Study of the reduction rate anti-fixation phenomenon by combining precursor porosity and relative vacuum mechanisms

Abstract

The high carbon emission (23 t CO₂ / 1 t Mg) and high energy consumption (5tce / 1 t Mg) of raw magnesium smelting seriously limit the expansion of its output. Compared with the vacuum continuous magnesium smelting process (RVCMS), the direct reduction after calcination can effectively reduce carbon emissions (11 ∼ 13 t CO₂ / 1 t Mg) and energy consumption (3 ∼ 3.5tce / 1 t Mg), and break the vacuum conditions to achieve continuous production. The improvement of reduction rate is an important factor to promote the industrialization of new process. In this paper, the reduction reaction model of prefabricated pellets was constructed and the mechanism of reduction process was studied by regulating the ratio of reducing agent in prefabricated pellets. The results indicate that prefabricated pellets composed of dolomite, magnesite, and aluminum powder were prepared by crushing and grinding. When the reducing agent content was 90 % of the theoretical amount, the pellets were first calcined at 1000 °C for 1 h. This led to MgCO₃ thermal decomposition, increased porosity, and the formation of additional Mg(g) release channels. The reduction reaction then proceeded at 1300 °C for another hour. Under this condition, the reduction rate of pellets increased from 91.05 % to 92.43 %. When the addition amount of reducing agent is less than 90 %, due to the lack of reducing agent involved in the reaction, some MgO cannot fully react, resulting in a relatively low reduction rate. When the addition amount of reducing agent is higher than 90 %, the excessive reducing agent will increase the densification degree of calcium aluminate sintering and reduce the number of pores. It is difficult for Mg(g) to escape from the reaction area in time to form a higher local vapor pressure inhibition reaction, which also leads to a decrease in the reduction rate. Combined with the mechanism of pore-forming degree and relative vacuum degree, the influence formula of reduction rate of prefabricated pellets was constructed, which was in good agreement with the results of reduction rate anti- fixation experiment. The optimized process shows excellent energy saving and emission reduction effect, which can improve the efficiency of raw magnesium smelting. When the reduction rate increases, the difficulty of secondary utilization of slag phase is significantly reduced. The calcium aluminate phase produced can be used in refractory materials, electronic ceramics, steelmaking agents and other fields to realize resource recycling and provide a feasible solution for the sustainable development of magnesium smelting industry.