| Fluorine(F) is an essential trace element of human bodies, and excess and lack of the F in the environment will affect human health. Soil is one of the important media for the F cycle in nature, in the modern agricultural production activities, fertilization will bring soil the F. Phosphorus(P)is the essential nutrient for plant growth, and the bio-availability of P, which is applied in soil by fertilization, is an important factor affecting the soil productivity. Massive P fertilization and irrigation of the sewage with F are the main factors which cause the F pollution in soil, so the migration and transformation of the P in soil have close relation with the pollution situations of the F. The mountain yellow soil from west Sichuan province was chosen. Simulation experiment and the selective dissolution method were conducted to study the characteristics of adsorption kinetics and thermodynamics and their influencing factors under the single system and the coexistence system of the F and P. The main conclusions are as follows:(1) The adsorption-desorption studies on F by yellow soil. In different pH systems, the adsorption capacity of F first increased with the pH increase, the maximum appeared at the pH5.0, then at pH6.0 and the minimum appeared at pH4.0. and that demonstrated an increasing trend with the time prolonged, the higher the initial concentration was, the faster the adsorption capacity increased, the adsorption process was divided into fast and slow reaction stage with 8-hour- balancing time. With the increase of the initial concentration, after the absorption completion, equilibrium concentration of the fluorion increased accordingly, adsorption capacity, the net adsorption, desorption and the desorption rate showed an increasing trend and the adsorption equilibrium solution pH value increased. Compared with the original soil, after the removal of the related components, the decrease of the F-absorption was:removal of amorphous iron oxide/amorphous iron aluminum>removal of the organic matter>removal of free iron oxide/freealumina, the difference of the F- absorption was significant after the removal of the free iron oxide/freealumina. Big difference of the absorption existed when adding or not adding TISAB, When added, the adsorption decreased.(2) The adsorption-desorption studies on P by yellow soil.the absorption of the P by the yellow soil in low concentration would not be affected by the initial pH, when in high concentration, that increased with the pH increase, the maximum was at pH6.0, while the minimum was at pH7.0. two procedures (fast and slow) existed in adsorption kinetics of P, In 10 h,80% of the added P was absorbed with a fast absorption rate, and in the slow reaction stage, the absorption lasted a pretty long time. When the P was at low initial concentrations, the absorption of the P by the yellow soil would increase rapidly with the increase of the concentration, and the adsorption curve slope was large, which meant the large majority of P in solution were adsorbed. With the increase of initial P concentration, the P absorption was in slow increase with the increase of the concentration, and the curve flattened. adsorption capacity, the net adsorption capacity increased with the equilibrium concentration of solution increased. The desorption and desorption rate of P of the experimental yellow soil were low and the desorption process could be divided into fast, medium and slow stages. compared with the original soil, after the removal of Fe and Al oxides by DCB, the P absorption significantly decreased, when the organic matters were removed by heating the H2O2, the P absorption increased to some extent.(3) The studies of adsorption kinetics on F by phosphate. When the existence of the phosphate ion, the curve of the adsorption kinetics of P changed significantly, but the adsorption process was still divided into fast and slow stages. Compared with the control, when phosphate ion existed, fast absorption shortened in 5 h. when the phosphate concentration was 10mg/L, in the fast absorption stage, the F absorption by the yellow soil could reach 90% of the equilibrium adsorption, balanced in 5 h,when100mg/L,that could be 95% about 3 h. afterwards, the absorption change became flat.Without phosphate, the Elovich equation and double constant equation had good fitting degree in the adsorption kinetics of F by yellow soil and the correlation coefficient reached 0.9 followed by the parabolic diffusion equation but the primary and secondary reactive equation had poor fitting degree. Under the different phosphate concentrations, the optimal fitting degree was the double constant equation followed by the Elovich equation. (4) The studies of adsorption kinetics on phosphate by F. The adsorption kinetics of the P by yellow soil could be divided into fast and slow adsorption stages. In the fast absorption stage, the P absorption capacity by the yellow soil took more than 90% of the total absorption capacity which demonstrated a close balance absorption characteristics. When the F concentration was10mg/L, it not only inhibited the P absorption by yellow soil but increased the P absorption, only when 100mg/L,did the P adsorption rate show a decreasing trend. But in the slow adsorption stage, whether the F concentration was high or low, the absorption curve showed that the P absorption capacity by yellow soil significantly decreased. Good correlation existed between the adsorption capacity and adsorption time of P by yellow soil. Without F, the adsorption data fitted best with the secondary reactive equation, which reached the very significant correlation. followed by the Elovich equation and double constant equation, but the primary reactive equation had poor fitting degree. Under different F concentrations, the descriptive effect of the Elovich equation and double constant equation was better.(5) The studies on F adsorption thermodynamics by phosphate. Compared with the control, when the initial F concentration was low, the yellow soil could increase the F absorption capacity to different degrees, and its increasing range increased as the phosphate concentration increased. the increase of the F absorption had very significant correlation with added P concentration, and the correlation coefficient was 0.8.but when the initial F concentration was high, as the initial concentration of phosphate ions increasing, the F absorption capacity continuingly decreased in this concentration range. Low concentration of the phosphate had little impact on the F absorption, but high concentration had significant impact on that. Three kinds of adsorption isothermal models could well describe the adsorption data of F:Langmuir equations had the highest fitting r value which meant the correlation coefficient was the highest and the fitting degree was optimal, Freundlich equations was at second place, and finally Temkin equations.(6) The studies on phosphate adsorption thermodynamics by F. Similar with F absorption by phosphate, with the increase of the initial F concentration, P absorption capacity by yellow soil changed differently. compared with the control, the P absorption first increased and then decreased with the F concentrations in the mixed solution increased. With the increase of the F concentration, the P absorption capacity decreased. Among the three kinds of adsorption isothermal models, Langmuir equations had the best fitting degree which was chosen to describe the characteristics of P absorption. The conclusions were: the experimental yellow soil had stronger absorption capacity, but had weak P availability with strong buffering capacity which meant the experimental yellow soil had strong storage of P. But Temkin equation and Freundlich equation fitted poorly. Before reaching the maximum adsorption, the isothermal slope of the phosphate adsorption was larger than fluorion. According to the theory of adsorption isotherms, the adsorption of phosphate had greater adsorption energy, it had stronger adsorption than the fluorion.(7)The desorption characteristics of the F and P in yellow soil. Whether the F and P were in the single system or the coexistence system, the first two desorption capacity accounted for 60% of the total five desorption capacity. From the third desorption, the desorption difference was small. to the fifth desorption the desorption demonstrated a similar trend. The results indicated:the desorption and desorption rate of F were greater than P in the yellow soil, which showed the activities and bio-availabilities in soil of F were greater than P.
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