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The Scope for Development of Magnesium Industry in India

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The Scope for Development of Magnesium Industry in India THE SCOPE FOR DEVELOPMENT OF MAGNESIUM INDUSTRY IN INDIA R. N. Misra V. S. Sampath P. P. Bhatnagar N THIS era of "sputniks" and "space flights", The endwise application of magnesium in U.S.A. ex- weight saving poses to be a problem of prince im- cluding export during 1956 as 31",, for structural and I portance with its direct influence over increasing 63'9°o for non-structural purposes'. speed and fuel economy. Magnesium and magnesium Increasing demand for magnesium created by its base alloys are known to be the lightest structural indispensable nature for wide range of applications is materials today, and have been employed not only responsible for the phenomenal rise in its production for space research and rocketry but for various types from a meagre 10 lb in 1900 to a peak value of of aero, marine and road transportation vehicles. 238,500 tons in 1943 and the present world production The low density of magnesium connhined with good is estimated at 0'IS million tons. Consequent to its mach inability, damping capacity, rigidity without large scale production and advancement in the know- weight penalty, wearing qualities, heat and electrical ledge of magnesium production, the price per pound conductivity and chemical resistance have rendered it of magnesium has dropped down from X5'00 in 1915 to eminently suitable for its multifarious applications. It 36 cents in U.S.A. can be subjected to sand or die-casting, rolling, simple The principal magnesium producing countries are or impact extrusion, forging, drawing. spinning, joining 11.S.A., U.S.S.R., Germany, U.K., France, Canada, by welding, brazing, bolting or revetting and other Norway and Italy. India's requirements of magnesium standard processes necessary for an excellent engineer- either as virgin metal or as finished product is niet by ing metal. imports alone. In the country's programme for self- As a light structural, magnesium has found extensive sufficiency in the basic materials and the expansion applications in the field of missiles, air-craft landing of aircraft industries, the demand for magnesium is wheels, reciprocating aero engines. wings, fuselage, bound to increase manifolds and it is essential that manufacture of commercial high way transportation serious efforts should, therefore, be made for taking up vehicles, industrial machinery tools, material handling the production of magnesium in the near future. equipment, packaging, foundry, printing, graphic arts, and for various military purposes such as construction Raw materials and resources of radar equipment, radios and accessories, tents, portable alert shelters, sleds, conveyors, shipping pal- The chief minerals of commercial importance for lets, instrument cases and endless varieties of similiar extraction of magnesium are dolomite, magnesite, items that must be carried by air. Besides the uses brucite and carnallite. India has vast resources of of magnesium as alloying element, deoxidiser and magnesium both as sea-water and as high grade desulphuriser, it has been widely used for the reduc- mineral deposits. Dolomite or dolomitic limestone tion of halides and oxides for the production of newer deposits have been found in Orissa, Bengal, metals like titanium, zirconium, Uranium, etc. Mag- Bihar, Maharashtra, Madhya Pradesh. Madras. nesium powder is used in pyrotechnics. The principal Mysore, Punjab, Rajasthan, Uttar Pradesh, Jammu chemical and electro-chemical uses of metallic magne- and Kashmir. The best known occurrences are in sium include cathodic protection of underground pipe- Birmitrapur area of Gangpur. Orissa and extend lines, construction of batteries, and preparation of over a distance of more than 60 miles containing an Grignard reagents for synthetic organic chemistry. estimated reserve of over 252 million tons2^6. Besides the high grade dolomites, certain low grade siliceous dolomites of Kashrnirr and other parts in the Messrs R. N. Misra , V. S. Sampath, Junior Scientific Officers and Mr . P. P. Bhatnagar , Assistant Director, National Metallurgi. Himalayan ran_ae containing about 6°;, impurities are cal Laboratory, Jamshedpur. also suitable for extraction purposes, Extensive 200 deposits of magnesite have also been located at various The powder, however, could be suitably treated in places in India and the Salem deposits in Madras are vacuum or under an inert gas to yield magnesium in an the most promising both for purity and the reserves. aggregate form. Carbothermic process was first attempted by Hansgirg and units were later set up in General methods of extraction Korea and in U.S.A. at Permanente, California'. The reducing agents used for direct reduction with Though magnesium was first isolated in 1808, the formation of non-volatile oxide include calcium carbide, production of the metal, based on fused salt electro- aluminium, aluminium-silicon alloy, iron-aluminium- lysis, started in 1886 and the industry grew with silicon alloys, calcium silicide, ferro-silicon and metallic remarkable rapidity during the First World War. At sodium. The ferro-silicon reduction process developed the outbreak of Second World War, great enthusiasm in Canada by Pidgeon is of outstanding commercial for production of magnesium was supplemented by importance, and has been employed at several places. development of direct reduction processes, and magne- The reduction of dolomite by Ferro-silicon is re- sium is produced today by both electrolytic and direct presented as: reduction processes. 