Chemically designed inorganic polymer filters for aqueous mercury separation

The disposal of mercury [Hg] in dental waste water is recognized as a serious pollution control problem. Although technologies exist for effectively removing aqueous Hg ions from dental emissions, they are not commonly used because they are expensive, they can leach Hg back into the environment, they usually require the implementation of multiple separation techniques, and they have no potential for metal recovery. As the dental profession is among the leading environmental contributors of this cumulative protoplasmic poison (~30 ktons/yr), it is essential that improved separation technologies be developed. As a novel solution, sol-gel processing technologies were used to develop chemically designed, inorganic polymer filters for the economic separation and recovery of aqueous mercury, N-[3-(Trimethoxysilyl) propyl] ethylenediamine [TRMSP-EDA, (CH₃O)₃Si(CH₂ )₃NH(CH₂)₂NH₂] was polymerized via acid catalyzed (HF) hydrolysis and polycondensation reactions with distilled water and ethanol solvent (C₂H₅ OH). The resultant silicone polymers covalently bond high concentrations of bidentate ethylenediamine (EDA) ligands which can chelate Hg into stable metal complexes at the polymer surface. To maximize filter efficiency and processing economy, the reactant concentrations and polymerization conditions were optimized to simultaneously maximize polymer yield and surface area. High surface area powders (20.11±0.48 m²/g) were obtained in theoretical yields (58.43%, 20°C) using respective molar ratios of 1.0 TRMSP-EDA: 3.0 H₂O: 2.0 C₂H₅OH: 0.05 HF. According to infrared spectroscopy, broad Si-O Si stretching frequencies of 1122 and 1038 cm^-1 confirm the formation of an extended silicone polymer network, whereas primary and secondary amine stretching frequencies of 3410 and 3337 cm^-1 confirm that the chelating EDA functional group is intact and unmodified. To evaluate the Hg filtration efficiency of these reactive polymer powders, cold vapor atomic absorption spectroscopy was employed by passing 1000 ppb solutions (8.5 ml) through reactive polymer powder (0.5 g) at various pH values (2-5). Single pass filtration effectively reduced the aqueous mercury concentration to undetectable levels, 13 ppb; corresponding to 99.97% filtration efficiency. FTIR analysis confirms the formation of surface Hg chelation compounds through N-H peak energy shifts and broadening, In conclusion, EDA functionalized silicone polymers can be used to effectively separate greater than 2000 ppb Hg