Formation of bonds in a dispersed phase with clarification of a suspension by flocculants

Abstract

A knowledge of the mechanism of bond (bridge) formation of flocculant molecules between solid particles during clarification of a suspension by means of water-soluble polymers is an indlspensible condition for selecting the type of flocculant and carrying out the flocculation process itself.Nonetheless, study of the composition (structure) of these bridges has received almost no attenution in the literature.Opinions existing in the literature are contradictory.One author [i, 2] assumes that during bridge formation individual polymer molecules take part, which indicates that the chain of the macromolecules in solution should have a length not less than i000 A. Another author [3, 4] assume that flocculant is adsorbed on solid particles in the form of associates (bundles, supermolecular structures) of molecules. In this case flocculant molecules in solution may have a considerably shorter length, since the length of an associate significantly exceeds the size of individual molecules.A number of authors [5][6][7] confirm that during bridge formation both individual macromolecules and their associates may take part.The aim of this study is to establish the number of flocculant molecules arriving at each solid particle, proceeding from flocculant consumption, its molecular weight, and the overall grain-size analysis of the solid phase for two specific natural suspensions. As suspensions use was made of coal flotation tailings at the Belovsk Central Enrichment Plant, clarified by means of polyacrylamide (PAA) [8, 9], and the feed to the clarifying cone (CC) of the Yakutalmaz Enterprise using technical grad PAA [i0]. The molecular weight of PAA specimens was determined by characteristic viscosity of their solutions in 10% NaCI solution and in formamide [ll]. The suspension of flotation tailings contained 27 g/liter, and the feed to the clarifying cone contained 24 g/llter of solid.In mineralogical composition flotation tailings were represented by 44% of argilla~eous minerals, According to data in [12] the size of clay particles may vary from i ~m to i0 A.The yield of material fractions coarser than 0.05 mm was determined by moist sieve screening.Material finer than 0.05 mm was divided into fractions according to hydraulic size in an ascending water current in a ADAP using sodium pyrophosphate as a solution stabilizer. The finest fraction of the ADAP, i.e., 2 ~m with a solid content for suspension of the coal flotation tailings of 200 mg/liter, and for the suspension of the feed to the clarifying cone of 140 mg/liter, was subjected to sedimentation analysis both in a gravitational field and in a centrifugal force field.In a gravitational field sedimentation analysis was carried out by the procedure in [13] using torsion weights.