Adsorption And Desorption Of Molybdate On Three Type Of Soils

This study collected three typical high-iron content soils that can adsorb molybdate (Mo), such as:red, purple and paddy rice soils. Through adsorption kinetics experiment, analyzing the experimental conditions which affected Mo adsorption-process on the soils, including the initial concentration and competitive anions. According to different physical and chemical properties of the three soils, analyzing the influence of different factors on soil-Mo adsorption-process. On the other hand, amendment of calcium carbonate to adjust different soil pH, studied their effect of Mo adsorbed by soils. The data of Mo adsorbed by soils fitted to kinetics, adsorption isotherm simulated equations and thermodynamical analysis, discussing the primary mechanism of soil-Mo adsorption of the three soils. Through three different soil desorption solutions (NaNO3, oxalic acid and Tamm solutions), analyzed Mo desorption quantities, discussing the most-possible major soil-Mo adsorption/desorption behavior in the soils. In the different initial MoO42- ion concentrations and different competitive existence conditions, the fitting results of soil Mo adsorption process has found that both the LJ and the pseudo-first-order adsorption equations can well describe the MoO42- adsorption on the red-soil.which means Fe-oxide can attract MoO42- in solution and perhaps a chemical reaction. Anionic competitive adsorption with Mo following the order as:PO43->SeO32->SO42->Cl->SeO42->NO3-.Comparison of Mo adsorption process of red, purple and paddy rice soils, purple and paddy soil affected the adsorption process of Mo on Fe-oxide. Under the amendments of high CaCO3, purple soil adsorption ability on Mo is decreased. Paddy soil has low ability in adsorbing Mo. Isothermal adsorption experiment data of soil-Mo, Freundlich equation can well fit the soil-Mo adsorption process; the maximum adsorption capacity of red soil is greater than those of purple and paddy rice soil. According to the four kind algorithms of the thermodynamic parameters of data against the law of thermodynamics, conventional adsorption thermodynamic analysis is not applicable to the mixture of soil system.Using oxalic acid solution, NaNO3 and Tamm solutions to desorb soil-Mo, showed that Tamm solution can desorb above 90% exogenous-added Mo in the soils, which further demonstrate the view that the MoO42- adsorption on the Fe-oxide is based on static-ion exchange, however, red and purple soils, oxalic acid solution desorb more soil-Mo rather than NaNO3 solution.