Coal is usually associated with its energy-producing components, mainly carbon and hydrogen, but many other value-added minerals and metals can be present. Commercial metal extraction from coal is not a new idea. Vanadium and silver extraction from enriched coal sources dates back to the 1800s, and germanium extraction is still active by companies such as Umicore.
When coal is combusted, some valuable components can be found in the fly ash captured by the electrostatic precipitators and/or fabric filters commonly applied at coal-fired power plants. Recently interest has increased in extracting 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 compounds found in coal. For example, companies in China are expected to scale up alumina production from coal ash to over six million tonnes per annum over the next few years, while other players have been developing recovery processess for strategic metals such as vanadium, titanium, germanium, gallium, rare earth elements, and scandium. These metals are important in various sectors, such as electronics, optics, batteries, catalysts, automotive, and clean energy applications.
Annual production of fly ash may be as much as 1.5 billion tonnes globally.2 The largest use for coal fly ash is for construction purposes, but data suggests that despite shortages of cementitious Class C fly ash in some regions, a considerable proportion of the total fly ash produced globally may be underutilized (e.g., used as low-value fill material) or unutilized.3,4 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 is not necessarily mutually exclusive.
“Fully utilizing all the components in coal fly ash can support movement toward an increasingly circular economy.”
Although metal and mineral recovery from fly ash occurs globally, there are national-level policies that may make it more interesting or attractive in certain areas. For example, the U.S. Environmental Protection Agency’s new ruling on the management of power station coal ashes in December stated that fly ash would not be considered a hazardous material.
FIGURE 1. Projected metal value in ash sources
Despite the political, societal, and environmental drivers, uncertainty remains about the regulatory and economic aspects, and data are lacking on the full environmental foot- print of the various metal recovery processes. Therefore, in a recent study titled “Commercial Recovery of Metals from Coal Ash – Global Review”, Lucid Insight reviewed the opportunities and challenges for metal recovery from coal fly ash. This independent review incorporates published data and insights from interviews with key stakeholders and experts globally to obtain a broad landscape of commercial activities, market drivers, and market barriers, and looks at some of the options for moving forward. This article provides a summary of key observations and conclusions from the comprehensive review.
WHAT’S IT WORTH?
The value of the metals in fly ash can vary greatly depending on the source of the coal (see Figure 1), and data are relatively sparse. However, analysis of 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). A set of data from the British Geological Society of 11 coal ash samples showed that even the lowest level of scandium seen in these samples was worth nearly US$5000 per tonne of fly ash, with the more enriched ashes reaching over US$40,000 per tonne of fly ash, and the maximum germanium levels at almost US$3500. The global scandium market is currently relatively small, at less than 15 tonnes per year in 2014, but developments in new applications, such as use in novel alloys and solid oxide fuel cells in batteries (e.g., for renewable energy storage), is predicted to boost demand considerably in coming years.
“Even the lowest level of scandium seen in these samples was worth nearly US$5000 per tonne of fly ash, with the more enriched ashes reaching over US$40,000 per tonne of fly ash...”
In addition, specific coals with enriched levels of dysprosium and yttrium may each return US$245 and US$210 per tonne of fly ash at the current market prices. Some groups in the U.S. are conducting research to identify coal seams with rela- tively high (>1000 ppm) rare earth elements (REE) content, which have attracted recent attention due to concerns over security of supply and growing demand.
TABLE 1. Example projects in the area of coal ash mineral and metals extraction
For example, Physical Sciences Inc. estimates that 10–15% of available fly ash could meet U.S. 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.
In addition, coal ash can be separated into different fractions to obtain those that contain higher levels of certain metals, which may present an opportunity for pre-treatment and segregation to increase the concentrations, resulting in more efficient processing. This is an area undergoing further exploration.
LEADERS IN COAL ASH METAL RECOVERY
Table 1 lists examples of companies developing commercial processes for recovery of metals from coal ashes for reuse (further details are available in the full study). Currently, germanium—used as a semiconductor, as a catalyst, and to produce wide-angle camera lenses and objective lenses for microscopes—is the principal metal component recovered from coal fly ash commercially, with operating plants in China and Russia. In fact, in these countries specifically enriched seams are mined and processed to recover the germanium from the ashes. There are also several examples of commercialized alumina extraction from fly ash in China, again from enriched coals, although when surveyed several experts opined that these operations currently may not be profitable.
WHAT NEXT?
Although metal extraction from coal ash is a challenging area, a number of companies appear to have technologies worthy of further interest, some of which are listed in Table 1. However, the commercial success of these emerging players will depend on specific details around feedstock selection, process optimization and costs, logistics, metal markets, supply chain, etc. In addition, understanding the environmental impacts of metal recovery requires further investigation as there is little data comparing metal extraction from virgin materials to the recovery from these residues, an area being further evaluated by some players.
Several scenarios would help facilitate the current development of economically viable recovery of metals from coal ash, some of which are already being addressed by players, and these include:
- Pre-treatments to increase metal concentrations to improve processing efficiency.
- The ability to efficiently extract a range of valuable trace metal salts into a concentrate for further processing.
- Centralized metal concentrate separation and processing facilities to benefit from economy of scale.
- Ability to simultanously recover both bulk materials, ideally for added value products, and metals to enable total utilization and revenues.
Fully utilizing all the components in coal fly ash can support movement toward an increasingly circular economy. The ultimate goal should be to cleverly segregate the different materials within the ash and utilize each component to its highest value, whether that be infill and commodity uses, functional materials for higher value applications in construction and the chemicals industry, or metal recovery.
- Indo Tambangraya Megah (ITMG)
- Bukit Asam (PTBA)
- Baramulti Sukses Sarana (BSSR)
- Harum Energy (HRUM)
- Mitrabara Adiperdana (MBAP)
- Adaro Energy (ADRO)
- Bumi Resources (BUMI)
- Samindo Resources (MYOH)
- United Tractors (UNTR)
- Berau Coal
