Jan Drzymala

Hydrophobicityand collectorless flotation of inorganic materials

Abstract Hydrophobicity and floatability of solids have been analyzed from the standpoint of properties of solid-water and solid-water vapors interfaces, chemical bonds, bulk properties, crystal structure of the solid, and reactivity of the solid with water. Although the hydrophobicity results from complex interactions in the solid-water-air system, simple equations and rules for predicting hydrophobicity and floatability are presented. The applicability of the Gaudin-Miaw-Spedden theory which states that molecular and sheet crystals, if their structure is controlled by the residual bonds across their basal planes, are floatable was confirmed. It was also shown that elements and compounds with different degrees of ionic-covalent and metallic-nonmetallic characters of bonds in the absence of residual bonds can be either hydrophilic, hydrophobic, or change their properties from hydrophobic to hydrophilic and vice versa . For some materials, hydrophobidty was found to be time-dependent. Decreasing hydrophobicity occurs with the oxidation and hydroxylation of the surface (oxides, metals), while increasing hydrophobicity takes place due to non-dissociative adsorption of water vapors on the surface (noble metals). Increased hydrophobicity can also be due to the formation of hydrophobic species such as sulfur species on the surface of Sulfides. It was demonstrated that the potential hydrophobicity of solids, expressed as the contact angle formed between the three involved (solid, water, and air) phases, can be evaluated from the Hamaker constants. This work supplements the Gaudin-Miaw-Spedden theory by showing that not only molecular crystals (paraffin, I 2 , S 8 , As 4 O 6 , As 2 S 2 ) and non-ionic sheet crystals (MoS 2 , Sb 2 S 3 , talc, graphite, As 2 S 3 , boric acid, BN) but also elements and crystalline compounds without residual bonds can be hydrophobic and floatable. A partial list of such materials includes Hg, Ge, Si, SiC, AgI, CaF 2 , and diamond (whose hydrophobidties are already well known) as well as BaSO 4 , FeTiO 3 , In, and Sn (whose hydrophobidties have been established in this work). It was also demonstrated that the hydrophobidty of some solids changes as a result of reaction of the surface with constituents of the air.

Characterization of materials by Hallimond tube flotation. Part 2: maximum size of floating particles and contact angle

Abstract An equation more complete than any existing one in literature for the upper size limit of flotation was presented and tested against mercury drops, spherical particles of sulfur, and paraffin-coated grains of different solids. It was demonstrated that flotation tests combined with the derived equation make it possible to characterize and measure floatability and hydrophobicity of spherical and irregular particles in the form of the equilibrium and detachment angle of the bubble-particle aggregate. The maximum size of floating particles values and the equilibrium as well as detachment contact angles were determined for various hydrophobic materials including sulfur, pyrite, mercury, germanium, silicon, talc, fluorite, silicon carbide, silver iodide, ilmenite, arsenic oxide, diamond, graphite, molybdenite, and boric acid. Also resulting from this study is the confirmation that the monobubble Hallimond tube is a valuable tool for characterizing and comparing flotation of different systems.

Removal of lead minerals from copper industrial flotation concentrates by xanthate flotation in the presence of dextrin

Abstract Potato starch and dextrins resulting from thermolysis of potato starch in the absence of reagents and presence of l -amino acids are promising depressants for separation of lead and copper minerals present in the Polish industrial copper concentrates. The polysaccharides were used for differential xanthate flotation of the final industrial concentrates produced by flotation with sulfhydryl collectors in the absence of depressants. The polysaccharides depressed galena and provided froth concentrate rich in chalcocite and other copper minerals as well as cell product containing lead minerals. The best results of separation were obtained in the presence of plain dextrin prepared by a thermal degradation of potato starch. The industrial concentrate containing 18.5% Cu and 5.5% Pb was divided into a froth product containing 38.1% Cu with 77% recovery of copper and a cell product assaying 7.3% Pb with 83% recovery of lead. It was accomplished using 2500 g/t of dextrin, 50g/t of potassium ethyl xanthate, and 50 g/t of frother (α-terpineol). The pH of flotation was 8.0–8.2.

