Optimization of operational variables for Ag nanoparticles recuperation from aqueous systems using a magnetic coagulation/flocculation process

MARIANA RAMIREZ; GIULIANA MAGNACCA; MARÍA EUGENIA PAROLO; LUCIANO CARLOS

Ciudad Autónoma de Buenos Aires

Congreso; 11th WORLD CONGRESS OF CHEMICAL ENGINEERING; 2023

Conventional coagulation/flocculation processes (CF) are of vital importance in wastewater treatments, due to the economic and efficient elimination of suspended solids, small particles, natural organic matter and, pathogens. However, CF have not been successfully implemented for nanoparticle recovery due to the irreversible nature of the aggregationprocess. Combining CF with magnetic separation processes would enable a new approach to nanoparticle separation challenges from water and could present an environmentally friendly solution for the recovery and reuse of a wide variety of engineered nanoparticles [1]. The present work presents partial results on silver nanoparticles (AgNPs) recovery fromaqueous systems by using core-shell magnetic nanoflocculants (MNF) coated with natural polymers and bio-based substances (BBS). Magnetite nanoparticles were synthesized by the solvothermal method, coated with non-porous silica and then functionalized employing the layer-by-layer technique (LbL). The selected biopolymers were chitosan as positively charged polyelectrolytes, alginate and BBS as negatively charged polyelectrolytes. Two types of nanoflocculants were synthesized, based on the combination of five alternating layers of chitosan-alginate (MMCA5) and chitosan-BBS (MMCB5). In both materials, the first and the last layer were chitosan. The samples were characterized by TEM, XDR, ATR, TGA, and Z potential. The flocculation performance of MNFs for the removal andrecovery of AgNPs from water was evaluated using response surface methodology (RSM) approach based on the Doehlert composite design. Three operational variables were analyzed and modeled, AgNPs concentration, nanoflocculant concentration and dispersion pH. The results obtained from the RSM analysis showed that, for the MMCB5, all the operational variables were statistical significative for modelling the % AgNPs removal, while for MMCA5, only pH and MNF dosage had a significant effect at 95% confidence level (p-values <0.05). The removal efficiencies increase with the MNF dose and decreasing pH until a plateau is reached. Both MNF achieved almost complete removal of AgNPs at pH 5 and high concentration of MNF (> 800 mg/L). At pH=7, MMCA5 removed between 30-60% of AgNPs, while MMCB5 only removed up to 15%. However, at pH=9, neither flocculant was able to remove AgNPs from water. It is important to note that no restabilizing effect at high MNF concentration was observed. These results indicate that themajor mechanism acting in the removal of AgNPs is charge neutralization, where the positively charged external chitosan layer of the MNF interact with the negatively surface of AgNPs.