Comportamento dos elementos-traço (arsênio, cádmio, chumbo, cloro, cobre, mercúrio e níquel) no processo de sinterização de minério de ferro

Abstract

The issues related to the environmental impacts caused by the industry have become more relevant every day, leading to greater restrictions in environmental legislation. The steel industry, notably known for its high generation of air pollutants, pays special attention to the control of this type of emission. Trace elements are among the pollutants that have received attention in modern legislation, due to the relevant impact caused by such pollutants on the environment and human health. In this scenario, this thesis evaluated the behavior of the trace elements in a pilot iron ore sintering process through mass balance and gas analysis, carried out in a test at a pilot sintering plant, basing and contextualizing the results with the knowledge available in literature. Three distinct behaviors were observed between the trace elements. Some elements remain mostly in the solid state during the process, such as copper and nickel. Other trace elements partially volatilize and recondense along the exhaust gas system, such as cadmium, lead and arsenic. Mercury and chlorine volatilize and are emitted in gaseous form. In the present study, it was identified that the main factors that affect the behavior of the trace elements are the physical and chemical characteristics of the inputs, the process conditions and the emission control mechanisms adopted. Although it is not always possible, the choice of raw materials with a low concentration of trace elements has a direct impact on emissions. It has also been shown that raw materials with less chlorine content have a positive impact on reducing emissions of some trace elements, such as copper, nickel and arsenic. From the process, in general, a lower burning temperature, a less oxidizing atmosphere and less presence of chlorides and sulfides reduce volatilization and, consequently, the emission of trace elements. Finally, the appropriate choice of air pollution control devices has a strong impact on the emission of these elements. Through an extensive bibliographic review it was identified that although specific technologies for the control of trace elements are not usual, most elements can be retained in equipment with high efficiency in controlling the emissions of fine particulate materials. The elements most likely to be emitted in gaseous form are more difficult to be retained with conventional technologies, requiring the use of alternative techniques, such as the use of adsorbents to capture these elements.