Removal of lead, copper, cadmium, zinc, and nickel from aqueous solutions by alkali-modified biochar: Batch and column tests

Engineered biochar was obtained through slow pyrolysis of hickory wood and then further modified with NaOH. After modification, biochar's surface area, cation-exchange capacity, and thermal stability were significantly improved. The modified biochar exhibited much larger (2.6-5.8 times) metal adsorption capacities than the pristine biochar. Competitive batch adsorption of mixed metal ions (Pb²⁺, Cd²⁺, Cu²⁺, Zn²⁺, and Ni²⁺) showed preferential adsorption of Pb²⁺ and Cu²⁺ onto the modified biochar. The alkali-modified biochar in a fixed-bed column also showed strong ability to filter heavy metals from aqueous solutions. The alkali-modified biochar thus can serve as alternative absorbent for heavy metals.