Valorization Potential of Polish Laterite Leaching Residues through Alkali Activation

Abstract

In this study, the valorization potential of Polish laterite leaching residues through alkali activation with the use of NaOH and Na2SiO3 solutions as activators was investigated. The effect of the main factors, namely the H2O/Na2O molar ratio in the activating solution, the curing temperature, and the ageing period on the main properties of the produced alkali activated materials (AAMs) was assessed. The experimental results showed that AAMs with sufficient compressive strength were only produced when the laterite leaching residues were mixed with significant quantities of metakaolin; thus, when the mass ratio of laterite leaching residues and metakaolin was 0.50, after curing at 40 °C for 24 h and ageing for 7 days, the produced AAMs acquired compressive strength that slightly exceeded 25 MPa. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy (SEM–EDS) analysis were used for the characterization of the raw materials and selected AAMs. Furthermore, the structural integrity of the specimens was investigated after immersion in distilled water and acidic solution (1 mol L−1 HCl), or after firing at higher temperatures. Finally, the toxicity of the produced AAMs was assessed with the use of standard leaching tests.