Formation of hexavalent chromium by reaction between slag and magnesite-chrome refractory

The goal of this work was to understand how Cr6+ formation is affected by the interaction between chromite phases present in magnesite-chrome refractory and different slag compositions. In addition, the formation of Cr6+ 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 Cr6+. However, the replacement of Al2O3 by SiO2 in calcium aluminate slags decreases the formation of Cr6+. SiO2 reacts with CaO to form stable 2CaO·Al2O3·SiO2 and CaO·SiO2 phases, consequently decreasing the amount of uncombined CaO available to react with the chromite phase to form Cr6+. Moreover, the content of Cr6+ is decreased by increasing chromite particle size and increasing the cooling rate of magnesite-chrome refractory.