Base metal mix in HCL & separation

[voeckel]

Hi,

as part of my better understanding for the reactivity series and usage in our context in the first stages of leaching, I sit here on a kind of intellectual exercise to get things straight. I leave the economical aspects aside here for it is clear that i wouldn't go through the below for a few hundred grams of Pb, etc.

Let's assume we have leached BMs and have now plenty of used HCl with unknown content up to - but without - Cu. Maybe several kilos of each base metal that is in solution, but the types of BMs in solution are unknown.

According to the reactivity series, I could start with the metal of highest reactivity and would add the next lower in list to precipitate. I.e. I have Al in there. Hence, i add Mn and Al would precipitate.

This would be a hell of two steps (precipitating, filtering) for each metal until I end up with adding Cu to precipitate Pb.

What if I hang in a piece of Cu and precipitate all higher ones in one go, but having a mix of metal chlorides precipitating? This is what is mentioned as a good way to go for dealing with our waste.
Can this mix be heated to the several melting points and the metals could be separated that way? Sounds somehow easier to me but I do not know if metal salts can be treated like that or if the metals would just return to their metal state to make ingots.

Just a hypothetical exercise. It is a way for me to better understand and digest what I see about the invovled chemistry here and shown on the net.

How would you go for separating all metals dissolved in your HCl batch?

Thanks.

 

[tek4g63]

Are you wanting to attempt to drop your base metals separately to try and sell them? Or do you just want to get all metals out of waste solutions to make them safe to discard?

 

[butcher]

Lead chloride is one of the exceptions of soluble chlorides, so you will not have much lead soluble in solution.

You cannot separate metals in a melting process, (except for very minor exceptions).

Aluminum in HCl can make a gelatinous substance, this gel depending on conditions can hold or trap other metals in solution, it is very hard to dry or deal with in waste if aluminum is used to cement metals from solution, aluminum dissolving in the acid also remove hydrogen from the acid as hydrogen gas as it forms aluminum chloride salts (gel), be careful the hydrogen gas, just like charging a battery you do not want to hang your head over a 5 gallon bucket with a cigarette in your mouth.

You can separate several metals from each other using the reactivity series and the different metals to replace metals in solution, but also you have to realize some of the metals have electrode voltage potentials that are so close together that it would be hard to selectively separate these from each other.

It would be hard to find a market for many of these metals even if you do get them, unless you had tons and found someone to buy them. Some of the metals would be very hard to melt back to metal form, and when you could it will cost more in fuel time and trouble than the metal was worth.

 

[voeckel]

Are you wanting to attempt to drop your base metals separately to try and sell them? Or do you just want to get all metals out of waste solutions to make them safe to discard?

It is more a theoretical exercise. I try to better understand, how to work with our acids and their metallic products. Most of us are not in the position to have commercial amounts available. It is more about the general understanding, what would be possible and how so that those who want to focus on Tin recovery from the BMs in the HCL bath could get their Tin, others their... whatever one might be after.

In the end, we will have dealt with waste HCl, cleaning it for reuse, but still have left lots of base metals precipitated, that will accumulate over time. So what to do with it?
Just bringing it to a scrap yard? Or would this output-mix have to be treated by a special disposal company? I am clear about the liquid side of things but try to understand, what I should do with my precipitated leftovers once I filtered them out.

I.e. for solder, it would mean that someone would have to - following the reactivity series - add more tin to precipitate all higher metals (from Nickel upwards), filter, then add copper to precipitate Sn & Pb.

These two could then be brought back to their metal state for reuse? How? By exposing it to heat, melting? Asking for this scenario for we don't have HBF4 and Ti4+ as small refiners to remove solder selectively...

I know that recovery of Tin has been discussed several times on the forum but it shall serve as a logical example for any type of BM dissolved, that one would like to go after. That's because I think it is Tin that most would be interested in to be shown in a clear step-by-step example due to its market price and amounts available.

EDIT:
Adding the reactivity series for those who haven't had a look at it or don't know what it is. Also one more question please. It is said several times on the forum in different posts that ph influences the precipitation process. Hence, what would i have to google for if i would like to know about what metal needs what kind of ph environment to accommodate precipitation? Stuck with this, I just don't really understand it and don't know what to look after (search keywords, etc).

 

[ericrm]

can someone tell me why palladium and many other metal are never shown is the reactivity serie that i fond on the internet?

 

[Gratilla]

It is said several times on the forum in different posts that ph influences the precipitation process. Hence, what would i have to google for if i would like to know about what metal needs what kind of ph environment to accommodate precipitation? Stuck with this, I just don't really understand it and don't know what to look after (search keywords, etc).

The Solubility Curves on This Link should get you started on selective precipitation by pH adjustment.

Additionally, metal salts can be individually recovered using Solvent Extraction (SX), although perhaps only copper, nickel and tin would be economically viable. Once you get above the 2 liter volume limit (?) of separatory funnels, there are some quite simple counter-current SX systems that you could probably build yourself. In all of this though the caveat of economic viability applies.

 

[voeckel]

Thanks Gratilla!

This is a good link for starting to learn about it. It provides the phrases and keywords for a continuous research on this to better understand this process. :idea:

 

[butcher]

Precipitating metals from solution using pH works, but it is not very selective at all, theoretically it can somewhat be done, but doing it selectively is practically impossible, it is very hard to adjust the pH to a certain point, and most of the metals overlap and will precipitate out with other metals, notice in the chart how many of these metals begin to precipitate at about the same pH range, at a certain pH you would have many of these metals as precipitants in different ratios and also many in solution at different ratios.

The document is discussing treating waste solutions (or waste water), here the chart (solubility of metal hydroxides) is very good (and using pH to precipitate metals from solution is useful) this chart shows us that pH9 is best to drop most metals from our waste solution, and then we can bring the pH back down to pH7 leaving Iron in a saltwater solution.