1 Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, H3G 1M8, Canada.
2 Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, H3G 1M8, Canada. Electronic address: chunjiang.an@concordia.ca.
3 Department of Chemical and Materials Engineering, Concordia University, Montreal, H3G 1M8, Canada.
4 Faculty of Engineering and Applied Science, Memorial University of Newfoundland, St. John's, A1B 3X5, Canada.
5 Fisheries and Oceans Canada, Ecosystem Science, Ottawa, K1A 0E6, Canada.
6 Institute of Energy, Peking University, Beijing, 100871, China.

In the present study, an innovative, environmentally benign recyclable, and magnetically mediated surface washing fluid based on water-dispersible magnetite nanoparticles has been designed and investigated for the cleanup of oiled beach sand. The characterization results showed that the as-prepared magnetite nanoparticles had a spherical morphology with an average diameter of around 250 nm and the particle surface was successfully functionalized with carboxyl groups. The magnetite nanoparticles could be easily re-dispersed by lightly shaking the dispersion after withdrawing the magnet. In addition, prolonging the magnetic field strength and response time promoted the oil recovery from the washing effluent. Thermodynamic modeling was applied to theoretically elucidate the mechanism and the results were in alignment with the experimental findings. Four mechanisms were identified to likely affect surface washing performance. The magnetic fluid had a relatively low operation cost and good reusability for a number of multiple cycles. In terms of other operational limitations, it was noted that washing performance declined as clay (kaolinite) concentrations and salinity values increased. Based on these findings, the proposed stable, low-cost magnetite fluid formulation warrants further investigation as the basis for an operational system for the cleanup of sand beaches contaminated by oil spills.