Competition Adsorption-desorption Behaviors Of As And P On Micro-aggregate From Yellow Soil Of The Mingshan River Watershed

In this study, batch culture experiment was conducted to investigate the adsorption-desorption characteristics of arsenic (As(V)) and phosphorus (P) on various size fractions of aggregates (2-0.25mm,0.25-0.053mm,0.053-0.002mm,< 0.002mm) from old alluvial yellow soil, and the competition adsorption-desorption characteristics of arsenic As and phosphorus (P) was also investigated, as well as the adsorption-desorption characteristics of arsenic As and phosphorus (P) after removal of organic matter (the free iron oxide).The major research conclusion are shown as follows:(1) As and P exhibited similar adsorption and desorption characteristics on various size fractions of aggregates. The isothermal adsorption of As(V) and P conforms to both Langmuir and Freundlich equations, and Langmuir was the best fitting equation;in addition, their kinetic adsorption conforms to Elovich equation and double constant equation, and the Elovich was the best fitting equation, which indicated that the adsorption of As(V) and P were specific adsorption-based and supplemented by non-specific adsorption. The maximum adsorption of As(V) on the various particles decreased in the following order:(<0.002mm)> bulk soil> (0.0530.002mm)> (0.25-0.053mm)> (2-0.25mm). As for P, the order was:(<0.002 mm)> (0.053-0.002mm)> (0.25-0.053 mm)> bulk soil> (2-0.25mm), which suggested that the smaller the particle size, the higher adsorption amount of P. The adsorption amount of As and phosphorus on various size fractions of aggregates is not only related to the soil particle size, also associated with soil organic matter, CEC and free iron oxide.(2) As with the dynamics of P adsorption process can be divided into fast and slow reaction in two stages. Namely that the As and the dynamics of the P adsorption process including adsorption and obligate not obligate adsorption. Rapid response phase, mainly exchange adsorption; Slow reaction stage mainly by the ligand adsorption (adsorption) obligate to give priority to. Elovich equation and double constant equation of adsorption dynamics of the As, P data fitting can reached extremely significant level, indicates that the original soil and micro particle size of aggregate on the dynamics of the As, P adsorption process is a complex reaction process, may include absoiption, diffusion, dissolution, mineralization and other complex process.(3)Exponential correlations were found between the desorption amount and absorption amount for both As(V) and P on various size fractions of aggregates. The adsorption of As(P) was significantly reduced after the organic matter (the free iron oxide) removal, it suggests that organic matter and free iron oxide has a promoting effect on the adsorption of As(P) on various size fractions of aggregates, The isothermal adsorption of As(V) and P also conforms to both Langmuir and Freundlich equations, and Langmuir was the best fitting equation., means that the original soil and the particle size of aggregate after the removal of organic matter (the free iron oxide) of the As, P adsorption is still the uniformity of monolayer adsorption.(4)The adsorption of As(P) was significantly restrained by P (As) when they coexisted. The adsorption amount of As(P) decreased with the increasing concentration of P (As), while the desorption amount of As(P) increased with the increasing concentration ofP (As). However, the influence of P (As) on the adsorption-desorption of As(P) was smallest on <0.002mm fraction aggregate. As (V), P coexist, the As (V), P adsorption have been suppressed, and the As (V) by inhibition of larger; As the competition (V) and P adsorption capacity with the decrease of the particle size decreases. Pseudo secondary dynamics equation of adsorption dynamics of As (V), P the best fitting effect of data. As (V), P coexist in the desorption amount of excess presence of desorption quantity alone. As competition (V) and P desorption capacity with the decrease of the particle size decreases. As (V), P coexist, the As (V), P desorption have been promoting each other, and As (V) by promoting greater; Elovich equation and double constant equation are described and the micro particle size of aggregate on the original soil As the best equation, P desorption process.