Exponential population growth has led to rampant industrial development and the consequent pollution of water sources with heavy metals and toxic organic waste. The need for an immediate solution to the occurrence of these major pollutants in our environment that is both efficient and cost-effective has driven myriad studies as well as changes in environmental legislation that necessitate the development of advanced processes. Our recent results show that the sol-gel process can be exploited to prepare ion exchange columns that can be applied for the development of efficient and green wastewater treatments – for the removal of heavy metal ions – that meet the highest environmental regulatory standards (e.g. UO22+, Sr2+, Cs+, Pb2+, Cd2+, Cr3+ and Hg2+). The sol-gel technology offers a simple preparation procedure of silica-based sorbent materials with tailored separation properties. Moreover, this method enables the recycling of heavy metals that can then be reused in the industrial processes that require them.
Two approaches to the synthesis of the sol-gel matrices were studied: 1. “The ligand method”- by entrapment of nitrilotri(methylphosphonic acid), ATMP, as a ligand during the sol gel process. 2. "The imprinting process” in which the sol-gel matrix was prepared in solutions containing the desired cation: 0.10M UO22+. Adsorption capacity experiments were performed by immersion of the sol-gel matrices in a metal ions solution, containing 1.0x10-3 M Ce3+, Co2+, Cr3+, Ni2+, Pb2+ and UO22+ ions.
By the imprinting process, the adsorption capacity of uranyl, cerium and chromium equals to 70%, 20% and 50% of the initial ion concentration, respectively, whereas by the “ligand method”, equals 95%, 83% and 10%, respectively. The results point out that the “ligand method” is more selective to the uranyl and cerium ions and more efficient than the imprinting process.