Manganese

OCCURRENCE OF MANGANESE
Manganese is a chemical element with symbol Mn and atomic number 25. Manganese comprises about 1000 ppm (0.1%) of the Earth's crust, the 12th most abundant of the crust's elements.  It is not found as a free element in nature; it is often found in minerals in combination with iron. Manganese is a metal with important industrial metal alloy uses, particularly in stainless steels.
Manganese is widely distributed in the terrestrial crust. It is usually associated with the iron ores, in relatively small concentrations. The principal manganese ores are:
pyrolusite (MnO2),  psilomelane, manganite (MnO(OH)), braunite (3Mn2O3.MnSiO3) and hausmannite (Mn3O4), that can be found in Brazil, Gabon, India, Ghana, Congo and South Africa. Other manganese ores, although less important, are: rhodochrosite (MnCO3) and rhodonite (MnSiO3).
Historically, manganese is named for pyrolusite and other black minerals from the region of Magnesia in Greece, which also gave its name to magnesium and the iron ore magnetite . By the mid-18th century, Swedish-German chemist Carl Wilhelm Scheele had used pyrolusite to produce chlorine . Scheele and others were aware that pyrolusite (now known to be manganese dioxide ) contained a new element, but they were unable to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, which he did by reducing the dioxide with carbon .
Manganese phosphating is used for rust and corrosion prevention on steel. Ionized manganese is used industrially as pigments of various colors, which depend on the oxidation state of the ions. The permanganates of alkali and alkaline earth metals are powerful oxidizers. Manganese dioxide is used as the cathode (electron acceptor) material in zinc-carbon and alkaline batteries.
In biology, manganese(II) ions function as cofactors for a large variety of enzymes with many functions.  Manganese enzymes are particularly essential in detoxification of superoxide free radicals in organisms that must deal with elemental oxygen. Manganese also functions in the oxygen-evolving complex of photosynthetic plants. While the element is a required trace mineral for all known living organisms, it also acts as a neurotoxin in larger amounts. Especially through inhalation, it can cause manganism , a condition in mammals leading to neurological damage that is sometimes irreversible.
MINING METHOD OF MANGANESE
Mining is the extraction of valuable minerals or other geological materials from the earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. These deposits form a mineralized package that is of economic interest to the miner. Ores recovered by mining include metals, coal, oil shale, gemstones, limestone, chalk, dimension stone, rock salt, potash, gravel, and clay. Mining is required to obtain any material that cannot be grown through agricultural processes, or feasibly created artificially in a laboratory or factory. Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or even water.
Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials, and final reclamation of the land after the mine is closed.
Mining is the process of taking out the ores from the mines, when an ore occurs near the surface of the earth and can be directly dug out. Such mining is termed as open-pit mining. When an ore is taken out form greater depths, then the mining is termed deep mining and these are the two basic method of mining manganese.
BENEFICIATION ROUTES FOR MANGANESE ORE
MATERALS AND METHODS
The materials employed for this work include: a composite sample of Wasagu manganese ore. The equipment used were small size laboratory jaw crusher, cone crusher, pulverizing machine,
standard sieve shakers, Wifley shaking table, spiral concentrator, high intensity magnetic separator, XRF spectrometer.
Sample preparation
Composite sample of Wasagu manganese ore weighing 50 kg were collected from four (4) pits at 5 m interval and a depth of 6 m. The pits were dug by local artisanal miners. The average size of a sample is about 8 cm. The sample was dried, crushed, using the cone crushers to sizes
ranging from 0.2 cm to 0.5 cm and was finally pulverized and sieved through the mesh sizes  -710+500 μm, -500+355 μm, -355+250 μm, -250+180 μm,-180+125 μm,-125+90 μm,-90+63 μm.



