Varying growth behavior of redox-sensitive nanoparticles on 1:1 and 2:1 clay surfaces: mechanistic insights on preferential toxic ions removal in mono, co and multi-metal contaminated waters

International audience ; In the current study, contrasting growth behaviour of redox sensitive Fe0 nanoparticles (nZVI)was observed on different clay surfaces i.e., 1:1 non-swelling kaolinite (K-nZVI) and 2:1swelling bentonite (B-nZVI). Osmotic swelling of bentonite led to Fe0 nucleation and growthof 5-7 nm size particles in the broadened interlayer spaces. B-nZVI had negative zeta potentialdue to the domination of the surface charge of bentonite clay. Whereas kaolinite has showndominant surface growth of nZVI particles (>24.8±7.4 nm) and positive zeta potential,suggesting domination of Fe0 nanoparticles (nZVI) characteristics. This surface-dependentvariation led to higher and faster removal of oxy-anions with K-nZVI, i.e., chromium andarsenic (87.5 and 157.35 mg/g) than B-nZVI (18.4 and 86.9 mg/g). In comparison, B-nZVI hasshown higher sorption of cations i.e., nickel and cadmium (36 mg/g and 46 mg/g) than K-nZVI(25 and 27 mg/g). XPS and pXRD analysis of reaction precipitates confirmed reductivesorption of chromium, co-precipitation/ complexation of arsenic, electrostatic attraction andcomplexation of nickel and cadmium as major removal mechanisms. Drastically higher totalcontaminant sorption capacities of B-nZVI (327 mg/g) and K-nZVI (372 mg/g) in multicontaminant(Cr+As+Ni+Cd) solutions than individual capacities in mono-ionic solutions wasdue to co-operative effects and newer sites induced via sorption and redox-transformation ofother ionic species. K-nZVI removed chromium and arsenic to below drinking waterpermissible limits whereas B-nZVI succeeded in separating nickel and cadmium to drinkablelevels in groundwater, freshwater, river water, and wastewater samples, emphasizing theirapplicability in high cationic—low anionic and low cationic-higher anionic speciescontaminated waters, respectively.