Improving the Efficiency of Cement Mortar to Immobilize Sulfate in Industrial Wastewater Using Different Nanoparticles

The disposal of industrial wastewater (IWW) discharged from factories is a significant topic in the environment field, and the use of cement-based materials is a useful way to treat materials with unexpected ions. In this work, IWW with abundant SO42− collected from a factory was utilized to prepare cement mortar (IWWCM), and three kinds of nanomaterials (NMs), including nano-SiO2 (NS), nano-CaCO3 (NC), and nano-metakaolin (NMK), were used to improve the performance of IWWCM. The compressive strengths, hydration degree, hydration products, and micropore structure of the specimens were investigated. The test results showed that IWW reduced the strength of the specimens, and the use of NMs could compensate for this strength reduction. To be specific, the 28-day strength of the freshwater (FW) mixed specimen was 44.6 MPa, and the use of IWW decreased this value to 41.8 MPa. However, the strengths of the specimens with NMs were all higher than 50 MPa, indicating the advantage of NMs for the strengths of the IWWCMs. Moreover, the IWWCM showed a lower hydration degree with a poor pore structure, whereas the use of NMs in IWWCMs refined these properties, explaining the strength increase in the specimens. The results of the SO42− content measurements also showed that the use of NMs could improve the SO42− binding ratio, which is conducive to relieving the pressure of IWW disposal for industrial factories.