Chromium oxide, Cr
2O
3, was solidified by heating with the mixture of Na
2CO
3, CaCO
3 and SiO
2. The leach test was appled to determine the environmental adequacy of the ternary system Na
2O-CaO-SiO
2 as chemical fixation agents for Crcontaining Sludge. In the present work the content of Cr
2O
3 was kept at 0.5 mol.% and the mixturs were heated at the temperatures from 800-1200°C for 2 hr. The pH's of the leaching mediums were 1.0, 6.0 and 10.5, respectively. By firing at 1000°C, the heated mass whose composition falled within 15-23 mol.% of Na
2O, 0-9% of CaO and 72-81% of SiO
2 gave the concentration of extracted Cr less than 2 ppm. At 1100°C such area was extended as 10-26% of Na
2O, 0-12% of CaO and 71-86% of SiO
2. Further elevation of the firing temperature, however, no longer broadened the compositional area of the solidified mass which gave low concentration of extracted Cr.
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