By-product Metals Research Articles

Gold occurrence in the footwall of the Lappberget Deposit, Garpenberg Mine, Sweden: Implications for recovery efficiency

By-product metals have a significant potential to bring additional economic benefits to mines. However, a detailed characterization of their distribution is generally required to fulfill this potential and should preferably be integrated into a geometallurgical assessment. This contribution presents a detailed mineralogical and textural investigation of gold-bearing phases at the footwall of the Zn–Pb–Ag–(Cu–Au) Lappberget Deposit, Garpenberg Mine, Sweden, using optical microscopy, scanning electron microscope with energy dispersive spectroscopy (SEM-EDS), electron probe microanalysis (EPMA), laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS), and bulk chemical analysis applied to drill core and Knelson concentrator samples. Gold is a by-product at the Garpenberg mine, but it is unclear how the mineralogy, occurrence, and distribution of gold-bearing phases impact on gold recoveries during mineral processing. Our results show that Au-dominant electrum is the most abundant gold-bearing phase in the footwall of the Lappberget deposit, occurring strongly associated to sulfides in a variety of textures and grain sizes. Electrum grains commonly occur within sulfide borders, as inclusions, intergrowth and overgrowths of chalcopyrite, pyrite, galena, sphalerite, and pyrrhotite. Gangue minerals may also contain disseminated electrum and inclusions. Electrum grain sizes range from ∼5 µm to 300 µm, predominantly below 100 µm. The potential of sulfide lattice-bound invisible gold in the form of solid-solution gold and colloidal gold was also investigated, showing Au depletion within the analyzed sulfide carriers. The analysis of the concentrate samples from the Knelson gravity concentrator showed 584 and 431 ppm of gold content. High degree of liberation is observed among the gold-bearing phases in the concentrate, and gold recovery is highest among fractions coarser than 106 µm mesh. Pyrite and galena are the most abundant minerals in the concentrate samples. The gold-bearing phases were categorized based on its mineralogy, texture, grain size, and association and their influence on gold processing, especially textures and grain size, which implicates its liberation in milling and recovery by the gravity separator.

Dynamic spillover of upstream primary metals and by-product metals market and its impact from the downstream new energy vehicles market

Dynamic spillover of upstream primary metals and by-product metals market and its impact from the downstream new energy vehicles market

Tracking the global anthropogenic gallium cycle during 2000–2020: A trade-linked multiregional material flow analysis

Byproduct metals are essential to global low carbon transition since they are irreplaceable in modern renewable energy technologies. Gallium (Ga) is classified as one critical byproduct metal due to its extensive use in electronic applications and low carbon technologies, as well as its limited resource endowment. It is urgent to uncover the global and regional Ga stocks and flows so that the potential supply risks can be mitigated. This study maps the global and regional Ga cycles for the period of 2000–2020 by employing a trade-linked multiregional material flow analysis (MFA) method. Our results show that 79% of the global Ga co-mined from bauxite ended up in red mud or entered the aluminum cycle as an impurity, indicating a significant recycling potential. Different involved regions have different but complementary roles in the global Ga supply chain. China dominates the global primary Ga production, accounting for 97% of the global total in 2020. Japan and the United States are key players in high-purity Ga refining and rely on Ga to support their electronic devices manufacturing. Unfortunately, Ga recycling practices are still not occurring due to the low Ga concentrations in major applications. Since the global demand for Ga will continue to grow in the near future, it is urgent to initiate collaborative efforts so that Ga recycling can be enhanced. These efforts are critical to ensure the sustainable Ga supply and facilitate the global transition toward low carbon development.

