Fundamental Research On Growth Control Of Spinel In Stainless Steel Slag

Stainless steel slag is a main byproduct in the production of stainless steel.Chromium in unstable phases of slag can be oxidized to a highly toxic water-soluble Cr6+ in the natural environment,posing a serious threat to the surrounding environment and human health.Therefore,the resource utilization of the stainless steel slag is still a troublesome problem.Spinel phase is regarded as a suitable phase for sequestrating chromium in the stainless steel slag since its high stability even in the severe environment.It is believed that the large spinel crystals size is beneficial to the stabilization of chromium,while the reported methods of stainless steel slag modification are not able to promote the spinel growth.Inspired by the achievement of geological mineralization of chromite,shear force was introduced in the traditional modification technology,and the effect of shearing rate and duration on the growth behavior of spinel in the molten stainless steel slag is studied.The main conclusions obtained from this work are as follows:(1)At 1500?,the application of an appropriate shear rate can promote the growth of spinel crystals and reduce the density of spinel grains,which is beneficial to the formation of large size spinel.When the shear rate was too high,the nucleation of the spinel was promoted and,as a consequence,the growth of the crystals was inhibited.In the cooling process at the rate of 5?/min,the shear force has little effect on the growth behavior of spinel.(2)The crystal growth mechanism of spinel crystals under static condition is the supply-controlled Ostwald ripening.When the shear rate is 10.83s-1,the crystal growth mechanism is surface-controlled growth.Moreover,when the shear rate is 21.67s-1,the crystal growth mechanism is nucleation and growth with constant or accelerating nucleation rate.(3)Under the experiment conditions of this study,the shear force has little effect on the molar fraction of silicon-oxygen structure unit in the molten stainless steel slag.The NBO/T and the structure of silicate melts did not show a notable change.(4)An appropriate shear rate is helpful to form regular spinel and promote the crystal aggregation.But the high intensity of the shear force could increase the irregular degree of the spinel.Furthermore,the distribution of spinel crystals in slag tends to disperse.