Optimization of nano-scale nickel/iron particles for the reduction of high concentration chlorinated aliphatic hydrocarbon solutions

The use of nano-scale particles as a means of environmental remediation still provides a comparatively novel approach for the treatment of contaminated waters. The current study compares the reactivity of micro-scale Fe, nano-scale Fe and nano-scale Ni/Fe (nickel/iron) particles specifically for dechlorination of solutions containing 350 mg L−1 of TCE (concentration measured at a contaminated site in Derbyshire, UK). The results indicated that employing 1 g L−1 of reactive material for dechlorination in the monometallic form (both micro- and nano-scale) exhibited very little reduction capability compared with the bimetallic Ni/Fe nano-scale particles, containing 28.9% Ni (in molar), which achieved complete dechlorination of the TCE in solution within 576 h. Experiments were also performed to determine the optimum bimetallic composition of the Ni/Fe particles for TCE reduction. This revealed that 3.2% Ni was the optimum Ni/Fe molar ratio for both maximum dehalogenation performance and minimum release of Ni into solution. Using particles of the most effective bimetallic composition, experiments were carried out to determine the concentration required for optimal TCE reduction. Over the range of nano-scale particle concentrations tested (0.1–9 g L−1), reduction rates of TCE increased with greater TCE:nano-scale particle ratios. However, a concentration range of 1–3 g L−1 was selected as the most appropriate for site remediation, since more concentrated solutions demonstrated only small increases in rates of reaction. Finally, in order to test the long term performance and reactivity of the 3.2% Ni/Fe bimetallic nano-scale particles, weekly spikes of 350 mg L−1 TCE were injected into a 3 g L−1 nano-scale particle batch reactor. Results showed that the bimetallic nano-scale particles had the ability to reduce 1750 mg L−1 TCE and remained active for at least 13 weeks.