Comparative adsorption of tetracycline onto unmodified and NaOH-modified silicomanganese fumes: Kinetic and process modeling

Silicomanganese fumes (SMF) are industrial waste and a potential low-cost adsorbent for the removal of contaminants from water. In this study, the adsorption performance of SMF and NaOH-modified SMF (SMF-Na) for the removal of tetracycline (TC) from an aqueous solution was investigated. The characterization results showed the presence of functional groups (SiO₂, -OH and C-O-C), a considerably higher surface area of the SMF-Na (142.59 m² g⁻¹) compared to the SMF (7.73 m² g⁻¹). The TC adsorption was favored under acidic conditions (pH 2–3) and increased with an increasing amount of adsorbent. The adsorption equilibrium was achieved in 360 min, and the presence of Na⁺ ions insignificantly influenced the TC adsorption. The Avrami model fitted better to the kinetic data with R² = 0.995. The isothermal data was well represented by the Redlich-Peterson and Langmuir model. The maximum monolayer adsorption capacity of SMF and SMF-Na was 117 and 129 mg g⁻¹, respectively. The thermodynamic results confirmed that the TC adsorption was endothermic and predominantly governed by physical forces. The removal of TC onto SMF and SMF-Na was maintained above 90 % even after five regeneration cycles The results suggested that SMF-Na is a promising alternative adsorbent for the removal of tetracycline antibiotics from wastewater streams.