Heavy metal removal with lignin

Increasing discharges of toxic heavy metals and the concomitant environmental damage has resulted in stringent standards for effluent disposal. Techno‐economic limitations of conventional metal removal methods dictate the development of alternate, inexpensive techniques to meet the discharge criteria. Heavy metal removal with lignin, a multifunctional group polymer easily recovered from pulp and paper industry waste, appears to be a potential solution. Copper and cadmium removals by solid lignin are governed by the pH of the metal solution, lignin dose and lignin / metal ratio. The optimum pH for maximum metal removal was 5.5 for copper (1.2 mg/gm lignin) and 6.5 for cadmium (2.5 mg/gm lignin). The optimum contact time was one hour. Metal removal was accompanied by release of hydrogen ions in solution, which at higher concentration seem to adversely affect the metal removal. Maintenance of constant optimum pH increased the metal removal efficiencies by 38 % for copper and by 125 % for cadmium.