The formation of different Zn species on biochars confirmed heterogeneous property of these materials which resulted in the co-existence of various sorption mechanisms during Zn retention by biochars. The consumption of OH−, CO32−, or the sorption sites (oxygen-containing functional groups) on biochars by Zn2+ to form different Zn species led to the release of Ca2+ and Mg2+. When the studied raw biochars were added into the acid solutions, the ions OH− and CO32− in biochar were consumed and even some oxygen-containing functional groups were protonated. This was against the formation of different Zn species, which could lead to the decrease in the sorption capacities of Zn on biochars.