Determination of the polyacrylamide content and its degree of hydrolysis in a commercial ammoniacal flocculant

Abstract

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...

The influence of the depth of hydrolysis of polyacrylamide flocculant on its interaction with electrolytes

“…With specimens of PAA in the H form, these salts interact like NaOH [6] in equivalent quantities with an inflection on the potentiometric titration curves. When A and B are added to the solutions, the pH of the solution rises and its viscosity fails.…”

“…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.…”

Effect of the degree of hydrolysis on the chemical activity of polyacrylamide flocculant

“…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].…”

“…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 carboxyl groups (weak acid) of HPAA at different degrees of hydrolysis was determined by two methods.…”

“…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].…”