Studi Termodinamika Adsorpsi Ion Nitrat oleh Biochar Termodifikasi Kalsium dari Cangkang Telur

Abstract

In this study, the physicochemical properties of Ca-modified and protonated biochar and its thermodynamic adsorption behavior towards nitrate were evaluated. Biochar modification using Ca sourced from eggshells was carried out by slow co-pyrolisis at 280-400℃ followed by protonation using oxalic acid. The modified biochar was characterized by its physical and chemical properties including functional groups analysis using FTIR, moisture and ash content analysis, pH and pHpzc.The adsorpstion study included adsortion capacity, adsorption isotherm and adsorption thermodynamics. Calcium modified biochar has been proven to improve nitrate adsorption capacity into 7,583 mg/g at optimum concentration (PB-Ca224) compared to Corncob biochar (CB) with 4,43 mg/g. Adsorption of nitrate at 298,308 and 318 K following Langmuir isothermal models with R2 value 0,9563 over Langmuir’s model, indicating monolayer adsorption. Observed thermodynamical parameter such as enthalpy ΔH, entrophy ΔS and Gibbs free energy ΔG. The results shown that ΔH value 23,920 kJ/mol indicating endothermic process, ΔS value falls at 181,661 J/mol and ΔG value respectively at -30,241 ;-32,031 and -33,848 kJ/mol for 298,308 and 318K, indicating spontaneous adsorption. Based on these results, the adsorption of nitrate by Ca-modified biochar is physical adsorption (physisorption)