Adsorption Equilibrium of Nitrates Ions onto Oil Palm Shells-based Activated Carbons
In this study, two oil palm shells-based activated carbon adsorbents were prepared by physicochemical activation and were evaluated for their ability to remove nitrate ions from an aqueous solution in a batch process. Steam was used as physical activation agent in combination with H3PO4 and KOH as chemical activating agents, respectively. The H3PO4-carbon (ACOPS-H3PO4) and the KOH-carbon (ACOPS-KOH) oil palm shell activated carbons had a BET surface area of 564 and 838 m2/g, respectively, and were essentially microporous. The effects of various parameters such as contact time, initial solution pH and adsorbent dosage on nitrate ions uptake were investigated. The experimental results obtained showed that the adsorption equilibrium was reached within 70 mn. The amount of nitrate intake was observed to gradually increase when the amount of adsorbent used was varied from 0.2 to 1.2 g reaching a maximum value as from 1 g of adsorbent. The initial pH of sample solutions, varied from 3.5 to 6.5, significantly influenced the adsorption of nitrate by both adsorbents; increase in pH decreased the adsorption, with the maximum adsorption occurring at pH 3.5. The equilibrium adsorption data for ACOPS-H3PO4 and ACOPS-KOH were well correlated by Langmuir isotherm model (r2 = 0.969 and 0.995, respectively) and by Freundlichisotherm model (r2 = 0.967 and 0.961, respectively), indicating that both models were suitable for the description of the adsorption process. The maximum adsorption capacities were found to be 65 mg/g, and 68.166 mg/g for (ACOPS-H3PO4) and for (ACOPS-KOH) oil palm shell activated carbons, respectively. The kinetic studies performed showed that the pseudo-second-order kinetic model best described the adsorption process of nitrate ions onto both prepared activated carbons. The results proved that the prepared oil palm shells-based activated carbons were effective adsorbents for removal of nitrate ions from aqueous solution.
