Highlights: A new approach developed by a research group from Xi’an Jiaotong University tackles the long-standing problem in magnesium industry: stable, large-scale and cost-effective production of high-quality magnesium.

High-end magnesium alloys need high-purity and stable primary magnesium with affordable price. However, current commercial primary magnesium either has poor quality (e.g. Mg9990) or is of high purity but with very high price. Prof. Zhiwei Shan’s research group of Xi’an Jiaotong University (funded by a project from Fugu, Shaanxi province), has tackled this problem by developing a cost-effective technology, being capable of large-scale production of high quality pure magnesium. They have built the first thousand-ton Mg9995A demonstration line in China successfully, without reducing the total production or increasing operational complexity. The popularization and application of this technology will produce significant social and economic benefits.

Applications of Magnesium

As the lightest structural metal materials, magnesium and its alloys are attracting worldwide interests because of their potential to reduce energy cost in aeronautics, astronautics and transportation industry. Magnesium also shows broad applications in medical biological implant material, reducing agents for titanium, zirconium and hafnium, considered as strategic materials, as well as hydrogen storage devices.

Primary Magnesium

Primary magnesium is the feedstock for manufacturing magnesium products. China is the largest producer of primary magnesium. Chinese primary magnesium production accounts for more than 80% of the world’s total, while Shaanxi's primary magnesium production takes up about 60% of the national total. Most of the primary magnesium in China is produced by the Pidgeon process, which has long been considered unable to produce high-quality magnesium stably and economically.

Strong demand for high-quality primary magnesium

Manufacturing high-quality magnesium products requires high-quality primary magnesium since impurities in feedstock can be delivered into final products and cause serious problems like fast corrosion. For example, the tolerance limit of Fe for corrosion in pure magnesium is only ~170 ppm, representing the corrosion rate of magnesium will dramatically increase when Fe content exceeds this value. If some Si exists in magnesium, the corrosion rate will drastically increase by three orders of magnitude when the Fe content increases only from 3 ppm to 25 ppm. Acutally, as early as 1942, it was pointed out that the excellent corrosion resistance of magnesium alloys is often masked because of their extreme sensitivity to certain impurities and combinations of impurities (Hanawalt, et al., J. trans. AIME 147, 273–299, 1942). However, there is still no available technology to produce high quality primary magnesium at affordable price. Most primary magnesium in use today is usually of low purity, while further purification requires additional processes that are usually of very high cost, hindering the healthy and fast development of the entire magnesium industry.

Achievements

After 8 years of research and development, Prof. Zhiwei Shan’s research group developed a cost-effective technology that is capable of producing large-scale high quality primary magnesium. They have built the first thousand-ton Mg9995A demonstration line in China successfully, based on horizontal reduction retorts (the main equipment where magnesium is reduced and collected) that are currently widely employed by the factories. During a month’s trial period, the total yield of Mg9995A exceeded 90%. It is worth noting that the usage of this new technology will not reduce the total production or increase operational complexity, which allows large-scale applications in the magnesium industry.  

A committee composed of government personnel, chief engineers of magnesium enterprises and senior researchers of research institutes highly praised and affirmed this project and made the comment that it paves a new way for producing high-quality primary magnesium, which is expected to benefit the entire magnesium industry.