H+-promoted dissolution of Ni(OH)(2): A turbidimetric study

Results related to the dissolution mechanism of beta-Ni(OH)(2) particles in acidic (HClO4) media are reported. The influence of the H+ concentration and temperature on the dissolution kinetics of these particles was followed using a turbidimetric method, which appeared to be a useful tool for this kind of study. Surface charge (H+ adsorption) and electrokinetic measurements were also used to characterize the adsorption and charging behavior of the Ni(OH)(2)-aqueous solution interface. The point of zero charge was in the pH 10.4 +/- 0.2 range. Protons as well as temperature promoted the dissolution of Ni(OH)(2). All the studied samples exhibited a fractional reaction order of 0.35 +/- 0.03 when the dissolution rate law was expressed in terms of the H+ concentration in the aqueous solution; conversely, an integer reaction order of 2 was found when the rate law was expressed in terms of protonated surface site density. The results suggest that Ni(OH)(2) dissolves through a surface-controlled reaction in which two proton adsorption steps precede the detachment of Ni(II) species. The apparent activation energy of the process was 9-10 kcal mol(-1).