Solubility and transport of Cr(III) in a historically contaminated soil – Evidence of a rapidly reacting dimeric Cr(III) organic matter complex

Abstract

Chromium is a common soil contaminant and, although it has been studied widely, questions about its speciation and dissolutions kinetics remain unanswered. We combined information from an irrigation experiment performed with intact soil columns with data from batch experiments to evaluate solubility and mobilization mechanisms of Cr(III) in a historically contaminated soil (>65 years). Particulate and colloidal Cr(III) forms dominated transport in this soil, but their concentrations were independent of irrigation intensity (2-20 mm h). Extended X-ray absorption fine structure (EXAFS) measurements indicated that Cr(III) associated with colloids and particles, and with the solid phase, mainly existed as dimeric hydrolyzed Cr(III) bound to natural organic matter. Dissolution kinetics of this species were fast (≤1 day) at low pH (<3) and slightly slower (≤5 days) at neutral pH. Furthermore, it proved possible to describe the solubility of the dimeric Cr(III) organic matter complex with a geochemical equilibrium model using only generic binding parameters, opening the way for use of geochemical models in risk assessments of Cr(III)-contaminated sites.

Leaching of Five Pesticides of Contrasting Mobility through Frozen and Unfrozen Soil

“…A solution of artificial rainwater (Löv et al, 2017) was prepared [0.58 mg L −1 NaCl, 0.70 mg L −1 (NH 4 ) 2 SO 4 , 0.50 mg L −1 NaNO 3 , 0.57 mg L −1 CaCl 2 ] and acidified with HCl (0.95 mL L −1 37%) to a pH of ~5. The artificial rainwater was stored at ~4°C in 20‐L plastic containers.…”

Modeling rare earth elements binding to humic acids with model VII

“…For Fe, formation of a polynuclear species was also considered, since spectroscopic studies have shown that HA can stabilize such species of poorly soluble elements, such as Fe(III) (Gustafsson et al, 2007;Karlsson and Persson, 2010;Mikutta and Kretzschmar, 2011;Vantelon et al, 2019), but also Cr(III) (Löv et al, 2017) or Pu(IV) (Marsac et al, 2014). Because these complexes might involve from two to four metal cations, the formation of a trimer was considered for every HA site according to the following reaction:…”

Eco-functionality of organic matter in soils

“…Although the selectivity of these classical extractions can be challenged (i.e. their ability to fully distinguish between organic and inorganic trace element fractions), recent measurements by extended X-ray absorption fine structure spectroscopy (EXAFS), which enables identification of specific chemical bonding, demonstrated predominant association with SOM for trace metals such as Fe, Cd, Cu and Zn (Gustafsson et al 2007;Löv et al 2017;Sarret et al 2004;Strawn and Baker 2008).…”