CHAPTER 1: Elemental Sustainability and the Importance of Scarce Element Recovery

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.¹  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.²  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.^3,4  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.^5,6  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.⁷  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.⁸  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.⁹  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.⁹ 

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.^10,11  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.¹⁰  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.¹³  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.¹²  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.

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.⁹  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.^9,13–19  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”.⁹ 

The National Research Council of the National Academies (NRCNA, USA) developed a two‐dimensional “criticality matrix” as a graphical representation of critical elements.¹⁷  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.¹⁷  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.

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.⁹  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.⁹  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.²¹  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.⁹ 

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.²²  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).⁹  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.²²  In 2009, a diplomatic dispute between China and Japan resulted in a temporary halt in REE exports to Japan.⁹  Such restrictions could be devastating for the Japanese economy which currently consumes 30% of the world’s annual rare metal production.²³  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.^9,15,22 

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.¹⁴ 

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.²⁴  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.^25,26  A 2003 UN Security Council report highlighted that a significant amount of ore was being smuggled out of the country by militia.^27,28  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.²⁵ 

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.⁹  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.^1,9  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.²⁹  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).²⁹  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.^29–33  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.

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).³⁴  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.^35,36  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.^1,12  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.

The critical element markets are vulnerable to production concentration and price volatility. There has been a significant drop in the production and sale of tantalum from African mines since the dramatic spike in the price of this metal in the year 2000.³⁷  This unprecedented spike in the market was a result of supply fears caused by nervous dealers scrambling to lock themselves into long‐term contracts at dramatically high market prices.³⁷  In September 2001 the US House of Representatives passed a resolution banning the purchase of tantalum from the war ravaged Democratic Republic of Congo, further fuelling the frenzy to secure future delivery from legitimate sources.²⁵  Since 2010 similar panic buying and increases on the markets have been observed in response to growing concerns over security of supply.

There is a significant negative societal impact which is associated with the increased global demand and supply of critical elements. This issue will need to be addressed on a global scale. The development of effective recycling methods, strategies for greater materials efficiency in manufacturing and the pursuit of new substitute raw materials from technological innovations are imperative to meet these challenges. In order to mitigate the risk of supply and become more self‐reliant in terms of elements, developed nations should look at their waste as a valuable resource ready for exploitation.

A great concern of the government bodies of developed nations investigating critical elements is about the impact of the scarcity on emerging energy technology.^9,20  Rare earth metals are extensively used in the modern solution to energy and pollution woes such as in the batteries of electric cars or energy efficient light bulbs (Table 1.3). Their use also extends to applications in photovoltaic cells, generators (i.e. for wind, tidal and wave turbines) and catalytic converters for the abatement of emissions from automobile exhausts.^9,20  Other critical elements are also used extensively in consumer goods, typically electronics (LCDs, hard drives of computers, lasers etc.), while their application has also spread to specialist alloys for engineering (e.g. platinum aluminde for aircraft turbines), resistant glass, ceramics, direct medical applications (e.g. cancer treatment with cis‐platin derivatives) and extensively as catalysts in the chemical and related industries.^9,20  In 2008 alone, 1300 million new mobile phones produced worldwide, consumed approximately 12 000 tons of copper, 4900 tons of cobalt, 325 tons of silver, 31 tons of gold and 12 tons of palladium.³⁹  300 million new personal computers and laptops were produced which consumed 150 000 tons of copper, 9100 tons of cobalt (Li‐ion batteries for laptops), 300 tons of silver, 66 tons of gold and 24 tons of palladium.³⁹  Seemingly the types and volumes of applications where critical metals are used are ever increasing and thus demands for these elements are also rising.

Many of the critical elements mentioned above are used as catalysts (e.g. PGMs, Co, Ce, Ge, Sb and In) and reagents (Li) used in the chemical and related industries. Therefore their scarcity would also have an impact on a plethora of chemical transformations used in the generation of pharmaceuticals, plastics, fuels, home and personal care products and packaging. A variety of these transformations have been regarded as green (e.g. the atom economy of metathesis) and even applied in the valorisation of waste, a key move towards a more sustainable chemical industry.⁴⁰  Statistical data from the Green Chemistry Journal (RSC) and ChemSusChem (Wiley) show that since their inception in 2003 and 2008, respectively, there have been numerous articles demonstrating the use of some of these critical metals, typically as catalysts (Figure 1.5).

