Cr(VI) formation in ferrochrome-smelter dusts

Area of Science:

• Metallurgical Engineering
• Environmental Science
• Analytical Chemistry

Background:

• Ferrochrome smelting produces dusts containing various chromium species.
• Understanding chromium speciation in dust is crucial for environmental and health risk assessment.
• Previous studies have not fully elucidated Cr(VI) formation mechanisms within the smelting environment.

Purpose of the Study:

• To investigate the distribution and speciation of chromium (Cr) in dusts from a pilot-scale DC arc furnace.
• To identify the formation mechanisms and locations of hexavalent chromium (Cr(VI)) within the smelting dust.
• To correlate Cr(VI) presence with specific dust components and furnace conditions.

Main Methods:

• Sampling of dust from furnace freeboard, cyclone, and baghouse.
• Synchrotron-based micro-X-ray fluorescence (µ-XRF) analysis.
• Micro-X-ray absorption near-edge structure (µ-XANES) spectroscopy at the chromium (Cr) K-edge.

Main Results:

• Dusts contained Cr(0), Cr(III), and Cr(VI).
• Cr(VI) was primarily associated with Si-Ca-Mg-rich glassy micro-spherules in both freeboard and cyclone dusts.
• Cr(VI) formation was observed within the closed DC-arc furnace, even under reducing conditions.

Conclusions:

• Hexavalent chromium (Cr(VI)) can form in aerosolized dusts during ferrochrome smelting.
• High temperatures and flux composition likely influence Cr(VI) formation in closed furnace systems.
• The glassy micro-spherules are key carriers of Cr(VI) in the investigated dusts.