This study was conducted to evaluate the phosphate sorption properties of eggshell (ES) and calcined ESs (C-ESs) in a high-concentration phosphate solution. The C-ESs yield decreased rapidly at 900 °C, indicating that the CaCO3 constituting the ES was converted to CaO by the high calcination temperature. The optimum calcination temperature for phosphate removal using C-ES was 900 °C. The actual sorption amount of phosphate by ES and C-ES900 was in agreement with the Langmuir isothermal sorption equation, and the maximum sorption capacities derived from this equation were 178.6 and 270.3 mg/g, respectively. The sorption rate of phosphate by ES and C-ES900 was divided into two stages: an initial fast sorption stage, followed by a slow sorption stage. The sorption of phosphate by ES was dominantly influenced by the initial pH and salt concentration, whereas C-ES900 exhibited a constant sorption capacity regardless of environmental changes. The SEM–EDS and XRD results demonstrated that phosphate was successfully adsorbed on the ES and C-SE900 surfaces. In this study, it was found that the sorption of phosphate by ES occurred via ion exchange and precipitation reactions and that the sorption of phosphate by C-ES900 was dominantly affected by precipitation. Above all, C-ES can be applied as an effective adsorbent for removing high concentrations of phosphate under a wide range of environmental conditions.

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The fine particulate structure of biochar limits its use as a heavy metal adsorbent, and makes separation of the biochar from the solution technically challenging, thereby reducing recovery of the heavy metals. To address this issue, this study prepared biochar beads under various mixing conditions and investigated their efficiency in removing Pb from aqueous solutions using adsorption models. The biochar beads were produced by mixing alginate and biochar at different ratios: alginate bead (AB), 1% biochar + bead (1-BB), 2.5% biochar + bead (2.5-BB), and 5% biochar + bead (5-BB). The results revealed that the Freund-lich isothermal adsorption pattern of the biochar beads to Pb was of the L-type. The highest Langmuir isothermal adsorption capacity (28.736 mg/g) was observed in the 2.5-BB treatment. The dominant mechanism among the kinetic adsorption characteristics of biochar beads for Pb was chemical adsorption. Additionally, the optimal pH range for Pb adsorption was found to be between 4 and 5.5. The highest Pb removal efficiency (97.9%) was achieved when 26.6 g/L of biochar beads were used. These findings suggest that biochar beads are an economical and highly efficient adsorbent that enables separation and recovery of fine biochar particles.

Food waste (FW) emissions in South Korea amounted to 4.77 million tons in 2021, and continue to increase. Various technologies have been developed to treat FW, with recent research focusing on biochar production through pyrolysis to reduce FW. However, the agricultural application of food waste-biochar (FWBC) is limited by the salt accumulated during pyrolysis. This study investigated salt removal from and the kinetic characteristics of FWBC, and subsequently evaluated its agricultural applications. FW was pyrolyzed at 350°C for 4 h, and subsequently washed for 0.1, 0.25, 0.5, 0.75, 1, 5, 15, and 30 min to remove salt. FWBC had a salt concentration of 5.75%, which was effectively removed through washing. The salt concentration decreased rapidly at the beginning (1 min) and then slowly decreased, unlike in FW, in which the salt decreased continuously and slowly. The salt removal speed constant (K) was 1.5586 (Stage 1, FWBC) > 0.0445 (Stage 2, FWBC) > 0.0026 (FW). In a lettuce cultivation experiment, higher biomass was achieved using washed FWBC than when using unwashed FWBC and FW, and soil properties were improved. Overall, these findings

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