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What type of binder is user for making activated carbon briquettes for water purification? Answered

Hello everyone, I am trying to make a water purification device which needs to have compressed activated carbon filter. I am facing the problem of binding the charcoal dust together so that it does not come out when contacted with water. I tried making the briquettes with starch but it is water soluble. I have read some papers on binding the charcoal using extrusion process but could not find what exactly is the binder used. Here the binder should not cover the surface area of the carbon particles as well.
I am looking to find here, what is the binder used and how is it used, i.e, ratios. I want to make something like this in the image which is water insoluble. 

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You might find some ideas in old US patents. For example if you go to this page,

http://www.freepatentsonline.com/search.html

and ask it for

abst/"activated carbon" and abst/binder

Also tell it you want the results in chronological order. Then, I suggest looking at the oldest results first, because these will tend to be patents using older, and usually more simple, technology.

As a bonus, if the patent is more than 20 years old, then the patent is expired and the invention it describes is public domain, and thus anyone can make, use, sell, etc, that invention without infringing on patent law.

And that is why Coke has no patent, just a secret...

Why go through all the trouble?
Simply use a suitable pipe with a fine stainless steel meash at the end to prevent the charcoal from getting out.
For the ones I made ages ago I used a 90mm PVC pipe.
Screw caps on both ends with the quick connectors for the water.
Filling from inlet side to outlet side:
Some non-scratch pot cleaning pads cut to size
Coarse (boiled) sand
Another layer of the pads
Very fine sand like for sandpits or better metal casting use
Another layer of the pads
Granulated activated charcoal
Two layers of the pads cut to form a pot so no charcoal gets past
A sheet of fine filter paper

The charcoal is lightly pressed once filled, the sand is watered once filled to make it settle down properly and once the pipe is completely filled the last pads make sure all stays in place and bigger stuff coming from the water tank won't make it into the sand.
With two persons and normal drinking and cooking use the 90mm pipe was good for over a year until it needed cleaning and charcoal replacement.
Although if I were to build another one I would go the pipe-bomb route instead.
Using 3 smaller pipes with connectors makes the cleaning and replacing of goods so much easier....