Melting with litharge on polishing waste

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adoreman
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Melting with litharge on polishing waste

Post by adoreman » January 9th, 2014, 11:32 pm

Hi everyone,

Any help will be much appreciated. I am a smelter and refiner from asia. Here is what i did.

What i usually do is i burn the polishing waste from my gold factory. I use red rouge for polishing.

After burning, i then sieve the materials using a size 40 sieve.

I get about 2.5kg of the sieved material and mix it with 50% assay grade litharge (1.25kg)

I mix in 400% borax (10kg)

I melt this material in my furnace and add about 500g of metallic lead while melting.

I mix it thoroughly and let the particles settle.

The next step i do is remove the flux and then i would remove the impurities and lead by focusing the torch of the flame into my button.

I usually end getting a button weighing around 120grams (18k) : about 90g of pure gold

----------
I do this exact same process this year and just got 90g of 18k : only 67g of pure gold

I sent off a sample to the assaying laboratory and The result showed i should be getting about 90g of pure gold per 2.5kgwaste.

I tried to do the same melting processvusing assay grade litharge with just using 1kg of polishing waste sample and used 100% litharge and 500% borax.
I did not get the gold amount i needed.

I bought a new batch of litharge but they only had commercial grade litharge. I done my 1kg sample again but bad results again.

Does anyone hqve any knowledge n this or any suggestions? And may i ask what is the difference between commercial grade and assay grade litharge? Thanks very much everyone.


Regards,
Adoreman

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Re: Melting with litharge on polishing waste

Post by butcher » January 9th, 2014, 11:57 pm

Hokes book and Harold, give good methods to deal with jewelers sweeps.
With very little experience with what you are trying to do, I may not be the best to answer your question.

I would thing it probably is not as much the litharge as the several other chemical reactions going on in the melt.

The assayer you sent your sample to, if he did a fire assay basically done what you are trying to do, but he will adjust the chemistry of his flux to recover the metals in the lead button, cupel the lead and part the gold and metals to determine How much metals you sent him in the sample.

To decide what chemistry he may need to choose for his flux he may do a teat sample of your material with litharge to see how much lead he gets back, he will then adjust his flux form what he finds in this test, either adding an oxidizing or reducing agents, as well as flux to make sure the melt is fluid enough for metals to combine in the melt.

Read Hokes book, and check out Harold's posts, I bet you may find a better solution to your problem, and also find many other things that can help you in your business.

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Re: Melting with litharge on polishing waste

Post by 4metals » January 10th, 2014, 12:52 am

Have you ever considered recovering the gold by cupellation? It would eliminate burning off the lead with a torch. What you are doing is essentially a big assay fusion but you are not adding any reducing agents to the flux mix. You are also not separating out any silver or platinum that may be in your rouge, your method produces a dore bead not fine gold.
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Re: Melting with litharge on polishing waste

Post by adoreman » January 10th, 2014, 1:18 am

butcher wrote:Hokes book and Harold, give good methods to deal with jewelers sweeps.
With very little experience with what you are trying to do, I may not be the best to answer your question.

I would thing it probably is not as much the litharge as the several other chemical reactions going on in the melt.

The assayer you sent your sample to, if he did a fire assay basically done what you are trying to do, but he will adjust the chemistry of his flux to recover the metals in the lead button, cupel the lead and part the gold and metals to determine How much metals you sent him in the sample.

To decide what chemistry he may need to choose for his flux he may do a teat sample of your material with litharge to see how much lead he gets back, he will then adjust his flux form what he finds in this test, either adding an oxidizing or reducing agents, as well as flux to make sure the melt is fluid enough for metals to combine in the melt.

Read Hokes book, and check out Harold's posts, I bet you may find a better solution to your problem, and also find many other things that can help you in your business.
Thank u butcher,
You are very helpful. I have spoken to you in this forum before and you assisted.
What do you mean by adjusting the flux? How do they adjust the chemistry of the flux?
And (yes they did a fire assay on my sample)

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Re: Melting with litharge on polishing waste

Post by adoreman » January 10th, 2014, 1:28 am

4metals wrote:Have you ever considered recovering the gold by cupellation? It would eliminate burning off the lead with a torch. What you are doing is essentially a big assay fusion but you are not adding any reducing agents to the flux mix. You are also not separating out any silver or platinum that may be in your rouge, your method produces a dore bead not fine gold.
Hi 4metals. Thank you.
I searched on the cupellation and i believe that that is what i do when i concentrate the flame on my button. In my country it is called "pa-suka" translated "to vomit out" this is when we use the high temperature of the torch to oxidize out the lead and other metals and the gold button will remain ( when i do it it looks like the button is vomiting out the lead and impurities)

What do u mean by reducting agents?

