Magnetic colloid mediated recovery of cadmium ions from an aqueous solution using a flow-through hybrid field-gradient device

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A flow-through hybrid magnetic field gradient device that uses polymer-coated magnetic particles as a mobile solid affinity phase was developed for the removal of cadmium ions from an aqueous solution. The device consists of a horizontal glass tube rotating about its axis, with repeating hybrid magnetic units positioned along the outside of the tube. Two arrangements for the magnetic units were used. In the first configuration, four hybrid pairs were distributed axially - each pair consisted of an alternating current carrying solenoid, followed by four azimuthally distributed permanent magnets that rotate with the chamber. In the second configuration, all four solenoids were placed first, followed by the four sets of four azimuthally distributed permanent magnets. The polymer-coated (ion exchange resin) magnetic particles and the cadmium-ion containing solution flow concurrently through the tube. The azimuthally flowing alternating current in the solenoid introduces axial and radial forces as well as a torque on the magnetic particles, permitting more contact between the particles and the surrounding solution, and allowing cadmium ions to absorb efficiently on to the particle surfaces. The particles are then immobilized on the chamber walls, while the depleted cadmium solution flows through the end of the tube. The 1-10 μm diameter magnetic particles with iron oxide nanoparticles embedded within a quaternary ammonium cellulose matrix (MagaCell-Q, Cortex Biochem, San Leandro, CA) at a starting concentration of 0.5 mg particles/mL were used as the mobile solid support. The feed consisted of a 10.0 mg/L cadmium sulfate solution, at a flow rate of 35 mL/min. The depleted cadmium solution was collected and used as feed for a second stage, where it contacted with a fresh batch of magnetic particles. This was repeated for a third stage. For the first arrangement, the Cd(II) concentration at the exit of the third stage dropped to 0.97 mg/L. The second configuration produced a final Cd(II) concentration of 0.68 mg/L. For the first arrangement, three stage processing resulted in an overall ∼90% w/w cadmium removal, and the second configuration removed ∼94% of the original cadmium ions. While the specific system studied here consists of removal of cadmium ions from an aqueous solution, the general principle of magnetic colloidal separation using this flow-through device can be exploited for other environmental and biotechnological applications where large volumes of sample must be processed with high capture efficiency.

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Separation Science and Technology