Transport of green rust and biochar mixtures in porous media for in-situ remediation of chlorinated ethylenes

Composite materials consisting of green rust (GR) and bone char (BC) have proven effective for reductive dechlorination of chlorinated solvents and could be used in the remediation of contaminated aquifers by injection of the materials. However, the injection of the materials is complex because successful dechlorination requires contact between the two types of particles post-injection. In this study, the transport and retention properties of GR and BC mixtures were investigated and improved in a series of sand column experiments and the data were used for development of a transport model. The mobility was improved significantly by sieving prior to injection because a fraction of particles/aggregates with larger diameters were removed or disaggregated. Depending on the preparation of the composite material, GR and BC exhibited either similar or dissimilar transport, likely because of the formation of hetero-aggregates, where GR acted as an anchor for transport of BC. Furthermore, by increasing the injection rate or the inlet concentration of the composite material the mobility increased accordingly. To simulate particle mobility, we developed a model based on the existence of a continuum number of retention sites with variable affinity for particle uptake. Although not all empirical aspects were correctly reproduced by the model, it provided a simpler and reasonably accurate description of particle mobility, setting the stage for simulations of injections in larger and more complex systems. Collectively, our findings indicate that reactive composite materials consisting of GR and BC can be injected in fine sand for the purpose of in-situ remediation.