Faster IPA Recycling for Your Resin Print Workflow

If you’ve printed with photopolymer resins, you know that you need alcohol. Lots of alcohol. It makes sense that people would like to reuse the alcohol both to be environmentally responsible and to save a little money. The problem is that the alcohol eventually becomes so dirty that you have to do something. Given time, the polymer residue will settle to the bottom and you can easily pour off most of the clean liquid. You can also use filters with some success. But [Makers Mashup] had a different idea. Borrowing inspiration from water treatment plants, he found a chemical that will hasten the settling process. You can see a video of his process below.

The experimentation started with fish tank clarifier, which is — apparently — mostly alum. Alum’s been used to treat wastewater for a long time. Even the ancient Romans used it for that purpose in the first century. Alum causes coagulation and flocculation so that particles in the water wind up sinking to the bottom.

It isn’t as simple as just adding alum to the waste liquid. To encourage particles to coagulate, real waste treatment plants agitate the water and that is required here, too. For best results, the video says to mix a solution of alum and distilled water and then stir the alcohol, resin, and solution together, rapidly at first and then more slowly.

After a 45 minute stir, you’ll need to let it all settle for a few hours, but you can see large clumps forming almost immediately. In the video, he uses a magnetic stirring rig, but he also points out that if you have a wash station, it can do the same job. In fact, if you don’t have a wash station, this might be the justification you need to buy one!

One important note: the tests were done with pure aluminum sulfate (the right name for alum). If you buy alum at the store, it is likely to have potassium or other additives and that might change the results or even the safety of this procedure.

If you want to build a magnetic stirring machine, we’ve seen several homebrew units. If you wonder if you are diluting your alcohol with this procedure, you could test the proof of the resulting liquid.