Thermosensitive polymer Enhanced Filtration (TEF) process: An innovative process for heavy metals removal and recovery from industrial wastewaters

Abstract

This study reports on a new process for the removal and recovery of metal elements from wastewaters, associating a sorption step on a thermosensitive copolymer bearing phosphonic acid moieties, namely the poly(N-n-propylacrylamide-stat-hydrolyzed (dimethoxyphosphoryl)methyl 2-methylacrylate) (P(NnPAAm-stat-hMAPC1)), with a separation step by filtration. The phosphonic acid groups enable high sorption capacities for multi-component solutions (Ca2+, Ni2+, Cd2+, Al3+), while the thermosensitive behavior of the polymer allows, for temperatures higher than its LCST (25.6°C), to get copolymer–cations non soluble particles. In the presence of aluminum, which was shown to have simultaneous coagulation and neutralization actions, these particles form aggregates of mean diameter 27–63μm easily removed by conventional filtration (pore diameter >10μm), leading to a lower energetic separation process compared with the well-known Polymer Enhanced Ultrafiltration (PEUF) Process. To recover metal ions and regenerate the thermosensitive copolymer sorbent, an acidic (H2SO4) regeneration step was studied. A decrease of the regeneration solution pH from 4 to 1 led to 100% desorption when the pH was set to 1. Such low pH conditions simultaneously allowed (i) a decrease of the copolymer LCST down to 19.5°C, and (ii) to reach the isoelectric point of copolymer particles to finally lead to the formation of regenerated copolymer particles which could be recovered by filtration and reused in additional sorption–filtration cycles without any loss of sorption capacities.