However, one of the principles of green chemistry is that reagents are renewable and it is a disappointing oversight that many researchers do not carry this through to consideration of the renewability of their catalysts. For elements that have high criticality there are major concerns about both their high consumption and long‐term supply. As such, high criticality elements can also be viewed as elements with major sustainability concerns (our non‐renewable use of them now would prevent future generations having access to these metals). It could therefore be further argued that any transformation, even of bio‐derived chemicals, is no longer sustainable if critical elements have been used for catalysis. A requirement for any process claiming to form a sustainable product should be that all aspects and auxiliaries of that process are themselves sustainable and this would therefore require the development of truly sustainable reagents, solvents and, of course, sustainable catalysts. For critical elements to be used as truly sustainable catalysts their recovery, ideally total, after use followed by subsequent reuse is required, thus progressing to an ideal circular economy.

An alternative to the total recovery of critical metals from catalytic processes is to seek replacements for active catalysts, either via the use of non‐metallic catalysts (e.g. enzymes) or by using metals with less criticality. Many critical elements used in catalysis today, such as palladium, ruthenium and cerium, have replaced lesser or non‐critical elements from earlier versions of catalytic processes. One such example of this is the metathesis reaction (Figure 1.6), including olefin cross‐metathesis (CM), ring‐closing metathesis (RCM) and ring‐opening metathesis polymerisation (ROMP).⁴¹ 

Metathesis has long been touted as a key “green” reaction owing to its versatility, atom efficiency (if all products are useful) and applicability to emerging and established bio‐derived commodity chemicals (i.e. unsaturated fatty acids, cinnamic acid and fumaric acid).^42–44  Metathesis is also well known for the 2005 Nobel Prize won by Chauvin, Grubbs and Shrock, although key breakthroughs in this reaction protocol date back several decades earlier.⁴⁵  Modern understanding and application of olefin cross‐metathesis is dominated by ruthenium catalysts such as those developed by Grubbs and Hoyveda. From the discussions above it is evident that ruthenium is an element of global critical importance, with major issues in supply security, recyclability and high usage in current and emerging technologies. Clearly for olefin cross‐metathesis to play a role in sustainable catalysis, alternatives to the currently preferred Ru catalysts must be found. Early research into olefin cross‐metathesis made use of tungsten and molybdenum carbene catalysts with these often being found to have higher activity then Ru equivalents but with poor water, air and functional group tolerance.^46,47  Although W and Mo are highlighted as critical metals in some reports, they are not as unanimously perceived as critical in the way that Ru is (Table 1.1). At first glance it may then seem that W and Mo could be exploited as candidates for more sustainable metathesis catalysts, especially when considering the extensive reserves of both elements compared to Ru. However, there are major issues with both W and Mo, which are:

• Recycling rates for W are only comparable to Ru (10–25%), Mo is a little better (25–50%), although this is predominately via recycling and reuse of steel alloys containing Mo.¹⁰ 

• Both W and Mo are considered by the BGS to have greater supply risk than Ru (Table 1.2).

• Mo is currently primarily produced as a hitch‐hiker in Cu production (Table 1.2) and therefore its price and availability are linked directly to the demand for another element.

• Although W is primarily produced from mines that focus on it as an attractor metal (i.e. not a hitch‐hiker), consumption of currently known reserves will be exhausted in less than 50 years if current demand is maintained (Figure 1.1).

• Reserves of W and Mo are 3.2 and 11 million tonnes respectively,¹⁰  this being considerably higher than the 5000 tons for Ru,⁴⁸  though rates of use of W and Mo are significantly higher.

Various metals other than Ru, W and Mo have also been utilised as metathesis catalysts (Figure 1.7); these include Re, Os, Ir, Ti, Cr, Co, Nb, Rh and Ta.⁴⁵  Unfortunately, all these elements have been cited nationally or even internationally as being critical (Table 1.1). When taking each of these metals individually, as for the Mo and W catalysts above, major issues around supply risk, recycling or global reserves can be found. Some, such as Cr, also suffer from concerns regarding toxicity and are thus unviable as a result of international legislation such as REACH.⁴⁹  At first glance Ti seems to offer a glimmer of hope. Although Ti was highlighted by two national reports as being critical,^18,19  it has high recycling rates (91%),⁵⁰  has global mineral reserves totalling more than 2 billion tonnes and is not regarded as having a supply risk (Table 1.1).⁵¹  To date, the utilisation of Ti catalysts for metathesis seems to be limited to ROMPs and occasional examples of cross‐metathesis, such as those using Tebbe’s reagent (Figure 1.7), but reagents typically need to be devoid of carbonyls to prevent Wittig type methenylations (the original purpose for Tebbe’s reagent) and quantitative amounts of the titanium “catalyst” are required.^52–54 

