Investigation on pollution potential and stabilization of extraction residue generated in hydrometallurgical zinc production plant

In the hydromettalurgical zinc production, as the zinc leached by sulphuric acid, hazardous leaching residue that contains heavy metals and insoluble impurities forms. It is necessary to make it harmless environmentially by an appropriate stabilization/solidification (S/S) method before it is discharged. In this study, the pollutants and pollution potential of the zinc extraction residue (ZER) were determined, and its S/S by Portland cement (PC), lime, phosphate rock (FK) and fly ash (FA) were investigated. Primarily, the mineralogical and chemical compositions of ZER were determined by XRD and XRF analyses. Main constituents of the ÇEA were found to be 19.02% Pb, 7.98% Zn, 6.19% Ca, 5.44% Fe, 6.74% Si, 1.85% Al and 12.25% S. In addition, it has been determined that ÇEA contains minor components such as Cu, Cd and Ni in the concentrations of 602, 310 ve 224 mg/kg, respectively. It has been determined that the main components in the structure are lead in anglesite [PbSO4] and massicot [PbO], zinc in franklinite [ZnFe2O4], calcium in gypsum [CaSO4.2H2O], iron in maghemite [Fe2O3] and hercynite [Al2FeO4] and silica in quartz [SiO2] crystal structures. The effects of contact time (30-240 min), liquid/solid ratio (5-100) and pH (3-12) on the releasing of pollutants, and the pollution potential of the ZER by TCLP (Toxicity Characteristic Leaching Procedure), SPLP (Synthetic Precipitation Leaching Procedure), eluat test and MEP (Multiple Extraction Procedure) were examined. It was determined that the releasing concentrations of pollutants decrease with increasing liquid/solid ratio, increase slightly with the increasing contact time. But, they do not change significantly with pH (except pH 11 and 12). With the applied TCLP, SPLP and eluate tests, 69 and 2.9, 3 and 0.9, 3.82 and 0.68 mg/L of toxic components released into the solution, respectively. With the MEP test, it was determined that even in the 21st extraction, lead released above the TCLP limit value of 5 mg/L. Depending on the released lead and cadmium values, it has been determined that ZER has a significant pollution potential, therefore, it cannot be stored with household waste or thrown into the environment indiscriminately. With S/S applied to prevent the dissolution of the contaminants, ZER stabilized and solidified in the presence of 10% PÇ, 30% UK, 50% FC and 50% lime, the heavy metals stabilized and solidified with transforming into the insoluble hydroxide compounds by the S/S.