(1) Influence of surface active substances

For example, when there is a lack of surface active substances in the water, the small bubbles always have the tendency to break through the bubble wall and merge with the large bubbles, thereby destroying the stability of the air-floating body. At this time, it will be necessary to add a foaming agent to the water to ensure the stability of the air bubbles in the air flotation operation. The so-called foaming agents are mostly surfactants composed of polar-non-polar molecules. The molecular structure symbols of surfactants are generally represented by 0, and the rounded ends represent polar groups, which are easily soluble in water and extend toward In water (because water is a strong polar molecule); the tail represents a non-polar group, which is a hydrophobic group and extends into bubbles. Due to the repulsive effect of the same number of charges, the merger and collapse of the bubbles are prevented, and the foam stability is enhanced, so most surfactants are also foaming agents.

When air flotation is used to treat wastewater with little organic pollutant content, the air bubbles must have a certain degree of dispersion and good foam stability (such as air flotation filtration of drinking water). However, when its concentration exceeds a certain limit, the surface tension of the water decreases due to the increase of surface active substances, the polluted particles in the water are seriously emulsified, and the surface potential increases. At this time, the water contains the same charge as the polluted particles. Turning to the opposite side, at this time, although the foaming phenomenon is strong, the foam formation is stable; but the air sticking is not good, and the air flotation effect becomes low. Therefore, how to master the optimal content of surface active substances in water has become one of the important issues to be discussed in air flotation treatment.

(2) Charged flocs produced by coagulant dosing

For industrial wastewater containing finely dispersed hydrophilic particulate impurities (such as pulp, coal slime, etc.), when air flotation is used to treat industrial wastewater, in addition to the aforementioned method of adding electrolyte coagulant for surface neutralization, it can also be added to the water. The addition (or presence in water) of a flotation agent can also change the hydrophilic surface of the particles to be hydrophobic and able to adhere to air bubbles. When the polar end of the flotation agent (also a surface active substance composed of amphiphilic molecules) is adsorbed on the surface of the hydrophilic particles, its non-polar end faces the water, so that the substance with a hydrophilic surface is transformed into Hydrophobic, so that it can adhere to air bubbles and float with them to the surface.

There are many types of flotation agents. Whether they can work when used depends on whether their polar ends can be attached to the surface of hydrophilic pollutants, and the strength of their binding force with bubbles depends on their non-polarity. The length of the end chain.

For example, the flotation agent used in separating pulverized coal in coal washing wastewater is dephenolized light oil, medium oil, diesel oil, kerosene or pine oil.

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