A bit of background: One of our cats has been sick over the past month, and had stopped eating or drinking for a while. Lost 1.75 lbs (about 20% of her 9 lb body mass from just a month earlier). While we still haven't quite figured out from all the tests what caused this, she does seem to be on the mend at this time, and has started eating & drinking more, and is more active. During the vet visits, she got several injections of subcutaneous fluids, and they gave us a home kit and trained me to administer the ~50cc of fluids, to continue the procedures every couple of days without having to drive her back to the vet & pay for each visit, etc.
The practical upshot of this is that I suddenly have a supply of single-use hypodermic needles that need to be disposed of, and I wasn't that thrilled with the idea of tossing medical waste "sharps" into the garbage/landfill/recycling stream.
While talking to the technician at the Vet's office, getting my training, I mentioned Robert's book, & my recent forays into learning Chemistry again, and how much I was enjoying it. And I suddenly hit on the idea that I could drop those needles into some acid & do my own recycling, stripping out the iron atoms for some other use, and eliminating the "sharps" problem altogether, leaving just the plastic bits (the Luer Taper and its attendant caps) which could go into the plastics bin without worry.
The technician laughed, and shook her head at the "crazy" (but good) idea, saying that she had taken a "Chemistry for Poets" class years ago, but had never gotten that into the field, so she was surprised at that sort of "tear it down to atoms and reuse it" kind of thinking that I've found to be so delightful in Chemistry.
(As an aside, I looked under the table we were working on while getting trained, and saw a 5-gallon bucket about 1/2-2/3 full of various discarded needles & syringes. That was just in one room of one small veterinary office in the mountains near where I live. Multiply that by all the medical offices/hospitals/vets/diabetic patients/etc. that are out there, and this "dissolving by acid" method may prove to be a very valuable method of clearing up a significant amount of fairly dangerous medical waste that we don't want washing up on our beaches, etc.)
Needless to say, I decided to give it a go.
I put about 10 ml of HCl (Muriatic Acid that I got from the hardware store last year) into a glass test tube. When I administer the subcutaneous fluids at home, I put on a fresh hypodermic just before starting, cap up the old one (to prevent jabs), and when finished with the medical procedure, bring it out to where my test tube rack sits.
Knowing that the metal dissolving would release H2 gas, I put on a rubber stopper with a single hole in it. That way, the gas could escape without pressure buildup, and I could keep potential spatters of acid to a minimum. (I did this after observing the first time, so I knew it wasn't going to foam over or anything.) It also keeps the HCl gas release to a minimum, though obviously not completely. Still, I don't smell the fumes like I do with an open test tube, and the air currents are probably almost nonexistent. Obviously, I could also run a tube and collect the H2 in a gas collection bottle, but I haven't set that up, yet. The main experiment was to destroy the needle, and see what happened.
Several interesting things happened, actually, which set me off on a flurry of Wikipedia research, learning about the compositions (there are many) of stainless steel, learning about the Luer Tapers mentioned above, the construction of hypodermic needles, etc.
I've learned that there are numerous metals in stainless steel, and that the alloys vary based upon the needs & performance required. After some further reading, it seemed likely (and somewhat obvious, in retrospect), that the needles were made of surgical stainless steel, so in addition to the original iron that I assumed, and the small amount of carbon I knew was used in steel-making, there was also chromium, molybdenum, and nickel, at least. Possibly Manganese, too.
I've also determined that there is another metal, which I suspect is aluminum, in the form of a ferrule (a sleeve connector) that joins the actual needle to the plastic. If you look closely at the full-resolution version of this image of the Luer Taper, you can see this ferrule as the flanged bit of metal embedded in the plastic, and extending out as a bit of whitish metal perhaps 0.5-1mm over the needle itself, outside the plastic.
