Microwave-assisted synthesis of high carboxyl content of lignin for enhancing adsorption of lead

An efficient lignin adsorbent for Pb2+ in water was synthesized by crosslinking microwave-assisted carboxymethyl lignin (C-MCML) and the saturated adsorption capacity for Pb2+ was 302.3 mg/g. Microwave irradiation showed a greater assisted ability in the carboxymethylation than that of traditional heating, and the carboxyl content of microwave-assisted carboxymethyl lignin could be raised to 3.61 mmol/g. The adsorption behavior of C-MCML also was studied by varying different parameters like pH, initial concentration of metal ions and shaking time. The adsorption isotherm was fitted well by Langmuir model, and the fitting saturated adsorption capacity was 323.6 mg/g. Meanwhile, the results of FTIR and XPS shown that main Pb2+ adsorption mechanimis was ion exchange by carboxyl. The adsorption capacity of C-MCML was still maintained at 90% after recycled for 10 times.