Abstract:
Modified lychee pericarps were employed for the adsorption of Pb(Ⅱ) using fixed-bed columns, and the effects of column heights (3.1,5.2 and 10.4 cm), flow rates (2,4 and 6 mL/min) and initial concentrations (50,0 and 200 mg/L) on the breakthrough curve, as well as mass transfer zone lengths, for Pb(Ⅱ) adsorption were investigated. The results showed that the breakthrough time would be shortened by reducing column height and increasing the flow rate and initial concentration. The average changing rate of height of mass transfer zone was under the three conditions of initial Pb(Ⅱ) concentration, column height and flow rate 0.076,0.090 and 0.004, respectively. This result showed that compared with the initial Pb(Ⅱ) concentration, column height and flow rate imposed more significant effects on the height of mass transfer zone. The column data were well fitted by the Thomas model (R
2 > 0.95), with the experimental values (q
exp) being more than 59.1 mg/g, and there was satisfactory coherence between the experimental and theoretical values (q
cal). This indicated that neither external nor internal diffusions were the limiting step for the adsorption processes. The bed depth service time (BDST) model was applied to predict the breakthrough time under different conditions. The results showed that the maximum error between the predicted and experimental values of breakthrough time were 7.14% and 8.45%, respectively, with reference to changing flow rates or initial concentrations.