(pH N 7) significantly limit the extent of Cr(VI) reduction. However,
there is a clear extension of the effective pH range of operation for the
foam with the smallest pore size. In particular, when the foam has a
pore size of 0.5 mm, the breakpoint of sudden residual Cr(VI) increase
is found at pH 6.8. A decrease in pore size to 0.3 mm signifies a shift of
the breakpoint to around 7.2. A possible explanation for this observation
is the almost doubled specific surface area, which in turn results in a
higher “effective” contact time.