Abstract
This paper describes the results of experiments on the coagulation mechanism of metal ion and oxidation reactivity of metal hydroxide at high temperatures with respect to chromium ion (Cr3+) and chromium hydroxide causing public discussion in waste water treatment and sludge disposal.
The following results were obtained:
(1) The water content of chromium hydroxide was maximum when the coagulation of chromium ion occurred at pH of 7-9. (It was less when the coagulation occurred at higher or lower values). As the result, the apparent specific gravity of chromium hydroxide produced at pH of 7-9 was minimum and its sedimentation rate was also minimum.
(2) Na content of chromium hydroxide increased with the increase of pH value at which coagulation occurred. Therefore, the Cr6+ content of the burned chromium hydroxide was also greater with the increase of pH value at which coagulation occurred.
(3) The Cr6+ content of the burned chromium hydroxide containing Na was maximum at about 300°C. However, when the oxidation temperature was higher than that, the Cr6+ content decreased owing to its decomposition.
