Analysis of metals in the ZnS-concentrate entering the roaster and calcine reaching the dry electrostatic precipitator

• ZnO, Zn 2 SiO 4 , ZnFe 2 O 4 , and ZnS were formed during the roasting of ZnS-concentrate. • Calcine particles had rounded shapes with aerodynamic diameters <1 µm to >200 µm. • Hg-data showed a bimodal distribution the probability density function. Heavy metals present in respirable particulate matter can cause carcinogenic effects in human lungs and other human organs. In particular, workers near electrostatic precipitators (ESPs) are exposed to highly toxic inorganic substances that could affect their health due to prolonged exposure. This study aimed to analyze the metallic elements present in calcine from a dry ESP, and their possible harmful effects on health. The feed rate to the ZnS- concentrate roaster is 50 tons/h (moisture <10% w/w) at 950°C, where a complex mixture of metal oxides called calcine is formed. ZnO is the main oxide in this mixture. The gases produced in the roaster transport some of the calcine and pass through a heat recovery unit to produce water vapor. At 350°C, calcine enters the ESP and is removed at 60,000 volts. Calcine samples were analyzed by SEM and X-ray diffraction. Several chemical species such as ZnO, Zn 2 SiO 4 , ZnFe 2 O 4 and calcine particles of different shapes with sizes less than 1 µm and greater than 200 µm were identified. Agglomerates of calcine particles are mainly included in the D10 range. The Hg-, Pb-, Fe-, Zn-, Cu- and S-concentrations in the concentrated mineral do not have a normal distribution, indicated by the K-S test. Respirable calcine particles containing heavy metals may represent a hazard to human health. It is imperative to do research to identify novel roaster operating conditions that may lead to the formation of non-respirable agglomerated calcine particles.