Electrolytic methods of phase separation

In electroflotation, the gases are generated electrolytically in a cell such as that shown schematically in Fig. 7.23 A pair of closely spaced (0.2-2 cm), horizontal-gauze or expanded-metal electrodes are placed towards the base of the tank and 

The electrophoretic deposition of organic paints onto steel is coniidered in Chapter 8. A much smaller scale ( 100 A) use of electrophoresis is the separation of biochemical species from natural sources including body fluids (such as blood plasma or muscle tissue extract). 

Electrophoresis also provides a useful technique in biosynthesis for protein and enzyme purification and production. 

24 (a) The principle of the Biostream process for continuous electrophoretic separation of proteins. (Courtesy Harwell Laboratory, UK Atomic Energy Authority,) 

The structure of this Biostream electrophoretic separator is shown in Fig. 7.24(a) white Table 7.5 indicates typical conditions. 

It is generally considered that the mechanism is, as in dissolved air flotation, purely mechanical as the bubbles of gas rise, they capture the organic particles and carry them upwards. In electroflotation it is also possible that there is an electrostatic contribution to the mechanism. If the gas bubbles leaving the electrodes carry small charges, then they can neutralize the electrical charges known to exist on colloidal particles and cause them to coalesce. 

Electroflotation cells vary in capacity between 1 and 50 m, the largest size giving the capability of dealing with up to 150m h of H2O. In a typical specification, the plant will reduce 1000 mg dm solids and 600 mg dm oils to 30 and 40 mg dm respectively. The components of the cell will be selected mainly for durability and low cost. The tank will be steel or a cheap plastic depending on size the cathode will be a steel and the anode platinized titanium or lead dioxide on titanium. 

In electroflocculation or electrocoagulation, the flocculating agent is introduced as a result of an electrode reaction and such processes permit a careful control of the amount of the reagent introduced into the effluent. Thus, for example, AP or Fe can be introduced by using an aluminium or iron anode and it is 

A recurrent problem in effluent treatment is the separation of soUd suspensions and emulsions or colloidal particles of oil or other organic compounds in water  

Electroflotation is now an attractive process for smaller-scale operation although it is unlikely to challenge dissolved air flotation in its larger-scale apphcations in mineral ore concentration and oil/water separation in the petroleum industry. Certainly the number of electroflotation plants seems to be on the increase and, for example, there are now about twenty such plants in the UK. 

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Electrolytic precipitation is a highly useful method of accomplishing separations. In this process, the more easily reduced species, either the wanted or the unwanted component of the sample, is isolated as a separate phase. This method becomes particularly effective when the potential of the working electrode is controlled at a predetermined level (see Section 22B). 

Based on the fact that aromatic sulfonic and carboxylic acids were successfully separated by reversed-phase chromatography in the presence of organic electrolytes, Chaytor and Heal (158) developed a method for the separation of 15 synthetic colors using a mobile phase containing o-phosphoric acid (Table 7). The presence of the electrolyte provided lower variation in response and retention over a period of time. Furthermore, eluted peaks were sharper than those seen in ion-pair chromatography. 

The electrolysis of the studied systems was carried out in the same cell as voltammetry measurements under the mode of either constant current or voltage. In the constant current mode, the applied current density was in the range of 0.01 0.2 A/ sm2 with reference to the surface area of the cathode before starting the electrolysis. Semi-immersed glassy carbon plate electrodes (cathode area - 5 sm2, anode area - 10 sm2) were used while electrolysis experiments. A powder product was either settled down onto the crucible bottom or assembled on the cathode in the view of electrolytic pear . The deposit was separated from salts by successive leaching with hot water. Thereafter, the precipitate was washed with distilled water by decantation method several times and dried to a constant mass at 100 - 150 °C. The electrolysis products were analyzed by chemical and X-ray phase analyses, methods of electron diffraction and electronic microscopy (transmission and scanning). 

The development of this experimental technique is largely the result of the work carried out by A. Tesilius and W. Grassmann in the ninteen fifties. Although a solution of an electrolyte held on a supporting medium is required, this method of separation does not require a mobile phase. Since the sample ions are not partitioned between a stationary phase and a mobile phase, electrophoresis is not a chromatographic technique. 

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