Theme: 08. Metals

Topic Area: 8a. Managing Chromium-Contaminated Sites

Formatted Title:

Innovative Treatment of Hexavalent Chromium in Alkaline Industrial Waste

Background/Objectives:

Industrial process wastes containing hexavalent chromium (Cr⁺⁶) are often disposed in above ground piles which can act as point sources contaminating soil, groundwater, and sediment environments. Remediation of these wastes presents significant technical challenges as highlighted below:

Common remedial approaches, such as alkaline precipitation may result in conversion of Cr⁺⁶ to Cr(OH)3 which is stable within only a narrow pH range and therefore subject to solubilization in the long-term and potentially “rebound”
High Cr⁺⁶ concentrations can prevent application of biological processes due to acute microbial toxicity
Stringent remedial goals may require development of a larger remediation tool box to meet site-specific objectives

Approach/Activities:

Selecting the best approach to treatment of Cr⁺⁶ in the vadose zone should consider several important factors including:

the long-term stability (i.e., permanence) of a potential treatment
short‐term efficacy (i.e., ability to attain remedial goals)
cost
application methodology

Combining in situ chemical reduction with in situ stabilization was viewed positively in term of efficacy, stability, cost, and applicability. It also results in treated waste characteristics that allow a broad range of post‐remediation land use options.

Results/Lessons Learned:

Results from comprehensive bench-scale treatability testing and a field-scale pilot from an Industrial Site in NJ will be presented. Areas of focus include:

Moderation of high pH can be achieved using an innovative approach based on addition of a dilute organic acid solution to the waste.
Amendment of the waste with iron-based reagents was effective in reduction or even complete removal of leachable (TCLP) hexavalent chromium.
- - For waste with an initial total chromium concentration of 600 mg/kg and pH of around 10, complete removal of leachable (TCLP) hexavalent chromium was achieved.
  - For waste with an initial total chromium concentration of 2,600 mg/kg and pH of 11.7, complete removal of leachable (TCLP) hexavalent chromium was not achieved; however, the leachable Cr+6 was reduced by approximately 60%
Overcoming the challenges in dealing with heavily impacted industrial process wastes can be difficult and may require application of innovative treatments
Using Soil mixing as a powerful and meeting site-specific goals while addressing significant variability in Cr⁺⁶ concentrations at large sites

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Majda Rabah