dissolving steel particles

[Yggdrasil]

This is all new to me, but very interesting. Where can I find more on “Eh”. Or the what Eh stands for.

I guess you know it better as ORP
Oxidisation-Reduction Potential

 

[Shark]

Yes, I know a little about that. Not much but enough to keep researching. My curiosity is how to use it more beneficially on items such as kovar based pins and other like materials.

 

[Southbound]

It is the negative Eh which drives the reaction, stannous chloride is a readily available strong reducing agent which used to be reasonably cheap.
Keep in mind that water sources used in the manufacture of HCl will have a natural positive Eh from dissolved minerals so you need to firstly add enough reducer to overcome this positive Eh.
A low level stannous solution in HCl may have an Eh of say around - 20mv.
A high level stannous solution in HCl may have an Eh of around - 140mv.
Theoretically you can get to -150mv but you are really throwing the stannous in to get there.
The lower the Eh the further and faster you can get the iron dissolution reaction to go.
The amount of stannous required depends on the starting Eh of the hydrochloric acid used, the starting Eh of your dilution water, usually run as 50%, how fast you want the reaction to go and how close to completion you want go.
There is no simple quantity for general use as all of the above factors will affect your final result.
Deano

Interesting!
I have not experimented with anything else yet. I heard heat would would make acid stronger. How much heat?
I am planning on trying to use a 5 gallon gal can and get a half gallon glass jar filled with muriatic acid and have the stone on the jar filled with acid, put the glass jar inside the galvanized can put enough water to cover them glass jar inside the can. I thought an getting it boiling hot then adding the jar and cut off the heat and place a lid not tight just to cover and keep fumes from going everywhere. What do you think? would this
make the acid stronger, and more effective at eating up the steel particles?

 

[4metals]

Any idea what the effect would be on stainless steel? Clients I have were seeing a lot of stainless with small gold inlay set with diamonds. (Cheap crap but they called them diamonds….. whatever). Classically I used reverse aqua regia with high nitric and very low Hydrochloric Acid to passivate the stainless and dissolve out the gold and loosen the stones leaving the stainless behind. It is effective but killing off the excess nitric to get the gold was a problem. Similarly with jet engine scrap.

Worth a try.

 

[Deano]

The process is good on all the grades of stainless I have tried, I expect that some of the more exotic varieties may have a problem with the included metals which are not HCl soluble.
Deano

 

[Southbound]

The process is good on all the grades of stainless I have tried, I expect that some of the more exotic varieties may have a problem with the included metals which are not HCl soluble.
Deano

Could you explain in layman's terms

"It is the negative Eh which drives the reaction, stannous chloride is a readily available strong reducing agent which used to be reasonably cheap.
Keep in mind that water sources used in the manufacture of HCl will have a natural positive Eh from dissolved minerals so you need to firstly add enough reducer to overcome this positive Eh.
A low level stannous solution in HCl may have an Eh of say around - 20mv.
A high level stannous solution in HCl may have an Eh of around - 140mv.
Theoretically you can get to -150mv but you are really throwing the stannous in to get there.
The lower the Eh the further and faster you can get the iron dissolution reaction to go.
The amount of stannous required depends on the starting Eh of the hydrochloric acid used, the starting Eh of your dilution water, usually run as 50%, how fast you want the reaction to go and how close to completion you want go.
There is no simple quantity for general use as all of the above factors will affect your final result."
How much acid and how much stannous chloride? Do i use the muradic acid 31% full strength?



Yeah i even tried a hydrochloric acid and sulfurac acid both strong strength and it didn't eat all the particles. This was some nasty powerful stuff..

 

[Yggdrasil]

Could you explain in layman's terms

"It is the negative Eh which drives the reaction, stannous chloride is a readily available strong reducing agent which used to be reasonably cheap.
Keep in mind that water sources used in the manufacture of HCl will have a natural positive Eh from dissolved minerals so you need to firstly add enough reducer to overcome this positive Eh.
A low level stannous solution in HCl may have an Eh of say around - 20mv.
A high level stannous solution in HCl may have an Eh of around - 140mv.
Theoretically you can get to -150mv but you are really throwing the stannous in to get there.
The lower the Eh the further and faster you can get the iron dissolution reaction to go.
The amount of stannous required depends on the starting Eh of the hydrochloric acid used, the starting Eh of your dilution water, usually run as 50%, how fast you want the reaction to go and how close to completion you want go.
There is no simple quantity for general use as all of the above factors will affect your final result."
How much acid and how much stannous chloride? Do i use the muradic acid 31% full strength?



Yeah i even tried a hydrochloric acid and sulfurac acid both strong strength and it didn't eat all the particles. This was some nasty powerful stuff..

Won’t it be better and faster to dress it with a diamond dressing wheel?
No nasty fumes to destroy your tools, just dust.

 

[Punterr]

It is the negative Eh which drives the reaction, stannous chloride is a readily available strong reducing agent which used to be reasonably cheap.
Keep in mind that water sources used in the manufacture of HCl will have a natural positive Eh from dissolved minerals so you need to firstly add enough reducer to overcome this positive Eh.
A low level stannous solution in HCl may have an Eh of say around - 20mv.
A high level stannous solution in HCl may have an Eh of around - 140mv.
Theoretically you can get to -150mv but you are really throwing the stannous in to get there.
The lower the Eh the further and faster you can get the iron dissolution reaction to go.
The amount of stannous required depends on the starting Eh of the hydrochloric acid used, the starting Eh of your dilution water, usually run as 50%, how fast you want the reaction to go and how close to completion you want go.
There is no simple quantity for general use as all of the above factors will affect your final result.
Deano

Hi Deano,
I have gold particles mixed with rust (from a steel crucible used to ash resin), I am currently trying this process on it to see if I can remove the iron. So far it seems to be working. Initially I used 'spent' stannous indicator that no longer worked and then added more HCL and stannous chloride and put it on the heat. I will leave it for some time and let you know what happens. Thanks for the info.

 

[kurtak]

I have an portable cooking eye

What is a cooking eye - never heard of it - I asked google "what is a cooking eye" & this is the results I got

https://www.bing.com/search?q=what+...edge..69i57j0l8.13144j0j9&FORM=ANAB01&PC=U531
Kurt

 

[FrugalRefiner]

I have heard the term "stove eye" referring to the burner on an electric stove. I'm guessing a cooking eye is similar, probably a hotplate.

Dave

 

[kurtak]

Thanks Dave - never heard of a hot plate called anything but a hot plate

It certainly didn't bring any hot plates up when I searched "cooking eye"

Another case where using the "right" terms in refining makes a difference

Kurt

 

[Deano]

Eh is usually checked using an ORP meter, handheld is the cheapest. Eh is another shorthand for ORP which stands for Oxidation Reduction Potential.
Do not leave the probe in the solution you are checking, put it into the solution to get your reading and then rinse the probe and put it into a beaker of water.
Probe readings are usually in millivolts, positive for oxidising solutions and negative for reducing solutions.
If you want to run a reducing leach without a meter it will be expensive as you will have to add a guesstimate of how much stannous to add to keep the Eh negative and this will need to err on the generous side.
HCl used in these reactions is usually diluted 1:1 with water, this is usually called 50% HCl as is is half the strength of the concentrated acid.
The only time that you would use the actual strength of HCl is when purchasing it, acid strengths commercially range downwards from 32% depending on the country of purchase.
Higher HCl strengths up to 36% are possible to buy but they are not in general use and the price reflects this.
Sulphuric acid is a strong oxidiser, in practice it does little to dissolve iron in a HCl solution. You need a reducing agent.
Deano