Removal of aquatic heavy metals by biosorption is practically important.In this paper,the effect of pH,reaction time and adsorbent dosage on adsorption capacity and removal rates of cadmium in aqueous solution were studied,with chestnut inner shell as adsorbent.The adsorption mechanism was investigated by model simulation,ion exchange experiment,scanning electron microscope and infrared spectroscopy.It was revealed that chestnut inner shell was an ideal absorbent for aquatic cadmium removal characterized by wide adaption range of pH（from 3 to 6）,short sorption equilibrium time（15 min）,high adsorption capacity（maximum of 14.706 mg·g-1） and high removal efficiency of aquatic cadmium（under the condition with an initial Cd2＋ concentration of 250 mg·L-1 and chestnut inner shell dosage of 10 g·L-1,the removal rate of aquatic Cd2 ＋ was up to 95%）.The adsorption process could be fitted with the pseudo-second-order kinetic model and adsorption isotherm models implying that the adsorption rate was controlled by chemical adsorption and mainly surface adsorption occurred.SEM photos showed that after adsorption of cadmium,a lot of particle or ash substance were deposited on the surface of chestnut inner shell.Dubinin-Radushkevich model simulation and ion exchange experiments verified that ion exchange was the main adsorption mechanism with K＋ and Ca2＋ as main exchange ions.FTIR spectra showed complexation was also one of the adsorption mechanisms with —OH,—NH,—COO-,—PO as the major functional groups involved.
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