Trapping heavy metals by using calcium hydroxyapatite and dielectrophoresis.

We propose a novel technique for the removal of heavy metal waste from contaminated water. Our method consists in using dielectrophoresis (DEP) to trap hydroxyapatite (HAP) particles of 1 microm size in water after they have adsorbed heavy metal (Pb, Zn, Cu, Co and Cr). Although HAP can adsorb heavy metals in water and as such offers great promise as a waste-cleaning tool , one of the current challenges is the efficient removal of the HAP particles once they have adsorbed the heavy metals. We show in this paper that DEP can be used to concentrate such particles in certain regions, thus rendering the rest of the solution volume nearly free of contaminated particles. We present here both experimental and numerical results for suspensions at low concentrations.

Electroosmotic mixing in microchannels.

Mixing is an essential, yet challenging, process step for many Lab on a Chip (LOC) applications. This paper presents a method of mixing for microfluidic devices that relies upon electroosmotic flow. In physical tests and in computer simulations, we periodically vary the electric field with time to mix two aqueous solutions. Good mixing is shown to occur when the electroosmotic flow at the two inlets pulse out of phase, the Strouhal number is on the order of 1, and the pulse volumes are on the order of the intersection volume.

Electro-hydrodynamic micro-fluidic mixer.

Fluid mixing in microchannels is needed for many applications ranging from bio-arrays to micro-reactors, but is typically difficult to achieve. A simple geometry micro-mixer is proposed based on the electro-hydrodynamic (EHD) force present when the fluids to be mixed have different electrical properties and are subjected to an electric field. The electrodes are arranged so that the electric field is perpendicular to the interface between the two fluids, creating a transversal secondary flow. The technique is demonstrated experimentally using the flow of two liquids with identical viscosity and density, but different electrical properties. The volume flow rate and average velocity are 0.26 microl s(-1) and 4.2 mm s(-1), respectively, corresponding to a Reynolds number Re= 0.0174. The effect of a continuous (DC) electric field and two alternating (AC)- sinusoidal and square - electric fields is explored. At the appropriate parameter values, very good mixing takes place in less than 0.1 s, over a very short distance (within a fraction of the width 250 microm of the electrodes).