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

MARCELO J. AVENA; CARLOS P. DE PAULI

COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1996 vol. 108 p. 181 - 189

0927-7757

Results related to the dissolution mechanism of fl-Ni(OH)2 particles in acidic (HC104) 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.