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

采用氯化物挥发法对城市垃圾焚烧飞灰中富集的重金属进行了回收和分离。用NH_4Cl与重金属形成氯化物络合物，提高了重金属的挥发性。本实验选取了电除尘器有无石灰喷吹酸性气体两种情况下的飞灰，分别在间歇式和连续式电炉中进行了N_2气氛和空气气氛下飞灰中重金属挥发的试验。重金属在本实验中的行为可表征如下：1）在间歇式电炉中，900 ℃时两种飞灰中Cd、Pb和Zn的残留率分别为5%、10%和20%; 2）在空气中比在N_23中更容易挥发Cu; 3）在连续式电渗析中，重金属挥发量不大，但残留在飞灰中的重金属大部分溶于水; 4）蒸发部分用Na_2S处理，使重金属沉淀。沉淀物中Pb含量高达28.3%。5）热化学数据证实了本实验中氯化物挥发的有效性。

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.