How joule heating recycles ash and red mud

Posted on 24 Feb 2022

American firm Universal Matter has recently gained a patent for the new recycling technique, joule heating. This is a promising technique that allows rare earth metals to be recycled from the ash created by coal incineration in an electricity power plant. Or from 'red mud', the waste product generated during aluminium production.

Towards less mining extraction?

The invention of joule heating is important for two reasons. Firstly, the technique allows the waste products from a production process to be used effectively. Secondly, the same technique can be used to extract rare earth metals, that are much sought-after for the production of smartphones and electric cars, among other things. In the future, this innovative technique could lead to reduced mining extraction as a ton of coal ash can provide half a kilogram of rare earth metals.

In practice

The process of joule heating involves packing the ash left over from coal incineration into a quartz tube. A huge surge of electricity is then passed along the tube for a second, reaching a temperature of 3,000 °C. The ash contains microscopic glass beads which are home to rare earth metals, such as europium and terbium. The heat cracks the beads open and the metals are turned from phosphates into a form of oxide.

This allows them to be extracted more easily by using mild acids. The process offers the additional advantage that toxic heavy metals can also be captured. Finally, the inventors have identified another interesting application: the extraction of rare earth metals from red mud, the waste generated by the production of aluminium. In other words, giving production waste a second (sustainable) life.


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