Separation and Recovery of Heavy Metals in Incinerator Fly Ash by Chloride Volatilization

利用氯化物挥发法对城市生活垃圾焚烧炉飞灰中的高浓度重金属进行回收和分离。用NH_4Cl形成氯络合物，提高了重金属的挥发性。本实验以两种不同类型的粉煤灰为样品，分别从喷石灰和不喷石灰的静电除尘器中取样，用间歇式电炉和连续式电炉在氮气或空气中测试了粉煤灰中重金属的挥发情况。实验中重金属的行为特征如下：1)根据两种粉煤灰的金属挥发结果，在900℃的温度下，采用批式电炉处理后的粉煤灰中，Cd、Pb、Zn的金属残留量分别为5%、10%、20%。2) Cu在空气中比在N_23中更容易挥发。在连续式炉中，重金属挥发较少，但大部分残留在灰分中的重金属溶于水。4)汽化部分经Na_2S处理析出重金属，析出物Pb浓度高达28.3%。5)热化学数据证实了氯离子挥发的有效性。

The concentrated heavy metals in the fly ash from municipal solid wasete incinerators were recovered and separated from that by chloride volatilization. The volatility of heavy metals was improved by forming chloride complex using NH_4Cl. Two types of fly ash in this experiment were sampled from electrostatic precipitator with or without lime injection for acid gas, The volatilization of heavy metals in fly ash was tested in N_2 or air atmosphere using both batch type and continuous type electric furnaces. The behavior of heavy metals in this experiment can be characterized as follows :1) According to the results of metal volatilization for both types of fly ash, the remaining ratios of metals in treated fly ash were 5% for Cd, 10% for Pb, and 20% for Zn at the temperature of 900ﾟC using a batch type electric furmace.2) The volatilization of Cu was facilitated more easily in air than in N_23) Heavy metal volatilization was not so much in a contimuous type furnance, but most of heavy metals remaining in ash became soluble in water.4) The vaporized part was treated by Na_2S to precipitate heavy metals, and the precipitate contained high concentration of Pb at 28.3%5) The validity of chloride volatilization in this experiments was confirmed by thermochemical data.