Using a low pH to leach copper from LR

[New Reefer]

A fellow reefer has inadvertantly polluted his reef tank with copper (we're still trying to think how, but suspect that either a brass screw or some copper wire "trimmings" were dropped into the tank during the initial setting-up of the system). His system has a total volume of 1500 liters (390 gallon) and about 200 kg (450 lb) of live rock.

Live rock is quite scarce, and *very* expensive here in South Africa, and if at all possible he would like to keep the rock, even if all life is killed off in the treatment process (most worms, etc. have already been lost due to the copper...). If the copper can be removed, a small addition of new live rock can then re-seed the dead treated rock.

With this as background, please answer the following questions:

1. I believe that copper is more soluble in water at a lower pH. Is this true?

2. If we treated the water by bubbling CO2 into it we should easily be able to drop the pH to 6, or even slightly lower, if necessary. Would it be a viable method to leach a large amount of copper from the rock? If yes, how low should we drop the pH?

3. Would it work better to use RO water, rather than salt water?

4. I'm proposing that we do one CO2 treatment and keep the low pH water in circulation for a day or two before discarding it. Would this be enough time to leach out the maximum amount of copper?

5. Any other suggestions?

Thanks for any feedback

[bertoni]

You could try a muriatic acid dip, if that's available. Be careful with it. The CO2 approach might work as well. I don't know how long it'd take to remove carbon with that method, though. Is the live rock set up such that removing it is difficult?

[New Reefer]

Hi Bertoni, and thanks for the reply.

Removing the rocks won't be difficult, just tedious (450 pounds of rock !!)

As the original rockscaping is looking quite nice I would prefer to treat the rocks in the tank - however, in practice the owner of the tank would have to remove just about all the rocks before he will be able to catch his fish, and removing the fish is a *must do*.

Any further thoughts/comments on the actual questions in the original post ?

[bertoni]

I can only guess at some of them. A low pH dip will do the trick. A pH of 6 should be low enough, but how long it's take to do the job is anyone's guess. I'd probably use RO water, since it's likely to dissolve the solids more efficiently. I don't know how long it'd take, but I'd monitor the rock and judge from that.

[New Reefer]

Thanks again for the input.

OK - final plan:

The rock will be moved to plastic 44 gallon drums, which will be filled with RO water.

CO2 will be bubbled into the drums, with the CO2 supply feeding directly into the intake of a circulating pump.

The CO2 drip rate will be monitored to maintain the pH at 5.9 - 6.1.

The rock will be treated for at least 12 hours after reaching the target pH.

A 100 water change will be done using RO water, and the process will be repeated.

Testing for copper will be done after each treatment cycle, and continued untill test does not detect any copper (<0.1ppm).

Rocks will then be kept in untreated RO water for at least one week - is still no positive copper, then returned to tank, and the tank started again with freshly made salt water.

Tank will then be cycled as normal, and one copper sensitive invert introduced to test for survivability before slowly returning all the other livestock over a period of a few weeks.

Comments, PLEASE.

[Icefire]

You could try a copper test and some Poly filter pad, they will turn blue while absorbing copper.

CO2/low ph will dissolve some of the rock.

A muriatic dip would be quicker, you could test it.

[New Reefer]

<a href=showthread.php?s=&postid=10301031#post10301031 target=_blank>Originally posted</a> by Icefire
You could try a copper test and some Poly filter pad, they will turn blue while absorbing copper.
Living at the southern tip of Africa makes it quite difficult to just get anything - I've searched, but have not yet found any dealer who stock Poly filter pads...

<a href=showthread.php?s=&postid=10301031#post10301031 target=_blank>Originally posted</a> by Icefire
CO2/low ph will dissolve some of the rock.

A muriatic dip would be quicker, you could test it.
Don't you think that the muriatic acid would also dissolve the rock?

Also, I'm not sure if a "dip" in the acid would allow copper trapped inside the porous rock to dissolve as well as a more prolonged "bath" in a slightly less acidic liquid such as the CO2 treated RO water.

Hennie

[New Reefer]

deleted double post...

[oct2274]

i would run some CupriSorb in the aquarium for quite a while after adding livestock to be on the safe side.

Here is a link to it
http://seachem.com/products/product_pages/CupriSorb.html

[Icefire]

Both will dissolve the rock

You might have a problem getting a low ph with CO2 as at 7.6, the rock will buffer the bath.

a 2-5 mins dip with some swiching in 1:10 diluted muriatic acid should be enought

[bertoni]

I agree that both treatments will dissolve some rock. The dissolution should be accompanied by some fizzing, so that'll be a visual sigh. I agree that dropping the pH might be rather difficult, as noted, but I'm not very sure about the dynamics of the situation.

[mavgi]

if you can take the rock and put them in big bucket with a new (fresh) RO/DI water for one month , and put there strong pump to circulate . you will need to change the water 2 time and on each time you change brush the rock . i did that in the past on 220lbs live rock and the copper gone . also on the tank make weekly 20% water change and the cooper will go to . when you do the water change try to brush the back of the tank and the glass corner to .

after i did that the cooper gone and on the rock was living back pods...

if he have sand in his tank it will be better to change it .

[New Reefer]

Thanks again for your thoughts.

<a href=showthread.php?s=&postid=10303826#post10303826 target=_blank>Originally posted</a> by mavgi

if he have sand in his tank it will be better to change it .
OK, the sand has been thrown away.

Treatment has started, but I have not spoken to him since... will report back on progress over the weekend.