Quartz sinking....feldspars floating..
Mineral Separation
Quartz sinking....feldspars floating..
Mineral Separation
University of Vermont
27 September, 1997
Mineral separates for quartz extraction:
Materials:
Deionized water
LST (specific gravity: 2.85 @ 25o C)
500 ml Pyrex glass separatory funnels
500 ml and 1000 ml Pyrex glass flasks
1000 ml Pyrex vacuum flasks
ring stands
1000 ml plastic and Pyrex glass beakers
porcelain Buchner funnels with rubber stops
funnel, polypropylene
filter paper (VWR grade 413, 7.5 cm)
glass trays for drying separates (Pyrex petri dishes)
stirring rods, polypropylene
quartz density chip
vacuum pump
Safety Equipment
vinyl disposable gloves
goggles
apron, polypropylene
laboratory hood
LST is a non toxic replacement for halogenated heavy liquids. It is unfortunately extremely expensive and an eye irritant. Therefore, gloves and goggles are necessary and we will attempt to reclaim as much of the LST as is practical. Such reclamation means that all glass ware should be well rinsed and the LST in the rinse liquid be recovered by evaporation. Such recovery is speeded if more concentrated LST is maintained separately from the less concentrated LST during the rinsing and recovery process.
Procedure:
1) Pour sample from bag into beaker. Use about 150 ml of the <710 - >250 micron size fraction.
2) Grease the stopcock for each of the separatory funnels; place it in the separatory funnel in the CLOSED position. Set separatory funnel in ring stand. Place a vacuum flask beneath each separatory funnel and attach to the vacuum hose line. Fit Buchner funnel with rubber stop into vacuum flask and drop in a sheet of filter paper. Wet the filter paper with a little deionized water. Lower the rings supporting the separatory funnels so that the lower tip of the funnels matches the height of the lip of the Buchner funnels (this step prevents splattering of the LST liquid).
3) Pour LST (density >2.7) into the separatory funnel using a polypropylene funnel. Put in enough liquid to fill the funnel about 1 to 2 cm above the supporting ring. Pour sample into funnel. ATTACH A PIECE OF LABEL TAPE TO THE SEP FUNNEL WITH THE SAMPLE ID WRITTEN ON THE TAPE.
4) Stir sample and allow 2-5 minutes for the mafics to sink to the bottom. Drain the mafics from the separatory funnel into the filter paper. Do this by opening the stopcock fully and then shutting it completely. Then, open and close the stopcock going smoothly in the other direction to remove grains sticking at the opening. Stir the sample vigorously and repeat process until most of the mafics are removed from the sample (some small additional amount of DI water may need to be added to allow the smaller and lighter mafics to sink). After the mafics have been dropped, turn on the vacuum pump to quicken the filtering of the LST. Once the dripping of the filter into the vacuum flask has ceased or slowed considerably, turn off the pump and remove the Buchner funnel. Place it into a separate 1000 ml flask to allow it to drip. As a precaution, inspect the LST in the flask for stray grains which may have bypassed the filter paper. If clean, pour the LST (r>2.7) from the flask into the LST bottle. If the LST is not clean, pour the liquid into a separate container for later filtering. Label this container "Ready, needs filtering". Return the vacuum flask with Buchner funnel to the vacuum line. Fill Buchner funnel with DI water until the mafics are completely submerged. Turn on vacuum to drain liquid. Repeat this process at least 3 times to ensure recovery of all of the LST, turning vacuum off between each rinse. Remove Buchner funnel and place it in the 1000 ml drip flask. Empty vacuum flask into a 1000 ml beaker labeled "Dilute". Discard filter paper and mafics and clean the Buchner funnel with a DI rinse. Inspect the funnel holes for trapped grains. Use a paper clip to clean the holes if necessary.
