Adsorption Of Anionic Polymer Research Articles

Polyacrylamides as co-depressant in hematite and quartz microflotation

In the present study, microflotation experiments were performed on pure minerals systems involving hematite and quartz in the presence of etherdiamine as collector. The influence of polyacrylamides as co-depressant was investigated in a blend with starch depressant. The results obtained demonstrated that all the polyacrylamides used were efficient in hematite depression, at different levels and following the order of effectiveness: cationic > non-ionic > anionic. The depressant power was proportional to the degree of ionicity and the molecular weight. It is proposed that the enhanced performance is due to the presence of two functional groups, the cationic group adsorbing by electrostatic interaction and the amide group –C(=O)NH2 adsorbing by hydrogen bonding. Non-ionic polyacrylamides indicated similar performances for different molecular weights and the proposed adsorption mechanism is hydrogen bonding associated with the amide group. Electrostatic repulsion did not have deleterious action on the adsorption of anionic polymers on hematite, nevertheless the adsorption on quartz was impaired. Polyacrylamides adsorb on quartz, although at a weaker intensity than on hematite.

Adsorption of anionic polymers on hematite – a study of zeta potential distributions

The effect of adsorption of two carboxymethyl celluloses and sodium lignosulfonate on the zeta potential distributions and the aggregation/dispersion behavior of hematite (isoelectric point at pH 6.7) was investigated at pH 5.5 and 10.5. At pH 5.5, all three polymers caused hematite aggregation at lower dosages followed by steric re-dispersion at higher concentrations. It was found that the width of the zeta potential distribution at pH 5.5 gradually increased with polymer adsorption and reached a maximum value at polymer concentrations that led to strongest aggregation of hematite. The results indicated that the main role of the polymers in hematite aggregation at pH 5.5 was to generate large variations in the zeta potential characteristics between individual hematite particles, producing populations of oppositely charged particles that readily underwent aggregation. In the absence of such polymer-induced variations (e.g., at pH 10.5), adsorption of the polymers resulted in strong dispersion of hematite. The width of the zeta potential distribution, rather than the adsorption density of the polymers, was found to be a common factor determining the onset of steric re-dispersion by the tested polymers regardless of the polymer type. Using the width of the zeta potential distribution as a measure of zeta potential variations among the particles, it was shown that steric dispersion at pH 5.5 started to occur when the hematite particles acquired very similar zeta potential characteristics as a result of polymer adsorption. The onset of steric dispersion coincided with a well-defined transition from broad to narrow zeta potential distributions. It was also shown that zeta potential distributions offered additional insights into the mechanism of the aggregating/dispersing action of the tested polymers, compared to the average zeta potential value alone.

Highly transparent flexible clay films modified with organic polymer: structural characterization and intercalation properties

We are developing transparent flexible clay films with high thermal resistance and gas barrier properties. The clay films were fabricated by casting aqueous dispersions of synthetic Na+-saponite mixed with various loadings of water-soluble organic polymer. In this paper, the structural, optical, and physical properties of the films are reported. The structure of these films has been found to have an alignment of densely packed clay platelets interspersed with polymer chains between clay platelet edges. The parallel stacking of clay platelets is enhanced by adsorption of anionic polymer on the positively charged edges of the clay platelets so that excellent optical transparency is maintained even for high clay loading (up to 90 wt%). Also, polymer chains bounded on particle edges are tightly confined by upper and lower layers of clay platelets, rendering these films more thermally stable. The degradation temperature of the films is more than 350 °C. Differential scanning calorimetry analysis reveals that the melting point of the polymer in the clay layers is shifted towards the higher temperature range, up to 440 °C. However, the segregation of polymers towards the film surface occurs with the polymer loading, which reduces the thermal resistance of the film due to weaker interaction of adsorbed polymer on the film's surface. Consequently, films with higher clay loading (>80 wt%) provide excellent optical and physical properties, these films will be promising for a wide variety of applications such as displays or other electronic devices.

