Development of Novel Sol-Gel Based Methods for the Recycling of Heavy Metal Ions and Radioactive Waste

A variety of methods have been suggested to achieve the goal of reducing the environmental concentrations of toxic pollutants that are already imposing a crippling burden on human health. In recent years, increased attention has been devoted to the study of sol-gel matrix properties and to the entrapment of active species, mainly large species. Here we propose the sol-gel process as the foundation of an easy and economical cheap treatment method, that can effectively combat the problem of radioactive and heavy metal wastes. The morphological and the surface chemical properties of the sol-gel can be controlled by changing the precursors used to prepare the matrix. In this research, different precursors (Tetramethylorthosilicate (TMOS), or Tetraethylorthosilicate (TEOS), were mixed with substituents that will be used as ligands that are specific to certain metal cations either for recycling purposes or for the durable, indefinite entrapment of the metals. Especially, when they are modified by covalently bound selective ligands, sol-gel matrices can function as ion exchange columns. Such columns can be used to separate and/or concentrate heavy metal cations and radioactive elements. After the entrapment of the radioactive ions, the sol-gel matrix can be melted and solidified in either a glass or a ceramic phase, in which metal cations (nuclear waste) and heavy metals that need long term storage can be immobilized. According to our results so far, the matrices that were prepared from the precursor TMOS with Nitrilotri(methylphosphonic acid) (ATMP) as a ligand, at pH=2 or 7, showed a good selectivity for Ce ions, and with the ligand N’-(3-Trimethoxysilylpropyl)diethylenetriamine (N1) at pH=13, a good selectivity for Cr ions. A good selectivity for Li ions was achieved using the precursor TEOS with ligands (ATMP) and Diethylenetriaminepentakis(methylphosphonic acid) (DTPMPA) at pH=13.