| 1. |
- Rao, K. Hanumantha, et al.
(författare)
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Flotation of mica minerals and selectivity between muscovite and biotite while using mixed anionic/cationic collectors
- 1990
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Ingår i: Minerals & metallurgical processing. - 0747-9182. ; 7:3, s. 127-132
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Tidskriftsartikel (refereegranskat)abstract
- Selective flotation of muscovite from a material containing muscovite (15.4%), biotite (13%), and siliceous gangue (quartz and feldspar), using a mixed collector system of sodium oleate and dodecylamine acetate has been described. Muscovite is found to float in preference to biotite, when the pulp is initially conditioned with oleate followed by amine at basic pH values. The results indicate that a product containing 63% muscovite with a recovery of 93% can be obtained, while using 75-150 g/t of oleate and 96 g/t of amine. The biotite grade and recovery are found to be around 30% and 20%, respectively. A good selectivity between muscovite and siliceous gangue is obtained. A final product containing 95% muscovite with an overall recovery of 75% is obtained when the flotation concentrate is subjected to magnetic separation. These studies indicate the possibility of separating muscovite from biotite by using a mixture of collectors.
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| 2. |
- Homberg, Uwe, et al.
(författare)
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Comparative anatomy of pigment-dispersing hormone-immunoreactive neurons in the brain of orthopteroid insects
- 1991
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Ingår i: Cell and Tissue Research. - : Springer. - 0302-766X .- 1432-0878. ; 266:2, s. 343-357
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Tidskriftsartikel (refereegranskat)abstract
- In a comparative study, the anatomy of neurons immunoreactive with an antiserum against the crustacean beta-pigment-dispersing hormone was investigated in the brain of several orthopteroid insects including locusts, crickets, a cockroach, and a phasmid. In all species studied, three groups of neurons with somata in the optic lobes show pigment-dispersing hormone-like immunoreactivity. Additionally, in most species, the tritocerebrum exhibits weak immunoreactive staining originating from ascending fibers, tritocerebral cells, or neurons in the inferior protocerebrum. Two of the three cell groups in the optic lobe have somata at the dorsal and ventral posterior edge of the lamina. These neurons have dense ramifications in the lamina with processes extending into the first optic chiasma and into distal layers of the medulla. Pigment-dispersing hormone-immunoreactive neurons of the third group have somata near the anterior proximal margin of the medulla. These neurons were reconstructed in Schistocerca gregaria, Locusta migratoria, Teleogryllus commodus, Periplaneta americana, and Extatosoma tiaratum. The neurons have wide and divergent arborizations in the medulla, in the lamina, and in several regions of the midbrain, including the superior and inferior lateral protocerebrum and areas between the pedunculi and alpha-lobes of the mushroom bodies. Species-specific differences were found in this third cell group with regard to the number of immunoreactive cells, midbrain arborizations, and contralateral projections, which are especially prominent in the cockroach and virtually absent in crickets. The unusual branching patterns and the special neurochemical phenotype suggest a particular physiological role of these neurons. Their possible function as circadian pacemakers is discussed.
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| 3. |
- Kadiyala, K. Rao, et al.
(författare)
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Forecasting with Generalized Bayesian Vector Autoregressions
- 1993
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Ingår i: Journal of Forecasting. - : John Wiley & Sons. - 0277-6693 .- 1099-131X. ; 12:3-4, s. 365-378
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Tidskriftsartikel (refereegranskat)abstract
- The effects of using different distributions to parameterize the prior beliefs in a Bayesian analysis of vector autoregressions are studied. The well-known Minnesota prior of Litterman as well as four less restrictive distributions are considered. Two of these prior distributions are new to vector autoregressive models. When the forecasting performance of the different parameterizations of the prior beliefs are compared it is found that the prior distributions that allow for dependencies between the equations of the VAR give rise to better forecasts.
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| 4. |
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| 5. |
- Rao, K. Hanumantha, et al.
(författare)
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Adsorption of oleate species on sparingly soluble calcium minerals from aqueous solutions : a comparison of theoretical and experimental thermodynamic chemical equilibria
- 1991
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Ingår i: 3rd International Symposium on Beneficiation and Agglomeration. - : Indian Institute of Metals. ; , s. 222-230
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Konferensbidrag (refereegranskat)abstract
- The adsorption of fatty acids on sparingly soluble minerals is a complex phenomena due to the fact that fatty acids are capable of forming precipitated phases with dissolved Ca ions from these minerals. A number of mechanisms have been proposed, but none has been fully substantiated. Adsorption and precipitation reactions in alkaline solutions of oleate in the presence of calcite, apatite, fluorite and scheelite have been explained through adsorption isotherms, electrokinetic studies and theoretical thermodynamic chemical equilibria calculations. The adsorption density at monolayer coverage corresponds to the condensed state of alkyl chain (liquid--crystal state) with a molecular coverage area of 33 A exp 2 . The application of two-dimensional condensation model is considered. These studies showed a bilayer formation in the case of apatite, fluorite and scheelite, and a monolayer formation in the case of calcite, prior to the three dimensional condensation of calcium oleate (precipitation) on the substrate
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Rao, K. Hanumantha, et al.
(författare)
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Mechanism of fatty acid adsorption in salt-type mineral flotation
- 1991
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Ingår i: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 4:7, s. 879-890
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Tidskriftsartikel (refereegranskat)abstract
- Our recent studies on the interaction of oleate with salt-type mineral surfaces have been summarized based on adsorption, infrared and zeta-potential measurements. Monolayer coverage in the case of calcite and a bilayer formation in the cases of fluorite, apatite and scheelite, preceding the precipitation of calcium soap has been suggested for the adsorption mechanism of oleate on these minerals. The monolayer coverage is shown to correspond to a condensed state of oleate with a molecular coverage area of 33 A2 (liquid-crystal state). Depending on the surface potential and its magnitude at basic pH values, oleate is either chemisorbed on the surface calcium or monocoordinated through counter sodium and calcium ions for the monolayer filling.
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| 10. |
- Rao, K. Hanumantha, et al.
(författare)
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Mechanism of oleate interaction on salt-type minerals : IV. Adsorption, electrokinetic and diffuse reflectance FT-IR studies of natural fluorite in the presence of sodium oleate
- 1991
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 145:2, s. 314-329
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of oleate interaction with fluorite is investigated through adsorption, electrokinetic, and diffuse reflectance FT-IR measurements coupled with theoretical thermodynamic chemical equilibrium calculations. The adsorption isotherms exhibit an infinite increase in the slope beyond an oleate density of 10 μmole m-2. This adsorption density corresponds to a bilayer formation of oleate by two-dimensional condensation with a reported molecular coverage area of 33Ao2 (liquid-crystal state). Comparison of the theoretical chemical equilibria with the experimental data shows that the infinite increase in the slope of the isotherms is due to the precipitation of calcium oleate. The solubility product of this three-dimensional phase is found to be in the pK range 14.4-14.5, and agrees with most of the values quoted in the literature. From IR studies, monocoordination of oleate through counter sodium and calcium ions is suggested for the monolayer filling. ζ potentials of fluorite are correlated to the adsorption of oleate up to bilayer formation, and formation on surface of calcium oleate (three-dimensional growth on substrate) at high oleate concentrations. Two-dimensional condensation of oleate on the fluorite surface followed by the association of hydrocarbon chains (tail-tail bond) for the second layer, prior to the precipitation of calcium oleate in the bulk solution, is proposed as the adsorption mechanism.
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