Fig. 3. Macroscopic dissolution behavior of aged Ni precipitates on gibbsite showing the relative amount of Ni remaining on the surface following extraction with (a) 1 mM EDTA at pH 4.0, (b) HNO₃ at pH 6.0, (c) 3 mM oxalate at pH 4.0, and (d) 3 mM acetylacetone at pH 6.0 plotted against the total number of replenishments. The stability of the Ni precipitates increases with aging time