Silver, cobalt and nickel mineralogy and geochemistry of shale ore in the sediment-hosted stratiform Nowa Sól copper–silver deposit, SW Poland

The Nowa Sól deposit is a part of the newly discovered Northern Copper Belt and is situated some 30 km NW of the Lubin–Sieroszowice mining district (the so-called New Copper District) in SW Poland. The ore horizon spans across the upper part of the Lower Permian (Rotliegend) terrestrial redbeds and the lower part of the Upper Permian (Zechstein) marine rocks. It comprises three lithotypes: sandstone, shale and carbonate. The high-grade shale ore has polymetallic characteristics and is a crucial host for by-product metals such as Ag, Co and Ni (studied in this paper), but also Mo, V and Re. The results of bulk-rock and electron microprobe as well as mineralogical (optical and scanning electron microscope) data of the mineralized, organic-rich shale ore from the Nowa Sól deposit are presented. This thin stratigraphic horizon, ranging from 0.06 to 0.59 m, shows notable concentrations of critical metals, including on average 15.9 wt% Cu, 715 grams per tonne (g t -1 ) Ag, 318 g t -1 Co and 345 g t -1 Ni. It constitutes less than 10% of the total ore mass, but accounts for 36% of the Ag, 40% of the Ni and 42% of the Co found within the deposit. The ore sulfides in the mineralized shale in the Nowa Sól deposit include chalcocite, djurleite and bornite, accompanied by digenite, covellite, tennantite, galena, sphalerite and pyrite. The Ag content within the Cu sulfides exhibits a linear decrease: chalcocite > djurleite > bornite. Three primary Ag minerals are identified within the shale ore, namely native Ag, Ag amalgam and stromeyerite. Two types of Ag amalgam are observed: Hg-rich and Hg-poor. Cobaltite and gersdorffite represent the primary Co and Ni minerals, occurring as micrometre-sized inclusions within chalcocite and djurleite. Textural observations suggest that the Ag, Co and Ni mineralization postdates the major phase of Cu sulfide precipitation. It is shown that in the Nowa Sól deposit, the Kupferschiefer horizon has acted as a geochemical barrier for the above-mentioned metals during protracted time, from early syndepositional to late epigenetic stage of basin evolution. Supplementary material: The supplementary material contains the results of the electron microprobe analyses and the specific experimental conditions employed for these analyses – available at https://doi.org/10.6084/m9.figshare.c.6873631

Material efficiency strategies across the industrial chain to secure indium availability for global carbon neutrality

A global energy transition toward carbon neutrality system requires increased critical metals, and the availability of critical byproduct metals raises concerns due to their dependence on host metals. To ensure the supply security of critical byproduct metals, material efficiency (ME) strategies are needed. Taking indium as an example, this paper explores the indium availability for global energy transition goals, and then illustrates the effects of ME strategies on securing indium availability throughout the whole industry chain. The system dynamics model serves to understand the joint production mechanism of zinc-indium and the nexus between energy transition and indium demand. Results show that the indium supply shortage for global energy transition could be intensified due to a less zinc-intensive economy. To address this challenge, focusing on indium demand reduction is more effective than emphasizing expanding indium supply for global sustainable development goals and material content reduction is the most promising strategy among the five ME strategies. Whereas, eliminating the concerns of indium availability thoroughly for facilitating a carbon neutrality transition requires coordinated ME strategies both from supply-side and demand-side. Moreover, the proposed analysis framework of ME strategies for securing indium availability for energy transition could also be applied for other byproduct metals.

Effects of heterogeneous ICT on critical metal supply: A differentiated perspective on primary and secondary supply

How to ensure supply security of critical metals is a common challenge for China and even developed countries. With the rapid development of information and communication technology (ICT), its impacts on the supply of critical metal need to be discussed. Taking China as an example, this article studies the influences of heterogeneous ICT on primary and secondary supply of critical metals and explores their influencing mechanisms. The results show that: (1) In the primary supply, ICT has inverted U-shaped influences on the host metals, while the impacts on byproduct metals antimony and nickel are U-shaped and linear promotion respectively; ICT has linear promoting effects on secondary supply. (2) Compared with hardware and communication equipment, software products have the most obvious impact on both primary and secondary supply. (3) Industrial scale of mining (SM) and smelting (SS), energy structure (ES) and energy efficiency (EE) can enhance the impacts of ICT on the primary supply; while only SS enhances the impacts on the secondary supply. (4) In the primary supply of host metals, the improvement of EE and ES will shift the inflection point to the left due to crowding-out effect, while the opposite is true for SM.

