Preparation Of Organically Modified Attapulgite And It’s Removal For Aqueous Chromium

Chromium pollution is a harmful environmental problem.Chromium pollution not only damage people’s health, but the whole ecosystem of nature has some hazards. So how to remove chromium is essential.Attapulgite itself has a large surface area and high porosity, which play a role in the removal of heavy metals in water. In this study, PEI-ATP, EDA-ATP, TETA-ATP, TEPA-ATP, and EDTA-ATP were synthesized and used as adsorbents to remove aqueous chromium in water, examining the various factors and the characterization of the adsorbent, clarify adsorbents in water adsorption behavior and mechanism of chromium,some conclusions are as follows:Adsorption of Cr(VI) on PEI-ATP(1) Compared with attapulgite, after the PEI-modification, the surface of attapulgite becomes more rough, and the content of amine groups is 1.71 mmol/g, the crystal form has not changed.(2) PEI-ATP has good adsorption properties for Cr(VI). With the increasing of adsorbent dosage, the adsorption capacity is reduced, the optimum dosage is 20 mg(0.4 g/L). Under the experimental conditions, the maximum amount of PEI-ATP adsorption of Cr(VI) was 51.81 mg/g, the adsorption of Cr(VI) can be fitted by Langmuir adsorption isotherm model equations. The adsorption almost reached equilibrium within 500-600 min, and its kinetic data can be fitted by the pseudo second-order kinetic model. Cr(VI) adsorption on PEI-ATP increases with increasing solution p H at low p H and decreases at high p H range. The existence of Cl-, SO42-, PO43- inhibit the adsorption of Cr(VI), PO43- is particularly evident. The adsorption capacity to be reduced from 46 mg/L to 4.78 mg/L.PEI-ATP has a good recycling performance.Adsorption of Cr(VI) on EDA-ATP、TETA-ATP、TEPA-ATP(1) After the organic modification, with the increase of the content of the organic amine reagent, the surface of the adsorbent gradually becomes rough, and the contents of amine groups were 2.95 mmol/g, 4.95 mmol /g, 5.86 mmol/g, respecitively, The specific surface area gradually decreases and the crystal did not change.(2) The maximum adsorption capacity of Cr(VI) on EDA-ATP、TETA-ATP and TEPA-ATP were 154.56 mg/g, 254.24 mg/g, 270.88mg/g, respectively. Adsorption isotherms can be fitted by the Freundlich equation, and with the increasing content of amino groups of the adsorbent, the amount of Cr(VI) adsorption increases and the adsorption rate increases, the adsorption kinetics can be fitted by the psrudo second-order kinetic equation. Adsorption of Cr(VI) on EDA-ATP、TETA-ATP and TEPA-ATP increases and then decreases with the increasing of p H, The exist of Cl-, and PO43- inhibit the adsorption of Cr(VI), PO43- is particularly evident. The adsorption capacity to be reduced from 143.80 mg/g, 207.11 mg/g, 215.83 mg/g to 61.39 mg/g, 113.06 mg/g, 122.99 mg/g.According to the results of XPS analysis, the adsorption of Cr(VI) onto PEI-ATP, EDA-ATP, TETA-ATP and TEPA-ATP rely on electrostatic interactions, as well as the reducation of Cr(VI) to Cr(III), which coordinated with the adsorbent to achieve the purpose. Adsorption of Cr(III) on EDTA-ATP(1) Compared with the previous modification, after EDTA grafted onto the surface, it can be seen that the surface of the adsorbent was surrounded, the amine content of 4.78 mmol/g, and the crystal did not change.(2) The maximum adsorption capacity of Cr(III) on EDTA-ATP is 131.37 mg/g. The adsorption for Cr(III) can be fitted by Langmuir adsorption isotherm model equations, and its kinetic data can be fitted by the pseudo second-order kinetic equation analysis. salt ions inhibits the adsorption of Cr(III), the order of effects on adsorption is Ca2+> Na+. With increasing solution p H, the adsorption capacity increases. The presence of organics can promote the removal of Cr(III) on EDTA-ATP, compared with APTES-ATP, EDTA-ATP is much better.From the XPS analysis, the adsorption of Cr(III) onto EDTA-ATP mainly rely on the coordination of Cr(III) with the carboxy of adsorbent.