Perhaps the answer to sustainable metathesis catalysts lies in the development of ligands for Ti centred catalysts that both improve the air and moisture stabilities of the catalyst and also prevent carbonyl methenylations, while still promoting the desired cross‐metathesis. Above all, the example of metathesis highlights how the approach of replacing an efficient but critical metal, such as Ru, with others that are less critical is not always feasible. It is certainly not simple and therefore methods of more effective metal recovery and reuse are a must. Concerns about the application of critical metals in catalysis should not only focus on sourcing, but also on using them (or other metals) in a more sustainable manner.

Sustainable and green methods for the recovery of elements are imperative. Hyperaccumulation of metals by plants has become a significant research focus in recent years owing the significant potential for metal extraction by phytoremediation. Hyperaccumulation refers to the accumulation of elements at 100 times greater concentrations (normally toxic to plants) than typically observed for traditional plants growing in the same location (hyperaccumulation is discussed in detail in Chapter 5).⁵⁵  These plants can be harvested, combusted (thus producing energy) and then smelted to enable production of pure metal.⁵⁶ 

Phytoremediation opens up the opportunity not only to restore degraded land and generate energy by burning the biomass but also allows elements to be recovered from low grade ores, contaminated soils, mine tailings and wastewaters that would typically be uneconomic to exploit. Plants need to be able to tolerate elements, be capable of rapid growth and have high biomass yields. At present, no plant is known that has all of the above attributes.⁵⁷  Genetic modification could hold the key to opening up this technology in the future, but this must be done in way that would not introduce negative ecological impacts. Recovery of waste metals via hyperaccumulation (bioremediation) and subsequent re‐use as catalysts or catalyst precursors is of growing interest. This is of great potential value in a sustainability and critical metal circular economy sense.^58,59  For example it has been demonstrated that Friedel–Craft alkylation and acylation Lewis acid catalysts can be prepared from extracts of metal hyperaccumulating plants.⁶⁰ 

Harnessing the ability of bacteria to solubilise elements selectively could become a major new technology owing to industrial interest focused on copper, nickel, cobalt, zinc, gold and silver.⁶¹  This bioleaching process has been successfully used to treat over 160 000 tonnes of copper ore daily.⁶²  Bioleaching has also been studied extensively for the recovery of Pd from waste streams, with some bacterium (Desulfovibrio desulfuricans and Shewanella oneidensis) found to generate Pd(0) nano‐particles with a narrow size distribution, located on the outer parts of the cell and adequate cell adherence for use in catalysis.⁶³  However, these bacteria suffer from Cu(II) inhibition which is a major issue for Pd recovery from printed circuit boards as Cu(II) often makes up >25 wt% of the solid in this waste leachate.

A potential method for metal recovery and catalyst preparation from wastewaters can be the use of biosorbents. Polysaccharides are ideal for such processes, as they interact with metal ions by electrostatic interactions, ion exchange or to form complexes with metal ions.⁶⁴  It is likely that bioremediation processing will result in mixed‐metal recovery as the location where bioremediation occurs contains waste with an array of mixed metallic ions. This will either require separation of the various metals, or alternatively may result in the growth of catalysis via mixed metals.

There is increasing interest in the field of bimetallic (or alloy) catalysts, as this often accesses improved efficiency compared to monometallic catalysts.⁶⁵  The synergistic effect of metal combinations could offer vast potential for the future of catalyst design. A greater understanding of bimetallic synergistic effects and mixing patterns will ultimately lead to greater possibilities for predicting suitable applications for metals derived from mixed‐metal wastes and alloys of base or low criticality metals may give more active catalyst than those currently derived from pure high critical elements.

Ultimately we have to seek 100% recovery of critical metals from catalytic processes and with this also understand better the synergistic effects of mixed metals from waste, whilst also maximising the metals catalytic activity. In the mid‐term, finding non‐critical metals, such as Fe, for a wider range of catalytic processes is a possibility, but the topics addressed in this book focus on the ideal scenario whereby even scarce critical metals can be used as sustainably catalysts long into the future if total recovery from anthropogenic cycles is guaranteed.

