THE REMOVAL AND RECOVERY OF OXO-ANIONS FROM AQUEOUS SYSTEMS USING NANO-POROUS SILICA POLYAMINE COMPOSITES.
Environmental contamination due to anthropogenic wastewater discharges containing high concentrations of toxic metals is omnipresent in the environment. Heavy metal ions from manufacturing sources can compromise the integrity of various ecological cycles as well as negatively impacting the health of humans through drinking water and the food chain. Increased levels of well known poisonous metals such as arsenic, selenium, lead and mercury are frequently detected in aqueous wastes. Arsenic and selenium are highly toxic elements to human health and the environment. The Maximum Contaminant Level (MCL) for both these toxic metals continue to become more and more stringent. Although there are several metal remediation technologies available commercially, most of them are not feasible and/or are very expensive. The ferrihydrite process (precipitation with iron (III) oxyhydroxides) is by far the most economical and effective of these technologies and has been widely employed on a large scale. However, it has the significant disadvantage of creating a large amount of sludge for ultimate disposal and leaching of colloidal iron oxides into aquifers. The other methods suffer from a lack of specificity, low selectivity over sulfate (ion exchange), low mass-to-volume concentrations (bio-reduction), and/or high cost (membrane technologies). This led us to the development of silica polyamine composites (SPCs) functionalized with metal selective ligands for the removal of heavy metals from wastewater streams. High capacities were obtained for arsenic, selenium, molybdenum, and tungsten oxoanions by immobilizing zirconium on the phosphonic acid modified SPC (BPAP). The oxo-anions of these metals bind to the net positive charge on the zirconium, thereby removing them from the wastewater stream and reducing the metal concentrations below their respective MCLs. These silica polyamine composites can also be acid stripped and regenerated for reuse. This aspect is very useful in commercial applications where the toxic metal ions can be selectively extracted and efficiently recovered from acid mine drainage in the presence of high sulfate concentrations, and in their removal from seawater systems. Alkylated SPCs tested for the removal of bacteria and viruses from drinking water systems have also shown promise. Further characterization of the SPCs are being carried out using surface analytical techniques and the SPC chemistry is being extended for applications on surface oxidized silicon wafers.
© Copyright 2009 Varadharajan Kailasam