Removal of Cd by dried biomass of freshwater moss Vesicularia dubyana: batch and column studies

Abstract

Adsorption of Cd by dried biomass of the freshwater moss Vesicularia dubyana from model solutions under conditions of batch and continuous column systems was studied using γ-spectrometry and 109CdCl2 as radiotracer. The Cd adsorption by moss biomass was a rapid process and concentration equilibrium was reached within 60 min of exposure. The efficiency of the adsorption process and removal of Cd from the solutions was significantly dependent on the value of pH (2–8), initial concentration of CdCl2 (20–320 μM) and changes in Cd speciation induced by the presence of Cl− anions in the solutions. Experimental data of Cd adsorption by designed packed bed column system comprising dried moss biomass at an initial concentration 36 mg/l CdCl2 and flow rate 0.80 ml/min of solution in the column were well described by adsorption kinetic models according to the Clark (R2 = 0.981), Thomas (R2 = 0.964) or Yoon–Nelson (R2 = 0.962) and modified dose–response (R2 = 0.954) models. The suitability of the mentioned models was also evaluated on the basis of differences in the values of root mean square errors, residual sum of squares or corrected Akaike’s information criterion. Adsorbed Cd was removed from the dried moss biomass with high efficiency (>92%) by desorption with 0.1M HCl or EDTA-Na2 solutions under batch conditions, whereby the desorption efficiency Deff decreased in the order: 0.1M HCl (93%) ≈ 0.1M EDTA-Na2 (92%) > 0.1M ZnCl2 (85%) > deionized water (20%). The high desorption efficiency in the case of 0.1M EDTA-Na2 was also confirmed under conditions of a continuous column system.