Utilization of lead–zinc mine tailings as cement substitutes in concrete construction: Effect of sulfide content

Abstract

Production of acid mine drainage and emission of heavy metals from tailings, especially sulfide tailings, to the environment is one of the serious challenges in the management of mine tailings. The use of cementation process and replacement of cement with mine tailings in the manufacture of concrete is one of the practical approaches to the management of mine tailings. In this study, two different lead-zinc mine tailings (T1 with 0.4% and T2 with 19% sulfide content) were separately used as a cement substitution in concrete construction. Toxicity characteristic leaching procedure (TCLP), acid generation potential, compressive strength tests, and mercury intrusion porosimetry (MIP) were conducted on the constructed concrete samples. The TCLP test results revealed that with increasing the curing time of the samples, the leaching rate of toxic metals (arsenic, cadmium, chromium, cobalt, nickel, copper, zinc, and lead) in all samples was reduced to lower than the permissible criteria, indicating the good stabilization of heavy metals in concrete samples. The MIP test results also revealed that with increasing the curing days and subsequently the hydration process, the intruded mercury volume decreased, indicating that heavy metals were stabilized in concrete samples. The compressive strength test findings revealed that in constructed concrete containing 20% cement-replacing T1, with increasing the curing time of the sample from 28 to 90 days, the compressive strength increased from 16.9 to 19.8 MPa, and the leaching rate of heavy metals decreased from 39.64 to 23.65 μg/L,. In addition, in the sample with 20% T2, the compressive strength increased from 10.59 to 16.4 MPa, and the leaching rate of heavy metals decreased from 44.65 to 26.5 μg/L. Comparing the Scanning Electron Microscope (SEM) and Energy Dispersive X-ray analyzer (EDX) results, it was found that the Ca/Si ratio was lower in the samples prepared with mine tailings compared to the control, indicating insufficient amount of calcium available to form the main hydration product (C–S–H). Therefore, less C–S–H gel was formed in these samples. Also, according to the elemental distribution analysis, it was revealed that other heavy metals were scattered throughout the concrete matrix and stabilized in the concrete structure by forming new compounds. In general, it could be concluded that cement replacement with lead-zinc mine tailings up to 20% without the use of any improvement technique may be possible. Further, the formation of hydration products affected by high sulfide content and causes the production of sulfide salts that attack the concrete sample over time, thereby reducing cementitious properties and strength.