Separation of Metal Nugget from Self-reduced Product of Coal Composite Stainless Steel Dust Briquette

Abstract

To efficiently recycle valuable metals such as chromium and nickel in stainless steel dust, a research was made to separate metal nugget included chromium and nickel from self-reduced products of coal composite stainless steel dust briquette, here is defined as a CCSB. Metal nuggets and slag were formed in self-reduction process of CCSB. After reduction, a large amount of C₃S and a little C₂S existed in slag due to its high basicity. However, C₂S content was increased by solidification of oxide melt in slag, and then, it was much increased by decomposition reaction of C₃S as reduced products were kept up at low temperature. The transformation of β C₂S→γ C₂S was occurred in slag during cooling as slag was shattered due to volume expansion, and then separation of metal nugget was achieved. The effect of basicity on separation of metal nugget was considered. Thermodynamics equilibrium calculations and non-equilibrium cooling calculations were carried out on chemical reactions in CCSB, and separation mechanism of metal nugget and the effects of holding time and temperature on separation were investigated. The optimum holding temperature and time were 1100°C and 15 min, respectively. Recovery ratio of iron, chromium and nickel were 92.5%, 92.0%, and 93.1, respectively. Metal nuggets were separated from self-reduced product of CCSB without using any auxiliary materials. This separation method can indicate one innovative process for stainless steel dust comprehensive utilization.