I actually separate the silver in my next step after when i refine the gold to get 99.9 using nitric acid.

I do not have any platinum in my rouge. Thank u

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Re: Melting with litharge on polishing waste

Post by Harold_V » January 10th, 2014, 2:21 am

I'm far from being knowledgeable on the subject of fluxing, but I had an experience which yielded excellent results. The slag from my operation was assayed and found to contain far too little value to justify further processing.

I used no litharge. A good portion of my waste material was silica, which is a good thing.

Consider adding soda ash to your flux mixture, as well as a small amount of fluorspar. The soda ash will help in recovering any silver that might be present in the way of silver choride, and the fluorspar will thin the flux considerably, so tiny prills are not as likely to remain suspended. I expect that with your use of litharge and lead, you should get a quite good recovery. Your losses are now most likely suspended in the slag. If you haven't discarded the waste, you can re-run a small amount with each of the batches you process in the future, to recover what has been lost. That's assuming you thin your flux, as recommended, and you allow the charge to "cook" long enough.

Harold
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Re: Melting with litharge on polishing waste

Post by 4metals » January 10th, 2014, 10:52 am

Cupellation involves using a bone ash cupel in a furnace to melt the gold bearing lead alloy which will be adsorbed into the cupel leaving a bead of only precious metals. The torching method you mention will volatilize the lead causing it to gas off into the air that you breathe.

The ingredients mentioned by Harold will help but carbon in the flux mixture, usually added as common white flour, will help to reduce the metal and help it accumulate in the lead.

Overall I think your sweeps to flux ratio is low. Running a fire assay with a crucible fusion followed by cupellation will tell you how much gold is in the material before you start, then you will know how much to expect. Your procedure seems to be somewhat effective at recovery but if you do not know what you started with you will never know if the slags are still holding values.
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Re: Melting with litharge on polishing waste

Post by butcher » January 10th, 2014, 11:35 am

I have very little experience in fluxing, and have practically no experience in assay, although I have tried playing with these a little.

Flux a broad term to describe a mix of materials added to a melt (or to welding, brazing or even soldering), flux came from the word to flow, it can have different properties depending on what we are trying to do with it, I wont describe welding or soldering here, as we are more concerned with melting metals and other gangue material like Ore, or in this case polishing waste which contains values.

Normally we will start with a basic flux, which will normally contain some basic chemicals, chosen because of how they can help to make our melt "flow" or to become fluid, and also provide us with a molten glass slag (silicates that will absorb metals into this glass).

A basic flux normally will contain three main ingredients such as suggested by Hokes:
5 parts soda ash (sodium carbonate Na2CO3, also called washing soda),
4 part borax glass (Sodium tetraborate Na2B4O7),
2 parts Ground glass (window glass or quartz silica...)

I will try to tell some of why these are in the basic flux.
With flux we want to help make the melt flow or to become fluid, this is important for the melt to mix, as what we are doing is a chemical reaction with in this melt, and we want the reaction to be able to mix the ingredients in our chemical reaction, we want metals and acids or bases to combine, oxidizers to oxidize some and reducers to reduce others, we want unwanted metals to oxidize and the acid glass silicates to form a glass slag of metal oxide silicates, we want the more precious metals, or metals we are using as collectors to combine with the values, or just metals we are trying to reduce back to metal to combine in the melt and reduce to molten metals. The flux being fluid is important for the mixing and combining of chemicals and metals, and for the metals once combined to be able to combine and sink in the melt by gravity, and for the metals to become oxidized and to form glass silicates (slag that can float to the top of the melt), fluxes can also help in changing the temperature at which things will fuse or melt, than they may otherwise.

The three ingredients above can help to make the melt fluid, and the have other properties to list some:

Borax can help to protect the melting crucible from metals adhering, help the melt to flow, it can act as an acid flux, and help in slagging, can act as a shield to help keep out atmospheric oxygen or oxygen from the torch or furnace burners and so on, it is also helpful with iron, magnesia, zinc oxides...

