Determination of reaction rate parameters for the acid copper chromate fixation reactions on oak (<i>Quercus castaneifolia</i> C. A. Mey) sapwood

Acid copper chromate fixation reactions on oak (Quercus castaneifolia C. A. Mey) sapwood were characterized by at least two distinguished reaction periods which differ in their kinetic behavior, particularly reaction rate. In this research, chemical rate equation parameters were studied in detail as a function of chromium fixation time. Theoretically, the kinetic data were distinguished between the adsorption and reduction reactions and consequently, the rate parameters were determined for each stage distinctly. The obtained results showed that at the investigated thermal range (25–33°C), almost for every 3°C increase in temperature the reaction duration has decreased 20.4 min for the first reaction period and 78 min for the second reaction period. Besides that, in all sample replications, up to 58.3% of hydrogen ions function at the reduction reactions of the initial period, demonstrating that acidity (H+ ions) has a major effect on reaction rate constant. Accordingly, adsorption reactions of the hexavalent chromium at the starting point follow a pseudo-first-order kinetic reaction. Different to the adsorption reaction the CrVI reduction reaction is exothermic with a measured exothermal energy of 48.2 kJ/mol.