The economic benefit accruing from the use of polyacrylamide flocculants for accelerating the precipitation and clarification of the mineral suspensions handled in the beneficiation of minerals depends markedly on the polyacrylamide (PAA) content and its degree of hydrolysis in the commercial product. Practice has shown that polyacrylamide flocculants do not have the same flocculating capacities. One of the most important factors determining the flocculating capacities of polyacrylamides is the configuration of the polymer molecule in the solution [1][2][3], which depends on their degree of hydrolysis, i.e., on the ratio of the percentage content of COO groups x + to the total number of functional groups of the polymer.During synthesis of commercial PAA, some of the amide groups are hydrolyzed to carboxyl groups [2] and neutralized by alkali (milk of lime, ammonia, NaOH). Thus in all cases commercial PAA is a copolymer of acrylamide and salts of acrylic acid, their ratios depending on the method of preparation. The gelatinous PAA solution, produced in our factories, contains up to 10% of pure PAA and up to 18% of impurities (ammonium, potassium, and sodium sulfates).In the manufacturing plants, the PAA content of the final product is equated to the monomer content of the reaction mass before polymerization, although the yield of the polymer depends on the polymerization procedure. The monomer content is determined by bromination of the double bonds [4], which are present before polymerization in both acrylamide and acrylic acid; therefore the degree of hydrolysis in the final product cannot be established.The absence of monitoring of the PAA content and its degree of hydrolysis in the final product at the manufacturing plant is due to the fact that existing methods of determining these parameters [2, 3, 5] are unsuitable for analysis of the commercial product, which contains up to 16% of ammonium sulfate. This paper gives a method for determining the content of PAA and its hydrolyzed part in commercial ammoniacal PAA (from the Leninsk-Kuznetsk Semicoking Factory), containing up to 16% of (HN4)zSO4, which makes it the most difficult type to determine. The (NH4)iSO a content of PAA was determined from the SO~-ion by quantitative precipitation with BaC12 from a 0.05% hot acid solution; it was 15.3%.Procedure. A weighed sample of commercial gelatinous PAA was dehydrated in acetone, the free ammonia being removed during this process. The impurities, mainly (NH4)2SO4, were then removed by repeated leaching with aqueous acetone until BaC12 gave a negative reaction for the SO l" ion. The concentration of the aqueous solution of acetone was selected experimentally so that the impurities, but not the PAA, dissolved. Drying at 70~ gave a residue of 9.2%; its ash content after baking at 800~ for 2 h was 1.45%. The increase in weight of the solid polymer to 9.2%, as against the standard value of 7.4%, might be due to residual moisture; to the presence of impurities in the iattial product -acrylonitrile; to the presence of co...

One method of increasing the effective action of polyacrylamide flocculant (PAA) in the clarification of suspensions is its preliminary hydrolysis in the presence of NaOH fil-3].Aref'eva et al. [4,5], who discussed the interaction of simple electrolytes with the polyeleetrolytes (PE) K-4, PAK, PAA-1, and Ca-PAA, concluded that these PE undergo ion exchange with the cations of simple electrolytes; the capacity depends on the nature of the electrolyte cation and the composition of the functional groups of the PE. Unfortunately they did not give the chemical compositions of their PE or state whether they contained impurities which might distort the results.We have studied the interaction of PAA with simple electrolytes in relation to their degree of hydrolysis a, using purified specimens of ammoniacal PAA with a= 13 or 69% in 0.1% solutions, by means of potentiometric titration, viscosity measurements, or visually from the state of aggregation of the mixed solutions. A PAA specimen with a = 69% was obtained by artificial hydrolysis of commercial PAA in 1% solution in the presence of NaOH. The PAA specimens were purified and the chemical composition of the flocculants determined by the method in [6]. Flocculants in the H form were obtained by passing their solutions through KU-2 cation-exchange resin. The PAA specimens were chosen so that amide groups predominated in one of them and carboxyl groups in the other. In our opinion, this fiocculant composition makes it possible to distinguish most clearly between the interactions of the flocculants with the electrolytes.In Fig. 1, the solid curves are potentiometric titration curves of 50 ml of 0.1% solutions of two PAA specimens with a = 13 % (specimen A) and a = 69 % (specimen B) versus 0.1N solutions of chlorides and sulfates with univalent, divalent, and trivalent cations; the dashed curves represent the pH changes of 50 ml of distilled water when the same electrolytes are added.The chemical compositions of the PAA specimens in 50 ml of 0.1% solutions were as follows:,,B ~ ~A,t mv' I o

