 65.55 mg/g,respectively,indicating that the model can describe the dynamic adsorption processes of Cu（Ⅱ）and As（Ⅴ）well.