On the removal of hexavalent chromium from a Class F fly ash

Abstract

Coarse and fine samples of a Class F fly ash obtained from commercial combustion of Illinois bituminous coal have been exposed to two long-term leaching tests designed to simulate conditions in waste impoundments. ICP-AES analysis indicated that the coarse and fine fly ash samples contained 135 and 171mg/kg Cr, respectively. Measurements by XAFS spectroscopy showed that the ash samples originally contained 5 and 8% of the chromium, respectively, in the hexavalent oxidation state, Cr(VI). After exposure to water for more than four months, the percentage of chromium as Cr(VI) in the fly-ash decreased significantly for the coarse and fine fly-ash in both tests. Combining the XAFS data with ICP-AES data on the concentration of chromium in the leachates indicated that, after the nineteen-week-long, more aggressive, kinetic test on the coarse fly ash, approximately 60% of the Cr(VI) had been leached, 20% had been reduced to Cr(III) and retained in the ash, and 20% remained as Cr(VI) in the ash. In contrast, during the six-month-long baseline test, very little Cr was actually leached from either the coarse or the fine fly-ash (<0.1mg/kg); rather, about 66% and 20%, respectively, of the original Cr(VI) in the coarse and fine fly-ash was retained in the ash in that form, while the remainder, 34% and 80%, respectively, was reduced and retained in the ash as Cr(III). The results are interpreted as indicating that Cr(VI) present in Class F fly-ash can be reduced to Cr(III) when in contact with water and that such chemical reduction can compete with physical removal of Cr(VI) from the ash by aqueous leaching.

Karakteristik C–4–etoksi–3–metoksifenilkaliks[4]resorsinarena trifenilfosfonium klorida dalam mengadsorpsi anion Cr2O72–

“…Kromium merupakan salah satu jenis logam berat yang sering dijumpai dalam ekosistem perairan dan banyak digunakan dalam berbagai bidang industri seperti electroplating (Zakkiyah, 2018), pigmen dan pewarnaan (Natalina and Firdaus, 2018), penyamakan kulit, dan finishing logam (Daneshvar et al, 2019). Meskipun kromium memiliki bilangan valensi mulai dari −2 hingga +6, namun bentuk Cr (III) dan Cr (VI) relatif lebih stabil di lingkungan dibandingkan bentuk lainnya (Huggins et al, 2016;Pradhan et al, 2017).…”

Interactive Relationship between Cementitious Materials and Acid Mine Drainage: Their Effects on Chromium Cr(VI) Removal

“…During the combustion of coal, Cr is usually oxidized from Cr(III) to Cr(VI). When exposed to water, Cr(VI) may leach out from the adsorbents [63]. Maximum Cr(VI) concentration levels of 4.27 mg/L and 0.558 mg/L were attained at pH levels of 13.6/8.77 of the treated mine water, under the dosage of 60 g of CEM I/FA in 200 mL of AMD, respectively.…”

Pyrite-Based Cr(VI) Reduction Driven by Chemoautotrophic Acidophilic Bacteria

“…The toxicity of Cr(III) is far lower than that of Cr(VI), and it can be easily precipitated as Cr(OH) 3 , while Cr(VI) is soluble over a wide pH range. Reduction represents an efficient strategy for Cr(VI) remediation (Parker et al, 2011;Huggins et al, 2016).…”