| Popis: |
Assessing element speciation and solubility control mechanisms in multi-contaminated soils poses great challenges. In this study, we examined the speciation and mechanisms controlling the solubility of As and Zn in a soil historically contaminated with As, Cu, Cr, and Zn salts used for wood preservation. The leaching behavior of dissolved species, particles, and colloids was studied in an irrigation experiment with intact soil columns. Batch experiments were used to study the solubility of dissolved species as a function of pH (2-8). The speciation of As and Zn in bulk soil and leached particles was studied with microscale X-ray fluorescence (mu-XRF) and extended Xray absorption fine structure (EXAFS) spectroscopy. Chemical speciation and solubility were evaluated by geochemical modelling. mu-XRF of bulk soil and particles showed that As and Zn were correlated in space. Bulkand mu-EXAFS of As and Zn, in combination with calculated ion activity products of possible As-Zn minerals, suggested a koritnigite (ZnHAsO4 center dot H2O) phase controlling the dissolved fraction of As(V) and Zn with an apparent log K-sp of 21.9 +/- 0.46. This phase lowered the solubility of As by almost two orders of magnitude in soil at pH > 5, and could therefore be of great importance at other multi-contaminated sites. |
