Formation of hexavalent chromium by reaction between slag and magnesite-chrome refractory
- Michigan Technological Univ., Houghton, MI (United States). Dept. of Metallurgical and Materials Engineering
Magnesite-chrome refractories have been used in steel, copper, and glass industries. The service life of magnesite-chrome refractory varies with the process and serverity of conditions to which it is exposed. Under normal industrial temperatures and oxidizing conditions, Cr{sup 3+}, which is present in the refractory, can oxidize to Cr{sup 6+}. Spent magnesite-chrome refractory is classified as a solid hazardous waste when it has over 5 ppm Cr{sup 6+}, because Cr{sup 6+} is solube in water and is known to be carcinogenic. Iron and steel industries are increasingly conscious of this problem due to more stringent environmental regulations. Therefore, bigger efforts have been made to recycle and reduce solid wastes. The goal of this work was to understand how Cr{sup 6+} formation is affected by the interaction between chromite phases present in magnesite-chrome refractory and different slag compositions. In addition, the formation of Cr{sup 6+} as a function of chromite particle size and cooling rate due to the chromite phase/slag interaction was investigated. The following slag compositions were studied: calcium aluminate, calcium aluminum silicate, and calcium silicate. It was found that the presence of uncombined CaO in the calcium aluminate slags is responsible for a higher yield of Cr{sup 6+}. However, the replacement of Al{sub 2}O{sub 3} by SiO{sub 2} in calcium aluminate slags decreases the formation of Cr{sup 6+}. SiO{sub 2} reacts with CaO to form stable 2CaO {center_dot} Al{sub 2}O{sub 3} {center_dot} SiO{sub 2} and CaO {center_dot} SiO{sub 2} phases, consequently decreasing the amount of uncombined CaO available to react with the chromite phase to form Cr{sup 6+}. Moreover, the content of Cr{sup 6+} is decreased by increasing chromite particle size and increasing the cooling rate of magnesite-chrome refractory.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 634651
- Journal Information:
- Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science, Vol. 29, Issue 2; Other Information: PBD: Apr 1998
- Country of Publication:
- United States
- Language:
- English
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