The reason I noticed this was because that ferrule behaves VERY differently than the rest of the needle when dropped in HCl. Firstly, the plastic in the Luer Taper floats the entire thing in the acid, so the needle hangs suspended. In the first few seconds, small bubbles form over all of the metal surfaces, but then the spot near the top begins to effervesce and "boil" vigorously. (In fact, the test tube got rather hot to the touch, but not so hot that I had to put it down.) This led to the splattering I noted, and hence the single-hole rubber stopper I employed. While this action is going on, I notice a lot of dark, "sooty"-looking grey in the bubbles & foam, which remind me of the picture of Aluminum dissolving in HCl that Robert has put in the Illustrated Guide. (That picture looks black & white, but I think it's color like all the rest. The grey you see in the foaming bubbles is the aluminum as it's being torn apart very fast.)
The vigorous action goes on for several minutes, and eventually the needle itself drops away from the Luer Taper, which continues to bubble furiously while the rest of the ferrule dissolves. (There's also vigorous bubbling on the end of the needle as the last of it dissolves from there.)
The stainless steel itself is "corrosion resistant", and I found out just what this means! It dropped to the bottom of the test tube, turned black, and then continued a very slow bubbling of H2 release for approximately 36 HOURS, before finally completely dissolving, leaving only a bit of residue in the bottom of the tube. It also turned a lovely emerald green color, which I suspect is Chromium(III) chloride, based on the color & description, and the fact that there's Chromium & Chlorine in that solution.
(I could be wrong, though, and perhaps it's just the naked Chromium ions, or something else altogether.) Since we were giving the fluid injections every other day, I've had new needles to add, and chances to re-observe the process several times. I've done 4 of them, now, removing the plastic Luer Taper each time with a glass rod and dropping it into a baking-soda solution to neutralize before touching it, then rinsing and reconnecting it with the caps it came with.
The first 2 needles each took about 36+ hours to dissolve completely. The 3rd took a bit more than 48 hours (it was still present when I added #4), and the 4th took a bit over 72 hours. (We've just scaled back administration of the fluids to every 3rd day, as Xochi (our cat) has been doing better and starting to eat/drink/be active on her own.) The solution has become darker emerald green with each addition, and is now getting harder to see details of the black needle in the solution, even when held up to fluorescent back lighting. I suspect that this means that the acid has been getting weaker as it dissolves the needles, and have held off adding the 5th needle, which I got during tonight's administration of fluids.
I haven't weighed the original needle vs. the Luer Taper that's left at the end of the process, to calculate the weight of the metals in question, and they aren't THAT massive, but I suppose the HCl only has so much it can do with the ~10ml I started with.
Where to go from here? I'm not sure. Going to be looking into further info about separating out individual ion species from a mixed solution, since there are now at least 5 different metal elements in there. (I suspect the lab on analyzing seawater from the Illustrated Guide will start pointing me in the right direction.) Any other suggestions/pointers are welcome.
Overall, this has been very interesting, intriguing, entertaining, and educational. For most of a year now, I've thought about dissolving various bits of metal from my recycle bin to produce H2, and thence to use the materials to synthesize other compounds, but for one reason or another (including not quite knowing where to go from there) I've held off, not gotten around to it, etc. But every beer bottle cap, Altoids tin, crumpled piece of foil, cat food tin, or tin wrapper from the top of a wine bottle gets my mind racing, thinking about it. (Honestly, it's been doing this on every single thing I toss in the metals bin for about a year! It's crazy!) I think perhaps it's just that I was prompted by not wanting to drop the hypodermics into the waste that finally got me to start this experiment, and I'm very glad that I did!
I recommend that people try it with some of their waste metals, such as bottlecaps or whatnot. (Needles not required!
) For one thing, it will strip out the metal, letting you better see the remaining plastics & coatings, which may give you new thoughts & ideas about how we package things & recycle them. For another, it opens up a bunch of questions, from the simple "what do I do with this now?" to "what can I make with this?" and "how do I dispose of this?" (That last question, disposal, is also one I'm working on.) From what I've read, Chromium salts are "generally regarded as toxic", but to varying degrees. Now that I've released the elemental genie from its stainless steel alloy bottle, I have to figure out how to use it properly. And hey, since Chromium isn't something I come by every day, I might as well save it. But first I have to learn how to separate it properly.
More as it happens...
I've also just found this Wikipedia page on 