  The infiltration of a solute in a fractal porous medium is usually anomalous,
but chemical reactions of the solute and that material may increase the
porosity and affect the evolution of the infiltration. We study this problem in
two- and three-dimensional lattices with randomly distributed porous sites at
the critical percolation thresholds and with a border in contact with a
reservoir of an aggressive solute. The solute infiltrates that medium by
diffusion and the reactions with the impermeable sites produce new porous sites
with a probability $r$, which is proportional to the ratio of reaction and
diffusion rates at the scale of a lattice site. Numerical simulations for
$r\ll1$ show initial subdiffusive scaling and long time Fickean scaling of the
infiltrated volumes or areas, but with an intermediate regime with time
increasing rates of infiltration and reaction. The anomalous exponent of the
initial regime agrees with a relation previously applied to infinitely ramified
fractals. We develop a scaling approach that explains the subsequent time
increase of the infiltration rate, the dependence of this rate on $r$, and the
crossover to the Fickean regime. The exponents of the scaling relations depend
on the fractal dimensions of the critical percolation clusters and on the
dimensions of random walks in those clusters. The time increase of the reaction
rate is also justified by that reasoning. As $r$ decreases, there is an
increase in the number of time decades of the intermediate regime, which
suggests that the time increasing rates are more likely to be observed is
slowly reacting systems.
