Carbo-Iron – An Fe/AC composite – As alternative to nano-iron for groundwater treatment

Carbo-Iron®1 is a novel colloidal composite consisting of activated carbon colloids (ACC) with a d50 particle size of 0.8 μm and anchored deposits of zero-valent iron clusters. This study discusses the principal material properties of Carbo-Iron colloids (CIC) relevant for groundwater treatment in comparison to commercially available nano-sized zero-valent iron (nZVI). CIC with 10–25 wt% Fe0 have been developed and tested in laboratory studies for their suitability as dehalogenation reagent and are especially designed to overcome some limitations known from the utilization of nZVI: CIC combine the sorption properties of ACC and the chemical reactivity of nZVI. In column tests, flushed-in CIC showed an enhanced mobility in sediment material compared to nZVI, without the need for colloid stabilizers. However, adding 1–3 wt-% of carboxymethyl cellulose (CMC) related to CIC as colloid stabilizer was found to assure long-lived stable suspensions under laboratory conditions which may additionally support the already improved mobility of the CIC and the homogeneity of particle deposition on the sediment matrix. The hydrophobic character of the ACC carrier provides a high affinity of CIC to non-aqueous phase liquids (NAPL). In undisturbed flow, the reactive particles are collected at the water-NAPL interface. The reagent accumulation at the organic phase is necessary for a successful source attack.

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► Composite of iron and activated carbon for in-situ groundwater treatment.
► Carbo-Iron colloids combine the enrichment of pollutants and the destruction in the sorbed state.
► Carbo-Iron colloids show enhanced mobility in porous media.
► The composite particles are collected by solvent droplets.