For PN550 and WS550, with the volatilization of organic matters and completion of thermal decompositions, the ash content increased, which made the fraction of Zn precipitates/minerals close to 100%. Compared with PN350, PN550 contained much more CO32− and OH−, thus the sorption capacity of Zn on PN550 was higher than that of PN350. For WS550, a large fraction of hemimorphite was formed. This was due to a considerable amount of released Si species. The formation of hemimorphite on WS550 can be divided into three steps57 (Fig. 4, Path 4): (1) the formation of colloid of Zn(OH)2 under alkaline condition, (2) the adsorption of dissolved silicates on Zn(OH)2 colloid and co-precipitation of silicate and Zn(OH)2, and (3) the reconstruction of the co-precipitates structure and formation of amorphous hemimorphite. Due to the complexity of the sorption system and short reaction time, the well-crystallized hemimorphite was unlikely to form. Thus, it cannot be detected by the method of XRD. Although there were also some Si species released from WS350, only a small portion of hemimorphite was formed. This may be caused by the low amounts of OH− and Si species released from WS350 biochar.