Synthesis of aminated calcium lignosulfonate and its adsorption properties for azo dyes

A low-cost adsorbent, aminated calcium lignosulfonate (ACLS) was prepared and successfully applied to the adsorption of Congo red and the Titan yellow dyes. The adsorbent was characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), elemental mapping images (EMIs) and Brunauer–Emmett–Teller (BET) analysis. And the efficiency of ACLS for the removal of Congo red and the Titan yellow dyes was evaluated by several factors, such as temperature, pH, adsorbent dose, contact time and initial concentration of dyes solution. And the test ranges of temperature, pH, adsorbent dose, contact time and initial concentration of dye solution were 25–45 °C, 2–12, 0.005–0.05 g, 1–48 h, 10–200 mg L−1, respectively. The adsorption results demonstrated a good ability to remove dye with the removal rates of 97% and 91% for 30 mg L−1 Congo red and 40 mg L−1 Titan yellow, respectively. The adsorption kinetic and adsorption isotherms can be well described by the pseudo second order kinetic and the Langmuir isotherm model for the both dyes, respectively. Moreover, the maximum adsorption capacity of Congo red and Titan yellow reached 258.4 mg g−1 and 190.1 mg g−1 in the study of the Langmuir adsorption isotherm, respectively. Thermodynamic studies show that the adsorption of the two dyes is a spontaneous endothermic process. The results indicate that the ACLS has the potential to be used in the treatment of dye wastewater.