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

Abstract

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(R2>0.974), which was a single molecular layer adsorption process. The average adsorption free energy E ranged from 0.913 to 1.00 kJ·mol-1 when 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.