Two-step preparation of steel slag–lignin hybrid materials for effective removal of methylene blue

In this work, a steel slag–lignin hybrid material (SS–AL) was obtained by compounding steel slag (SS) and alkali lignin (AL) to be used to treat dye wastewater. AL was modified by introducing more reactive functional groups (–COOH, –OH, etc.). Then, it is complexed with SS to obtain a hybrid material with more active functional groups. SS–AL was characterized for its chemical structure, physical properties and adsorption properties. The results of adsorption experiments showed that the adsorption of methylene blue (MB) by SS–AL followed the Langmuir and Freundlich model, indicating that the adsorption process involved both monolayer and multilayer adsorption. The maximum adsorption capacity at 338 K was 78.13 mg/g. The removal efficiency can reach 92.98% in 30 min. The adsorption process of SS–AL also conformed to the pseudo-second-order kinetic model, demonstrating the involvement of chemisorption in the adsorption process. SS–AL also had good recyclability, and after five cycles, its removal efficiency of MB can still be maintained at more than 80%. This work proved the feasibility of composite steel slag and lignin biomass materials, and also provided a new idea for SS–AL in the purification of dye wastewater, which realized the resourceful utilization of steel slag and lignin.