Charcoal

[gonewild]

Horticultural charcoal is different from activated charcoal. So I searched for "forest fire charcoal runoff water contamination".
Science minded readers might want to read a sample link....
https://www.news-medical.net/news/2...ldfire-charcoals-remain-stable-for-years.aspx

 

[Ray]

Charcoal filters by adsorption -- stuff just sticks to it. This adsorption will continue until it is full up with stuff. In aquariums we experience the problem of the carbon suddenly dumping all the stuff it has absorbed into the water column with little provocation hence the need to replace it regularly. For aquariums we could regenerate the carbon by putting it in boiling water.

Given Ray's observation that is "build up minerals faster than other components" I suppose there is a threat of it releasing all the stuff it has absorbed suddenly or the fertilizer components forcing all the bad stuff back into the medium.

Tyrone, I really have to “wonder out loud” about the “suddenly dumping” part.

Adsorption doesn’t work that way. In that process, there is an energy-reduction driving force that causes the ions to be attracted to-, and adhere to the surface of the substrate. Activated charcoal is so commonly used because it has such high surface area per volume. Once adhered, it takes even more energy to shift the energy profile such that it reverses the adhesion, so in a more or less stable environment, that just won’t happen. That’s why, heat is applied to do just that and “clean it up”.

I’d bet that the “sudden” part in aquaria and pots comes when the charcoal simply cannot adsorb more and the concentration of toxin(s) it is intended to trap become high enough to lead to perceptible changes in the cultivated critter - that is, the “operator” suddenly realizes there is an issue.

 

[TyroneGenade]

I share you skepticism, Ray. What I expect is that the tank pH drops suddenly or some other perturbation and this increase in H+ or other molecules forces other molecules off the carbon. I don't expect it has the same affinity for all molecules and ions...

Whether activated or not, charcoal has adsorptive properties. This is greatly increased by activation. I expect regular charcoal gets saturated much sooner but once some salts have been adsorbed the salt creep will set in -- which I guess is what you are seeing, Ray.

Activated carbon is often washed with acid to get rid of the remaining wood ash.