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Element Recovery and Sustainability
By Andrew J. Hunt
The Royal Society of Chemistry Copyright © 2013 The Royal Society of Chemistry
All rights reserved.
Elemental Sustainability and the Importance of Scarce Element Recovery
ANDREW J. HUNT, THOMAS J. FARMER AND JAMES H. CLARK
Green Chemistry Centre of Excellence, Department of Chemistry, The University of York, Heslington, York, YO10 5DD, UK
1.1 The Issue of Elemental Sustainability
Important topics including climate change and peak oil have been making headlines with increasing intensity over the past decade. The subject of green, clean sustainable energy, fuels and chemicals is an important topic of focus for the scientific community and is a fundamental component of the long term wellbeing of planet Earth. The necessity to be carbon neutral is well known and as a consequence solutions are being sought to lessen our dependence on fossil resources. New legislation and a growing movement towards the development of "low carbon technologies" are driving this technological change towards a sustainable carbon future. Unfortunately there is a serious problem, as many "low carbon technologies" including wind turbines, electric cars, energy saving light bulbs, fuel cells and catalytic converters, require rare and precious metals for their production and use. Traditional supplies of such elements are "running out", thus creating other challenges in the form of a resource deficit. In fact, such elements are not running out or being destroyed but are being quickly dispersed throughout our human environment or what has been referred to as the technosphere. This makes recapture of these unique elements both highly problematic and costly. Such challenges must be tackled through the development of multidisciplinary partnerships and a sustainable holistic approach to the extraction, processing, use and recovery should be adopted for all elements within the periodic table. The only exception to this would be radioactive materials which cannot be recovered in the initial state once decay has occurred. As such, it is essential to develop new sustainable routes and strategies for the recovery and reuse of these elements.
Elemental sustainability is a concept whereby the sustainability of each element in the periodic table is guaranteed. For an element to be sustainable, its use by this current generation should not impair or restrict future generations from also utilising that same element. Within these constraints, it is also important to consider the triple bottom line of sustainability, that is, the environmental, societal and economic effects of these elements and their use. All elements within the Earth's crust are available in finite amounts, although some, like aluminium, iron and silicon, are available in many orders of magnitude higher abundances than others, like platinum, silver and selenium. Each element in the periodic table also has varying levels of demand. This demand varies as new technological advances come on-stream and others become obsolete. Rising demand for some elements is caused by both developed and developing nations which require advanced materials for consumer goods products (e.g. mobile phones and flat screen televisions) and the level of demand for each element often varies from nation to nation and region to region. As the world's population continues to rise, the growing middle classes will continue to demand a higher standard of living, fuelling a need for consumer goods and cleaner energy. This combination of known availability of certain elements and their current level of demand has caused some to have been flagged up with concern. Although we should endeavour to use all elements in the periodic table sustainably, those whose current rates of use risk depleting known reserves in the near future should be of greatest focus in the short to mid-term. Reserves are known tonnages of metals that can be economically and legally extracted using existing technologies. These reserves represent only a small proportion of the element compared to the significant abundance in the Earth's crust, while the resources of elements are represented in the locations or concentrations of that element or ore that have reasonable prospects of being recovered in the future.
As shown in Figure 1.1 numerous elements fall into the range where current known reserves will be consumed in less than 50 years if current rates of extraction are retained. Some of these are at high risk as a result of exceptionally low crustal abundances and these include the precious metals where the annual production of the majority is below 200 tonnes. It is not only elements with low crustal abundances and small annual productions that are of concern as known reserves of both strontium (Sr) and manganese (Mn)would be consumed in less than 50 years at current annual production levels of 380 000 and 16 000 tonnes, respectively. However, both the consumption and reserves of these finite elements are continually changing in response to movements in markets, discovery of new mineral deposits, development of new applications, advances in extraction technologies and improvements in the efficiency of use, recovery and recycling. As such, care must be taken when using the rate of consumption versus known reserves as a metric for the criticality of elements (Figure 1.1). Current known reserves of indium, an element which is vital for the production of display devices, solar cells and semiconductors, may run out in as little as 13 years at the current rate of consumption, thus fuelling concerns over the security of supply. If investment is made into developing technologies for recovery at end-of-life, in addition to using the remaining reserves more efficiently, it is hoped that supplies of this element will not be depleted and thus by utilising them in a sustainable manner reserves will be left for future generations.
