Adsorption and Kinetic Study of Activated Carbon Produced from Post-Consumer Low-Density Polyethylene (LDPE) Wastes

Abstract

Post-consumer polymeric wastes in form of \nlow-density polyethylene (LDPE) can now be considered suitable as a precursor \nfor the synthesis of low-cost activated carbon (AC). This study produced AC \nfrom LDPE using sulphuric acid (H2SO4) and potassium hydroxide (KOH) as the \nactivating agent. The reaction conditions for pyrolysis were varied in the \nrange of 0.50 - 2.00 M, 400°C - 500°C, and 45 - 60 minutes. Physico-chemical \ninvestigations reveal that AC yield is significantly dependent on both \ncarbonization temperatures and time. The obtained optimum values of 446.50°C \nand 51.09 mins gave a yield of 24% for the base-activated carbon. The high \niodine numbers obtained strongly indicate the presence of large surface area \nand pore volumes is further confirmed using the Scanning Electron Microscopy \n(SEM) analysis which reveals the presence of pores on the external surface of \nthe carbons. Fourier Transform Infrared Technique (FTIR) analysis further shows \nthat the synthesized compounds are purely carbon with rich oxy-gen-surface \ncomplexes on the surface which is as a result of the introduction of the \nchemical oxidizing agents. The produced carbons were found to have high \nadsorption affinity for selected inorganic ions which are: Mn7+, Co2+, and \nCr6+. Adsorption isotherm results show the adsorption process to be favourable \nwith the Langmuir isotherm parameter RL having values of <1, while the \nFreudlich adsorption model was found to perfectly fit the data at selected \nadsorbent dosages and adsorbate concentrations. The pseu-do-second-order model \nprovides the best correlation for the kinetic analysis. The acid-activated \ncarbon was found to have better adsorption capacities than the base-activated \ncarbon.