Waste Incineration and Heavy Metal Emission—Laboratory Tests

Abstract

The main sources of environmental pollution with heavy (ecotoxic) metals include industry, including utility and municipal power engineering, but also waste incineration plants. Fuel shortages and their constantly growing prices raise concerns that energy will be commonly obtained from waste outside of installations intended for this purpose (i.e., outside waste incineration plants). The greatest concern stems from the risk of burning waste in low-power boilers—domestic boilers. Waste incineration plants and utility power plants are equipped with flue gas cleaning installations (FGD), but low-power boilers are not. The exhaust gases are directly introduced into the atmosphere, which results in the introduction into the air of, inter alia, toxic heavy metals. Therefore, it is necessary to conduct activities aimed at retaining ecotoxic metals in the solid–slag residue. The paper presents the results of laboratory tests of the emission capacity of Cd, Cu, Zn bound in various chemical forms—nitrates (V), chlorides and sulphates (VI). The tests were carried out at 1073 K, 1173 K and 1273 K. It was found that the emissivity of metals increased with increasing temperature. This is innovative as there are no reports of experiments with pure forms of metal salts. The advantage of this type of research is the lack of influence from other factors, apart from temperature, on metal emissions. To check the possibility of reducing metal emissions, additives (bauxite, dolomite, V2O5) immobilized in a solid residue were tested. The mechanism of action of each of the additives to limit the mobility of metals was different. The use of V2O5 for this purpose is new. The additives kept the metals solid in the residue, but their effect was different for each of the metals. The effectiveness of the tested additives was checked in the same temperature conditions, burning waste such as: rubber, sewage sludge and SRF fuel from waste. The effect of the additives depended on the type of waste, type of metal and the furnace temperature. If the additive effectively retained metals, then their amounts in the ashes were higher by several to several dozen percent in relation to the amount in the ashes remaining after waste incineration without additives. The results of the experiment with waste are open to research on the influence of other factors (except temperature) on the emissivity of Cd, Cu, Zn and the possibility of its reduction. The next step will be to verify the effects of laboratory tests in real conditions.