[Adsorption of Hg(â ¡) in Water by Sulfydryl-Modified Sepiolite].

In order to develop highly efficient and low-cost treatment technique for heavy metal wastewater and promote the resource utilization of sepiolite, natural sepiolite was modified by using thioglycollic acid and characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), specific surface, Zeta potential and infrared spectrum (IR) analysis, and the adsorption kinetic and thermodynamic characteristics of the modified sepiolite to Hg(Ⅱ) in water were studied by static adsorption experiments. The results showed that sulfydryl groups were grafted onto sepiolite, and the surface of the modified sepiolite became smoother with more gaps and negative charges to improve the adsorption ability for Hg(Ⅱ). The optimal pH for Hg(Ⅱ) adsorption on the modified sepiolite was 6, and the adsorption process reached equilibrium in 60 min at 30℃. This process could be described by the pseudo second-order kinetic equation, and the initial adsorption rate constant was 0.063 mg·(g·min)-1. The adsorption thermodynamic characteristics could be well described by Langmuir isothermal adsorption model, and the maximum adsorption capacity was 3.256 mg·g-1. The investigation revealed that the adsorption process was a spontaneous endothermic process, resulting in physical adsorption and chemical adsorption, which was dominated by physical adsorption.

[Influence of Three Low-Molecular-Weight Organic Acids on the Adsorption of Phenanthrene in Purple Soil].

The effects of three low-molecular-weight organic acids (citric acid, malic acid and oxalic acid) on the adsorption of phenanthrene in purple soil were studied by static adsorption experiment. The results showed that the adsorption kinetic process of phenanthrene in purple soil could be described by the second-order kinetic model, and the adsorption rate constant would significantly decrease in the presence of the three low-molecular-weight organic acids ( LMWOAs). The adsorption thermodynamic process could be well described by linear adsorption model, which was dominated by distribution role. The three LMWOAs could promote the adsorption of phenantherene in purple soil when their concentrations were less than 5 mmol · L⁻¹, whereas inhibit the adsorption when their concentrations were more than 10 mmol · L⁻¹, and the inhibition would increase with increasing concentrations. Moreover, the inhibitory ability displayed a decreasing order of citric acid, oxalic acid, and malic acid when their concentrations were 20 mmol · L⁻¹, which is related to the molecular structure and acidity of the three LMWOAs. Compared with the control, the content of dissolved organic matter (DOM) released from purple soil showed a trend of first decrease and then increase with increasing LMWOAs concentration, and the adsorption capacity of phenanthrene in purple soil was negatively related to DOM content.