Release And Removal Of Chromium During Municipal Solid Waste Incineration

As the rapid economic development and increase of urban population, Municipal SolidWaste（MSW）has become a big problem in many cities. Incineration has been one of the mostimportant ways for the treatment of MSW in China for its most reduction of waste volume，nearly complete destruction of organic compounds and energy recovery. Chromium releasedduring MSW incineration is toxic and carcinogenic, Cr(VI) emission should be kept as low aspossible as Cr(VI) is known to be more toxic than Cr(III). Experimental study in a drop tubefurnace and thermodynamic simulation by HSC software have been conducted to investigatethe speciation and release of chromium during MSW incineration,effects of temperature,residue time,O2, chlorine and moisture on release and removal of different forms of chromiumduring MSW incineration were studied.The results showed that most of chromium existed in the bottom ash, higher temperature,longer residue time, more oxegen and chlorine promoted the release of chromium andformation of Cr(VI),however, moisture had little impact on chromium release andspeciation.The removal rates of the four sorbents for total Cr followed the sequence of BC>PAC> CaO> zeolite> bentonite> Al2O3， while the removal rates of the four sorbents forCr(VI) follows the sequence of CaO> bentonite> zeolite> BC> PAC> Al2O3. CaOpromoted the Cr(III) oxidation to Cr(VI) by chemistry reaction. BC and PAC had highremoval rates of total Cr and Cr(VI),and C in PAC and BC was an effective reducing agent toreduce Cr(VI) to Cr(III). The change of temperature and chlorine had a huge impact onadsorption of CaO.The thermodynamic calculation showed that the major species of chromium wereCr2O3(s), CrO2(g) and CrO3(g), CrO2Cl2(g) and CrCl3(g) were generated when chlorinewas was added in. More oxygen promoted the formation of Cr(VI). CaCrO4and CaO Cr2O3were the major species of chromium when adding CaO.