Heavy Metals Uptake from Aqueous Effluents by Novel Adsorbent derived from Tannin Extracts Role of Tannin Source

Environmental contamination by heavy metals is one of the main pollution concerns nowadays. Researchers are urged therefore to find new and more efficient methods for the removal of these dangerous pollutants, mainly from water effluents. The challenge of environmental sustainability is thus directly linked to the development of more effective solutions for these recalcitrant menaces. Under this perspective, adsorption can be considered an interesting remediation procedure, but adsorbents are still expensive materials. With the scope of developing new adsorbents, novel tannin-based adsorbents were tested on heavy metals removal. Up to 10 heavy metals (Cd²⁺, Cr³⁺, Pb²⁺, Hg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, UO₂²⁺ and Mn²⁺) were removed with different adsorbents that involved tannins from Acacia mearnsii de Wild, Schinopsis balansae, Cupressus sempervivens and Pinus pinaster. These tannin extract were gelified with formaldehyde in basic medium. The whole study was conducted under a statistical point of view, so ANOVA tests were carried out in order to evaluate the optimum concentration of formaldehyde, the most reactive tannin extract and the easiest metals for being removed. These considerations drove to the optimum tanningel derived from cypress, concentrated formaldehyde, with a high affinity to UO₂²⁺, Hg²⁺ and Pb²⁺. This study has been conducted under the hypothesis of minimum energy consumption, maximum natural materials involved in the process and maximum efficiency in the removal of these metals. The results are promising since high efficiencies were achieved, thus this new adsorbents are competitive with traditional ones, such as clays, activated carbons or biosorbents.