Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: scientizscht on 30/07/2019 22:04:15

Title: How to calculate change in concentration in a solution with activated carbon?
Post by: scientizscht on 30/07/2019 22:04:15

Hello

If I have a water solution in a bottle with a pollutant dissolved in a specific concentration.
I then put a small piece of adsorbent like activated carbon in the bottle.

How can I calculate how fast the concentration of the pollutant will drop?

Is there an online calculator to help me with that?

What physical parameters do I need to know and how do I use them to calculate the drop in concentration?

Thanks!

Title: Re: How to calculate change in concentration in a solution with activated carbon?
Post by: Bored chemist on 30/07/2019 22:13:47

Quote from: scientizscht on 30/07/2019 22:04:15

How can I calculate how fast the concentration of the pollutant will drop?

You probably can't.

For a start, "activated charcoal" comes in many different grades.
Also, for gases, there's this (other models also get used)
https://en.wikipedia.org/wiki/BET_theory

but having a solvent present makes it more complex.

And that all just gets you the equilibrium concentration you will reach.
Trying to calculate rates makes it even more challenging (except in a few simple cases).


Once again, it's more likely that you will get something useful if you actually say what you are trying to do.

Title: Re: How to calculate change in concentration in a solution with activated carbon?
Post by: evan_au on 31/07/2019 05:22:15

As BET theory states, a major impact is surface area - and activated carbon has a large surface area.

You can use the BET method to estimate the surface area:
https://en.wikipedia.org/wiki/BET_theory#Activated_carbon

Finely dispersing the activated carbon (rather than leaving it in a big lump) and continual stirring will also affect the rate of absorption.

Of course, then you have the problem of removing the activated carbon, and safely disposing of its pollutant load...

Title: Re: How to calculate change in concentration in a solution with activated carbon?
Post by: scientizscht on 31/07/2019 09:17:47

OK but I suppose there must be some values calculated or measured already that can give me an estimate?
Can you find any paper?

As soon as it is for a water solution, the values will be applicable, despite the amount of active carbon (other materials can be used).

Title: Re: How to calculate change in concentration in a solution with activated carbon?
Post by: evan_au on 31/07/2019 19:02:36

Will water as a polar solvent interact well with activated carbon (which is non-polar)?

Will you need a "wetting agent" to help with the pollutant adsorption?

Title: Re: How to calculate change in concentration in a solution with activated carbon?
Post by: Bored chemist on 31/07/2019 19:30:17

Quote from: scientizscht on 31/07/2019 09:17:47

OK but I suppose there must be some values calculated or measured already that can give me an estimate?
Can you find any paper?

OK, if the pollutant is salt the concentration won't change.

Why don't you understand that we can give a better answer if you tell us what the actual question is.

Title: How to calculate change in concentration in a solution with activated carbon
Post by: BeJimmiecot on 23/09/2019 02:30:51

Thanks for that Phil, got a question how would you saftely reduce the ph of rainwater to ph 5.5 since there is hardly any hardness in it.
My rainwater is normally ph 7.0
cheers
Mike