还原焙烧电镀污泥中的金属形态和浸出性

Speciation and leachability of metals in reduction-roasted electroplating sludge

分别以煤粉和稻杆为还原剂对电镀污泥进行还原焙烧,并通过酸浸回收焙烧渣中的金属。研究了焙烧温度、焙烧时间和还原剂投加量对目标金属Cu浸出率的影响以及主要杂质金属的浸出性,并采用BCR逐级提取法分析了焙烧前后污泥中的金属形态分布。结果表明,当在电镀污泥中投加30%的煤粉在600℃下焙烧1 h后Cu的浸出率达到97.78%,当投加50%的稻杆时浸出率为89.47%,而氧化焙烧后浸出率仅为37.71%;并且还原焙烧渣中多数杂质金属的浸出率较低,从而可以实现Cu与杂质金属的初步分离。氧化焙烧容易导致金属从易浸出的非残渣态向难浸出的残渣态转化,而还原焙烧则能抑制这种转化过程,金属形态是决定其浸出性的重要因素。

Electroplating sludge was reduction-roasted using coal powder and straw as reductants, and then metals were leached from roasted sludge by sulfuric acid. The effects of roasting temperature, roasting time and reductant amount added on the leaching rate of target metal copper were analyzed, and moreover, the leachability of major impurity metals was evaluated. BCR sequential extraction procedure was adopted to determine the speci- ation of metals in the sludge before and after roasting. Results showed that leaching rate of copper reached 97.78% when sludge was roasted with 30% coal powder at 600℃ for 1 h, and being as high as 89.47% when roasted with 50% straw correspondently, but only 37.71% of copper was recovered from oxidation-roasted sludge. Copper could be preliminarily separated from impurity metals by reduction-roasting because of the low leachability of most impurity metals. The speciation of metals changed from easily leached non-residual form to difficultly leached residual form by oxidation-roasting, while reduction-roasting could restrain the transformation process. The speeiation of metals was the key factor that impacted the leachability of metals.