In the midst of the USA EPA’s new ruling on management of power station coal ashes in December, a report by Lucid Insight outlines the opportunities and challenges for metal recovery, including commercialisation activities for scandium, titanium, germanium, gallium, vanadium, and REEs. The independent review incorporates insights from interviews with key stakeholders and experts globally to obtain a broad landscape of commercial activities, market drivers and barriers, and looks at some of the options for moving forwards.
Commercial metal extraction from coals is not a new idea, with vanadium and silver extraction dating back to the 1800s, and germanium extraction still active. However, more recently there has been increasing interest in other metals from residue coal ashes, as concerns have grown over the overall management of fly ash, as well as environmental issues, and the risk of supply of certain minerals found in coal.
Annual production of fly ash may be as much as 1.5 billion tonnes globally. There is a common belief that all fly ash produced in Europe is being utilised in construction already, but this predominately applies to Class C ashes, not the non-cementitious Class F ashes, and data suggests that even now over 40% of the total fly ash is under-utilised (low value fill material) or un-utilised. In addition, some of the leading players in metal recovery are developing routes to recover the bulk minerals as well as the metals, meaning that production of metals and construction materials may not have to be mutually exclusive.
Metal Content and Value
The value of the metals in fly ash can vary greatly depending on the source of the coal and data is relatively sparse. However, analysis of the available data suggests that scandium and germanium enriched coals may present the highest extractable value, based on prices at the time of the report (this excludes the very rare examples of precious metal enriched coals). Even the lowest level of scandium seen in these samples was worth nearly $5,000 per tonne of fly ash, with the more enriched ashes reaching over $40,000 per tonne of fly ash, and the maximum germanium levels at almost $3,500.
In addition, from the data seen, there seems to be coals with enriched levels of dysprosium and yttrium that may each return $245 and $210 per tonne of fly ash at the current market prices. Some groups in the US are conducting research to identify coal seams with relatively high (>1000ppm) REE content. For example, Prakash Joshi, of Physical Sciences Inc., estimates that 10 to 15% of available fly ash could meet US REE demand by 2020, even with the REE content of ash at much lower levels than in minerals, and accounting for both REE content variability and process yield.
It has also been found that different fractions within coal ash may contain higher levels of particular metals and this may present an opportunity for pre-treatment and segregation to increase the concentrations, making processing more efficient, and this is an area undergoing further exploration.
Estimated valuations for selected metals based on the minimum and maximum concentrations from various fly ash sample data sources (US$/tonne fly ash)*
- Selected metals were those estimated to be worth over $10 per tonne fly ash for maximum concentrations
- Sources of metal concentrations: Rare earth metal content estimated from laboratory analysis for ash from coal deposits in US, Russia, China and Middle East, (Seredin & Dai, 2012), and a range of concentrations measured from coal fly ash collected from power facilities in Europe, US, Mexico and Spain (Median et al, 2010; Arroyo et al, 2009; Mardon & Hower, 2004; Zhang et al, 1997) as summarised by Mayfield & Lewis, 2013. Also, unpublished data from analysis of power station fly ash from coals from Russia, Columbia, S. Africa, US, UK and unknown sources.
- Prices obtained from the London Metal Exchange, www.mineralprices.com, www.asianmetal.com, and www.metal-pages.com from data between May – September 2014
- For full details see Appendix C of Commercial Recovery of Metals from Coal Ash – Global Review, Lucid Insight Ltd www.lucid-insight.com/briefings
Although this is a challenging area, there are a number of companies that appear to have promising technologies worthy of further investigation. However, the environmental impacts of metal recovery require further consideration as there is little data comparing metal extraction from virgin materials to the recovery from these waste streams.
In addition, several scenarios are identified in the report which would help facilitate economically viable recovery of metals from coal ash, given the current state of play in the US and Europe, such as:
- Increased regulations of coal ash management and disposal
- Pre-treatments to increase metal concentrations to improve processing efficiency
- Centralised metal concentrate separation and processing facilities to benefit from economy of scale
- Ability to simultaneously recover both bulk materials, ideally for added value products, and metals to enable total utilisation and revenues.
In terms of a truly circular solution the ultimate goal should be to cleverly segregate the different materials within the ash and utilise all these to their highest value, from infill and commodity uses, through to functional materials for higher value applications in construction and the chemicals industry, as well as metal recovery.
Full report or sections, with full profiles of players, can be obtained from www.lucid-insight.com/briefings
Finkelman R.B. & Brown R.D., (1991), Coal as a host and as an indicator of mineral resources, in Peters D.C., ed., Geology in coal resource utilisation: Fairfax, Va., Tech Books, p471-481
- (2013), BP, Statistical Review of World Energy 2013, Historical Data Workbook: http://www.bp.com/content/dam/bp/excel/Statistical-review/statistical_review_of_world_energy_ 2013_workbook.xlsx
- Dr Prakash Joshi, A Low Cost Rare Earth Elements Recovery Technology, Physical Sciences Inc, presented at the World of Coal Ash Conference, 2013
- Smolka-Danielowska (2006), Heavy Metals in Fly Ash from a Coal-Fired Power Station in Poland, Polish J. of Environ. Stud., 15 6: 943-946