K. Hanumantha Rao

Mixed collector systems in flotation

The interactions between differently structured surfactant molecules at the solid/liquid and air/liquiid interfaces and their effectiveness for efficient flotation were recognised during the 1950s ...

Surface characterization of Acidithiobacillus ferrooxidans cells grown under different conditions

The growth characteristics of a strain of Acidithiobacillus ferrooxidans isolated from mine water with ferrous ion, sulfur, or pyrite mineral as sole source of energy have been established. The electrokinetic behaviour of the bacterial cells was investigated and the cell surface groups were characterized by diffuse reflectance FT-IR and FT-Raman spectroscopies. The surface charge on the iron-grown cells (i.e.p., pH 2.0) is different from that on the solid-substrate-grown cells (i.e.p., pH 3.0–3.5) and the surface charge depends on the growth history of the bacteria. The FT-IR and FT-Raman spectra revealed a higher amount of protein content on the surface of the sulfur- and pyrite-grown cells compared to the iron-grown cells. These results suggest that the altered surface charge on the cells is due to differences in the protein content synthesized by bacteria exposed to different growth conditions.

Mechanism of oleate interaction on salt-type minerals, Part II. Adsorption and electrokinetic studies of apatite in the presence of sodium oleate and sodium metasilicate

Abstract The mechanism of oleate interaction on apatite is investigated through adsorption and electrokinetic studies. The adsorption density at monolayer coverage corresponds to a condensed state of surfactant molecule with a molecular area of 33 A 2 . The isotherm at pH 8 showed the monolayer coverage followed by the precipitation step of calcium oleate, whereas at pH values 9, 10 and 11, the isotherms showed bilayered structure of oleate on the surface before the precipitation step of calcium oleate. The vertical step characterizing calcium oleate precipitation after bilayer formation is found to be dependent on the solid/liquid ratio. The zeta-potentials correlate to the adsorption of oleate up to bilayer formation. The presence of sodium silicate has no influence on the adsorption of oleate.

Surface chemical characterisation of Paenibacillus polymyxa before and after adaptation to sulfide minerals

A heterotroph Paenibacillus polymyxa bacteria is adapted to pyrite, chalcopyrite, galena and sphalerite minerals by repeated subculturing the bacteria in the presence of the mineral until their growth characteristics became similar to the growth in the absence of mineral. The unadapted and adapted bacterial surface have been chemically characterised by zeta-potential, contact angle, adherence to hydrocarbons and FT-IR spectroscopic studies. The surface free energies of bacteria have been calculated by following the equation of state and surface tension component approaches. The aim of the present paper is to understand the changes in surface chemical properties of bacteria during adaptation to sulfide minerals and the projected consequences in bioflotation and bioflocculation processes. The mineral-adapted cells became more hydrophilic as compared to unadapted cells. There are no significant changes in the surface charge of bacteria before and after adaptation, and all the bacteria exhibit an iso-electric point below pH 2.5. The contact angles are observed to be more reliable for hydrophobicity assessment than the adherence to hydrocarbons. The Lifschitz–van der Waals/acid–base approach to calculate surface free energy is found to be relevant for mineral–bacteria interactions. The diffuse reflectance FT-IR absorbance bands for all the bacteria are the same illustrating similar surface chemical composition. However, the intensity of the bands for unadapted and adapted cells is significantly varied and this is due to different amounts of bacterial secretions underlying different growth conditions.

Mechanisms of amine–feldspar interaction in the absence and presence of alcohols studied by spectroscopic methods

Abstract The adsorption of long-chain primary amines on feldspars at neutral pH 6–7 was investigated using Hallimond flotation, zeta-potential, FT-IR and XPS studies. Two-dimensional (2D) followed by three-dimensional (3D) precipitation mechanism of amine adsorption on quartz reported earlier (Langmuir 16 (2000) 8071) was further substantiated. The orientation and packing of dodecyl- and hexadecylammonium acetate and chloride adsorbed on albite in the different regions of the adsorption isotherm were determined. It was shown that these characteristics depend strongly on the substrate. The influence of long-chain alcohols on the adsorption of amines in mixed amine/alcohol on feldspars, i.e. albite (NaAlSi3O8) and microcline (KAlSi3O8), was also examined. Coadsorption of the counterion was not revealed, but the counterion was found to affect indirectly the adsorption at concentrations above the concentration of the bulk amine precipitation. It was proved spectroscopically that co-adsorption of long-chain alcohols along with amine cations leads to formation of a closed packed surface layer as compared to the case of adsorption of pure amine alone at the same concentration. The highest order and packing at the surface were observed when the alkyl chain length of mixed amine and alcohol were the same. The condition of same chain length of amines and alcohols adsorbing at the surface corresponded to maximum flotation recovery. The results also confirmed the synergistic enhancement of amine adsorption in the presence of alcohols. A mechanism of mixed long-chain amine and alcohol adsorption onto silicates (albite and quartz) consistent with the primary adsorption species of alkylammonium–water–alcohol complex, where deprotonation of ammonium groups in the adsorbed layer leading to 2D precipitation of molecular amine was illustrated.

