Activated Charcoal and Leach Back?

[Biollante]

Hi,

What is the story on folks and activated charcoal or any other adsorbent material and "leach back?"

Once activated charcoal or Purigen adsorbs something it tends to stay there. While it is possible to desorb either activated charcoal or Purigen that condition would be really, really hard on our plants and critters.:eek-new:

I am curious how activated charcoal or Purigen “leaches back” stuff into the water.

• When the adsorbent is full, it simply does not take on any more stuff.
  
• It is possible that some heavier stuff could knock some lighter stuff off,
  
  • but this is minor, usually it will just drive stuff further in.
    

In the case of activated charcoal in air filters, once the filter has adsorbed as much as it can heavier gas molecules will tend to dislodge lighter molecules.

Lenntech, one of my personal favorites has Activated carbon adsorption page with a nice overview and lists of stuff activated charcoal will probably remove.

Most of us I assume understand cation-exchange capacity (CEC) and for that matter Anion Exchange Capacity (AEC) are not the same as adsorption.:highly_amused:

Biollante

 

[Gerryd]

Hi Bio,

At the risk of getting in way over my head...

1. Could not the totally adsorbed media itself now be a source of water 'contaminants' similar to water flowing over various rock alters the water chemistry?

2. That said, if we could determine when the media is 'full' IMO it should be removed as it is no longer 'actively effective'. Similar to removing mechanical filter media once it is dirty...

I am very interested to follow this discussion although I do not use either product much, although I am currently using both So, am interested in the answers...

I am now off on the path to elightenment so that I fall under your last assumption I understand they are different but not the details of either CEC or AEC. The TLA, yes, the understanding, not yet.

 

[client]

Spread the news

I still fail to understand where on earth was someone assuming that activated carbon of the first category I have tried to describe and purigen will leach back. It was about a certain activated carbon, with positive sites represented by heavy metals like Zinc, that was adsorbing nitrates at a pH of 6.2. The desorption of Zinc into the water column at that pH was about 1.4 ppm for a carbon activated with elemental Zinc and somewhere around 1.8 ppm Zn and 0 sulfate for a carbon activated with ZnSO[sub]4[/sub].

A ZnCl[sub]2[/sub] activated carbon will leach back into the water column at a pH of 7.00 a bit under one percent adsorbed nitrate: 1 gram of activated carbon in 50 mL of 200 ppm NO[sub]3[/sub], with a removal rate of 52%, rinsed afterward in distilled water and placed in 20 mL of a solution without nitrates; for 24 hours it was shaken mechanically. From here the presumption that the enzymatic and microbial processes will leach back nitrates, consulting also the Zn availability/solubility graph on the pH scale. None to little comment on the CEC/AEC thing. It isn't even logical to think that way. All I did was to state some pH units at which the exchange could take place in the substrate, not in the activated carbon. I wanted at least to correlate the date found in some cec/aec clay-related books with the pH unit at which the heavy metals, from the experiment I was reading, were available, and to understand what advantages or disadvantages some other malefic device would have to keep me low on the toxicity gradient.

I guess the hobbyist world already took fire and there is a new colorful coat in town. Clown-like. What do I have to gain from sharing what I have read and I became curious about if not an opinion or thought from Bio. Spread the news, like these hobby related things shouldn't be discussed on forums, because, on forums people come to ask if there is a leach out of the activated carbon and they get cold at heart, trembling beneath the storms of yet another junk science oriented device guy.

Nitrate Adsorption 01 ; Nitrate Adsorption 02 .

 

[Tom Barr]

Leaching can occur when bacterial communities form and attack the GAC. As they attack the substrates(the things the GAC adsorbed), their breakdown products are released back into the system. These products may be less harmful(typically for us), the same, or more toxic.

Client: does the pH factor use CO2 as the method to adjust pH, or is it some other acid in solution? Acids are used to leach metals from their sulfate salts, but I'm not aware if CO2 and water change used to do this task/function.
I do know that low alkalinity will favor dissolution of metals(say 20ppm) and keep them in solution longer than say high alkalinity(100ppm +).

In the paper, they do not cite how the pH was set at 6.2.

The notion that adding Zn to the GAC helps adsorb anions like NO3 is interesting. Most chemical adsorbants for aquariums do not do this I would suggest. The metals might be able to bind NO3, but they also have the potential to leach depending on the environment.
In aquariums that can vary widely. In filters,sediments etc........ the Redox values will also govern adsorption. The more negative values will release these anions and cations for that matter.......into the water column.

