Impact of Physicochemical Properties of Biomass-based Fly Ash on Lignocellulose Removal from Pulping Spent Liquor

A biomass-based fly ash was fractionated and ground to produce fly ash adsorbents of various compositions and particle sizes. It was determined that grinding had no noticeable impact on the surface area and micropore volume of the fly ash, but it increased the mesopore volume of the fly ash remarkably. Isotherm analysis on the lignin and chemical oxygen demand (COD) removals from a thermomechanical pulping (TMP) pressate (i.e., spent liquor) was performed. It was determined that the adsorption process followed the Freundlich model, and the estimated maximum adsorption capacities for the lignin and COD on the fly ash were identified. The highest adsorption capacities for the COD and lignin were 204 mg fly ash/g TMP pressate and 149 mg fly ash/g TMP pressate, respectively, which were achieved under the treatment conditions of 298 K, 100 rpm when mixing the fly ash and pressate for 24 h. The potential impact of various physicochemical properties, such as the ionic strength and metals content of the fly ash, on the adsorption capacity for lignin and COD was also evaluated.