Humic acid adsorption behavior and mechanism comparison between biochars and activated carbon

Treatment of Wastewater from Soil Washing with Soluble Humic Substances Using Biochars and Activated Carbon

“…Based on the C i values, the rate-controlling mechanism of HA adsorption was mainly chemisorption but simultaneously affected by multiple mechanisms [69]. Other authors have confirmed that the sorption of soluble organics in the form of humic acids is not dominated by intraparticle diffusion [56]. Omri et al [70] concluded that humic acid molecules are slowly transported via intraparticle diffusion into the particles of activated carbon and finally retained in their pores.…”

“…The first mechanism to consider is a pore-filling mechanism, in which the organics are at the surface of the biochar, which possesses mesopores (2-50 nm) and micropores (<2 nm) [50]. The presence of mesopores was shown to be crucial for the adsorption of humic acids onto biochar and activated carbon [56]. In the present study, ACN and BW had the best textural characteristics in terms of total pore volume and volumes of mesoand micropores (Table 2).…”

“…According to Liu et al [57], biochar prepared at 900 • C after modification with hydrochloric acid had a large specific surface area (459.3 m 2 /g) and a high porosity, and it removed over 80% of humic acids in aqueous solution at pH 5.0-9.0. Yan et al [56] demonstrated that humic acids are better adsorbed on bamboo biochar than on helmpalm biochar and activated carbon. This is because bamboo biochar has a larger pore volume and wider pore size distribution and contains more polar functional groups on the surface, which makes it easier for it to bind humic acid than the other adsorbents.…”

“…Omri et al [70] found that adsorption of humic acid onto almond shell activated carbon from aqueous solutions at different concentrations (10-100 mg/L) increased sharply in the first 180 min of contact time and that equilibrium adsorption was reached within 300 min. Yan et al [56] observed that the capacities of bamboo biochar, helm palm biochar, and activated carbon to adsorb humic acid were highest during the first 4 h. The fast rate of adsorption at the beginning of the process was caused by humic acid adsorption on the exterior surface of activated carbon. After saturation of the exterior adsorption surface, humic acids can enter pores and are adsorbed by the interior surface [70].…”

“…This indicates that the adsorption of soluble organics from the SWW, which had a very high initial concentration (1934 mg/L), was not determined by only one type of mechanism; instead, physical adsorption, chemisorption, and intraparticle diffusion were responsible for the removal of soluble organics (R 2 values for all three models were between 0.90 and 1.00). Many studies that have used carbon-based adsorbents to adsorb humic acids from aqueous solutions with concentrations up to 100 mg/L have indicated that the adsorption of humic acids appears to be controlled mainly by chemisorption processes [56,69,70].…”