A.K. Suri

Investigations on Flowsheet Development for the Treatment of Niobium-Tantalum Bearing Cassiterite

Abstract The paper presents the results of experimental investigations carried out for developing a flowsheet for the treatment of niobium-tantalum bearing cassiterite containing about 23%of mixed niobium and tantalum oxide. Three different approaches viz. direct smelting of cassiterite to tin metal and niobium-tantalum bearing slag, reduction roasting-acid leaching and alkali fusion-leaching to separate tin from niobium-tantalum followed by recovery of tin as oxide and finally carbothcrmic reduction to tin metal have been examined on laboratory scale. It has been observed that alkali fusion—leaching—tin oxide smelting is quite attractive to obtain a good purity tin metal and also recover niobium and tantalum as mixed oxides.

Studies on Processing of an Alnico Scrap

Abstract This paper presents the results of research and development work on processing of alnico scrap, a secondary resource of nickel and cobalt, generated during the manufacturing of alnico magnets. The scrap contains 8-10% nickel, 10-12% cobalt, 32-50% of iron, 8-10% aluminium, 2% copper and remaining silica. Various processes such as acid leaching, aqueous chlorine leaching, salt roasting and cupric chloride leaching were studied in detail. Of these cupric chloride leaching was found to be most effective with respect to recovery and purity. It has been possible to obtain pure nickel and cobalt salts by cupric chloride leaching of the scrap, solvent extraction and precipitation of the salts. The overall recovery by the above process was almost 99%.

Magnetron Sputtered TiN Coatings Modified by Chromium, Nickel and Electroless Nickel (EN) Interlayers on Mild Steel

Abstract TiN films were deposited by reactive d.c. magnetron sputtering on mild steel substrate. Because of presence of inherent porosity and internal stresses, TiN coatings cannot be relied to give corrosion protection; also TiN coatings need a good load support. Electroplated chromium and nickel and electroless nickel (EN) were deposited by plating as interlayers below the TiN coatings to study comparatively the effect of these interlayers. Chromium was electrodeposited from conventional sulfate catalysed chromic acid bath and nickel using Watts bath while EN by electroless deposition process using acidic hypophosphite bath. Three different thicknesses viz. 2. 4 and 10 μm of interlayers were employed to study their influence on TiN coatings. The corrosion behaviour of TiN coated mild steel samples with and without the interlayers was studied using potemiodynamic measurement technique in deaerated IN H2SO4 electrolyte. It was observed that TiN coatings on mild steel without any interlayer almost mimic the behaviour of the substrate, while the presence of any of the three interlayers showed a considerable improvement in the corrosion resistance. Microhardness measurements have shown that the surface hardness values of TiN coatings on mild steel increased to 1907 HK25 from about 1000 HK25 when employed with chromium interlayer. and to 1484 HK25 with EN interlayer, while electroplated nickel as an interlayer increased the hardness to a lesser extent (1289 HK25). X-ray diffraction analysis has shown that the phases present in the TiN coatings were mainly TiN (200) and TiN (111). Chromium coated samples were found to show the broadening of Fe (110) peak, which also corresponds to Cr (110) peak. Interlayer nickel showed the presence of mainly Ni (200) and Ni (111) phases while EN was amorphous in structure. The crystalline phases Ni3P and Ni were evident when TiN top-coat was given by d.c. magnetron sputtering on EN plated mild steel samples.

Studies on Processing of Low Grade Indian Molybdenum Sulphide Concentrate

In India, a low grade molybdenum sulphide concentrate containing 25–30% molybdenum is recovered as a by-product of uranium operations at Jaduguda. This concentrate contains a high association of copper and nickel. If it is processed by the conventional route, both copper and nickel would decrease molybdenum recovery. Such concentrates need a different processing route. Various processes such as soda ash roasting, lime roasting, oxychlorination, and electro-oxidation have been studied. The processes aimed at converting molybdenum into a soluble form, then purified by chemical processing as well as by carbon adsorption-desorption route to yield pure molybdic oxide. The oxide was then reduced to metal with hydrogen. In an alternate scheme, molybdenum values in solution have been converted into molybdenum intermediates such as calcium molybdate/ferrimolybdate. This paper presents the result of these investigations.

Studies on Processing of Nickeliferrous Sources in India

Nickel requirement in India is met through imports although there are known deposits of nickel laterites. In addition, there are secondary sources such as nickel sulphide in multimetal sulphides associated with uranium ore, low grade nickel bearing lateritic overburden of chromite mining and industrial wastes, such as spent catalyst and grinding waste of alnico. The primary deposits are extensive but the grade is low. All the other sources are small and some of them are quite complex. Recovery of metal values from such sources is important on account of resource conservation. The paper reviews the studies carried out in different laboratories in India.

Processing of Secondary Sources of Refractory Metals

Abstract Refractory metals belonging to the Group IV to VIA of the periodic table have assumed very important role in variety of high-tech applications. Extraction of these metals so far has been accomplished mainly from primary and byproduct sources. Depletion of primary sources, non-availability of the sources of these metals in certain countries, relatively large applications and greater emphasis on environmental preservation have led to increased awareness in using secondary sources of these metals. Use of secondary sources in fact makes a better economic source particularly for these high value metals This paper is based on extensive studies carried out in the Materials Group of BARC on the recovery of refractory metals such as tungsten, molybdenum, niobium, tantalum, vanadium and zirconium from a variety of secondary sources available within the country. Major objective has been to develop processes which can be operated even on a small scale with variable grade of the source using indigenously available equipment