Sodium carbonate, A basic flux, when melted with silica gives off CO2, to help form make the silicates more fusible, and to help form the sodium silicate compounds (slag glass) important to form or absorb the base metals oxides as silicates in the glass slag, soda ash can also act as a desulfurizer (important for many Ores).

Crushed glass, (SiO2) silica (such as white sands) or quartz provide the main ingredient for our slag, to help form silicate base metal glass slag,
SiO2 silica is a very strong acid flux which combines with metal oxides to form silicates (slag’s, or metal slag glass), silica can also help to protect crucibles from attack from other ingredients in a flux chemistry (such as litharge which will dissolve the crucible), silica can aid in fusion of things.
Using way too much silica can also cause loss of values in the Matte; it is an acid flux that can also act as an oxidizer.
Also your material you are melting can be high in silica so you may not need to add much as flux.

The above just gives us some basic ingredients to our flux; we may need some other chemicals or ingredient added to help the chemistry of our melt depending on the material we are melting.

First we may need to know, or understand some of the chemistry of what it is we are melting, in an assay they will test the material they will assay to get an idea of what its chemistry may react in a melt, is it oxidizing or reducing in nature, like will it oxidize lead to litharge, or will it reduce litharge to metal lead, this can be important to know as if the material is an oxidizing nature it can easily oxidize base metals, or if it is reducing can reduce base metals, it can also react with our basic flux changing the properties of flux.

Remember we are not just melting a chemical mix of flux but our Ore (as an example) or polishing sweeps also have a chemistry they add to the melt, this chemical reaction is done at high heat, and can be acidic or caustic, oxidizing or reducing, basically a chemical reaction, with our material being a very big part of the chemistry as well as the chemistry we choose for the flux, we adjust the chemistry of our flux to get the desired results or reaction with our Ore or whatever we are melting.

Litharge lead oxide PbO, is a strong oxidizer (it can even oxidize our crucible), with silica can form a lead silicate (lead glass Pb2SiO4), or act as a collector of other metals like precious metals of gold and silver, litharge can also act as a desulfurizer, litharge readily gives up oxygen and can act as an oxidizer to oxidize base metals, lead as stated above can act as a collector.

In a melt other metals can act as collectors of values, or help to reduce the melting points of other metals, some collectors like silver or copper bismuth...

Carbon, sugar, flour, charcoal, wood... these are carbon sources which act as reducing agents, or to offset the chemical reaction of oxides, the use of flour in flux is very common, the carbon can take oxides from metals in a melt, offset an oxidizer in the melt or flux. Carbon and oxygen normally burn off as CO2 gas (CO if not enough oxygen involved), carbon can also help to lower the oxygen absorbed into a melt from air or oxygen in the torch or used in the burner of the furnace...

Say we are using litharge as a collector in a melt, and the Ore (or material we are melting) like red rouge (Fe2O3) polishing waste that may contain many other oxides aluminum oxide (Al2O3) from the grinding wheels or chromium Oxide (Cr2O3) in buffing grinding compounds) and our melt is of such an oxidizing nature, that we cannot get the litharge (PbO) to reduce back to lead (it will not collect gold), we may need to add flour or another carbon source to reduce the oxides (and to reduce the lead to metal where it can pick up the fine gold in the melt)...

There are several other reducing agents used in fluxes.

Sometimes we need an Oxidizer to the flux or melt, to help oxidize base metals to get them to dissolves as silicates in the slag glass, such as potassium nitrate KNO3.

Sometime sulfur may be a problem and Iron can help in the melt as a desulfurizer or collector.

Salt, or carbon is sometimes used as a cover.

Fluorspar or cryolite used as fluidizers to help with fluidity and with some materials in a melt...

Flux can use many things, or combination of things to help change the chemical properties of the melt...

Basically you are melting (doing a a chemical reaction with high heat) your flux is mixed to help to get what you want back out of this chemical reaction.


Also since this is a chemical reaction how you perform the melt can also be a very be important part of this chemical equation, the melting environment can be oxidizing or reducing (in the furnace), a torch may not get the melt hot enough for the melt to mix well or can also be oxidizing or reducing, a furnace where you can get a good hot melt to get the melt fluid, and keep it fluid for metals and flux to react, and have more control on temperature of the melt...
A torch melt would not work well for most procedures we are looking at here.

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Re: Melting with litharge on polishing waste

Post by adoreman » January 12th, 2014, 9:37 pm

Hi harold v, butcher and 4 metals.

