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Fig. 3. Cumulative amounts of (a) Fe, (b) Zn, and (c) S leached from sludge and sludge–calcite samples in the flow-through experiment. Each value is the mean of two replicates. The standard error bar (two replicates) is not shown when its length is similar to or smaller than the size of the corresponding marker. Despite the large standard errors for the sludge samples (solid symbols), the rates of leaching of either Fe, Zn, or S (as measured by the slope of the corresponding y–x regression line) did not differed significantly (P < 0.05) between replicates.
