In order to convert MSWI fly ash into useful materials, the toxic heavy metals in the ash has to be removed or stabilized. The current technologies such as electrochemical, sintering and vitrification have many limitations, i.e. high cost, high-energy consumption and the generation of more waste. Our technology is featuring a practical, scalable, low energy-consumption and economically viable solution to process the MSWI fly ash in a way that binds and immobilizes toxic heavy metals that are present in the ash. The process is based on the use of novel silica nanoparticles which have high surface areas and medium-sized pores. The process can be scaled up and integrated with the incineration site to minimize production costs.
The process utilizes a continuous stirred-tank reactor (CSTR) that is able to treat about 10 kg/day of municipal solid waste incineration (MSWI) fly ash. The CSTR setup is scalable, has a small footprint and is integrated with water recycling process in the reactor to allow water reclamation for subsequent stabilization reactions. In general, the CSTR system consists of four major systems: (i) feed preparation, (ii) a reactor made of borosilicate glass with temperature and pH control systems, (iii) a salt recovery system which consists of evaporator-crystallizer, condenser and water recycling system, and (iv) two vacuum filtration systems for collection of stabilized incineration fly ash and salts, respectively. The process utilizes specialized silica nanoparticles, and is expected to increase the entrapment efficiency of heavy metals by 20-30% as compared to competing processes which reduces the amount of silica needed. The treated fly ash is expected to comply with European Standards, EN12457-2 and NEN7375. The commercial viability of the system has been demonstrated by incorporating the treated fly ash into polymer-matrix composite products.
This technology is able to integrate with waste-to-energy plants to utilize the MSWI fly ash generated directly for reuse. Companies producing composite materials would also be able to utilize this renewable material for their production for high quality composites. These composites have a wide application in aerospace, automobile, marine, wind power, infrastructure and sport equipment. Thus, this technology will not only reduce disposal cost, but instead generate revenue from waste.