Manganese

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MANGANESE:
INTRODUCTION:
 Manganese is the 12th most abundant element in Earth’s crust. Manganese is a silvery grey in colour, chemically
active element. It is a hard metal and is very brittle. It is hard to melt, but easily oxidized. Manganese is reactive
when pure, and as a powder it will burn in oxygen
 For modern industrial societies, manganese is a crucial component. Its main application is in the production of steel,
where it is used as an alloy to turn iron into steel and as a purifying agent in the refinement of iron ore.
 Chemical properties of manganese: Atomic numner-25; Electron Configuration- [Ar] 3d5
4s2
; Melting point-
1246°C; Boiling point- 1246°C; Density-7.3; Relative Atomic Mass-54.9;
 Manganese is a potentially mobile element and occurs in three oxidation states in nature (+2, +3, +4). The most
stable oxidation state is +2.
 Deposits of manganese that can be used for commercial purposes can be found on land, as well as on the ocean
floor and in lacustrine basins.
 Manganese have different minerals like Pyrolusite – MnO2; Psilomelane – Mn2O3.2H2O; Braunite –
Mn2+
Mn3+
6[O8|SiO4]; Wad – MnO; Rhondocrosite – MnCO3; Rhodonite – MnSiO3; Hausmanite – Mn3O4; Polianite
– MnO2; Manganite (MnO (OH)); Kutnahorite-CaMn(Co3)2
 The formation of Manganese ores requires specialized geologic conditions that concentrate manganese at several
hundred times its average crustal abundance. The most important manganese deposits occur in ancient marine
sedimentary rocks that are now exposed on continents as a result of subsequent tectonic uplift and erosion.
 Indian manganese ore deposits occur mainly as metamorphosed bedded sedimentary deposits associated with
Gondite Series (Archaeans) of Madhya Pradesh (Balaghat, Chhindwara & Jhabua districts), Maharashtra (Bhandara
& Nagpur districts), Gujarat (Panchmahal district), Odisha (Sundargarh district) and with Kodurite Series
(Archaeans) of Odisha (Ganjam & Koraput districts) and Andhra Pradesh (Srikakulam & Visakhapatnam districts)
GEOLOGY BEHIND MANGANESE DEPOSITION:
 Average crustal rocks contain about 0.1 percent manganese, but manganese concentration varies according to rock
type. Mafic rocks, such as basalt, typically contain about 0.16 percent manganese, whereas granitic rocks contain
about 0.06 percent.
 Manganese ores contain a minimum of 15 percent manganese, but most ores are considerably higher grade, ranging
up to about 50 percent manganese. The formation of manganese ore, therefore, requires a geochemical system that
concentrates manganese.
 All manganese ores have formed as a result of the transport of manganese in water solutions, and precipitation of
manganese minerals out of those solutions in sufficiently high concentrations and volumes to form minable
orebodies.
 On continents, most manganese occurs in trace amounts in reduced (+2) form in silicate and carbonate minerals. It
can be released by continental weathering where some of it is dissolved in surface water and eventually transported
by rivers to the world’s oceans.
 The most significant sources of dissolved manganese in seawater are (a) dissolved manganese in rivers entering
the oceans, (b) manganese released from marine sediments by post-depositional alteration, and (c) manganese
from deep-sea hydrothermal vents.
 The solubility of manganese is strongly controlled by the acidity (pH) and oxidation potential (Eh) of manganese-
bearing solutions, which include surface water, ocean water, and high-temperature fluids in various subsurface
environments.