1.2 What are Critical Elements?
An element that is classed as critical can be defined in various ways depending on the purpose of the assessment (e.g. for a specific application such as mobile phones) and the different needs of the individual country or territory. Many assessments of critical elements have been made, all of which apply different criteria and as such generate a diverse list of critical elements (Table 1.1), although in all instances there is an appreciation that current and projected demands for that element will result in rapid depletion of known reserves. Often elements that are considered to be critical in one territory, nation or company may be omitted from the list of another. Assessments of critical elements have been generated by the European Union, United Kingdom, United States of America, Japan and a global assessment was made by the United Nations. Table 1.1 demonstrates the wide variety of elements that have been classed as "critical" in these international assessments. In our discussions, elements that are found on three or more of these international assessments are considered as critical elements of global importance.
A significant number of both the national and international reports that discuss elements of concern use terms such as "strategic" or "critical" for the raw materials. It is important to differentiate strategic elements from those that are critical. Elements of "strategic" importance to a nation are those vital for defence or military applications, whilst elements with significant international supply risk issues, which if restricted could harm a nation's economy, are considered to be "critical".
The National Research Council of the National Academies (NRCNA, USA) developed a two-dimensional "criticality matrix" as a graphical representation of critical elements. Elements can be added to such a matrix once the impact of supply restrictions and the supply risk of a mineral have been assessed. This study highlighted elements including platinum group metals (PGM), rare earth elements (REE) and indium, manganese and niobium as being most critical as they represent elements with both high supply risks and high impact if the supply of that element is impaired. For a true assessment of elemental sustainability, the environmental impact of an element's extraction and use should also be taken into account. Figure 1.2 demonstrates this in a graphical illustration giving a three-dimensional representation of elemental sustainability which inherently includes criticality. As criticality increases so the sustainability of the element decreases.
1.3 Why is there a Growing Security of Supply Issue?
In many cases developing economies have significantly greater potential reserves and production capacity of critical elements than nations with established economies (Table 1.2). Frequently these developing economies are adopting aggressive trade restrictions, thereby obtaining exclusive domestic use of their elemental reserves. These strategies include the systematic tightening of exports through the application of taxation, implementation of strict quotas, subsidies, price-fixing or restrictive investment, distortion of international trade, elevated export duties and investment policies which are frequently at odds with international trade agreements. The combination of export restrictions, political factors and the manipulation of markets has resulted in REE supply shortages and significant price increases. Consumption patterns, materials efficiency and applications all change over time, thus demand for these raw materials is also in a state of flux. The ability to respond quickly to such changes can restore balance to markets. The technical and economic obstacles of increasing production (by opening new mines) are considerable and take many years to achieve. To alleviate supply restriction issues, a number of new REE mines are due to be opened in South Africa, Kazakhstan, Malaysia, Burma and Canada. In cases where the production of minerals or elements is limited to a small number of countries, these producers can gain political or commercial advantages by influencing supplies and markets. In some cases these aggressive trading strategies have been used to provide a competitive advantage for domestic industries over their international competitors.
Elements such as antimony, gallium, germanium, indium, magnesium, REE and tungsten now have a high supply risk (Table 1.2). In 2010, China controlled 95% of the world's supply of rare earth metals. When one nation has a monopoly in terms of production of an element it results in issues relating to the longer term security of supply (Table 1.2). Countries whose manufacturing or technology base depends on imported critical elements are beginning to look for alternative sources, whilst other countries and companies that are dependent on rare earths elements are racing to secure control of mineral rights in Australia, South Africa and Greenland. In 2009, a diplomatic dispute between China and Japan resulted in a temporary halt in REE exports to Japan. Such restrictions could be devastating for the Japanese economy which currently consumes 30% of the world's annual rare metal production. Similar risks are also true for PGM, where South Africa generates 89% of the world's production, 40% of the world's cobalt is from the Democratic Republic of Congo (DRC) and 90% of the niobium is produced in Brazil.
