Sorption and desorption of 1,4-dichlorobenzene on peat

Sorption and desorption of 1,4-dichlorobenzene (DCB) on peat (>92% organic matter) display large-scale hysteresis and nonlinearity. The magnitude of desorption hysteresis decreases in the order: untreated Pahokee peat (P)> acid treated peat (FP)> humin (TP). The desorption percentages are lower than 28% of the sorbed 1, 4-DCB after desorbing for 6 days. The sorption and desorption isotherms are well fitted to Freundlich equation, whose parameter 1/n ranges from 0.055 to 0.527. Moreover, the parameter 1/n of the desorption isotherm is significantly lower than that of the sorption isotherm, but the parameter logK increases on contrary to 1/n. The desorption isotherms are very well fitted to Langmuir equation, whose Q(m) decreases in the order: TP>FP>P. The apparent partition coefficients (K-p) increase with increasing sorption time or decreasing aqueous equilibrium concentration of DCB. And K-p of P is significantly higher than that of FP or TP.