The PH of copper/Cu & referenceable source for the info?

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 Timmd 26 Apr 2021

Am I right in thinking that the mineral Cu is around a PH of 7, and does anybody know of a university worthy referenceable source for including in some work? I seem to have a brain fog about finding one.

It's about changes to the PH of water running from Burbage Brook and into the river Sheaf, and it seems to be that lead and copper can leach into the river system, which may effect the PH (but not solely).

Thanks.

Post edited at 12:26
 Philip 26 Apr 2021
In reply to Timmd:

Its pH not PH. Small p to indicate -log base 10 of H, concentration of H+ (which in reality is actually H3O+). A small point, but one that may help you research.

Solids don't have pH, you can only measure the pH of water, and dissolution of small amounts of things will change the pH, but probably more significant the other way, change in the pH can effect the dissolution of solids. Maybe this will help you find some more details.

A quick Google finds a lot on pH and it's effect on solubility of lead and copper. One of the top hits is a thesis with probably plenty of background and references.

https://core.ac.uk/download/pdf/217194663.pdf

As for universities - Cranfield have a strong water science/engineering group.

Hope that helps whatever you issue is.

 Philip 26 Apr 2021
OP Timmd 26 Apr 2021
In reply to Philip:

I think the small 'p' would definitely help, I thought it somehow didn't look right.  I should get it finished today.

Many thanks, re both posts.

 wiwwim 26 Apr 2021
In reply to Timmd:

Also, metals can become more and less soluble at different pH's and consequently more/less bio-avaliable and toxic.  Aluminium and acid rain being an example.

Wiwwim

 hang_about 26 Apr 2021
In reply to Timmd:

You want what's known as a pH Eh diagram (Google this with Cu and you will find lots).

The redox state (Eh) and pH will determine what's in solution (or not).

A lot of Peak streams are reddish brown due to iron (Fe). Underground things become anaerobic (low Eh) and acidic (low pH) which solubilises Fe as Fe2+. As it hits the surface, it oxidises to Fe3+ (as the Eh rises) and that gives the rust colour. Similar things will happen with Cu but the mineraology differs.

Microbes strongly influence this. In some US acid mine drainage the pH is -2.5 - that's Alien blood territory!

OP Timmd 26 Apr 2021
In reply to wiwwim:

> Also, metals can become more and less soluble at different pH's and consequently more/less bio-avaliable and toxic.  Aluminium and acid rain being an example.

> Wiwwim

Yes, that is what is seeming to surface, that the pH of the water effects solubility. 

OP Timmd 26 Apr 2021
In reply to hang_about:

Is the redox state affected by the amount of oxygen in the water, with that and pH both influencing how soluble an element may be?

 CantClimbTom 26 Apr 2021
In reply to Timmd:

It's not an easy matter. Metalliferous ores tend to be deposited together, so a seam of galena (lead) with very likely be mixed in with blende (zinc), silver, copper and iron + traces of nasties like cadmium etc.  You typically get a big mishmash of stuff with a lode that is richer in one mineral and mined for that but as mining progresses and ore prices change the mine may move on to extracting another mineral from the same mine. This means the water in the area is likely to be affected by a wide variety of minerals rather than one or two

 hang_about 26 Apr 2021
In reply to Timmd:

If there's lots of oxygen in the water then the Eh will be high. It's not just oxygen though - but the switch from anaerobic to aerobic is low Eh to high Eh.

As CantClimbTom says, it's complex as we're never dealing with single molecules. My geochemical colleagues use software that calculates all of the different interactions and spits out an answer - that sometimes I believe!

OP Timmd 26 Apr 2021
In reply to hang_about:

Ha, there's some amazing software out there, I found something online a while ago which let you calculate how wind interacts with a landscape, if you entered in the approaching wind direction and windspeed.

I'm juggling a few bits of work in my first year and only need to pass, and have a sense of where to aim at to pass now I think (I get given a second go too). 

In my second year I must start the bits of work earlier.

Post edited at 15:05
 Pbob 26 Apr 2021
In reply to hang_about:

It's probably the one called called PHREEQC (awesome). 

 Wilberforce 26 Apr 2021
In reply to Timmd:

What do you mean by Cu mineral? 

As is mentioned upthread, copper (Cu) can commonly be found in one of several oxidation states (0, +1, +2) which each has different speciation chemistry.

Elemental copper (copper on its own) is poorly soluble and has limited impact on solution pH so long as it retains its oxidation state.

Cupric (Cu2+) and cuprous (Cu+) copper ions are usually (but not always) associated/combined with other elements/molecules to make compounds - such as minerals. These behave quite differently to elemental copper and their properties depend on what the other elements/molecules involved are.

For instance, cuprous oxide (Cu2O) is more soluble than cupric oxide (CuO), whilst cuprous chloride (CuCl) is less soluble than  cupric chloride (CuCl2).

Moreover, cupric oxide is mildly basic (upon dissolving in water it will increase the pH), whilst cupric chloride is a reasonably strong lewis acid (upon dissolving in water it will lower the pH).

Chemistry is complicated!

There are some simple rules of thumb though for copper/iron behaviour: 

solubility is higher at low pH and lower at high pH (due to oxide/hydroxide formation)

dissolving oxide or hydroxide minerals will increase solution pH - whilst forming these minerals will reduce pH 

dissolving other compounds such as chlorides or sulfates will reduce the pH

I hope this helps... I can send you some general references and/or solubility product constants tomorrow if you'd like.

Post edited at 23:54
 Red Rover 27 Apr 2021
In reply to Timmd:

As others have said, solids don't have a pH. But also, you can't say 'the pH of copper dissolved in water' either, because the pH of something dissolved in water depends on the concentration of the thing that is dissolved. You can only talk about the pH of a specific concentration in water.


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