Influence of reduction of structural Fe(Ⅲ)in clay on Cd(Ⅱ)capture under anoxic conditions
The structural Fe(Ⅲ)in clay minerals is one of the primary forms of iron in soils.During flooding conditions,the Fe(Ⅲ)in clay minerals' structure can be reduced to Fe(Ⅱ),resulting in changes in the microstructure and surface chemical properties of the minerals.However,the effects of structural Fe(Ⅲ)reduction on Cd(Ⅱ)capture by these minerals are still unclear.In this study,iron-containing nontronites prepared through a chemical method were used to investigate the effects of structural Fe(Ⅲ)reduction on Cd(Ⅱ)adsorption performance under anoxic conditions.The results showed that the total iron content in the synthetic nontronite was 31.3%,with structural iron accounting for 98.6%of the total iron in the minerals.After chemical reduction,the Fe(Ⅱ)/Fe ratio in the reduced nontronite significantly increased from 3.9%to 67.4%.XRD,SEM,BET,and XPS analyses revealed an increase in the interlayer spacing and the amounts of surface hydroxyl groups with structural Fe(Ⅲ)reduction.Moreover,the specific surface area of the minerals increased from 151.6 m2·g-1 to 184.0 m2·g-1.The adsorption capacities of the reduced minerals for Cd(Ⅱ)were lower than those of the unreduced minerals,whereas the desorption rates of the reduced minerals were slightly higher than those of the unreduced minerals.The Langmuir model best fit the adsorption isotherm data of Cd(Ⅱ)on minerals before and after reduction.The maximum adsorption capacities of Cd(Ⅱ)on reduced and unreduced minerals were 23.5 mg·g-1 and 33.4 mg·g-1,respectively.The adsorption capacities of minerals for Cd(Ⅱ)decreased before and after reduction with an increase in ionic strength,and the reduction in Cd(Ⅱ)adsorption on reduced minerals was significantly lower than that on unreduced minerals.The reduction of Cd(Ⅱ)adsorption performance on reduced clay minerals is mainly attributed to the migration of structural Fe(Ⅱ)into the interlayer during the reduction process,inhibiting Cd(Ⅱ)from entering the interlayer of minerals during the adsorption process.
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