Enhanced As(Iii) Sequestration Using Nanoscale Zero-Valent Iron Modified By Combination Of Loading And Sulfidation: Characterizations, Performance, Kinetics And Mechanism

Nanoscale zero-valent iron (nZVI) and sulfides have been confirmed to be effective in arsenic sequestration from aqueous solution. In this study, attapulgite supported and sulfide-modified nanoscale zero-valent iron (S-nZVI@ATP) are synthesized to realize the superposition effect of enhanced arsenic sequestration. The results indicated that nZVI clusters were well disaggregated and the BET specific surface area increased from 19.61 m(2).g(-1) to 46.04 m(2).g(-1) of S-nZVI@ATP, resulting in an enhanced removal efficiency of arsenic from 51.4% to 65.1% at 20 min. The sulfides in S-nZVI@ATP mainly exists as mackinawite (FeS) and causes the spherical nanoparticles exhibiting a larger average particle size (94.6 nm) compared to bare nZVI (66.0 nm). In addition, S-nZVI@ATP exhibited a prominent ability for arsenic sequestration over a wide pH range of 3.0-6.0. The presence of anions SO42- and Cl- can enhance the arsenic removal whereas HCO3- inhibited it. The arsenic adsorption by S-nZVI@ATP could be explained by the pseudo-second-order kinetic model and the Langmuir model, with the maximum adsorption capacity of 193.8 mg.g(-1). The mechanism of As(III) sequestration by S-nZVI@ATP involved multiple processes, mainly including precipitation conversion from FeS to As2S3, surface-complexation adsorption and co-precipitation.