Impregnation of Nano Zero-Valent Iron in Biomaterials for Remediation of Wastewater

Nano zero-valent iron (nZVI) is widely used to remediate groundwater and wastewater from heavy metals and stable organic pollutants (Permeable Reactive Barriers). This is caused by the fact that Fe0 reduces several halogenous hydrocarbons, chlorine-containing pesticides, organic dyes, nitrozo compounds, explosives and others. The restoring ability is used for reduction of CrO4-2, Cr2O7-2, ClO4-, NO3- ions and elimination of Hg+2, Ni+2,Cd+2, Pb+2 as well as of a number of radionuclides from water. nZVIs had found wide application in the USA but in Europe this method appeared later. The cost of these methods for remediation of water depends on many factors (type of pollution, cost of reagents, the purpose and degree of remediation, remediation methods and other). That is why revealing of new reductants and methods for reduction of Fe+2 and Fe+3 up to Fe0 is an actual problem. The objective of the present research is impregnation of nZVL in bioorganic materials and obtaining of hybrid organic-inorganic reactive barriers. In this paper, we present preliminary results on the development of methods for impregnating of the nZVI in biopolymers. On the basis of these materials, it is possible to obtain cheap biosorbents with versatile properties able to simultaneously remove the heavy metals (including radio nuclides) and stable organic pollutants. Biopolymers contain many complex-forming functional groups, including hydroxyl, carboxyl, carbonyl, ether and other groups. These groups have the ability to stabilize the nanosize particles and prevent formation of large-size particles. Biosorbents have a high sorption capacity towards ions of heavy metals, which are higher than a similar capacity of inorganic sorbents. The matrix (biomaterial) plays a role of a sorbent of heavy metals and on the other hand the particles of impregnated iron are reactive barriers for toxic metal ions and stable organic pollutants. A method for activation of biomaterials (wood processing wastes, sawdust, shavings, chips, cereal crop residues) has been developed, which includes their hydrothermal treatment at 2000C at a pressure of 2,0-2,5 MPa(for 1 h) and then rapid reduction of pressure that leads to decomposition of the wood structure and increase of the surface. Immobilization of nZVI in biopolymers and in wood of some plants has been carried out by chemical method (by sodium borohydride) and by plant extracts. It was determined that the wood of some local plants is a reduction agent for iron compounds. The possibility of obtaining nZVI in wood present in its reducing agents gives us hope that it is possible to create a new type complex biosorbent by methods of "green chemistry" that excludes stages extraction of reductants from biomaterials. It is determined that with similar methods, it is possible to impregnate (apply) nZVI in porous inorganic compounds. Microstructure of sorbents has been studied by optical and electronic scanning microscopes (NIKON ECLIPSE LV 150, NMM-800TRF, NANOLAB-7). Sorbents have been analyzed by XRD method on the diffractometer DRON-3M (Cu-KI±, Ni filter, 2O/min).