The adsorption of the different ions and molecules in a solution depends on the electrical charge of the surface of the minerals undergoing flotation. The hydrophobicity and float, ability of minerals are governed by the adsorbed ions and molecules.From a study of the capacity of a double electric layer in the presence of adsorbed molecules, A. N. Frumkin et al. [1,2] derived a theory explaining the influence of an electrode's electrochemical potential on the adsorption of uncharged molecules.According to these authors, the capacity of a double layer in the field of adsorption is greatly reduced because between the layer's plates an interlayer of a substance is introduced, having a lower dielectric constant than water. A capacitor's electric field resists introduction of a body between the capacitor's plates if the dielectric constant of this body is lower than that of the medium filling the capacitor. The double layer's electric field therefore opposes adsorption of molecules reducing the layer's capacity, but assists that of water molecules. The adsorption of uncharged organic molecules is greater on surfaces with smaller charges, irrespective of the sign of the charge.Wetting with water is poorest at potentials closest to the zero charge, and increases sharply with polarization of the surface.To study the changes in the overall electrochemical potential, a limonite electrode with L = 40 mm and d = 5 mm was turned on a grinding wheel. One end of the electrode was fixed in a holder consisting of a special Plexiglas tube. Contact between the electrode and the current conductor was obtained by filling the tube with mercury.The change in E-the potential jump with changing solution pH-was measured as follows. The electrode was thoroughly cleaned on the grinding wheel in an aqueous suspension of quartz, and washed in distilled water; adhering particles of quartz were removed with filter paper, and it was then placed in a beaker with distilled water. It was placed in the agitation compartment of a flotation machine and treated with an aqueous emulsion of kerosene (500 mg/liter) for 5 min at a given pH. Without removing it from the flotation machine, it was transferred to a beaker to determine E-the potential with respect to a calomel comparison electrode.The solution pH was changed by means of H2SO 4 and NaOH. It will be seen from the change in limonite potential at various pH in an aqueous emulsion of kerosene (see figure) that the surface of limonite treated with such an emulsion has a negative charge. With increasing solution pH the negative potential of the surfaces increases owing to adsorption of the excess free hydroxyl (OH-) ions.H + and OH-ions have a very great influence on the state of the double electric layer of limonite, and, therefore, on its reaction with nonpolar reagents (hydrocarbons).The figure plots the floatability of limonite (size class 0.0'/4 mm) by kerosene (500 mg/liter) with addition of frothing agent (pine oil, 50 mg/liter) in an NIGRIzoloto flotation machine (v = 50cm 3 , n = 2000 rev/min...

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Study of flocculation of Kuzbass coal slurries revealed better flocculating capacity of polyacrylamide in pulps with low pH [1]. With low consumptions of polyacrylamide, we obtain transparent discharge liquors and its adsorption of the coal particles is improved.In this paper an attempt is made to explain the effect of the pH of the medium of flocculatton from the viewpoint of a change in the structural forms of polyacrylamide. Changes of the flocculant structure and the accompanying phenomena in solutions at different pH values of the medium were observed by electron and optical microscopy.We studied 0.1% aqueous solutions of polyacrylamide from the Leninsk-Kuznetsk semicoktng factory; the pH of the medium was established by HC1 and KOH solutions.The specimens for the Tesla BS-242 electron microscope (direct magnification 2000) were prepared by obtaintng a thin transparent film from the surface layer of an air bubble, injected into the solution under investigation [2]. Kovrizhnykh and Bochkarev [3] established that polyacrylamide has a three-dimensional reticular structure, consisting of interwoven filamentary supramolecular formations and concretion centers at the sites of such interweaving. A change in the pH of the medium leads to structural transformations of polyacrylamide.In an aqueous solution at pH 3 we observe extension and regrouping of the molecular rod associations, with formation of a less closely spaced but distinct network in the central and peripheral parts of the concretion centers. During regrouping, the molecular rod associations are compacted and become thicker. At the periphery of the concrettons, at the points where branching of the molecular rods occurs, the filamentary associations are characterized by a compacted structure, a decreased degree of branching, and a greater length of the individual filamentary formations ( Fig. la and b).At pH 7 we observe extension of the concretion centers, leading to formation of ellipsoidal and globular clots of molecular rod associations, similar to those of analogous structures of the initial polyacrylamide [2].In a solution with pH 9 the filamentary associations of molecular rods become less compact, and decrease in lengtk, thickness, and density; the reticular structure formed from them is converted to a fine-cellular structure (see Fig. lb and d). The shapes of the elongated, branched association of molecular rods in the branched region of the concretions differ from those of the structures of the initial polyacrylamide by the somewhat greater degree of branching and the less compact character.The structural changes of polyacrylamide, revealed by the electron microscope, are confirmed by examinations under optical microscopes.In an aqueous solution with pH 3 we observed the following: tightly folded forms of molecular rod associations on the bottom of the vessel, smaller than 0.03 ram; filamentary forms of molecular rod associations with localized concretion centers, exhibiting branched associations at the periphery, part of which settles on the bo...

