**3.1 Electrocoagulation-electroflotation theories**

This technique is based on the in situ formation of coagulant as the sacrificial anode (usually aluminum or iron) corrodes due to an applied current (figure 7). Aluminum and iron materials are usually used as anodes, the dissolution of which produces hydroxides, oxyhydroxides and polymeric hydroxides. In EC, settling is the most common option, while flotation may be achieved by H2 (electroflotation) or assisted by air injection.

Electrochemical Probe for Frictional Force and Bubble Measurements

Al Al3+ + 3e-

4 OH- **2** H2O + O2 + 2 e-

2 H2O + 2 e- 2 H2 + 2 OH-

At the anode, takes place oxidation:

At the cathode, takes place reduction:

production of Fe(OH)n follow two mechanisms.

For higher current density:

adsorb or precipitate.

a. Mechanism 1:

b. Mechanism 2:

Anode : Fe Fe2+ + 2e-

Cathode : 2 H2O + 2 e-

Anode : 4Fe 4Fe2+ + 8e-

Cathode: 8H+ + 8e- 4H2

Fe2+ + 2OH- Fe(OH)2

Overall : Fe + 2H2O Fe(OH)2 + H2

4Fe2+ + 10H2O + O2 4Fe(OH)3 + 8H+

Overall: 4Fe + 10H2O + O2 4Fe(OH)3 + 4H2

configuration can be divided into three modes:


range.

and Innovative Electrochemical Reactors for Electrocoagulation/Electroflotation 55

Although the sacrificial anodes deliver Al cation, their dissolution produces hydroxides, oxyhydroxides or polymeric hydroxides as a function of pH (Chen et al., 2004). These can

Al3+ ions may generate Al(H2O)63+, Al(H2O)5OH2+, Al(H2O)4(OH)2+. Many monomeric and polymeric species will be formed by hydrolysis such as, Al(OH)2+, Al(OH)2+, Al2(OH)24+, Al(OH)4-, Al6(OH)153+, Al7(OH)174+, Al8(OH)204+, Al13O4(OH)247+, Al13(OH)345+ over a wide pH

In the case of iron electrodes, Fe(OH)n with n = 2 or 3 is formed at the anode. The

Polymeric hydroxy complexes are also generated namely : Fe(H2O)63+, Fe(H2O)5(OH)2+,

Because of the workable rate of metal dissolution, a two-electrode EC is not always suitable. That's why large surface area is needed for a good performance. The electrodes

As observed in figure 8, the parallel arrangement consists of pairs of conductive metals plates placed between two parallel electrodes and DC power source. All cathodes are connected to each other and to negative pole of DC; in the same manner, all sacrificial anodes are connected to each other and to positive pole of DC. The electric current is

divided between all the electrodes in relation to the resistance of the individual cells.

Fe2(H2O)8(OH)24+ and Fe2(H2O)6(OH)44+, depending on the pH of aqueous medium.

2 H2 + 2 OH-

Fig. 7. Schematic diagram of two-electrode electrocoagulation (EC) cell.

Three successive stages occur during EC:


The pollutants can be in form of:


It is impossible to use the decantation as a technique to eliminate the maximum of particles. This remark is especially valid for colloids. Thus, colloids are organic or mineral particles in which the size is between some nanometers and approximately 1 responsible for color and turbidity.

The destabilization mechanism of the pollutants can be summarized as follows:

