ABSTRACT
Two municipal solid waste incineration fly ashes were selected for washing by deionized water and Na2CO3 solution for comparison. Results showed that the benefits of washing were two folds: (1) Washing was able to reduce the contents of Cl- and SO42- while increased the contents of CaO, SiO2, Al2O3 etc.; (2) Washing by Na2CO3 solution showed increased stability of heavy metals (Cr, Ni, Cd, Cu, Zn and Pb) and fly ash was safe for later reuse. Release of Cl- was high at more than 90% regardless of washing solution. SO42- and Ca2+ removal was highly dependent on the dissolution and precipitation equilibriums. Na2CO3 washing promoted the formation of CaCO3. Thus SO42- was washed off instead of precipitating as CaSO4 and retained in fly ash solid. SO42- removal was raised to more than 80% by Na2CO3 washing as compared with about 30% by deionized water. At the same time, Ca removal by Na2CO3 dropped to 1-2%. In addition, the basicity of fly ash was important as high basicity helped SO42- removal. Overall, washing by Na2CO3 appears to be a promising option for fly ash treatment.
Subject(s)
Metals, Heavy , Refuse Disposal , Cadmium , Carbon , Carbonates , Coal Ash , Incineration , Lead , Metals, Heavy/analysis , Particulate Matter , Refuse Disposal/methods , Silicon Dioxide , Solid Waste/analysis , WaterABSTRACT
Waste printed circuit boards (WPCBs) were co-pyrolyzed with iron oxides and iron salts. Solid, liquid, and gaseous products were collected and characterized. Co-pyrolysis with FeCl2, FeCl3, or FeSO4 was able to increase the yield of liquid product which was rich in phenol and its homologues. Also, the addition of co-pyrolysis reagents reduced the release of brominated organics to liquid as Br was either fixed as FeBr3 in solids or released as HBr. In particular, FeCl2 showed the best ability to reduce the release of Br-containing organics to liquid compared with FeCl3 and FeSO4. Solid residuals were rich in iron oxides, glass fibers, and charred organics with surface areas of 20.6-26.5 m2/g. CO2 together with a small amount of CH4 and H2 were detected in the gaseous products. Overall, co-pyrolysis could improve the quantity and quality of liquid oil which could be reused as chemical or energy sources. Pyrolysis of waste printed circuit board was promising as a method for recycling.
