【作者】 柳林；

【导师】 谌宏伟；

【作者基本信息】 长沙理工大学 ， 水文学及水资源， 2011， 硕士

【摘要】 本文选用我国南方地区广泛分布的红壤作为吸附材料处理含砷水,通过静态吸附平衡实验,研究砷在红壤中的吸附-解吸行为以及各因素对吸附的影响,并较为系统的探讨了红壤对砷的吸附机理。该研究为饮用水水源砷污染超标的处理工艺设计提供了理论指导,并可为其他污染水如隔、铬和生活污水等的处理研究提供借鉴,具有极强的现实意义。另外,以土壤为吸附材料,取材比较方便,处理成本低廉,设计的处理工艺适合在农村分散式取水地区使用和推广。本文研究内容如下:1、研究初始溶液As（Ⅴ）浓度、反应时间、体系pH值、反应温度以及共存阴离子等单因素条件对红壤吸附砷的影响,并通过L₁₆（4⁴）正交试验考察综合因素影响下的吸附效果。2、对体系进行吸附动力学研究。研究初始溶液As（Ⅴ）浓度、体系pH及反应温度对吸附动力学的影响,并通过各因素下动力学模型数值模拟探讨吸附机理与模式。3、对体系进行吸附热力学研究。对不同温度、不同初始浓度下的吸附实验结果进行等温吸附模型模拟,进一步探讨吸附机理;并对吸附做热力学分析,研究其热力学效应。4、对吸附后的土壤做解吸实验研究,考察砷在土壤中的稳定性及迁移规律。分析影响解吸的因素,并对砷在土壤中的解吸行为进行动力学研究。本文结论主要有:1、影响因素研究。红壤对砷的吸附与初始溶液砷浓度、接触时间、体系pH值、反应温度及共存离子等有关,四因素对吸附影响大小顺序为:体系pH值>接触时间>初始溶液砷浓度>反应温度。吸附剂对砷的去除率随着初始浓度的增大逐渐降低;在反应初期土壤吸附率迅速增大,随着时间的延长增幅下降并逐渐趋于吸附平衡;体系pH值对红壤吸附砷的影响较大,吸附率随着体系pH值的增大总体呈减少趋势;温度对吸附有促进作用,土壤材料对砷的吸附量随着温度的升高逐渐增加;H₂PO₃^-、SiO₃^3-的存在明显抑制土壤对砷的吸附,SO₄^2-添加浓度增大到一定程度才对砷吸附有促进作用,HCO₃^-离子的添加使土壤对砷的吸附率逐渐增加,而Cl^-、NO₃^-对砷的去除率没有显著影响。2、吸附动力学及热力学研究。砷在红壤中的吸附用Langmuir吸附模型拟合效果最好,计算出的土壤最大吸附容量为1250mgkg^-1,Langmuir吸附模型分离因子0<RL<1,表明土壤对砷的吸附为优惠吸附;由Freundlich吸附模型计算0.1<1/n<0.5,说明砷酸根离子在土壤表面易被吸附;吸附自由能变ΔG<0,说明吸附反应能自发进行,吸附焓变ΔH>0,表明土壤对砷的吸附是吸热反应,吸附熵变ΔS>0,说明土壤吸附砷的过程中还伴随着砷的解吸,另外可能是砷酸根进入吸附点位交换下了更活泼的离子,或者是由于吸附水分子的置换所引起的熵的增加大于离子吸附所引起的熵值降低。通过对红壤吸附砷的热力学研究,初步得出吸附是包括物理吸附和化学吸附的复杂过程。动力学实验结果表明红壤对砷的吸附过程遵循Lagrange二级动力学模式,吸附过程除了颗粒间扩散还有其它步骤控制。3、解吸行为研究。土壤中吸附态砷的解吸行为研究表明,砷在土壤中的吸附行为是专性吸附与非专性吸附共存的过程。随着土壤中吸附态砷的含量增大,易解吸的砷占总砷吸附量的比例也随之增大;砷的解吸随时间变化趋势为:反应开始阶段,土壤中吸附态砷的解吸迅速,随着解吸时间的延长,解吸量逐渐趋于平缓;当pH<7时,解吸量随pH的增大先有一个缓慢增加的过程,之后增加幅度变大,pH>7时,解吸量趋于平缓。更多还原