An underexploited invisible gold resource in the Archean sulphides of the Witwatersrand tailings dumps

The tailings dumps originating from gold mining in South Africa’s Witwatersrand still contain notable gold endowments. Most tailings reprocessing operations target a native gold fraction using re-milling and carbon-in-leach extraction; however, up to 50–70% of the remaining gold is still not recoverable and instead discarded to the re-dump stream along with abundant sulphides. The mineralogical deportment of this unrecoverable gold underwent a detailed investigation. Using in situ laser ablation ICP-MS mineral chemistry measurements, we show that this gold that is inaccessible to conventional recovery is hosted preferentially in pyrite and arsenian pyrite. Importantly, complementary optical and electron microscopy observations reveal that the rounded detrital forms of these minerals contain the highest gold concentrations (0.01–2730 ppm), showing some similarity to values reported for sulphides from primary orogenic gold deposits found in surrounding Archean-aged granite-greenstone belt remnants. We suggest that detrital auriferous sulphides have been overlooked by historical primary and secondary beneficiation, and thus represent a large (up to 420 tons Au) and under-exploited Au resource currently residing in easily-mined (surficial) Witwatersrand tailings dumps. We further suggest that targeted re-mining of sulphide mineral fraction has the potential to improve gold recovery, recuperate ‘sweetener’ by-product metals (e.g. Cu, Co, Ni) and directly eliminate heavy metal pollution and acid mine drainage issues associated with surficial tailings dumps.

THE IMPORTANCE OF GEOLOGY IN ASSESSING BY- AND COPRODUCT METAL SUPPLY POTENTIAL; A CASE STUDY OF ANTIMONY, BISMUTH, SELENIUM, AND TELLURIUM WITHIN THE COPPER PRODUCTION STREAM

AbstractThe ongoing global transition to low- and zero-CO2 energy generation and transport will require more raw materials and metals than ever produced before in human history to develop the necessary infrastructure for solar and wind power generation, electric power grid distribution, and electric vehicle componentry, including batteries. In addition to numerous critical elements, this transition will also require increased production of a range of other metals. This includes copper, with increased production of this metal providing the minerals industry with enhanced opportunities to secure the additional supply of associated or potential by-product elements. These include tellurium, selenium, bismuth, and antimony (among others), some of which are already predominantly produced as by-products from copper anode slimes. This study examines the geologic origins of over 240 active copper mines and over 200 electrolytic and electrowinning copper refineries worldwide. Although porphyry copper deposits dominate the copper supply trend, significant amounts of copper are supplied from the mining of sediment-hosted, massive sulfide, volcanogenic massive sulfide (VMS), and iron oxide-copper-gold (IOCG) mineral deposits. We integrate sources of copper concentrate with publicly available operational data for 32 copper electrorefineries to evaluate the geologic controls on the by-product supply potential of tellurium, selenium, bismuth, and antimony from copper anode slimes. These data represent some 32% of worldwide copper refineries and indicate that electrolytic refining of copper has the potential to supply ~777 t/yr tellurium, ~4,180 t/yr selenium, ~1,497 t/yr antimony, and 1,632 t/yr bismuth if 100% recovery of the by-product critical element proxies outlined in this study could be achieved. This is compared to current global production of ~490, ~2,900, ~153,000, and ~17,000 t/yr from all sources (rather than just copper by-products), respectively. Our analysis shows that there is no correlation between by-product potential and the amount of refined copper cathode production per year, but instead, the geologic origin of the copper concentrates is the key control on refinery by-product potential. This is exemplified by the fact that copper anode slimes derived from concentrates sourced from magmatic sulfide and VMS orebodies have an order of magnitude higher tellurium concentrations than those derived from porphyry deposits, reflecting the different abundances of tellurium within these mineral systems. These results are not surprising but demonstrate the possibilities for the development of robust proxies for by-product critical element supply potential using downstream data from copper (and potentially other base and precious metal) refineries. Equally significant, this study demonstrates the importance of downstream-up assessments of critical element potential as a complement to the more typical upstream-down deportment analyses undertaken to date. Finally, this type of approach allows the more accurate targeting of key parts of the metal supply chain with the capacity to increase by-product critical element production, rather than diluted or scattered approaches that assume that by-product metals are derived from one or two mineral deposit types (e.g., porphyry systems for the copper sector).