As we disperse materials throughout the environment there are several potential new sources of elemental recovery including municipal and industrial solid waste, electrical and electronic products (WEEE‐waste), landfill sites, low grade ores, mine tailings and aqueous wastewaters.¹  These offer reductions in hazardous waste and supply an alternative to virgin resources.

The amount of waste electrical and electronic equipment (WEEE) produced globally is increasing rapidly. Global WEEE generation annually is estimated to be 50 million tonnes per year.⁶⁶  This waste is a significant potential resource for the supply of scarce and valuable metals. However, WEEE also frequently contains toxic and hazardous materials and therefore requires careful or special treatment. Globally, only a small portion of well separated e‐waste is treated; two good examples of industrial practice are at Umicore in Belgium and New Boliden in Sweden.^39,67  Illegal trading of e‐waste from the western world to developing countries causes serious environmental problems and a high risk to human health. The effective recycling and refining of WEEE has become a global issue. Chapter 8 highlights economic, technological, social and environmental concerns relating to WEEE recovery.

The annual estimated worldwide generation of municipal solid waste (MSW) is 1636 million tonnes and rising.^68,69  As such, MSW offers a great potential for the recovery of elements.⁶⁹  There are further discussions on the potential for recovery from MSW in Chapter 9.

Ultramafic soils from weathered mineral landscapes are relatively high in nickel, chromium, manganese, cobalt, titanium, iron and other metals, as are industrially contaminated soils.⁵⁶  Not only is there a growth in saving energy by recycling elements but also new sources of recovery must be sought, including that of roadside dust as a source of PGM (up to 1.5 ppm of platinum) from catalytic converter emissions.^70,71 

Mining processes can utilise aqueous/organic‐based metal extraction systems which generate large volumes of wastewater containing low concentrations of dissolved metals.⁷²  At source recovery of valuable and environmentally hazardous elements can prevent damage to local ecosystems. The nuclear industry, electroplating and metal processing operations also produce wastewaters containing Cr, Ni, Cd, Zn, Cu, U and precious metals.⁷³  Exploitation of these new sources of elements at low concentrations could lead to further recovery and enhance security of supply but as previously discussed it is of significant importance that green and sustainable recovery methods are employed.

Reuse, recovery and recycling are an answer to avoiding a future resource deficit and improving the sustainability of all elements. The recovery and recycling of metals from wastes and end‐of‐life products is not new. The recovery and recycling of metals from waste streams can be an efficient, economical and environmentally beneficial route to valuable materials. In fact in recent years, significant quantities of steel,⁷⁴  aluminium,^75,76  zinc,⁷⁷  copper⁷⁸  and lead,⁷⁹  supplied to the market have been produced from secondary resources. Significant energy saving can be made through the recycling of metals compared to processing ores to generate these metals.^80,81  Steel recycling is carried out alongside primary steelmaking using basic oxygen furnace (BOF) or electric arc furnace (EAF) steelmaking processes. These processes save 74% energy, 90% of virgin materials, reduce 86% of air pollution, 40% of water use, 76% of water pollution, 97% of mining waste and a considerable amount of consumer wastes generated, when compared with production from virgin materials.⁸²  However, these metals are still not recovered to their maximal extent and such strategies should be adopted for all elements (metals). Development of efficient physical and metallurgical recovery technologies is vital to ensure that the ideal of 100% recovery is achieved.

On the other hand, there is little or no recycling of many of the elements highlighted in the numerous national and international reports that are viewed as critical, even those that are required for the emergence of renewable energy sources (Figure 1.8). Figure 1.8, prepared from data given in the UNEP 2011 report, shows a mixed range of recycling rates of the critical elements.⁵⁰  As stated in the report, numerous difficulties in data collection were encountered and as such the figures given are predominately from the years 2000–2005 and thus are likely to ignore the ripple effect of recent supply and demand concerns for many of these elements. Perceived error margins in the data also mean that UNEP only felt comfortable quoting ranges rather than exact figures. Elements not included in the UNEP report, such as Rb and Cs were added using data from the relevant USGS reports.^10,50  The UNEP report also included additional elements not presented in Figure 1.8 as only critical elements from the national and international reports (Figure 1.1) were taken as relevant for this discussion.^9,13–18  The range of rates presented in Figure 1.8 are the end‐of‐life recycling rates (EOL‐RR), being the percentage of the metal, either in pure or alloy form, that is recovered after use and entered into the recycling chain.⁵⁰ 

