Volume 19, Issue 2
April 1996, pages 177-427
pp 177-177 April 1996
pp 179-199 April 1996
A critical review of the current status of tungsten resources, of state-of-the-art processing technology and of product development in India vis-a-vis the world scenario is presented. An attempt has been made to identify technology gap areas requiring attention.
pp 201-265 April 1996
Tungsten is a strategic metal for India, and almost the entire requirement is met by imports. Extensive search for tungsten in recent years has led to the discovery of several deposits. However, almost all these are of low grade compared to world resources. Techno-economic exploitation of these deposits depends to a great extent on the development of suitable beneficiation technology within the framework of an ore-to-product integrated approach. This paper presents a review of the current research and development status of beneficiation technology applicable to these deposits.
The deposits covered are: (i) Degana, comprising of four distinct types, namely, quartz vein, eluvial, phyllite and granite, (ii) Balda, (iii) Khobna-Kuhi-Agargoan, (iv) Burugubanda-Tapaskonda, (v) Scheelite-bearing gold ores of Kolar and Hutti, and (vi) Madurai. Investigations on these ores have been mainly carried out by BARC, IBM, BRGM (France), NML and RRL (Bhubaneswar). While studies of BARC have been described in detail, those of the other laboratories are briefly discussed. Emphasis has been laid on discussing the industrial flow-sheets recommended during these investigations.
The strategy needed for the techno-economic feasibility of beneficiation of low grade tungsten ores are (i) effective pre-concentration at as coarse a size as possible, (ii) emphasis on higher recovery rather than on high grade of the concentrate, (iii) a two-product approach, one of high grade feasible by physical beneficiation methods and the other of low grade, to be upgraded by chemical methods to directly usable products, thus maximizing recovery, and (iv) a maximum utilization concept, aiming to recover all possible byproducts. The flow-sheets developed for the beneficiation of individual deposits are discussed in the light of the above strategy.
pp 267-293 April 1996
Recent advances in the design of fine gravity concentrators and high gradient magnetic separation devices have led to significant improvements in the recovery of tungsten values in fine and ultrafine size range. Amongst the more promising techniques of fine particles processing, encouraging results are reported on froth flotation, shear flocculation and spherical agglomeration of tungsten ore slimes. Development of highly selective reagents such as alkyl hydroxamates, phosphonic acid derivatives and alkylated nitrosonapthols is vital for enhancing separation efficiencies in the slimes size range. Froth flotation of Indian tungsten ore slimes (particularly at Degana) using appropriate reagent combinations appears promising and needs to be examined in greater detail.
pp 295-312 April 1996
Tungsten, because of its high strength and high melting point occupies a prime position amongst metals. With depletion of high grade resources considerable R and D work is still being carried out in tungsten producing countries around the world for the processing of low grade and secondary resources. The paper gives a brief review of the hydrometallurgical processes developed to recover tungsten from low grade concentrates.
The R and D work carried out on purification and recovery of tungsten as tungstic oxide/ammonium paratungstate (APT) from a number of off-grade products such as table concentrate (WO3=66%, SiO2=2·2%, S=1·8%), middlings (18–20% WO3, and 28–30% S) and jig concentrate (4·6% WO3) are discussed in this paper. It has been found that more than 75% of silica and 90% of sulphur could be removed from the table concentrate by curing with hydrofluoric acid and subsequent roasting of the desilicated product at 650°C. In the case of middlings, it was possible to recover over 90% of tungsten as tungstic oxide by an oxidative roast followed by pressure leaching with soda.
A detailed study on the low grade jig concentrate to recover tungsten as APT, showed that over 90% extraction was possible by adopting the pressure leaching-solvent extraction route. Effect of parameters such as soda concentration, time, temperature and pressure during leaching; as well as extraction and stripping behaviour of tungsten from leach solution at different pH and aqueous to organic ratio during solvent extraction with Alamine-336, were studied and a flow-sheet was developed for processing of jig concentrate analysing 4·6% WO3.
pp 313-329 April 1996
Experiments/testworks were carried out on Degana tungsten ore by various R & D organizations to recover the strategic mineral wolframite. Process flowsheet developed after tests on the dump ore assaying 0·151% WO3 is being tried on a very small scale till the 150 tpd pilot beneficiation plant is commissioned. Tungsten bearing granite samples were also found amenable to physical benefication. Hence 168 Mt granitic resources analysing 0·08% WO3 has ushered a hope for large scale exploitation subject to detailed exploration. By-product recovery of lithium, caesium, rubidium and some other trace elements, if feasible, will be of added advantage.
pp 331-343 April 1996
The determination of tungsten in low grade ores and geological samples is one of the most difficult and challenging tasks. Many of the associated elements, especially molybdenum interfere. These have to be overcome by suitable methods of separation or suppression of the interfering elements. Since the concentrations are low, instrumental methods are preferred over the classical methods. Thus spectrophotometry, fluorometry, atomic absorption spectrometry, atomic emission spectrometry, X-ray fluorescence, neutron activation analysis, electro analytical methods and chromatography are preferred. These are discussed in this review.
