Optimization of cemented paste backfill with carbon nanotubes as a sustainable treatment for lead-containing tailings

Pb(II)-containing tailings are serious hazards to the environment. Their rationalization and harmless treatment are of great significance to the construction of the green mine. Cemented paste backfill (CPB) plays an important role in the large-scale disposal of tailings. However, Pb(II) in tailings harms the hydration reaction of ordinary Portland cement (OPC), thus reducing the early strength of CPB. The smooth running of mining was hampered. Besides, CPB is also essential for the effective immobilization of Pb(II). In this study, carbon nanotubes (CNTs) were used to optimize the properties of CPB. The influence of CNTs on OPC hydration and the phase composition of hydration products were studied by isothermal calorimeter test, X-Ray diffraction, and thermogravimetry analysis. The property changes of CPB, including flowability and strength development, caused by CNTs were investigated. The hydration of OPC was accelerated when CNTs were added. And more hydration gels generated to form a more compact structure of CPB. Due to the denser structure and more hydration gels caused by the CNTs, as well as the adsorption of Pb(II) on CNTs, the early strength of CPB was improved. And the Pb(II) immobilization was enhanced.