Mercury is an interesting metal and element, but it rarely occurs naturally. The most commonly found form in nature is mercury sulfide, which is also known as cinnabar. Depending on how it crystallizes, mercury sulfide can exist in two major forms. So here we have the alpha form which is the most common one. It has a really strong red color so when it's in a rock like this one, it's usually pretty easy to spot. It depends on the conditions, but it can sometimes also form these very nice crystals. Historically red cinnabar was isolated, ground up, and used as a pigment called vermilion. The pigment was used in many things like paints, cosmetics, and carved Chinese lacquerware However, due to toxicity issues, it has been almost completely phased out and replaced by safer synthetic pigments. The black form also known as beta mercury sulfide or meta-cinnabar. It is a little bit rarer, and it's not as pretty. When mercury sulphide is produced chemically like I did in my other mercury waste video, it's usually in the beta form. However, if it's heated above 400 °C, and then allowed to cool, it usually converts to the red form. The mercury metal can be extracted from the sulfide in two major ways: thermally, and chemically. When heated in the presence of oxygen, mercury sulfide breaks down into metallic mercury and sulfur dioxide gas. The heating process is normally incredibly hot and it's above the boiling point of mercury, so the metallic mercury boils off and needs to be re-condensed and recovered. It will still have a lot of other metal impurities in it though, so it often has to be redistilled and cleaned up. chemically? The heating process is often done with metals like iron or zinc or other compounds which can help pull the sulfur off the mercury. The major downside of this method is that it produces mercury vapor which can be quite dangerous. The other option is to chemically reduce the mercury sulphide back to the metal. The typical way to do this was to dissolve the mercury sulphide in a solution of sodium sulfide, and then to add aluminum. As the mercury metal is formed, it will sink down and collect at the bottom. The chemical method is safer because it doesn't produce any mercury vapor. However, it inevitably makes a lot of mercury-contaminated waste that needs to be dealt with. I've decided to go with the chemical method for safety reasons and the process that I use will be slightly different from the typical one. This method was developed by plant1999 on the sciencemadness forums And it was designed to be more accessible to the amateur instead of using sodium sulfide we prepare a polysulfide solution using sodium hydroxide and sulfur which are usually much easier to get. All of the waste here is heavily contaminated with celite, silica gel and paper, and I'm not sure how much is actually mercury sulfide. It's also still slightly wet, but in any case the total mass is about 210 g The stuff in the smaller bottle is much drier, and it has a total mass of about 59 g, so in total I have 269 g of waste and I'm just going to assume a hundred percent of it is mercury sulfide. This will allow me to recycle all of the mercury that's present, but it also means I'll be doing it on a much larger scale that I probably need to. Okay, so now what I need to do is make a polysulphide solution. The first step is to make a strong sodium hydroxide solution by mixing 400 g of sodium hydroxide in 1,100 milliliters of distilled water. I turn on very strong stirring and then I dump in all of the sodium hydroxide. One thing to keep in mind is that dissolving sodium hydroxide in water is very exothermic, so it's going to heat up a lot. When everything dissolves, the solution might be a little bit cloudy still, but that's fine as long as there's no solids. Now it's time to make the poly sulphide solution, so I start adding the sulfur. With excess sodium hydroxide, the sulfur reacts to produce mostly sodium sulfide, but it will also make some polysulfides. The polysulfides have the general formula Na2Sx where it can have anywhere from 2 to 5 sulfur atoms
(sulfur is an atom, not a group, NileRed) However, because I have such a large excess of sodium hydroxide, I imagine the polysulfides that do form are the shorter ones with at most around 2 or 3 sulphurs. This reaction requires things to be hot so in some cases, it's going to need to be heated. In my case though, the heat that was generated by dissolving the sodium hydroxide was more than enough. The reaction isn't very fast, and it took about an hour to completely dissolve all of the sulfur. On top of this, even when it's done, I need to wait for it to cool down before moving on. In general, sodium sulfide solutions are completely colorless, so this dark red color is coming from the polysulfides. Eventually, it was only warm or slightly hot to the touch so I took it off the hot plate and transferred it to another container I could have done things directly in the large flask, but at the end it would have been a huge pain to clean everything out. In the polysulphide solution, you might notice some black flakes floating around, but this isn't going to affect the reaction in any way, and there's no point in filtering