Repeatable use of wood ash to remove lead from contaminated water

The present study conducted lead sorption experiments using wood ash to elucidate its capacity and mechanisms of lead removal, to evaluate the recovery of lead removed by wood ash and the reuse of wood ash residue left after lead recovery. The maximum lead removal capacity of wood ash was 3.08 mmol g⁻¹, which was higher than previously reported values. An X-ray diffraction analysis showed that the lead phase removed by wood ash was mainly hydrocerussite probably resulting from the sequential reactions of wood ash with lead ions, dissolution of carbonate ions from wood ash, precipitation of cerussite reacting with lead ions and then alteration to hydrocerussite from cerussite. In addition to the precipitation of hydrocerussite, lead sorption by the acid-insoluble matter in wood ash was also evident. The percentage of lead removed by wood ash in pH 2 solution was very low at 17 %, whereas that at pH 6 was 99 %. Almost all lead removed by wood ash was easily recovered using 0.1 M HNO₃, and the residue remaining after lead recovery was able to remove lead repeatedly at rates of 13–22 mg g⁻¹.