By using the list of critical elements of global importance we can surmise that in a global sense all of the elements are of concern and could be significant supply risks in the coming decades.
Many of the critical elements are located in parts of the world that are often viewed as politically unstable (Figure 1.3). Niobium and tantalum are extracted from tantalite ore, of which significant quantities come from the Democratic Republic of Congo. In recent years, the illegal mining of these ores in the Democratic Republic of Congo has significantly contributed to instability and aided in financing conflict in the region. A 2003 UN Security Council report highlighted that a significant amount of ore was being smuggled out of the country by militia. Such illegal uncontrolled mining can have serious environmental and social impacts, whilst also damaging local wildlife. Eastern mountain gorilla and elephant populations in the Congo have been severely reduced through hunting by miners and militia.
A key concern regarding the availability of these elements in the future is their abundance and ease of accessibility. Currently, the majority of critical elements are mined and extracted from primary ore in highly energy intensive processes that require a sufficient concentration of the element of interest. As already indicated, the geological abundance of most mineral resources is potentially high, however, the concentration of elements within the ores compared to industrial or base metals (such as iron) can be very low. The exploitation of these lower grade ores and the challenges of having to mine in geographically and politically hostile locations can have a significant bearing on the cost and could have a potentially negative impact on the surrounding environment. This is compounded by the fact that the production volumes of elements of critical global importance are much smaller than industrial metals and frequently require difficult extractive metallurgy. Mining will continue to contribute a significant proportion of critical element supply in the future. Consequently, improving mineral detection in order to locate new deposits and focussed investment on research into sustainable mining are of vital importance to the long term security of supply of these elements.
A holistic approach to elemental use must be adopted throughout the life cycle, including processing, manufacture, recycling and substitution. A significant impact on future availability of certain metals will be achieved if more efficient processing methods are developed. These will improve the yields of elements that are mined as "by-products" of or "hitchhikers" on primary or "attractor" metal deposits. The Institut Européen d'Administration des Affaires (INSEAD) report (2012) highlights the current scenario whereby many of these critical elements are predominately produced as a by-product of mining and processing of base "attractor" metals (e.g. Zn, Cu and Pt) and as such are dubbed "hitch-hiker elements" (e.g. In, Co and Ru). This scenario could have major implications for future increases in demand for the specific critical element. Either the rate of mining of the attractor metal would have to increase or the rate of recovery of the critical metal from the base metal ore would have to improve or new resources of the critical metal, independent of a base metal, would have to be found. The first option above is unlikely to make economic sense unless demand for the base metal also increases, while the latter two options require technological advances and increased initial capital expenditure. The only other viable alternative is for further technological advances to be implemented that result in significant improvements in the rates of critical hitch-hiker metal recycling. Table 1.2 demonstrates the percentage of current production via hitch-hiker recovery and from what base metals these are predominately derived from the previously highlighted list of globally significant critical elements. More efficient use of resources, recycling and also substitution with alloys or more abundant elements, can be very effective in alleviating pressure on existing diminishing reserves.
1.3.1 Trends in Elements
You have only to study the recent trends in the price and production of many elements to realise that the consumption of reserves is increasing at an alarming rate (Figure 1.4). Markets for critical elements are highly volatile and are frequently influenced by supply risk. This can be observed in the price of REE, which has risen dramatically following growing concerns over security of supply from China (Figure 1.4). Production and consumption rates of many critical elements such as gallium are also rising at a dramatic rate from a relatively low base level (Figure 1.4).
The price of elements can also be influenced by a rapidly growing demand for use in new applications. Indium prices rose a staggering 800% in 6 years from approximately US$85/kg in 2002 to US$685/kg in early 2008 (Figure 1.4), paralleling a growth in large screen televisions sales. As many of these elements are "hitch-hikers" it means that increases in production cannot be easily achieved and if demand for attractor elements decreases, so too will the production of the rare by-products. This has resulted in predictions that the demand for some elements will soon outstrip supply. The key question is what will happen to the prices next and how will demand for all these metals that underpin our technologically advanced lifestyles be met sustainably in the future.
Excerpted from Element Recovery and Sustainability by Andrew J. Hunt. Copyright © 2013 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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