Aging effect on Zn retention on a calcareous soil: Column experiments and synchrotron X-ray micro-spectroscopic investigation

- Zinc retention on soil column induced a calcium release.
- Increasing soil aging time enhanced its zinc retention capacity.
- Zinc decreasing mobility over time is evidenced by leaching experiments.
- Zn redistribution occurred from exchangeable sites to stronger binding sites.
- Zn redistribution occurred from organic matter to primarily iron oxy(hydr)oxides.

In this study, a combination of column experiments and micro-analytical techniques exploiting synchrotron generated X-rays was used to assess the effect of aging time on Zn retention and mobility in the specific case of calcareous soils (high pH value, ≈ 8). The samples were subjected to aging for 2, 6, 17, and 63 days. Freshly added Zn mainly existed as an exchangeable form, and this metal fraction decreased over time due to Zn redistribution to stronger binding sites. Thus, after aging for 63 days, 45% of Zn is remobilized from exchangeable sites to stronger binding sites. μ-XRF maps were used to find correlations among elements in the sample, and μ-XANES spectra were recorded to precise Zn speciation. These analyses evidenced an increasing partitioning of Zn from organic matter to iron oxy(hydr)oxides over time. The occurrence of hydrozincite is evidenced in all samples.