Adsorption of chromium(III) on lignin.

In order to assess the possibility of using lignin to remove Cr(III) from waters, the adsorption of Cr(III) on lignin isolated from black liquor, a waste product of the paper industry, was investigated. The influences of pH, lignin dosage, contact time, ionic strength, Cr(III) concentration and other metals were investigated. The Cr(III) adsorption was strongly dependent on pH and adsorbent dosage, but independent of ionic strength and other metal ions. The adsorption kinetic data can be described well with pseudo-second-order model and the equilibrium data can be well fitted using Langmuir two-surface model with a maximum adsorption capacity of 17.97 mg/g. Cr(III) adsorption on lignin was mainly through the ion-exchange mechanism and formed inner-sphere complexes with lignin. Successful application in removing Cr(III) was achieved by using a real wastewater sample. This study indicates that lignin has the potential to become an effective and economical adsorbent for the removal of Cr(III) from wastewaters.