Lead removal by a reusable gel cation exchange resin containing nano-scale zero valent iron

- A new lead selective adsorbent (C100-Fe0) has been prepared with size range 20 nm.
- The material is reusable, durable and can be synthesized onsite.
- The inner-sphere surface complexes between lead and iron were observed by EXAFS.
- Lengthy fixed-bed column runs were used to validate the performance and reusability of C100-Fe0.

The practical applications of nano-scale zero valent iron (nZVI) particles in flow-through treatment systems are limited due to unfavorable mechanical and hydraulic properties caused by their tiny size. On the other hand, nZVI, when dispersed within suitable host material, can overcome these limitations to have synergistic improvement in its adsorption capacity. This study aims to synthesize, characterize, validate the performance of hybrid cation gel exchanger dispersed with nZVI particles, named as C100-Fe0, for selective trace Pb(II) removal from contaminated water. C100-Fe0 had Fe content of approximately 22% w/w as determined by double acid digestion method. The characterization studies revealed that nZVI particles of size range 20 nm were well dispersed throughout the gel phase of the polymeric resin beads; XANES spectral analysis confirmed the presence of zero oxidation state of Fe nanoparticles within both the newly synthesized and regenerated C100-Fe0. Equilibrium batch studies demonstrated that Pb(II) adsorption capacity was unaffected by the presence of high concentration of competing ions such as Na+ and Ca2+ ions whereas, presence of SiO2 decreased the capacity. The batch adsorption isotherm fitted well with Freundlich model. During column study with C100-Fe0, breakthrough of USEPA permissible limit of 15 µg/L was observed after the passage of 4200 bed volumes of challenge water (NSF/ANSI Std.53) having Pb(II) concentration of 150 µg/L. More than 87% of adsorbed Pb (II) could be recovered within 15 bed volumes during regeneration with acid. Wide availability and low price of iron salts as well as of cation exchange resins, combined with the possible reusability make C100-Fe0 an attractive option for use in the field for removal of Pb(II) from contaminated water.

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