Evaluation of cadmium and other metal losses from various municipal wastes during incineration disposal

The Japanese intake much more Cd through food than people in other countries, this may be partly caused by the activity of municipal waste incineration disposal. The present study was carried out to examine the behavior of Cd and to identify the other lost metals during municipal waste incineration. Thirty-eight waste samples, including food scraps (FS), animal wastes (AW), horticulture wastes (HW) and sewage sludges (SS) were collected from various places in Japan. Treatment temperatures of 500, 850, and 1000°C were conducted to these samples in laboratory, and thirty-nine kinds of metals were examined. The results showed that average Cd losses were 69% (2.4 mg kg^-1) and 74% (2.6 mg kg^-1) at 850 and 1000°C, respectively. Furthermore, the losses of 20 other metals were also found, i.e. Sn lost at 500°C, K, Mg, Na, Bi, Cr, Ge, Li, Pb, Sn, Tl, Zn lost at 850°C, and nine more metals, Al, Be, Cs, Nb, Sb, Sr, Th, Y, Zr lost at 1000°C. The lost metals were considered to be transferred into the combustion flue gas, mainly in the forms of metallic chloride compounds, e.g. CdCl₂, SnCl₄, SnCl₂, ZnCl₂, PbCl₂, etc. On the other hand, no significant losses for Ca, Fe, Ag, Ba, Co, Cu, Ga, Hf, Mn, Mo, Ni, Rb, Sc, Ta, Ti, U, V, W were found at 0.05 probability level. Total metal losses could be calculated at 9.9 and 20 g kg^-1, in which major metal (Al, K, Mg, Na) losses were 9.5, 19 g kg^-1 and minor and trace metal losses were 0.4, 0.6 g kg^-1 at 850 and 1000°C, respectively. Among the four types of waste materials, Cd losses were 0.8-3.7 mg kg^-1, occupied about 60-80% at 850°C, and 0.9-3.9 mg kg^-1, occupied about 65-85% at 1000°C. The total major metal losses from the four types of waste materials could be calculated at 6.5-15 g kg^-1 at 850°C, and 11-31 g kg^-1 at 1000°C, minor and trace metal losses were 0.03-1.3 g kg^-1 at 850°C, and 0.3-1.5 g kg^-1 at 1000°C, respectively.