西北黄土对五氯酚钠的吸附及影响因素研究

Study on the adsorption and influential factors of sodium pentachlorophenol on the loess soil in Northwestern China

以西北地区天然黄土为供试土样，通过吸附热力学和动力学试验研究了五氯酚钠（PCP—Na）在黄土上的吸附行为，并对可能的影响因素如溶液DH值、初始质量浓度及土壤粒径对PCP—Na在供试土样上吸附的影响进行了探讨。结果表明：PCP—Na在西北黄土上的动力学吸附过程符合准二级吸附动力学模型，其平衡吸附时间为16h；西北地区黄土对PCP—Na的等温吸附较好地符合Freundlich吸附模型；黄土对PCP—Na的吸附自由能变（△G^∞）、吸附焓变（△H^∞）及吸附熵变（△S^∞）均为负值，表明吸附是一个自发的放热过程，并且吸附过程中体系混乱度减小。溶液pH值和初始质量浓度对PCP—Na在黄土上的吸附影响较大。溶液pH值在4-10之间升高，PCP—Na平衡吸附容量呈先减小后增大的趋势，当溶液pH值为6时吸附容量最小；PCP—Na初始质量浓度从6nltg／L增至40mg／L，其在黄土上的吸附容量从33．43ms／kg增至100．93mg／kg。黄土颗粒粒径越小，PCP—Na在土样上的吸附容量越大，黄土粒径由0．075mm增至0．425mm，吸附容量由134．26mg／kg降至28．71ms／kg。

This paper intends to evaluate the adsorption behavior of the sodium pentachloropbenol to the loess soil in Northwestern China. The experiments of dynamics and thermodynamics have been conduct- ed on the adsorptive behaviors of sodium pentaehlorophenol to the loess soil at 25 ℃ , 35 ℃ , 45 ℃ and 55 ℃ , respectively. The re- suits indicate that the adsorption of sodium pentachlorophenol on the loess soil can reach equilibrium within 16 hours, and the adsorption of sodium pentachlorophenol by the losses soil could be described by the pseudo-sec0nd-order kinetic model. The adsorption thermodynam- ics of sodium pentachlorophenol onto the loess soil is nonlinear by nature and well fitted with the Freundlich isothermal model. The ad- sorption capacity of sodium pentachlorophenol tends to decrease with the increase of the environmental temperature. When calculating the thermodynamic parameters of Gibbs free energy （△G^∞）, enthalpy △H^∞） , and entropy （△S^∞） , the negative value of AH suggests the exothermic nature of the adsorption, whereas the negative values of A G tends to prove the spontaneous nature of the adsorption process. The adsorption process also suggests that the pH value, the initial concentration of sodium pentachlorophenol and the particle size of the loess soil have significant effects on the adsorptive behaviors of the sodium pentaehlorophenol in the Northwestern China. The results in- dicate that the adsorption capacity of the sodium pentachlorophenol tends to decrease with the increase of the pH value below 6, while it tends to increase when the pH value is bigger than 6. When the ini- tial concentration of the sodium pentachlorophenol increased from 6 mg/L to 40 mg/L, the adsorption capacity of the sodium pen- taehlorophenol would increase from 33.43 mg/kg to 100.93 mg/kg. Besides, when the particle size of loess soil increased from 0. 075 to 0.425 mm, the sorption capacity of sodium pentachlorophenol on loess soil is likely to decrease from 134.26 mg/kg to 28.71 mg/kg.