The heating effects of discharge triggered at the appearance of metals are important under microwave irradiation but special studies have rarely been carried out. In our experiments, the heat generation was successfully isolated by embedding metal in quartz sand and measured through an indirect calorimetric method. All the experiments and analyses indicate that the discharge triggered by metals under microwave irradiation has remarkable heating effects. The microwave power, irradiation time, metal amount, and atmosphere are all important factors to influence the discharge intensity and then the heating effects. The understanding of the effects of metal discharge will help us to further research on the treatment of solid waste, such as the microwave pyrolysis of electrical waste. It may also be a good idea to use the discharge phenomena and their heating effects by embedding some metals to the microwave field in some certain applications. (C) 2012 American Institute of Chemical Engineers AIChE J, 2012