Sustainable synthesis of a Faujasite-Na/geopolymer composite from kaolin residues for water treatment

Abstract This paper presents a novel method for preparing Faujasite-Na/geopolymer composite using kaolin-based aluminum sulfate residue (KASR), along with meta-kaolinite (MK), to remove methylene blue (MB) from wastewater. Raw kaolinite from kaolin deposits in intercalated sedimentary rocks in South Sinai, Egypt, was thermally treated for 90 min at 700 °C to create MK. KASR was obtained from Al-Shabba Al-Masria Company of Egypt. MK and KASR were characterized using X-ray fluorescence (XRF) and X-ray diffraction (XRD) analysis. Faujasite-Na was synthesized by hydrothermal reaction of MK with a 1.0-N NaOH solution, along with the addition of KASR as a source of amorphous silica, at 80 °C for 80 h under atmospheric pressure and then cooled and filtered. Following a 24-h drying process at 110 °C, Faujasite-Na zeolite, with the chemical formula Na 56 (Al 56 Si 136 O 384 ), was formed. The successful production of Faujasite-Na was confirmed by the results of XRD, XRF, SEM, and EDS. Geopolymer was synthesized by the alkaline activation of a mixture consisting of MK, Faujasite-Na zeolite, KASR, and NaOH. Methylene blue (MB) was removed from wastewater with the maximum removal of 97.7% using 1 g of 40% Faujasite-Na/geopolymer composite (ZGP-40). The adsorption capacity was 58.6-mg MB/g composite at a pH of 7 and at 25 °C. The isothermal and kinetics study confirms Langmuir and the pseudo-second-order model for the dye removal description. One-layer adsorption proceeds regarding that the rate depends on MB and the type of adsorbent that was applied. The adsorption process of MB on Faujasite-Na-geopolymer composite was mainly shown through the electrostatic interaction mechanism as indicated from the FTIR analysis before and after the adsorption process. Therefore, KASR, which is often disposed of in landfills, can be used sustainably to create Faujasite-Na/geopolymer composite that can be used to treat water and generate environmental benefits. Future studies are recommended for regeneration potential and reusability of the spent Faujasite-Na-geopolymer composite and long-term stability as a sustainable development approach.