[Desorption kinetics of 1,2,4,5-tetrachlorobenzene in sediments]

Sediment desorption batch technique experiments were conducted to study the influence of different types of natural organic matter (NOM) of sediment, initial solid-phase solute loading levels and temperatures on the desorption rates of 1,2,4,5-tetrachlorobenzene. A 4-parameter biphasic first-order kinetic model described the desorption of 1,2,4,5-tetrachlorobenzene from the sediments. The results indicate that the rate constants k(s) for the slowly desorbing fraction of each sample is up to 2 orders of magnitude lower than the corresponding rate constants k(r), for the rapidly desorbing fraction, suggesting that the slow desorption is the rate-limiting step. Desorption rate constants for the slowly desorbing fraction are found to range from 1.19 x 10(-3) h(-1) to 2.88 x 10(-3) h(-1) for sediments that contain different types of NOM, respectively; rates and extents of 1,2,4,5-tetrachlorobenzene on several sediments increases with lower degree of sediment NOM condensation. When the sorbed initial solid-phase 1,2,4,5-tetrachlorobenzene concentration increases from 13.3 microg x g(-1) to 25.3 microg x g(-1), the constant k(s) increases from 1.26 x 10(-3) h(-1) to 2.52 x 10(-3) h(-1). Moreover, the rate constants for desorption increase strongly with increasing temperature, and the activation enthalpies for slow desorption appears to be 9.45-21.43 kJ x mol(-1), which can provide information on the feasibility of bioremediation of aged contaminants.