Thank u for the in depth explanations. I have read thru them but will need a bit more time to thoroughly analyze the explanations. I will get back to you asap. Thanks

Regards,
Adoreman

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Re: Melting with litharge on polishing waste

Post by adoreman » January 13th, 2014, 12:21 am

4metals wrote:Cupellation involves using a bone ash cupel in a furnace to melt the gold bearing lead alloy which will be adsorbed into the cupel leaving a bead of only precious metals. The torching method you mention will volatilize the lead causing it to gas off into the air that you breathe.

The ingredients mentioned by Harold will help but carbon in the flux mixture, usually added as common white flour, will help to reduce the metal and help it accumulate in the lead.

Overall I think your sweeps to flux ratio is low. Running a fire assay with a crucible fusion followed by cupellation will tell you how much gold is in the material before you start, then you will know how much to expect. Your procedure seems to be somewhat effective at recovery but if you do not know what you started with you will never know if the slags are still holding values.
thanks for the info on cupellation 4metals. i will do more research on it and try it out. (if i can find bone ash cupel in my country).
regarding the common white flour, what is your suggestion on the amount of white flour i should use? and also the sweeps to flux ratio.

regarding the values that remain in the slag, i put it in a rod mill (ball mill) to grind it and i pan the sludge using my shaking table. i was able to see gold in the material while i panned it. however i have not yet melted the material.
thanks 4metals

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Re: Melting with litharge on polishing waste

Post by adoreman » January 13th, 2014, 12:25 am

Harold_V wrote: I used no litharge. A good portion of my waste material was silica, which is a good thing.

Consider adding soda ash to your flux mixture, as well as a small amount of fluorspar. The soda ash will help in recovering any silver that might be present in the way of silver choride, and the fluorspar will thin the flux considerably, so tiny prills are not as likely to remain suspended. I expect that with your use of litharge and lead, you should get a quite good recovery.

Your losses are now most likely suspended in the slag. If you haven't discarded the waste, you can re-run a small amount with each of the batches you process in the future, to recover what has been lost. That's assuming you thin your flux, as recommended, and you allow the charge to "cook" long enough.

Harold
thanks harold. regarding the soda ash and fluorspar, what ratio do you reccomend i should use in my mix? and regarding my losses suspended in the slag, as i have mentioned to 4metals, what i do is grind the materials and pan it.

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Re: Melting with litharge on polishing waste

Post by adoreman » January 13th, 2014, 12:59 am

butcher wrote:I have very little experience in fluxing, and have practically no experience in assay, although I have tried playing with these a little.

Flux a broad term to describe a mix of materials added to a melt (or to welding, brazing or even soldering), flux came from the word to flow, it can have different properties depending on what we are trying to do with it, I wont describe welding or soldering here, as we are more concerned with melting metals and other gangue material like Ore, or in this case polishing waste which contains values.

Normally we will start with a basic flux, which will normally contain some basic chemicals, chosen because of how they can help to make our melt "flow" or to become fluid, and also provide us with a molten glass slag (silicates that will absorb metals into this glass).

A basic flux normally will contain three main ingredients such as suggested by Hokes:
5 parts soda ash (sodium carbonate Na2CO3, also called washing soda),
4 part borax glass (Sodium tetraborate Na2B4O7),
2 parts Ground glass (window glass or quartz silica...)

I will try to tell some of why these are in the basic flux.
With flux we want to help make the melt flow or to become fluid, this is important for the melt to mix, as what we are doing is a chemical reaction with in this melt, and we want the reaction to be able to mix the ingredients in our chemical reaction, we want metals and acids or bases to combine, oxidizers to oxidize some and reducers to reduce others, we want unwanted metals to oxidize and the acid glass silicates to form a glass slag of metal oxide silicates, we want the more precious metals, or metals we are using as collectors to combine with the values, or just metals we are trying to reduce back to metal to combine in the melt and reduce to molten metals. The flux being fluid is important for the mixing and combining of chemicals and metals, and for the metals once combined to be able to combine and sink in the melt by gravity, and for the metals to become oxidized and to form glass silicates (slag that can float to the top of the melt), fluxes can also help in changing the temperature at which things will fuse or melt, than they may otherwise.

