对羟基联苯在黄河兰州段底泥上的吸附行为

Adsorption Behavior of p-hydroxy Biphenyl onto Sediment of the Yellow River in Lanzhou

为研究典型有机污染物在黄河兰州段的吸附规律及影响因素,以黄河兰州段的底泥为供试样品,选择对羟基联苯(phydroxy biphenyl,PHB)为代表性有机污染物,采用批量实验法研究了底泥对PHB的吸附动力学和热力学特征及其影响因素.结果表明,黄河兰州段底泥对PHB吸附动力学的最优模型为准二级动力学模型,吸附热力学过程更符合单分子层吸附的Langmuir等温吸附模型(R2>0.974),在25~45℃温度范围内,PHB在黄河兰州段底泥上的吸附平均自由能(E)在0.913~1.00 k J·mol^(-1)之间,吸附过程中,ΔGθ和ΔHθ均小于0,ΔSθ均大于0,表明黄河兰州段底泥对PHB的吸附过程主要是物理吸附,属于自发放热过程且体系的混乱度是增加的.分析黄河兰州段底泥对PHB吸附影响因素的结果表明,粒径越小,黄河底泥对PHB的吸附量越大;PHB的初始质量浓度越高,黄河底泥对PHB的吸附量越大;当p H在4.23~7.00之间时,吸附量随pH升高而缓慢下降,当pH>7.00时,吸附量随pH升高急剧下降,且在pH=10.3附近,吸附量几乎为零;体系中离子强度增大,PHB吸附量增大,但当离子强度到一定值时,由于竞争吸附作用,会抑制底泥对PHB的吸附,造成吸附量的下降.

In order to study the adsorption behavior of organic pollutants in sediment of the Yellow River in Lanzhou,p-hydroxy biphenyl（ PHB） was selected as the typical organic pollutants to understand the adsorption kinetics and thermodynamics of PHB onto sediment of the Yellow River in Lanzhou based on the batch experiments. Meanwhile,the effects of systemic temperature,such as the particle size,the initial concentration of PHB,pH value,and the ionic strength,were also investigated for the adsorption of PHB onto sediment of the Yellow River. The results indicated that the adsorption kinetics of PHB onto sediment of the Yellow River could be better described by Pseudo-second-order model,and the boundary layer and intraparticle diffusion were both involved in the adsorption kinetic process. The adsorption thermodynamics of PHB onto sediment of the Yellow River were fitted well with the Langmuir model（ R^2 〉0. 974）,which was a single molecular layer adsorption process. The average adsorption free energy E ranged from 0. 913 to 1. 00 k J·mol^-1when the systemic temperatures increased from 25℃ to 45℃,suggesting a physical adsorption. Thermodynamic parameter analysis indicated that Gibbs free energy（ ΔGθ） and Entropy（ ΔHθ） were less than zero,but Enthalpy（ ΔSθ） was more than zero in the adsorption process,which tended to prove the spontaneous nature of the adsorption process,the endothermic nature of the adsorption process and the increased randomness at the sediment surface. Furthermore,the smaller the particle size,the greater the adsorption capacity of the PHB. The adsorption capacity was increased with the increase of the initial concentration of PHB. When the pH value in a range of 4. 23 to 7. 00,the adsorption capacity of PHB showed a slow decreasing trend,while the decreasing was sharp when pH value was greater than 7. 00,and the adsorption capacity was almost zero when pH value was about 10. 3. With the increase of ionic strength,the adsorption amount of PHB was also increased,but when the ionic strength increased to a certain value,due to the competitive adsorption,the adsorption of PHB onto sediments would be inhibited,resulting in decreased amount of adsorption.