Latrobe Magnesium - turning residual ash into useful magnesium metal

Technology

HYDROMET PROCESS

The hydromet process has been developed jointly with Ecoengineers Pty Ltd over the last five years.

The process involves the treatment of the fly ash by chemicals to reduce sulfur, iron and silicon to acceptable levels so that the beneficiated material can be used as a feedstock in the thermal reduction process.

In September 2013, an Australian patent was approved on the hydromet process developed by Ecoengineers Pty Ltd and Latrobe Magnesium Limited.  In 2015 patents have also been granted in USA and China. Applications in EU, India and Indonesia are currently at the examiners stage.  LMG has the worldwide marketing rights for this technology.

THERMAL REDUCTION PROCESS

The thermal reduction process is a simple and proven process which was invented in early 1940’s by Dr. Lloyd Montgomery Pidgeon of the Canadian National Research Council. The first plant was built in 1941 in Haley, Ontario, Canada. This plant operated for 66 years, most recently by Timminco Metals. In the past 10 years, the Pidgeon process has come to dominate the world magnesium production. China is the dominant magnesium metal supplier, relying almost exclusively on this method.

Magnesium is produced from calcined dolomite under vacuum and at high temperatures using silicon as a reducing agent.

The following is an outline of the normal thermal reduction process.

Calcination

In the process, the finely crushed dolomite (magnesium/calcium) carbonate is fed to rotary kilns where it is calcined, and where the carbon dioxide is driven off leaving a product – dolime.

Mixing

Normally, the dolime is then pulverized in a roller mill prior to mixing with finely ground ferrosilicon and fluorspar. The fine dolime, ferrosilicon, and fluorspar are weighed in batch lots and mixed in a rotary blender.

Briquetting

This mixture is then briquetted in briquetting presses. Briquettes are then conveyed to the reduction furnaces.

Retorting

The reduction operation is a batch process releasing magnesium in vapour form, which condenses in the water cooled section of the retort outside furnace wall. The residue from the reduction charge, which is inert, is removed from the retort and will be sent back to the existing tailings dams.

Casting

After removal from the furnace, the magnesium “crown” is pressed from the sleeve in a hydraulic press.

SUMMARY

Whilst LMG is using the thermal reduction process it is proposing to have automated vertical retorts instead of the normal horizontal retorts. The benefits of vertical retorts are:

  • lower gas usage
  • better magnesium recover
  • smaller labour force
  • bigger retort batches
  • smaller infrastructure requirements

These benefits result in both lower capital and operating costs.



This page updated: 22/10/2014