Clear-cut & effective
remediation of hexavalent chromium

Pollution of soil and groundwater with the heavy metal chromium and more specific its hexavalent form (Cr(VI)), is one of the most frequent encountered soil problems in the industrialized world since chromium is used abundantly in the sector of wood conservation and metal plating.

MAVA has developed a rather clear-cut and very effective technique to remediate hexavalent chromium called DivIRed (Divalent Iron Reduction). This technique aims to precipitate Cr(VI) into the less toxic and insoluble trivalent chromium (Cr(III)) form by the technique of In-Situ Metal Precipitation (ISMP) by In-Situ Redox Manipulation (ISRM).
The key role in this remediation technique is reserved for divalent iron (Fe(II)) which directs the predominant chemical reaction and the chemical dithionite which keeps iron in its divalent and soluble form.

Site specific conditions determine if there is enough native iron available or that additional iron has to be supplied, and if the prevailing soil conditions support the long term stability of the formed non-toxic precipitates. The stability of the precipitates, and hence the remediation, is mainly governed by the presence/absence of natural occurring manganese minerals. It is already clear based upon our experience that sites where conditions regarding stability are negative, are very rare.

This remediation technique can be applied after following preliminary phases:
•    Formulating a conceptual site model (SCM)
•    Determination of site specific parameters (main soil properties such as pH, redox status, mineral composition, and granulometry; natural       soil reductive demand; natural available iron; co-contaminants; stability of formed precipitates; ….)
        Go-No-Go decision
•    Determination of the optimal injection technique (direct push, push-pull, gravitational, hydraulic fracturing, …)
•    Pilot scale remediation
        Go-No-Go decision
•    Design of full-scale remediation

MAVA has already a nice reference of DivIRed on the Brussels Airport of which the results were presented during an oral presentation  on the 2010 international Consoil Conference in Salzburg, Austria.

The DivIRed-technique was recently rewarded by the VITO (Flemish Institute of Technology) as the best available and most innovative in-situ metal precipitation (ISMP) technique and is demonstrated on the EXOBOIS site in Sint-Pieters-Leeuw (near Brussels).
We aim with this technique for businesses with chromium pollution in the sectors of wood preservation and metal plating.