Coal preparation plants in the Soviet Union make extensive use of flocculation of fine coal slm-ries by pelyacrylamide; this greatly intensifies the functioning of one of the most unsatisfactory units of preparation plants, i.e., the water-slmry complex. However, the flocculation mechanism remains largely unexplained; in particular, no relation has been established between flocculation performances and a number of physical and chemical factors due to major differences in the material composition of the coal, the chemical and physical properties of the liquid phase of the pulp (the pit wamr), etc.The present paper deals with the interrelationship of the pH of the medium and free COz, relams the consumption of flocculation agent and plant performance to the pH and the presence of CO z, and examines the variation in adsorption of polyacrylamide on the coal with the CO l content in the pulp. In these tests we took into account the fact that the flocculation of coal slurries by polyacrylamide can be performed over arelatively wide range ofpH [1].We studied four samples of coal fines with particle size 1-0 ram, obtained from coals of the Baidaev, Abashevo, Maneikha, and No. 4 (Kuzbass) pits. * The samples were crushed bY the wet method to -0.074 mm, and the pulp density increased to 40 g/liter. The experiments were perfoimed in distilled water in a 500 ml cylinder.Coal pulps of these samples were slightly alkaline, the pI-I of the medium was adjusted with solutions of HC1 and KOH. The polyacrylamide concentration was 0.1% ; it was fed to the pulp all at once (6.0 ml/liter). The factor governing the effect of the mediun's pH on flocculation was taken to be the residual content of solid particles in the supernatant liquid after flocculation.It will be seen that the solids content in the liquid decreases sharply from 3.35 g/Liter in an alkaline medium to 0.12 g/Liter in an acid medium. Optimum clarification occurs at pH 3-5.5. It is, therefore, necessary to determine the optimum polyacrylamide consumption in an established pH range. The experiments were performed on sample No. 4 at pH 5.2. The result~ are given in Table 1.As seen from Table 1, satisfactory clarification it attained with addition of 4.0 ml of 0.1% polyaorylamide per liter of pulp; with this consumption of flocculant, the initial pulp gave a supernatant liquid with a solids content of 2.72 g/Liter (experiment 6).Study of the ionic composition of pulps of coals from different Kuzbass deposits [2] established that the presence of free COz in the pulp improves flocculation.It was necessary to determine the effect of CO z on the change in pulp pH; CO 2 was added directly to the pulp from a cylinder, the flow rate being measured with a T-2-80 rheometer.It was found that even a small amount of cO s (Fig. 2) markedly reduced the pH of the medium, but that further additions had practically no effecLWe determined the optimum amount of CO 2 necessary to obtain a clean liquid after flocculation with pelyaorylamide. The same amount of polyacrylamide (6.0 ml of 0.1~ sol...