Dr. Rajender Kumar Chadha is a distinguished geophysicist and retired Chief Scientist from CSIR-National Geophysical Research Institute (NGRI), Hyderabad. With a Ph.D. in Applied Geophysics and over 130 peer-reviewed scientific publications, Dr. Chadha has been instrumental in assessing seismic hazards for India’s critical infrastructure including nuclear power plants and dams. Recognized as Fellow of the National Academy of Sciences and recipient of the prestigious Raja Ramanna Fellowship (2021) from the Department of Atomic Energy, Dr. Chadha brings three decades of expertise in earthquake seismology, geological stability, and risk assessment to the rare earth minerals discourse. His insights, during that conversation with Rashmi Kumari of Neo Science Hub, on balancing rapid mineral extraction with environmental and structural safety are invaluable for India’s rare earth strategy.
Dr. Chadha, given your expertise in seismic hazard assessment for critical infrastructure, what seismic and geological stability considerations should regulate rare earth mining in geologically sensitive regions of Andhra Pradesh and odisha?
Seismic hazard assessment for the construction of critical structures like Nuclear Power Plants or Dams or tall bridges is done based on geology or rock types, sediments or soil cover, structures like faults, fractures, tectonics and seismicity using earthquake catalogues of the area. Extensive geophysical surveys including seismic and gravity are carried out to ascertain the subsurface basement structures at the site and Landsat imageries to map faults or lineaments in the area. Armed with such a priori information, estimates of shaking (Peak Ground Acceleration and spectrum) due to a probable Maximum Credible Earthquake in the area are modelled using existing seismological data. These studies provide critical inputs for designing earthquake resistant structures.
In case of mining of Rare Earth Minerals, it is more an issue of environment degradation and ecological imbalance caused due to unregulated mining. Firstly, we need to understand what we mean by Rare Earth minerals. Are these really rare? The answer is No. Let me explain. Minerals are substances that are formed naturally in the Earth by combining two or more elements. So far, 118 elements have been discovered of which 93 are metallic elements (e.g. Iron, Copper, Aluminium, etc), 18 are nonmetals (e.g. hydrogen, oxygen, carbon, phosphorus, sulphur, etc) and 7 are metalloids(eg. silicon, germanium, arsenic etc). Metalloids are elements with properties that are a mix of metals and nonmetals. Pure silicon is a semiconductor, and its electrical conductivity property can be precisely controlled by doping it with impurities making it a foundation material of modern electronics. All the elements discovered are arranged in Periodic Table according to their atomic numbers.A group of 15 chemically similar metallic elements with atomic numbers from 57 to 71 are called lanthanides (e.g. Cerium,Neodymium)plus scandium and yttrium, are the known 17 Rare Earth Elements.
When minerals get concentrated in a host rock, it becomes an ore. An ore is defined as any mineral that can be economically mined. For example, Iron (abbreviation Fe) occurs in igneous, metamorphic, and sedimentary rocks, but most major iron ore deposits are found in sedimentary rocks called Banded Iron Formations. Similarly, Aluminium (Al) occurs in Bauxite, a sedimentary rock. On the contrary Rare Earth Minerals, though abundant in Earth’s crust occur as accessory minerals or trace elements along with major ores. For example, Gallium, though not a Rare Earth Mineral isclassified as a trace elementbecause of its scarcity and importance for high-tech applications like semiconductors. It occurs as a trace element in Bauxite (Aluminium ore) and zinc ores like sphalerite or germanite.
So, the name “Rare” is a misnomer, however, it is called “rare” because it is not found as concentrated ores that can be easily mined like other metals. Since, these Rare Earth Minerals are dispersed, it is a challenge to extract them without harming the environment and process in economical quantities. But it is important to extract them irrespective of economics because these minerals have certain properties that are crucial for many high-tech applications such as magnets, electronics and catalysts. Magnets are needed for high-tech applications because their magnetic fields can generate electricity, store data, and enable mechanical motion. They are essential for creating electric motors, data storage devices like hard drives, and power generation, and are used in specialized technologies such as medical imaging (MRI), navigation systems, and scientific instruments like particle accelerator. The entire modern day technology depends on Rare Earth Minerals.
In India Rare Earth Mineral deposits are primarily found in coastal monazite rich beach sands and inland alluvium in states like Andhra Pradesh, Odisha, Tamil Nadu, and Kerala, with smaller deposits in West Bengal, Jharkhand, and Gujarat. Monazite is a reddish-brown phosphate mineral that is an important source of rare earth elements like lanthanum, cerium, and neodymium, as well as thorium. Since its discovery in 1909 in Kerala beach sands, Odisha is at present a major producer of rare earth minerals from monazite sands, while Andhra Pradesh also has significant deposits.
But mining Rare Earth Minerals from monazite rich sand beach deposits requires careful balance for sustainable exploitation as any excesses may cause depletion of sand in the streambed and along coastal areas causing deepening of rivers and estuaries, and the enlargement of river mouths and coastal inlets. It may also lead to saline-water intrusion from the nearby sea. The effect of mining may be compounded by the effect of sea level rise. Any volume of sand exported from streambeds and coastal areas is a loss to the marine ecosystem.
Rare earth extraction often requires deep subsurface operations. How should geophysical monitoring systems-adapted from earthquake early warning technology-ensure long-term stability of mining and tailings facilities?
There are two part: i) Exploration of Rare Earth Minerals: Techniques for rare earth mineral exploration includegeophysical methods like radiometric and magnetic surveys, geochemical sampling using methods such as X-ray fluorescence (XRF) for on-site analysis, and litho-geochemical and mineralogical studies. Other advanced methods involve innovative drilling techniques to go deeper, and detailed lab-based analyses like Inductively Coupled Plasma Mass Spectrometry (ICP-MS), ii) Exploitation or separation of Rare Earth Elements from ores: This is the most challenging part as it affects the environment. Since chemicals, solvents and acids are employed in the processing and separation of rare earths from the ores, with millions of gallons of water necessary for the separation, screening, collection, processing, and finishing of rare earths, a combination of environmental engineering technologies and mechanical engineering technologies need to be deployed to minimize the impact on the environment degradation. Refining of Rare Earth Elements produces a lot of waste, and potentially toxic waste that needs to be disposed safely or recycled.
The geophysical and geological techniques can be used to cite suitable locations for underground tailings storage facilities depending on factors like topography, seismic activity, and rainfall. Improper storage can lead to leaks or breaches, causing significant environmental damage due to the heavy metals and other contaminants present in the waste.Effective tailings management is crucial for the safe and sustainable operation of mines, with efforts being made to treat the waste or even utilize it in other applications like road construction.
Your work shaped nuclear facility safety standards through seismic assessment. What mandatory geophysical prerequisites should India establish for rare earth mining licenses to balance rapid scaling with geological safety?
Since monazite sand mining is the primary source of all our Rare Earth Minerals exploitation at present, it needs to be primarily controlled by government-owned companies, as rare earth elements are also classified as atomic minerals with the presence of large amounts of thorium.With plans to increase domestic production and exploration in the future PPP models will emerge. Strict compliance needs to be implemented to treat toxic waste before it is released and should be made a necessary condition for granting licenses to private sector.
