Removel Of Cadmium And Arsenic From Water By Modified Biochar

Arsenic and cadmium are toxic heavy metals.They often coexist in metal smelting wastewater and mine drainage,which will pollute soil and environmental water.Therefore,effective methods should be taken to remove them.Biochar is widely used in wastewater treatment as an adsorbent with low cost,simple preparation and good adsorption effect.In this study,rice husk,Fe₃O₄ and nitric acid were used as raw materials to synthesize a new biochar adsorbent,which was characterized by SEM and XRD,and the adsorption of As³⁺and Cd²⁺in simulated wastewater was studied.In the single factor experiments,the influence of pH and the amount of adsorbent on the adsorption effect was investigated;the adsorption mechanism was studied by adsorption kinetics experiment and adsorption isotherm experiment;by response surface method,at pH4-6,the amount of adsorbent 0.6-1.0 g/L and the initial concentration of cadmium and arsenic 10-50mg/L,the adsorption effect of modified biochar on cadmium and arsenic was optimized to determine the best adsorption conditions.The influence of initial concentration of ions and the order of adding cadmium and arsenic on the adsorption performance of modified biochar was studied by coadsorption experiments of cadmium and arsenic.The main conclusions are as follows:?1?Scanning electron microscopy?SEM?and X-ray diffraction?XRD?analysis showed that Fe₃O₄ was successfully loaded on the surface of biochar,which made the modified biochar have more adsorption sites,enhanced the adsorption performance,and has strong magnetic properties,and can be easily separated from aqueous solution.?2?The results of single factor experiment show that biochar has better adsorption effect on cadmium and arsenic under weak acid or neutral conditions,and the removal rate of cadmium and arsenic can be increased by increasing the amount of adsorbent within a certain limit on the premise of ensuring the unit adsorption amount.When the pH is 5 and the amount of adsorbent is 1.0g/l,the adsorption capacity per unit of biochar and the removal rate of cadmium and arsenic are the best.?3?The results of adsorption kinetic model experiment show that cadmium reaches adsorption equilibrium in 0.5 h,arsenic reaches adsorption equilibrium in 2 h,and the quasi second-order kinetic model is more suitable for describing adsorption process,which shows that adsorption process is controlled by chemical action;adsorption isotherm experiment results show that Freundlich isotherm is more suitable for describing adsorption process,which shows that the adsorption of cadmium and arsenic on biochar is monolayer and uniform.?4?The results of response surface method showed that the removal efficiency of Cd²⁺and As³⁺was the highest at pH 5.0,initial concentration of 10 mg/L and adsorbent dosage of 1.0 g/L,reaching84.80%and 72.08%respectively.?5?The results of co-adsorption experiments show that the adsorption capacity of 50 mg/L cadmium can be increased from 17.44mg/g to 31.91 mg/g by the pre-balanced biochar with concentration of 10mg/L arsenic,indicating that the addition of arsenic is conducive to the adsorption of cadmium;the adsorption capacity of arsenic will not be increased by the pre-balanced biochar with concentration of 10 mg/L cadmium,but the adsorption capacity will be inhibited when the pre-balanced concentration of cadmium reaches 20 mg/L.When the concentration of arsenic is 10 mg/L and the concentration of cadmium is50 mg/L,the adsorption effect of cadmium and arsenic is the best.