Section Nine
PHYSICAL-CHEMICAL: GENERAL
33    IMMOBILIZATION OF Pb(II) AND Cd(II) IN
BLASTING WASTES BY PORTLAND CEMENT
COMPOUNDS
Brian A. Dempsey, Charles S. Tricou, Wenjun Liu, and Matthew Hemming
Department of Civil & Environmental Engineering
The Pennsylvania State University
212Sackett Building
University Park, Pennsylvania 16802-1408
ABSTRACT
This report addresses the effectiveness of Portland Cement-Soluble Silicates (PCSS) blasting
additives for reduction of TCLP metals and for reduction of long-term liabilities upon disposal.
The work was performed on blasting wastes from the Marine Corps Logistics Base (MCLB) in
Albany, Georgia. TCLP Cd exceeded TCLP limits in half of Black Beauty samples without PCSS
or with only 10% (w/w) PCSS. Cd exceedances were eliminated with 15 or 20% PCSS. Pb exceeded TCLP limits on 15% of regular blasting wastes, but 10% PCSS eliminated ail Pb exceedances. Steel blasting wastes had 83% exceedances for TCLP Cd, and plastic or glass wastes
frequently exceeded TCLP Pb and Cd.
Leaching experiments were performed on each blasting waste with and without laboratory addition of PCSS. If pH was continuously adjusted with rapid mixing so that the leaching environment never rose above pH 5, then every sample (including those with PCSS) exceeded TCLP
standards for Cd and there were several exceedances for Pb.
These results are consistent with thermodynamic principles modified by chemical kinetic considerations. High temporary pH permits instantaneous precipitation of PbSi03(s), CdSi03(s), or
calcium silicate hydrate (CSH). These materials then dissolve very slowly. PCSS is very alkaline, keeping the TCLP test pH well above 5 and preventing immediate acid titration for all reasonable disposal scenarios.
PCSS was not physically separated from the blasting materials during dry sieving, and inconsequential separation of PCSS materials from blasting wastes are expected during accumulation,
storage, transfer, and disposal operations. This was confirmed by scanning electron microscopy
(SEM) and energy dispersive spectroscopy (EDS).
Recommendations included: (1) segregation of wastes likely to result in TCLP exceedances;
(2) reducing contamination through selection of blasting materials and through masking operations; (3) use of PCSS on wastes that may result in TCLP exceedances; (4) mono-fill disposal to
maintain alkaline; and (5) studies of the long-term leachability of TCLP metals under disposal
conditions.
INTRODUCTION
The objectives were to determine the short- and long-term stability of blasting wastes with and
without addition of PCSS. Short-term refers to RCRA regulations. Long-term refers to Super-
fund regulations, liabilities, and environmental responsibilities.
The work included an initial site visit, evaluation of historic data, critical evaluation of PCSS
materials, theoretical investigation of the effects of PCSS on the reactivity and mobility of trace
52nd Purdue Industrial Waste Conference Proceedings. 1997. Ann Arbor Press, Chelsea. Michigan 48118. Printed in
U.S.A.
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