Liquid Copper and Iron Production from Chalcopyrite, in the Absence of Oxygen

Clean energy infrastructure depends on chalcopyrite: the mineral that contains 70% of the world’s copper reserves, as well as a range of precious and critical metals. Smelting is the only commercially viable route to process chalcopyrite, where the oxygen-rich environment dictates the distribution of impurities and numerous upstream and downstream unit operations to manage noxious gases and by-products. However, unique opportunities to address urgent challenges faced by the copper industry arise by excluding oxygen and processing chalcopyrite in the native sulfide regime. Through electrochemical experiments and thermodynamic analysis, gaseous sulfur and electrochemical reduction in a molten sulfide electrolyte are shown to be effective levers to selectively extract the elements in chalcopyrite for the first time. We present a new process flow to supply the increasing demand for copper and byproduct metals using electricity and an inert anode, while decoupling metal production from fugitive gas emissions and oxidized by-products.

Byproduct critical metal supply and demand and implications for the energy transition: A case study of tellurium supply and CdTe PV demand

The transition towards low-emission energy generation, storage and transport will require metal production beyond the already historically high production levels the minerals industry is achieving. This is problematic for several reasons, one being the fact that a majority of the metals required for these technologies are considered critical and are currently supplied as low volume byproducts of other main commodities, such as Cu or Zn. The low volume and specialist nature of these byproduct metals means that economic drivers to optimize their recovery are absent, causing these important resources to be lost to mine waste. Thin-film cadmium-telluride (CdTe) photovoltaics continue to be an emerging energy technology alternative to Si-based solar panels. However, the Cd and Te used to manufacture these panels are almost exclusively sourced as byproducts of either Zn or Cu. This study presents new Te supply and demand scenarios for CdTe photovoltaics based on a new Te material intensity value of 15.2 Mg/GW, outlining potential variations in demand as a result of the energy transition. We also examine how market demand and downstream low-emissions energy generation can be used to drive improved byproduct critical metal recovery from the Cu sector. This improved recovery of byproduct critical metals could ultimately lead toward the more responsible use of finite non-renewable resources as well as providing increased amounts of the raw materials for the power generation infrastructure required by the energy transition.

Agent-Based Modeling for By-Product Metal Supply—A Case Study on Indium

With rapid development and deployment of clean energy technology, demand for certain minor metals has increased significantly. However, many such metals are by-products of various host metals and are economically infeasible to extract independently. Meanwhile, by-product metals present in the mined ores may not be extracted even if they are sent to smelters along with host metal concentrates if it is not economically favorable for the producers. This dependency poses potential supply risks to by-product metals. Indium is a typical by-product metal, mainly from zinc mining and refining, and is important for flat panel displays, high efficiency lighting, and emerging thin-film solar panel production. Current indium supply–demand forecast models tend to overlook the volatile and competitive nature of minor metal market and are mostly based on top-down approaches. Therefore, a bottom-up agent-based model can shed new light on the market dynamics and possible outcome of future indium supply–demand relationship. A multi-layered model would also be helpful for identifying possible bottlenecks of indium supply and finding solutions. This work takes indium as an example of minor metal market and sets up an agent-based model to predict future market situation and supply–demand balance. The market is modeled as a Cournot competition oligopolistic market by refineries with capacity restriction based on host metal production. The model maintains active Nash equilibrium each year to simulate competitions between suppliers. The model is validated and verified by historical data and sensitivity analysis. Several scenarios are also explored to illustrate possible uncertainties of the market.

