Co-utilization of spent aluminum refractory lining and microsilica for low-energy Portland cement clinker

Abstract

Abstract Purpose This study investigates the potential of integrating two industrial wastes—leached spent chamotte lining (SCL) from aluminum electrolyzers and amorphous microsilica (MS)—into Portland cement clinker production as a partial replacement for traditional clay. Methods A binary composite (SCL + MS) was designed to compensate for silica deficiency in SCL and enhance raw meal reactivity. The raw mix was optimized using the Pearson envelope method targeting LSF = 0.90 and SR = 2.3, with the composite replacing 14.5 wt.% of the raw meal. Laboratory firing experiments ( n = 3 per condition) were conducted in a muffle furnace up to 1450 °C. Clinker and cement were characterized by TGA/DTA, XRD-Rietveld, SEM–EDS, and standard mechanical testing (GOST 310.4). Leaching tests were performed according to EN 12457–2. Result Thermal analysis revealed a 20–30 °C reduction in decarbonation temperature for the experimental mix under laboratory conditions. This acceleration is attributed to a synergistic combination of: (1) the high specific surface area and reactivity of amorphous microsilica, (2) residual sodium acting as a fluxing agent, and (3) trace amounts of fluoride ions retained in the leached SCL. XRD-Rietveld quantification confirmed standard clinker phases (C₃S: 52 ± 2%, C₂S: 25 ± 2%, C₃A: 8 ± 1%, C₄AF: 12 ± 1%), with a slight shift towards higher belite content compared to the control. The resulting cement met PC 300 grade specifications, achieving 28-day compressive strength of 29.6 ± 1.5 MPa, which was statistically comparable to the control (29.8 ± 1.5 MPa, p = 0.78, two-sample t-test, n = 6). Leaching tests confirmed effective immobilization of F⁻ (0.9 ± 0.2 mg/L) and Na⁺ (18 ± 3 mg/L) below regulatory limits (SanPin ≤ 10 mg/L and ≤ 100 mg/L, respectively). Conclusions This work demonstrates the viable valorization of leached SCL and MS into competitive Portland cement. The composite additive shows promise for reducing clinkering temperatures, though projected energy savings require pilot-scale verification. The approach contributes to circular economy principles by diverting hazardous waste from landfills while producing a marketable construction material.