5) With the Buchner funnel and vacuum flask in place on the vacuum line, place a new sheet of filter paper in the funnel and wet with DI water. Squirt a small amount of water (just enough to see a layer of water floating on top of the LST) into the separatory funnel and stir the sample. The goal here is to have the quartz sink to the bottom and the feldspars remain floating at the surface. Because feldspar and quartz have very similar densities, this task can be difficult an separations may result in a sample <50% quartz. The amount of water added will vary from sample to sample; continue adding water in very small amounts and stirring until the majority of quartz settles to the bottom. OVER-SHOOTING TO A DENSITY LESS THAN FELDSPAR IS EASY. If this happens, add more heavy liquid to increase the density. Usually when enough water has been added, the quartz will sink to the bottom rather rapidly in a large mass (the feldspars will rise to the surface).
The new vacuum filtration appartatus..
6) Let the quartz through the separatory funnel into the funnel below. MOVE THE LABEL FROM THE SEP FUNNEL TO THE BUCHNER FUNNEL. Turn on the vacuum pump and let the heavy liquid drain. Turn off the pump and place the Buchner funnel with quartz in the drip flask. Empty the heavy liquid in the vacuum flask into a 1000 ml beaker labeled "Almost There". Repeat the rinsing process described in step 4 to clean the quartz. Be sure to keep the "Dilute" and "Almost There" liquid separate.
7) With tweezers, remove the filter paper with the quartz in it from the funnel and place in a shallow dish. TAKE THE LABEL FROM THE BUCHNER FUNNEL AND PLACE IT ON THE DISH. Place the dish in the oven. Once the filter paper is dry and the quartz grains no longer stick to it, remove it and allow the quartz to continue drying. ONCE THE QUARTZ IS DRY, place it into a small ziplock, transferring the label and writing "mineral seped" on the bag. Place the bag in the drawer to be ultrasounded.
8) After rinsing the Buchner funnel, return the funnel and vacuum flask to the vacuum line and put in a new, wetted sheet of filter paper. Empty the remaining sample (feldspars) from the separatory funnel into the filter paper. Turn on the vacuum pump to filter liquid. Put this liquid in the "almost there" beaker. Repeat the rinsing procedure described in step 4. Discard the cleaned feldspars and filter paper.
9) Use DI water to rinse the separatory funnel, vacuum flasks, stir rods and drip flask into the "dilute" beaker. After all LST has been removed rinse the sep funnel well with tap water to remove all the quartz. RINSE THE SEP FUNNEL AND ALL GLASSWARE WITH DI WATER; it can now be used again or can be placed back in the drawer.
10) Heavy liquid remaining from the mineral separation can be used again after the water has been evaporated and the liquid filtered to remove the mineral grains. This evaporation is done on the hotplate at sub boiling temperatures. When the liquid has achieved a density at which the quartz chip floats, filter it back into storage bottle. Do not pour unfiltered liquid back in bottles. DO NOT LEAVE LIQUID UNCOVERED FOR LONG PERIODS OF TIME IN THE HOOD. IT GETS DIRTY...
If liquid remains cloudy after initial filtration, refilter with fine paper.
Waste disposal
Place all contaminated filter paper, unwanted portion of separated sample, and any other disposable material in a plastic or glass jar and seal. Dispose of jar in trash.
Safety:
Mineral separates: Goggles, PVC gloves, and a lab apron should be worn whenever handling the LST. Work involving this liquid should be performed in a hood. It is an eye and skin irritant.
Waste disposal: When handling the waste produced from working with LST, eye and skin protection should be used.
Tips on LST recovery:
-If the liquid is left out to evaporate for too long, it will begin to crystallize. If this happens, simply add a little DI water and stir until the crystals have dissolved.
-Sometimes, dust will accumulate in the evaporating liquid as it sits out, causing the liquid to reduce and turn a deep blue or blackish color. If this happens, reoxigenate the liquid with 3 to 4 drops of hydrogen peroxide 30%. Within 12 hours, the liquid should return to its original color.