【作者】 夏丽；

【导师】 夏建国；

【作者基本信息】 四川农业大学 ， 土壤学， 2010， 硕士

【摘要】 氟是人体必需的微量元素,环境中氟的过量和缺乏都会影响到人体健康,土壤是自然界氟循环的重要介质之一,在现代农业生产活动中,氟会通过施肥进人土壤。磷是植物生长的必需营养元素,而磷的生物有效性是影响土壤生产力的重要因子,磷通常作为肥料施入土壤中。磷肥的大量施用和含氟污染水的灌溉是造成农业土壤氟污染的主要因素,因此土壤中磷的迁移和转化与氟污染状况总是紧密联系在一起的。本文以川西山地黄壤为研究对象,采用模拟试验和选择溶解方法,研究了氟磷单一体系、共存体系下的吸附动力学和热力学特征及其影响因素。得到的主要结论如下：(1)黄壤对氟的吸附-解吸研究。不同pH体系对氟的吸附量先随pH的增加而增加,约在pH5.0时吸附量达最大,其次是pH6.0时的,而pH4.0时吸附量最小。氟吸附量随时间的延长呈增加趋势,初始浓度越高,吸附量增加速度越快,其吸附过程分为快速和慢速两个反应阶段,平衡时间约为8小时。随着初始浓度的增大,吸附完成后氟离子的平衡液浓度相应地增大,吸附量、净吸附量、解吸量以及解吸率也呈增加趋势,吸附平衡液的pH值上升。与原土相比,去除黄壤相关组分后,对F-吸附降低量由小到大为去无定形氧化铁/铝>去有机质>去游离氧化铁/铝,去除游离氧化铁/铝后F-吸附量差异最明显。加入TISAB与不加入TISAB时吸附量相差很大,加入情况下吸附量下降。(2)黄壤对磷的吸附-解吸研究。黄壤对磷的吸附量在低浓度时不受初始溶液pH的影响,高浓度时随pH的上升而增加,pH6.0吸附量达最大,而在pH7.0吸附量最小。磷吸附动力学存在快、慢两个过程,在10h内,加入磷80%以上被吸附,吸附速率较快,而慢速反应阶段则延续相当长时间。磷初始浓度较低时,黄壤吸附的磷量随浓度上升增加很快,吸附曲线斜率较大,溶液中的磷大部分被吸附。随着初始磷浓度增大,土壤吸附磷量随浓度上升较慢,曲线渐趋平缓。磷吸附量、净吸附量随溶液平衡浓度的升高而增加,供试黄壤的磷解吸量、解吸率较低,解吸过程可分快、中、慢3个阶段进行。与原土相比,黄壤用DCB去除铁铝氧化物后,磷的吸附量明显降低,而用H202加热去有机质后吸附量有一定程度的上升。(3)磷酸根对氟吸附动力学研究。在磷酸根离子存在条件下,氟的吸附动力学曲线发生了明显变化,但吸附过程仍分为快速和慢速两个反应阶段。与对照相比,有磷酸根存在时,快速吸附时间缩短,约在5h内完成,当磷酸根浓度为10mg/L时,快速吸附阶段黄壤对氟的吸附量可达平衡吸附量的90%,在5h左右吸附达到平衡,当浓度为100mg/L时,可达平衡吸附量的95%,3h左右达到平衡,随后黄壤对氟的吸附量变化趋于平缓。在无磷酸根存在条件下,Elovich方程和双常数方程对于黄壤氟吸附动力学过程的拟合度都非常好,相关系数都达到了0.9以上,其次是抛物线扩散方程,而一级反应式和二级反应式拟合效果较差。不同浓度磷酸根存在情况下,黄壤对氟的吸附动力学过程以双常数方程的拟合效果最佳,其次是Elovich方程。(4)氟对磷酸根吸附动力学研究。黄壤对磷的吸附动力学均可分为快速和慢速吸附阶段。在快速吸附阶段,黄壤对磷的吸附量均占了总吸附量的90%以上,表现出了近似于平衡吸附的特征。当添加的氟浓度为10mg/L时,不仅没有阻碍黄壤对磷的吸附,反而磷的吸附量有所增加,只有当氟浓度为100mg/L,黄壤对磷的吸附速率才表现为下降趋势。而在慢速吸附阶段,无论添加氟浓度的高低,吸附曲线都显现出黄壤对磷的吸附量明显降低。黄壤对磷的吸附量与吸附时间都存在着较好的相关性,在不添加氟浓度的情况下,吸附数据与二级反应式方程拟合的最好,达到了极显著的相关性,双常数方程和Elovich方程次之,而一级反应式拟合效果较差。在不同氟浓度存在下,双常数方程和Elovich方程描述的效果较好。(5)磷酸根对氟吸附热力学研究。与对照相比,在氟的初始浓度较低时,黄壤对氟的吸附量都有不同程度的增加,其增加幅度随加入磷酸根浓度的增加而增加,黄壤氟吸附的增加量与加入的磷浓度呈极显著正相关,相关系数为0.8以上。而当氟的初始浓度为高浓度时,随着加入磷酸根离子初始浓度的不断增大,氟的吸附量在此浓度范围内不断减少。低浓度的磷酸根对氟吸附影响较小,高浓度磷酸根影响显著。三种吸附等温方程模型都能较好地描述氟的吸附数据,其中,Langmuir方程拟合的r值最高,即相关系数最大,拟合程度最佳,Freundlich方程次之,最后为Temkin方程。(6)氟对磷酸根吸附热力学研究。与磷酸根对氟吸附的影响类似,随着加入氟离子初始浓度的不断增大,黄壤的磷吸附量有不同的变化,与对照相比,黄壤对磷的吸附量随着混合液中氟浓度的增大先增加后减少。随着氟浓度的增加,磷的吸附量又降低。三种等温吸附式中,以Langmuir方程的拟合度最高,所以本试验用Langmuir方程来描述磷的吸附特性,可知供试黄壤的吸附能力较强供磷能力较弱,缓冲能力大,土壤贮存磷能力强。Temkin方程和Freundlich方程拟合效果较差。在达到最大吸附量之前,磷酸根的吸附等温线的斜率比氟离子大的多。根据吸附等温线的理论,磷酸根的吸附有较大的吸附能,它的吸附比氟离子强的多。(7)氟、磷在黄壤中的解吸特征研究。无论氟和磷在单一体系和共存体系下,其前两次的解吸量占五次解吸总量的60%左右。从第三次解吸开始,解吸量差异变小,到第五次解吸时,解吸量已趋于一致。研究结果表明,黄壤中氟的解吸量和解吸速率大于磷,说明氟在土壤中的活动性和生物有效性大于磷。更多还原

【Abstract】 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.更多还原