Question

Please provide me a brief summary and important points of Floatation (Chapter 10 class 9 ncert)

Answer 1

                                                 Flotation

Flotation is a process of solid-liquid or liquid-liquid separation which applies to particles whose density is lower than that of the liquid containing them.

Natural Flotation: the difference in density is of course sufficient for separation .

Assisted Flotation: It consists of an instillation of air bubbles within the liquid mass to improve the separation of the naturally float-able particles.

Induced flotation: in this case, the density of the particle is initially higher than that of the liquid. It is artificially reduced by gas bubbles (air in general). Indeed some solid or liquid particles can be combined with bubbles to form "bubble particle" couplings less dense than the liquid.

There are two types of assisted flotation depending on the size of the gas bubbles:

Mechanical flotation: it uses dispersed air with bubble production of 0.2 to 2 mm in diameter (velocity: about 20 cm s-1).

Dissolved air flotation (FAD): it uses very small air bubbles (micro-bubbles) of 40 to 70 microns in diameter (velocity 100 times less than that of mechanical flotation).

Equation of the velocity of a bubble of gas:

It is given by the Stokes equation
V = (g / 18) * (1 - g) * d²
D: diameter of the bubble: dynamic viscosity
L: density of liquid g: density of gas