Synthesis Lignin-Mg(OH)₂ from Lignin Bagasse as Green Adsorbent of Heavy Metal Pb (II)

Abstract

The development of green adsorbents from natural resources for heavy metals in polluted water is due to their abundance, environmentally friendly, and low cost. The second most abundant natural polymer after cellulose is lignin. However, lignin capability for heavy metal ion adsorption especially Pb (II) is still very low. Therefore, modifications of lignin is needed by adding a new functional group to the lignin such as Mg (OH)2. It is expected to improve the adsorption ability of lignin to Pb (II). In this research, we used lignin from bagasse as a source. After isolating the lignin molecule, a lignin-Mg (OH)2 has been synthesized by reflux method forming hydrogen bonds with Mg (OH)2 which can be seen from the results of characterization using FTIR. The synthesized lignin-Mg (OH)2 has diameter 300-450 nm with an irregular shape. Adsorption ability of lignin-Mg (OH)2 to Pb (II) was conducted using an UV-Vis spectrophotometer by the addition of Alizarin Red S (ARS) as complexing agent. The kinetics study of adsorption process was elucidated by pseudo-first-order and pseudo-second-order models. Adsorption process was described by the Freundlich and Langmuir models. The adsorption process of lignin-Mg (OH)2 to Pb (II) was endothermic and spontaneous in nature. The experimental results show that lignin-Mg (OH)2 has a greater capability of adsorption to Pb (II) than lignin bagasse. Lignin-Mg (OH)2 has maximum adsorption capacity to Pb (II) of 40.16 mg/g at 25°C and percent removal up to 96%. Meanwhile, lignin bagasse has a maximum adsorption capacity of 12.85 mg/g at 25°C and a percent removal of 68%.