Disolving Borax after melting

[BikerBudgie]

Hi all, my first post

firstly great forum, I have 'lurked' for many years but this is my first time registering and posting. I have worked in various scrap buying operations for the past 8 years but have rarely got involved in the actual refining other than 2 days in an AR lab recovering stones set in jewellery.

This should be a fairly simple question ( I hope) i have a barrel full of 'slag' predominantly Borax decahydrate that has been melted with carat level gold and silver. I know some metal is held in there and in the past i have remelted it adding sodium nitrate or potassium nitrate to retrieve as much as possible before sending it away for final refining. I was wondering if there was an easier method? after-all powdered borax will dissolve in hot water, how hard can it be to separate the 2 after combining? (probably very lol)

your Help appreciated
BB

 

[MarcoP]

Hi and welcome!

10% sulfuric acid and little heat will do the job just fine, you could also break the borax slag to speed up the process.

Marco

 

[g_axelsson]

When you melt borax decahydrate the water is lost, so what you now have is anhydrous borax.

I agree with MarcoP, crush fine and treat with sulfuric acid.

Göran

 

[BikerBudgie]

Hi and welcome!

10% sulfuric acid and little heat will do the job just fine, you could also break the borax slag to speed up the process.

Marco

Thank you both for swift replies, MarcoP you mention a little heat - are we talking hot plate or furnace?

I also had an idea, instead of using Aqua Regia for diamond removal from gold/silver mixed scrap would melting it up and then treating the 'flux' to your method return stones too? do diamonds get damaged at 1000 deg C? it maybe a cheaper way for tiny 1 point stone clusters en masse

 

[MarcoP]

I would stay in the 60-80 Celsius range, but no more then that, just to speed up the reaction. Even with no heat it should be fine.

 

[FrugalRefiner]

I also had an idea, instead of using Aqua Regia for diamond removal from gold/silver mixed scrap would melting it up and then treating the 'flux' to your method return stones too? do diamonds get damaged at 1000 deg C? it maybe a cheaper way for tiny 1 point stone clusters en masse

According to Wikipedia, "Being a form of carbon, diamond oxidizes in air if heated over 700 °C."

Dave

 

[Lou]

Heating them can ruin them.

Lou

 

[METLMASHER]

I've been saving melt slags for a long time also. I reckon as no-one is perfect, I will find some values in the digestion. I use pickle in a small covered crockpot under my workbench. I'm sure it's just what Marco P said: weak sulfuric.

When the acid becomes unable to digest scale, I can scrape the crusty deposits from the sides of the crock, add water, and revive the solution.

This tells me the evaporation has been a detriment, and there must be too little oxygen in the solution.

After a while, its usefulness is lowered to the point that the volume would be more than it's worth to revive. At that point I stock it into a catch jug for later breakdown of slags.

This is when I'll find the values again. Any fouled crucibles, prills, spills, melting plates, and firebrick, will be relieved from the slags upon them, for this recovery.

 

[FrugalRefiner]

I also had an idea, instead of using Aqua Regia for diamond removal from gold/silver mixed scrap would melting it up and then treating the 'flux' to your method return stones too? do diamonds get damaged at 1000 deg C? it maybe a cheaper way for tiny 1 point stone clusters en masse

It took me a little searching, but I knew I remembered a post about this:

Back in the late '80's I owned a refinery and one of the services we provided was chemical stone removal. One day while I was out a client came in with over 200 ounces of gold jewelry scrap for chemical stone removal. If I was in the office that day it would not have been a problem because I was aware that people from India refer to digesting gold in acid as "melting".

The secretary wrote up the receipt as a melt because that is what the customer said. He signed the receipt and left the job.

The job was placed on the incoming melt shelves and one of the melt shop staff melted it, no biggie, it melted fine and made a nice bar. Well needless to say, the customer was not happy with the result. After his attempt to sue me for ruining a gadzillion dollars worth of diamonds I only escaped financial ruin because he signed the receipt and the receipt said melt.

Dave

 

[nickvc]

An old jewellers trick was to coat any set diamonds with borax before applying heat to repair or size items items, if the stones were badly included it didn't save them but if they were good stones it stopped them from smoking the surface.

 

[BikerBudgie]

thanks all, i will stick to original plans of AR for the stones then , the outbound flux will most likely have some stones in anyway so will keep an eye for those too - just not a good plan to use as a commercial recovery method.