Abstract: Activated carbon（AC）was prepared from pulping back liquor lignin with chemical and physical methods and the adsorption capacity of AC was investigated. The results showed that，for H₃PO₄ activation agent，the AC preparation needed not secondary activation. However，for ZnCl₂ activation agent，the AC preparation needed secondary activation. The optimal operation parameters were temperature at 550 ℃，time for 2 h，impregnation ratio 2∶1 for H₃PO₄. For ZnCl₂，the optimal operation parameters of the first activation were temperature at 550 ℃，time for 2 h，impregnation ratio 2∶1，the optimal operation parameters of the secondary activation were the flow rate of CO₂ was 80 mL/min，the activation time was 30 min and the temperature was 850 ℃，the AC prepared with this method met the standards of first class of AC for purification water. Generally，the secondary activation by CO₂ de?creased the yield of AC，but increased the proportions of mesopores and macropores in AC.

Key words: lignin, activated carbon, phosphoric acid, Zinc chloride, carbon dioxide