The goal of the Project is to develop and demonstrate the technology for fabrication and practical use of polymeric materials for remediation in anthropogenic areas. In order to clean up contaminated soil by high toxic metals/elements (chrome, cobalt, arsenic), radionuclides the non-stoichimetric interpolyelectrolyte complexes (NIPEC) with an excess of either component, cationic or anionic polymer including natural one - humic acids are proposed. A polymer, taken in excess, is usually referred to as the lyophilizing, and taken in shortage as the blocking. NIPECs are formed in the presence of minimum salt concentration, in the order of 10-3 M, that practically has no effect on the water-salt balance of soil. Depending on chemical nature of polymers and linear charge densities in macromolecules, water-soluble NIPECs can be prepared with long sequences of interpolymer salt bridges (hydrophobic blocks) in which up to 50 mol% of the lyophilizing polymer units can be involved. Due to hydrophobic blocks and residual non-compensated charges, NIPECs are effectively bound to soil particles and cannot be washed away with rainfall, or artificial irrigation, or water from melted snow. NIPEC solutions with low salt concentrations are actually “one-solution” formulations without producing a negative effect on the water-salt balance of soil.
Additionally, NIPECs are able to bind effectively a majority of toxic heavy metals: chrome, cadmium, cobalt, copper, zinc and others, due to incorporation of metals inside hydrophobic NIPEC fragments generated by mutually neutralized cationic and anionic units. As a result, thermodynamically stable structures are formed with a central metal ion surrounded by functional groups of both polyelectrolytes. This allows the extraction of heavy metals even from extremely diluted solutions.
A separate problem to be examined in the Project is to apply commercially available biodegradable polyelectrolytes (carboxymethylcellulose, sodium alginate, humic acids, chitosan) for NIPEC formation. In such polycomplexes, both polymers or either of them can be biodegradable. These formulations ought to be used in combination with sowings of perennial herb seeds. This approach ensures formation of stable grass covering in a shortest period of time which prevents wind and water erosion and suppresses spread of heavy metals. After completing the protection function, the formulation is destructed, being affected by soil microorganisms, and transformed down to simple non-toxic substances that will improve the environment.
Thus, use of NIPEC will allow to solve two interrelated problems: extraction and concentration of heavy metals and radionuclides and prevention of their spread by means of wind and water erosion.
The research program consists of the following tasks:
1) To study polycation-to-polyanion complexation, composition and structure of resulting NIPECs;
2) To investigate complexation of NIPEC with heavy metal and radionuclides cations,
3) To assess binding of NIPEC to dispersed (soil) particles,
4) To study binding of NIPEC-metal ternary complexes to dispersed (soil) particles,
5) To estimate protective properties of polymeric formulations,
6) To analyze contaminated and remediated soils in terms of content and speciation of heavy and radioactive metals, humics and enzymatic activity of soil,
7) To scale-up of the NIPEC technology and pilot batch production, including solutions, concentrates, and powders,
8) To perform field testing of produced NIPEC formulations for stabilization of contaminated soils.
In the course of the Project, formulations will be prepared and tested in the lab and in the field, fabricated from commercially available polymers, anionic (polyacrylic acid, hydrolyzed polyacrylonitrile, carboxymethycellulose, lignosulfate, carboxylated lignin, alginic acid) and cationic (polydimethydiallylammonium chloride, caustamine, polyethyleneimine, chitosan). Anionic groups in polymers are represented by carboxylic (-COOH) and sulfo groups (–SO3H), cationic by different amino groups, from primary to quaternary. Molecular mass of polymers is varied from 2?103 до 105 кDa that approximately equal to 20-103 degree of polymerization. All the above mentioned polymers are soluble in water and water salt media at 1-10 wt% concentrations that are typical for polymer-based soil-stabilizing formulations. In some cases – for clarifying the details of interpolymer complexation, interaction of NIPEC with dispersed particles, polycation-polyanion-metal ternary complex formation, etc. – polymers will be used with chromophores (e.g. quaternized polyvinylpyridines) and/or fluorescent labels (e.g. labeled polyacrylic acid).
Accomplishment of the Project will allow the change from NIPEC theory to practice and a large-scale use of NIPEC stabilizers for remediation of contaminated territories. The innovation technique will be thus developed and carried to the industry. The novel techniques of production and application of NIPEC can be easily adjusted for other tasks related to remediation of injured biocenosis.
