Contrast effect of biochars and attapulgite clay on the adsorption and removal of cadmium ions from metal contaminated aqueous solution

Aim To study the contrasting effect of adsorption and removal of cadmium ions using wheat straw biochar, rice straw biochar and attapulgite clay in contaminated aqueous solution. Methodology : Batch sorption experiment was carried out to investigate the parameters influencing the adsorption capacity such as pH, initial cadmium concentration, adsorbent dose and contact time. The physical and chemical characteristics of biochars and clay were studied and adsorption mechanism was analyzed by scanning electron microscopy, infrared spectroscopy, Brunauer-Emmett-Teller and X-ray diffraction, which indicated high adsorption and removal of Cd+2 ions by wheat straw biochar was mainly due to the presence of surface carboxyl functional groups -OH, C-O, COOH that reacted Cd2+ ions. Results : The adsorption effect of wheat straw biochar (WSB), rice straw biochar (RSB) and attapulgite (ATP) clay were compared. The results showed that adsorption isotherms were best fit to Langmui isotherm model. The adsorption kinetics study well matched with pseudo second order model and the maximum adsorption equilibrium of WSB, RSB and ATP reached to 100, 160, and 120 min, respectively. The results showed that adsorption rate was maximum at pH 6 with 0.1 g dose of adsorbent, 40 mg l(-1) metal concentration, and contact time of 100 min at 30 degrees C for WSB. The maximum percent removal of cadmium ions from aqueous solution was in the order WSB>ATP>RSB, 95%, 91% and 88%, respectively. [GRAPHICS] Interpretation : The results explored that wheat straw biochar has high Cd2+ adsorption rate and removal efficiency in contaminated water than others. Hence, the results explored that WSB is a potential, low-cost adsorbent and can be used as cadmium decontaminant in polluted water with no secondary pollution.