Tracking silver in the Lappberget Zn-Pb-Ag-(Cu-Au) deposit, Garpenberg mine, Sweden: Towards a geometallurgical approach

The complex mineralogy and low concentration of silver in polymetallic ores makes mineralogical characterization and extraction challenging. In this study, quantified mineralogical characterization of the flotation products from batch flotation tests was undertaken for a silver-rich zinc-lead ore using QEMSCAN® (Quantitative Evaluation of Minerals by Scanning Electron Microscope), scanning electron microscope with an energy dispersive spectrometer (SEM-EDS), and electron probe microanalysis (EPMA). Ten major silver minerals were identified and their behavior during flotation was discussed based on their different mineralogical and textural characteristics. Results from this study also showed the variability in the composition of some silver minerals (e.g., tetrahedrite and electrum), the presence of structurally bound silver in galena, and the formation of sulfur-based silver coating on chalcopyrite, galena, and tetrahedrite. A metallurgical balance generated using the QEMSCAN® data shows a very strong linear correlation (R2 = 0.99) against the chemical assay derived using inductively coupled plasma mass spectrometry (ICP-MS). This suggests that the quantification of mineralogical data produced using automated mineralogy is possible even for tracking trace minerals. The effectiveness of this methodology lies upon the creation of a robust mineral library based on a comprehensive mineralogical study, which can be used for tracking of by-product metals during the flotation of complex ores.

Geology and Mining: Mineral Resources and Reserves: Their Estimation, Use, and Abuse

Editor’s note: The Geology and Mining series, edited by Dan Wood and Jeffrey Hedenquist, is designed to introduce early-career professionals and students to a variety of topics in mineral exploration, development, and mining, in order to provide insight into the many ways in which geoscientists contribute to the mineral industry. Abstract Resource and reserve estimation is a critical step in mine development and the progression from mineral exploration to commodity production. The data inputs typically change over time and reflect variations in geoscientific knowledge as well as the modifying factors required by regulation for estimating a reserve. These factors include mineral (ore) processing, metallurgical treatment of the ore, infrastructure requirements for mine and workforce, and the transportation of processed products to buyers; others that will affect the production of metals and/or minerals from a deposit include economic, marketing, legal, environmental, social, and governmental factors. All are needed by the mining industry to quantify the contained mineralization within mineral deposits that likely warrant the significant capital investment required to build a mine. However, these resource and reserve data are estimates that change over time due to unpredicted variations in the initial inputs. Paramount to the two estimates are the quality and accuracy of the geologic inputs and the communication of these to the professionals tasked with making each estimate. Geostatistical processing of the grade of the resource has become a dominant element of the estimation process, but this requires transparent and informed communication between geologists and mining engineers with the geostatistician responsible for mathematically processing the grade data. Regulatory constraints also mean that estimated resources and reserves seldom capture the full extent of a mineral deposit. Similarly, co- and by-product metals and minerals that are commonly produced by mines may not be captured by resource and reserve estimates because of their limited economic contribution. This suggests that reporting standards for co- and by-products—particularly for the critical metals that may have a sharp increase in demand—need improvement. Finally, the importance of these data to the mining industry is such that informing investors and the broader public about the nature of resource and reserve estimates, and the meaning of associated terminology, is also essential when considering the global metal and mineral supply, and the role of mining in modern society.

Evaluating metal constraints for photovoltaics: Perspectives from China’s PV development

Chinese PV industry can be expected to grow rapidly of until 2050, driven by ongoing decarbonization of the energy mix. Such large-scale deployments generate significant increases in metal demand that may induce resource dilemmas. In this study, dynamic material flow analysis is combined with scenario analysis to estimate future metal demand from Chinese PV industry and complemented by a supply risk assessment. It is found that the maximum annual copper and silver demand up to 2050 equals 79.6% and 58.5% of China’s annual production in 2019. Similarly, the baseline scenario projects maximum annual demand of Tellurium and Indium corresponding to 598.1% and 161.8% of China’s annual production in 2019. Cumulative base metal demand by 2050 for China’s PV sector is 17.3–22.8 times that of in 2018, while cumulative silver demand increases by 4.5–6 times from 2018 to 2050. In the baseline scenario, cumulative byproduct metal demand by 2050 is 14–27.3 times larger than in 2018. High annual and cumulative supply pressures indicate not only the general scarcity of base, precious, and byproduct metals but also highlights the importance of building stable trade relationships for future PV developments in China. Two different measures are identified and assessed for reducing short- and long-term supply risks. Prolonging the lifetime from 25 to 30 years can achieve a cumulative metal conservation of 6.7–24.2%, while shorter lifetime will give rise to secondary supply if recycling technologies are implemented. A clean energy shift indicates that metal availability will become an important perspective for assessing energy security, implying that resource constraints should be considered in different planning levels for renewable energy developments. Strong interconnections between energy and metal supply chains indicate that coordination and holistic nexus views are required for achieving simultaneous sustainability in both systems.

