By Dr. A.K. Williams, PhD.
San Pedro, Costa Rica
- Mercury is the only metal which occurs as a liquid at ordinary temperatures
- Mercury is one of only two metals which occurs naturally in both its metallic and oxidized state, The other being copper.
- Mercury will form amalgams with almost all metals except Iron and Aluminum.
- Occurrence in earthís crust 0.5 ppm. That is 0.5 mg/kilo.
- Melting point is Ė38.87 C.
- Boiling point is 356.72 C
- Density at 25C 13.534 gr/cubic centimeter (cc)
- Vapor pressure at 25C 2 X 10 Ė3 mm
- Surface tension 484 dynes/cm
- Electrical resistivity 95.76 microohms/cm
- Does not tarnish in air at normal temperatures, but when heated near the boiling point will convert to Mercuric Oxide
- It will react slowly with sulfur at normal temperatures to form Mercuric Sulfide.
- It will react with Nitric Acid and with hot concentrated Sulfuric Acid.
- It will not react with dilute Hydrochloric Acid, cold Sulfuric Acid, or Alkalis.
- It will react with ammonia in the presence of oxygen.
- Metallic Mercury can be recovered from solution by the addition of hydrogen peroxide in the presence of alkali hydroxides such as Caustic Soda or Lye.
- Mercury can be recovered from solution by cementing with Copper, Aluminum, Zinc, etc.
- Mercury will react rather violently with Aluminum. Do not use Mercury in an Aluminum Gold pan or try to store it in an Aluminum vessel.
Mercury like all heavy metals is toxic. It behaves just like other heavy metals such as Lead, Copper, Arsenic, Zinc, etc. Heavy metals have the characteristic of not being easily excreted from the body. If you ingest a large amount of Mercury for example it will stay in your body for a long time. If you ingest a little Mercury each day it will accumulate in your body until if, you take no action, it could produce toxic symptoms such as hair loss etc.
Mercury has a relatively high vapor pressure, which means that at normal temperatures if you left a bowl of mercury out in the air a significant amount would vaporize and would be in the air. If you continued to breathe this Mercury containing air you certainly would ingest a significant amount of Mercury. The most dangerous thing about Mercury is that the lungs readily absorb the vapors. This you must avoid. So far as I can determine metallic Mercury is only slowly absorbed through the skin or mucous membranes. In fact, Mercury in various forms has been used for medical purposes for 100ís of years. How many of you have used mercurichrome or merthiolate to disinfect cuts etc or to swab out a sore throat? There was at one time a much-used medicine called "Blue Pill or Blue Mass" which was a mixture of metallic Mercury and honey. Merck Index states " occasional swallowing of Mercury is without harm".
I am not saying that Mercury is not toxic. It definitely is but so is almost any chemical that you come in contact with; It is just a matter of amount. There are a few precautions that you must follow when working with Mercury. These will be discussed in a following section. What I'm trying to say is that Mercury deserves respect but not fear. It has taken a very bad rap at the hands of the do-gooders whose only knowledge of ,or experience with it is that they once took their temperature with a rectal thermometer.
If any one of you feel that you have a problem with heavy metal poisoning, hair loss, loose teeth, kidney damage, muscle tremors etc please have a check for heavy metal intoxication. Itís simple and inexpensive. If you have a problem there is a treatment which involves infusing EDTA (ethylene diamine tetracetic acid) into your blood. This is a treatment known as "chelation" and it will very effectively remove the heavy metals from your system.
- When working with Mercury always use latex gloves, itís cheap and is good procedure.
- Always store Mercury in tightly closed containers (not Aluminum).
- Always put a layer of water on top of the Mercury unless it is charged Mercury.
- Never heat Mercury or amalgam in an enclosed space.
- If you must heat Mercury do it in the outdoors or a well-ventilated space.
- Always stand upwind of hot mercury. Do not breathe the fumes.
- Do not let Mercury contact Aluminum. It will destroy it.
- Avoid spilling mercury. It is very difficult to clean up.
- Never heat Mercury indoors or in any enclosed space.
- Never try to distill (retort) Mercury in a glass retort.