2(CaO.MgO)-I-(Fe). Si =(CaO)2Si02+2Mg+(Fe) Electrol_t•tic process: The electrolytic processes as The presence of time in the dolomite is beneficial as it practised at different plants are essentially similar combines with silica as soon as it is formed, thus con- except in the cell characteristics, and the use of siderably decreasing the activity of silica in the reaction magnesium chloride with different degrees of dehydra- mixture. The continuous removal of magnesium from tion. Use of magnesium oxide in a fluoride bath the reaction zone at the operating temperature and similar to production of aluminium was not commer- pressure shifts the equilibrium to the right and the cially attractive, when compared to the chloride reaction goes to completion. The kinetics of reaction process. Magnesium chloride used for electrolysis is are thus governed by the rate of removal of magne- prepared either by dehydration of the hexa-hydrate or sium either by vacuum technique or use of an inert direct production of anhydrous salt by chlorination of carrier gas. Reaction in a continuously moving stream magnesium oxide in presence of carbon. The dehydra- of hydrogen has proved to be hazardous while use of tion of magnesium chloride hexa-hydrate by heating argon or helium is prohibitive on economic grounds. requires rigid control owing to its tendency for decom- The present commercial practice is to carry the re- position to the oxide and hydrochloric acid. In the actions under vacuum. This has been possible owing Dow Chemical process, the operation is carried out in to advances in vacuum technology and today silico- two stages ; first by converting it to tetra-hydrate and thermal process is gaining ground. Availability of subsequently with dehydration to an indefinite com- proper equipment and a fund of know-how evolved pound containing 1.25 molecules of water, which is the possibility of producing thousands of pounds of used as a cell feed. The dry chlorination process has magnesium per day at low pressures. been followed by several producers including the In Pidgeon's process, the reduction of briquetted Pioneer German firm-I. G. Farben-industries. Princi- calcined dolomite with ferro-silicon is carried out in pal differences in cell characteristics lie in the fact that heat resisting retorts at II50°C under a vacuum of in one case a steel pot with external heating arrange- 0.1 mm Hg. The use of ferro-silicon as reducing ment is employed, whereas the other makes use of a agent is preferred as it grinds readily. Flourspar has refractory lined cell without any external heating been used as a catalyst and it has been observed to source. Power consumption in both the cases ranges hasten the reaction. Both dry and wet practices have between 8-5-9 kWh per pound of magnesium. been followed for briquetting the mixture. Wet Direct reduction : Earlier attempts for the direct process offers comparative ease in briquetting, but an reduction of magnesium oxide did not bear fruit on additional drying step is required before the briquettes account of the high affinity of metal for oxygen. The are charged into retorts. The use of molasses or a chief difficulty encountered for the direct reduction of suitable oil for binder has also been suggested. MgO was the difficulty of attaining the desired tem- The proper heat distribution in the retort charge is perature for reaction or evolving means to remove one one of the chief requisites of the process and this has of the reaction products to enable the reaction to go to limited the retort dimensions in the Pidgeon's process. completion. The reduction of MgO by carbon may Amongst the various silico-thermal processes for the be represented as : production of magnesium either independently deve- MgO+-C=CO+Mg (g) loped or modified after the Pidgeon's process may be It was shown by Slade' that carbon can be used as a mentioned the internal heating used by Pistors in reducing agent if a reaction temperature of the order Germany and Bagley in U.S.A. of 1,900,C is attained. The reverse reaction of Mg A recent development in the silico-thermal reduction with CO forming MgO and C prevented the successful of dolomite has been the "Magnetherm process"' exploitation of carbon reduction till Hansgirg' develop- developed and patented by Le Magnesium Thermique ed a successful method for shock-cooling, the reaction Magnetherm, France. product thus preventing the re-formation of MgO.
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