Flocculant selection

Natural polymers such as modified starch, guar gum or dextran are employed to boost the particle size of substrates but, due to their lower molecular weight relative to synthetics, their use is mainly focused on improvements to fines capture and clarity. 

Synthetic polymers can achieve large aggregate structures which can deliver the highest throughput requirements in terms of settlement or filtration rates, especially in high rate equipment where high-shear conditions apply at the floe formation stage. 

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Flotation is certainly the major separation method based on the surface chemistry of mineral particles. It is, however, not the only method. Selective flocculation and agglomeration may be mentioned as other methods used commercially to a limited extent. The former is for hematite, while the latter is for coal and finely divided metallic oxide minerals. Both processes use the same principles as described for flotation to obtain selectivity. In selective flocculation, polymeric flocculants are used. The flocculants selectively adsorb on the hematite, and the hematite floes form and settle readily. Thereby separation from the sili-... 

S Sg/L Flocculation, selective flocculation, slime coatings, thickening... 

Coagulant and/or Flocculant Selection Coagulants and flocculants are widely used to enhance the settling rate which reduces thickener and clarifier size and improves overflow clarity and/or underflow sluriy density. The terms coagulation and flocculation are sometimes used interchangeably however, each term describes separate functions in the particle agglomeration process. 

In general, flocculants are used in solid-liquid separation processes such as thickening and filtration. Inorganic salts are also used sometimes to aggregate fine particles. Flocculation technique has been developed further for special applications of selective flocculation, selective dispersion and agglomeration flotation. 

Selective flocculation. Suppose X23 is positive but now the dispersion medium is adjusted to be a worse than 0-solvent for, say, polymer 2 (Xi2>2 but Xi3 < 2)- Homoflocculation of the particles coated by polymer 2 will ensue. Provided that xii is not excessively large, heteroflocculation would be expected to be absent. This implies that it should be possible under such conditions to flocculate selectively one species of sterically stabilized particles in a mixed dispersion. Apparently polymer coated particles are able to discriminate between self and not-selF when undergoing Brownian collisions in such dispersion media, coagulation only occurring between particles of the same type. Of course, if the dispersion medium were made a worse than 0-solvent for both polymers (xi2. Xi3>tX both 2-2 and 3-3 homoflocculation would occur. Heteroflocculation would only be possible if... 

The best approach is to seek and follow suppliers reconunendations on handling of their products. Suppliers data also help in the preliminary selection of an agent, but best results usually require testing on plant brine. Previous experience with similar brines is also very valuable. Finally, the flocculant selected must not have any deleterious effects on the operation of the cells when present in a recycle brine stream. In a membrane-cell plant, preference should be given to those that have been shown to be compatible with the membranes. 

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