KINETICS AND MECHANISM OF THE ENHANCED REDUCTIVE DEGRADATION OF CCL4 BY ELEMENTAL IRON IN THE PRESENCE OF ULTRASOUND

Enhanced rates of sonolytic degradation of CCl4 in the presence of Fe- 0 are demonstrated. In Ar-saturated solutions, the first-order rate co nstant for CCl4 degradation is k(US) = 0.107 min(-1), whereas in the p resence of Ar and Fe-0, the apparent first-order rate constant is foun d to depend on the total surface area of elemental iron in the followi ng fashion: k(obs) = (k(US) + k(Fe0)A(Fe0)) min(-1), where k(US) = 0.1 07 min(-1), k(Fe0) = 0.105 L m(-2) min(-1), and A(Fe0))= reactive surf ace area of Fe-0 in units of m(2) L-1. In the coupled ultrasound and i ron system, the contribution to the overall degradation rate by direct reaction with Fe-0 results in an overall rate enhancement by a factor of 40. These enhancements are attributed (I)to the continuous cleanin g and chemical activation of the Fe-0 surface by the combined chemical and physical effects of acoustic cavitation and (2) to accelerated ma ss transport rates of reactants to the Fe-0 surfaces. Additional kinet ic enhancements are due to the production of H+ during the course of t he reaction. Furthermore, the concentrations of the principal reaction intermediates, C2Cl6 and C2Cl4, are influenced substantially by the t otal available surface area of Fe-0.