Environmental chemistry, chemistry in environment and the human role

Step 1 - Activities

Water purification by means of adsorption

Adsorption. Methods for water purification
Adsorption is the process of absorbing substances called adsorbate, from the surface of other substances referred to as adsorbent( solids) which occur due to forces of attraction between atoms , molecules and ions in solid state. The following types of adsorption are distinguished:

• Physical (adsorbate molecules retain their individuality) – physical adsorption takes place quickly and the relatively small thermal effect does not allow it to be reversible.
• chemical (chemosorption) takes place when on the surface of the adsorbent a new phase or component appears as a result of chemical reaction.

Adsorption methods are used in additional purification of waters and elimination of pollutants such as suspended, dissolved and colloidal substances. Various natural and artificial materials could be used as adsorbents such as peat, crushed coke, saw dust, silicagel etc. A number of requirements are to be met by the adsorbents:

They should

• feature high adsorption capacity such as displayed by porous and too dry materials of high porosity and developed volumetric microstructure;
• be highly selective in absorbing particular components;
• possess mechanical strength;
• be thermally resistant;
• be recyclable;
• have comparatively low cost and accessibility.

Adsorbents are classified according to their capacity to regenerate and according their content( coke, oil products, wood, fruit stones, silicagels, zeoliths and other inorganic materials such as resins, cellulose ,polysterol, phenol etc..

Required materials and tools
200 – 250 ml contaminated water for purification, 1 -2 teaspoonfuls of char coal, funnel, filtering paper, 2 vessels with capacity of 250 – 300 ml.

Fig. 1

Step 1: The funnel is fixed at a proper place or on a post. Then the filtering paper which is cut out in the shape of the funnel is inserted. A vessel of capacity 250 – 300 ml is put underneath for collecting filtered water (purified water) (fig.1).

Fig. 2

Step 2: Pour 150 - 200ml of contaminated water into a vessel of 250 – 300 ml capacity. Add 1-2 teaspoonfuls of ground char coal (fig.2).

Fig. 3

Fig. 4

Step 3: The mixture is stirred well and with care (fig.3). After that it is poured in portions through the funnel coated with filtering paper. The filtrate (purified water) is collected in the vessel under the funnel (fig.4).

Quantitatively the rate of purification by means of char coal is evaluated through determining the dilution indexа. Purity can be rated visually by setting purified water against the background of a white sheet of paper. This evaluation is qualitative, however, it is prone to very high subjective error.