The three ingredients above can help to make the melt fluid, and the have other properties to list some:

Borax can help to protect the melting crucible from metals adhering, help the melt to flow, it can act as an acid flux, and help in slagging, can act as a shield to help keep out atmospheric oxygen or oxygen from the torch or furnace burners and so on, it is also helpful with iron, magnesia, zinc oxides...

Sodium carbonate, A basic flux, when melted with silica gives off CO2, to help form make the silicates more fusible, and to help form the sodium silicate compounds (slag glass) important to form or absorb the base metals oxides as silicates in the glass slag, soda ash can also act as a desulfurizer (important for many Ores).

Crushed glass, (SiO2) silica (such as white sands) or quartz provide the main ingredient for our slag, to help form silicate base metal glass slag,
SiO2 silica is a very strong acid flux which combines with metal oxides to form silicates (slag’s, or metal slag glass), silica can also help to protect crucibles from attack from other ingredients in a flux chemistry (such as litharge which will dissolve the crucible), silica can aid in fusion of things.
Using way too much silica can also cause loss of values in the Matte; it is an acid flux that can also act as an oxidizer.
Also your material you are melting can be high in silica so you may not need to add much as flux.
.
thanks for all the useful information butcher! i appreciate it. (especially all the in depth info about the flux and the oxidation)
im keen to experiment on the basic flux mixture you are talking about because i normally just use borax as my flux. (5xsoda ash, 4xborax glass and 2xground glass)
do you think using common white sand as the silica instead of ground glass will be sufficient to use as part of my mixture?
also, as 4 metals have mentioned about using common flour as part of the mixture; what is your take on this?

what ratio do you recommend that i use if i mix in your flux mixture and 4metal's common flour with my polishing waste?

thanks.

regards,
adoreman

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Re: Melting with litharge on polishing waste

Post by butcher » January 13th, 2014, 1:56 am

Silica is where we get most of the glass in the form of silicates (the slag used to collect the base metal oxides, as base metals silicate glass (like lead glass), too much silicates in the melt can trap values as small beads, depending on what you are melting, you may already have silicates in the melt, many ore samples will have silicates involved in the ore, Sand, quartz, or crushed window glass can be used as a source of SiO2 silica.

White quartz sand works well for a source of silica, ground glass was basically sand at one time, and will also work as a source of SiO2, the glass can be a bit cleaner and can give a little less trouble capturing values as the crushed quartz or silica sand will, I assume this is because the glass is cleaner, or has been refined by fire previously.

Flour is a reducing agent, it adds a carbon source to the melt, its purpose is to reduce metal oxides, like base metal oxides (oxides of copper, lead, or other metals), if the material you are melting is naturally an oxidizer, it may need carbon added to be able to reduce the metal oxides (reduced metals like lead or copper can also act as collectors of values in the melt), the carbon takes the oxide from these metals and forms carbon dioxide gas so the metals can be melted to their elemental state, instead of becoming slag glass silicates.

The flux recipe sometimes has to be experimented with you can pick one close to what you think you may need and adjust the ingredients of the flux as needed.

Using a carbon source like flour here is a good Idea you want to reduce your litharge to lead, I am guessing your polishing sweeps are oxidizing in nature, and the carbon can help to offset it oxidizing nature, you want the gold, oxidizing base metals is not that much of a concern.


just as an example of a flux recipe
30g sweeps
10 g borax
10g silica (your sweeps may contain some from grinding wheels or alumina oxides...)
30g litharge
30n g soda ash
3g flour


Harold and 4 Metals can advise you better on specifics, and probably get you a better flux recipe to begin with than I can.

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Re: Melting with litharge on polishing waste

Post by adoreman » January 19th, 2014, 7:36 am

butcher wrote:Silica is where we get most of the glass in the form of silicates (the slag used to collect the base metal oxides, as base metals silicate glass (like lead glass), too much silicates in the melt can trap values as small beads, depending on what you are melting, you may already have silicates in the melt, many ore samples will have silicates involved in the ore, Sand, quartz, or crushed window glass can be used as a source of SiO2 silica.

White quartz sand works well for a source of silica, ground glass was basically sand at one time, and will also work as a source of SiO2, the glass can be a bit cleaner and can give a little less trouble capturing values as the crushed quartz or silica sand will, I assume this is because the glass is cleaner, or has been refined by fire previously.

