Adsorption and kinetic studies on removal of levonorgestrel (lng) from aqueous solution using chemically modified and carbonized sawdust as adsorbent: DFT calculation

Chemically activated and carbonized adsorbents were prepared from Sawdust by chemical activation of the pulverized sawdust by steeping into saturated ammonium chloride solution for 24hrs and air dried to serve as the chemically activated sawdust adsorbent (ASD), A portion of the ASD was carbonated in a muffle furnace at 623k for 30mins. The carbonated material was washed repeatedly to remove ash, then air dried and stored as carbonized sawdust adsorbent (CSD). The adsorbents were characterized and evaluated for their ability to remove the common contraceptive – levonorgestrel (LNG) from an aqueous solution. The effects of operational parameters such as initial pH (2-11) and concentration (60-300mg/L LNG), adsorbent dosage (0.5–2.0 g), temperature (298–328 K) and contact time (0–120 min) were investigated. At equilibrium, optimal removal efficiencies for Levonorgestrel were 97.60% and 84.98 % which were achieved at solution pH 6, adsorbent dose of 0.5 g for CSD and ASD, respectively. The equilibrium adsorption data fitted into both the Freundlich and Tempkin isotherms. The overall kinetic data was well-modelled by the Blanchard pseudo-second-order equation. These results may find applications in the use of low-cost adsorbents for the removal of micro-contaminants of pharmaceutical origin from wastewater. The batch adsorption experimental data obtained confirmed that the adsorption characteristics of Carbonized sawdust were better than those of activated sawdust. The linear plots of intra-particle diffusion demonstrated that the adsorption process is mainly governed by pore diffusion. The research concluded that chemically activated (ASD) and carbonised (CSD) Sawdust have sufficient porosities and surface area and have a good potential to remove LNG from the aqueous phase, but the overall results showed that CSD gave better output.