Adsorption of bisphenol A on lignin: effects of solution chemistry

Adsorption of bisphenol A on a lignin isolated from black liquor, a waste product of the paper industry, was investigated to assess the possibility of using the lignin to remove bisphenol A from waters. Effects of pH, ionic strength, heavy metals, and dissolved organic matter (DOM) on adsorption were examined. Adsorption equilibrium was approached within 5 h. The adsorption capacity of bisphenol A on lignin was as high as 237.07 mg/g. Ionic strength had no influence on the adsorption, while higher pH above 7.5 inhibited bisphenol A adsorption due to the repulsive electrostatic interaction between bisphenolate anion and the negatively charged lignin surface. The presence of heavy metals of copper and lead increased the adsorption by 11.90 and 26.80 %, respectively, possibly through modifying the physiochemical configuration characteristics of labile fraction of the lignin and reducing the polarity of it. No obvious impact of DOM on the adsorption was observed. The results of this study suggest that lignin is a promising adsorbent material to remove bisphenol A in wastewater containing complex components such as heavy metals and DOM, particularly at acid and neutral conditions.