Formation and Immobilization of Cr(VI) Species in Long-Term Tannery Waste Contaminated Soils

Abstract

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 CrFeO 3 , and CaCrO 4 (13.2−25.3). Our results demonstrate that (i) Cr(VI) is immobilized in soils and (ii) mechanisms of Cr(VI) immobilization are CaCrO 4 precipitation and recrystallization with Fe (hydr)oxides.

Evolution of redox activity of biochar during interaction with soil minerals: Effect on the electron donating and mediating capacities for Cr(VI) reduction

“…As shown in Fig. S20, the distribution of Cr was overlapped with soil mineral ions (Al and Ca) on the biochar surface, probably due to the complexation of chromate with mineral ions, immobilization of Cr on newly formed minerals (Shi et al 2020), or co-precipitation into new minerals (Mullet et al 2007).…”

Atomic Spectrometry Update: review of advances in elemental speciation

“…The researchers point out that the device is field-deployable and thus the accuracy of determination of the separated species at a later time is unaffected by any interconversion that may occur during transport and storage. To study Cr speciation in soils contaminated by tannery waste, Shi et al 111 applied (a) US EPA method 3060A (alkaline extraction) and US EPA method 7196A (spectrophotometry with DPC), and (b) synchrotron-based XANES and spatially resolved XRF. The XANES results indicated that a significant portion of the Cr VI , was not removed by the phosphate buffer extraction, and the XRF maps showed that Cr was associated with both Mn and Fe.…”

Improvement of the Stability of IO3–-, SeO32–-, and SeO42–-Coprecipitated Barite after Treatment with Phosphate

“…It shows excellent performance in the removal of cations (e.g., Cs + , Ca 2+ , Sr 2+ , and Ra 2+ ) from aqueous media. − It is generally believed that coprecipitated ions are not released unless the host mineral is dissolved. Thus, coprecipitation with barite − or other minerals − is expected to function as a cost-effective method to immobilize long-lived radionuclides and is a promising tool to remove toxic and/or radioactive elements from polluted solutions.…”