Efficient adsorption of methylene blue and lead ions in aqueous solutions by 5-sulfosalicylic acid modified lignin.

As a kind of biomass that exists widely in plants, lignin shows much diversity as a functional material. In order to improve the adsorption ability, lignin was chemically modified by 5-sulfosalicylic acid and then used to adsorb methylene blue (MB) and Pb2+ from aqueous solutions. The results showed that the 5-sulfosalicylic acid modified lignin exhibited a high adsorption ability for dyes or heavy metals. The maximum adsorption capacity of the adsorbent approached 83.2 mg/g for MB and 39.3 mg/g for Pb2+ with the adsorbent dosage of 5 g/L at pH 5.85 or 5.35 (corresponding to MB or Pb2+, respectively), initial adsorbate concentration of 200 mg/L, temperature of 318 K and contact time of 12 h. The adsorption kinetics and isotherm studies indicated that both the adsorption of MB and Pb2+ onto SSAL followed the pseudo-second-order model and Langmuir isotherm model. It means that the adsorption process fits the model of mono-layer adsorption and it was mainly chemical process and accompanied with surface adsorption. The proposed SSAL is low-cost, eco-friendly and highly efficient therefore a promising material for adsorptive removal of MB and Pb2+ from wastewater.