Is silica gel poisonous? It says do not eat!

With the gift-giving holidays upon us, we need to talk about those ubiquitous little packets of poison. You know, the ones that come with shoes and electronics and say alarming things like, “Throw away,” “Do not eat,” and sometimes even “Dangerous.”

You’ll notice the packets usually also say “silica gel,” even though they don’t feel like gel at all.

Perhaps you — or your child — have gotten curious and torn one of those little packets open. Perhaps one of you was surprised to find it held hard little translucent balls, and one of you was surprised to find they had no flavor and couldn’t be chewed.

So what is this stuff, and is it poisonous?

Let’s start with the silica part

Silica is also known as silicon dioxide and is found in nature as quartz, the second most common mineral on Earth. You may know it better as sand, but gemstones like amethyst and citrine are also forms of quartz.

Silica gel is a synthetic form of quartz that’s made by acidifying sodium silicate. In its liquid form sodium silicate is also known as waterglass and is used in detergents, dyes, food preparation and many other products and industrial processes.

Why is it called gel?

Silica gel is technically a xerogel. “Xero-” is the same root word as found in Xerox (dry copies) and xerostomia (dry mouth) and, yes, it means “dry.” Silica gel is a dry gel.

All gels — toothpaste, pudding, some would say your heart and lungs — start out as some variety of nanoparticles suspended in liquid. Under the right circumstances the nanoparticles begin to fuse together and form a 3-dimensional structure that holds the liquid in and gives it shape — even if that shape is a bit squishy.

To make a gel into a xerogel, the liquid is removed. The nanoparticle structure that’s left behind is lightweight and extremely porous. Dry silica gel might also be considered an aerogel, as its pores are filled with air.

Air always contains some amount of water, and in an enclosed space — like a shoe or camera box — that water can condense on whatever is in that space, causing damage. Silica gel packets are added to adsorb the water and protect whatever they are packed with.

So silica gel absorbs water?

Silica gel adsorbs water. The difference is that water molecules cling to the surface of the silica gel, rather than actually penetrating it. Silica gel beads are tiny but they have millions of microscopic pores that vastly increase their surface area, making room for an enormous number of water molecules.

There’s still a physical limit to the amount of water silica gel can adsorb though, and once its surface is completely covered it can’t take on any more. But because the water is just hanging on to the outside of the silica gel beads, rather than reacting with them, it can be driven off with heat.

But is it poisonous?

Silica gel, like sand, is inert and if swallowed will pass through the GI tract and come out the other end unchanged.

There is one caveat, however, The silica gel that comes in little packets you can’t see through is non-indicating, which means it always looks the same whether or not water is present.

Silica gel
Silica gel

But there’s another kind called indicating silica gel that changes color as the gel becomes saturated. The appearance of the gel itself doesn’t change, so it has chemicals embedded in it that do.

Blue indicating silica gel has cobalt chloride added. Anhydrous (without water) cobalt chloride has cobalt atoms bonded to chlorine atoms and in this form appears blue. When exposed to water, some of the chlorine atoms are swapped out for water molecules and the resulting compound appears pink. If the gel dries out the color will return to blue.

An accidental or experimental taste of blue indicating silica gel would not be particularly harmful, but cobalt chloride is generally rather toxic. It’s gradually being replaced with orange indicating silica gel, which changes from orange to green in the presence of water using much less toxic methyl violet.

How to dry silica gel packets for re-use

Silica gel will begin releasing the water molecules on its surface when heated to about 220 F. The packet that holds the gel is likely to be damaged if heated about 250 F, however, so you’ve got a pretty narrow temperature range to work with.

Indicating silica gel is dried until it returns to its original color. Non-indicating gel is a little trickier, as it will be hard to judge when the water has all been driven off, so times are approximate.

NB: Never dry or re-use silica gel that has been contaminated with anything other than water!

  • Spread the silica gel packets on a baking sheet.
  • Place in the oven as far from heating elements as possible.
  • Set the temperature to between 220 F and 250 F.
  • Allow to dry for at least two and up to 24 hours.

How to dry loose silica gel

There are some uses for silica gel that work better with the loose beads. If you have a lot of packets you can always open them and mix the beads together. Without the packaging you can turn the oven up to 300 F and dry them in about 3 hours.

Loose beads can also be microwaved. Indicating silica gel is microwaved at 3-minute intervals until the color changes. Again, it’s hard to say how long to heat non-indicating gel.

Uses for silica gel packets

  • Wet cell phone Remove battery, SIM and SD cards and place phone in a bowl or bag filled with silica gel packets for 24 hours
  • Razors and razor blades Store in a closed container of gel packets to retard dulling
  • Important documents Add packets to file box, drawer or envelope to avoid moisture damage to paper
  • Electronics Add packets to camera cases and hearing aid holders
  • Gardening seeds Store seed envelopes in a box with gel packets
  • Prevent tarnish Add packets to silver drawer and jewelry box

DIY: Make your own silica gel packets

Silica gel beads can be purchased in bulk from many stores, and empty tea bags are easy to find on eBay if you can’t find them elsewhere. Fill the tea bags with the gel and use as desired.

More information

Silica gel on Wikipedia

8 clever uses for silica gel

7 great things to do with those gel packets

Demystifying silica gel (technical)

The sol-gel process

Colloids, gels and suspensions

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