Cupellation of Pb boats

B

Braxx

New Member
#1
I have a high grade caustic solution. An aliquot is evap'd in a Pb boat which is then folded and cupelled. The ensuing spitting is very disconcerting. The solution has a high content of dissolved solids. Anyone have any suggestions/pointers to eliminate said spitting. Thanks
 
fireguy

fireguy

Supermoderator
#2
Braxx said:
I have a high grade caustic solution. An aliquot is evap'd in a Pb boat which is then folded and cupelled. The ensuing spitting is very disconcerting. The solution has a high content of dissolved solids. Anyone have any suggestions/pointers to eliminate said spitting. Thanks
Are you sure the material is completely dry? What is causing the spitting if not moisture? You may want to try a higher termpeature drying step. Put the cupel with the rolled lead boat into the oven, and heat to a temperature below the melting temperature of lead- maybe 500F. Dry a this temperature for 30 minutes, then cupel without allowing it to cool (if possible). This will keep the material from picking up any moisture from the air.

Let me know how that works :p
 
C

Crucible2

New Member
#3
There are 2 "old timer" methods that are used in gold mill assay labs for accurate assay of high grade caustic (cyanide) solutions such as found in electo-winning cells.

The first is a "Spike" method where 75 grams of flux and 1/2 tsp.flour is mixed in crucible, a cavity is made with a spatula in flux and 5 or 10 ml of solution is pipetted into cavity. Cavity is covered with flux, inquarted with 4 times expected gold content and sample is fused, cupelled, parted and weighed as normal fire assay.

Second method is "Test Lead" method where 50 to 100 ml of solution is measured into a 500 ml beaker and diluted with DI water to 300 ml. 8 to 10 grams of granulated test lead is sprinkled into beaker and beaker placed on hot plate under fume hood. 10 ml of concentrated Hydrochloric acid is added and solution brought to a boil for 15 minutes.
Beaker is then cooled and solution carefully decanted leaving the lead on bottom of beaker. Beaker is placed on hot plate to thoroughly dry granulated lead. A 4 inch (8 gram) piece of lead foil is formed into a cone and the granulated lead is brushed into the cone and foil is folded and compressed into a tight cube, cupelled, parted and weighed as
regular fire assay sample. This method also works extremely well with very low grade gold solutions such as mill tailing solutions. A volume of up to 750 ml can be used in a 1000 ml beaker to accurately assay solutions as low as 0.03 g/tonne as the resulting fillet will be large enough to weigh gravimetrically.
 
fireguy

fireguy

Supermoderator
#4
The "Chiddy" method is also a good old fashioned method:

1) Heat solution to 50-60C. Volume of solution is typically about 300-400 ml. Adjust volume according to grade.
2) Add 7.5 grams of lead acetate and 5 ml of acetic acid simultaneously.
3) Add 2.5 grams of merrilite zinc. Merrilite zinc is a special form of very fine zinc metal powder with high surface area:
www.lmine.com/product/18322-50.html
4) Wait 15 minutes
5) Add 60 ml concentrated hydrochloric acid (HCl)
6) Wait 45 minutes.
7) Decant and wash.
8) Gather resulting sponge and place on a "lead boat" made from lead foil:
www.lmine.com/category/test_lead_and_foil.html
9) Before folding the lead boat, dry the sponge at low temperature.
10) Inquart with 3-4 times as much silver as expected gold content.
www.lmine.com/category/inquarts.html
11) Wrap foil and cupel normally.
 
K

KRowe

New Member
#5
There are 2 "old timer" methods that are used in gold mill assay labs for accurate assay of high grade caustic (cyanide) solutions such as found in electo-winning cells.

The first is a "Spike" method where 75 grams of flux and 1/2 tsp.flour is mixed in crucible, a cavity is made with a spatula in flux and 5 or 10 ml of solution is pipetted into cavity. Cavity is covered with flux, inquarted with 4 times expected gold content and sample is fused, cupelled, parted and weighed as normal fire assay.
I use a similar method, but I use 30 g of solution added to a my standard flux in the crucible, inquart 3x and add a sprinkle of borax on top. That's it - proceed as if it were a normal solid sample.
 
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