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...

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