焚烧飞灰中六价铬化合物碳热还原脱毒

Detoxification of hexavalent chromium compounds in incineration fly ash by carbothermal reduction

碳热还原是垃圾焚烧飞灰中六价铬化合物还原脱毒的有效手段,但碳热还原条件和飞灰的组分变化会影响铬的形态转化。使用竹炭(bamboo charcoal,BC)和粉末活性炭(powered active carbon,PAC)与Na_(2)CrO_(4)反应探索碳热还原中Cr(Ⅵ)形态转化的过程,并分析碳热反应中4种氧化物对Cr(Ⅵ)形态转化的影响。实验结果表明,1000℃以下Na_(2)CrO_(4)被还原为NaCrO_(2),高于1000℃则转化为Cr_(3)C_(2)。氧化物存在时,高于1000℃后Fe_(2)O_(3)与被BC还原的铬反应生成FeCr_(2)O_(4),在CaO含量高时转化为CaCr_(2)O_(4);若添加过量BC则仍以Cr_(3)C_(2)为主。在喷钙的飞灰中,CaO与被还原的Cr反应生成CaCr_(2)O_(4);若添加过量的BC,Cr(Ⅵ)则被还原为Cr_(3)C_(2)。

Carbothermal reduction is an effective means of reducing and detoxifying hexavalent chromium compounds in waste incineration fly ash,but carbothermal reduction conditions and changes in the composition of the fly ash can affect the speciation transformation of chromium.Bamboo charcoal(BC)and powered active carbon(PAC)were used to react with Na_(2)CrO_(4) to explore the process of carbothermal reduction on the morphological transformation of Cr(Ⅵ),and the effects of four oxides on the morphological transformation of Cr(Ⅵ)in the carbothermal reaction were analyzed.The experimental results showed that Na_(2)CrO_(4) was reduced to NaCrO_(2) below 1000℃and converted to Cr_(3)C_(2) above 1000℃.In the presence of oxides,when the temperature was higher than 1000℃,Fe_(2)O_(3) reacted with the chromium reduced by BC to form FeCr_(2)O_(4).When the CaO content was high,it was converted into CaCr_(2)O_(4),if an excessive amount of BC was added,it was still dominated by Cr_(3)C_(2).When trace amounts of BC were added to calcium-sprayed fly ash,the reduced chromium reacted with CaO to form CaCr_(2)O_(4);when excessive amounts of BC were added,Cr(Ⅵ)was reduced to form Cr_(3)C_(2).