Arsenic, lead, and zinc compounds in contaminated soils according to EXAFS spectroscopic data: A review

The application of the synchrotron technique of the third generation in soil science has permitted researchers to perform a quantitative mineralogical microanalysis in undisturbed samples and to reveal the relationship between the microelements and the solid phase of soils. Three principal methods are used in this technique: microfluorescence (μXRF), microdiffraction (μXRD), and the expanded analysis of the fine structure of the adsorption spectra. By the data of EXAFS spectroscopy, secondary arsenic was found to occur in three forms in soils, i.e., As adsorbed on iron hydroxides, scorodite (FeAsO 4 · 2H 2 O, and As 5+ containing jarosite. Despite the high share of carboxyl groups in the organic substance of soils, lead is more readily chelated by the functional groups of aromatic rings to form bidentant complexes. Lead phosphates are the most stable form of Pb in soils. One of the phosphates, i.e., pyromorphite Pb 5 (PO 4 ) 3 Cl has been found in ore tailings, lawn soils, soils near some chemical plants, and in soils within geochemical anomalies. The secondary Zn compounds are represented by Zn-containing silicate (kerolith) Si 4 Zn 3 O 10 (OH) 2 and, to a lesser extent, by zinc fixed by manganese oxides (birnessite) and iron hydroxides (feroxyhyte).