Purification of quartz powders by removal of microparticles of refractory materials
Described is a process for the refinement of a quartz powder, comprising the step of separating microparticles of refractory minerals, in particular minerals containing rare earth metal compounds, from the quartz powder by an elutriation step.
1. A process for the refinement of a quartz powder, comprising
separating microparticles of refractory minerals out of the quartz powder by an elutriation step, wherein the microparticles of refractory minerals comprise minerals containing rare earth metals and/or thorium and/or uranium; and
carrying out the elutriation step in a fluidised bed reactor, in which a controlled upward flow of a liquid elutriation phase is provided, by which the microparticles of refractory minerals are carried upwards in the fluidised bed reactor;
whereas the quartz powder remains in the lower region of the fluidised bed reactor.
2. The process according to claim 1 , wherein the microparticles of refractory minerals carried upwards in the fluidised bed are either discharged out of the fluidised bed reactor or are separated from the liquid elutriation phase.
3. The process according to claim 2 , wherein the liquid elutriation phase is recycled into the elutriation step and the microparticles of refractory minerals contained therein are separated from the elutriation phase by filtration.
4. The process according to claim 3 , wherien the microparticles of refractory minerals are separated from the elutriation phase by filtration using a filter with a filter having a pore size of 0.7 μm or less.
5. The process according to claim 4 , wherein the filter is an acid-resistant filter.
6. The process according to claim 1 , wherein the separation of the microparticles of refractory minerals from the quartz powder is facilitated by means of ultrasonic agitation before or during elutriation.
7. The process according to claim 1 , wherein the elutriation step is carried out before or after a calcination and/or hot chlorination step.
8. The process according to claim 1 , wherein the particle size distribution of the refined quartz powder is homogenised before removal out of the fluidised bed reactor.
9. The process according to claim 8 , wherein the homogenisation of the refined quartz powder is carried out by ultrasonic agitation, or by agitation caused by a flow of a liquid or gas.
10. The process according to claim 1 , wherein the quartz powder to be refined has a size from 75 to 1000 μm, whereas the rare earth minerals have a particle size of less than 50 μm.
11. The process according to claim 1 , wherein the liquid elutriation phase is a leaching an aqueous acid comprising one or more of hydrofluoric, hydrochloric, nitric and sulphuric acids.
12. A process for the refinement of a quartz powder, comprising separating microparticles of refractory minerals out of the quartz powder by an elutriation step, wherein the quartz powder to be refined has a size from 75 to 1000 μm, whereas the microparticles of refractory minerals have a particle size of less than 50 μm.