Fast and high adsorption of cadmium ions from aqueous solutions by acid-activated and pyrolyzed coconut coir

Activated coconut coir (ACC) was prepared by activation of raw coconut coir dust with 50 wt.% phosphoric acid followed by pyrolysis at 450°C in a nitrogen atmosphere. ACC demonstrated high efficacy in the removal of Cd(II) from aqueous solutions. Batch adsorption studies were carried out to study the effect of adsorbent dose, agitation time, pH and initial concentration of Cd(II) on the adsorption of Cd(II) on ACC. It was found that adsorption equilibrium was achieved rapidly within 10 min of agitation time and 98% of Cd(II) was removed from 10.00 mg L–1 Cd(II) solution at pH of 6 with 0.200 g of ACC. The rate of adsorption of Cd(II) on ACC followed pseudo-second-order kinetics. The equilibrium adsorption obeys linear Langmuir isotherm model for Cd(II) concentrations in the range of 10.00–100.00 mg L–1, whereas, in the entire concentration range of Cd(II) from 10.00 to 664.00 mg L–1, adsorption obeys non-linear Freundlich isotherm model. The maximum Cd(II) adsorption capacity of ACC was 45.02 mg g–1. The desorption study suggests that the ACC can be easily regenerated by simply washing it with 0.025 mol L–1 HCl solution. Because of the very rapid and simplicity of the adsorption and desorption processes, ACC has potential application as a promising adsorbent in the removal of cadmium ions from wastewater and water purification applications.