Abstract:The wastewater from synthetic dye industries contains substantial amounts of Congo Red (CR) and Amaranth (AM), which pose significant toxic threats to ecosystems. Consequently, magnesium-based adsorbents have been widely applied for the treatment of such dye-containing wastewater. Approximately 50% of magnesite ore is converted into tailings during mining and processing. These tailings, which contain about 40 wt% MgO, are mainly disposed of by landfilling. In this study, magnesite tailings were employed as a precursor to synthesize a structurally stable MgO-based adsorbent through electrochemical deposition. CR and AM were chosen as representative anionic dyes to assess the adsorption performance of the adsorbent. The main conclusions are summarized as follows. The primary crystalline phase of the product obtained under optimized electrolysis conditions was MgO, with a trace amount of S24Mg16Ca12O96, which facilitated the adsorption process. The product exhibited a flocculent morphology with uniformly dispersed particles, which could be attributed to the enhanced steric hindrance induced by Ca and S co-doping. The prepared adsorbent exhibited a specific surface area of 74. 43 m2/g, an average pore diameter of 22. 66 nm, and a pore volume of 0. 0027 cm3/g, and the pore-size distribution was centered at approximately 20 nm, confirming its mesoporous nature. Under optimal conditions (adsorbent dosage = 10 mg, initial CR and AM concentrations = 500 mg/L, pH = 7-11, and contact time = 50 min), the maximum adsorption capacities for CR and AM reached 995. 66 mg/g and 759. 56 mg/g, respectively. Coexisting ions such as Cl?、SO42- 和 NO3- showed minimal influence on adsorption efficiency, while HCO3- and humic acid (HA) exhibited only minor effects. The adsorption process was dominated by multilayer adsorption, with the kinetic data fitting well to the pseudo-second-order model. The adsorbent showed excellent regeneration performance, retaining CR and AM removal efficiencies above 95% and 68.5% after five successive cycles. The adsorption of CR and AM onto MgO was mainly governed by electrostatic interactions and hydrogen bonding. Meanwhile, the incorporation of S24Mg16Ca12O96 further enhanced the structural stability and surface reactivity of the adsorbent, thereby improving its overall adsorption performance compared with pristine MgO. The magnesium-based adsorbent prepared via this method exhibited high adsorption capacity, fast adsorption rate, and excellent reusability. Moreover, its synthesis did not require high-purity precursors, templates, or additives, providing a promising strategy for the resource utilization of magnesite tailings.