Flour is a reducing agent, it adds a carbon source to the melt, its purpose is to reduce metal oxides, like base metal oxides (oxides of copper, lead, or other metals), if the material you are melting is naturally an oxidizer, it may need carbon added to be able to reduce the metal oxides (reduced metals like lead or copper can also act as collectors of values in the melt), the carbon takes the oxide from these metals and forms carbon dioxide gas so the metals can be melted to their elemental state, instead of becoming slag glass silicates.

The flux recipe sometimes has to be experimented with you can pick one close to what you think you may need and adjust the ingredients of the flux as needed.

Using a carbon source like flour here is a good Idea you want to reduce your litharge to lead, I am guessing your polishing sweeps are oxidizing in nature, and the carbon can help to offset it oxidizing nature, you want the gold, oxidizing base metals is not that much of a concern.


just as an example of a flux recipe
30g sweeps
10 g borax
10g silica (your sweeps may contain some from grinding wheels or alumina oxides...)
30g litharge
30n g soda ash
3g flour


Harold and 4 Metals can advise you better on specifics, and probably get you a better flux recipe to begin with than I can.
Hi butcher. Im sorry for the late reply. I have been busy the past few days. This week i will try that mixture or parts of that mixture. What i am planning to do is just grind some glass bottles in my rod mill to use as my silica. Thanks for the info and sample recepie. I also ordered some soda ash to use in my mix, it should arrive in a day or two. However i am not able to find any supplier of fluorspar in my area. Ill update u guys on the results of my experiment and which of the recepies i end up using.

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Re: Melting with litharge on polishing waste

Post by 4metals » January 19th, 2014, 12:44 pm

I still see problems with lead in your process. I would consider using copper, you can recover and reuse your copper melt after melt. The fluorspar is critical to this working as it thins the mixture allowing the values to settle out in the molten mass. If you cannot find fluorspar consider using cryolite in its place.

For polishing sweeps I have successfully used a flux made up as follows

Borax (Anhydrous is best) 45%
Silica sand 20%
Soda ash 20%
Sodium nitrate 10%
Fluorspar 5%

This is mixed together and used in equal portions with the ashes of your polishing sweeps.

This is often used without copper (or litharge) but if you have a rotary furnace the pool of molten copper is an effective collector. I like to use 1/4 or a pound for every pound of ash in the melt.

Using any process to melt sweeps always requires a slag remelting day. Collect your slags and remelt them with 1/4 of the original flux charge and no copper or lead as a collector. The liquid flux is poured into a cone mold and the remaining metal is collected at the base of the mold. Judging from how much is recovered in the slag re-melts you can adjust your original proportions accordingly to collect more on the first melt but you will never get it all the first time so the re-melts are a necessary evil.

The resulting copper based bar can be digested in nitric acid and the insolubles (gold) is recovered with aqua regia, the copper can be recovered and reused by cementing with iron after additional copper is added to cement the silver in the alloy.

Ideally the copper and PM alloy is poured into anodes to be electrolytically recovered in a copper sulfate cell. The resulting copper is reused over and over and the slimes are refined in aqua regia. This is the method used by large refineries.

Silver is also an effective collector and it consumes less nitric than copper and it can also be recycled to use in the process over and over.
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Re: Melting with litharge on polishing waste

Post by 4metals » January 19th, 2014, 12:48 pm

The flour was not used in the method I listed above because if you do not use the lead oxide you will not need it. The method you are using with litharge is totally different than the method I listed. Carbon (flour) helps in the litharge method, not in the method I listed.
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Re: Melting with litharge on polishing waste

Post by adoreman » January 22nd, 2014, 9:22 pm

4metals wrote:I still see problems with lead in your process. I would consider using copper, you can recover and reuse your copper melt after melt. The fluorspar is critical to this working as it thins the mixture allowing the values to settle out in the molten mass. If you cannot find fluorspar consider using cryolite in its place.

For polishing sweeps I have successfully used a flux made up as follows

Borax (Anhydrous is best) 45%
Silica sand 20%
Soda ash 20%
Sodium nitrate 10%
Fluorspar 5%

This is mixed together and used in equal portions with the ashes of your polishing sweeps.

This is often used without copper (or litharge) but if you have a rotary furnace the pool of molten copper is an effective collector. I like to use 1/4 or a pound for every pound of ash in the melt.

