Self-reduction mechanism of coal composite stainless steel dust hot briquette

To efficiently recycle valuable metals such as chromium and nickel in stainless steel dust, self-reduction experiments were carried out to study the reduction mechanism of metal oxides in coal composite stainless steel dust hot briquette, which is defined as a CCSB here. Self-reduction of CCSB is proceeded by volatile matter and fixed carbon contained within CCSB. Experiments were performed to study the effects of temperature and carbon to oxygen (C/OCoal) ratio on self-reduction of CCSB. At 1400 and 1450 °C, volatile matter in coal used for experiment could take the place of about 40% of fixed carbon in coal. Under the present experimental conditions, reduction product of chromium appears as FeCr2O4, Cr2O3, Cr7C3, and [Cr] in turn during reduction. To evaluate the formation of metal nuggets in self-reduction process of CCSB, metal nuggets containing chromium and nickel were observed in outside of reduction products under various conditions, and thermodynamic equilibrium calculation was carried out for possible products and formation of molten metal by fixed carbon. SEM and EDS analyses were made for metal nugget and slag in reduced product. The results reveal that it is reasonable to achieve the metal nuggets at 1450 °C, 0.8 of C/OCoal ratio and 20 min of reduction time. The nugget formation can indicate one innovative process for comprehensive utilization of stainless steel dust.