Citation:

Chattopadhyay, S. AND P M. Randall*. EVALUATION OF CHEMICALLY BONDED PHOSPHATE CERAMICS FOR MERCURY STABILIZATION OF A MIXED SYNTHETIC WASTE. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-03/113 (NTIS PB2004-103500), 2003.

Impact/Purpose:

To evaluate the stabilization and encapsulation technique (called the Chemically Bonded Phosphate Ceramics technology) developed by Argonne National Laboratory for Hg- and HgCl₂-contaminated synthetic waste materials.

Description:

This experimental study was conducted to evaluate the stabilization and encapsulation technique developed by Argonne National Laboratory, called the Chemically Bonded Phosphate Ceramics technology for Hg- and HgCl₂-contaminated synthetic waste materials. Leachability tests were carried out by the constant-pH leaching test, the Toxicity Characteristic Leaching Procedure (TCLP), and the TCLP "Cage" modification. X-ray diffraction and spectroscopic techniques, using scanning electron microscope, energy-dispersive spectrophotometer, and wave-dispersive spectrophotometer, were used to identify the solid-state mineral phases. Data obtained from this study showed that stabilization of wastes reduced the leachability of Hg considerably. TCLP results showed that leachability of Hg decreased by a minimum of two orders of magnitude and a maximum of five orders of magnitude. The variation in the decrease in leachability was dependent on the amount and state of Hg in the waste. Maximum reduction in leachability of stabilized wastes was observed with wastes containing elemental Hg at 50 wt% loading, followed by wastes containing HgCl₂ at 50 wt% loading, HgCl₂ at 70 wt% loading, and elemental Hg at 70 wt% loading, respectively. The three test methods produced similar amounts of leached mercury, but the constant-pH leaching procedure samples released slightly higher levels (at pH=2) compared to the TCLP methods. On comparing the results obtained with the standard TCLP and the TCLP "Cage" modification, it was observed that leachates from stabilized wastes containing 50 wt% loading of elemental Hg and HgCl₂ were within the Land Disposal Restrictions (LDR) requirement. Moreover, leachability indices measured with the TCLP "Cage" modification procedure showed high leachability indices, which indicates that Hg was retained well within the solid matrices. However, wastes containing 70 wt% loading of Hg and HgCl₂ had leachate concentrations exceeding the 0.2 mg/L treatment standard and therefore did not meet RCRA disposal requirements. Comparing typical cost data, as available in the literature, for several competing treatment technologies for mercury-contaminated hazardous wastes, the cost estimate ranges from $2.88/kg for sulfur polymer cement stabilization/solidification (SPSS) to $16.37 per kg for conventional Portland cement stabilization (both including disposal). The total cost, including both raw materials, labor, and disposal for the CBPC process at $15.45 per kg was found to be on the high end of the treatment cost scale.

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