Activated carbon is “activated” when its surface area is increased by physical and chemical processes. The most popular uses for activated carbon are water filtration, and treatment for acute poisoning. It reacts with various substances by binding them to its surface, so the greater the surface area, the more effective it is. Imagine you’re painting a sphere made of solid wood. The amount of paint you need depends on the amount of surface area on the sphere. But now imagine you’ve drilled hundreds of holes into the sphere — now you’ll need a lot more paint.
Carbon works the same way. If you’re filtering city water to remove the chlorine, the chlorine molecules are “adsorbed” to the surface of the carbon, and once the surface is covered with chlorine, it won’t filter anymore. But if you can “activate” the carbon to increase its surface area, it will remove much more chlorine from the water, and do it much faster.
Activated Carbon Process
First, understand that this is not a rigorous process in a controlled environment. If you need activated carbon, buy it. But if you can’t buy and you need activated carbon, this method will get you a batch that is moderately effective for water filtration or poison treatment.
- Make charcoal. You get your carbon from charcoal, and the main problem with activating it at home is the temperature at which you make the charcoal from wood. It needs to be cooked between 900 and 1400 degrees Farenheit, and it’s difficult to reach and control those temperatures in the back yard. When we made charcoal (read this article), it was questionable whether we reached those temperatures, but if you can do it, by all means go for it.
- Powder the charcoal. I know that pea-sized chunks are easier to handle, but because this backyard activation process is not 100% effective, you need the smallest pieces charcoal you can get, so go ahead and powder it.
- Make a 25% solution (by weight) of calcium chloride. Calcium chloride is widely available and generally considered non-toxic, so it’s safe to handle. To make a 25% solution, weigh 3 parts of water and mix in 1 part calcium chloride. For example, dissolve 100 grams of calcium chloride in 300 grams (same as 300 mL) of water.
- Make a paste with the calcium chloride solution and your powdered charcoal. Watch the video to get an idea of how much solution to use, and how thick the paste should be.
- Spread the paste to dry.
- Rinse with clean water.
- Bake at 225 degrees F for 30 minutes.
Notes and Tips
- When you dissolve the calcium chloride, the water will get hot enough to scorch, so be careful!
- The finer your carbon, the finer your filter must be when you rinse it. The powdered carbon is so fine some will even go through a coffee filter. You’ll lose a little, but you’ll still have a usable amount left, so go ahead.
- Whatever filter you use, make sure it’s clean, but that it hasn’t been washed with scented detergent or bleach, because these will react with your carbon and make it less effective.
- Same goes for the water you use in the rinse — it should be carbon-filtered, distilled, or reverse-osmosis filtered.
Low-Tech Coconut Shell Activated Charcoal Production
Cheap way to make activated carbon