Promoting spinel formation and growth for preparation of refractory materials from ferronickel slag

The study provides a method for improving the quality of the refractory material prepared from ferronickel slag by promoting the spinel formation and growth in the slag which was sintered with sintered magnesia and chromium oxide in a broad sintering temperature range from 1200°C to 1500°C. According to the thermodynamic analysis, except for forsterite due to the addition of sintered magnesia, a number of high-melting point spinel phases can also be formed in the presence of chromium oxide and this trend becomes more apparent with increasing sintering temperature, along with declined presence of low-melting point clinopyroxene, mainly enstatite. This expectation was verified by conversion of a part of the original phase of ferronickel slag, olivine, to two main spinel phases, including magnesium aluminate spinel and donathite which was produced by the replacement of nontoxic Cr³⁺ ions with Fe³⁺ ions in the octahedral vacancies of magnesium chromate spinel. The formation and growth of these spinel phases were promoted by elevating temperature from 1200°C to 1500°C, which accelerated the transition of initially generated enstatite to a glassy phase, in favor of densification. The formation and growth of spinel during sintering contributed to high refractoriness and compressive strength of the resulting refractory materials.