Hexavalent chromium removal by ferrochromium slag

Area of Science:

• Environmental Engineering
• Materials Science
• Chemical Engineering

Background:

• Ferrochrome production generates wastewater containing hexavalent chromium (Cr(VI)).
• Jigging operations for ferrochrome recovery can lead to Cr(VI) generation.
• Effective treatment methods are needed to manage Cr(VI) in industrial wastewater.

Purpose of the Study:

• To investigate the potential of ferrochrome slag (FS) for Cr(VI) removal from wastewater.
• To demonstrate the reduction of Cr(VI) to trivalent chromium (Cr(III)) and subsequent precipitation.
• To optimize parameters for Cr(VI) reduction and Cr(III) precipitation using FS and sulfuric acid.

Main Methods:

• Batch experiments were conducted to study Cr(VI) reduction.
• Key parameters investigated include acid amount, contact time, FS dosage, initial Cr(VI) concentration, and temperature.
• TCLP (Toxicity Characteristic Leaching Procedure) test was used to assess the environmental stability of solid residues.

Main Results:

• Cr(VI) concentrations in jigging water reached 0.61 mg/l after 50 batches.
• Acid amount was the most critical factor for Cr(VI) reduction.
• Optimal conditions for Cr(VI) reduction: 10 g/l FS, 3.5 ml/l H2SO4 (5M), 60 min contact time, 25°C, and 10 mg/l initial Cr(VI).
• A 60 g/l FS dosage effectively precipitated Cr(III) and Fe ions from the reduced solution.

Conclusions:

• Ferrochrome slag and sulfuric acid can effectively treat Cr(VI)-containing jigging water from ferrochrome plants.
• The process reduces Cr(VI) to Cr(III) and precipitates metal ions.
• The resulting solid residues are environmentally stable, as confirmed by TCLP testing.