Adsorption of Cadmium to Diatomite

Abstract

Unnatural levels of cadmium have been detected in rural and urban runoff, as well as surface and ocean waters globally. The universally toxic effects of cadmium on humans, plants, animals, and microbial life alike emphasize the importance of concern from these discoveries. Cadmium is introduced into the environment both naturally and anthropogenically, but the contribution of cadmium from anthropogenic sources has been increasing, restructuring the cadmium biogeochemical cycle. Anthropogenic sources of cadmium include expelled wastewaters and the displacement of contaminated soils from industrial sites- often urban adjacent. There is a known ability of raw diatomite (amorphous bio-silica), a low-cost biosorbent, to adsorb cadmium; but measures of the adsorbance capacities and binding mechanisms have varied markedly. In this study, Raman spectroscopy as well as Fourier transform infrared (FTIR) spectroscopy are employed to inform a more replete understanding of the physical chemistry of cadmium binding to diatomite. The influence of varying pH within environmentally relevant ranges and cadmium concentration on the diatomite's capacity to sorb cadmium is evaluated. This us done through adsorption isotherms, as a function of Cd concentration and pH, and the amount of Cd removed from solution is monitored using Inductive Coupled Plasma Optical Emission Spectroscopy (ICP-OES). FTIR spectroscopy was used to determine the bulk binding mechanisms, while Raman spectroscopy helps us determine the variations of Cd sorption as a function of diatom morphology. Reconciling the behaviours of cadmium against diatomite at environmentally relevant conditions aids attempts to mitigate cadmium pollution and modeling its current and future biogeochemical cycle.

Department: Physical Sciences

Faculty Mentor: Dr. Janice Kenney