Influence of air on oil agglomeration of carbonaceous solids in aqueous suspension

Abstract Graphite or coal particles in aqueous suspension were agglomerated with various paraffinic hydrocarbons in a specially developed system which made it possible to exclude air from the system or to conduct agglomeration with controlled amounts of air present. The agglomerates were recovered by screening the suspension. Under certain conditions air was incorporated in the agglomerates which increased the recovery of carbonaceous material with a given amount of liquid hydrocarbon. Incorporation of air occurred when lower molecular weight alkanes (i.e., smaller than octane) were used as the collecting or bridging phase in limited amounts. Air had no effect on the system when higher molecular weight alkanes were employed or when larger amounts of the collecting phase were used.

Characterization of materials by Hallimond tube flotation. Part 1: maximum size of entrained particles

Bubbling gases through water in monobubble Hallimond tubes cause entrainment of fine particles. The particles are entrained with a layer of water traveling behind bubbles. Four modes of bubble movement in the monobubble Hallimond tube — the vertical coalescent string of bubbles, Archimedean spiral, symmetrical spiral, and lateral bubble movement in the inclined part of the Hallimond tube — were distinguished and discussed. Maximum vertical velocity of the bubbles in all four regions of the Hallimond tube was found to be within 13.1 ± 0.7 cm/sec. The Reynolds number of the bubbles produced in the monobubble Hallimond tube is between 385 and 947 indicating a near turbulent or turbulent flow in the layer of water behind the bubble. The particles traveling with the water layer behind bubbles are subjected to gravity which causes their settling. Particles which settle slower than the velocity of the water layer behind a bubble can be entrained with the bubbles and transferred to the receiver of the Hallimond tube. On the basis of this principle two equations for the maximum size of entrained particles (dmax) in the monobubble Hallimond tube were derived. The equation for particles which obey Newtons law of settling is: dmax(ρp−ρ1)ρl≅LH=3(wbO)2ζ4g(cm) while for particles which settle according to Allens law, the equation is: dmax(ρp−ρ1)ρl)0.75≅LL=wbO113.2(cm) where ϱp is the density of the particles (g/cm3), ϱ1 density of the liquid (g/cm3), wbo vertical velocity of a bubble within the slowest region of the Hallimond tube (cm/s), ζ drag coefficient (dimensionless number whose value depends on Reynolds number), g acceleration due to gravity (cm/s2), and Lh and Ll are constants. Experimental tests carried out in a monobubble Hallimond tube using 13 different hydrophilic materials confirmed the applicability of formula (a) for materials with densities above 2.0 g/cm3 and formula (b) for lighter substances. This was so, since the following experimental formulae were obtained for regularly shaped particles: max(ρp−ρ1ρl=LH=0.0023±0.002(cm)(forρ≥2.0g/cm3) and max(ρp−ρ1ρl)0.75=LL=0.0020±0.002(cm)(forρ≤2.0g/cm3) However, the theoretical value of Lh was 2.5 and Ll 5.5-fold greater than that obtained experimentally. Factors which may be responsible for the discrepancy were indicated.

An improved estimation of water-organic liquid interfacial tension based on linear solvation energy relationship approach.

An equation based on the linear solvation energy relationship (LSER) was proposed to predict the interfacial tension between organic liquid and water. The equation takes into account five parameters characterizing properties of the organic liquid molecule: excess molar refraction, solute dipolarity/polarizability, effective hydrogen bond acidity, effective hydrogen bond basicity, and the McGowan molar intrinsic volume. The proposed equation provides a better approximation of the interfacial tension than a similar one derived earlier by Freitas et al. (J. Phys. Chem. B 101 (1997, 7488-7493), which is based on seven terms.

