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JMEPEG https://doi.org/10.1007/s11665-020-04801-1

Reduction and Immobilization of Chromate Using Nanometric Pyrite Amelia Bergeson, Travis Reed, and Allen W. Apblett (Submitted November 15, 2019; in revised form February 11, 2020) Two very fine pyrites were prepared using a top-down and a bottom-up method. A natural pyrite was extensively ball-milled and then sieved to obtain the fraction less than 25 lm (surface area 17 m2/g), while sub-micrometer pyrite (FeS2) rods with a surface area of 77 m2/g were prepared by the hydrothermal reaction of ferrous sulfate with sodium sulfite. The ground natural pyrite was found to fairly rapidly reduce chromium(VI) in a 100 ppm solution to chromium(III), but it only immobilized 65.6% of the chromium(III) product so it failed to lower the total chromium below the maximum contaminant level (MCL) for drinking water. However, the synthetic sub-micrometer pyrite completely reduced the chromium(VI) to chromium(III) within one minute and to reduce the total chromium concentration below the detection limit of 0.5 ppb within 3 min. The reactivity of FeS2 toward chromium(VI) does not correlate well with surface area due to the complex series of reaction that occur in both the redox and metal immobilization processes. Nevertheless, size reduction makes it progressively possible to completely remove chromium from chromate-containing solutions. Keywords

green industry, nanomaterials, waste treatment

1. Introduction Over the years, chromium (VI) species such as chromate and dichromate have been invaluable in the processing of materials such as in leather tanning, chromium plating, metal cleaning and processing, corrosion protection, wood preservation and chromium alloy preparation (Ref 1). Unfortunately, chromium(VI) is hazardous to people and animals and can cause numerous adverse health effects including cancer, respiratory irritation, pulmonary congestion, edema, and asthma, kidney and liver damage, skin erosion and skin ulcers (Ref 2). On the other hand, chromium(III) is an essential trace element that is involved in the maintenance of proper carbohydrate, protein and lipid metabolism by amplification of the actions of insulin (Ref 3, 4). The differences between the two forms of chromium can be exemplified by their least dose for 50% mortality (LD50) for oral exposure in rats: that LD50 values for chromium(VI) compounds (dichromate as the ammonium, sodium, potassium, and ammonium salts and sodium chromate) range from 13 to 28 mg chromium(VI)/kg in male rats, while the LD50 for chromium(III) as chromium acetate was reported to be This article is an invited paper selected from presentations at the ‘‘11th International Symposium on Green and Sustainable Technologies for Materials Manufacturing and Processing,’’ held during Materials Science & Technology (MS&TÕ19), September 29–October 3, 2019, in Portland, OR, and has been expanded from the original presentation. Amelia Bergeson, Department of Chemistry, Tulane University, New Orleans, LA 70118; and Travis Reed and Allen W. Apblett, Department