The goal of this work is to establish the technical feasibility of producing activated carbon from pulp mill sludges. KOH chemical activation of four lignocellulosic biomass materials, two sludges from pulp mills, one sludge for a linerboard mill, and cow manure, were investigated experimentally, with a focus on the effects of KOH/biomass ratio (1/1, 1.5/1 and 2/1), activation temperature (400–600°C) and activation time (1 to 2 h) on the development of porosity. The activation products were characterized for their physical and chemical properties using a surface area analyzer, scanning electron microscopy and Fourier transform infrared spectroscopy. Experiments were carried out to establish the effectiveness of the lignocellulosic biomass-derived activated carbon in removing methylene blue (MB), a surrogate of large organic molecules. The results show that the activated carbon are highly porous with specific surface area greater than 500 m2/g. The yield of activated carbon was greater than the percent of fixed carbon in the dry sludge, suggesting that the activation process was able to capture a substantial amount of carbon from the organic matter in the sludge. While 400°C was too low, 600°C was high enough to sustain a substantial rate of activation for linerboard sludge. The KOH/biomass ratio, activation temperature and time all play important roles in pore development and yield control, allowing optimization of the activation process. MB adsorption followed a Langmuir isotherm for all four activated carbon, although the adsorption capacity of NK-primary sludge-derived activated carbon was considerably lower than the rest, consistent with its lower specific surface area.
Keywords: activated carbon, adsorption, KOH activation, pulp mill sludge