Study On The Influence Of Iron Oxides On The Adsorption Characteristics Of Pb In Soils

In recent years, with the rapid development of industry, the problem of heavy metal pollution in soil has become increasingly prominent, and all kinds of heavy metal pollution incidents have occurred frequently. Effect of heavy metals in soil adsorption-desorption and the morphological changes of heavy metal chemical caused by many factors, to research the chemical behavior is conducive to the understanding of the mechanism of reaction mechanism and provide indicators for risk assessment of heavy metals in the soil. Selected paddy soil widely distributed in Shanghai area, lead to the soil heavy metal pollution has become more and more serious as the research object, through the indoor cultivation method, adsorption-desorption experiments and speciation analysis of heavy metals as research methods, to explore the chemical behavior of Pb and its harm. Research contents include the effect of iron oxides on the adsorption-desorption of Pb in soils, the effect of moisture and organic matter on exogenous heavy metal Pb speciation transformation and analysis the differences in iron oxides under different water conditions. The main results obtained are as follows:1. Effect of iron oxides on the adsorption and desorption of Pb in soilsThrough the comparison of the original soil, the soil removal of the amorphous iron oxide and the soil removal of the free iron oxide,0.01 mol/L NaNO3 as background electrolyte solution, study the adsorption-desorption experiments on three kinds of soils. The results showed that:(1) After removal of iron oxides, adsorption capacity of soil to Pb decreased with the description of iron oxides in soil can increase Pb2+ adsorption capacity. (2) Three kinds of soil are the specific adsorption mainly, the desorption capacity of the three soils is the soil removal of the free iron oxide> the soil removal of the amorphous iron oxide> original soil, iron oxides in soil can make adsorption of Pb more firmly. (3) Fitting with three kinds of mathematical models, found Langmuir equation is the best fitting equation to Pb in three kinds of soils.The adsorption process of heavy metal Pb in three kinds of soils is mainly chemical adsorption or strongly physical adsorption. The maximum adsorption capacity calculated from the Langmuir equation of Pb, the original soil is 29.21 g/kg, amorphous iron oxide contribution value was 3.52 g/kg, the contribution value of free iron oxide was 8.32 g/kg, the amorphous iron oxide contribution to the adsorption capacity of Pb is 5 times of free iron oxide. (5) Speciation analysis of heavy metals Pb in three soils, the original soil and the soil removal of the amorphous iron oxide adsorbed mainly transformed CAR-Pb, the soil removal of the free iron adsorbed mainly transformed EXC-Pb and CAR-Pb, which illustrate that the soil removal of free iron oxide, adsorption capacity of heavy metal Pb in soil decreased and the potential harm is increased.2. The effect of water content and organic matter on the form transformation of exogenous heavy metal Pb(1) Without the addition of heavy metal Pb in soil mainly existed in RES-Pb. The residual in the proportion of 50.84%. (2)The addition level of the yellow humic acid can affect the distribution of heavy metals Pb in soil. The addition level of the yellow humic acid was positively correlated with the level of EXC-Pb and OM-Pb, was negatively correlated with the proportion of OX-Pb. Under three kinds of water conditions, the addition of yellow humic acid significantly activated the heavy metals Pb in the soil, and increased its mobility in soil. (3) The Elovich diffusion equation was used to characterize the rate of decline of EXC-Pb in soils under different water conditions. In the three water conditions, EXC-Pb in the soil decreased with the time: flooding>dry wet alternate>70% field water capacity. (4) under three soil moisture conditions of amorphous iron oxides and free iron oxide content do significantly test. The statistical results show that the content of free iron oxide without significant difference (P>0.05), the differences in the content of amorphous iron oxides significantly (P<0.01).