The sorption experiments showed that some Zn precipitates/minerals may be formed on biochar, thus XRD analysis were performed on these biochars. As PN350 had a relatively low sorption capacity of Zn2+, we just focused on other three biochars (PN550, WS350, and WS550) and biochars loaded with Zn (denoted as PN550 + Zn, WS350 + Zn, and WS550 + Zn). Figure 2 shows the XRD spectra of the samples. The main mineral in PN550 was CaCO3, the peaks of quartz in PN550 were not obvious. The peak intensities of CaCO3 and quartz show that there could be large amount of CO32− and low amount of Si contained in PN550. In WS350 and WS550, two minerals can be detected, they were quartz and sylvine. Compared with PN550, WS350 and WS550 contained larger amount of Si species.