Enhanced Cr(?) Removal From Chromium-Containing Wastewater By Amino-Functionalized Vermiculite Supported Nanoscale Zero-Valent Iron

With the rapid development of industry,the problem of chromium pollution caused by chromium-containing wastewater discharged from industrial activities is becoming more and more serious,causing great harm to human health and the environment.If left untreated,it will cause great harm to human health and the environment.Therefore,the repair of chrome rinse wastewater has become an important environmental issue.Nanoscale zerovalent iron?nZVI?technology based on chemical reduction-precipitation method developed in recent decades has attracted increasing attention due to its significant advantages of huge specific surface area,simplicity,low cost,and high reactivity with Cr?VI?.It is an environmental nanomaterial that is currently widely studied.Unfortunately,there are still technical challenges associated with its application.The nZVI,as a magnetic nanomaterial,shows a strong tendency to agglomerate into larger particles and,resulting in an adverse effect on both effective surface area and catalyst performance after utilization.Aiming at these problems,the amino-functionalized vermiculite-supported nanoscale zero-valent iron?AVT-nZVI?materials are prepared by liquid phase reduction method,and applied to the removal of Cr?VI?in wastewater.The main contents are as follows:?1?The preparation conditions and ratio of AVT-nZVI were optimized and the Cr?VI?removal performance by AVT-nZVI was investigated.Nano-iron particles?AVT-nZVI?supported on AVT were successfully prepared by reducing the Fe³⁺by KBH₄ with amino-functionalized vermiculite?AVT?as the carrier.The experimental results showed that the maximum Cr?VI?removal rate was obtained with AVT-nZVI when the AVT-nZVI mass ratio ratio of 1:4,whereas only 87.5%was achieved by nZVI.The surface morphology of the bare nZVI and AVT-nZVI is analyzed by TEM.The dispersion of AVT-supported nZVI particles were greatly enhanced?D=20-50nm?.The bare nZVI sample was mostly spherical and chain-like and was aggregated,due to the magnetic interactions between particles as well as surface tension interactions.It has been shown that AVT has the potential to act as a dispersant and stabilizer during the synthesis of AVT-nZVI,which weakened the agglomeration of nZVI.?2?The AVT-nZVI material was used to remove Cr?VI?from simulated electroplating rinse wastewater.The parameters affecting Cr?VI?removal by AVT-nZVI,such as AVT-nZVI dosage,initial pH,initial Cr?VI?concentration,reaction temperature,dissolved oxygen and co-existing ions,were investigated.The reusability and stability performance of the AVT-nZVI particles were also investigated.The experimental results showed that 100%of Cr?VI?removal was obtained with AVT-nZVI after the material dosage of 0.625 g L^-1,T=303 K,pH=5and the initial Cr?VI?concentration of 20 mg L^-1.After four cycles,the removal efficiency of Cr?VI?by AVT-nZVI was still maintained at above 70%,suggesting that AVT-nZVI exhibited a good performance of reusability.The stability of AVT-nZVI particles was better than nZVI,which was confirmed by antioxidant experiment.?3?The kinetics studies showed that Cr?VI?removal fitted well to the pseudo-second-order adsorption model.The k_s values of AVT-nZVI are 0.0070 g mg^-1min^-11 and q_e is 47.35 mg g^-1.Based on the experiments and characterization analysis,the possible mechanism of Cr?VI?reduction by the AVT-nZVI was unraveled.The protonated amino groups?-NH₃⁺?on the AVT promoted the negative Cr?VI?species to be adsorbed on the surface of AVT-nZVI.Besides,Cr?VI?was reduced to Cr?III?by Fe?0?.Eventually,Cr?VI?was removed in a way of Cr?III?-Fe?III?co-precipitates adsorbed on the surface of AVT-nZVI particles.Therefore,all the results demonstrated that the AVT-nZVI was a promising material for the removal of heavy metals from wastewater.