Comparative Metal Ion Binding to Native and Chemically Modified Datura innoxia Immobilized Biomaterials

Abstract

Removal of toxic heavy metal ions from contaminated water is required to provide safe drinking water. This can be effected either within the waste stream at contaminate source or at point of use. Incorporation of remediation technologies at either location requires the removal of pollutants at parts per million and parts per billion concentrations from water containing more benign metal ions (e.g., Ca2+, Mg2+, and Na+) at concentrations three to six orders of magnitude higher. Materials derived from plants or microorganisms (e.g., algae and fungi) have been shown to enable the reduction of trace concentrations of heavy metal ions to below regulatory limits (Davis, et al., 2003). Such nonliving biomaterials have been reported to have exhibit high capacity, rapid binding, and selectivity towards heavy metals (Drake and Rayson, 1996). It is postulated that functional groups native to the lipids, carbohydrates, and proteins found in the cell walls of the biomaterial are responsible for uptake (biosorption) of metal ions (GardeaTorresdey, et al., 1999; 2001; Drake and Rayson, 1996; Drake, et al., 1997; Kelley, et al., 1999). For biomaterials to become a commercially viable method of metal remediation and recovery these functional groups must be identified and their contribution to overall metal binding capacity quantified. Knowledge of such informaiton would allow either simple chemical alteration to the biomaterial, allowing for targeting of specific metals, or an enhancement of biomaterial metal binding. Significant progress has been made to identify the chemical functionalities involved in the biosorption of numerous metal ions by a variety of plant and algal tissues (GardeaTorresdey, et al., 1999; 2001; Riddle, et al., 2002; Fourest and Volesky, 1996; Drake, et al., 1997;Jackson, et al., 1993). Several techniques have been reported to probe local chemical environments of biosorbed metal ions. These have included X-ray absorption (GardeaTorresdey, et al., 1999; Riddle, et al., 2002), lanthanide luminescence (Drake, et al., 1997; Serna, et al., 2010), and metal NMR (Xia and Rayson, 1996; 2002; Kelley, et al., 1999; Majidi, et al., 1990) spectroscopy. Analysis of total metal ion binding isotherm data modeling (Volesky, 2000) has also been described. Efforts to address the chemical heterogeneity of those biosorbed materials have also employed regularized regression analysis of isotherm data (Lin, et al., 1996). Additionally, these chemical intensities have been studied through selective removal of binding moieties by their reactive modification (Drake, et al., 1996).