Time-Dependent Changes of Zinc Speciation in Four Soils Contaminated with Zincite or Sphalerite

Abstract

The long-term speciation of Zn in contaminated soils is strongly influenced by soil pH, clay, and organic matter content as well as Zn loading. In addition, the type of Zn-bearing contaminant entering the soil may influence the subsequent formation of pedogenic Zn species, but systematic studies on such effects are currently lacking. We therefore conducted a soil incubation study in which four soils, ranging from strongly acidic to calcareous, were spiked with 2000 mg/kg Zn using either ZnO (zincite) or ZnS (sphalerite) as the contamination source. The soils were incubated under aerated conditions in moist state for up to four years. The extractability and speciation of Zn were assessed after one, two, and four years using extractions with 0.01 M CaCl(2) and Zn K-edge X-ray absorption fine structure (XAFS) spectroscopy, respectively. After four years, more than 90% of the added ZnO were dissolved in all soils, with the fastest dissolution occurring in the acidic soils. Contamination with ZnO favored the formation of Zn-bearing layered double hydroxides (LDH), even in acidic soils, and to a lesser degree Zn-phyllosilicates and adsorbed Zn species. This was explained by locally elevated pH and high Zn concentrations around dissolving ZnO particles. Except for the calcareous soil, ZnS dissolved more slowly than ZnO, reaching only 26 to 75% of the added ZnS after four years. ZnS dissolved more slowly in the two acidic soils than in the near-neutral and the calcareous soil. Also, the resulting Zn speciation was markedly different between these two pairs of soils: Whereas Zn bound to hydroxy-interlayered clay minerals (HIM) and octahedrally coordinated Zn sorption complexes prevailed in the two acidic soils, Zn speciation in the neutral and the calcareous soil was dominated by Zn-LDH and tetrahedrally coordinated inner-sphere Zn complexes. Our results show that the type of Zn-bearing contaminant phase can have a significant influence on the formation of pedogenic Zn species in soils. Important factors include the rate of Zn release from the contaminant phases and effects of the contaminant phase on bulk soil properties and on local chemical conditions around weathering contaminant particles.

Integrated Approaches of X‐Ray Absorption Spectroscopic and Electron Microscopic Techniques on Zinc Speciation and Characterization in a Final Sewage Sludge Product

“…However, there are also field‐scale studies showing the presence of ZnS NPs in oxic water conditions, indicating their persistence and dominance (of the total load) in such an environment (Priadi et al, 2012). Dissolution of bulk ZnS is known to take several years in moist, aerated soils, suggesting that the sulfide phase is relatively insensitive to the oxidation process (Hilber et al, 2007; Hita and Torrent, 2005, 2006; Voegelin et al, 2011). Further systematic investigations on the persistence and dominance of the ZnS phase by the type of sludge processing mode and the type of soil are required for a better understanding of the fate and behavior of ZnS NPs when they enter the soil environment through biosolids application.…”

Microscale Investigations of Soil Heterogeneity: Impacts on Zinc Retention and Uptake in Zinc‐Contaminated Soils

“…The NY whole soil fit identified Zn‐containing MF phases, which were also present in the μ‐XRD and have been identified previously (Yoon et al, 2012), although these phases were not present in the fraction‐averaged LCF. Although it was difficult to separate the MF from the LF and HF in the NY soil due to the extremely high LF mass, the whole soil results may indicate the presence of Zn‐phyllosilicate minerals, Zn‐containing hydroxy interlayer minerals, or Zn‐bearing layered double hydroxides for Zn retention in this soil, which have been shown to be Zn sinks in highly Zn‐contaminated soils after ZnS dissolution (Jacquat et al, 2009; Voegelin et al, 2011). Conversely, ZnS, which was identified in the fraction‐averaged LCF (40%) and many individual ROIs as well as via μ‐XRD (Table 2; Supplemental Fig.…”

Association between Field Liming and the Epidemic of Type 1 Diabetes

“…In the soil sample, whose pH was 7.7 (very high), (topsoil, calcareous, high organic matter content, Northern Switzerland), 13% from added Zn was tetrahedrallycoordinated after 4 years of incubation. [16] Soils contain various zinc sorbents. One of the most effective zinc sorbent is a clay mineral vermiculite.…”