it off. The stirring is turned on again, and then I start to dump in the mercury sulphide. At first I tried to just dump it in directly, but it led to a lot of splashing, so instead I had to transfer it in small portions to a piece of paper, and then dump it in gently. As more is added, the solution slowly loses its red color and becomes more orange, and we also see some sulfur precipitating out. I eventually finish adding all of my mercury sulfide from both of the waste containers. At this point, there's a whole bunch of mercury sulfide that still hasn't dissolved, so I continue to stir things for about 30 minutes. When I come back, there's still a little bit left, but it's not nearly as much as before. In the liquid there's a bunch of solid stuff floating around, which is mostly just silica gel and celite. It's not a big problem though, and it won't really interfere with the reaction. At this point, I think we're ready to get things going so I dip in some aluminum foil. I decided to start things out slowly just to get an idea as to how vigorous the reaction is. The foil very quickly turns black and we start to see some bubbling. If we look closely, we can see that little pieces and flakes are slowly falling off. The process is actually quite slow, but the portion that's in contact with the solution will eventually be completely degraded. Okay, so now that I know the reaction isn't too crazy I can dump in a little bit more aluminum. When I did this it initially seemed pretty tame, but eventually it started to take off. My fear was that if I added too much it could bubble things out of the container, but with aluminum foil, it doesn't seem to be a big issue. Some impatient people have tried using aluminum powder instead, and this definitely leads to a bubbling issue. After reacting for about 10 or 20 minutes, most of the aluminum disappears. From this point on it's basically just a cycle of the same thing over and over. We add aluminum foil, stir it occasionally and wait for it all to disappear, and then load it up again with more aluminum. Okay, so now to just quickly talk about what's going on here. When the mercury sulphide is added, it reacts with the sodium sulfide to form a water soluble complex. In the presence of sodium hydroxide and aluminum, the mercury in this complex is reduced back to mercury metal. The sodium sulfide is both regenerated and produced in this reaction, and we also make sodium aluminate and water. A large excess of sodium hydroxide is used here mostly to prevent the hydrolysis of sodium sulfide and the other polysulfides. If the concentration of sodium hydroxide falls too low, the sodium sulfide will be converted to sodium bisulfite and the mercury sulfide will not be soluble anymore. Also, the amount of polysulfide solution that we need is hard to calculate because it tends to react with other metals that might be present like arsenic or antimony. It isn't really an issue for me because I should really only have mercury sulfide here, but it is an issue when people try to purify natural cinnabar. At some point, some crazy spider decided to explore the reaction. He slowly went down and landed on a piece of the aluminum, but then quickly bailed. At first, I thought he was a goner and maybe I'm a monster for not trying to save him, but he was able to escape. However, unfortunately, in his desperate scramble to get out, his web broke and he fell back in. As I continue to add more aluminum the reaction slows down a lot and it becomes black. Aluminum foil is only 98 or 99% pure and most of this black junk is likely just due to impurities. If I lift the container, and take a look at the bottom we can see a whole bunch of small mercury blobs. At this point I think I'm more or less done, but just to be sure I did five more rounds of adding aluminum. With red cinnabar, we have a visual cue because when we're done, we shouldn't be able to see any cinnabar left. However, with the black stuff it kind of mixes in with the goo that's formed during the reaction, and the end point is really hard to tell. To make sure I was done, I just used a huge excess of aluminum, probably three or four times the amount that I needed. So when I figured I was done, I added an equal amount of distilled water. At the end, the stuff I have is pretty goopy, and this serves to loosen it up a little. I stirred around a little, and the goal is to make sure that all of the mercury metal sinks to the bottom. As I let it sit there, the solid stuff should slowly separate. I left the whole thing overnight, and in the morning I had relatively good separation. So now I try to pour off just the liquid portion. The water here is pretty stinky because it's still full of polysulfides, and it's also very strongly basic because of all of the sodium hydroxide. For the time being, this is covered in plastic wrap and placed on the side. I'll come back to it later in the video. Into a separate container, I start to pour off the sludgier stuff. Mercury metal is really dense and unlike this black impurity, it doesn't get suspended in water, so the idea here is to keep adding water and swirling it around to suspend the black junk and then pouring it off which should leave the