The environmental cost of the continued mining of rare earth oxides in China is seeing a great deal of press of late. Both The Guardian and the BBC have run stories recently about the tremendous environmental and social costs of the Chinese rare earth industry. China appears to be aware of the problem and concerned. The recent change in the tax structure for rare earth could be a means of curbing incentive to slow down development, and the consolidation of the Chinese national rare earth sector will theoretically result in easier oversight of the sector.
The problem is well detailed in this 2013 report from Elsevier’s Journal of Environmental Development: China's ion-adsorption rare earth resources, mining consequences and preservation.
Ion-adsorption clay rare earth deposits are unique to China and as such the mining and processing methods used to exploit them were also developed in China. As these rare elements became a more important part of modern devices, the pace of exploitation of these rare earth deposits quickened, but little has been done to make the exploitation of those deposits safer or more efficient.
While only about 1/3 of the total rare earth tonnage in China comes from ion-adsorption clays, that production is significant, as it contains mostly medium and heavy REEs. Heavy and medium REEs strike a balance between utility and scarcity resulting in a far greater realized economic value. The report has China’s ion-adsorption clay deposits “accounting for more than 80% of world's total medium and heavy REEs.”
The clay deposits are mined by simple techniques, and processed by either heap leach or tank-leach processes. Aqueous solutions (in this case ammonium sulphate), are poured over the freshly excavated clay, then collected and processed further to yield various different concentrates of rare earth oxides. The process results in leftover effluent and excavated clay that no longer contains rare earth materials. The mining of the clay and disposal of the leftovers are creating their share of problems:
“Using traditional surface / mountaintop mining and heap leaching techniques it is estimated that for the production of 1t rare earth oxide from ion-adsorption rare earth ores, 300m2 vegetation and top soil are removed, 2000t tailings are disposed into adjacent valleys and streams, and 1000t wastewater containing high concentrations of ammonium sulfate and heavy metals is produced.”
The paper details an effort made in the 1980s to limit surface disruption and tailings piles by going to in-situ leaching techniques. This process involves saturating the clay in solution while it is still in the ground. While the technique successfully limited tailings, it proved to be more costly, less effective and had its share of problems including effluent contamination of groundwater and a disturbing increase in fatal landslides caused by geotechnical disruption. In many cases, in-situ leaching operations changed the ph of the topsoil, killing the very vegetation that the process was supposed to save.
Hopefully, the recent efforts to clean up the sector will help to limit the ongoing damage caused by the mining of these ion-adsorption clays. It seems clear that better planning of their exploitation may at least result in a throttling of the damage. But it’s an uncomfortable truth that the mining of these deposits will continue, at least for the time being. Modern devices including, ironically, clean energy technology like solar cells and wind turbines rely on heavy and medium rare earths and it’s hardly feasible to ignore 80% of the world’s current reserves for any reason.
The long term solution to the problem, globally, is to build HREE deposits that are capable of being operated with low environmental impact. Texas Rare Earth is proud to be building such a deposit in Texas.
