Abstract
Introduction: Cadmium (Cd) has been reported to accumulate in paddy fields, and there is concern about its toxicity. Bagasse (BG), which is a by-product of sugar production, has been utilized as an adsorbent for heavy metals due to its large specific surface area (SSA). Therefore, the treatment method of BG suitable for Cd removal and the detailed mechanism of adsorption were investigated.
Methods: BG was calcined in the temperature range of 200‒1000°C. BG was added to a Cd solution and shaken for 24 h under multiple conditions. The equilibrium Cd concentration was measured using inductively coupled plasma–optical emission spectroscopy. The SSA, pore volume, and pHpzc (pH of the point of zero charge) were measured.
Results and discussion: The pHpzc of the BGs ranged from 4.27‒6.51, suggesting that the BG surface may be negatively charged at conditions above these pH values. The amount adsorbed was higher at pH 4‒8 than at the pH 2 and 10. These results indicate that the negative charge on the BG surface and the presence of Cd(Ⅱ) cations are important for adsorption. The amount adsorbed and the SSA of BG increased with increasing calcination temperature and were the highest in BG calcined at 800°C. The amount of adsorbed was significantly associated with the SSA (r=0.837, p=0.038), mesopores (r=0.841, p=0.036), and pHpzc (r=0.818, p=0.046). These results suggest that the Cd adsorption is related to SSA, the negative charge on the BG surface, and the presence of Cd(Ⅱ) cations, and that BG calcined at 800ºC is suitable for Cd adsorption.
