ENHANCED SLUDGE WASHING FOR PRETREATING HANFORD TANK SLUDGES

摘要

The term "Enhanced Sludge Washing" (ESW) refers to a method by which tank sludges are leached with aqueous sodium hydroxide solutions (several molar in NaOH). The ESW process is designed to leach aluminum, chromium, phosphate, and sulfate from the sludges. Removing these nonradioactive components will reduce the amount of high-level waste being processed for final disposal. Aluminum is removed by dissolving aluminum oxides/hydroxides as sodium aluminate. We presume that phosphate and sulfate are removed by metathesis of insoluble phosphates and sulfates to the corresponding metal hydroxides and soluble sodium phosphate and sulfate. Earlier we presumed that chromium would be removed by dissolution of Cr(III) as Cr(OH)_4~2-, but experimental evidence suggests that the removal of Cr by this mechanism is unfavorable. In this paper, we summarize ESW studies on actual tank waste samples. The behavior of the various sludge components as functions of waste type and processing conditions are discussed.