Quantifying the contribution of different sorption mechanisms for 2,4-dichlorophenoxyacetic acid sorption by several variable-charge soils.

摘要: Previous research with phenolic, carboxylic, and urea type organic acids demonstrated that hydrophilic sorption was primarily due to anion exchange, which linearly correlated chemical acidity (pKa) the soil exchange capacity. However, for dichlorophenoxyacetic acid (2,4-D), by a kaolinitic much higher than expected relative all other acid-soil data. The enhanced hypothesized involve calcium bridging of 2,4-D domains. In this study, mechanisms contributing variable-charged soils were probed quantified measuring from CaCl2, KCl, CaSO4, KH2PO4, Ca(H2PO4)2 solutions. Linear coefficients estimated different electrolytes decreased as follows: CaCl2 > KCl CaSO4 approximately equal KH2PO4. Differences in phosphate solutions attributed domains, ranged between 46 94% across soils. specifically Ca-bridging 2,4-D's carboxyl group silanol edge on kaolinite quartz negligible 40% depending mineral type. 16 91%, followed trends pKa developed previously acids, well cation capacity ratio (AEC/CEC). sum contributions agreed be All hydrophobic processes, linear free-energy relationship pH-dependent carbon-normalized octanol-water partition several acids.