Using any process to melt sweeps always requires a slag remelting day. Collect your slags and remelt them with 1/4 of the original flux charge and no copper or lead as a collector. The liquid flux is poured into a cone mold and the remaining metal is collected at the base of the mold. Judging from how much is recovered in the slag re-melts you can adjust your original proportions accordingly to collect more on the first melt but you will never get it all the first time so the re-melts are a necessary evil.

The resulting copper based bar can be digested in nitric acid and the insolubles (gold) is recovered with aqua regia, the copper can be recovered and reused by cementing with iron after additional copper is added to cement the silver in the alloy.

Ideally the copper and PM alloy is poured into anodes to be electrolytically recovered in a copper sulfate cell. The resulting copper is reused over and over and the slimes are refined in aqua regia. This is the method used by large refineries.

Silver is also an effective collector and it consumes less nitric than copper and it can also be recycled to use in the process over and over.
January 19th, 2014, 12:48 pm
Re: Melting with litharge on polishing waste
The flour was not used in the method I listed above because if you do not use the lead oxide you will not need it. The method you are using with litharge is totally different than the method I listed. Carbon (flour) helps in the litharge method, not in the method I listed.
Thanks 4metals for the information. I will try and find cryolite in my area because there is no fluorspar available. Ill need that to try out your recepie. Right now i am mixing my testing.
Will update u guys on what ill use

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Re: Melting with litharge on polishing waste

Post by adoreman » January 22nd, 2014, 9:32 pm

Heres what i mixed just then. I used a bit of everyones input.

500g polishing sweeps
250g litharge
1000g borax
500g silica ( i used ground glass from drink bottles)
500g soda ash
100g flour

And i will use 250g metallic lead as a collector.

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Re: Melting with litharge on polishing waste

Post by adoreman » January 23rd, 2014, 2:56 am

adoreman wrote:Heres what i mixed just then. I used a bit of everyones input.

500g polishing sweeps
250g litharge
1000g borax
500g silica ( i used ground glass from drink bottles)
500g soda ash
100g flour

And i will use 250g metallic lead as a collector.
I finished smelting this sample. Thanks everyone who assisted(butcher 4metals and haroldv) ! I was able to achieve the result i needed.
According to the assay, i should be getting up to 90g of pure gold per 2.5kg sweeps.

Doing this mix in the quote, i was able to recover 22.9g of 18k from my 500g sample
This converts to 85.875g of pure gold if i do 2.5kg sweeps
(95.41%recovery compared to assay sample is pretty good)

The supplier gave me two types of soda ash. One dense soda ash and one light soda ash.
I used the dense soda ash for my 500g sample. Anyone know the difference between the two?

Also i will do another testing (to minimize use of litharge and metallic lead)
On a 1000g sample
I will do the same experiment but remove the litharge and metallic lead.
I will use powdered silver instead (the silver you get in powder form before u melt it,
from doing the caustic soda and syrup method )

1000g polishing sweeps
500g silver powder ( to be mixed thoroughly with the sweeps before mixing in the other ingredients)
2000g borax
1000g silica ( i used ground glass from drink bottles)
1000g soda ash
200g flour

Any comments about this method? Thanks!

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Re: Melting with litharge on polishing waste

Post by Harold_V » January 23rd, 2014, 4:23 am

I'm a little late getting back to you in regards to the addition of fluorspar and soda ash.

Here's the ratio of additives I used.

(3) parts waste material (parts by volume, not weight)

(1 1/2) parts silica sand

(3 1/2) parts soda ash

(1/2) part fluorspar

(2) parts borax

I'm not suggesting that this mix is ideal for you. It worked perfectly well for me, however. I had a considerable amount of silver chloride in my waste material, which I relied upon to act as a collector. That may help explain the amount of soda ash I used.

Take note that I blended all of this material, then I added enough water to form a thick slurry. It sets hard in a few minutes, which turned out to be a very good thing for me. I poured the slurry to a shallow mold (I used plastic lids from ice cream buckets), then after they were dry I broke them in pieces, so they could be loaded to the furnace without loss by dusting. My furnace was not a crucible type, but a reverberatory, where flame impinged directly on the charge.

Fluorspar will thin your slag, so traces that may not be being recovered now can be. Do your best to locate some, at least to experiment to see if it helps you in any way. I took note that you can't locate any, but if there's a maker of welding rod in your community, they may be able to supply you with a small amount. You don't need a lot, and it makes a big difference.

Fluorspar and soda ash are hard on refractory. My furnace was lined with 94% alumina and had to be relined after about 30 heats. A small price to pay for very good extraction.

