Adsorption Of Pb²⁺ And Zn²⁺ By Red Mud Modified Grains Biochar And Its Application

Heavy metals will enter water bodies in different forms through different ways,aggravating water pollution and posing a potential threat to human life and health and ecological security.The solution of heavy metal pollution in water has become one of the key research topics.In recent years,biochar as a new type of heavy metal adsorption material has been favored by the majority of researchers.Studies have found that the modification of a single biochar can effectively improve the adsorption capacity of heavy metals.Therefore,in this study,this paper uses grains as raw materials,red mud was used as modifier to prepare red mud modified grains biochar,and its adsorption properties on Pb²⁺and Zn²⁺were explored.The adsorption mechanism of red mud modified grains biochar on Pb²⁺and Zn²⁺was revealed by means of SEM-EDS,BET,FTIR,XRD,XPS and other methods.The optimum adsorption conditions of Pb²⁺and Zn²⁺by modified lees biochar were selected and applied to acid mine wastewater through adsorption experiment,so as to discuss the treatment effect of actual acid mine wastewater,and to provide a theoretical reference for the treatment and restoration of acid mine wastewater.The main research results are as follows:（1）The adsorption capacity of Pb²⁺and Zn²⁺of red mud modified distillers grains biochar prepared at the pyrolysis temperature of 600℃is stronger.Under the conditions of initial concentration of Pb²⁺100 mg/L,solid-liquid ratio 1.33 g/L,p H=5,the adsorption capacity of Pb²⁺by distillers grains biochar was 24.63 mg/g,and Zn²⁺under the conditions of initial concentration of 100 mg/L,solid-liquid ratio 5.00 g/L,p H=6.The adsorption capacity of Zn²⁺by distillers grains biochar was 5.79mg/g.With the increase of pyrolysis temperature,the adsorption effect of Pb²⁺and Zn²⁺on red mud modified distillers grains biochar also increases gradually.When the pyrolysis temperature is 600℃,the initial concentration is 100 mg/L.The adsorption capacities of Pb²⁺and Zn²⁺on RM-BC600 with p H 5 and 6 were 72.30 mg/g and19.50 mg/g,respectively,indicating that the modification effect of red mud was obvious.（2）The adsorption of Pb²⁺and Zn²⁺by RM-BC600 reached saturation state at 24h.In the adsorption kinetics model,the fitting effect of pseudo-second-order kinetic equation on the adsorption of Pb²⁺by RM-BC600 was better（R²=0.984）,indicating that the adsorption of Pb²⁺by RM-BC600 existed chemical adsorption.The adsorption rate is controlled by chemisorption.Meanwhile,the adsorption of Zn²⁺by RM-BC600 also conforms to the pseudo-second-order kinetic equation,and the fitting effect of the pseudo-second-order kinetic equation（R²=0.975）is better,indicating that the adsorption of Zn²⁺by RM-BC600 is mainly chemical adsorption.The results of adsorption isotherm experiments showed that the Langmuir-Freundlich model had a good fitting effect on the adsorption of Pb²⁺and Zn²⁺by RM-BC600(Pb²⁺:R²≥0.987;Zn²⁺:R²≥0.998).The experimental results of adsorption thermodynamics show that the adsorption of Pb²⁺and Zn²⁺on RM-BC600 is a spontaneous endothermic process,and the adsorption is mainly chemical adsorption and supplemented by physical adsorption.（3）Characterization analysis of RM-BC600 samples before and after adsorption of Pb²⁺and Zn²⁺:SEM-TDS results showed that RM-BC600 was attached to the surface of biochar after adsorption of Pb²⁺and Zn²⁺.XPS spectra showed that the C 1s spectra of RM-BC600 changed significantly after adsorption,and Pb 4f spectra showed that Pb²⁺had been successfully fixed to RM-BC600,mainly because Pb²⁺combined with Ca,Mg,Al,Si,etc.,to form new compounds during the adsorption process.After adsorption of Zn²⁺by RM-BC600,Zn 2p spectra appeared,indicating that RM-BC600 had a good adsorption effect on Zn²⁺.（4）In the adsorption experiment of acid mine wastewater（AMD）,according to the optimal indoor simulation experiment conditions,RM-BC600 was put into AMD,and the removal rate increased with the increase of the dosage,so did the p H.When the dosage was 33.33 g/L,the removal rates of Pb²⁺and Zn²⁺by RM-BC600 reached92.84%and 90.31%.However,in this experimental treatment,the indoor effect was not achieved,mainly because the element composition in AMD is complex,and there is competitive adsorption between metal elements.