Equivalent flocculation

The example put forward above of dicomplex flocculation of nucleate with cations, gives us the opportunity to discuss yet another point, namely the so-called equivalent flocculation which is often encountered in dicomplex flocculations. This phenomenon is present here for hexol nitrate and Co(NH8)gCl3. 

This equivalent flocculation ii also encountered in silver halide sols, pepti2 ed by halide ions which are flocculated by equivalent amounts of silver ions or in Fe(OH)3 sols, peptized with HCl which are flocculated by NaOH. In these last two cases a more than equivalent addition of the flocculating electrolyte leads to a second region of stability, where the charge of the sol proves to be inverted in sign ... 

In experiments of Freundlick on the coarsening of HgS after it had been coagulated with a dye-stuff like new fuchsin, the desorption of the flocculating ion was very marked. The sol of HgS could be flocculated by new fuchsin in such quantities that the supernatant liquid remained practically uncoloured (equivalent flocculation). 

Most synthetic latices contain 5—10 wt % of nonelastomeric components, of which more than half is an emulsifier or mixture of emulsifiers. One reason for this relatively high emulsifier concentration as compared with natural latex is that emulsifier micelles containing solubiHzed monomer play a principle role in the polymerization process. A high emulsifier concentration is usually necessary to achieve a sufficiently rapid rate of polymerization. Secondly, a considerable fraction of the surface of the polymer particles must be covered by adsorbed soap or equivalent stabilizer to prevent flocculation... 

The method is apphcable for unflocculated pulps or those in which the ionic characteristics of the solution produce a flocculent structure. If polymeric flocculants are used, the floccule size will be highly dependent on the feed concentration, and an approach based on the Kynch theoiy is preferred. In this method, the test is carried out at the expec ted feed solids concentration and is continued until underflow concentration is achieved in the cyhnder. To determine the unit area, Talmage and Fitch (op. cit.) proposed an equation derived from a relationship equivalent to that shown in Eq. (18-45) ... 

Similar remarks apply to the determination of bromides the Mohr titration can be used, and the most suitable adsorption indicator is eosin which can be used in dilute solutions and even in the presence of 0.1 M nitric acid, but in general, acetic (ethanoic) acid solutions are preferred. Fluorescein may be used but is subject to the same limitations as experienced with chlorides [Section 10.77(b)], With eosin indicator, the silver bromide flocculates approximately 1 per cent before the equivalence point and the local development of a red colour becomes more and more pronounced with the addition of silver nitrate solution at the end point the precipitate assumes a magenta colour. 

The crucial question is at what value of <)> is the attraction high enough to induce phase separation De Hek and Vrij (6) assume that the critical flocculation concentration is equivalent to the phase separation condition defined by the spinodal point. From the pair potential between two hard spheres in a polymer solution they calculate the second virial coefficient B2 for the particles, and derive from the spinodal condition that if B2 = 1/2 (where is the volume fraction of particles in the dispersion) phase separation occurs. For a system in thermodynamic equilibrium, two phases coexist if the chemical potential of the hard spheres is the same in the dispersion and in the floe phase (i.e., the binodal condition). 

When Of a, the potential energy of interaction between an elementary particle and a hoc is equivalent to the potcntiul energy 4(h) between a particle and a fiat plate thus 4(h) used by Huckenstcin and Prieve (1976) still applies. Furthermore, if the conditions necessary for Equation (13) of that paper apply, then (berate constants for reversible flocculation inay be calculated as K/ = 4 / Kf and Kr — Aoaf K where X/ and K, are given by Equation (13). 

A major source of water for leaching is the normally acidic run-off water from the mining operation itself. O Leary (02) describes a technique of cleaning up to 900 gal/min of mine and tailings water at the Butte operation of the Anaconda Company. The suspended solids, which at times are in excess of 2% by weight, are equivalent to about 50 tons of mud per day. Since copper is recovered from this stream by precipitation and the barren liquor is used to leach the mine w aste dumps, solids, and colloidal materials have to be removed. With a flocculant, a 98% reduction in solid content is attained with a feed stream containing 0.22% solid. 

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