Janusz S. Laskowski

Effect of flotation frothers on bubble size and foam stability

In order to study the effect of frothers on the size of bubbles, experiments were carried out using single- and multi-hole spargers and a flotation cell. It was found that the size of bubbles strongly depends on frother concentration only when multi-hole spargers are utilized (or when measured in a flotation cell). At low frother concentrations (C<CCC), the bubble size is much larger, indicating coalescence as a main mechanism determining the size. Coalescence can be prevented at frother concentrations exceeding the critical coalescence concentration (CCC). The foamability tests indicate that stability of foams under dynamic conditions is determined by bubble coalescence.

The adsorption of polysaccharides onto mineral surfaces: an acid/base interaction

Natural polysaccharides such as starch, dextrin, guar gum, cellulose and their derivatives are promising non-toxic organic depressants. Although generally perceived as non-selective, these polymers have found use in commercial processes or have been tested in laboratories in practically all flotation systems involving every type of minerals. In this communication, the adsorption mechanisms of natural polysaccharides are reviewed, with the objective of promoting the wider applications of the polymers. While it seems generally accepted that natural polysaccharides interact with minerals via surface metal-hydroxylated species, an acid/base interaction model between the natural polysaccharides and mineral surfaces is proposed to explain many observed adsorption and flotation phenomena.

Effect of surface functional groups on the flotation of coal

Abstract The flotation behavior of a series of coals is described in terms of the predominant oxygen-containing functional groups. These groups control not only the thermodynamics, but also the kinetics of coal flotation. It is shown that the maximum flotation response occurs close to the isoelectric point of the demineralized coal. The correlation between content of phenolic and carboxylic groups and the flotation response of a range of coals was found to be excellent. Functional groups control coal wettability through the balance of hydrophobic/hydrophilic sites, and control flotation kinetics by their influence on surface charge.

The interactions between dextrin and metal hydroxides in aqueous solutions

Abstract Dextrin, a common dispersing/depressing agent in flotation systems, was found to coprecipitate with metal hydroxides but not with metal cations in aqueous solutions. Such interactions caused a decrease in the solution pH. The optimum pH for dextrin-metal hydroxide coprecipitation was 7.5 for ferric, 8 for aluminum, 9 for cupric, 11 for lead, and 12 for magnesium ions. The pH ranges of the optimum coprecipitation coincide quite well with the IEP of the metal hydroxide. Infrared tests with the precipitates revealed that the reaction between dextrin and metal hydroxide eliminates the glucose ring deformation. Based on such observations it is concluded that the interactions between dextrin and metal hydroxide result from formation of chemical complexes and are not a result of hydrogen bonding.

The role of metal hydroxides at mineral surfaces in dextrin adsorption, I. Studies on modified quartz samples

Abstract In order to investigate the interaction mechanisms between dextrin and mineral surfaces, the floatability, wettability and adsorption tests were conducted on quartz samples. The quartz samples were either made hydrophobic by methylation, or lead-coated, or subjected to both forms of surface modifications. In sharp contrast to the published results, it was observed that surface hydrophobicity does not contribute significantly to the adsorption of dextrin. The adsorption, however, depends critically on the presence of metal ionic species on solid surfaces and seems to result from the chemical interaction between dextrin and the surface metal hydroxide groups.

The role of metal hydroxides at mineral surfaces in dextrin adsorption, II. Chalcopyrite-galena separations in the presence of dextrin

Abstract The adsorption of dextrin on chalcopyrite and galena was studied with a concomitant examination of the flotation behaviour of these minerals in the presence of dextrin. It was found that dextrin adsorbs on the sulphide surfaces through interactions with the surface metal hydroxide species. Since lead hydroxide and copper hydroxide appear in different pH ranges, selection of proper pH values, in line with these findings, was shown to lead to the separation of the chalcopyrite/galena mixtures when potassium ethyl xanthate (KEX) and dextrin were used.

Flocculation of the Syncrude fine tailings: Part I. Effect of pH, polymer dosage and Mg2+ and Ca2+ cations

Abstract In a new process of fine tailings disposal, after extraction of bitumen from Athabasca oil sands, the slurry, which contains clays, sand and a small amount of bitumen, is flocculated and thickened into a paste. The effects of pH, polymer dosage and presence of divalent cations on the flocculation of the Syncrude tailings have been studied. The tests were carried out using a high molecular weight polyacrylamide flocculant (Percol 727) over a pH range from 3 to 11. The effect of Mg2+ and Ca2+ ions was also tested. These factors were analyzed by fitting the experimental data to a polynomial model, which plots flocculation response in the form of contour maps. The maps identify the conditions for obtaining high initial settling rates (isr) and/or low solids content (sc) in the supernatant. At low pH, in which clays tend to coagulate, the domains of a high initial settling rate (isr) and low solids content (sc) coincide. In alkaline pH, in which clays form stable suspensions, the addition of the flocculant leads to the development of bimodal size distributions consisting of flocs and dispersed fine particles. Flocculation is much more efficient in the presence of divalent cations over this pH range.

Fundamental properties of the polyoxypropylene alkyl ether flotation frothers

Abstract A series of polyoxypropylene alkyl ethers, which includes common flotation frothers such as DF-200, DF-250 and DF-1012, have been tested. The “frothing” properties of these compounds were investigated through measuring their effect on bubble size and dynamic foamability index. The tests revealed a definite relationship between the number of propoxy groups in the CH3(OC3O6)nOH molecule and the critical coalescence concentration (CCC) values, and the values of the dynamic foamability index (DFI). The results also show a clear correlation between the CCC and DFI values. Such a correlation was earlier reported for the hexanol derivatives. It has been shown when testing frother blends that the molar ratios of blend constituents can be based on the corresponding CCC values of the individual frothers.

Sphalerite activation: Flotation and electrokinetic studies☆

Abstract Sphalerite is commonly floated in an alkaline environment and under such conditions the overall activation mechanism is obscured by the hydrolysis of Cu 2+ and precipitation of Cu(OH) 2 . Electrokinetic and kinetic flotation tests showed that the activation of sphalerite is a two-stage process; the activation products formed on the surface of sphalerite in near neutral and in alkaline solutions in the first rapid activation stage are “flotation-inactive”. These layers, when formed in an alkaline solution, are unstable and are transformed into the “flotation-active” form in the second stage. However, the surface layers formed during activation in alkaline environment by copper in the presence of lead ions are very stable and even after a long conditioning time the flotation rate is not improved. Consequently, while both Cu 2+ and Pb 2+ activate sphalerite flotation, quite unpredictable effects may result when both are present in the solution.

Oil agglomeration and its effect on beneficiation and filtration of low-rank/oxidized coals

Abstract Low-rank/oxidized coals respond poorly to oil agglomeration. Emulsification of kerosene in the presence of surfactants dramatically reduces the size of the kerosene droplets, lowering the consumption of kerosene needed to agglomerate oil down to 0.25–0.5%. Surfactants can also entirely change the interaction between oil droplets and coal particles. Consequently, kerosene cationic emulsions can efficiently agglomerate oxidized coal particles. The agglomerates obtained in such a process can still be recovered by screening.