Interfacial interactions and mechanical properties of mineral filled polymer composites: wollastonite in PMMA polymer matrix

Abstract The nature of stearic acid and polymethylmethacrylate (PMMA) adsorption onto wollastonite has been studied from basic, neutral and acidic organic solvents by infrared (IR) spectroscopy. The roles of acid-base interactions on adsorption and wollastonite dispersion in polymer matrix have been discussed with the determined mechanical properties of surface-treated (stearic acid) and untreated wollastonite-filled PMMA polymer composites. Maximum adsorption of either stearic acid or PMMA occurs from a nonpolar solvent, and the adsorption is found to decrease with increasing acidity or basicity of the solvents. The adsorption corresponds to two geometrical layers either from nonpolar (carbon tetrachloride) or from slightly basic (benzene) and acidic (methylene dichloride) solvents. Increased acidity (chloroform) or basicity (tetrahydrofuran) of solvents led to a monolayer or a fraction of the monolayer coverage. The primary adsorption of stearic acid is thought to be the formation of hydrogen bonds between surface hydroxyl groups and carboxylic acid groups. The tensile and impact strength properties of the composites that are filled with stearic acid-treated wollastonite are improved when compared to the untreated filled composite. The results suggest a stronger interfacial bonding between stearic acid and filler than that of polymer to the filler. Thus, the application of stearic acid for surface modification of acidic fillers such as wollastonite is emphasized.

Mechanism of oleate interaction on salt-type minerals. V : Adsorption and precipitation reactions in relation to the solid/liquid ratio in the synthetic fluorite-sodium oleate system

The mechanism of adsorption of oleate onto a synthetic fluorite sample at different solid/liquid ratios in alkaline solutions is elucidated through adsorption isotherms in conjunction with ζ-potential and diffuse reflectance Fourier transform-infrared spectroscopic studies. These studies show that the chemisorption of oleate on surface calcium species followed by the physical adsorption of hydrocarbon chains (bilayer formation) precede the precipitation of calcium oleate in bulk solution. With an increase in the solid/liquid ratio, the bulk precipitation of calcium oleate after bilayer formation is found to be reduced, and at a high solid concentration, the isotherm is seen to level off with bilayer formation. As the solid concentration increases, the concentration of calcium in bulk solution decreases because of its adsorption on the head group of the hydrophilic layer of oleate (bilayer), and hence the extent of bulk precipitation decreases. The adsorption density for a monolayer coverage corresponds to the condensed state of an alkyl chain with a cross-sectional area of 33A˚2 (liquid-crystal state). Application of the two-dimensional condensation model is considered and no evidence for the surface precipitation process is observed.

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

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 33A˚2 (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.

Mechanism of oleate interaction on salt-type minerals part I. Adsorption and electrokinetic studies of calcite in the presence of sodium oleate and sodium metasilicate

The adsorption mechanism of oleate on calcite is investigated through adsorption and electrokinetic studies. The adsorption isotherms at pH 9, 10 and 11 show a plateau value at an oleate adsorption ...

Bio-modulation of galena and sphalerite surfaces using Thiobacillus thiooxidans

The interaction of Thiobacillus thiooxidans (T. thiooxidans) with sphalerite and galena has been investigated through adsorption, electrokinetic, and flotation studies. The amount of T. thiooxidans cells adsorbed onto galena and sphalerite is found to be almost independent of pH. However, a greater amount of cells is adsorbed onto galena compared to sphalerite. The adsorption isotherms of T. thiooxidans onto both galena and sphalerite exhibit Langmuirian behaviour. Electrokinetic measurements reveal that the isoelectric points (iep) of galena and sphalerite are located around pH 2, while that of T. thiooxidans is around pH 3. The isoelectric points of the minerals are shifted to higher pH values after interaction, consequent to bacterial cell attachment, indicating specific adsorption. Additionally, the electrophoretic mobilities are found to become less negative as a function of time after bacterial interaction. Such a trend is also followed in the case of the cells after interaction with the minerals for different time intervals. On a comparative basis, the cells after interaction with sphalerite are less negative vis-a-vis those after interaction with galena. The flotation recovery of sphalerite, beyond 1 h of interaction with T. thiooxidans cells is not affected but galena is totally depressed in the presence of T. thiooxidans cells, in the pH range 5–11. The differential flotation tests on a synthetic mixture of galena and sphalerite reveal that sphalerite can be selectively floated from galena in the presence of T. thiooxidans.