The price relationship between main-byproduct metals from a multiscale nonlinear Granger causality perspective

Basing on the relationship of joint production, we take lead-bismuth, lead-selenium, zinc-cadmium, and zinc-germanium as examples to study the nonlinear Granger causal relationship between the prices of main-byproduct metal pairs. The price relationship between the main metal and byproduct metal is nonlinear and varies with the time scales. Therefore, we use an Ensemble Empirical Modal Decomposition method (EEMD) to break down the price series of the main metals and byproduct metals into different frequency bands, and then test these different frequency bands for nonlinear Granger causality. The results show that a two-way nonlinear Granger causal relationship exists between the prices of the main metals and byproduct metals, and this nonlinear Granger causal relationship is reflected primarily in the short- and medium-term time scales. Moreover, the effect of the main metal price on the price of the byproduct metal is not as significant as previously thought, and the influence of the byproduct metal price on the main metal price has been previously underestimated.

Multi-Analytical Characterization of Slags to Determine the Chromium Concentration for a Possible Re-Extraction

The CHROMIC project (effiCient mineral processing and Hydrometallurgical RecOvery of by-product Metals from low-grade metal contaIning seCondary raw materials) aims to recover chromium from steelmaking and ferrochrome slags to regain valuable resources and simultaneously reduce potential environmental impacts. To develop the recovery flowsheets and reliably calculate metal recovery, an accurate assessment of chromium concentration and distribution is essential. Therefore, model streams were thoroughly characterized using a combination of analytical techniques. In all materials, chromium is present in distinct but often small spinel phases, intergrown with other minerals and showing a considerable zonation in Cr content with higher amounts in the cores. The small size of the Cr-rich particles makes recovery by mineral processing challenging. Measured chromium content was found to differ largely based on the chemical dissolution method applied. The analysis of insoluble residues and comparison with a standard reference material evidenced that standard acid dissolution procedures based on HCl/HNO3/HBF4 and HNO3/HF/H2O2 are insufficient to fully dissolve spinel structures, leading to severe underestimations of chromium content. A sodium peroxide treatment is required for a full dissolution of spinels. This is noteworthy, since most of the legislation for the reuse of slags is currently based on acid dissolution methods.

Causality between metal prices: Is joint consumption a more important determinant than joint production of main and by-product metals?

Research on metal price determinants has been driven by increasing price volatilities and realization of metals as financial assets. A sound understanding of metal prices enables producers, consumers, policy makers and traders to anticipate and better prepare themselves for short and long-term price trends. Metal prices are related to each other via their nature of either being jointly produced or jointly consumed. While the effects of joint production of metals have been the subject of increased analysis lately, the effects of joint consumption on metal prices have yet to be studied systematically. Therefore, we aim to analyze the effects of both joint consumption and joint production on the causality relationship between metal prices. In doing so, we use the Toda Yamamoto approach to conduct pair-wise Granger-causality tests between various metals that are either jointly produced or jointly consumed. Our results indicate that joint-consumption of metals has a significant impact on the Granger-causality relationship between metals and that it is indeed an important determinant of metal prices.