As with any complex flow system, the weakest link in the chain is always the controlling factor in the overall efficiency of that process and in the EOL‐RR process this is predominately the collection of waste metal directly after use. Pt and Pd already have well established recycling routes as their use is dominated by the automobile catalyst application. Their recovery after use is well understood and collection of these is inherent in the current processes for dealing with end‐of‐life catalytic convertors.⁵⁰  In contrast to base metals, recovery of scarce and precious metals is much more difficult owing to their very low concentrations and dispersion in a wide range of waste streams. Collection and concentration are the first and most important steps. The current industrial practice is to capture precious metals with heavy metals such as copper and lead. Smelting of copper and lead with e‐wastes brings PGMs into the base metal stream. Electrorefining transports PGMs to the anode slime. Further leaching, roasting (a high temperature pyrometallurgical conversion process) and electrowinning processes enrich the anode slime PGMs (or precious metals). Ion exchange and adsorption are broadly used in precious metals recovery from solutions.⁸²  Anthropospheric losses of PGM are discussed in Chapter 7, which maps the flow of metals through the element’s lifecycle.

The term “rare” in REE is somewhat misleading as these have an equal abundance in the earth’s crust to that of copper (50 ppm) and lead.⁸³  REE are scarcely dispersed in wastes and are not widely recycled, further strategies for REE recovery are discussed in Chapter 6. Efficient collection, separation and recovery technologies are not yet available, but efforts to develop the processes for recovery of neodymium and dysprosium from REE magnet powder from hard disc drives are being made.⁸⁴  The mass of REE in a single product is usually very low and is mostly embedded in complex assemblies combined with other elements, which complicates recycling. Not only technology but also economic factors play an important role in the recycling and recovery of REE. In recovery, if the REE are combined with precious metals, this creates an economic recycling incentive, which can lead to recovery of the REE by‐products. If precious metals are absent, the economic attraction of REE will not exist. Significant advances in the recovery and sustainability of such elements may be made if products are designed for disassembly or component reuse.

Some metals, such as Mn and Mo have decent levels of recycling as a result of their recovery and recycling via alloys, while other current applications, including catalysis, may pose significant technological difficulties to be overcome to improve EOL‐RRs further.⁵⁰  Although ELO‐RRs are below 1% for 35 of our highlighted critical elements, this shows that there is great potential in the future for reducing dependence on virgin resources if these rates can increased. In many cases increased rates of recycling would also be highly desirable to counteract current fears about supply security (Table 1.1 and 1.2).

At the end of their life products containing these elements, such as mobile phones, televisions and computers, are ending up in landfills or being incinerated and the elements are being lost. Japan has already highlighted that waste resources will become increasingly important for its economy as concerns over securing supplies increase.²³  Analyses of the ash from waste incinerators in Japan has revealed the composition to include zinc, lead, copper, silver, indium, palladium, nickel, chromium, tantalum, vanadium, zirconium, potassium, calcium, antimony and sodium. The sources of many of these scarce elements in incineration residues are expected to be WEEE or flame retardant materials in the case of antimony.^85,86  In developed countries, it is estimated that WEEE can contribute 8% by volume of MSW.⁶⁰  New approachs are being tried to recover all elements and to re‐use them in close‐looped systems by designing the direct recycling of elements through intelligently designed disassembly of materials at their end of life. These measures should limit the demand for new supplies of elements and increase the lifetime of our reserves infinitesimally.

In the example shown in Figure 1.9, increased rates of recycling would move towards a circular economy and would reduce reliance on hitch‐hiker element production. It should also be noted that following the discussion above regarding the difficulty of increasing critical element production when that element is predominately produced as a hitch‐hiker, recycling in a circular economy is the only viable way to deal with further increases in demand for that element. The concept of the circular economy is discussed in greater detail in Chapter 9.

It is evident from all of the above discussions that for these critical elements to be used in a sustainable manner, recycling rates must increase and this includes the recovery of these metals from wastes such as those in landfill sites and mine tailings, a true resource for the future. Included in this book is an in‐depth assessment of current greener approaches to critical metal recovery along with future prospects and ideas about where research should be directed in the coming decades. The concept of elemental sustainability or being sustainable for all elements, not just those regarded as being critical, is likely to become increasingly important in the future. Now is the time for producers and users alike to progress to circular economies and embrace elemental recovery and sustainability.