# copper sulfate in the flux



## ericrm (Mar 20, 2016)

hi, i dont remember who (it was from a knowledgable member so the trust is there), but longtime ago someone told me that i could use copper sulfate in a melt to upgrade the copper content on a copper/iron anode bar. but looking at copper sulfate stat is says i doent melt it "decompose" a 600deg to form anydrous copper sulfate than decompose some more to make copper oxide way before the melting temp of anyting in the crucible is obtained.
to what i understanded it was the same thing as cementing copper with iron but in a melt...

my question would be, how is it possible to do or what do i dont understand about that technique because right now i dont see how i could work...

thank you


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## FrugalRefiner (Mar 20, 2016)

I'm guessing you're referring to the Non-Chinese PCBs thread.

Dave


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## ericrm (Mar 20, 2016)

yes exactly thanks, i see that skippy didnt received an answer for the same question.



freechemist said:


> Ericrm
> The sulfate remains dissolved in the flux, the slag respectively, while Cu(II) is reduced by any metal, less precious than copper, present in the smelt-mix, to Cu(0), metallic copper. The reducing metal itself is oxidized and dissolved in the flux (slag), as a cation.
> The same redox reaction occurs in water, too, if you treat an aqueous solution of copper sulfate with e.g. metallic zinc, the sulfate-anion remaining in solution, virtually unaffected.



does it work because the copper sulfate being disolved in the flux so it decomposition temp change? because i still dont understand...


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## Platdigger (Mar 20, 2016)

Let's see if I "get it".
Once dissolved in the smelting process the copper sulfate added separates into copper and sulfate
in essence at least when like he said, the cu(11) is reduced by any more active metal (less noble)
in the mix. The copper reporting to the metal portion of the smelt and the sulfate reporting to the slag.
Right?
So the melting temperature of copper sulfate or copper oxide does not need to be reached, only the melting temperature of the copper alloy. What ever that may be.


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## ericrm (Mar 20, 2016)

platdigger, i always tought that the cementing was made to the salt figure 1. but if i follow you correctly ,once the salt is dissolved it is not a salt anymore???????????? and since it is not a salt it DOSENT have a melting point anymore ???????? am i understanding you correctly???


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## Platdigger (Mar 21, 2016)

Just learning along with you ericrm. I was mostly just trying to understand what freechemist wrote.
After doing some reading on Wiki about copper extraction techniques from ore I think my interpretation of this is wrong.
From Wiki: "Copper sulfide and iron oxide can mix, but when sufficient silica is added, a separate slag layer is formed.[18] Adding silica also reduces the melting point (or, more properly, the liquidus temperature) of the slag, meaning that the smelting process can be operated at a lower temperature.[18]

The slag forming reaction is:

FeO + SiO2 → FeO.SiO2[17]
Slag is less dense than matte, so it forms a layer that floats on top of the matte."

And then futher down talking about Coverting this is stated: "The matte, which is produced in the smelter, contains 30–70% copper (depending on the process used and the operating philosophy of the smelter), primarily as copper sulfide, as well as iron sulfide. The sulfur is removed at high temperature as sulfur dioxide by blowing air through molten matte:

2 CuS + 3 O2 → 2 CuO + 2 SO2
CuS + O2 → Cu + SO2
In a parallel reaction the iron sulfide is converted to slag:

2 FeS + 3 O2 → 2 FeO + 2 SO2
2 FeO + SiO2 → Fe2SiO4"


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## g_axelsson (Mar 21, 2016)

In a melt with copper oxide and iron metal you would get this reaction.
Fe + CuO → FeO + Cu
or some version of it as both copper and iron can have more than one oxidation state.
The clue here is that copper oxide is reduced while iron is oxidized into iron oxide. It's a standard redox reaction. The oxidation of iron gives off more energy than the reduction of copper consumes since iron is more reactive.

Correct me if I'm wrong since this is chemistry and I'm a physicist. :mrgreen: 

Göran


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## 4metals (Mar 21, 2016)

I would be more inclined to gas the melt with oxygen with a flux cap. The oxygen would be more inclined to react with the iron and put it in the slag.


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