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Chromium speciation in naturally contaminated soils appears more complex than spiked studies have shown. This study characterized Cr speciation (oxidation states; availability; molecular geometry) intended to highlight the genesis of immobile Cr(VI) species in long-term tannery waste-contaminated soils. In a series of samples obtained from Shuitou in China, chemical extraction methods showed that Cr(III) was dominant(>96.7% of total Cr), with Cr(VI) concentration up to 144 mg kg–1. Of the total Cr(VI) present, immobile Cr(VI) represents >90%. Synchrotron-based X-ray near-edge structure spectroscopy (XANES) showed the occurrence of Cr(VI), which was not removed by phosphate buffer extraction, confirming a significant amount of immobile Cr(VI) fractions in soils. X-ray fluorescence maps exhibited the heterogeneous distribution of Cr in soils associated with both Mn and Fe. Such a distribution suggests Cr(III) oxidation to Cr(VI) by Mn oxides and a possible immobilization of both Cr(III) and Cr(VI) onto Fe (hydr)oxides. Linear combination fitting of XANES spectra revealed that fractional weights (%) in samples were CrFeO3(49.3–53.6), CrOOH (22.3–30.8), and CaCrO4(13.2–25.3). Our results demonstrate that (i) Cr(VI) is immobilized in soils and (ii) mechanisms of Cr(VI) immobilization are CaCrO4precipitation and recrystallization with Fe (hydr)oxides.

An ionic liquid (IL), 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([Emim][BF4]), was investigated for its effectiveness on enhancing oil recovery from hazardous crude oil tank bottom sludge using a solvent. A range of solvent (cyclohexane)/sludge ratio (2–8 mL/g), shaking speed (100–400 rpm), extraction duration (10–120 min), and IL/sludge ratio (0.25–1.0 mL/g) were examined. The addition of IL (i.e., 1 mL/g of IL/sludge ratio) increased total petroleum hydrocarbon (TPH) recovery by 9.4% (from 84.4 ± 2.4 to 93.8 ± 2.3% at the solvent/sludge ratio of 8 mL/g). An orthogonal experimental design was subsequently applied to optimize extraction conditions. The use of IL (i.e., 0.1 mL/g of IL/sludge ratio) with the solvent yielded higher TPH recovery (above 95%) at shorter extraction duration (10 min), lower solvent/sludge ratio (4:5 mL/g), and lower energy consumption (100 rpm). The recovered oil had similar calorific value but a higher F3 fraction compared with crude oil. The results suggested that the IL-enhanced solvent extraction with lower solvent consumption is an effective approach for oily sludge treatment.

The molarity of ethanol droplet (MED) test is a popular rapid method for assessing soil water repellency under field and laboratory conditions. This paper reviews the theoretical basis of the MED test, discusses controllable and uncontrollable sources of error affecting its results, and proposes a detailed protocol for its standardization. Soil water repellency is a function of soil surface chemistry. More specifically, it is a function of the free energy of the solid/gas interface in soil (γSG). Because γSGis not directly measurable in the laboratory, soil water repellency must be assessed using thermodynamically related parameters such as the initial advancing contact angle () or the work of wetting (WW). The MED test can be used to determine , and in turn WW, but only if some simplifications are accepted and the test is performed under standard controlled conditions. Wetting theories exclude the dissolution or swelling of the solid by the liquid or chemical reactions between the liquid, solid, and gas phases that change system composition. Consequently, for MED tests to give valid estimates, system composition must not change measurably during 10 s of solid/liquid contact. We discuss system conditions that should be controlled before and during MED testing to improve the validity of test results. Finally, we propose a detailed MED testing protocol for possible adoption by commercial analytical laboratories and the soils research community.

Ratios of 15N to 14N often differ between pools within ecosystems, and measurement of these natural‐abundance ratios might allow transfers among pools to be traced. We tested this approach for its ability to trace biologically‐fixed N in conifer plantations. Ratios of 15N to 14N were measured in soil total‐N, ammonium, and nitrate, and in foliage of Douglas‐fir [Pseudotsuga menziesii(Mirb.) Franco] and red alder (Alnus rubraBong.) at four sites. Two ecosystems were sampled at each site, one a pure conifer stand and the other a mixed alder‐conifer stand. Isotope ratios differed significantly among stands, but no pattern was consistent across all locations. Soil NH+4at all sites (and soil nitrate at one site) was significantly depleted in 15N relative to other N pools. Isotope discrimination clearly occurs during N transfers at these sites, but the 15N natural‐abundance method does not provide a simple picture of N cycling at the ecosystem level.