Manganese
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[edit] Overview
Manganese (Mn) is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing, and alloying properties. Steelmaking, including its ironmaking component, accounts for most domestic manganese demand, presently in the range of 85% to 90% of the total. Manganese ferroalloys, consisting of various grades of ferromanganese and silicomanganese, are used to provide most of this key ingredient to steelmaking. Products for construction, machinery, and transportation are leading end uses of manganese. Manganese also is a key component of certain widely used aluminum alloys and, in oxide form, dry cell batteries. As ore, additional quantities of manganese are used for such nonmetallurgical purposes as plant fertilizers, animal feed, and colorants for brick.
Manganese minerals are widely distributed; oxides, silicates, and carbonates are the most common. The discovery of large quantities of manganese nodules on the floor of the oceans may become a source of manganese. These nodules contain about 24% manganese, together with many other elements in lesser abundance.
Most manganese today is obtained from ores found in Russia, Brazil, Australia, South Africa, Gabon, and India. Pyrolusite and rhodochrosite are among the most common manganese minerals. The metal is obtained by reduction of the oxide with sodium, magnesium, aluminum, or by electrolysis.
[edit] Applications
1.Manganese and Steelmaking- Steel is basically an alloy of iron and carbon, consisting of an iron phase and iron carbides. Crude steel produced from iron contains an undesirable amount of oxygen and some sulphur. Manganese plays a key role because of two important properties: its ability to combine with sulphur and its powerful deoxidation capacity. When there is insufficient manganese the sulphur combines with iron to form a low melting point sulphide, which melts at hot rolling temperatures, causing a surface cracking phenomenon known as “hot shortness”. Desulphurisation processes reduce the need for manganese in this respect. Some 30% of the manganese used today is still used for its properties as a sulphide former and deoxidant.
2.Other Metallurgical Uses of Manganese- Manganese is used as an alloying element up to its solubility limit of about 1.5%. Aluminum-manganese alloys and aluminum-manganese-magnesium alloys, which have been sold under different trade names, have found applications in such diversified areas as kitchenware, roofing, car radiators and transportation. By far the most important use of aluminum-manganese alloys is for beverage cans, of which some 100 billion units are produced each year. The market for aluminum-manganese cans has grown steadily, thanks to the fact that such cans can be recycled.
3.Non Metallurgical Uses- Batteries-The most important non-metallurgical application of manganese is in the form of manganese dioxide, which is used as a depolarizer in dry-cell batteries. Dry cell consumption in the world exceeds 20 billion units per year. The function of manganese in batteries is simple. In the battery cell, the anode and cathode are essentially humid. During discharge, hydrogen generated at one of the electrodes coats the latter with a gas film, preventing any further wetting, hence cutting off electrical generation. The role of the manganese dioxide is to oxidize the hydrogen and form water. The rate at which this occurs depends on the reactivity of the dioxide. Chemicals-Potassium permanganate is one of the best known manganese products. It is a powerful oxidizing agent with bactericidal and algicidal properties, which enable it to be used in purifying drinking water and treating waste water. It is also used for odour control, including deodorization of discharges from paint factories, fish-processing plants, etc. Permanganate has a variety of other applications as an oxidant. [1]
[edit] Production
Total world production of manganese alloys reached 11.8 million metric tons, up by 14% from 2005. As in past years, manganese alloy production was dominated by China, producing approximately 42% (4.9 million mt). All other regions of the world showed marked increases in production except Japan and the Americas, which saw decreases of 15% and 18% respectively.In 2006, the global unit consumption of manganese ferroalloys was approximately 10 kg alloy per mt of steel produced. This figure varies significantly from region to region with the differences related to the steel production process, the quality of raw materials used, (such as iron ore grades) and types of steel products produced.
[edit] Demand
World demand for manganese depends directly on the needs of the steel industry. There are numerous grades of steel and each requires a different amount of manganese. Unit consumption is determined by calculating the average requirement of manganese per ton of steel. Some manganese which is to be converted into steel is present in the iron (hot metal) coming either from the iron ore charge or from the addition of manganese ore to the blast furnace. This manganese is only a small part of the total requirement and it is partly oxidized during the different processes that convert the hot metal into steel. Hence most of the manganese addition is made in the steel melting shop. The majority of it is in the form of manganese ferro-alloys, but there are some cases when it can be added in the form of ore.
Part of the manganese is lost in the steelmaking process through oxidation. In the 1960’s and 70’s, when the oxygen-blown process progressively replaced the open hearth, Bessemer and Thomas processes, the subsequent improved manganese yield caused a decline in unit consumption. In the 1980’s further improvements in steelmaking (brought about by the development of combined blowing processes) meant even better manganese yields. Today, the average unit consumption for industrialized countries is a little over 7.5 kg of manganese per ton of steel. Changes in steel grade chemistry have had an effect on manganese requirements. For a constant unit consumption, manganese demand follows the growth in steel production. Manganese requirements for other metallurgical applications or for non-metallurgical uses do not represent a quantity large enough to significantly affect the evolution of the overall manganese demand as a direct function of steel production growth. [2]
[edit] World Market Trend
International manganese trade has long been closely linked with the demand of industrialized countries in Europe, North America, Japan and South East Asia. In the early 1980’s, a slowdown in steel production combined with a decrease in manganese unit consumption resulted in a decrease in the demand for manganese. This was partly compensated by new demands from China and CIS, all wanting to upgrade their own resources. These trends, added to the decrease in demand for ferruginous ore, increased the share of high grade ore in world trade.
Out of a manganese ore production of over 34 million tons per year, 13 million tons come onto the international market. A few producing countries, Australia, Brazil, Gabon and South Africa, account for over 85% of the world’s supply. From the mid-1970’s, South Africa, Brazil and Mexico started upgrading their exports by locally processing part of the ore into manganese-containing ferro-alloys.
Today, most of the manganese requirements of industrialized countries are supplied in the form of alloys. As a result, the UK and Germany have has almost completely abandoned local production of manganese alloys and the USA is now only a minor producer. In Europe, countries such as France, Norway and Spain have continued to be large exporters of these ferro-alloys.