How to Clean Mercury
The term "clean" can mean different things to different people. It can mean simply Mercury that has no black crud floating around on top of it, or, it can mean that the Mercury is mirror bright, silvery without the usual yellow film of mercuric oxide floating on top. Or, it can mean that the Mercury is pure Mercury and contains no other metals dissolved in it.
In order to remove the usual black crud that inevitably floats around on top of your Mercury is very simple. Get yourself a funnel and a coffee filter. Take the round filter and fold it in half twice. Open it so that one side has one layer of paper and the other has three layers. Put this cone filter in the funnel. Now take a pin or needle and put a very small hole in the very tip of the paper. Pour in your cruddy Mercury. The Mercury should pass through the filter in tiny drops. If it does not pass through, open the hole just a bit. If it runs through in a steady stream, the hole is too big and you will have to start over. This method will remove all of the floating oxides etc and give you Mercury that you can work with.
Second. If you have Mercury that has other metals amalgamated in it and is sort of thick with what appears to be "clots" floating around on it you can filter these amalgam clots by several methods. The first and easiest is to purchase a syringe (10 ml or larger) from the drug store. Make a ball of absorbent cotton and push it into the bottom of the syringe. Push in the plunger to pack it as tightly as possible. Pour in your Mercury and force it slowly through the cotton with the syringe plunger. The residue on the cotton will contain most of the amalgams including Gold. Probably the best way to recover the amalgamated metals including gold is to simply take the cotton ball from the syringe and burn it with a propane torch or other. Be sure you are outside or in a well ventilated space.
A second way to remove amalgamated materials from Mercury is to squeeze it through a piece of chamois. Be sure to wear gloves when using this method. This method is somewhat cleaner than the cotton filter in that the amalgam usually separates from the chamois and you eliminate the need to incinerate the cotton.
Remember, although you have filtered your Mercury, you still have metals in the Mercury, which are in true solution and that cannot be removed by filtration. In order to remove all the dissolved/amalgamated metals from Mercury you will have to retort or distill it. In order to distill Mercury you should purchase a Mercury retort. They are relatively inexpensive. Yes, you can make one from pipefitting etc, but they are usually rather clumsy, massive affairs, which are a bit of a grunt to use. Theyíre two types of Mercury retorts. Vented and non-vented. The non-vented type is simply a boiling vessel and a cooling tube from which the Mercury drips into a catch vessel. With this type of retort NEVER put the exit end under water in a catch vessel. If you do, a very slight drop in the temperature of the boiling Mercury will create a vacuum sufficient to suck water back through the system right into the boiling Mercury at 675 F. Please believe me when I tell you, that is BAAAAD! It will ruin your whole day and probably put you in the hospital (if you are lucky).
The vented type of retort is made specifically to prevent this problem. In this type, near the exit end of the retort there is a very small tube, which extends upwards a few inches. The purpose of this tube is to allow you to immerse the exit end of the retort in water. If your heat source should fail and the temperature in the "hot vessel" drop, air will be sucked in through the small tube instead of water through the exit. In any case, If you retort your Mercury you will now have Mercury, which is, for all practical purposes, clean and pure. Any amalgamated metals such as gold will be left behind in the retort. Actually, in order to have Mercury which is considered chemically pure it must be distilled three times. Triple distilled Mercury. This has no practical value for mining.
Applying Mercury to Copper Plates
Every time I see someone trying to apply Mercury to a copper or brass plate it makes me react just like they were scraping their fingernails on a blackboard. I see people spending hours trying to clean the plate by sanding, scrubbing with steel wool, washing with acid, etc.. Then, worst of all, trying to put metallic Mercury directly onto the plate by chasing it all around with rags, sponges, squeegees, and any number of other devices. Of course, most of the Mercury ends up in their shoes, in the water, on the ground, everywhere except on the plate. Gentlemen, this is NOT the way to do it. The simple, effective, professional way to coat one metal with another is to apply a solution of metal salt onto the other metal and let the resulting battery action reduce the salt to metal which will then coat the base metal with a even, thin film.
