Sorption of toluene by humic acids derived from lake sediment and mountain soil at different pH.

Contamination of soil and groundwater with BTEX compounds (benzene, toluene, ethylbenzene, and xylene) depends on the sorption behavior of these compounds by soil organic matter (SOM) and humic acids (HAs). In this study sorption of toluene by HAs extracted from lake sediment and mountain soil was investigated. HA suspensions were adjusted to pH 4.00, 6.00, or 8.00 and made to the concentration of 200 mg L(-1). Each HA suspension or solution was subjected to particle size analysis using high performance particle sizer (HPPS). The particle size of HA from lake sediment was around 1000-1200 nm while that from mountain soil was 220-320 nm at suspension pH 4.00. Kinetic studies showed that sorption of toluene by the two HAs followed pseudo-first-order and mainly pseudo-zero-order kinetics. At suspension pH 4.00, the sorption of toluene by the two HAs was best described by Langmuir and Temkin adsorption isotherm models. Further, sorption of toluene by the lake sediment HA was significantly greater than that by mountain soil HA. It was thus suggested that the lake sediment HA with larger particle size may develop beneficially chemical conformation for sorption of toluene and related compounds in soil and associated environments.

Effect of Cl-, SO4(2-), and fulvate anions on Cd2+ free ion concentrations in simulated rhizosphere soil solutions.

The binding between heavy metals and corresponding ligands affects their chemical behavior and toxicity in soil environments. The mechanisms of competitive complexation and/or chelation between Cd(2+) free cations and preferential concentrations of Cl(-), SO(4)(2-), and fulvate anions were investigated in simulated soil solutions at pH 4.00, 5.00 and 6.00. The Cd(2+) concentrations were calculated by a proposed equation, simulated by MINTEQ software, and directly determined by ion chromatography (IC). When Cl(-)/Cd or Cl(-)/Cd with SO(4)(2-)/Cd molar ratios of 3.18 and 4.05, the differences among Cd(2+) concentrations calculated by equation, simulated by MINTEQ software, and directly determined by IC were not significant, but their differences were pH independent for considering Cl(-)/Cd molar ratio and pH dependent for Cl(-)/Cd and SO(4)(2-)/Cd molar ratios. When Cl(-)/Cd, SO(4)(2-)/Cd, and additional FA/Cd molar ratios of 3.18 and 4.05, the Cd(2+) concentrations calculated by equation were significantly larger than those simulated by MINTEQ and determined by IC because in simulation and determination of Cd(2+) concentrations by IC, the complexation of Cd(2+) with ligands to form CdCl(+), CdSO(4), FACd(+) and FA(2)Cd had been considered, whereas in calculation this complexation aspect was ignored. Though IC can be used to determine Cd(2+) concentration in rhizosphere soil solutions ion chromatographic peak of Cd(2+) in 0.1M HCl saturation extract of slightly acidic soil and in deionized distilled water saturation extract of acidic soils still may be shielded by the vicinal chromatographic peaks of Mg(2+) and Mn(2+), respectively. The Cd(2+) concentrations in rhizosphere soil solutions of acidic or slightly acidic soils calculated by equation and/or simulated by Model may thus be used as potential alternatives for those determined by IC.