Chemical Fractionation and Environmental Risk Assessment of Lead in Lead-Zinc Mine Tailings

Investigating the leaching amount of trace elements from environmental pollutants such as tailings is very crucial for determining the risk of these materials and sustaining environmental quality. This research was carried out to determine the concentration, risk level and leaching behavior of lead from Zn-Pb mine tailing of Zanjan. For this purpose, two composite samples (0-20 cm) were taken from both types of tailings from the Zn-Pb mine and the pH, time, particle size and liquid to solid ratio was determined using a batch leaching test. Determination of elemental composition and mineralogical characterization of mine tailings were performed using x-ray fluorescence (XRF) and x-ray diffraction (XRD) analytical techniques respectively. The morphology of tailing particles was determined by scanning electron microscope (SEM). For evaluation of tailings risk level, leaching protocols such as Field Leaching Test (FLT), Synthetic Precipitation Leaching Procedure (SPLP), Toxicity Characteristic Leaching Procedure (TCLP) and Leaching Extraction Procedure (LEP) were used. Also, for identification of lead distribution among different fractions of tailings, the sequential extraction method was applied. The concentration of lead in all extracts was measured by ICP-OES. The results showed that the time, particle size, pH and the liquid to solid ratio are more effective on the concentration of lead leaching from tailings and the maximum concentration of lead discharged from the tailings occurred in a different range of particle size. The maximum amounts of lead in the studied tailings were respectively observed in residual, carbonaceous, exchangeable, organic, iron and manganese oxides and solution parts. The results of the leaching protocols also made it clear that both types of waste have great environmental effects and are considered to be hazardous waste residues. Therefore, special measures should be taken to safely store these substances in the environment and prevent lead leaching.