If this seems complicated, its because I sort of set you up. Itís so simple as to make your old method seem like building a H bomb. All you need is a little nitric acid and some Mercury. Dilute your nitric acid with an equal volume of water; put it in a plastic bottle with a good tight top. Now put a small glob of Mercury in the bottle and let it stand for awhile. When you are ready to apply the Mercury to a plate simply be sure there is no grease on the plate by wiping with a detergent solution. No matter how curdy the plate looks, not to worry, simply dip a swab into the acid solution and wipe it onto the plate. MAGIC. Your plate is now coated with Mercury. A bottle/swab such as shoe polish comes in works nicely for this.
I think that most folks believe they should have a thick coat of Mercury on the plate. Actually, the opposite is true. You should remove excess Mercury with a squeegee or other because as gold sticks to the plate the mercury film gets thicker and thicker. When this happens, gravel, which is usually moving over the plate, will scrub the excess off the plate and you will lose mercury and any gold that it contains. Erosion of thick amalgam layers from sluice plate is a common problem and one that usually goes unnoticed.
How Amalgamation Works
I get a distinct idea that most folks have a distorted idea of just how amalgamation works. First of all, the way we in the gold business talk about amalgam is a bit of a misnomer. A true amalgam is when one metal is actually dissolved in another in which case we would not be able to filter out the gold from our amalgamated concentrates. It would simply pass right through the filter. We normally utilize the unique properties of partially amalgamated gold in order to recover it easily.
Visualize a gold particle like a golf ball. When it comes in contact with mercury the mercury begins to dissolve in the gold. Now we have a gold particle with a layer of mercury sticking to its surface because of the very high surface tension of mercury. The mercury will now continue to dissolve in the gold and penetrate deeper into the particle. This process, however, is rather slow and the deeper it penetrates the slower it goes. Yes, if you have enough mercury and enough time the gold will eventually dissolve into the mercury (or vice/versa). However, in our theoretical particle what we now have is a center of gold/no mercury, a surface of gold/mercury, and on top of that a layer of mercury/no gold. Right, we have our amalgamated gold and now we want to get rid of the mercury. We just need to heat it, right. Yeah, but look what happens. As we heat it the excess mercury coating boils off. Now the true amalgam at the surface gets hot and the mercury boils off leaving the gold, right? Dead wrong! What happens is as the mercury evaporates from this surface area the gold which was dissolved in it falls away from the parent particle and is left as a usually black powder which you normally throw away because it donít look like gold. This same effect is true if you use nitric acid to remove the mercury.
So, the fact is that every time you amalgamate gold particles and recover the gold the particles get a little smaller. If you have any doubts try it. Take some rather fine gold and amalgamate and recover it several times. After three or four times you will notice that the particles get smaller and smaller. If you continue this process, eventually you will end up with very fine, black, gold powder and no yellow particles. Of course the finer the gold that you amalgamate the more you will convert to the black powder form. This is because the finer the gold particles, the more surface area that is exposed for amalgamation and the larger the percentage of conversion (or loss).
Recovering Mercury from Solution
Iím sure that all of you who use mercury for catching or cleaning up concentrates also occasionally use nitric acid also. This means that you surely will end up with nitric acid solutions, which contain mercury. Please let me encourage to not throw this solution away. O.K. Iím the same. I donít have time or inclination to spend the time to recover a couple of grams of mercury. What I do is that I have a "stock pot". A plastic jug in which I put any leftover mining chemicals. No matter what, acid, caustic, mercury solutions, anything that even might have something worth recovering or things that I donít want to pour down the sink. When I feel like it I recover the mercury by cementation usually with a copper strip suspended in the waste. Assuming that the waste solution is not too acidic, the mercury will drip to the bottom ready for use again. You can also use aluminum. You can drop in a little table salt and a white cloud of silver chloride will settle out. Filter this off and store it for later silver recovery. If you think there might be some gold in the solution you can filter it through a coffee filter add some powered zinc, mossy zinc, or just chunks of zinc. Any precipitate you get might contain gold. Iím sure most of you have your own pet methods and thatís fine, just donít throw all that stuff away. Keep it for when the weather has you housebound.
