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Excessive amounts of fluoride in water cause irreversible harm to people and seriously threaten human health. Therefore, fluoride ion in water should be deeply removed. The waste liquor of itaconic acid fermentation contains many organic acids, residual sugars, proteins, and other impurities, which are difficult to remove. Thus, in this study, the itaconic acid fermentation waste liquid was successfully mixed with urea to prepare N-doped porous carbon (PC-N). The prepared PC-N was applied for the removal of fluoride in water. The specific surface area of PC-N is as high as 1803 m2 g−1, and the SEM results show an abundant pore structure. The FTIR results showed that the adsorbent surface had an abundant functional group structure. The removal rate of F− by PC-N was 91% when pH = 6. After 6 cycles of recycling, PC-N performance remains stable at about 73% of that of the fresh adsorbent. Moreover, Freundlich and PSO can better fit the adsorption data, indicating that F− on PC-N adsorption results from the joint action of physical and chemical adsorption. After calculating the adsorption thermodynamics, ΔH and ΔS are −14.5529 kJ mol−1 and 13.6507 J (mol K)−1, and ΔG is negative, indicating that the adsorption process is exothermic and spontaneous. The outcome results of this work have achieved the goal of "treating waste with waste" and realized the dual protection of the environment. [ABSTRACT FROM AUTHOR]

Carbon microspheres were synthesized using itaconic acid fermentation waste liquid as the raw material by the hydrothermal method. The sequential porous adsorbent was prepared (by chemical activation) using carbon microspheres as a carbonaceous framework. The adsorbent was characterized by SEM, BET, Raman, XRD, XPS, and elemental analysis. Also, the adsorption performance of the adsorbent was tested using the batch adsorption method. The effects of several parameters such as pH, adsorbent dose, and concentration of Cr(VI) on the sorption of Cr(VI) were investigated. The results indicate that an outstanding adsorbent with a specific surface area of 1802.16 m2 g−1 and a maximum adsorption capacity for Cr(VI) of 270.14 mg g−1 has been acquired. According to the adsorption isotherm model, the kinetic model, and the intra-particle diffusion model, it was found that the adsorption process of Cr(VI) by the adsorbent conforms to the Freundlich model and the quasi-second-order kinetic model. The evaluation of the thermodynamic parameters (ΔH > 0, ΔS > 0, and ΔG < 0) revealed that the adsorption process was endothermic and spontaneous. The mechanistic studies showed that the adsorption of Cr(VI) likely involved electrostatic attraction and a redox reaction. After 5 cycles of repeated usage, the adsorbent maintains good adsorption stability to Cr(VI), favoring its practical application. [ABSTRACT FROM AUTHOR]