values tested (26.50% and 21.77% removal degrees for the
0.15 m and 2 mm samples respectively) (Fig. 2b). The increase of
solution pH can enhance the deprotonation process on biochar surface
and create more negative sites that enhance the adsorption of
Pb2+ (Mohan et al., 2014). Hence the amount of Pb2+ adsorbed was
significantly greater at higher initial pH values (99.92% and 92.83%
removal degrees for the 0.15 mm and 2 mm samples respectively
at initial pH of 10, P < 0.001 compared with removal degrees at
pH of 2 for both samples) (Fig. 2b).