| This paper takes nitrobenzene as the target pollutant to explore its characteristics andinfluencing factors of behaviors of natural sediments adsorption and desorption in Weihe bybatch equilibrium method.From the laboratory study on adsorption characteristics of sediments in Weihe, theresult shows that:1. The nitrobenzene adsorption processes of different Weihe sediments includingbottom silt and river sand can be divided into three processes: fast, slow and equilibriumadsorption. When the adsorption experiment has been conducted for around11hours, theunit medium adsorption amount has not changed obviously as time goes by, which showsthat the adsorption system has reached to a steady state. Therefore, the adsorptionequilibrium time is set as24-hour. In fitting the kinetic curves of Weihe sediment adsorption,it is found that Elovich equation fitting has better effects with the degrees of fitting: bottomsilt R2=0.953and river sand R2=0.934.2. The results of using different adsorption model for adsorption isotherm fitting showthat modified dual mode model can better describe solid-liquid adsorption system andisothermal equilibrium adsorption process which are made up of Weihe silt sediments, riversand and nitrobenzene solution. Using convection-diffusion model to derive dual moderetardation factors shows that at15℃, retardation factors with the initial concentration of4.78mg/L are: Bottom silt Rd=18.64, river sand Rd=14.87.3. The results of adsorption experiments under different environmental factors showthat:(a) When the particle diameter is in the range between0.01-5(μm), if the particle sizeof sediments is smaller, the adsorption capacity is greater; when the particle diameter ofsediments is within the range of0.01to0.1, the maximum amount of adsorption reaches20.9971mg/kg.(b) When sediment organic matter content is higher, the adsorption capacityis greater. When organic matter content is0.397%, the adsorption capacity reaches up to38.928mg/kg.(c) When the ambient temperature is within15℃-30℃, sediment adsorptionamount gradually decreases with rising of temperature. When the temperature is30℃,sediment adsorption amount reaches its minimum25.7412mg/kg.(d) When the initial concentration is4.996-48.9579(mg/L), the adsorption amount increases with the increase ofinitial concentration. When the initial concentration is48.9579mg/L, the adsorption amountreaches up to88.006mg/kg.(e) pH value has no significant effect on the adsorption ofnitrobenzene of Weihe sediments. When pH=6.59, the maximum adsorption capacity is36mg/kg.The research on the characteristics of desorption of Weihe sediments finds that:1. The desorption of Weihe sediments experiences2stages: quick desorption andequilibrium desorption. Weihe sediments has reached a relatively stable state for desorptionof nitrobenzene after about6hours. In fitting the kinetic curves of Weihe sedimentadsorption, it is found that Elovich equation fitting has better effects with the degrees offitting: bottom silt R2=0.9548and river sand R2=0.9757.2. In contrast to the adsorption and desorption kinetics and other researches onisothermal processes, it is found that adsorption is not the reverse process of desorption.Instead, there would be some lags in the desorption process. By comparing the lagcoefficient HI, HI of bottom silt=0.0765, and HI of river sand=0.0700.3. Study on the influence factors of the desorption process displays that:(a) When theparticle diameter is in the range between0.01-5(μm), if the particle size of sediments issmaller, the desorption rate is greater; when the particle diameter of sediments is within therange of0.01to1(μm), the minimum desorption rate is39.3%.(b) When the adsorption is17.265-88.006(mg/kg), the desorption rate increases with the increase of the initialadsorption amount of sediments. When the initial adsorption amount is88.006mg/kg, thedesorption rate reaches its maximum39%.(c) When sediment organic matter content ishigher, the desorption rate is smaller. When organic matter content is0.397%, thedesorption rate reaches its minimum39%.(d) Solid-adsorption systems of different pHvalues have no significant effect on the adsorption of nitrobenzene of Weihe sediments.(c)When the ambient temperature is within15℃-30℃, sediment desorption rate graduallyincreases with rising of temperature. When the temperature is30℃, sediment adsorptionamount reaches its maximum36.53%.Through introducing retardation factor Rd and lag coefficient Hi to study retardationduring the research of adsorption-desorption characteristics, it finds that lag coefficients and retardation factors of two sediments in Weihe have a positive relationship in isothermaladsorption and desorption. It comes out that with the increase of lag coefficient, retardationfactor increases, showing that the retardation effect is stronger and pollutants are less proneto migrate. |
PDF Full Text Request