Solidification/stabilization of Pb²⁺ within a blast furnace slag-steel slag based cementing agent for paste backfilling

Backfilling material specimens were prepared with Pb-bearing ore tailings and a blast furnace slag-steel slag based cementing agent(BSCA) used as a replacement for cement in traditional backfilling materials. Other types of specimens with ordinary Portland cement(P·I 42.5) as cementing agents were also made for comparison. Flowability and compressive strength tests were performed to study the working performance of the specimens,and leaching tests were done to investigate the immobilization of Pb²⁺ in the specimens. The phase composition of the hydrated specimens was analyzed by means of X-ray diffraction,Fourier transform infrared spectroscopy and differential scanning calorimetry. It is found that the backfilling material with BSCA has a flowability of 50 mm higher than that with ordinary cement. The 28-d compressive strength of the BSCA-based specimens reaches 3.0 MPa,which meets the strength requirement for underground backfilling. The quantities of Pb²⁺ leached from the BSCA-based specimens aged for 28 d are below 0.05 mg·L^-1,which is the threshold value of Pb²⁺ concentration for Type Ⅲ ground water in Chinese quality standard for ground water GB/T 14848-93. In comparison,the quantities of Pb²⁺ leached from the cement-containing specimens aged for 28 d are 0.1 mg·L^-1. The reason for this higher immobilization degree of Pb²⁺ in the hydrated BSCA-based specimens is that a higher amount of ettringite forms in them. Moreover,the formation of zeolite-like facies in the hydrated BSCA-based specimens is favorable for immobilizing Pb²⁺.