Sheet 506 / 5

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Instructions

22-Nov-11

C506_5_Mabor_Inst_FA.doc

 

WORKING WITH BIG "MABOR" CUPELS / BULLION BLOCKS
GOLD DETERMINATION IN MINERALS / CONCENTRATES / RESIDUES FOLLOWING ISO 10378

Behaviour of Mabor Cupels & Bullion Blocks - Do's and Don'ts

Don't use Cupels / Blocks more than once

● Attempts to re-use will lead to cracking / breakage / loss of sample

No need to preheat Cupels / Blocks

● Warm / cold load: both possible. If preheated, time to be < 30 min.

Don't use up all Cupels' litharge retaining capacity

● At 980C Cupels absorb & retain near 70 % of PbO (wt / wt %)
○ Thus at 980C Cupel #8A (wt 100 g ) may retain up to 70 g PbO

● Leave safety margin
○ So that
PbO doesn't leak down to furnace floor

● Spare capacity is visible as a non tanned white strip below Cupel

● Retaining capacity decreases as temperature increases
○ PbO becomes more fluid at high temperatures

● Increase Cupel capacity by augmenting Cupel mass
○ Use Cupels of greater diameter
○ If floor space scarce use taller Cupels / compact 4SAHB blocks

Don't leave Cupels "dwelling" in a hot furnace

● Cupels / Blocks are:

○ Sophisticated high temperature filters:
◊ Stop penetration of molten metal
◊ Allow flux to come in and stay in

○ Efficient porous containers
◊ Capable to trap great amounts of flux
◊ Inert to chemical attack of flux

● Cupels / Blocks are not:

○ Refractory "fixtures" designed to stay long in a furnace
◊ Long exposition to high temps causes cracks in cupels

Don't load Cupels / Blocks in a Furnace if wetted

● Though non hygroscopic, may become wet in contact with water

● If wetted, moist Cupels should be dried in oven before use

Don't force Cupels when they stick to hearth

● Use MgO powder as parting media to prevent sticking

Maborite MgO powder also aid at improving refractory lining life

 

 

Step

Cupellation Sequence

Image

Time (min.)

1

Start (from cold)
Switch Furnace electric power / burner ON
Set temp. control to 900 C

 

- -

2

Preheat Furnace (empty)
Allow temp. inside Furnace to reach 900 C (variable time)
Time depends on furnace power and refractory lining thermal inertia

 

20

3

Load empty cupels
Open door
Place empty Cupels inside furnace
Close door
Set temp. control to 860 C (if both Au and Ag are determined)
Set temp. control to 900 C (if only Au is to be determined)

1

4

Allow temp. inside Furnace to reach 860 C / 900 resp.

 

2

5

Load samples
Open door
Charge the cups of the Cupels with:
Lead buttons (30 - 45 g)
Close door

1

6

Allow temp. inside Furnace to reach 860 C / 900 resp. again

 

2

7

Cupellation process begins (variable time)
Watch the driving process
Make sure that no spitting occurs
Make sure that no freezing of litharge occurs
Wait for play of colours to appear
When play of colours ceases,

cupellation process is completed

30 - 40

8

Switch furnace electric power / burner OFF

 

- -

9

Ensure no sprouting occurs
May happen if Au + Ag bead cools too quickly
Slow bead cooling rate to allow O2 degassing before crust solidification

- -

10

Withdraw cupels from furnace
Set them preferably on a non metallic refractory tray to cool

1

 

Total Cupellation Time (excluding / including furnace preheating)

 

~ 40 / ~ 65

 

● Unaffected by atmospheric changes / moisture
● Quick absorption of large quantities of litharge
● Special range for micro-cupellation methods
● Manufacturing experience: 111 years !
● Continuous R & D + Testing in own assay lab
● ISO 9001 - ISO 14001 QM & EM Certificates

● Consistent low losses
● Reduced tendency to freeze
Robust mechanical strength
● Perfect uniformity of quality
● No spitting of lead
● Latest manufacturing machinery

● Absorption ~70% cupel weight at 980C
● Quality immune to storage time
● 20-kg box easy to handle / store
Beads easily removed
● Free from cracking and pitting
Accuracy 5 times better than ICP

 

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