Fluxing gold sweeps

[Ayham Hafez]

I had read different threads talking about recovering gold from sweeps,but I didn't find a specific one talking about fluxes types and quantities.

My customer has about 1,200 Kg of gold sweeps, I made a sampling for whole quantity and after incineration ,milling then incineration again then magnetic separation, I make an aquaregia test and make some calculation, sweeps contain about 1 ounce of pure gold per 100 kg.

I don't have copper electrolysis cell, so I'm planning to use lead as a collector metal, the gold sweeps looks like clay sand, I believe that it contains a lot of silica so I will not use silica sand, but I don't have any idea what fluxes I have to use and how much lead, I read that I have to use fluorspar as a thinning agent but don't know the quantity of it.

Have anyone some ideas about a good recipe with lead as a collector metal to process gold sweeps?

 

[4metals]

What was the source of the sweeps. 1 oz per 100 kg seems very low. is it possible the sweeps are from casting vestment and not polishing rouge?

 

[4metals]

If it is incinerated and milled polishing sweeps the flux should 10 parts soda ash, 10 parts borax and 1 part fluorspar. If you are doing this in a crucible you will need to mix in litharge to supply the lead. To the above blend I would start with 5 parts litharge.

Mix the flux so it is in equal parts to sweeps and mixed together. The lead from the litharge will rain down through the sweeps and hopefully collect the gold.

I prefer rotary furnaces when using collector metals as the material is constantly exposed to a pool of molten metal as the furnace rotates. In a crucible the pool ends up on the bottom and the passing molten metal only gets one shot to make contact.

 

[Ayham Hafez]

What was the source of the sweeps. 1 oz per 100 kg seems very low. is it possible the sweeps are from casting vestment and not polishing rouge?

Sweeps collected from central Drainage hole in gold market.

 

[4metals]

So this material is like the material they collected in the storm drains in the gold district in Manhattan. Pretty low grade.

 

[Ayham Hafez]

So this material is like the material they collected in the storm drains in the gold district in Manhattan. Pretty low grade.

Yes, same customer has rotary furnace,he brought it for processing these sweeps but the technical guy who should recover the gold left him,he only process 500 kg and got less than 0.7 ounce per 100kg, he only used borax and copper as a collector metal, I have the option of using the rotary furnace, but I have one question, can I use lead instead of litharge?

 

[Ayham Hafez]

So this material is like the material they collected in the storm drains in the gold district in Manhattan. Pretty low grade.

Is there any differences between light and dense soda ash? Since there is no dense soda ash in the local market.

 

[4metals]

In a rotary furnace yes because the lead will pool on the furnace floor. The reason you would use litharge is to blend it in with the sweeps and make contact as it rains down in a crucible

 

[4metals]

Is there any differences between light and dense soda ash? Since there is no dense soda ash in the local market.

They are chemically identical just one is more dense so use what you have. The trick with the flux is to get the entire charge liquid and flowing.

 

[Ayham Hafez]

They are chemically identical just one is more dense so use what you have. The trick with the flux is to get the entire charge liquid and flowing.

Ok many thanks for your usual support.

 

[4metals]

When you get the proportions right for flux to sweeps to produce a fluid mass you should charge the furnace and get a load molten. Add enough lead to create a pool in the furnace when the lead melts. After it is rotating for a while the lead collector should load up with values leaving a fluid mix of slag with the values in the collector metal.

You should take advantage of the heat in the furnace at this point and slag off about half of the molten flux. The values will be in the molten lead which will not pour out until you fully tip the furnace when pouring. Refill the furnace to the level it was at before you slagged off with more fluxed sweeps and let it run.

Inspect the slag closely for particles of gold. Gold will indicate you didn't allow it to rotate long enough. By using the heat in the furnace the new material should liquify faster but still let it rotate to be sure it all collects.

Continue slagging off and adding fresh sweeps with flux until you are done. The last pour will contain the molten collector and the values. It is quite obvious when the molten metal is pouring out instead of flux.

If you can, send a photo of the furnace you will use. If the owner of the furnace had someone who did this and did it with copper, perhaps he has a copper cell you can buy cheap. Copper would be my preferred collector.

 

[4metals]

When melting sweeps the most difficult part is getting the flux ratios right. since every sweep is different it takes some experimenting.

