Studies On The Adsorption-desorption Of Organic Pollutants At Maganese-oxides/water Interfaces

Adsorption and desorption process has received considerable attention as one of the most important processes affecting the mobility, degradation and biological activity of organic pollutants in the environment. Desorption of many organic pollutants from natural sediments has been observed to be irreversible. The irreversible behavior affected the environmental quality criteria, remediation efficiency and the potential danger of pollutants in natural water body. In this thesis, adsorption-desorption experiments were used to investigate the adsorption and desorption behavior of methyl orange, p-chlorophenol and H-acid onto a series of absorbent including 6 MnO2 ( I), δ MnO₂ (II) å’Œ α MnO₂. The influence of surrounding factors ( pH, temperature, ions intensity) to adsorption isotherms of three organisms was discussed.According to different types of adsorbates, there are three parts in my dissertation: (1) the adsorption and desorption of methyl orange on manganese oxides;(2) the adsorption and desorption of H-acid on manganese oxides;(3) the adsorption and desorption of p-chlorophenol on manganese oxides. Here are the main conclusions:(1) pH-variable adsorption isotherms have been determined at three concentrations of NaN0₃, i.e 0. OK 0,05 and 0.1 mol/L. Constant-pH isotherms were obtained at pH6. 0 and 0. 01 mol/L concentration of NaN0₃ . The results showed that the adsorption capacity minished along with the increase of pH value and ions intensity in methyl orange adsorption systems. The adsorption isotherms kept to the law of Langmuir. At high temperature the adsorption on 8 MnO₂ ( I ) and α Mn0₂ increased, while theadsorption on 5 MnO2 (II) became decreased . Adsorption and desorption isotherms were performed with different absorbate concentrations (100, 200, 400mg/L). There was an obvious Cp effect in methyl orange adsorption systems and the adsorption of methyl orange onto MnO2 was largely irreversible (big adsorption hysteresis). The adsorption irreversibility increased with the increasing of Cp. Circulative pH scanning adsorption desorption experiments showed that a change to a less favourable pH did not cause desorption, whereas a change in the opposite direction led to additional adsorption. Adsorption reaction was not reversible to H\(2) The experiments in H-acid adsorption systems indicated that the adsorption capacity decreased with the increase of pH value and ions intensity. The adsorption isotherms could be fitted by Freundlich model. The adsorption capacity increased with the rise of temperature. A clear Cp effect was obsearved in H-acid system. The adsorption of H-acid on MnO2 was largely irreversible, and the irreversibility increased with the increasing of Cp. Circulative pH scanning adsorption desorption experiments showed that the adsorption isotherms differed from the desorption isotherms ,The adsorption was irreversible .(3) The experiments in p-chlorophenol adsorption systems showed that the adsorption capacity decreased with the increase of pH value and ions intensity. A clear Cp effect was obsearved and the p-chlorophenol system has high irreversibility. The irreversibility of p-chlorophenol increase with the increasing of Cp. Circulative pH scanning adsorption desorption experiments showed that a change to a less favourable pH did not cause desorption, whereas a change in the opposite direction led to additional adsorption.