Turning the tables on wasted elements
Let’s pay tribute to Dmitri Mendeleev’s periodic table of elements, which turned 150 this year, by preserving some of its endangered members, say chemists Prathama S. Mainkar*, Ambica V* and Srivari Chandrasekhar*.
doi:10.1038/nindia.2019.90 Published online 15 July 2019
Many of the star elements of the periodic table may no longer be around by Dmitri Mendeleev’s 200th birthday in 2034, unless we begin preserving them. Endangerment or extinction is not confined to living species such as animals. Elements are equally vulnerable to human exploitation. Stoking this exploitation are factors such as rapid urbanisation, infrastructural projects, high-end technology, electronic products and increase in population.
Mendeleev published his periodic table of elements based on their atomic weights in 1869. Since then, gaps he left in the table have been filled with newly discovered elements. The current periodic table has 118 elements, and there are continuous efforts to identify many more through laboratory controlled experiments.
But the euphoria around the discovery of new elements must be balanced by awareness that we run the risk of vacant spaces again by endangering elements that may fall off the table.
On the edge of the table
The growing use of technology in all spheres of modern life has had a cascading effect on the availability of many elements.
In the future, for example, helium1 balloons may be difficult to find. How can the second most abundant element on earth be endangered? Helium is widely used in all research labs and in the pharmaceutical industry. This inert gas, the best coolant, stands the risk of escaping Earth’s gravitational pull, meaning helium in the atmosphere is constantly depleting. Hydrogen can be a substitute for helium in many applications but due to its very reactive nature, adequate safety precautions must be used to handle it.
Moving from lightweight gasses to heavy magnets, we are also observing the loss of neodymium which is used in magnets for the wind energy sector, hospital equipment and electric motors. Elsewhere, aluminum-scandium alloys (preferred due to their light weight and strength), fuel cells, ceramics, lasers and radioactive isotopes use scandium. And as a compound in super-conductivity research, yttrium finds use in production of phosphorus that aids in functioning of cell phones, display lighting and general lighting.
Indeed, among the 17 rare-Earth elements (REE), scandium, neodymium and yttrium are the most sought after for use in high-end technology. However, the recycling of such elements from batteries, permanent magnets and fluorescent lamps is minimal. How long will they last?
Rare-earth elements tend to occur together, and the process to extract them is gruelling. Currently, China produces about 90% of the world’s supplies of rare earth elements2. Since the process to extract them is tough, new mines mean more earth-damaging acid concentrations and unwanted chemical by-products.
The silvery grey transition metal hafnium is highly threatened, and may just disappear. Hafnium and zirconium are found together, and the method to separate them is difficult because of their chemical similarity. The 2019 US Geological Survey said zirconium and hafnium appear in zircon3 at a ratio of about 36 to 1. Hafnium production is very low, compared to its increasing use in nuclear reactors and chemical industry.
The platinum-group metals – ruthenium, rhodium, iridium, palladium, osmium and platinum – are in high demand for use in catalytic convertors to control automobile emissions, chemical production, petrol refining, medical devices, electronic applications and the jewellery industry. They mostly occur together in mineral deposits and have similar chemical and physical properties. The surge in demand for these elements may outstrip their supply in the near future.
Lithium, found generally locked in minerals and salts in the earth’s crust, is preferred for removing impurities in metals. Being lightweight and with a large electro chemical potential, lithium is used extensively in batteries. Mobile phones, cars and rechargeable batteries use this element in huge quantities. Copper, silver, zinc, tellurium are a few more in the risk list.
One solution to dwindling element supplies is looking to replace them with more abundant alternatives.
Sodium-ion batteries4 can be an alternate to those that rely on increasingly scarce lithium. Not only do they use a less expensive and less toxic raw material, sodium is also available abundantly. And in a variety of applications that use platinum, palladium, rhodium and other such rare and expensive metals, graphene and carbon nanomaterials were found to be almost equally useful.
Alloys can also play an important role in element conservation. Substitution alloys5, interstitial alloys6 and a combination of both alloys can mitigate the use of single at-risk elements. Tin or zinc atoms can be substituted in bronze and brass, for example, and steel is an example of interstitial alloy where carbon fits in the interstices of iron matrix to enhance the properties of iron.
Research on the use of abundant materials as various catalysts is also gradually gaining ground. Abundant materials are cheap, less susceptible to supply fluctuations, and are environment-friendly. “Chemists are developing novel reaction schemes that use homogeneous catalysts made with cheap metals,” says Morris Bullock, Director of the Center for Molecular Electrocatalysis at the Pacific Northwest National Laboratory (PNNL)7.
Noble metals such as rhodium, palladium, ruthenium, silver and indium involve huge extraction costs, so a composite with such metals can be a solution to reduce dependency without diluting performance. Lithium, hafnium, platinum group metals and REEs require good recycling technology. Research on recycling discarded devices which use ‘risk elements’, may assist in preserving elements.
None of this is enough, however, and we need to create a sustainable economy in order for all elements to continue to exist. It is a promising sign that countries are imposing more stringent rules to prevent overexploitation of resources, in a move to prevent environment degradation and check illegal mining. And introduction of more stringent emission standards for automobiles in some countries may also result in increased demand for platinum group metals. In addition, better methods of isolation of these REEs should be taken up on a priority basis. As all the precious elements, viz. gold, silver, platinum, palladium are recycled all the REEs should also be reused.
With no rigid recycling norms, protecting elements will involve cooperation from all the countries in the world. Science across borders needs to focus on a unified effort. ‘Circular science’ that gives back to the Earth the elements we have taken from her can be part of a set of solutions that must also avoid disruption to supply chains, and be in line with environmental approaches.
A real tribute to Mendeleev will be in the form countries and importantly scientists coming together to focus on developing better technologies that will aid in the discovery of alternate solutions and preserve all elements in the periodic table.
[*The authors are from the Department of Organic Synthesis & process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, India.]
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