I always used a hot assay furnace and 30 gram crucibles. I start with a basic flux mix as described above and add equal parts of flux and sweep and mix it well. Then I put it in the assay furnace and let it get to temperature. I usually set the furnace to 1100ºC for this. A graphite stir rod will easily stir the molten mixture when you have the right proportions and when you pull out the rod, the flux sweep mixture should flow easily off the rod and not cling in lumps. Usually jewelers sweeps worked with this mix. But your material, being dug up floor drains may take more flux than sweep.

Once you have the right mix, you can mix up and flux the entire batch so it can feed easily into the furnace. The key is thin flux so the gold can sink. Common mistakes are using off the shelf laundry borax which has water in it. That stuff foams up and makes a froth that can keep gold suspended. You want anhydrous borax. For mixes that will not thin with the mix listed above, lower the borax to 5 parts (half of the normal mix) and allow the soda ash to help thin it. Don't forget the fluorspar.

 

[Ayham Hafez]

When you get the proportions right for flux to sweeps to produce a fluid mass you should charge the furnace and get a load molten. Add enough lead to create a pool in the furnace when the lead melts. After it is rotating for a while the lead collector should load up with values leaving a fluid mix of slag with the values in the collector metal.

You should take advantage of the heat in the furnace at this point and slag off about half of the molten flux. The values will be in the molten lead which will not pour out until you fully tip the furnace when pouring. Refill the furnace to the level it was at before you slagged off with more fluxed sweeps and let it run.

Inspect the slag closely for particles of gold. Gold will indicate you didn't allow it to rotate long enough. By using the heat in the furnace the new material should liquify faster but still let it rotate to be sure it all collects.

Continue slagging off and adding fresh sweeps with flux until you are done. The last pour will contain the molten collector and the values. It is quite obvious when the molten metal is pouring out instead of flux.

If you can, send a photo of the furnace you will use. If the owner of the furnace had someone who did this and did it with copper, perhaps he has a copper cell you can buy cheap. Copper would be my preferred collector.

The customer told me that after he brought the rotary furnace,the technical guy preferred to work with small gas furnace,he said that he think the technical guy don't have experience enough to work with rotary furnace so he preferred normal one,so the furnace is still new its not used at all, and by the way I was looking for a furnace for my business, so I found this customer and after discussing he told me that he has gold sweeps and he offered me the furnace free in case I recovered his gold .

I worked with rotary furnace in lead smelting from acid batteries, usually we don't slag off slags, we just pour the molten lead and after we notice the slag start to go out from the pouring hole we immediately make the furnace rotate to stop pouring,then when we want to take off the slag out the furnace,we make a small hole Infront of the furnace and coat it with cement powder, and we pour the whole slag into it,this hole will collect any molten lead still in slag into it.

I think you meant that I have to open the infront door of the furnace and slag off slags before open the pour hole and pour the lead by using an iron stick,so when open the pouring hole I will get only molten lead without slag, am I right? Incase the heat of the furnace is affordable for me so I can stand Infront of it and slag off, then I will make this technique. Please correct me if I misunderstood.

Incase we slagged off the slag and molten lead still in the furnace,can we make some cupollation by increase the lead heating time so we can reduce the lead quantity before make final cupollation?

And from the photos,do you think this kind of refractory can handle copper smelting? Or its better to build a new layer above current layer and use chrome-magnesium refractory bricks? Since I'm willing to use this furnace to smelt E-waste in near future.

 

[goldshark]

The customer told me that after he brought the rotary furnace,the technical guy preferred to work with small gas furnace,he said that he think the technical guy don't have experience enough to work with rotary furnace so he preferred normal one,so the furnace is still new its not used at all, and by the way I was looking for a furnace for my business, so I found this customer and after discussing he told me that he has gold sweeps and he offered me the furnace free in case I recovered his gold .

I worked with rotary furnace in lead smelting from acid batteries, usually we don't slag off slags, we just pour the molten lead and after we notice the slag start to go out from the pouring hole we immediately make the furnace rotate to stop pouring,then when we want to take off the slag out the furnace,we make a small hole Infront of the furnace and coat it with cement powder, and we pour the whole slag into it,this hole will collect any molten lead still in slag into it.

I think you meant that I have to open the infront door of the furnace and slag off slags before open the pour hole and pour the lead by using an iron stick,so when open the pouring hole I will get only molten lead without slag, am I right? Incase the heat of the furnace is affordable for me so I can stand Infront of it and slag off, then I will make this technique. Please correct me if I misunderstood.

Incase we slagged off the slag and molten lead still in the furnace,can we make some cupollation by increase the lead heating time so we can reduce the lead quantity before make final cupollation?

