Separation of particles adsorbed on carrier material

Abstract: A method is described according to which particles present in a fluid are separated from flakes adhered thereto. According to prior art separation takes place with the help of an ultrasonic field applied to the fluid. It appeared that a better separation is achieved, if the flakes are subjected to a substantial velocity gradient. This velocity gradient subjects the particles to shearing forces causing an effective separation of the elements. Tests have shown that a pump generates such velocity gradients, that a most effective separation is achieved.

Description: The present invention relates to a method for separating particles present in a liquid from flakes adhered to the particles by sheering forces, wherein the particles with the flakes adhered thereto are subjected to a velocity gradient in the fluid generating said sheering forces. Such a method is known from the article "Magnetic separation in water polution control", IEEE Transactions on Magnetics, vol. 11, No. 5, September 1975. According to a first method described in said document an ultrasonic field is applied on the fluid, and the separation of the particles and the flakes takes place only slowly, so that the process takes much time. Further the achieved separation is not complete; not-separated combinations of particles and flakes remain. According to a second method described in said document the fluid is pumped into a magnetic filtering device. This magnetic filtering device holds the magnetic particles while the non-magnetic flakes are washed away by the impact of the moving fluid. This method requires a substantial amount of equipment for the magnetic filter. The aim of the present invention is to provide a method for separating such particles, in which the separation process can take place in a short duration of time, in which a more complete separation is achieved, and for which only little equipment is needed. This aim is reached in that said velocity gradient in the liquid is equal to or greater than the velocity gradient consistent with the size of said particles. Subsequently, the present invention will be elucidated with the help of the accompanying drawings, in which: fig. 1: is a diagram for explaining the theoretical basis of the present invention; and fig. 2: is a schematic view of an embodiment of an apparatus for application of the method according to the present invention. In fig. 1 a channel 1 has been shown, in which a laminary liquid current is present, depicted with an arrow 2. The line indicated with 3 shows the velocity profile of the liquid current 2. As an example a particle 4 with size Δr has been drawn in the fluid current 2. The particle experiences a velocity gradient Δv in the position indicated. The partcle is subjected to a shearing force, which is proportional with G = dv dr . As a consequence of this force the particle will part into two elements. More in particular it appears from the literature that, when a certain value of G is present, the size of the flakes is limited to a value, being dependent on said value of G as greater particles will be pulled into elements by the shearing forces. By setting the value of G the maximal existable flake size can be controlled. The present invention uses this result by setting the value of G such, that the maximal existable flake size is equal to the size of the magnetite particles. The calcium phosphate- and calcium carbonate flakes adhered to the magnetite particles are being released from the magnetite particles. This is, however, a process taking place in great numbers, so that the microscopic approach above is not valid as a physical law. Thus, it is aimed for a method, in which a shearing force can be generated, so that the maximal existable particle size is equal to the particle size of the magnetite. Applicant has made some tests with several apparatuses to determine which apparatus would lead to the highest possible rate of separation according to the principle set out above. It has appeared that surprisingly during the separation of particles of magnetite and the flakes of calcium phosphate and calcium carbonate adhered thereto, a centrifugal pump would lead to the best results. Such a pump has been depicted in fig. 2. This pump comprises a housing 5, which has been located on a basis 6. In the house 5 a shaft 7 has been provided, on to which a van 8 has been provided. The shaft 8 is driven by an electromotor 9. Concentric with the shaft 8 a supply tube l0 has been provided, whereas in the well-known way a drain pipe 11 has been connected to the pump house 5. By rotating the van such a turbulence develops in the border area of the pump house 5, that substantial velocity gradients develop. As a consequence thereof a good separation between the particles and the flakes is achieved. A suspension of calcium phosphate-magnetite particles is fed to the pump, and it appears that in the effluent the greater part of the particles has been separated into elements.

Claims: Method for separating particles present in a liquid from flakes adhered to the particles by sheering forces, wherein the particles with the flakes adhered thereto are subjected to a velocity gradient in the fluid generating said sheering forces, characterized in that said velocity gradient in the liquid is equal to or greater than the velocity gradient consistent with the size of said particles. Method according to claim 1, characterized in that said velocity gradient in the liquid is being generated by an apparatus causing a turbulence. Method according to claim 2, characterized in that the apparatus causing a turbulence is a pump. Method according to claim 3, characterized in that the pump is a centrifugal pump. Method according to one of the preceeding claims, characterized in that the particles are magnetite particles, and that the flakes adhered thereto consist of calcium phosphate and calcium carbonate.

Inventors: BOERSMA RINTJE, BOERSMA, RINTJE
Applicants: OOSTERHOF HOLMAN MILIEUTECHNIE, OOSTERHOF HOLMAN MILIEUTECHNIEK B.V.
Application year: 1990
Main classification: B01D43
IPC codes: B01D21, B01D43, C02F1