Methods
Size-assay analysis of the composite sample was carried out in order to determine the 80 % passing and the distribution of manganese within the size fractions. The various size fractions
retained on each sieve was weighed and assayed for %Mn content using the XRF spectrometer.
Concentration Test was carried out using laboratory scale shaking table, on some samples of manganese ore ground to the following particle sizes -710+500 μm, -500+355 μm, -355+250μm, -250+180μm,-180+125 μm,-125+90 μm,-90+63 μm.
Each particle size fraction was prepared using 25 % solid by weight and was used for each batch of concentration test.
Concentration Test was also carried out on representative samples of manganese ore ground to the following particle sizes using spiral concentration with -710+500μm, -500+355 μm, -355+250 μm, -250+180 μm, -180+125 μm, -125+90 μm, -90+63 μm.
Each particle size fraction was prepared using 25 % solid by weight and was used for each batch of concentration test.
Magnetic Separator was also used to separate the magnetic from the nonmagnetic minerals. A representative sample of the ground ore was used, which was sized into various size fractions
ranging -710+500 μm, -500+355 μm, -355+250 μm, -250+180. μm,-180+125μm,-125+90 μm,-90+63 μm. These various size fractions were subjected to magnetic separation, using a dry belt high intensity magnetic separator. After which two products (concentrate and tailings) were produced for analysis.








EXTRACTIVE METALLURGY OF MANGANESE
HYDROMETALLURGY
Hydrometallurgical processes involve the removal of metals from different types of ores, concentrates and waste products by aqueous solutions containing different chemical reagents. These processes generally include the following unit operations: roasting (not always), leaching by acids, bases or water, removal of impurities such as iron, separation and recovery processes and refining of recovered metals.
Basic Steps in Hydrometallurgy
The actual process of extraction of a metal from its ore depends upon the nature of the ore and the metal. There is no universally operational method for the extraction of metals including manganese. Certain common steps, however, are involved in all metallurgical processes. These steps are:
Mining: Mining is the process of taking out the ores from the mines, when an ore occurs near the surface of the earth and can be directly dug out. Such mining is termed as open-pit mining. When an ore is taken out form greater depths, then the mining is termed deep mining.
Crushing: Extracted ore often occurs in big lumps. It is essential to break it into smaller pieces. The lumps are crushed to smaller pieces by hammering in a hammer mill or by help of a jaw crusher.
Grinding: The crushed ore is then finally grinded to fine powder state in a stamp mill or a pulveriser.
Ore Dressing: The removal of the undesired foreign impurities from the roe is called ore-dressing (beneficiation).
Any of the following methods is used for concentrating the ores, the various methods used in ore dressing include:
a) Hand picking: If the impurities present are quite different from the ore and are of large size, these may be removed by hand picking. This method is slow and is generally adopted in the initial stages of concentration.
b) Gravity or levigation separation: When the ore particles are heavier than the gangue particles, the ore is fed into a running stream of water and impurities are washed away and in order to concentrate the ore in bulk, a slanting vibrating wooden table with wooden strips called riffles is introduced in the process, such tables are termed Wilfley tables. Sometimes in the gravity method, a hydraulic classifier based on the gravity method is used. Ore is agitated by a powerful current of water pushing upwards through the bottom of a conical reservoir. The heavier ore particles settle down and are continuously removed from another opening near the bottom, while the lighter particles are washed away by water.
c) Magnetic separation: This is done especially in the case of hematite ore, were by the powdered ore is dropped on to leather or brass conveyer belt, which moves over two rollers one of these rollers, is magnetic. When the ore passes over the magnetic roller, it sticks to the belt due to the force of attraction and falls nearer due to the force of attraction of the magnetized roller. The gangue falls over readily further away.
d) Froth flotation process: This process is used for concentrating sulphide ores and the ores are preferentially wetted by oil while the gangue particles are wetted by water. Powdered ore is mixed with water and a little pine oil and the mixture is vigorously stirred by passing compressed air. The froth, which is produced rises to the surface and carries the ore particles along with it. The gangue is left behind.
Leaching: This is the most important starting point of hydrometallurgical processes. It involves the use of aqueous solutions containing a lixiviant which is brought into contact with a material containing a valuable metal. The lixiviant in solution may be acidic or basic in nature. The type and concentration of the leachant is normally controlled to allow some degree of selectivity for the metal or metals that are to be recovered. In the leaching process, oxidation potential, temperature and pH of the solution are important parameters and are often manipulated to optimize dissolution of the desired metal component into the aqueous phase.