Surface dissociation constants for solid oxide/aqueous solution systems

SummaryAn equation for the surface potential ψ0 was used to define the surface dissociation constant of surface hydroxyls at a solid oxide/aqueous solution interface.Using the measurements of the surface charge, the Gouy-Chapman theory and crystallo-chemical data for oxides, the calculations of the surface dissociation constants have been carried out. The values of the acidic surface dissociation constants (in minus logarithmic scale) fall in range 8.7±0.8 at ionic strength 1 M and in the range 7.2±0.7 at 10−3 M KNO3 These constants exceed by 2 to 5 orders of magnitude the dissociation constants of M(OH)naq species in solution.

Flotometric analysis of the collectorless flotation of sulphide materials

Abstract Collectorless flotation of different size fractions of sulphides and sulphur was conducted in a monobubble-type Hallimond tube. Flotation tests were carried out with sulphides of different origins at their natural pH and natural redox potential in distilled water. The floatabilities of sulphides were compared to the floatabilities of hydrophobic elemental sulphur and hydrophilic quartz and magnetite, taking into account the density of the investigated solids. It was established that chalcopyrite, pyrite, galena and copper (I) sulphide floated as well, or almost as well, as elemental sulphur. This indicated the presence of sulphur or a layer of sulphur-excess sulphide on the surface of these solids during flotation. The floatability of another galena and another pyrite, sphalerite, iron (II) sulphide and nickel (II) sulphide was found to be equal, or almost equal, to the mechanical carry-over of hydrophilic quartz and magnetite, most likely because of hydrophilicity of a fresh sulphide surface or the presence of such hydrophilic products as metal hydroxides or metal sulphuroxy compounds. It was also suggested that the so-called parameter L of the “flotometric equation” can be used to characterize the flotation properties of sulphides. The flotometric equation has the form a 50 ϱ′ = L 50 , where a 50 is the maximum diameter of the particle which can be successfully floated, while ϱ′ is the density of the solid in water.

Potentiometric titration of sodium oleate in dilute aqueous solutions

Acidification of sodium oleate aqueous solutions creates an oil phase which exists in the form of droplets 0.2-0.3 μm in diameter. On the basis of the thermodynamic solubility diagram for oleic acid it was assumed that the created oleic phase consisted of pure oleic acid molecules. The surface area of the oleic acid droplets was determined by utilizing light transmittance measurements of the emulsions and the Mie theory. The concentration of surface oleate species at the oil-water interface was calculated from pH-metric titration data for 5 × 10−4, 10−3, 5 × 10−3, and 10−2M sodium oleate solutions. It was found that the electrical charge at the oleic acid droplets-aqueous solution interface estimated from the above data increased with pH up to 800 μC/cm2 significantly exceeding the theoretical maximum value 128 μC/cm2. Therefore, the assumed model in which only surface oleate anion and simple oleate species such as Olaq−, HOl · Olaq−, Ol2aq2− are present in the sodium oleate-HCl-H2O system is useless for the interpretation of sodium oleate titration curves.

Flotometry—Another way of characterizing flotation

On the basis of various flotation tests with quartz and magnetite a new method of evaluating flotation processes is described. The proposed method, called flotometry, relies on carrying out a series of flotation (recovery, R, vs time, t) tests using increasing particle size until the particles become too heavy to be floated. The flotation tests are conducted with a monobubble-type Hallimond tube and analyzed with the flotometry equation in the form aR,t,sρ′ = LR,t,s′, where aR,t,s is the size fraction of the solid for which recovery is R after time t of flotation, s denotes surface properties of the solid in the flotation system, and ρ′ and LR,t,s represent particle density in water and a constant, respectively. Flotometry seems to be a useful method for determining the type of flotation, solid hydrophobicity in the flotation solution, upper critical particle size for flotation, strength of the solid-bubble contact, and other factors in flotation systems.