Now we have arrived at the mystery of mercury. A lot of folks have heard of it. Most havenít. Most that have heard of it respond " oh yeah, thatís the stuff that company X sells (for a lot of $ís). Itís some mysterious stuff that you canít get anywhere else". Baloney! Merlin the magician died a long time ago and there just ainít been no magic since. You can make all you want right in your carport and it shouldnít cost you more than $5.00 tops.
First thing is that I donít like the term "charged mercury" but since I canít think of a better one, we will use it. Now we all understand amalgamation, right? We also understand that gold is not the only metal that will form amalgams with mercury. Mercury will form an amalgam with two other metals of interest. Sodium or potassium. Doesnít matter which, they are very similar and for our purposes it doesnít matter which you use. "Charged mercury" is nothing more than a mercury/sodium amalgam. The trick is how do we make it? O.K., you could just take some sodium metal and drop little chunks of into hot mercury. However, there are two things wrong with that procedure. First, dumping anything into hot mercury is a little hazardous since it tends to make little mini-explosions. Second, sodium is a metal, white, very soft, can cut it with a knife, it would be a little hard to lay your hands on. Itís not a common material. Also, you would have to store it under oil or kerosene because water vapor in the air will cause it to burn. It reacts violently with water and can cause explosions. Not to worry, there is a better way. There are many ways to skin a cat. The problem is that first you must catch the cat. We got him! Actually, a gentleman/scientist named Faraday caught the cat for us. If I can paraphrase Faradays Law it states in effect that for every 28.6 ampere/ hrs of current you can deposit 1 mole of metal (in the case of sodium, 23 grams) from solution onto the cathode of an electrolytic cell. Well that certainly is impressive. So, what does it mean to us? It gives us a way to produce all the sodium amalgam that we want cheaply and easily. This will be discussed in detail later. What can this "magic mercury" do for us? Sodium amalgam is one of the strongest reducing agents known to science. If you take a metal oxide such as common rust (iron oxide) and you "reduce" it you will end up with metallic iron and oxygen. Sodium amalgam will cause this reaction to occur. It is the absolute best rust remover that you could ever devise. It will also reduce other materials such as zinc, magnesium, manganese, sulfides, etc.. This Ďcharged mercury" or mercury amalgam will always be mirror bright and shiny with no yellow film of mercuric oxide floating on the surface. In order for mercury to amalgamate with gold the two metals must be able to come in contact with each other. If either the mercury or the gold has a coat of anything on it you will never get it to amalgamate. Itís like the gold is enclosed in little plastic bags. They just canít get together. Now the mercury surface is perfectly clean due to the reaction of the sodium with the water. When this stuff touches a particle of gold which has itís own coat of iron or other metallic oxide or sulfide, it will immediately reduce that too, leaving only the fine powder metal that will wash away leaving a nice clean gold surface just waiting to be amalgamated by the mercury which is also present. One thing that the amalgam will not remove is oil/grease. For that you will have to use a detergent. When you get some of this stuff and put it in water you will note that it fizzes giving off hydrogen gas. That is why it works. As we said before, sodium reacts with water. What we have done is to make a sodium battery. When the fizzing stops it means that all the sodium has reacted and it is now "discharged" to ordinary mercury. Now you must recharge it.
"Charging " Mercury
Charging mercury is such a simple procedure that it is amazing that almost no one knows how to do it. Yes, there are a few folks out there who manage to obtain a tiny fraction of their mercury as sodium amalgam. Usually, less than one percent. It does work but it canít work for very long before it is discharged and must be recharged. Maybe there are a few of you who know much more than I do about it. If so, please contact me.
In order to charge your mercury you must have a charging vessel. I will be glad to sell such high tech vessels for only $29.99 plus postage. Also I will sell you the necessary "charging salts" for the amazing price of only $9.99 plus postage. For those of you who insist on making your own I will provide instructions free of charge. Howís that for a deal! (Iím working on a kickback deal from your local supermarket).
It will require a trip to the super. You should purchase an "Old Fashioned" tumbler glass of the hard, clear, plastic type. Donít try to get around me by using one of those soft, polyethylene "Tupperware" types. They wonít work. In order to save a trip back to the store, buy a container of good ol Red Devil Lye. You now have 90% of your materials in hand. If you donít have any epoxy glue, you should pick up a tube of that too.