And from the photos,do you think this kind of refractory can handle copper smelting? Or its better to build a new layer above current layer and use chrome-magnesium refractory bricks? Since I'm willing to use this furnace to smelt E-waste in near future.

An interesting furnace, I am trying to get my head around how it works. Most horizontal furnaces I have seen, have a trunnion type bearing for the heat source introduction, vent on top. This looks like a decent design for continuously adding material, rake the slag out the end, repeat. Perhaps I am not getting the benefit of the design. How do you pour the metal?

 

[Ayham Hafez]

An interesting furnace, I am trying to get my head around how it works. Most horizontal furnaces I have seen, have a trunnion type bearing for the heat source introduction, vent on top. This looks like a decent design for continuously adding material, rake the slag out the end, repeat. Perhaps I am not getting the benefit of the design. How do you pour the metal?

There is a small hole in the middle of it, usually use clay to close it before start smelting then open it with iron stick to pour the molten, this furnace brought from Italy.

 

[Shark]

I like the design as well. I would also like to see more pictures of the drive system if possible.

 

[Ayham Hafez]

T

I like the design as well. I would also like to see more pictures of the drive system if possible.

Will take more pictures tomorrow and send them here

 

[goldshark]

There is a small hole in the middle of it, usually use clay to close it before start smelting then open it with iron stick to pour the molten, this furnace brought from Italy.

The door end doesn't look like it has much of a lip, to contain the melt. I will look for the new pictures, thanks.

 

[Ayham Hafez]

When you get the proportions right for flux to sweeps to produce a fluid mass you should charge the furnace and get a load molten. Add enough lead to create a pool in the furnace when the lead melts. After it is rotating for a while the lead collector should load up with values leaving a fluid mix of slag with the values in the collector metal.

You should take advantage of the heat in the furnace at this point and slag off about half of the molten flux. The values will be in the molten lead which will not pour out until you fully tip the furnace when pouring. Refill the furnace to the level it was at before you slagged off with more fluxed sweeps and let it run.

Inspect the slag closely for particles of gold. Gold will indicate you didn't allow it to rotate long enough. By using the heat in the furnace the new material should liquify faster but still let it rotate to be sure it all collects.

Continue slagging off and adding fresh sweeps with flux until you are done. The last pour will contain the molten collector and the values. It is quite obvious when the molten metal is pouring out instead of flux.

If you can, send a photo of the furnace you will use. If the owner of the furnace had someone who did this and did it with copper, perhaps he has a copper cell you can buy cheap. Copper would be my preferred collector.

For my main business,I asked an engineer to prepare a design for copper sulphate cell, it will recover 1400 gram per hour,he advised me with the following parameters:
1 power supply 8 volts, 1,000 Amp
2 pvc pools each one 80 cm x 60 cm x 60 cm
5 anodes per pool,total anodes 10
15 cm between anodes
Anode weight is about 50 kg,will use filter bags

Your recommendations are highly appreciated

 

[4metals]

This is a very similar type of rotary furnace I have worked with.

the pour hole is plainly visible in the center. This furnace did not rotate 360 degrees, it rocked back and forth, the pour spout never was below the liquid charge level when operating and the charge chute was also always above the level of the charge.

The material to melt was loaded in the top chute and there was a lid to keep heat in. The furnace in normal operation rocked slowly back and forth always stopping and reversing before the molten charge was near the pour hole.

In order to slag off the rocking rotation was stopped and a manual control allowed the rotation to go past the normal stopping point and allow slagging off or complete emptying of the furnace.

I have seen furnaces like you have in South America and the pour was from a tap hole as you described. I never liked it because the pour was all or nothing once the plug was tapped into the furnace.

The furnace I saw in south America was in the early 1980's and I assume they have improved the design.

Does the furnace have a controller to allow the rotation to reverse at a certain point? It would be easy to install that type of control with some fixed stops welded to the outer steel so when the barrel reaches a certain point it hits a switch and changes direction. Then you have to configure it to bypass that point to drain the furnace. Much better than a knock out plug.

The furnace you have been offered is nice with the door to open to charge more material because you can easily see how much is added and never fill it above the door rim.

Look into making the furnace rock back and forth during the melt cycle if it isn't configured that way already. It will greatly simplify the process.

Also realize to totally drain the molten metal pool the drain needs to be pointed straight down. So the furnace needs to be mounted high enough to get the molds or slag trays under the furnace to do that. The cone molds in the photo above rolled right under the drain hole and the drive allowed the operator to tilt the furnace to pour and tilt it back to stop the pour.