Destruction of Perchlorate and Nitrate by Stabilized Zero-valent Iron Nanoparticles and Immobilization of Mercury by a New Class of Iron Sulfide Nanoparticles

Abstract

This research compares representative standard strong-base anion (SBA) and weak-base anion (WBA) exchangers, a bifunctional resin (A-530E), a class of polymeric ligand exchangers (PLE’s), and an ion-exchange fiber (IXF) with respect to perchlorate sorption capacity, kinetics, and regenerability. The sequence of the perchlorate sorption capacity factor (Af) follows: A-530E >> IRA 900 > DOW 66 > Smopex-103x > DOW 3N-Cu >> WA21J > DOW 3N > XAD1180 3N-Cu >> XAD7HP 3N-Cu ˜ IRA 958. The sequence of the ion-exchangers’ regeneration efficiency is IRA 958 > WA21J > XAD7HP 3N-Cu > IRA 900 > DOW 3N-Cu > A-530E. A new class of stabilized zero-valent iron (ZVI) nanoparticles was developed and used for complete destruction of perchlorate in both fresh water and ion-exchange brine. The stabilized ZVI nanoparticles were prepared successfully using a low-cost and food-grade carboxymethyl cellulose (CMC) as a stabilizer and were used for perchlorate reduction. The mean diameter of stabilized ZVI nanoparticles was 13.7±2.3 nm. Batch kinetic tests showed that at an iron dose of 1.8 g/L and at moderately elevated temperatures (90-95 oC), ~90% of perchlorate in both fresh water and a simulated ion-exchange brine (NaCl=6% (w/w)) was transformed within 7 hours. The stabilized ZVI nanoparticles were also tested for reductive transformation of nitrate in fresh water and ion-exchange brine. The observed pseudo first-order rate constant (kobs) for nitrate reduction with the stabilized ZVI nanoparticles was more than 5 times greater than that for non-stabilized ZVI particles. With a ZVI-to-NO3- molar ratio of 2.5, N2-N accounted for two thirds (66%) of the nitrate reduction products, 30% greater than that with a ZVI-to-NO3- molar ratio of 3.9. An innovative in-situ mercury (Hg) immobilization technology using stabilized iron sulfide (FeS(s)) nanoparticles was investigated in this study. The FeS(s) nanoparticles were successfully prepared using carboxylmethyl cellulose (CMC) as the stabilizer. The particle size of freshly prepared FeS(s) nanoparticles was measured to be 38.5±5.4 nm. Column tests proved that the stabilized FeS(s) nanoparticles reduced the mercury leachability of the Hg-laden sediment by as much as 66.7% and the extracted Hg in TCLP solutions was reduced by 76.9% when the sediments was treated with 0.5 g/L stabilized FeS(s) nanoparticles. Column tests also proved that stabilized FeS(s) nanoparticles were highly mobile in a clay loam sediment and ~100% of FeS(s) nanoparticles passed through the sediment with 18.4 PV’s (pore volumes) of 0.5 g/L stabilized FeS(s) nanoparticles.