Optimizing Cu2+ adsorption with low-temperature sintered dolomite-based geopolymer

Sintering process significantly improves Removal Efficiency (RE) of Copper (Cu) ions by enhancing microstructural properties, creating new active sites and increasing geopolymer material densification. However, geopolymer typically requires high-sintering temperature above 1200˚С, leading to substantial energy consumption and increased production costs. In contrast, geopolymer dolomite reduces the sintering temperature to 900 ˚С by producing metal oxides like periclase (MgO) and lime (CaO), which act as self-fluxing agent during the sintering process. Therefore, this study aims to develop a sustainable geopolymer adsorbent using dolomite as the primary precursor, utilizing different low sintering temperature between 600 ˚C to 900 ˚C. The effects of low sintering temperature on the microstructure, pore sizes, chemical changes and RE of Cu²⁺ ions were investigated. Characterization techniques such as Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX), X-ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and Synchrotron Radiation X-ray Fluorescence (SR-XRF) were used to study the physicochemical properties of the developed geopolymer. Heating geopolymer dolomite at 800˚С achieved the highest RE of 99.81 %, followed by unsintered geopolymer dolomite (46.92 %) and raw dolomite (14.53 %). The results showed that sintering at 800°C with a heating rate of 5 °C/min produced a rounded shape with a formation of necking growth. Additionally, the formation of MgO and CaO further enhanced the removal of Cu²⁺ ions. SR-XRF analysis detected 93.11 % % of Cu on sintered geopolymer dolomite after adsorption, suggesting that Cu 2+ has successfully replaced Ca 2+ using ion exchange mechanisms. Thus, the sintering process influences final microstructure formation, improving RE of Cu²⁺ ions. This indicates that sintered geopolymer dolomite using low sintering temperature (800˚C) can effectively remove Cu²⁺ ions in wastewater treatment.