Remove heavy metals. The presence of heavy metal ions such as copper, lead, iron, nickel, zinc in the water is a serious problem for the environment due to their high toxicity, and also due to the inability of microorganisms to process them. The main water pollutants with such metals are ferrous and non-ferrous metallurgy and machine-building facilities.
As a result of outdated technologies, a large amount of industrial pollutants including toxic heavy metals (lead, cadmium, manganese, cobalt, nickel, copper, iron, zinc and others) are discharged into waterways. The total amount of pollution entering waterways and over the surface flow in urban areas is about 15-20%. During the 1990s, the concentration of copper, zinc and lead in waterways increased by 1.5-3 times compared with the 1980s. Even today, the ions of heavy metals pollute water from bottom sediment. Therefore, the problem of efficient extraction of heavy metals requires effective methods for wastewater treatment.
There are many methods of sewage treatment, but each has its own disadvantages. The disadvantage of the extraction method is its complex technological process. The majority of extractants dissolve in the treated water to a varying degree. The disadvantages of the reagent methods are the significant costs of reagents and contamination of wastewater with them, making the water unsuitable to return into the cycle due to its high salinity. The disadvantage of the settling method is a large number of Na+, K+ and Ca2+ ions. The disadvantage of the ion exchange method of wastewater treatment is a low exchange capacity of ion exchangers. For coagulation method it is the generation of non-recyclable waste and low quality of treatment.
Adsorption is widely used for the final deep cleaning of wastewater to remove dissolved organic substances as a post-treatment after biological treatment of wastewater, and also for local treatment if the concentration of organic substances in wastewater is negligible and they do not decompose biologically and are not highly toxic.
The advantages of adsorbers are:
- Natural sorbents are available in many countries;
- They are easily obtained;
- Adsorption technologies provide a high degree of purification;
- The used adsorbent is utilized in other productions;
- They do not require regeneration;
- They can be regenerated.
The efficiency of adsorption treatment is 80-95%, depending on the chemical nature of the adsorbents, their chemical structure and adsorption surface, and their adsorbing ability in water solution. The adsorbents used in treatment are activated charcoal, synthetic adsorbents and some waste products (ash, sludge, etc.) Non-carbon sorbents of natural and synthetic origin such as clay rocks, zeolites and other materials are also commonly used. The wider use of such sorbents is due to their high exchange capacity, selectivity, ion exchange properties of some of them, relatively low cost and availability.
Each adsorbent has its individual characteristics. For example, glauconite ensures prolonged action and low desorption rate (2-8%), with no need for recycling.