Research On Perchlorate Adsorption By Organically Modified Adsorbents

Perchlorate as a kind of novel persistent pollutant, has been widely distributed in China. And it is presented in dringking water and milk, which poses potential threat to human health. In recent years, activated carbon adsorption treatment of perchlorate in wastewater is become more and more attention, but the domestic research in this area is also small. Mulberry shoot powder and zeolite are widely available and low-cost, which has not been reported in the adsorption of perchlorate. In this paper, modified adsorbents were prepared by tailoring granular activated carbon, mulberry shoot powder and zeolite with cetyltrimethyl ammonium chloride. Then the there types organically modified adsorbents were used for the adsorption of perchlorate in water. The effects of adsorption time, pH value, the initial perchlorate concentration and co-existed anions on the adsorption of perchlorate were investigated. The adsorption isotherms were ditermined at different temperatures, and the experimental date were fitted by Langmuir, Freundlich and Tempkin isothermal models. Adsorption dynamics were fitted by the pseudo-first-order rate model, pseudo-second-order rate model, Bangham model, Elovich model, inner diffusion model and external diffusion model. The adsorption mechanism was also disscussed.The results show: simple activated carbon, mulberry shoot powder and zeolite are less effective in perchlorate adsorption, but the removal rate of 1.0 mg/L ClO₄^- significantly increased from 5% to 95% after modified with cetyltrimethyl ammonium bromide. The perchlorate removal rate influenced by the pH value, and acidic environment is favorable to the adsorption of ClO₄^- in water. At pH 3, the perchlorate removal rate of modified activated carbon is 95%, and the perchlorate removal rate of modified mulberry shoot powder and zeolite are all 100%. The adsorption capacity of ClO₄^- on modified adsorbents decreased with increasing sorbent dose, and increased with increasing ClO₄^- initial concentration. The ClO₄^- removal rate were 94%, 96% and 97% When the dosage of modified activated carbon, mulberry shoot powder and zeolite reacheed 0.1 g/L, 3.0 g/L and 1.0 g/L, respectively. The ClO₄^- removal rate can reach 100% when ClO₄^- initial concentration is down to 0.1mg/L. The competitive adsorption exists between co-existed anions and ClO₄^-, and the order of competitive effect was S₂O₃^2- > SO₄^2- > Cl^- > H₂PO₄-≈NO₃-≈ClO₃^-. Quaternary ammonium function groups on modified adsorbents play an important role in adsorption of ClO₄^-. The ClO₄^- saturated modified adsorbents can be regenerated by NaCl sollution and NaOH sollution. The adsorption of ClO₄^- on modified adsorbents accorded with the Langmuir, Freundlich and Tempkin isothermal models in the range of experimental concentration. The interaction of ClO₄^- adsorbed by modified adsorbents were exothermic, lower temperatures were conducive to adsorption in the range of 150C and 350C.The law of dynamics for the adsorption can be simulated by the pseudo-first-order rate, pseudo-second-order rate, Bangham and Elovich models. The adsorption rate controlling step is determined by inner and external diffusion models.