| dc.description.abstract | The unique high?temperature properties of tungsten and its alloys are responsible for increased demand for this metal, particularly in the forms of carbide and pure metal. It is also an important strategic material for defence, nuclear, and space research applications. India imports large quantities of tungsten concentrates to meet domestic demand. The production of concentrates in the country is very meagre and restricted to high?grade tungsten deposits of limited extent. As such, there is an urgent need for the beneficiation of the vast low?grade deposits available in the country.
The phyllite deposits of Degana, Rajasthan, contain tungsten values in the form of wolframite (Fe,MnWO?) to an extent of 0.06% WO?. From thin and polished sections of selected samples, a detailed mineralogical analysis has been conducted to identify the various associated minerals in the ore. The major gangue minerals identified are quartz, iron oxides, and mica, along with minor amounts of graphite, fluorite, and sulphides. Quantitative analysis of the ore revealed 0.06% WO?, 14.30% Al?O?, and 67.14% SiO?.
The amenability of the ore to gravity concentration has been studied by heavy?liquid separation of different size fractions of the ore and on Mozley’s Laboratory Mineral Separator. A combination of tabling and dry magnetic separation was adopted for ?100?mesh ore. Magnetic separation on dry?ground ore was conducted to study the effect of magnetic intensity on wolframite recovery. The results indicated limitations in using gravity and dry?magnetic separations at fine particle sizes.
Flotation experiments were carried out in a laboratory?size Fagergren sub?aeration machine using 250 g of dry?ground feed (80% passing 200 mesh), employing stagewise flotation.
Carbonaceous materials were floated using terpineol,
Pyrite using potassium ethyl xanthate, and
Wolframite using sodium oleate.
The effects of varying concentrations of sodium silicate, lactic acid, sodium oleate, and pH on the recovery of WO? and on separation effectiveness were studied. The results have been explained on the basis of the isoelectric point of wolframite, the pK? value, and the critical micelle concentration (CMC) of sodium oleate.
Flotation experiments on wet?ground ore were carried out using statistically designed experiments, and the effects and possible interactions among variables were examined. Concepts such as probability, variance, and tests of significance were used in the analysis. Three factors were selected:
Concentration of collector (sodium oleate)
Concentration of depressant (sodium silicate)
pH
The effects of sodium silicate and pH on separation effectiveness were significant. A set of experiments based on an orthogonal hexagonal design was conducted to determine the influence of these variables, from which a regression equation was developed. Response contours were plotted, showing that separation effectiveness increases with decreasing pH and decreasing sodium?silicate concentration.
The “path of steepest ascent” was used to determine maximum response. A “near stationary region’’ was identified at pH 4 and 0.595 kg/ton of sodium silicate at 2 kg/ton of sodium oleate, where the maximum S.I. of 0.5408 was obtained, with 65.82% recovery of WO?.
For comparison, the best S.I. for dry?ground ore was 0.3841 at pH 4. The better performance in wet?ground ore is attributed to the addition of depressants during grinding, improving selectivity. | |
