Selective Polymer Flocculation

Selective flocculation of various polyacrylamides in the mixture of gangue and hematite particles can be found from Table 5.2. The orders of electronegativities of various polyacrylamides are as follows  

As shown in Table 5.2, the selective flocculation of A70 to hematite is the strongest. The selective flocculation of Aioo to quartz is the strongest. 

Flotation results show that SF-D technology can improve the separation index. Take the SF-D flotation of hematite in Marquette mill, America, the separation index is improved, and the reagent dosage is reduced. The related flotation results can be seen from Table 15.3. And the reagent system is as follows  

Flocculant Product Settling time (min) Hematite Silicate  

Technology Product Yield (%) Grade Recovoy rate of Fe (%) 

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Other Organic Flocculants and Selective Polymer Flocculation... 

One would like to see more experiments carried out with mixed dispersions in the presence of polymers (leading to selective flocculation ), and on the interaction of particles with macroscopic surfaces. Both of these areas have long-term implications in biological studies. (Selective cell ahesion adhesion of microorganisms to surfaces.)... 

The major difference in the flocculation behaviour of PEG 40,000 at pH 5.3 and pH 2.3 is demonstrated by the absorbance in the supernatant solution E,., (fig. 13). At pH 2.3 a small addition of polymer leads to significant flocculation and therefore a small absorbance, i.e. a high transparency of the supernatant liquid. The time dependences of the absorbances with and without polymer are shown for pH 5.3 and ca.pH 2 in fig. 14. Fig. 15 shows similar curves for a selection of salt concentrations. Similarly the time dependence of the absorbances Ej with and without polymer is illustrated for pH 5.3 and ca.pH 2 in fig. 16 and for different salt concentrations in fig. 17. 

Adsorption of nonionic and anionic polyacrylamides on kaolinite clay is studied together with various flocculation properties (settling rate, sediment volume, supernatant clarity and suspension viscosity) under controlled conditions of pH, ionic strength and agitation. Adsorption and flocculation data obtained simultaneously for selected systems were correlated to obtain information on the dependence of flocculation on the surface coverage. Interestingly, optimum polymer concentration and type vary depending upon the flocculation response that is monitored. This is discussed in terms of the different properties of the floes and the floe network that control different flocculation responses. Flocculation itself is examined as the cumulative result of many subprocesses that can depend differently on system properties. 

In order to generate information on the mechanism of flocculation by polymers it is, however, necessary to correlate flocculation with various system properties, particularly adsorption. Thus, if particle/polymer-polymer/particle contact is the aggregation mechanism, the flocculation responses should be expected to continuously increase with surface coverage. On the other hand, if particle/polymer-particle contact is predominant and if the polymer adsorption is essentially irreversible, maximum flocculation might be expected under submonolayer conditions. In order to determine the nature of this relationship for the present systems, selected flocculation responses are plotted in Figures 8 and 9 as a function of surface coverage for the nonionic and the anionic polymer respectively. The assumptions involved in the computation of the surface coverage are to be noted at this point ... 

The method described here provides a convenient means of determining the specific filtration resistance of fairly dilute suspensions. Results for clay suspensions flocculated by cationic polymers show that the specific resistance gives a sensitive indication of flocculation and is a useful guide in the selection of optimum flocculant concentrations. In a series of trials not reported here, it has been shown that the specific resistance results are very well matched by re-filtration rate data, as expected. The results also agree well with other, unrelated techniques. For more concentrated suspensions, some discrepancies have been found between permeability methods and other measures of flocculation (4). 

Mineral segregation in industry relies heavily on the selective adsorption of macromolecules onto the surfaces of those minerals that have particular industrial applications. This selectivity is governed mainly by the surface chemistry of the mineral and the type of polymer used as a flocculant. " Effectiveness of flocculation depends upon the charge, concentration and molecular weight of the polymer, and also the pH and salt concentration of the clay suspension. The bonding between the anionic flocculant polyacrylamide (PAM) and clay mineral surfaces has been effectively reviewed recently by Hocking et al and the reader is referred to this should they require an in-depth literature review. For more information on general colloidal chemistry of clay suspensions the reader is referred to the review of Luckham and Rossi." ... 

This paper contributes to the literature by quantifying anionic polymer adsorption onto the clay minerals kaolinite, feldspar, mica and quartz by X-ray photoelectron spectroscopy (XPS). XPS measures the sorbed amount directly rather than by a subtraction technique. This enables an insight into how effective selective flocculation is for obtaining kaolinite from a mineral mixture. Atomic force microscopy (AFM) is also used to image polymer adsorption onto mineral surfaces and the effectiveness of this technique applied to mineral surfaces is discussed here. 

XPS can be used to quantify HPAM adsorption onto minerals at various polymer bulk concentrations. It is seen here that kaolinite has twice the affinity for HPAM than feldspar at pH 9.0 and 50 ppm. Little or no adsorption was monitored on the surface of quartz or mica. Imaging XPS to monitor selective adsorption of mineral mixes proved difficult. Flocculating a mineral mixture of kaolinite, mica and quartz caused the kaolin floes to encapsulate the other minerals. This created a layer of kaolin on the quartz and mica prohibiting polymer mapping on their surfaces. It is shown that the effectiveness of the kaolin recovery is more strongly affected by encapsulation of other minerals during flocculation rather than the selective adsorption process. 

The current theories of steric stability (3-6) predict that provided the particles are well-covered and the polymer is well-anchored particles bearing non-ionic polymers should flocculate at or near the 0-point of the stabilising chains. The available experimental date ( 3, 7 9 8) confirm this result in as much as critical flocculation temperatures and pressures have been found to correlate tolerably well with the relevant 0-points for a wide range of systems. Where the correlation has been less than satisfactory the discrepancy has often been understandable in terms of multiple anchoring, selective adsorption of lyophobic blocks, or other specific effects (9, 10). 

In order to ascertain that the selective dispersion effect of PAAX was truly due to the modified polymer itself and not to the associated poly-sulfides in the crude reaction, the flocculation testing was repeated with the purified PAAX solution. By using 300 mg/l of the purified PAAX solution, about 96 percent of the coal suspension flocculated in 5 minutes, while the pyrite suspension remained stable. These tests confirmed that the selective dispersion action was due to the PAAX (polyxanthate polymer) itself. 

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