Soluble, Exchangeable, and Total Hexavalent Chromium Levels in Slag with Focus on US EPA Methods 3060A/7199 with XANES Comparison

Environmental Forensics
Oral Presentation

Prepared by D. Gratson
Environmental Standards, Inc., 1704 Llano Street, Santa Fe, NM, 87505, United States


Contact Information: [email protected]; 505-660-8521

ABSTRACT

The US EPA regulates chromium under many statutes including the CWA, CAA, CERCLA, RCRA, SDWA and TSCA. These statutes focus on the toxic hexavalent form of chromium, Cr(VI), and the US EPA has published methods employed to extract and measure Cr(VI) in aqueous and solid matrices. Solid matrix extraction typically entails use of US EPA
Method 3060A, alkaline digestion, to measure total Cr(VI) using the approach developed by James et al and Vitale et al. Due to the redox-sensitive nature of chromium, the digestion process is performed under alkaline conditions with reagents designed to prevent interconversion of Cr(III) and Cr(VI). Analysis of the digestate via reaction with diphenycarbazide is noted in US EPA Method 3060A as the most reliable technique for Cr(VI) measurement.
Though US EPA Method 3060A has been used and accepted for many soil types, its use for slag materials is less well documented. Slag produced from steel and iron are composed primarily of nonmetallic calcium, magnesium, and aluminum silicates (USGS 2022) and often contain chromium. Most slag materials are highly alkaline due to use of limestone (CaO) in iron and steel production, making them a unique and complex matrix for characterization via US EPA Method 3060A. Studies have been conducted to understand the potential risk for using slag material based on Cr(VI) level data for slag (Proctor 2000). Yet, a comprehensive study of these slag materials utilizing the leaching approaches that James et al. (B. R. James 1995) employed to quantify the soluble, exchangeable, and total chromium in slag materials has not been performed to date. Data will be presented of Cr(VI) levels in four different furnace-type slags using comparison of levels within the soluble (ASTM D3987-12), exchangeable (phosphate buffer), and total (US EPA Method 3060A) extraction fluids. Total chromium levels within the soluble and exchangeable fluids were also measured via inductively coupled plasma-mass spectrometry (ICP-MS) as a mass balance forensic understanding of chromium behavior. Analysis of selected slag samples for chromium species was also performed using synchrotron-based X-ray fluorescence mapping and micro-X-ray spectroscopy (XANES) analysis at Brookhaven National Laboratory (New York, USA) using the National Synchrotron Radiation Lightsource-II (NSLS-II) on beamline 4-BM. XANES data will be compared and contrasted with that obtained from the conventional methods.

References:
James, Bruce R., John C. Petura, Rock J. Vitale, George R. Mussoline. 1995. "Hexavalent Chromium Extraction from Soils: A Comparison of Five Methods." Environ. Sci. Technol. 29: 2377-2381.
Proctor, D. M. 2000. "Physical and Chemical Characteristics of Blast Furnace, Basic Oxygen Furnace, and Electric Arc Furnace Steel Industry Slags." Environ. Sci. Technol 1576-1582. doi:10.1021/es9906002.
USGS. 2022. “iron-and-steel-slag-statistics-and-information.” Accessed January 25, 2022. https://www.usgs.gov/centers/national-minerals-information-center/iron-and-steel-slag-statistics-and-information.
Vitale, R. J. 1997. "Cr(VI) Soil Analytical Method: A Reliable Analytical Methods for Extracting and Quantifying Cr(VI) in Soils." Soil Sediment Contamination 6: 581-593.