Removing heavy metals through sorption
High amounts of metallic elements, such as lead, cadmium and copper, make water toxic. Sequestration of these elements from water is the only possible way to make water safe for use. Recently, Rais Ahmad and Anam Mirza from the Aligarh Muslim University synthesised a chitosan-iron oxide nanocomposite to remove heavy metals from wastewater.
Chitosan is a natural biopolymer derived from chitin by deacetylation. Biopolymer-metal oxide nanocomposites are biocompatible, biodegradable, nontoxic and reusable. The researchers dissolved chitosan in lemon juice and then ferric chloride solution followed by sodium hydroxide, to synthesise the nanocomposite.
The team probed the resulting material using various scientific tools such as scanning electron microscope, transmission electron microscope, and X-Ray diffraction analysis, and found the nanocomposite to be highly porous, cross linked networks with iron oxide entrenched in the chitosan matrix.
The scientists collected effluents from local electroplating and battery manufacturing industries as well as hospital effluents and treated them with the chitosan-iron oxide composite and agitated the contaminated water to complete the process.
The scientists resolved the issue of diversity of metal ions in industrial wastewater by studying the ion selectivity of the nanocomposite for lead, cadmium, copper and nickel. After the sorption, they analysed the concentration of lead, cadmium, copper and nickel using atomic absorption spectrometry. The concentration of the lead and cadmium was reduced by the chitosan-iron oxide. This makes the nanomaterial a promising sorbent for the removal of lead and cadmium from wastewater.
“This is, perhaps, a multi-step chemisorption mechanism”, says Rais Ahmad. “First there is surface diffusion. Then, sorption of the metal ions into the nanocomposite and the final step, where an equilibrium is achieved”.
“The nanocomposite can be regenerated successfully for upto five cycles”, says Anam Mirza.
The research, funded by the UGC, can be upscaled and made into a cost-effective tool for the remediation of water contamination.
Cleaner Prod., 186: 342-352
Smitha G Nair