Abstract
Sedimentation dynamics of magnetite (γ-Fe3O4) nanopowders (10 - 20 nm) in water in the presence of a gradient magnetic field was studied by optical and Nuclear Magnetic Resonance (NMR) relaxometry methods. The magnetic field B ≤ 0.3 T, dB/dz ≤ 0.13 T/cm was produced by the system of permanent strip magnets. The initial sedimentation rate of the nanoparticles in water and under magnetic fields is higher for less concentrated suspensions (c0 = 0.1 g/l) than for more concentrated ones (c0 = 1 g/l). This might be connected with the formation of gel structures due to strong magnetic attraction between ferromagnetic nanoparticles. In the gravitation field, the suspensions of the particles (10 - 20 nm) remain stable for over 20 hours. The sedimentation process can be greatly accelerated by the action of a vertical gradient magnetic field, reducing the sedimentation time down to several minutes. In a gradient magnetic field enhanced by a steel grid, sedimentation of the nanopowder (c0 = 0.1 g/l) for 180 minutes resulted in reduction of the iron concentration in water down to 0.4 mg/l. In flowing water regime, the residual iron concentration in water 0.3 mg/l is reached after 80 minutes.
Highlights
Separation of suspended solids from water is an important stage of water cleaning technology
As the aggregation process is crucial for the sedimentation dynamics, one can expect the influence of interparticle distances on the aggregates formation, in particular, for the different solid face concentrations
As the optical registration of transparency/turbidity for t > 50 min can not supply a good precision, the residual concentration of the magnetite nanoparticles in the water was measured by Nuclear Magnetic Resonance (NMR) relaxometry as it is shown in the Figure 4 where the comparison of water clarification dynamics for different starting magnetite concentration c0 is presented
Summary
Separation of suspended solids from water is an important stage of water cleaning technology. (2015) Separation of Fe3O4 Nanoparticles from Water by Sedimentation in a Gradient Magnetic Field. If the nanoparticles have magnetic moments, their separation from aqueous solution can be enhanced by gradient magnetic fields. In our previous papers [8] [9], the sedimentation of the nanoparticles (10 - 100 nm) in water in a gradient magnetic field produced by two sets of permanent magnets was studied. The sedimentation dynamics of magnetite nanopowders with the particle sizes of 10 - 20 nm in aqueous media in the presence of a gradient magnetic field B ≤ 0.3 T, dB/dz ≤ 0.13 T/cm was studied by optical and Nuclear Magnetic Resonance (NMR) relaxometry methods. This study will be helpful for optimization of nanosorbent sedimentation conditions for practical application
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