Effect of CaO/Na2SiO3 ratio on mechanical properties, microstructures and environmental leaching characteristics of neutralization slag based geopolymers
Junfeng Wang, Jin Lai, Liulei Lu, Lin Chen, Wenyao Wang, Xiaozhong Xie, Rong‐Chuan Zhuang, Qi Luo
Abstract
Neutralization slag (NS) of copper smelting is a waste residue mainly composed of calcium sulfate, which is produced during the process of metal smelting. The large accumulation and storage of NS poses a significant threat to the environment. Therefore, it is imperative to explore a new economically and environmentally friendly approach for recycling NS. This study proposes a method for preparing a new eco-friendly geopolymer material by utilizing NS. A geopolymer with satisfactory mechanical properties was created by employing a hybrid solid activator consisting of CaO-Na2SiO3. The effects of hybrid solid alkali activators calcium oxide (CaO)/sodium silicate (Na2SiO3) ratio on the hydration properties of the NS-based geopolymer were studied, and its curing mechanism was discussed. The results show that, when the hybrid solid activator CaO/Na2SiO3 ratio was 3:1, the maximum 28 d compressive strength of the geopolymer reached 27.8 MPa. The solid activator at a suitable ratio can accelerate the hydration reaction, form higher amounts of C-A-S-H gel and ettringite, reduce the proportion of harmful macropores in the geopolymer, and improve the microstructure of the geopolymer. Toxicity characteristic leaching procedure (TCLP) test confirmed that the NS-based geopolymer had a solidification effect on heavy metals. The leaching concentration of elemental Pb from the neutralised slag feedstock was 7.241 mg/L, while the lowest concentration was 0.286 mg/L in the NS based geopolymer. As a green cementitious material, the NS-based geopolymer is expected to be applied in engineering practice.