Subspeciation of sulfidic nickel in particulates. Determination of Ni3S2, NiS2, and NiS in reference and fly ash samples by carbon paste electrode voltammetry

Abstract

Nickel speciation of fly ash by sequential extraction lacks specific identification of the chemical forms in the sulfidic nickel phase. A new voltammetric analysis of Ni₃S₂, NiS, and NiS₂ in a carbon paste electrode is reported. Characteristic peaks were observed in acetate (pH 5) as the electrolyte; the anodic peak for Ni₃S₂ gave a linear dose response with microgram sensitivity. Reference compounds included heazlewoodite, millerite, commercial Ni₃S₂, NiS₂, and NiS, but the latter was shown to be mainly the subsulfide. No Ni₃S₂ was found in two types of laboratory generated ash: an oil ash containing mainly soluble nickel and a high sulfur petroleum coke ash enriched with nickel.