| 摘要 |
PURPOSE:To recover harmless trivalent chromium from hexavalent chromium and to regenerate and use a spent refractory by extracting hexavalent chromium with water from a spent hexavalent chromium-containing refractory and oxidizing, reducing and adjusting pH. CONSTITUTION:A spent refractory material containing harmful hexavalent chromium such as K2CrO4, CaCrO4 is pulverized and fed into an extraction vessel 1 to dissolve and extract hexavalent chromium with the water in the vessel 1 and, if necessary, is transferred to a separation and storage vessel 3 with a water collecting vessel 2 to naturally settle and separate the fine particles 22 of the contained refractory. A hexavalent chromium containing water is transferred to a vessel (b) after fed to a vessel (a) of multistage reaction vessels 4 by a pump 23 and is adjusted in pH by adding dilute sulfuric acid from a tank 7. Next, the water is transferred to a vessel (c), where hexavalent chromium is reduced to trivalent chromium to made harmless trivalent Cr(OH)2 by adding a sodium sulfite solution as a reducing agent from a tank 8, and after the reducing reaction is completed by adding a neutralizing agent and a reaction assistant to a vessel (d), the resulting water is transferred to a vessel (e), where Cr(OH)3 is flocculated by adding a high molecular flocculating agent, and Cr(OH)3 is recovered in a sedimentation vessel 5. |
