Fig. 8. (a) Cumulative amounts of Zn leached from 95%–5% sludge–sphalerite mixtures either with or without calcite, and (b) extractable forms of Zn in 95% sludge–5% sphalerite mixtures mixed with calcite, as a function of number of leaching steps in the flow-through experiment. The standard error bar (two replicates) is not shown when its length is similar to or smaller than the size of the corresponding marker.