Physical and chemical characteristics of slag produced during Pb refining and the environmental risk associated with the storage of slag

Abstract

AbstractMetallurgical waste originating from the Zn and Pb refining process presents varying chemical composition and physical properties and contains varying quantities of pollutants. In the study, both fresh and weathered samples of production slag from the final Pb refining process were used to determine its physical parameters and chemical composition as well as to perform an environmental risk assessment (RAC, mRAC) related to its storage. This paper focuses on determining parameters such as natural humidity (1.8%) and bulk density (1267 kg/m3) of the slag. Also, its toxicity was analysed using bio-tests, its pH was measured (11.92) and the content of sulphates (3.5 wt%), chlorides (0.3 wt%) and selected heavy metals (Cd, Cu, Fe, Mn, Zn, Pb) was determined. The Individual Contamination Factor was determined, yielding the following order of the hazard level: Pb > Cu > Zn > Cd > Fe > Mn. Based on the mobility of metals determined using the Mobility Factor, it was concluded that the hazard level followed the sequence Cd > Pb > Zn > Mn > Fe > Cu. The obtained water leaching results were compared to the values found in the legal regulations in force. Based on this comparison, it was established that the slag studied constitutes toxic waste containing considerable quantities of sulphides and chlorides. The material is also a considerable source of readily leaching elements (Cd, Zn and Pb), and thus any product created using the slag may become hazardous to the environment. Also, the waste studied must not be used in the form in which it is currently stored due to the leaching of particularly toxic elements (Cd and Pb) in water solutions with increasing acidity.