The geometallurgical assessment of by-products\u2014geochemical proxies for the complex mineralogical deportment of indium at Neves-Corvo, Portugal

Many by-product metals are classified as critical. However, they are only of marginal interest to many mining companies and are rarely part of detailed resource statements or geometallurgical assessments. As a result, there is a general lack of reliable quantitative data on the mineralogy and spatial distribution of these metals in ore deposits—hampering assessments of future availability. We propose here an innovative approach to integrate by-product metals into geometallurgical assessments. As an example, we use the distribution and deportment of indium at Neves-Corvo, a major European base-metal mine (Cu + Zn), and one of the largest and richest volcanic-hosted massive sulfide (VHMS) deposits in the world. Based on a combination of bulk-ore geochemistry and mineralogical and microanalytical data, this study is the first to develop a quantitative model of indium deportment in massive sulfide ores, demonstrating how regularities in indium partitioning between different minerals can be used to predict its mineralogical deportment in individual drill-core samples. Bulk-ore assays of As, Cu, Fe, Pb, S, Sb, Sn, Zn, and In are found to be sufficient for reasonably accurate predictions. The movement of indium through the ore processing plants is fully explained by its mineralogical deportment, allowing for specific mine and process planning. The novel methodologies implemented in this contribution for (1) the assessment of analytical uncertainties, (2) the prediction of complex mineralogical deportments from bulk geochemical data, and (3) the modeling of by-product recoveries from individual mining blocks, are of general applicability to the geometallurgical assessment of many other by-product metals in polymetallic sulfide ores, including Ga, Ge, Mo, Re, Se, Te, as well as the noble metals.

Quantifying the relative availability of high-tech by-product metals – The cases of gallium, germanium and indium

There are considerable concerns about the supply security of certain high-tech elements produced as by-products. To determine in how far these concerns are justified by the actual availability of these elements, we compare the supply potentials for three particularly relevant examples – gallium, germanium and indium – to current and historic production volumes. Our assessment is based on detailed estimates of the amounts extractable from various raw materials given contemporary market prices and technologies. While the estimate for gallium is taken from a previous publication, the estimate for germanium is recalculated from an earlier estimate of recoverable germanium in reserves and resources, and the estimate for indium is compiled as part of this article.We find that the supply potentials of all three elements significantly exceed current primary production. However, the degree to which this is the case varies from element to element. While both the supply potentials of gallium and germanium are ~10 times higher than primary production, the supply potential of indium is ~3 times higher.Differences also exist in historic growth trends, with indium showing the fastest growth rate of the utilised supply potential. This makes it the most likely of the three to reach its maximum production level in the future. Based on these considerations we propose a new quantitative indicator for the future availability of by-products, time-to-maximum extraction as a by-product (TMEB), and show its utility in discriminating between the different supply situations of the three by-product elements.

Byproduct metal requirements for U.S. wind and solar photovoltaic electricity generation up to the year 2040 under various Clean Power Plan scenarios

The United States has and will likely continue to obtain an increasing share of its electricity from solar photovoltaics (PV) and wind power, especially under the Clean Power Plan (CPP). The need for additional solar PV modules and wind turbines will, among other things, result in greater demand for a number of minor metals that are produced mainly or only as byproducts. In this analysis, the quantities of 11 byproduct metals (Ag, Cd, Te, In, Ga, Se, Ge, Nd, Pr, Dy, and Tb) required for wind turbines with rare-earth permanent magnets and four solar PV technologies are assessed through the year 2040. Three key uncertainties (electricity generation capacities, technology market shares, and material intensities) are varied to develop 42 scenarios for each byproduct metal. The results indicate that byproduct metal requirements vary significantly across technologies, scenarios, and over time. In certain scenarios, the requirements are projected to become a significant portion of current primary production. This is especially the case for Te, Ge, Dy, In, and Tb under the more aggressive scenarios of increasing market share and conservative material intensities. Te and Dy are, perhaps, of most concern given their substitution limitations. In certain years, the differences in byproduct metal requirements between the technology market share and material intensity scenarios are greater than those between the various CPP and No CPP scenarios. Cumulatively across years 2016–2040, the various CPP scenarios are estimated to require 15–43% more byproduct metals than the No CPP scenario depending on the specific byproduct metal and scenario. Increasing primary production via enhanced recovery rates of the byproduct metals during the beneficiation and enrichment operations, improving end-of-life recycling rates, and developing substitutes are important strategies that may help meet the increased demand for these byproduct metals.