Purification of water from heavy metals is undoubtedly an important factor for obtaining a ready-to-use, clean and harmless liquid for humans. Heavy metals include chemical elements that have metallic properties and at the same time have significant atomic mass.
They have a destructive effect on the functions of animal and human organisms, and they also tend to accumulate in organs and tissues and cause irreparable harm to health. That is why it is important to install water filters on water treatment plants from iron, copper, lead, nickel, zinc, cobalt, mercury, cadmium and silver.
The need for such filtration is due to the fact that due to the active use of water for various industries, the concentration of these metals in the effluent is very high. Pollutants have different structures and properties, which means that for each of their species it is necessary to resort to different methods and devices.
Water purification from heavy metals in the form of ions is carried out chemically and is reduced to a change in the level of acidity of the medium to the necessary. Upon reaching a pH of 9.0-10.5, any metals become insoluble and precipitate, which is eliminated quite simply.
The choice of chemicals by which industrial water treatment is performed depends on the following factors:
- the necessary degree of purification;
- concentration of pollutant;
- the presence or absence of impurities.
After the substances are transferred into an insoluble form, the stage of their separation follows, most often using gravitational metal deposition. An operation is performed using special precipitating containers, from which the settled particles are pumped out for dehydration and drying. The advantage of this method is its simplicity, and the minus is its high sensitivity to the presence of extraneous compounds that can interfere with the deposition process. It can be soap, hydrogen peroxide or detergents.
Water purification from heavy metals is also carried out in a different way. It is called "membrane" and is carried out using a special installation with partitions. As a rule, in water purified by membranes, the concentration of metals does not exceed 1 mg per liter, and on the other side of the filter they themselves are concentrated in the form of a gel-like mass.
It is such a treatment of water from heavy metals that is considered to be the most effective and promising. Its high quality is due to the special properties of membranes, such as:
1. High selectivity, or, in other words, the ability to separate substances of excellent properties. The partition is semi-permeable and only water passes through it, completely freed from impurities. The latter accumulate on the other side of the membranes.
2. The alloy from which the partitions are cast is distinguished by its special strength and resistance to chemical influences.
3. The membrane is equally effective and fully fulfills the required functions throughout the entire period of use. The advantage of the method is that metal impurities do not settle on the filter surface and do not clog its pores, but are removed from the membrane in various ways.
The type of cleaning is reverse osmosis. This method is different in that pressure is applied to the solution (contaminated water) that exceeds its own. The disadvantages of the method include high demands on the quality of the materials from which the treatment plants are created and the difficulty with removing the concentration layer.
It is advisable to clean a large volume of liquid with an insignificant concentration of heavy metals by the ion exchange method. As you know, its technology is based on the use of ion-exchange resins, on the surface of which metal ions are accumulated. Installations for these works allow the operation of resins for several years, excluding their caking.
The most thorough cleaning method is the most difficult in terms of technical execution cyclic treatment with ultrafiltration. True, this method is used only in electrolysis and galvanic plants, the wastewater of which contains a huge percentage of spent solutions and is saturated with helanites. For such work, special reactors are used.