Other methods of extracting manganese include the following:
PYROMETALLURGY
This metallurgical process includes smelting and roasting. It involves heating in a blast furnace at temperature above 1500˚C to convert waste to a form that can be refined. The oxide (waste) is heated with a reducing agent such as carbon in the form of coke or coal, the oxygen of the metal combines with the carbon and is removed as carbon dioxide gas. The waste material in non-metallic part is called gangue. It is removed by means of a flux which, when heated combines with it to form a molten mass called slag. Being lighter than the metal, the slag floats on it and can be skimmed or drawn off.
BIOMETALLURGY/BIOLEACHING
Bioleaching is a technology in which metal ions are extracted from low-grade ores and nodules by direct or indirect actions of micro-organisms. The advantages of bioleaching include the absence of noxious of gases or toxic effluent, simplicity of plant operation and maintenance, economic and simple process requiring low capital and low-operating costs and applicability to various metals. The principal bacterium in ore leaching is Thiobacillus ferrooxidans, which is capable of oxidizing ferrous iron as well as sulphur compounds. The thermophilic sulfolobus plays a role in leaching at elevated temperature. Most of the biotechnical processes for leaching of metals have been developed using aerobic microorganisms.
However, the highly oxidized metal compounds such as MnO2 and Fe2O3 can be solubilized by reduction processes. Hence, Mn and Fe from MnO2 and Fe2O3 can be recovered by the direct or indirect actions of heterotrophic microorganisms that thrive under micro-aerobic or anaerobic conditions. In the former case, the microorganisms are capable of utilizing MnO2 as a final acceptor of electrons in the respiratory chain of their metabolism, instead of oxygen. That is, anaerobic heterotrophs such as iron-reducing bacteria, manganese-reducing bacteria, and sulphur-reducing bacteria donate electrons, which are produced by the oxidation of organic substrates to Fe2O3, MgO, MnO2, SeO4 and V2O3, and leach the reduced metal ions into the medium. In the second case, the reduction process is associated with the formation of reducing compounds, which are products of their metabolism. The anaerobic bioleaching technology of metals has not been commercialized. This is because it has to be adapted according to each type of metals. Moreover, there is a demand for a less expensive and more environmentally friendly anaerobic bioleaching process.
SOLUTION CONCENTRATION AND PURIFICATION
After leaching, the leach liquor must normally undergo concentration of the metal ions that are to be recovered. Additionally, some undesirable metals may have also been taken into solution during the leach process. The solution is often purified to eliminate the undesirable components. The processes employed for solution concentration and purification include: precipitation, cementation, solvent extraction,  electrolysis, ion exchange etc.












REFINING PROCESSES FOR MANGANESE
In pyrometallurgy, heating and refining of manganeses are made in blast furnaces using only coke as reductant and as energy source or in electric smelting furnaces. Depending on the ore quality the efficient electric furnaces consume about 2100 - 2800 kWh electric power per 1 t of ferromanganese alloy (Kroschwitz and Howe-Grant, 1982) and (Elvers et al, 1990).













PROPERTIES AND APPLICATIONS OF MANGANESE

PROPERTIES

Manganese is black manganese dioxide. Manganese can be welded, machined, and coldworked because they are less ductile and malleable. They have high strength and hardness

APPLICATIONS

Mn is necessary for a variety of metabolic functions including those involved in skeletal system development, energy metabolism, activation of certain enzymes, nervous system function, immunological system function, and reproductive hormone function, and is an antioxidant that protects cells from damage due to free radicals.
Mn also plays an essential role in regulation of cellular energy, bone and connective tissue growth and blood clotting.
In the brain, Mn is an important cofactor for a variety of enzymes, including the antioxidant enzyme superoxide dismutase, as well as enzymes involved in neurotransmitter synthesis and metabolism.
Manganese has three primary metabolic functions:
(i) it acts as an activator of the gluconeogenic enzymes pyruvate carboxylase and isocitrate dehydrogenase,
(ii) it is involved in protecting mitochondria1 membranes through superoxide
dismutase; and
(iii) it activates glycosyl transferase, which is involved in mucopolysaccharide synthesis.
The most important source of Mn for the general population is diet, and the average intake of Mn from food ranges from 2 to 9 mg/day.
In addition, vitamin and mineral supplements may contain 1 to 20 mg Mn/tablet.
Manganese is mainly used as an alloying agent in the manufacture of steel to increase its tensile strength. It is also added during the steelmaking process to remove sulfur as a slag.
Austenitic manganese steels are used for railroad trackwork, power shovel buckets, and rock crushers. Mediumcarbon manganese steels are used in the manufacture of car axles and gears