India’s Polymetallic Nodules programme is oriented towards exploration and development of technologies for harnessing of nodules from the Central Indian Ocean Basin (CIOB) allocated to India.
It has 4 components viz.
Survey & Exploration,
Environmental Impact Assessment,
Technology Development (Mining), and
Technology Development (Metallurgy).
In the 75,000 sq. km area of CIOB, the estimated polymetallic nodule resource potential is 380 million tones, containing 4.7 million tonnes of nickel, 4.29 million tonnes of copper and 0.55 million tonnes of cobalt and 92.59 million tonnes of manganese. Cobalt and nickel are strategically important metals.
While, the extraction of metals from the polymetallic nodules lying at the deep ocean floor is not yet found to be economically viable at this stage, an area of about 7860 square km has been identified in the CIOB for the First Generation Mine Site on the basis of detailed surveys & analysis. Environmental studies for mining of deep-sea polymetallic nodules were also carried out to evaluate the possible impacts of mining on deep-sea environment. A Remotely Operable Submersible (ROSUB 6000), capable of operating at 6000 m water depth was also developed and tested successfully at a depth of 5289 m for assessing environmental conditions beyond 5000 m. A remotely operable in-situ soil testing equipment was also developed for obtaining detailed geotechnical properties of the mining area at Central Indian Ocean Basin (CIOB) and tested successfully at 5462 m water depth. A mining system is under development. A demonstration pilot plant with a capacity to process 500 kg nodules per day was commissioned on semi-continuous basis successfully for extracting copper, nickel and cobalt at Hindustan Zinc Limited, Udaipur. Another pilot plant has been commissioned at National Metallurgical Laboratory, Jamshedpur with processing capacity of 500 kg per day for production of ferro-sillico-manganese ore from the residue obtained from the HZL plant.
India has entered into a 15-year contract with the International Seabed Authority in the year 2002 for pursuing developmental activities for polymetallic nodules in the Indian Ocean. India continues to pursue the polymetallic nodules programme coupled with research and development efforts. China Ocean Mineral Resources Research and Development Association (COMRA), China has been engaged in carrying out the activities pertaining to exploration of Polymetallic Nodules in the Pacific Ocean. The details of its activities are not known.
Vision of India
To explore the strategic minerals for the 21st Century
- Identification of a First Generation Mine site for nodules.
- Identification of the best ten blocks for ROV investigations.
- Extensive ROV investigations to identify the miner tracks, seafloor, subbottom and microtopography at high resolution
Manganese (Or Polymetallic) Nodules:
Increasing global population, demand for metals and dwindling land resources, has come to such a pass that the next alternative source for the metals could be in the world oceans. Oceans are considered as a ‘warehouse’ for minerals, amongst others, polymetallic nodules (Ferromanganese nodules), phosphorites, hydrothermal sulphides, placer deposits and sand. The first discovery of polymetallic nodules was made by scientists onboard the research vessel “H M S Challenger” during 1873. In comparison, India (by the efforts of the National Institute of Oceanography, Goa) recovered nodules in the Arabian Sea during 1981 onboard “R.V.Gaveshani.” In 1982, India was recognised as a Pioneer Investor in deep seabed mining, by the United Nations Convention on the Law of Sea.
Subsequently, a massive effort was put in by India for exploration of polymetallic nodules in the Central Indian Ocean Basin (CIOB) by using a number of research vessels. This national programme (running into crores of rupees) is being funded by Department of Ocean Development, New Delhi.
To-date, India has surveyed an area of nearly 4 million sq km in the CIOB. This resulted in the identification of two mine sites, each 150,000 sq km area with equal commercial grade (Cu+Ni+Co wt%) and abundance (kg/sq m) of nodules. In 1984, India filed her claim with the Preparatory Commission (PRECOM) for the International Sea Bed Authority (ISBA). In 1987, India became the first country in the world to be allocated exclusive rights for further exploration.
One of the mine site (A) of 150, 000 sq km has been allotted to India and as per the condition of the ISBA, 50 % of the area has been relinquished to this body.
What are polymetallic nodules and the criteria for their formation?
Polymetallic nodules are Fe-Mn oxide deposits, potato shape, porous, black earthy colour with size ranging from 2 to 10 cm in diameter.
In the Indian Ocean, nodules occur in different basins such as CIOB Wharton Basin, Crozet Basin, Madgascar Basin, Somali Basin, South Australian Basin and Arabian sea.
The prerequisite conditions to form the nodules are:
- Low sedimentation rate
- Availability of nucleus around which accretion of oxides takes place
- Oxidising environment
- Bottom currents of low velocity
How are nodules collected from the seafloor?
Boomerang grabs or free fall grabs are used for collection of the nodules. The recovery of nodules helps to estimate the abundance (kg.sq m). The abundance of nodules varies from traces up to 25 kg/sq m.
How are polymetallic nodules formed?
There are three processes for the formation of nodules.
- Hydrogenous process whereby metals are supplied from the water column and these accrete on a suitable nuceli. Hydrogenous nodules have smooth surface texture and are rich in Fe, Co, Ti, P and Pb content. The Mn/Fe ratio of these nodules is ~1.
- Diagenetic process supplies metals from the underlying sediment through the pore water by remobilisation. Diagenetic nodules have rough surface texture and are rich in Mn, Cu, Ni and Zn content. The Mn/Fe ratio is more than 2.5.
- Mixed type which is a combination of hydrogenous and diagenetic types.
The following are some significant scientific results:
- Nodule grade (Cu+Ni+Co %) is inversely related to abundance (kg/sq m).
- Manganese and iron show inverse relation suggesting their different source.
- Nodules with 2 to 6 cm size have high Mn, Cu, Ni and Zn concentration.
- Nodules grow with 1-2 mm per million year.
- Rare earth elements are supplied to nodules in association with Fe, Ti and P from the seawater.
Nodules of the CIOB
The formation of ferromanganese nodules on the ocean floor requires a nucleus, low sedimentation rate, oxidising conditions and low velocity bottom currents.
Bottom topography also plays an important role in the distribution of manganese nodules. The highest manganese concentration are generally found in nodules collected from high relief areas like valleys, followed by hilltops and slopes. Nodule abundance is least in the plains but have the highest content of Mn, Cu, Ni.
In contrast, nodules from hilltop have lowest concentrations of these metals. The size of nodule ranges between 2 and 10 cm in diameter, with a majority of them lying between 2 and 4 cm size range. Nodules in the CIOB are associated with practically all types of sediment and the nodule abundance varies from traces to 20 kg/m.
Nodules from siliceous sediment are smaller in size, rough surface texture, with todorokite as a dominant mineral enriched in Mn, Cu, Ni and Zn suggesting their supply through early digenetic process.
Ferromanganese nodules from red clay area are enriched in Fe, Co, Ti and P suggesting their supply mainly by hydrogenetic process. Rare earth elements are highly enriched in these nodules (~800 ppm) and are generally carried by a single authigenic phase consisting of Fe-Ti-P suggestive of their supply by seawater.
Ferromanganese nodules from the CIOB consist of ~75 % Mn as Mn (IV) and traces of Mn (III) was detected by electron spin resonance spectra. These nodules are formed under less oxic conditions compared to Pacific Ocean nodules. Mossbauer spectra of nodules exhibit a well-resolved doublet suggesting presence of paramagnetic Fe (III).