Rare Earth Minerals recovery from mining waste

A rather negatively-oriented article recently highlighted the developments in the Rare Earth Mineral industry in China. Unfortunately the article is rather light on technical details, choosing to highlight the environmental impacts. According to the article there have been many ‘pirate’ operations extracting Rare Earth Elements (REE), and extraction techniques include in situ leaching where chemicals are pumped into soil to dissolve and extract the elements from the soil. It is mentioned that other extraction techniques are in use and under development with lower impacts.

As posted earlier, LKAB in Sweden is studying the recovery of REE from iron ore tailings, and NW Russia have existing commercial operations doing this. The waste chemical mentioned in the article on China, “ammoniacal nitrogen” sounds like a potential resource for fertiliser production, or at least can be treated in an analogous manner to the treatment of sulphate in mining waste water being studied in the SEESIMA project WP5.

An article with more technical detail on the Chinese REE industry can be found here, This article focuses on the ion absorption type of REE deposits, which are only found in China. Although only representing less than 3% of China’s REE deposits, they have a higher content of medium and heavy REE and simpler extraction, being easily extracted by ion exchange with ammonium sulphate solutions. This is the basis for the in situ leaching processes, which avoided the environmental impact of open excavation.

Experimental work on sulphate reduction underway

Breakdown of sulphur-containing minerals often results in the release of sulphate (such as with acid mine drainage). One way to combat the environmental problems that this causes is to use certain types of bacteria that reduce the sulphate back to sulphur or sulphide compounds.

Sulphate reduction and metal sulphide removal experiments are going on at the University of Oulu. Sulphate reducing bacteria are cultivated in bottle scale and tested for utilization of KemiCond treated sewage sludge and succinate. At the same time synthetic mining water is treated, and iron is recovered as FeS. Furthermore, tests with other low-cost carbon sources and real mining waters, as well as reactor experiments are planned to be started in the autumn 2019.

sulphate reduction experiment over 2 weeks
Sulfate-reducing bacterial consortium cultivated in synthetic mining water at 6 °C with succinate as a carbon source.
continuous flow reactor for sulphate reduction experiments
Continuous up-flow reactor built up for biological sulfate reduction experiments

For more details, contact Hanna Virpiranta

LKAB investing in tailings valorisation

LKAB are planning to invest 45 million kronor in pilot plants for recovery of phosphorus and Rare Earth Minerals (REE) from the waste rock from their iron ore mining operation. This development was announced on 20 February 2019, read more here

The pilot plant trial is based on the CleanMAP process developed by Easy Mining, a daughter company of the waste treatment company RagnSells. Details of the CleanMAP process are given here. This seems to be based on the US Patent 8658117 B2, which however only refers to “known processes” for the digestion of apatite with sulfuric acid, hence presumably the traditional use of concentrated sulfuric acid. This patent does not mention the procedure for separation and purification of the rare earth elements. An example of a method to recover rare earth elements from digestion of apatite with strong acid is given in the patent by Genkin et al US 1001 1891.