The use of hydrolyzed polyacrylamide (HPAA) to intensify clarification of suspensions greatly reduces the consumption of flocculant in comparison with unhydrolyzed polyacrylamide (PAA) with a simultaneous improvemerit in the clarification rate and purity [1][2][3], but in some cases the effect obtained by means of HPAA is either negligibly small or zero [4]. The optimal degree of hydrolysis of PAA, determined by various procedures, ranges from 20 to 50~There is as yet no agreed theory of the mechanism of attachment of PAA molecules to solid particles or of its flocculating effect during clarification of suspensions.Hydrolyzed PAA is a polyelectrolyte. A general characteristic of electrolytes is their dissociation constant, the value of which governs their chemical activity in solution. The value of this constant enables one to assess the state of an electrolyte in an equilibrium system and to determine both the possibility of effecting the process in question and its direction.Literature reports in this field deal mainly with the conditions of use and the degree of hydrolysis of PAA, data on its chemical activity being scanty. Thus one can find the following values given for the dissociation constant of the hydrolyzed part of PAA (carboxylic acid) :2.9-10 -.5 for PAA with a degree of hydrolysis 20.6~ [5], 3.8.10 -s for PAA with a degree of hydrolysis 12.8~ [6], and 1.35-10 -s for polyacrylic acid (100~ hydrolysis of PAA) [7].The hydrolyzed part in HPAA is present as carboxyl groups (carboxylic acid), or as the salt of weak carboxylic acid with a weak (NH +) or strong (Na +, Ca 2+) base, markedly hydrolyzed in aqueous solution. During hydrolysis of PAA a change is observed in the proportion of amide groups and the hydrolyzed part, i.e., in the composition.When a mixture of solntions of a strong acid (HCI) and commercial PAA with various different degrees of hydrolysis was titrated with a strong base (NaOH), we noted [8] that if the degree of hydrolysis is low, differential titration of the strong acid from the hydrolyzed part of PAA in H form cannot be effected: at the equivalence point for titration of the hydrolyzed part of PAA in H form, with decreasing degree of hydrolysis of PAA the inflection and the pH jump on the potentiometric titration curves increase. These characteristics are manifested only in those cases when the dissociation constant of the carboxyl groups ofHPAA varieswith its degree of hydrolysis.The variation of the dissociation constants of the hydrolyzed part of HPAA with the degree of hydrolysis was determined on weakly hydrolyzed ammoniacal polyacrylamide flocculant of the Leninsk-Kuznetsk Semicoking Factory. Specimens of HPAA with high degrees of hydrolysis were obtained by artificial hydrolysis of this flocculant in 1 ~ solutions with different NaOH contents. All the HPAA specimens (1 ~/~ solution) were purified by the procedure in [9]. The content of the polymer and the hydrolyzed part were determined in solutions of these purified HPAA specimens [6]. The dissociation constant Kk of the ca...

OF THE STATIC UDC 622.75/76The choice of optimum operational and conStructional characteristics for enrichment machines (apparatus) presupposes a detailed study of the dynamics of "hydro-mixture" flow. Usually all research on flow dynamics in apparatus for enriching a two-phase medium is carried out with water or by some indirect means, and the results are tramferred to the two-phase mixture. This is necessitated by the lack of a satisfactory method of measuring the velocity, pressure and structure of a current of "hydro-mixture" [1][2][3][4].In this article we give preliminary data on an investigation (using water) to develop an apparatus for measuring the velocity and pressure in a current of hydro-mixture. This is based on a) the method, of counterpressure measurement used to measure the surface tensiom of liquids [5] and the demities of slurries in tanks [6]; b) measurement of the velocity and static pressure head.~ of a current of pure water by means of hydrodynamic tubes (Pitot, Prandtl) [7].

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.