pp 345-355 April 1996
Rare-earth doped strontium barium niobates were synthesized using usual ceramic technique. The dopants are La, Ce, Gd, Sm and Nd. The materials were characterized by XRD and density measurements. The grain sizes were determined from SEM analysis. Lattice parameters changed uniformly with rare-earth dopants in unfilled structures. Density measurements and SEM analysis confirmed only minute changes in the densities of the ceramics.
pp 357-371 April 1996
The Gibbs free energy difference (ΔG) between the undercooled liquid and the equilibrium solid phases has been studied for the various kinds of glass forming melts such as metallic, molecular and oxides melts using the hole theory of liquids and an excellent agreement is found between calculated and experimental values of ΔG. The study is made for non-glass forming melts also. The temperature dependence of enthalpy difference (ΔH) and entropy difference (ΔS) between the two phases, liquid and solid, has also been studied. The Kauzmann temperature (T0) has been estimated using the expression for ΔS and a linear relation is found between the reduced glass transition temperature (Tg/Tm) and (T0)/Tm). The residual entropy (ΔSR) has been estimated for glass forming melts and an attempt is made to correlate ΔSR,Tg,T0, andTm which play a very important role in the study of glass forming melts.
pp 373-381 April 1996
A glass of composition similar to that found in fireclay refractories was synthesized and subsequently nucleated with Cr2O3, V2O5 and TiO2. These glasses were heat-treated for crystallization of the mullite phase. The mullite content, the crystallization of mullite and the effect of temperature on the rate were investigated. The concentration of the nucleating oxides and the size and charge of their cations influence both the mullite content obtained and the crystallization rate.
pp 383-392 April 1996
Poor-grade fireclay products contain substantial amount of glass. A glass of similar composition was synthesized, nucleated and heat-treated for crystallization of mullite. The size and size-distribution of mullite crystals, the rate of change of size and the aspect ratio of the crystals were investigated in relation to the nucleating agents and temperature.
pp 393-404 April 1996
Glass of the nominal composition 64 wt%(SrO·TiO2)·35 wt%(2SiO2·B2O3)-1 wt%(CoO) was prepared. The glass samples were subjected to heat treatment at 900 and 950 C. The phase progression in these glass ceramics from X-ray diffraction studies shows the formation of Sr2B2O5 as primary crystalline phase followed by rutile (TiO2), Sr3Ti2O7, SrB2Si2O8 and Sr3B2SiO8 as secondary phases. The first DTA exothermic peak of glass corresponds to the crystallization of Sr2B2O5, rutile and Sr3Ti2O7 phase while second crystallization peak may be assigned to the formation of SrB2Si2O8 and Sr3B2SiO8 phases. From microstructure studies we find that strontium borate grows with larger grain size whereas the other phases like Sr3Ti2O7, TiO2 appear smaller in size. Cobalt oxide content in the strontium titanate borosilicate glass ceramic gives the thermal stability to dielectric behaviour and decreases the dielectric loss.
pp 405-409 April 1996
Amorphous inorganic ion exchangers zirconium phosphate, zirconium molybdate and zirconium phosphomolybdate have been prepared and characterized by elemental analysis, TGA, FTIR and surface area measurements. The protonic conductivity in these materials were determined at various temperatures and compared. It was found that the mixed material zirconium phosphomolybdate showed maximum conductivity at all temperatures.
pp 411-416 April 1996
Surface structure of thin silver films (200 Å) on two technologically important films, indium tin oxide (ITO) and aluminium oxide, has been studied using scanning tunneling microscope. ITO films were prepared by reactive electron beam evaporation. Aluminium oxide films were prepared by oxidizing 2000 Å thick aluminium films evaporated on to H2 terminated single crystal silicon substrates. The surface structure of silver on ITO and aluminium oxide appeared to be same and was characteristic of Stranski-Krastanov type. The observed asymmetry in the island shape was attributed to the anisotropic nature of the strain fields surrounding the nucleation centres.
pp 417-422 April 1996
The presence of different kinds of surface lattice defects such as missing atom, interstitial atom, line defects, in graphite single crystal have been identified by using scanning tunneling microscope. These defects cause displacement of atoms from their mean position and lattice strain is introduced. By measuring the displacement of atoms from their mean position. lattice strain has been calculated. It is found that among single point defects, vacancies cause maximum lattice strain.
pp 423-427 April 1996
We have fabricated light emitting diodes (LED) with poly (p-phenylene vinylene) (PPV) as the emissive layer and tin oxide (TO) as the transparent conducting positive electrode and aluminium as the negative electrode. The fabrication conditions are optimized for visible light emission in these TO/PPV/Al LEDs. The threshold voltage for substantial charge injection for visible light emission in these LEDs lies below 10V. The device fabrication and electrical characterization of TO/PPV/Al LEDs are discussed in this communication.
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