Valorization of Municipal Solid Waste Incinerated Bottom Ash via low CO2 Cement: Extent of Heavy Metal Encapsulation

Abstract

In 2015 about 33.5 million tons of Municipal Solid Waste in the U.S. was incinerated in a waste to energy facility. After incineration, the resulting ash is categorized into fly ash or bottom ash. Bottom ash accounts for 10 -15% by volume of the original waste and is rich in calcium and silicon oxides which make it a viable candidate for alkali-activation. It can contain elevated concentrations of heavy metals such as arsenic, lead, mercury and zinc depending on the waste being burned and is landfilled in the US.

In order to keep heavy metals from being leached into the surrounding environment from landfills and to reduce the amount of waste coming from an incineration plant, the research, under the direction of Professor Claire White, investigated the possible valorization of the bottom ash resulting from Municipal Waste incineration facilities into an alkali-activated and subsequently carbonated cement. Four cement pastes were made: two containing a 30% wt. replacement of ordinary portland cement class I with Municipal Solid Waste incinerated bottom ash, and two cement pastes that used municipal solid waste incinerated bottom ash as the sole precursor to alkali-activation with a sodium silicate/sodium hydroxide activator solution. One of each of the two cement types was subsequently carbonated for 4 days at relative humidity of 67%, a temperature 25C and a 25% CO2 concentration. The samples were leached in distilled water for 8 weeks, with leachate removed weekly for analysis via ICP-MS. It was found that alkali-activated MSWI BA cement followed by carbonation shows stable leaching behavior and can reduce leaching of Cr, Ba, and Pb enough to pass regulatory limits on hazardous waste.