Experimental Studies on the Sulfide Capacities of CaO-SiO₂-CrO_x Slags

To understand the desulfurization process during the refining of Cr-containing steel grades, this work was initiated to study the reactions between Cr-sulfur and chromium-containing slags. The sulfide capacities of CaO-SiO₂-CrO_x pseudo-ternary slags were measured using the traditional gas-slag equilibration technique between 1823 K and 1923 K. Sixteen different slag compositions were examined, and two different equilibrium oxygen partial pressures were used to understand the impact of the varying valence of Cr on the sulfide capacities. The results showed that log₁₀ Cs varied linearly with the reciprocal T, and the slope was higher than the corresponding value reported for the binary CaO-SiO₂ of corresponding composition. It was difficult to isolate the relative effects of the bi- and trivalent Cr in the slags because the Cr²⁺/Cr³⁺ ratio was influenced by the basicity of the slag. By using the equation developed by these authors earlier that related Cr²⁺/Cr³⁺ with basicity, oxygen partial pressure, and temperature, it was possible to obtain an approximate trend of the CrO effect on the sulfide capacities; viz. the sulfide shows a decreasing trend as Cr²⁺ replaces Ca²⁺ in the slag. With a continued increase of Cr²⁺ content, indications of the occurrence of a minimum point were observed; beyond which the sulfide capacities showed a slight increasing trend. The latter was attributed, based on slag-structure analysis by Gaskell et al., to the increasing extent of the polymerization reaction releasing oxygen ions for sulfide reactions.