Extraction of Lignosulfonate from Black Liquor into Construction of a Magnetic Lignosulfonate-Based Adsorbent and Its Adsorption Properties for Dyes from Aqueous Solutions

Lignosulfonate, one of the lignin derivatives, was extracted from the black liquor as a byproduct of the wood and paper industry. It was used to prepare magnetic aminated lignosulfonate/carbon (MALS/C) adsorbent for the adsorption of Congo red and methyl orange dyes from an aqueous solution. The physical and chemical characteristics of the synthesized samples were determined by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), thermal gravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM). The MALS/C adsorbent performance in the adsorption process of Congo red and methyl orange dyes was examined in a batch system. The effects of essential parameters, such as pH of the solution, adsorbent dosage, contact time, initial concentration of dye, and temperature, on the adsorption of the mentioned dyes, were assessed. The maximum removal efficiency of Congo red in the conditions (adsorbent dosage 0.01 g, contact time 120 min, initial dye concentration 20 mg/L, pH 6, and temperature 25 °C) and methyl orange in the conditions (adsorbent dosage 0.01 g, contact time 120 min, initial dye concentration 20 mg/L, pH 2, and temperature 25 °C) was 97.09 and 72.08%, respectively. Besides, after five regeneration times, the removal efficiency for Congo red and methyl orange dyes under a similar condition declined to 81 and 58%, respectively. The kinetics and adsorption isotherms examination were performed. The results demonstrated that the adsorption data for both dyes were consistent with the pseudo-second-order kinetic model and the Langmuir adsorption isotherm. The maximum adsorption capacity calculated by the Langmuir model was 167.61 and 121.28 mg/g for Congo red and methyl orange dyes, respectively. The thermodynamic studies indicated that the adsorption process was spontaneous and endothermic.