Cr(VI) concentration from batch contact/tank leaching and column percolation test using fly ash with additives

Area of Science:

• Environmental Science
• Geochemistry
• Materials Science

Background:

• Fly ash utilization in construction can lead to environmental concerns regarding heavy metal leaching.
• Chromium(VI) [Cr(VI)] is a toxic and mobile contaminant of concern in industrial byproducts.

Purpose of the Study:

• To investigate the factors influencing Cr(VI) concentration in leachate from fly ash treated with additives.
• To evaluate the effectiveness of cement, low alkalinity additive, and Ariake clay in mitigating Cr(VI) leaching.

Main Methods:

• Batch contact, tank leaching, and column percolation tests were performed on two types of fly ash (A and B) with various additives.
• Analysis focused on Cr(VI) concentration in the leachate under different conditions.
• Factors studied included solid/liquid ratio, pH, cementation, and adsorption characteristics.

Main Results:

• Fly ash A, with lower cementation (1.92% CaO), showed higher Cr(VI) concentrations in column tests compared to batch tests, indicating the importance of water contact.
• Adding Ariake clay reduced Cr(VI) more effectively in fly ash A due to its lower initial pH, favoring Cr(VI) reduction and adsorption.
• Fly ash B, with higher cementation (7.15% CaO), exhibited significantly reduced Cr(VI) after a 1-week curing period in column tests.

Conclusions:

• The choice of testing method is critical; methods simulating field conditions are necessary for accurate environmental impact assessment.
• Additives like Ariake clay and cementation play crucial roles in controlling Cr(VI) mobility from fly ash.
• Understanding the interplay between fly ash properties, additives, and environmental conditions is key to safe disposal and utilization.