mercury behind. It's very important to be careful here because if I mess up and pour out some of the mercury, I'm going to have to restart. This process is not exactly the most efficient, and it's going to use quite a bit of water, and unfortunately because of this it means I'm generating a decent amount of waste. Later in the video though, I'm going to show you guys exactly how I dealt with all of it. Anyway, eventually most of the junk was washed out, so I transferred the mercury to a beaker. It was still pretty dirty though, so I used a little bit more water to clean it up. When I was done, I was left with some nice and shiny mercury metal. The quality of the mercury at this stage really depends on the source of the mercury sulphide. Although my mercury sulphide was waste material, it's still a lot more pure than naturally occurring cinnabar. Some of the other metals in the cinnabar can amalgamate with the mercury and take away its shininess, or make it kind of chunky. In either case, regardless of how clean the mercury looks, it's probably still highly contaminated with other metals. To clean it up, we need to do two washings, first with some potassium permanganate, and then with nitric acid. I ended up having to leave the mercury for about a week or so, and when I came back it was all murky. The dirty water was transferred to another beaker, and the mercury was washed with a little bit of distilled water. The mercury also isn't shiny anymore, and there's a bit of scum at the top. Okay, now to clean things up, and to do this I add some dilute potassium permanganate solution. Potassium permanganate is a strong oxidizer which reacts with a lot of metals, but in these dilute conditions it shouldn't really touch the mercury. Many of the metals react to form their corresponding oxides, which can no longer amalgamate with mercury - they separate as a solid and I'm left with this clumpy mix. I swirl it around to give it a good washing, and then I let it sit for about five or ten minutes. I drain away as much as I can without losing any of the mercury. Using distilled water, it's washed several times until the purple color disappears. When I was done, I had a really dirty looking mixture. Luckily, it's very easily cleaned up by using a small amount of 10% nitric acid The nitric acid reacts with metals and metal oxide impurities and makes them water-soluble. After only like 30 seconds the mercury is already pretty shiny. I let it sit for a few more minutes, and the solution became completely colorless I now have nice and clean and relatively pure mercury, and it's time to dump off the nitric acid. Instead of mixing it with the potassium permanganate, I poured it off into its own separate beaker. The mercury was then washed a few times with a little bit of distilled water. All of the potassium permanganate and nitric acid waste is heavily contaminated with mercury, and I'm going to have to deal with this later Anyway, using a syringe I sucked out all of the mercury and transferred it to a small filter paper. I pulled up some water with the last little bit, but it's not a big deal - I just tilt the syringe back and push the water out. Any remaining water droplets should be sucked up by the filter paper. So once everything's loaded, I use a pin, and I poke a hole at the bottom. The mercury is able to push itself through the small pin hole but solid impurities should be trapped and left behind. When everything passed through, I cap the bottle and I'm pretty much done now. The final yield of mercury is 26 grams or 1.9 mL which corresponds to about thirty point two grams of pure mercury sulfide. Considering that I started with 270 grams of waste it means that most of what I had was just silica gel and celite. This actually makes sense because the reactions that I used the mercury in were all pretty efficient, so I wouldn't expect there to be too much in the waste. If all of my mercury sulfide had been somehow pure, I would have gotten around 230 grams of mercury metal, or 17.2 milliliters, which is nearly ten times more. In terms of use, the mercury here can either be kept as a souvenir or used in chemical synthesis. If it's kept as a souvenir it must be stored properly to avoid any spills, or leaks. I've used mercury metal a few times in past videos, and the most famous one is probably the Pharaoh's Serpent. If you guys are interested in seeing any of the mercury-related videos that I've done, I've provided a bunch of links in the description. Anyway, now it's time to clean up all of the wastes that I made. I decided to include the cleanup in a separate video, which you can get to by either clicking the link on the screen or in the description. So to promote this channel a little, I've decided to try something new and I'm going to be doing a giveaway of some NileRed beakers as well as keychains. It's going to be a random drawing, and the winner will have everything shipped to them totally free of charge. If you want to enter, just click on the link in the description and all you need to do is either subscribe to me on YouTube or Follow me on Twitter. The contest ends on Thursday, and the winner will be announced in my next video, which will be on Saturday.
