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

Abstract

The goal of this work was to understand how Cr 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 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 6+ . However, the replacement of Al 2 O 3 by SiO 2 in calcium aluminate slags decreases the formation of Cr 6+ . SiO 2 reacts with CaO to form stable 2CaO⅐Al 2 O 3 ⅐SiO 2 and CaO⅐SiO 2 phases, consequently decreasing the amount of uncombined CaO available to react with the chromite phase to form Cr 6+ . Moreover, the content of Cr 6+ is decreased by increasing chromite particle size and increasing the cooling rate of magnesitechrome refractory.

Effect of FeO on the formation of spinel phases and chromium distribution in the CaO-SiO2-MgO-Al2O3-Cr2O3 system

“…After leaving the EAF process, the slag is cooled and stored for other utilizations. It has been found by some studies [2][3][4][5] that hexavalent Cr can be generated from Cr oxides in the EAF slag in the period of slag processing and storage. Hexavalent Cr is toxic and easily leachable from the slag, leading to water pollution and some economic and ecologic issues.…”

Characteristics of steel slag under different cooling conditions

“…Chemical compounds containing hexavalent chromium (Cr 6+ ) are generally considered far more toxic than those containing the trivalent form (Cr 3+ ) (Plunkett, 1976;Windholz, 1976). According to Lee and Nassarella (1998), Cr 6+ is usually formed at lower temperatures and a rapid cooling reduces the formation by limiting the kinetics of the formation.…”

Degradation of low‐carbon MgO‐C refractory by high‐alumina stainless steel slags in VOD ladle slagline

“…However, the high cost and the potential toxic Cr 6+ pollution limit the application of the MgO‐Cr 2 O 3 refractory. Recently, attention has been focused on the development of chrome‐free refractories to displace MgO‐Cr 2 O 3 refractories in VOD ladles, such as MgO‐CaO refractories and MgO‐C refractories …”