Comparative evaluation of energy and resource consumption for vacuum carbothermal reduction and Pidgeon process used in magnesium production

With the fast development of the application of magnesium based alloys,the demand for primary magnesium is increasing dramatically all over the world.The Pidgeon process is the most widely used process for producing magnesium in China,but suffers from problems such as high energy,resource consumption and environmental pollution.While the process of vacuum carbothermal reduction to produce magnesium(VCTRM)has attracted more and more attention as its advantages,but it has not been well-practiced in industrial applications and there also is no comprehensive and quantitative analysis of this process.This study quantified the flows of resource and energy for the Pidgeon process and the VCTRM process,then compared and analyzed these two processes with each other from three aspects.The VCTRM process results in 63.14%and 69.16%lower of non-renewable mineral resources and energy consumptions when compared to the Pidgeon process,respectively.Moreover,the low energy consumption(2.675 tce vs.8.681 tce)and material to magnesium ratio(2.953:1 vs.6.429:1)of the VCTRM process,which lead to lower greenhouse gas(GHG)emissions(8.777 t vs.26.337 t)and solid waste generation(0.522 t vs.5.465 t)with a decrease of 66.67%and 90.45%,respectively.Results indicate that the VCTRM process is a more environmentally friendly process for magnesium production with high efficiency but low cost and low pollution,and it shows a good potential to be industrialized in the future after solving the bottleneck problem of the reverse reaction.

Fabrication of β-Sialon/ZrN/ZrON composites using fly ash and zircon

β-Sialon/ZrN/ZrON composites were successfully fabricated by an in-situ carbothermal reduction？nitridation process with fly ash, zircon and active carbon as raw materials. The effects of raw materials composition and holding time on synthesis process were investigated, and the formation process of the composites was also discussed. The phase composition and microstructure of the composites were characterized by means of XRD and SEM. It was found that increasing carbon content in a sample and holding time could promote the formation of β-Sialon, ZrN and ZrON. The proper processing parameters to synthesize β-Sialon/ZrN/ZrON composites were mass ratio of zircon to fly ash to active carbon of 49：100：100, synthesis temperature of 1550 °C and holding time of 15 h. The average grain size ofβ-Sialon and ZrN（ZrON） synthesized at 1550 °C for 15 h reached about 2 and 1μm, respectively. The fabrication process ofβ-Sialon/ZrN/ZrON composites included the formation ofβ-Sialon and ZrO2 as well as the conversion of ZrO2 to ZrN and ZrON.

Effects of synthesis temperature and raw materials composition on preparation of β-Sialon based composites from fly ash

β-Sialon based composites were successfully prepared from fly ash and carbon black under nitrogen atmosphere by carbothermal reduction-nitridation process. Effects of heating temperature and raw materials composition on synthesis process were investigated, and the formation process of the composites was also discussed. The phase composition and microstructure of the composites were characterized by X-ray diffraction and scanning electronic microscopy. The results show that increasing heating temperature or mass ratio of carbon black to fly ash can promote the formation of β-Sialon. The β-Sialon based composites can be synthesized at 1723 K for 6 h while heating the sample with mass ratio of carbon black to fly ash of 0.56. The as-received β-Sialon in the composites exists as granular with an average particle size of 2-3 μm. The preparation process of β-Sialon based composites includes the formation of O′-Sialon, X-Sialon and β-Sialon as well as the conversion processes of O′-Sialon and X-Sialon to β-Sialon.