Kinetics of hydrocarbon and pesticide removal from clay soils during thermal treatment in a pilot-scale rotary kiln

Abstract

The kinetics of hydrocarbon removal from contaminated clay soils during thermal treatment in rotary kilns were studied experimentally, and kinetic parameters were obtained for simple first-order models. Results are given for seven hydrocarbons: toluene, naphthalene, n-hexadecane, lindane (γ-HCH or 1,2,3,4,5,6-hexachlorocyclohexane), DDT (1,1′-(2,2,2-trichloroethylidene) bis [4-chlorobenzene]), DDD (1,1′-(2,2-dichloroethylidene) bis [4-chlorobenzene]), and DDE (1,1-dichloro-2,2-bis [ p-chlorophenyl] ethylene). The activation energies ranged from 18 kJ/mol for toluene on wet soil, to 90 kJ/mol for the chlorinated pesticides. All the kinetic data were obtained in a 130 kW pilot-scale rotary kiln. The wall temperature of the kiln was 700°C for the pesticides. Three of the hydrocarbons, toluene, naphthalene and n-hexadecane, were studied on both wet soil (5.0 and 8.5 wt%) and on oven-dried soil at temperatures ranging from 300 to 650°C in order to understand better the effects of water on desorption rates. Water increases the rate of desorption of toluene but decreases the rates for the heavier compounds. The pilot-scale data and correlations should be useful to those who are operating and/or designing rotary kilns to remediate soils thermally. A methodology for taking pilot-scale results and using them to estimate full-scale performance is given.