Anionic Polyacrylamide Polymer Adsorption by Pyrophyllite and Montmorillonite

AbstractThe mechanism by which the anionic polymers interact with platelets of 2:1 clay minerals is not fully understood. The objective of the present study was to evaluate the effect of the electric field associated with the basal and edge surfaces of the clay minerals on the adsorption of anionic polymers. Two negatively charged polymers, PAM90 and ACC86, of the same molecular weig ht (2 × 105 g mol−1) but with different degrees of hydrolysis (90 and 20%, respectively), were used. The effect of pH (6, 10), NaCl concentration (0, 10 mmolC L−1) and clay particle size on PAM90 adsorption by pyrophyllite and the effect of NaCl concentration on the adsorption of these polymers by Na-montmorillonite in aqueous suspensions were studied. Adsorption of PAM90 on pyrophyllite was greater at pH 6 than at pH 10 and greater in 10 mmol L−1 NaCl than in distilled water. Adsorption of PAM90 on pyrophyllite increased with decreasing particle size. On pyrophyllite the high-charge-density PAM90 was adsorbed to a greater extent than the low-charge-density ACC86; by contrast, ACC86 adsorption was greater than that of PAM90 on Na-montmorillonite. These results were attributed to the repulsive forces which develop between the negatively charged extended-chain polymer and the extended negative electric field associated with the basal surfaces, around the Na-montmorillonite platelets. The results may suggest that the edge surfaces play a major role in PAM adsorption.

Polymer and Water Quality Effects on Flocculation of Montmorillonite

AbstractWyoming Na‐montmorillonite (SWy‐1) was equilibrated with two synthesized waters, representing Friant‐Kern Canal or a typical well water of San Joaquin Valley (EC 0.05 and 0.7 dS m−1, respectively). Adsorption isotherms and flocculation patterns of the clay with three anionic and one nonionic polyacrylamide polymers and cationic, nonionic and anionic derivatized guar polymers, were observed. Polymer solutions of concentrations 0, 5, 10, 20, 50, and 100 mg L−1 were prepared and clay was added at a concentration of 1 g L−1. The test tubes were shaken and then periodically photographed to record floc formation and settling. Adsorption was in the general order: cationic > nonionic > anionic with the exception of the nonionic guar which was adsorbed about equally as the cationic guar. Adsorption of anionic polymers was greater from well water than canal water, whereas the opposite was true for the cationic polymer. Significant polymer water quality interactions on flocculation were observed. Anionic polymers promoted flocculation in the well water for polymer concentrations ≥ 5 mg L−1, but enhanced clay suspension stability in canal water. Floc volume increased with increasing cationic and nonionic polymer adsorption, whereas changes in floc volume were insignificant with anionic polymers. An optimal polymer concentration was found with well water. Flocculation with cationic polymer was attributed to charge neutralization, whereas flocculation with anionic polymers was explained by bridging and osmotic attraction.

Flocculation of clay suspensions by an anionic soil conditioner

Ca- and Na-montmorillonite and Na-kaolinite were flocculated from suspension by two anionic soluble polymers. Light absorbance at 280 nm served as degree of flocculation measure. A prerequisite for flocculation was that salt concentration in clay suspension should exceed 1.0 and 0.2 meq. l −1 for Na- and Ca-montmorillonite, respectively. Furthermore it was shown that the clay had to adsorb a minimum amount of polymer: 0.8 mg/g for a 0.735 g l −1 Na-montmorillonite suspension and 1.0 mg/g for a 0.436 g l −1 Ca-montmorillonite suspension. Saturation adsorptions of polymers on Na- and Ca-clays were estimated to be 4.6 and 7.0 mg/g. These levels of adsorption stabilized the suspension and prevented flocculation. Na-polymetaphosphate (Calgon) added to a Na-montmorillonite suspension after the polymer addition retarded flocculation whereas its addition at a level >2.7 mg/g prior to the polymer addition prevented flocculation. Increasing the pH of the Na-kaolinite suspension from 6.5 to 8.2 considerably reduced its flocculation by the polymer. The effects of both pH and Na-polymetaphosphate indicate the importance of the positively charged sites on the clay in adsorption of anionic polymers and contribute to understanding of flocculation mechanisms.