Preparation Of Activated Carbon Supported NZVI By Liquid Phase Reduction Method And Its Performance And Mechanism Of Cadmium And Nickel Removal

Cadmium and nickel wastewater is one of the most ecologically harmful industrial wastewater,which seriously threatens human safety and health due to its strong migration,solubility,and bioaccumulation.At present,the main treatment methods for cadmium and nickel wastewater include adsorption,membrane separation,ion exchange,and chemical precipitation.Among them,the adsorption method,which has the advantages of low cost,simple operation,and high removal efficiency,has obvious advantages in cadmium and nickel wastewater treatment.Activated carbon-loaded nano zero-valent iron（nZVI@AC）prepared by liquid-phase reduction（LPR）is considered one of the most promising materials for in situ remediation of contaminants in the aqueous environment.However,the complex operation and requirements for various agents limit the practical application of conventional liquid-phase reduction（TLPR）.In this study,an improved liquid phase reduction（ILPR）method with solid-state dosing of reducing agent as the main feature was proposed,the optimal process parameters for the preparation of nZVI@AC by ILPR were determined,and the differences in the physicochemical properties of nZVI@AC prepared by TLPR and ILPR were compared.In addition,the nZVI@AC prepared by ILPR was used in the adsorption experiments of cadmium and nickel wastewater to explore its adsorption mechanism on cadmium and nickel wastewater and to provide a theoretical basis for the removal of cadmium and nickel wastewater by nZVI@AC.The obtained experimental results are as follows:（1）The experimental results of material preparation and characterization show that when the removal rate of Cd²⁺is used as the evaluation index,the order of influence of each factor is Na BH₄ dosage>AC/Fe SO₄?7H₂O mass ratio>sonication time>reaction time.The optimized ILPR process is:AC/Fe SO₄?7H₂O mass ratio of 15∶1,Na BH₄ dosage of 8 g,sonication time of 1 h,reaction time of 20 min.The nZVI@AC（nZVI@AC-I）prepared by ILPR showed a removal rate higher than 92.00%for Cd²⁺,which was better than that of nZVI@AC（nZVI@AC-T）prepared by TLPR.In addition,the removal efficiency of nZVI@AC-I for Cd²⁺was not affected even without the use of polyethylene glycol and ethanol.nZVI@AC-I and nZVI@AC-T did not show significant differences in pore structure,iron content and FTIR spectra,but nZVI@AC-I had a more uniform distribution of iron-containing particles on the surface,smaller particles and higher Fe⁰ content.（2）The optimum p H for static adsorption of Cd²⁺by nZVI@AC-I was 5,the optimum dosage was 3 g/L,the reaction temperature and initial concentration were positively correlated with the adsorption amount,and the adsorption reached the adsorption equilibrium at about 25min.The optimum p H for static adsorption of Ni²⁺was 5 and the optimum dosage was 2.5 g/L.The reaction temperature and initial concentration were positively correlated with the adsorption amount,and the adsorption equilibrium was reached at about 8 h.The adsorption of both Cd²⁺and Ni²⁺by nZVI@AC-I followed the Langmuir model and the pseudo-second-order kinetics.The removal was mainly achieved by chemisorption,the adsorption process was spontaneous and favorable,and the removal mechanisms mainly included surface complexation,precipitation and ion exchange.In the dynamic adsorption experiments,nZVI@AC-I lost the adsorption capacity of Cd²⁺and Ni²⁺wastewater at 384 h and 288 h,respectively.（3）In the static simultaneous removal experiments,the adsorption of both Cd²⁺and Ni²⁺by nZVI@AC-I was significantly lower,and the adsorption capacity of nZVI@AC-I for Ni²⁺was slightly higher than that for Cd²⁺.In addition,the simultaneous removal of Cd²⁺and Ni²⁺followed the Langmuir,Temkin,and pseudo-second-order kinetic models better,which is a chemisorption-based heat absorption reaction.In the dynamic simultaneous removal experiments,nZVI@AC-I lost the adsorption capacity of Cd²⁺and Ni²⁺in the mixed wastewater at 168 h and 252 h,respectively.