Removal Of Hexavalent Chromium In Aqueous Solution By Alumium And Megnesium Based Alloy Particles

Heavy metals have the characteristics of non-biodegradability and bioenrichment.Heavy metal pollution in the environment affects the growth of animals and plants and human health.Heavy metal Cr(Ⅵ)has attracted much attention due to its strong mobility and high toxicity in the environment.Chemical reduction method based on zero-valent iron and nano-zero-valent iron reduction is the main method to remove Cr(Ⅵ).However,zero-valent iron and nano-zero-valent iron have disadvantages such as passivation,agglomeration,poor fluidity and secondary contamination of iron ions.In this study,two Al-Mg alloys(Al contents are 50%and 56%,abbreviate to Al-Mg50 and Al-Mg56)Al-Fe alloys(Al-Fe20),Al-Mg-Fe alloys(Al-Mg40-Fe20)are applied to remove Cr(Ⅵ).Initial pH values,reaction temperature,reaction time,alloy dosages,pretreatment time and temperature were discussed.Alloy particles before and after hydrogen generation and reaction were characterized by SEM and XRD to explore the Cr(Ⅵ)degradation mechanism.The results indicate that Cr(Ⅵ)removal efficiency increased with decreasing pH,increasing temperature and increasing alloy dosages.The order of materials on Cr(Ⅵ)removal is:Al-Mg40-Fe20＞Al-Mg50≈Al-Mg56＞Al-Fe20.70.1%25 mg/L Cr(Ⅵ)are removed in 9 h by Al-Mg40-Fe20,whose reduction reactivity is better than other three materials.It is showed that oxidation film on alloys surface affects the reactivity of materials.Pretreatment with deionized water can remove the oxidation film on the surface and hence improve the Cr(Ⅵ)removal efficiency.Pretreatment shows better effects with lower pH and higher temperature.Al-Mg40-Fe20 removed 99.7%Cr(Ⅵ)in 3 min after 1 h pretreatment at 45℃.Alloy phases such as Al12Mg17,Al13Fe4 and Mg,may contribute to the good reactivity of Al-Mg40-Fe20 alloys in Cr(Ⅵ)removal.Especially Mg/Al layered double hydroxides existed on the surface after pretreatment,where Cr(Ⅵ)entered the layer structure through ion exchange and adsorption results in fast removal of Cr(Ⅵ)reduction.Compared with zero-valent iron and nano-zero-valent iron,Al-Mg40-Fe20 has the advantages of not easy agglomeration,good fluidity,not easy passivation and no secondary pollution of iron ions.The adsorption of the layered Mg/Al layered double hydroxides on the surface of the material promotes the synergetic mechanism of pollutant removal,which provides a new idea for the development of new functional materials for water treatment and pollution remediation.