Treatability of chromite ore processing waste by leaching

Area of Science:

• Environmental Science
• Environmental Chemistry
• Waste Management

Background:

• Chromium-containing wastes pose regulatory challenges due to variable solubility and toxicity.
• Chromite Ore Processing Waste (COPW) is a hazardous waste requiring effective treatment and disposal strategies.
• Understanding chromium leaching behavior is crucial for developing health-based cleanup standards.

Purpose of the Study:

• To investigate the leaching characteristics of total chromium (Cr) and hexavalent chromium (Cr(VI)) from COPW.
• To assess the treatability of COPW through various leaching strategies.
• To identify leaching conditions that enhance chromium species mass removal rates.

Main Methods:

• Laboratory column studies were conducted using COPW from a Turkish industrial plant.
• Waste characterization included the U.S. EPA Toxicity Characteristic Leaching Procedure (TCLP).
• Column experiments involved plain COPW, COPW mixed with reducing agents (iron, manure), and COPW with different soil types, subjected to acidic, neutral, and alkaline leaching.

Main Results:

• TCLP analysis classified the COPW as hazardous waste.
• Maximum total Cr removal was achieved using acidic leaching (pH 4.78) of a COPW/manure mixture.
• Highest Cr(VI) leaching efficiency occurred with highly alkaline leaching (pH 12.0) of plain COPW or COPW/manure mixture.
• Leaching plain COPW with neutral water yielded the least effective removal for both total Cr and Cr(VI).

Conclusions:

• Leaching COPW/manure mixtures with acidic water is effective for total chromium removal.
• Alkaline leaching conditions are optimal for enhancing Cr(VI) removal from COPW.
• Land disposal of treated COPW mixed with clayey soils presents a viable management option.