The potential for highly reducing conditions in GAC inside a filter after few months and bacterial colonies is rather high. Small spaces will clog, preventing O2 from diffusing in.
If the Zn loaded GAC was used only for a little while, say 2-4 weeks, then it might serve a good purpose.

Or if you wanted a slow release form of trace metals or NO3 etc.......but that's what the fish are for

 

[Biollante]

Dissolved Solids Removed Or Added, the Force of Water

Hi Gerry,

Good questions, I had not thought of it this way round.

The quick answer is a rock giving up material to the water is a different process than activated charcoal removing material from the water, but the answer still is the force of water.

Please allow me an oversimplified explanation:gw

• The forces holding the molecules that make up the rock are weaker than the waters force to separate the molecules (dissolve the solid).
  
• The forces attracting the dissolved solid to the surface (adsorbent) are greater than the force of water to keep them apart.
  

To your second point, in the case of activated charcoal, replacement or reactivation on a regular basis, in the case of Purigen, reactivation, Seachem calls it recharging.

Empirically it is possible to determine the loading. For the cost, assuming you are using regular everyday aquarium activated charcoal, just replace, if it is Purigen “recharge it.”

For now, understanding that CEC is different and that clays and silt, operate differently is for the moment good enough and puts you far ahead of some folks I could name. Then we get back to willful ignorance.:highly_amused:

Biollante

Hi Bio,

At the risk of getting in way over my head...

1. Could not the totally adsorbed media itself now be a source of water 'contaminants' similar to water flowing over various rock alters the water chemistry?

2. That said, if we could determine when the media is 'full' IMO it should be removed as it is no longer 'actively effective'. Similar to removing mechanical filter media once it is dirty...

I am very interested to follow this discussion although I do not use either product much, although I am currently using both So, am interested in the answers...

I am now off on the path to elightenment so that I fall under your last assumption I understand they are different but not the details of either CEC or AEC. The TLA, yes, the understanding, not yet.

 

[Biollante]

Still Not Understanding The NO3 Thing

I still fail to understand where on earth was someone assuming that activated carbon of the first category I have tried to describe and purigen will leach back. It was about a certain activated carbon, with positive sites represented by heavy metals like Zinc, that was adsorbing nitrates at a pH of 6.2. The desorption of Zinc into the water column at that pH was about 1.4 ppm for a carbon activated with elemental Zinc and somewhere around 1.8 ppm Zn and 0 sulfate for a carbon activated with ZnSO[SUB]4[/SUB].

A ZnCl[SUB]2[/SUB] activated carbon will leach back into the water column at a pH of 7.00 a bit under one percent adsorbed nitrate: 1 gram of activated carbon in 50 mL of 200 ppm NO[SUB]3[/SUB], with a removal rate of 52%, rinsed afterward in distilled water and placed in 20 mL of a solution without nitrates; for 24 hours it was shaken mechanically. From here the presumption that the enzymatic and microbial processes will leach back nitrates, consulting also the Zn availability/solubility graph on the pH scale. None to little comment on the CEC/AEC thing. It isn't even logical to think that way. All I did was to state some pH units at which the exchange could take place in the substrate, not in the activated carbon. I wanted at least to correlate the date found in some cec/aec clay-related books with the pH unit at which the heavy metals, from the experiment I was reading, were available, and to understand what advantages or disadvantages some other malefic device would have to keep me low on the toxicity gradient.

I guess the hobbyist world already took fire and there is a new colorful coat in town. Clown-like. What do I have to gain from sharing what I have read and I became curious about if not an opinion or thought from Bio. Spread the news, like these hobby related things shouldn't be discussed on forums, because, on forums people come to ask if there is a leach out of the activated carbon and they get cold at heart, trembling beneath the storms of yet another junk science oriented device guy.

Nitrate Adsorption 01 ; Nitrate Adsorption 02 .

Hi Client,

Okay, I will try to answer this somewhere; this is after all a thread about adsorbents “leaching back.”

I am still not sure where the idea of nitrate removal comes from in the context of the thread that created all this angst. I will post this here though it could as well be in the thread referred too.

My understanding of what you are saying goes back to Florin’s Starting new tank - codename Frankenstein - critique wanted, your post [HASHTAG]#229[/HASHTAG].

I understand, understood your recommendations, I found your comments

I am still trying to figure when will someone actually want to do something about that organic material. It has a mystery source but it has its place in there?

snarky, churlish and uncalled for, given the context of the thread.

