dissolving steel particles

[Southbound]

I need your expertise, this has nothing to so with gold refining, but i know you can probably point me in the right direction.

I sharpen for various people and i use Vitrified aluminum oxide/corundum stones. When i buy them on eBay they are loaded with metal swarf because people didn't take care of them. Anyways i have tried using 31% full strength muradic acid to dissolve the metal particles, it has removed some but not to my satisfaction. I have had some in a closed container for 4 days and still aren't spotless. I know how to work with this stuff safely because i clean masonry with this stuff all the time, but not at full strength. Is there anyway to make this stuff stronger?

Thanks,

 

[Martijn]

Give it a bit of heat, 60 to 80 degrees Celcius on a hotplate in a sandbath in a heat-resistant glass. Preferably a labglass beaker and cover it loosely.
Acids work much better when hot.

Beware of the fumes and don't do this indoors unless you have a fumehood.

Test it on a small piece first to see the stone does not react or disintegrate itself.

 

[Southbound]

Give it a bit of heat, 60 to 80 degrees Celcius on a hotplate in a sandbath in a heat-resistant glass. Preferably a labglass beaker and cover it loosely.
Acids work much better when hot.

Beware of the fumes and don't do this indoors unless you have a fumehood.

Test it on a small piece first to see the stone does not react or disintegrate itself.

I have an portable cooking eye, and i could do outside. So what if i put it into a galvanized steel can (like the ones used for cooking while camping) so i can place the lid over it, that wat it doesn't put off fumes towards the neighbors ,and vehicles etc. So heat makes acid stronger? I know that room temperature 31% muradic acid doesn't eat these hard vetrifed aluminum oxide corundum stones. I did some research prior to doing this. Its technically a saffire.

 

[Southbound]

What i meant to say, was put the galvanized large can on the cooking eye, (outside)with water inside it then add the glass container filled with acid and the stone, and place it into the can filled with water (kinda lika a double boiler) and put a lid over until its heated.

 

[Shark]

Very dilute muriatic acid will remove galvanized coatings extremely fast with lots of smoke. I used it for years to remove galvanized coating from chain.

 

[Southbound]

I would think that 31% would eat all metal particles??? I may try the heat thing tomorrow. Just put the glass jar filled with muriatic acid and the stone inside the galvanized steel can and fill up the can so it will contact the glass and heat the jar with acid, i will put a lid on the galvanized can. On a serious note, it will not explode if a put a lid over the can??

 

[Shark]

Before you do that, take a small amount of acid in a glass and sit it near the bucket. Just being close to galvanized metal the acid will start to smoke. I am not sure how that would react in confined spaces. But it will eat at the metal.

 

[Southbound]

Before you do that, take a small amount of acid in a glass and sit it near the bucket. Just being close to galvanized metal the acid will start to smoke. I am not sure how that would react in confined spaces. But it will eat at the metal.

I am doing it outside. The acid will be in a jar inside the bucket of water, so the water inside the can will heat up the acid in the glass jar. Being outside i don't want heavy acid fumes going towards my vehicles or my neighbors, thats why i want to put lid on it.I just can't figure out why it will not eat all the particles coverd in acid in a plastic container for days . Its steel, but not chunk's,only steel dust ??

 

[Yggdrasil]

I am doing it outside. The acid will be in a jar inside the bucket of water, so the water inside the can will heat up the acid in the glass jar. Being outside i don't want heavy acid fumes going towards my vehicles or my neighbors, thats why i want to put lid on it.I just can't figure out why it will not eat all the particles coverd in acid in a plastic container for days . Its steel, but not chunk's,only steel dust ??

It may not all be steel, some blades are heavily alloyed and those metals may be less prone to acid attack.
Plain dirt/clay/oxides from the blades may also be filling the pores.
Have you tried a stiff brush?

 

[grainsofgold]

The swarf is only embedded so deep into the wheel correct ?

Why not use a diamond tip dresser and dress the stone thus removing the contaminated surface layer ?

GOG

 

[Yggdrasil]

The swarf is only embedded so deep into the wheel correct ?

Why not use a diamond tip dresser and dress the stone thus removing the contaminated surface layer ?

GOG

Excellent idea, that needs doing from time to time anyway.
At least when redressing the wheel.

 

[Martijn]

I would use an old stainless steel pan for that. I picked one up at the junkyard just for that purpose.
Just in case the glass breaks, you wont be able to stop the reaction with galvanized steel.
Keep the 'lid' on the glass and loose so it can breathe a bit. Any pressure build up will lift the lid and let the gases leak out. I use a glass teacup dish for that.
If you keep the lid on the can or pan, the fumes will fill the can.

 

[Deano]

Best dissolution of iron and iron complexes, greater than by aqua regia, is achieved by leaching with hydrochloric acid and a stannous compound, preferably stannous chloride, in a heated container.
The negative Eh from the stannous is what drives the reaction.
Deano

 

[Yggdrasil]

Best dissolution of iron and iron complexes, greater than by aqua regia, is achieved by leaching with hydrochloric acid and a stannous compound, preferably stannous chloride, in a heated container.
The negative Eh from the stannous is what drives the reaction.
Deano

Interesting indeed, can this be put to use in other settings?
Like refining other refractory ores?
Does it work only in HCl?

 

[Shark]

Any ratio's or would it depend on the exact material content? Temperature ranges?

 

[Deano]

Practically the stannous effect only works with HCl. You need a strong acid, preferably a mineral acid, to achieve reasonable rates of dissolution of iron. Both nitric and sulphuric acid are strong oxidisers and would change the stannous to stannic which does not work at all.
It will work with most refractory ores but the cost of the stannous prohibits the use of it for all but extremely high grade ores.
You need to have enough stannous present in the leach to keep the Eh negative, it really does depend on the ore composition as to how much stannous is needed.
Like most dissolution reactions the application of heat will drive the reaction to completion more quickly, simmering is OK.
Deano

 

[4metals]

That is interesting. Does the degree of negativity of the Oxidation, reduction, potential effect the reaction rate? Referencing any random ore that you have worked this way what is the Hydrochloric Acid to SnCl2 ratio. Surely a factor because as you said tin isn't cheap anymore.

 

[Yggdrasil]

Practically the stannous effect only works with HCl. You need a strong acid, preferably a mineral acid, to achieve reasonable rates of dissolution of iron. Both nitric and sulphuric acid are strong oxidisers and would change the stannous to stannic which does not work at all.
It will work with most refractory ores but the cost of the stannous prohibits the use of it for all but extremely high grade ores.
You need to have enough stannous present in the leach to keep the Eh negative, it really does depend on the ore composition as to how much stannous is needed.
Like most dissolution reactions the application of heat will drive the reaction to completion more quickly, simmering is OK.
Deano

Hmm, I’m intrigued.
Is it the Stannous that do it, or the negative eH?
Can a electrolytically induced eH do the same job?

 

[Deano]

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

 

[Shark]

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