Harold
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Re: Melting with litharge on polishing waste

Post by 4metals » January 23rd, 2014, 1:41 pm

Assaying at 90 grams per kilo is very good material, that converts to 1.3 ounces per pound here in the US. Back in the day when all of the jewelry manufacturing was here in the US that kind of assay was considered very high yield material.

The difference between light soda ash and dense soda ash is the density of actual sodium carbonate per unit of volume. The dense, as the name implies, is more dense so a scoop of dense contains more sodium carbonate than the same size scoop of light soda ash. Using weight in your flux makeup will make both the same in the end. Like they used to say "What weighs more a pound of lead or a pound of feathers?"

The extra 4.6% of the gold you did not recover as per your assay will likely come out by remelting the slags. All refiners using this process have a slag remelt day.

It is interesting to read that Harold used water to make his sweep flux mixture into bricks and then waited for them to dry. The flame hitting directly on the charge does blow off any loose fines and wetting them is a unique way of preventing this. Harold has posted a picture of his reverberatory furnace and it is a beautiful thing I might add.

I also melted large quantities of sweeps but prevented the dust by pelletizing the material in a pellet press after the flux and charge were mixed but I melted larger quantities and the furnace rotated as it heated. But we were adding the equivalent of 2, 55 gallon drums of sweeps flux mixture per day to keep up with the sweeps we had to process.

Legend in Sparks Nevada may ship you a bag of flourspar http://www.lmine.com/product/17120-50.html you should check. I cannot say it too often, it is a necessary component for recovery.
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Re: Melting with litharge on polishing waste

Post by adoreman » January 30th, 2014, 8:33 pm

4metals wrote:Assaying at 90 grams per kilo is very good material, that converts to 1.3 ounces per pound here in the US. Back in the day when all of the jewelry manufacturing was here in the US that kind of assay was considered very high yield material.

The difference between light soda ash and dense soda ash is the density of actual sodium carbonate per unit of volume. The dense, as the name implies, is more dense so a scoop of dense contains more sodium carbonate than the same size scoop of light soda ash. Using weight in your flux makeup will make both the same in the end. Like they used to say "What weighs more a pound of lead or a pound of feathers?"

The extra 4.6% of the gold you did not recover as per your assay will likely come out by remelting the slags. All refiners using this process have a slag remelt day.

It is interesting to read that Harold used water to make his sweep flux mixture into bricks and then waited for them to dry. The flame hitting directly on the charge does blow off any loose fines and wetting them is a unique way of preventing this. Harold has posted a picture of his reverberatory furnace and it is a beautiful thing I might add.

I also melted large quantities of sweeps but prevented the dust by pelletizing the material in a pellet press after the flux and charge were mixed but I melted larger quantities and the furnace rotated as it heated. But we were adding the equivalent of 2, 55 gallon drums of sweeps flux mixture per day to keep up with the sweeps we had to process.

Legend in Sparks Nevada may ship you a bag of flourspar http://www.lmine.com/product/17120-50.html you should check. I cannot say it too often, it is a necessary component for recovery.
Hi 4 metals im sorry for the late reply. Ive been busy with work. Yes the material im doing now is high grade material, iths the high grade part of my polishing waste. Thanks for the info on the soda ash. I actually tested the dense and the light soda ash using the same amount of each. I was surprised to see that the light soda ash actually was quicker and easier to melt than the dense. 2 hrs for the light and 2.5 hrs for the dense. And both produced good result.
What i do with the slag is i grind it with my ball/rod mill and then pan it in my shaker table. Im able to recover the other precious metals here.
Im also trsting right now on smelting without borax just to see the effect
Im doing
1kg sweeps
500 g litharge
3kg silica
1kg soda ash
200g flour
250g silver as collecting agent
Any comments on is one?

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Re: Melting with litharge on polishing waste

Post by adoreman » February 26th, 2014, 1:54 am

hi everyone.
a few quick questions.
i bought a few sacks of soda ash and it says on the bags that there is a two year expiry on it.
will expired soda ash have an effect on my smelting?
also, does flour expire too? and will this also have an effect on smelting if it is expired?

thanks!

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Re: Melting with litharge on polishing waste

Post by kjavanb123 » May 29th, 2014, 12:27 pm

Hi,

Can same flux be used to melt ashes from incinerating ICs in a cupola furnace?

Thanks
Kevin

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