As to your recommendation

Anion Exchange Resin

, if I thought Florin owned one I might have recommended it as a method to reset the water column, as a solution it like 3 out of 4 of the solutions, involved removing things that are desirable, in my opinion, if you have a differing opinion, present it in a coherent manner.

As to your recommendation

KOH, ZnCl2 or ZnSO4 Activated Carbon

, I was aware of the activated carbon Florin had and I was not in favor of removing Nitrates. These activated carbons are not in common aquarium use. I have no experience with these products so I am reluctant to recommend something I have not used unless I understand the product, I am not sure about possible side effects. Tell us your experience and why you think it is a practical action to take.

As to your recommendation

Sochting Oxydator

it may well be fine, again I was aware Florin had access to 3% Hydrogen peroxide and Potassium permanganate, both of known concentration. Though you proceeded to provide more and more information, none of it was particularly useful or actionable. I tried, perhaps not hard enough; too learn the quantities of Hydrogen peroxide into the aquarium so that we can analyze results. As far as I can tell there is no published data to allow me or any other reasonable person to make an informed decision. Perhaps sharing your personal experience and present us with empirical data would be persuasive.

The thing all your recommendations have in common is a distinct lack of information about your experience, always creates a certain level of doubt in my mind.

As to your recommendation

Even more siphoning and titanic care, it reads as maintenance.

My experience with Florin is that he is diligent in his maintenance, and an open and honest individual. Fair or not this line as much as any probably colored my few of your comments.

I am in the process of reviewing everything and I will post more as I see it.

As someone who has spent much of my life trying to express complex views to folks in languages other than my own, I may have misunderstood; if I did, I will apologize.

There is nothing wrong with expressing your views, when joining an ongoing conversation it is polite to understand the context and perhaps not assume the others are stupid. This can begin to look like willful ignorance or worse.

If it is an argument you think important, but disruptive to the thread, start another thread.

Biollante

 

[feh]

Interesting... so leaching is actually possible? Is there a link to this paper? I'd like to read it even if its over my head.

 

[Biollante]

More On This I think...

Hi,

If I may be blunt, I do not think any significant leaching of adsorbates from activated charcoal[SUP]1[/SUP] occurs under any “normal” aquarium operation.

The most commonly cited leachate seems to be Phosphorous or phosphates apparently in the olden days a phosphoric acid wash was used to finish the activation process. Apparently the howl from the reefer community[SUP]2[/SUP] let loose such a howl that even the cheap aquarium activated charcoal isn’t acid washed any longer.

Though the phosphate was leaching from the activated charcoal, phosphate was never an adsorbate, so doesn’t count for our purposes and phosphates really are not a problem for planted tanks anyway.

The biological leaching is the hardest for me to be sure of since by its nature, it is biological and by definition adsorbates are not chemically changed, so it seems reasonable they would remain yummy treats for various micro-critters.

Biollante
[SUP]1[/SUP]Give me a break, I mean commercially available aquarium hobbyist activated charcoal, cheap or expensive.
[SUP]2[/SUP]Folks who keep reef aquariums and smoke a certain Mexican ditch weed (for medicinal purposes only, of course).

 

[Biollante]

Passionate Guy, I Like Passion

I guess the hobbyist world already took fire and there is a new colorful coat in town. Clown-like. What do I have to gain from sharing what I have read and I became curious about if not an opinion or thought from Bio. Spread the news, like these hobby related things shouldn't be discussed on forums, because, on forums people come to ask if there is a leach out of the activated carbon and they get cold at heart, trembling beneath the storms of yet another junk science oriented device guy.
Last edited by client; Yesterday at 12:18 PM. Reason: Too bad there is no way to upload some materials.

 

[feh]

Hi,
If I may be blunt, I do not think any significant leaching of adsorbates from activated charcoal[SUP]1[/SUP] occurs under any “normal” aquarium operation.

I was referring to Tom's comment.

Leaching can occur when bacterial communities form and attack the GAC. As they attack the substrates(the things the GAC adsorbed), their breakdown products are released back into the system. These products may be less harmful(typically for us), the same, or more toxic.

I don't see any leaching but I also don't leave the GAC in the reactor very long and is changed out bi-weekly. I don't rely on it for phosphate removal. I didn't know about the phosphoric acid washing, but I think most PO4 issues in a reef tank come from over feeding and poor nutrient export practices.