Technology

shema111

Innovative technological solution is oriented in solving the problem of heavily polluted urban areas with potentially toxic metals.

Residents of contaminated areas are exposed to toxic metals primarily through direct entry of contaminated particles into digestive system, including by ingestion of food grown in contaminated soil and inhalation of contaminated dust particles. Since the soil is today often considered as the primary source of pollutants in the environment, the remediation of soil is an urgent measure to achieve sustainable impact of rehabilitation. Selection of remediation technology depends on the characteristics of pollutants, type of soil and land use. Before the selection of the remediation technology, it is necessary to carry out feasibility tests of individual technology to achieve the best ratio of efficiency, economic and ecological acceptability.

In the field of remediation of toxic metals, especially with lead contaminated soil, the following technologies are known and used:

  • Solidification and stabilization of the metals is a method in which materials such as phosphate, cement, lime or different sulphides are admixed and/or injected into the soil. Metals are not removed from the soil, however, their bio – availability is reduced.
  • Phytoextraction of pollutants from the soil exploits the ability of plants to accumulate metals in the aboveground plant parts. However, species with sufficient biomass and accumulation of sufficient quantities of lead are not known yet.
  • Soil washing, which removes metals from the soil by mechanical operations on the principle of separation. Here, the fractions of the soil, in which the metals are mainly bound, are removed. By this, organic matter and fine silt particles are mainly removed. In the case of soil from Meža valley, over 20 % of the soil particles would be removed by this method due to high content of organic matter in the soil. This would result in the loss of the soil function as a plant substrate.
  • Soil washing with solutions such as salts, acids and chelating agents is the only technology for the removal of toxic metals, especially lead from the soil. The most effective approach is to use ligands that form water-soluble metal complexes that can be transferred from the solids into the liquid form. This usually results in a huge quantity of contaminated process solution. The most used ligand is ethylenediamine tetraacetate (EDTA).

P3060267

The use of EDTA is widely used in the following areas:

  • As a medicine – at poisoning with lead, radioactive materials, in the treatment of heart and blood problems (irregular heartbeat as a result of exposure to chemicals, high blood pressure, high cholesterol, problems with blood circulation in the body, ..), cancer, diabetes, multiple sclerosis.
  • In the diet – for the preservation of food, to embellish the color, the texture and taste of food.
  • In agriculture – to improve the availability of nutrients (iron, magnesium, zinc, copper).

The feasibility tests have shown that soil washing with EDTA is more efficient than washing with acids in case of the carbonate soil with a high content of organic matter, which is an important Higher Meža Valley soil characteristic. Carbonate soils resist acidification and thereby increase the amount of acid in the washing solution.

The main technological problem of existing technologies of soil washing with EDTA is the removal of metal complexes and EDTA resulting from the process solution. Technologies for recycling of waste washing solutions exist, but they are costly and also produce a large quantity of toxic waste and are therefore not commercially available and implemented.

We have developed an innovative technology for soil washing, which enables recycling of EDTA and process water in a cost-effective way, in a closed loop process without any harmful emissions into the environment and producing only small quantities of waste. In the innovative procedure all the process water is recycled. Treatment of process water include chemical and electrochemical processes such as basic processes (metals precipitation and removal by filtration), acid process (EDTA recycling, EDTA precipitation and removal by filtration), electrolysis (decomposition of the residual EDTA, loading of metals on electrode). Developed innovative treatment method for process water during the soil washing brings, in comparison with the aforementioned known solutions, significantly lower (90 %) water consumption, significantly lower consumption of EDTA (> 70%), lower energy consumption and safe disposal of the toxic product.

The technology is patent-protected. Developed soil washing technology is, in addition to exceptional ecological benefits, economically interesting compared to existing technologies. We claim that the proposed technology is the only technology that allows the removal of toxic lead from heavily contaminated soil of carbonate origin that is rich in organic matter and retains its plant substrate function.

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