Now you should drill or melt a small hole in the glass at the very bottom of a size such that a solid copper wire of size # 14 or so can be inserted in the hole and extended to the opposite side of the glass. Seal around the wire at the hole and glue the loose end of the wire the bottom of the glass. This will be your reaction vessel with the cathode or negative terminal. You now must make an anode or positive electrode. This can be piece of re-bar, a steel bolt, an old screwdriver or whatever. I recommend using a bolt with two nuts and a disc of steel a bit smaller than the vessel. Cut a hole in the center so that it can be sandwiched between the nuts. While this is not absolutely necessary, It will allow a bit more current to flow through the cell with a resulting faster charge rate. Now fashion an anode clamp to hold the anode and prevent it from falling into the mercury. A piece of wood with a tight fitting hole works fine.
The following drawing illustrates what a Charging vessel should look like....
Now all you have to do is connect your reactor to a source of DC power capable of delivering at least 1 ampere of current. A 12 volt car battery is convenient for this purpose. You can use a battery charger if you like. If you have two batteries you can connect them in series and cut your charging time in half. You should watch the system in the beginning just to be sure you are not pulling too much current which will cause the cell to get too hot and maybe boil. Donít let it get that hot. This is not usually a problem and is easily fixed by simply reducing the amount of lye in the water layer or putting a light bulb in series with the system. The amount of mercury in the cell and the amount of current flowing through the system determine the time required. You will know when the mercury is well charged because it will be a gray, solid, puttylike mass. Not a liquid. At this point put on gloves and pour off the water/lye layer, wash the mercury surface with clean water and immediately dry it with an absorbent paper towel. Store it in a clean, dry, tightly closed plastic bottle or jar.
Usually, no matter how tight the bottle some water vapor will get in. You can fix this problem by putting a packet of drying agent such as silica gel, calcium sulfate, or calcium carbide in the container with the mercury. These materials will effectively scrub out any water, which gets in.
A Few More Thoughts
I t might be worth while discuss the subject of surface area as it of paramount importance when amalgamating. First let me explain that liquids always try attain a shape that results in the least surface exposed. What shape would that be? Spherical. When anything liquid or solid is in the shape of globe or sphere there is no way to reduce the surface area more. If you change the shape of a sphere to some other e.g., A cube, a cylinder etc. the surface will increase to some extent. However, If you want to increase the surface area by millions or hundreds of millions you simply divide it into several separate pieces. If you take a marble and divide it into 1000 smaller marbles the surface will increase by 100,000 times or so. Donít hold me to these numbers they are only for example. If you had divided it into 1000 cubes the area would have been much more than the marble or the 1000 spheres. If you want to increase it still further just grind it into finer and finer particles. I think I recall reading that one LB of carbon ground to face powder size or less would have a surface area more than that of the entire earth. Something like that.
Amalgamation is very dependent upon surface area. Especially of the mercury. If you keep your mercury in a single glob it will cause you less headaches because there is less surface to corrode which can cause "flouring". Also that single glob of mercury will take much longer to contact all the gold particles.
If you use charged mercury to recover gold from concentrates itís all right to allow it to break up into smaller globs. Things will go much faster but you should try to get the mercury back in one glob before it is discharged or the globs will corrode rapidly and will be much more difficult to recover.
So, the more that charged mercury is spread out or its surface area increased the more of the sodium is also spread out and the more contact it has with the water. The more contact it has with water the faster it reacts and the faster that it discharges. That is bad for us. I wish I could say that you could use charged mercury on a copper plate at the end of your sluice. Well, you can but it wonít work very well. That little glob of charged mercury that would last 30 minutes in your pan, when spread in a thin film on a plate probably will last no longer than 30 seconds.
I can already hear some folks saying, "he ainít so smart, Iíll just take a battery and connect it right to the sluice plate and keep the mercury charged all the time". I wish! It wont work because if the mercury is not discharging its not a reducing agent and will not clean either itself or the gold. It only works when it is discharging.
I must admit that I have sort of an idea how one might be able to use charged mercury on a plate but like a lot of my ideas I havenít put it to the test yet.