These processes generally use Portland cement and sludge along with certain other additives (some proprietary) including fly ash or other aggregate to form a monolithic, rock-like mass. Type I Portland cement, the cement normally used in construction, is generally used for waste fixation. Type II is used in the presence of moderate sulfate concentrations (150-1500 mg/kg), and Type V, for high sulfate concentrations (greater than 1500 mg/kg).
These processes are successful on many sludges generated by the precipitation of heavy metals. The high pH of the cement mixture keeps the metals as insoluble hydrox-
TABLE 11.16.1 EFFECTIVENESS OF S/S ON
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