Samples containing Carbonate must not be processed in this manner. Sediment samples must be cleaned beforehand with Calgon and ultrasonic to remove as much fine material as possible (peptisation will take place in the heavy liquid under the influence of the many Na-ions, which may cause the filters to get obstructed).
Use a laboratory coat and latex gloves. Safety glasses are compulsory. Check if everything is clean.
PRINCIPLE OF SEPARATION
In a liquid with density d particles with density >d will sink, and those with density <d will float.
A mixture of the particles to be separated as well as LST heavy liquid is put into a rotating conical cup. Particles heavier than the liquid (here marked with dark spots) will be flung to the outer part and, consequently, will stay in the cup. Particles lighter than the liquid will be flung, with an overmeasure of heavy liquid, out and collected via the overflow in a beaker.
With the 3 upper switches (5 l., 500 ml., 30 l.) a filter unit can be chosen. The switches 'washing' and heavy liquid' determine to which (storage) vessel the liquid will be pumped. The pump switches below activate the pumps concerned. When the buffer vessels 'washing' and 'heavy liquid' are full, the liquid will be pumped to the store vessel automatically.
The float streams into the 5 l. filter unit and the sink is filtered through the 500 ml unit.
LST heavy liquid is very expensive and environmentally damaging. That is why all the salt used will be collected and purified. Recovered?
EQUIPMENT
- Collecting container
- Various stainless steel mixing beakers
- Mixer small (kitchen)
- Mixer large (Bosch)
- Spatulas
- Density gauge
- Pipette
METHOD
Firstly, the density of the heavy liquid has to be checked (solution of Lithium heteropolytungstates in water). Draw off some liquid and measure the density with the density gauge. Density should be 2.82 g/ml. If this deviates, draw a larger quantity (as much as is thought necessary), and add LST or water accordingly. Use the mixer for better homogenising.
The filters of the two filtering units have to be assembled: the 5 l. unit, 1 paper filter (520 quality) and gauze in between. The 500 ml. unit one filter.
The main switch of the centrifuge is on the backside of the chest. The number of revolutions is set on 5500 rpm and the brake on 8. Place the centrifuge cup into the centrifuge and on top of this the overflow pipe (with outlet to filterunit 5 l.) with the lid and funnel (see text above the centrifuge for funnel size). Let down the security clamp. This prevents the centrifuge from getting open during rotating. Then start the machine with the red button (power) on the operating panel. The button 'heavy liquid' (yellow) is also pressed on the same panel.
Now the sample is transferred to the stainless steel mixing beaker(s). Don't fill more than 1/3 of the contents. Add a little more of the heavy liquid so that the sample/liquid proportion is about 40/60. Stir the sample well to have everything in suspension and to avoid lumps.
The centrifuge is started. At the rotation speed of 5500 rpm so much clear heavy liquid is poured into the funnel that the heavy liquid flows out of the outlet. Immediately the (well stirred) sample is poured into the funnel. Perform those actions quickly one after the other. Rinse the sample beaker once more with heavy liquid and then rinse the funnel with sample heavy liquid (empty the funnel entirely when rinsing it). When the funnel is empty, and the liquid flow from the outlet has practically stopped, the centrifuge can be switched off. Meanwhile the heavy liquid is filtered and pumped to the storage vessel. If filtering is too slow, the compressed air unit (max. 2 bar) can be connected. A lid with a compressed air connection should then be fixed with clamps. Never do this in combination with the (other) 0.5 l filter unit.
As soon as the centrifuge has stopped rotating, disassemblance can be started. Collect all parts in a developer tray and rinse with warm demi water.
The centrifuge cup is taken out and poured over the 500 ml. filter unit. (Do not do this if compressed air is on the other unit!) Don't forget to switch off this unit.
When the float has been filtered it has to be emptied out and transferred to a bucket with demi water for cleaning. Write on the bucket the sample number and the text 'wash' followed by 1 score.This is to indicate that the float is cleaned for the first time. Pour the upper liquid as soon as it is clear. Clean 5 times in total with demi water and stir well (with the big mixer e.g.). Score after every cleaning after 'wash'. After the cleaning the float will be dried in an oven and stored away.
Clean the sink in a stainless steel bowl in the same manner (a 32 µ sieve and a shaking appliance could be used). Drying, however, should occur at a temperature of not more than 500 C.
Catch the cleaning liquid and collect it in a developer tray.
CLEANING
All parts have to be cleaned thoroughly with demi water. LST residues have to be collected for recovery.