【Abstract】 This thesis uses the red soil which is widely distributed in southern China as the materials to absorb arsenic in the water. The adsorption - desorption behavior and the impact of various factors on the adsorption is studied through the static adsorption experiment, the mechanism of the red soil’s adsorption of arsenic systematically explored too. This study provides the theoretical guidance to the design of the treatment process of the drinking water with excessive arsenic contamination. In addition, the red soil as the adsorption material can be found conveniently and has low cost, which can be used and promoted for the design of treatment technology of distributed water in rural areas.The main reach contents of this thesis are as follows:（1） The single factor’s impact of the adsorption of arsenic, such as the initial concentration of As （Ⅴ） solution, reaction time, pH value, reaction temperature and coexisting anions, is studied. The adsorption effect under the influence of the combination of different factors is studied by L16 （44） orthogonal.（2） The kinetics of adsorption in the system is studied. The impact of the initial concentration of As （Ⅴ） solution, pH and reaction temperature to the adsorption kinetics is studied. The adsorption mechanism and pattern are investigated through the numerical simulation of dynamic model under different factors.（3） The adsorption thermodynamics in the system is studied. The experimental results of different temperatures and different initial concentrations are simulated by the adsorption isotherm model in order to explore the adsorption mechanism. The adsorption thermodynamic analysis is conducted to study the thermodynamic effect.（4） The desorption experiments of the soil after adsorption are conducted to study the stability and the migration of the arsenic in the soil. The factors that affect desorption are analyzed, the kinetics of arsenic desorption in the soil is also conducted.The conclusions in this thesis are as follows:（1） The research of factors affecting adsorption of arsenic The arsenic adsorption in the red soil has a close relationship with the initial concentration of the solution, contacting time of the solution and soil , the temperature of the system and pH value and coexisting anion in soil solution. The effect dimension sequence is: System pH>contact time> the initial arsenic concentration>temperature. The arsenic adsorption rate of the soil rapidly increased in the beginning of the reaction, the growing rate declined and tended to become adsorption balance with the extension of time. The pH value in the system has a great impact on the arsenic adsorption of the red soil, the adsorption rate decreased with the growing of the pH value in the system. Temperature have a accelerate action to adsorption. The existence of H2PO₃^- and SiO3₃^- obviously repressed the adsorption.Addition concentration of SO42- enlarged to certain extent can just accelerate the adsorption action.The addition of HCO₃^- makes adsorption rate increase gradually, but Cl^- and NO₃^- did not show obvious impact to the adsorption rate.（2） The research of the adsorption kinetics and thermodynamics Langmuir isotherms can explain the adsorption mechanism.The maximum adsorption capacity calculated is 1250 mgkg^-1. The dimensionless constant separation factor RL is 0< RL<1, represents the adsorption about in the Red Soil is favorable; 1/n calculated by Freundlich isotherms is 0.1<1/n<0.5,showing that arsenate can be adsorbed easily in the Red Soil; The standard Gibbs free energy changes （ΔG） for the adsorption process is negative, indicating that the adsorption is spontaneous. The enthalpy changeΔH>0, expresses that the adsorption is an endothermic reaction. Entropy changeΔS>0, shows a desorption process accompany with the absorption. Because the arsenate into the adsorptive sites and exchange some more lively ions, or the displacement of the adsorbed water molecules caused the entropy increase greater than the entropy decrease.The preliminary research about adsorption thermodynamics shows that the adsorption is a complex process including the physical and chemical adsorption.The experiment results are fitted with adsorption kinetic models, showing that the process of arsenic adsorption in the Red Soil follows Lagrange Second-order reaction model.In addition to particle proliferation, there are other steps to control the adsorption process.（3） The research of desorptionThe desorption studies of adsorbed arsenic in soil have shown that the adsorption behavior of arsenic in the soil is coexistence process of specific adsorption and non-specific adsorption. With the adsorbed arsenic in soil increase the ratio of easy desorption also increased; Arsenic desorption trend along with time is: In the initial reaction stage adsorbed arsenic desorpted rapidly.With the desorption time going, desorption tended to a stabilization gradually; When the pH <7, the desorption increases slowly with pH raised in the first process, and then the rate becomes larger. When the pH> 7, the desorption amount tendes to a stabilization.更多还原