CaCl_2高温热处理垃圾焚烧飞灰中重金属的挥发特性

Effect of CaCl_2 addition on heat treatment of heavy metals in municipal solid waste incineration fly ash

以深圳市某垃圾焚烧厂飞灰为原料,采用高温管式电阻炉,研究了在0.6 L/min N2气氛下,CaCl2在不同添加量、处理温度及处理时间下对飞灰中重金属Pb、Cd、Zn和Cu挥发特性的影响,并对收集到的二次飞灰进行成分及物相分析。结果显示,X射线衍射仪和EDS分析表明,二次飞灰主要是由NaCl、KCl和部分SiCl4组成,Zn主要以K2ZnCl4形式挥发,而Pb则主要以氧化物PbO和Pb3SiO5的形式挥发。最终得到CaCl2热处理飞灰的最佳二次气化条件:以0.6 L/min N2为载气,添加14 wt%的CaCl2,在1 100℃高温下处理2.5 h。经CaCl2热处理后的剩余飞灰,其浸出毒性达到了《生活垃圾填埋场污染控制标准》要求。

The agent CaC12 was used to enhance the evaporation of heavy metals including Pb, Cd, Zn and Cu from fly ash （collected in a municipal solid waste incineration plant located at Shenzhen） during the heating process by virture of an electric-heated tube furnace, and the secondary fly ash samples were collected after the cooling of evaporated gas. Experiments were carried out under the condition of N2 as carrier gas. The effects of such factors as percentage of CaC12 addition, heating temperature and heating time on heavy meals evaporation were examined in detail. The powder samples including fly ash and secondary fly ash were subjected to analyses by virtue of scanning electron microscopy-energy dispersive spectroscopy and X-ray powder diffraction. Results showed that the secondary fly ash was mainly composed of sodium and potassium chlorides （NaC1 and KC1） and a very small amount of silicon chloride （SiCI4） . During heating process, Zn mainly vaporized via formation of K2ZnC14, and Pb mainly via formation of PbO and Pb3SiO5. The optimal parameters for evaporation were ob- tained as follows： 14 wt% of CaC12 was added in the fly ash and the heating process was conducted at 1 10022 for 2.5 hours under the condition of N2 as carrier gas （0.6 L/min）. The leaching concentrations of heavy metals in the residual fly ash after evaporation were lower than their regulatory limits in Standard for Pollution Control on the Landfill Site for Municipal Solid Waste （GB 16889-2008）.