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Field Experiment of an Innovative In-situ Remediation Method for Chromate

Based on a R&D- project in the field of in-situ remediation of chromium contaminated soil, a new approach on source (‘hot-spot’) decontamination in connection with pump-and-treat-technique has been developed at the Institute of Sustainable Waste Management and Technology (IAE) at the Montanuniversitaet Leoben.

Chromate contaminated soil samples from a former leather tannery in southern Austria have been investigated in the laboratory, concerning redox-reactions by adding reduction agents (RA) to the soil. The main objective of the treatment was to change the hexavalent chromium (CrVI) to the trivalent state (CrIII), which results in detoxification and immobilisation of chromium. Beside ferrous iron solutions (e.g. FeSO₄ and FeCl₂) sodium dithionite (Na₂S₂O₄) has been successfully tested in soil column experiments. However, during the first exchanges of pore volumes by irrigation, despite reduction and immobilisation, a high concentration of CrVI was observed in the leachate. Anionic ions (esp. SO₄^2-) apparently exchanged with and displaced CrO₄^2--ions, which accumulated in the percolated solution.
Iron itself is a powerful reactant for many contaminants considering remediation by electrochemical and sorption mechanism. On the one hand, aqueous ferrous iron has shown to reduce chromate compounds in wastewater effectively, but increased salinity and changes in pH may led to interfering precipitation effects. On the other hand, elemental zero valent iron (Fe0) is successfully used in reactive walls to treat several hazardous species by providing additional electrons to the redox process. Although this Fe0-treatment is already state of the art, problems arise from precipitation, surface passivation and gas clogging at the wall. To avoid these inter-ferences and utilize the advantages of Fe0, iron granulates are put into motion in a fluidized bed reactor. This leads to mechanical abrasion and therefore no passivation of the iron particles surfaces takes place. Other than that, mentioned abrasion-particles provide additional electrons for redox-reactions and adsorption-places. Moreover, turbulent flow in the fluidized bed reactor assures a thorough mixing of the water to be treated.

Copyright:	© Lehrstuhl für Abfallverwertungstechnik und Abfallwirtschaft der Montanuniversität Leoben
Quelle:	Depotech 2012 (November 2012)
Seiten:	6
Preis:	€ 3,00
Autor:	Peter Müller
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