Extraction of kraft lignin from waste coconut pith and its application for removal of heavy metal ions from industrial effluent

Abstract

The Kraft lignin was extracted from waste coconut pith by pulping process. It was characterised by FTIR, XRD, SEM/EDS, TEM, TG/DTG/DSC, BET surface area analyzer and data were linked to their potential application in removal of heavy metal ions. The desorption of metal ions from the surface of Kraft lignin was investigated for efficient re-use. Differential pulse voltammetry (DPV) was used for quantitative study. Adsorption experiment was performed to investigate effects of initial pH, adsorbent dose, contact time, initial concentration and temperature on the adsorption capacity of Kraft lignin. The experimental results demonstrated that metal ion removal using Kraft lignin was a pH-dependent process, with the maximum adsorption capacity at an initial pH of 5-6+0.1. Adsorption was efficient with an adsorbent dosage of 8-10+0.2 mg/mL and temperature at 30+2o C used. Furthermore, the kinetics and equilibrium data are well explained by pseudo-second-order kinetics and the Freundlich adsorption isotherm model at 80 min contact time and 60+0.1 mg/L initial concentration. The best-fit adsorption isotherms and kinetics models were identified using statistical analysis. The thermodynamic parameters of the adsorption process were studied. Moreover, desorption and re-adsorption performance were studied. Kraft lignin still showed good adsorption performance up to six cycles of regeneration.