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 Manganese solubility is highest in more acidic (lower pH) conditions and less oxidizing (lower Eh) conditions in
which dissolved manganese exists primarily in the most soluble +2 oxidation state. Therefore, generally requires
the existence of oxygen-poor (low Eh) ocean water or surface water for transport manganese.
 During transportation of manganese in solution where the pH condition is changes from acidic to alkaline and Eh
condition also changes from low Eh to high Eh at that condition manganese going to deposit.
 Many manganese deposits are a direct result of deposition of manganese-rich sediment layers on the seabed, both
in present-day oceans and oceans of the geologic past, additionally, secondary enrichment of manganese-rich
marine sedimentary rocks by later continental weathering (supergene ores) has produced many high-grade
manganese ore deposits.
DEPOSIT TYPES:
A. LAND BASED DEPOSITS (ANCIENT MARINE SEDIMENTS AND ZONES OF SECONDARY
ENRICHMENT)
1. Manganese Deposits in Marine Sedimentary Rocks: The vast majority of land-based manganese resources occur as
extensive layers of manganese-rich sedimentary rocks, some of which formed as long as 2.5 billion years ago. These
rocks formed on ancient seabed’s and have since become part of continents through tectonic processes of uplift and
continental accretion. These deposits are mainly two types one types are iron rich and other types are iron poor.
Manganese associate with Iron these type of deposition occurs in the deep marine and deposition happen with
alteration with other iron rich sediment. Whereas iron poor manganese type of deposit occurs where in such water
masses, dissolved hydrogen sulfide is causes iron to be precipitated as sulfide minerals in black shale and leaves very
low concentrations of dissolved iron in the seawater and for that dissolved manganese concentrations (Mn2+) remain
high. This precipitation of the dissolved manganese caused by the mixing of the manganese-rich deep ocean water
with the more oxidized surface waters. Because of the increased Eh conditions, the water becomes saturated in
dissolved manganese, and manganese-rich sediments can be precipitated.
2. Secondary Deposit (Supergene Enrichment): These secondary enrichment types of deposits, form where chemical
reactions taking place within tens of meters of the surface redistribute manganese at a local scale and also leach out
nonmanganese components, which results in residual enrichment of the manganese. Supergene deposits are most
abundant and commonly developed in tropical regions. The generation of humic acids by decomposition of abundant
organic matter results in the dissolution of manganese-bearing minerals and transportation of manganese downward
in the soil profile. It is then reprecipitated where soil water encounters less acidic conditions. The same acidic soil
solutions dissolve and remove other components as well, resulting in a residual enrichment of manganese minerals.
Significant occurrences of these types of deposits are the Moanda deposit in Gabon, the Serra do Navio deposits in
Brazil, and numerous deposits in India. Supergene deposits are most abundant and commonly of the highest grade
in tropical regions where humid conditions and abundant vegetation are key factors in forming deep tropical soils.
B. SEABED DEPOSIT:
The ocean floor's seabed manganese deposit is a relatively recent time deposit. Ferromanganese nodules and
ferromanganese crust are the two subtypes of the seabed manganese deposit. Ferromanganese crusts are layers of
manganese and iron oxides and hydroxides, ranging from a thin veneer to 260 millimeters (mm) thick, that have
precipitated on hard rock substrates on the seabed. Ferromanganese nodules are geologically young features and
many continue to grow today. They form on the seabed at the sediment-water interface, mostly by precipitation of
metals that are mobilized by redox reactions in the underlying sediments. These Ferromanganese nodules and crust
are also containing substantial amounts of other valuable metals, such as nickel, copper, and cobalt, and potentially
valuable concentrations of rare-earth elements (REEs).
C. MAGMATIC DEPOSITS:

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Formed by the magma concentration forming manganese ore deposits usually associated with Kodurite rocks of
Andhra Pradesh of India.
D. METAMORPHOSED DEPOSITS:
Formed by the recrystallization of preexisting ore-deposits by temperature and pressure. e.g.- Gonditic deposits of
Madhya Pradesh, India, Postmasburg of South Africa and Olympic Mountains of Washington, USA.
FIGURE 1: WORLD MAP SHOWING THE LOCATION, RELATIVE SIZE, AND TYPE OF THE MAJOR TERRESTRIAL MANGANESE DEPOSITS (SOURCE
USGS)

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MANGANESE ORE SPECIFICATIONS:
The Bureau of Indian Standards (BIS) has classified the manganese ores as per IS: 11895-2006 depending on Mn, Fe,
SiO2 and MnO2 contents of the ores.
FIGURE 2:CLASSIFICATION OF MANGANESE ORE
FIGURE 3:END USE GRADE CLASSIFICATION OF MANGANESE ORE (SOURCE IBM)
RESERVE AND RESOURCE OF MANGANESE: (SOURCE IBM YEAR BOOK 2020)
 The total reserves/resources of manganese ore in the country as on 1.04.2015 has been placed at 495.87 million
tonnes as per NMI database, based on UNFC system.
 Out of these, 93.47 million tonnes are categorised as Reserves and the balance 402.40 million tonnes are in the
Remaining Resources category.

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 Statewise, Odisha tops the total reserves/ resources with 44% share followed by Karnataka (22%), Madhya Pradesh
(12%), Maharashtra & Goa (7%) each, Andhra Pradesh (4%) and Jharkhand (2%). Rajasthan, Gujarat, Telangana
and West Bengal together shared the remaining 2% resources.
USES OF MANGANESE
 Manganese is used to make a number of significant alloys, as well as to deoxidize and desulfurize steel.
 It is also used in dry cell batteries.
 Manganese is used as a black-brown pigment in paint.
 For added strength and improved workability, steel contains 1% manganese.
 Manganese steel has 13% manganese which is very strong and used for railway tracks, rifle barrels, safes and prison
bars.
 Aluminum drink cans are made from an alloy that contains 1.5% manganese to increase corrosion resistance.