Cadmium sorption by dried plant biomass – Reversibility studies

Abstract

Heavy metals such as cadmium are hazardous to biosystems and present possible human health risk. Thus, the removal of cadmium from liquid wastes is of great importance from an environmental and industrial point of view. There is a tendency to use agricultural wastes for the sorption of toxic metals as an alternative to the existing conventional technologies. The aim of this work was to describe Cd sorption and desorption equilibria by dried leaf biomass of tobacco (Nicotiana tabacum L.), hop (Humulus lupulus L.), pumpkin (Cucurbita pepo L.), sunflower (Helianthus annuus L.), cucumber (Cucumis sativus L.), pepper (Capsidum annuum L.), tomato (Solanum lycopersicum L.) and vine-grape (Vitis vinifera L.) using radiotracer technique with 109CdCl2. Cadmium sorption Q values (mg/g, d.w.) of all of plant biomass studied increased proportionally with the initial CdCl2 concentration within the range 0.01 – 10 mmol/L CdCl2. Mean sorption capacity of dried leaf biomasses of eight plants for Cd from the solution with the initial concentration C0 = 10 mmol/L CdCl2 in deionized water was Q = 213 μmol/g (d.w.). By single step desorption of Cd from leaf biomass for 30 min at 20 °C with deionized water, 0.1 mmol/L EDTA or 0.1 mmol/L HCl, up to 30 %, 85 % and 98 % of sorbed Cd, respectively, was removed. Obtained data can serve as a model for the prediction of sorption-desorption equilibria of biomass used for removing of Cd from polluted waters and Cd releasing back into waters containing other inorganic solutes. Formation of Cd2+, CdCl+, CdCl2 0, CdSO4 0, CdOH+, Cd2OH3+, Cd(OH)20 and Cd(OH)3- species in dependence on pH values and the presence of Cl- anions is also discussed.