Assaying and Smelting

O.K.. guys, we have a tendency to area unit happening somewhat excursion into the world of titration. what is "titration"? Well, it’s a method of checking out something that you just want apprehend|to understand|to grasp} by fitting an experiment in ranked steps in order that we are able to know when a definite event takes place. as an example, If you're close to deaf, like me, and choose a hearing take a look at one the things that they take a look at for is the frequency range that your ears answer. someone with traditional hearing can discover frequencies of concerning twenty to twenty,000 cycles/sec. As we have a tendency to develop we have a tendency to usually begin to lose our high frequency acuity.

When I got out of the Navy, when being around craft at dynamic  turn-up, for four Cyrus the Younger., my hearing acuity was concerning 20- 14,000 CPS. Now, i think it’s concerning 500-10,000 CPS.

Well guys, however the hell did we have a tendency to get to this point? we have a tendency to commenced to just make a case for some facts concerning mercury. It’s your fault. Well, perhaps just somewhat bit mine. Fact is, now that I have created a full new cluster of basement chemists out there (I take credit for that). But, you retain causing requests for additional and additional info therefore it kind of implies that plenty of you're hooked on basement chemistry and might ne'er be constant once more.

Let’s get on with it. First, what can we mean by the word "assay"? It means that determination of what is gift in no matter sample you're engaged on. Does’t need to be gold. we are able to assay for silver, rhodium, sulfur, water, bubble gum, anything. now you need to understand that there area unit two basic categories of assays. Qualitative and quantitative.

Qualitative tells you what. If someone brings during a sample of quartz rock and says, "I want to understand what is in it". we have a tendency to take it to the basement and run it through our procedure and issue a report that says "sir, you have got quartz, sulfides, arsenic, silver, copper, and gold". this is often a qualitative assay.

Of course, our shopper United Nations agency could be a prospector in real time asks "how abundant gold"? Our reply has got to be "who knows". $63.00, will that be cash or credit card? "But I have to understand what quantity gold is in it. Great, now we are able to run a quantitative assay for under $89.99. Gold only. Quantitative tells you how abundant.

Now I’m not telling you that everybody ought to run out and start shopping for equipment to install an assay laboratory in the basement. I just thought that you just might like to understand what is concerned once you take a sample to an assay laboratory and why it prices what it will.

I’m getting to put in additionally some Q&D strategies that you just can neutralize the field to assist you identify what spots have additional fine gold than others do. you're getting to hate ME as a result of I’m not getting to tell you wherever this gold mine of data is located on the page. Hence, you will need to scan the full issue so as to get this very necessary data. You would’t want to miss it, would you? which may enable your partner to understand over you. Would’t want that. Navaho, {you area unit|you're} a basement chemist and are hooked on data.

This page goes to be very difficult to write and it’s getting to take time but you guys seem to be worthwhile, so--- if you will hang with ME we have a tendency to area unit going for a MAGIC CARPET RIDE!!
  
Types of Assays
There area unit a few different ways of assaying for precious metals. a number of these area unit relatively new like "ion probe analysis". this is often wherever you take a sample (it has got to be in one piece) like a very little bb of metal to a laboratory and that they put it in the Scanning microscope and push the button. ZAP!! It spits out a chart with a plot of all the precious metals that area unit in the bb and the quantity of every. Another could be a method whereby you take ground sample and put it during a very little instrument known as a visible radiation spectroscope. this will provide you with a second readout of the quantity of gold etc. in your sample. we have a tendency to don't seem to be going into the details of those sophisticated strategies. we have a tendency to area unit getting to concentrate on the tried, true and additional offered strategies like "Aqua regina Assay" and the additional acquainted "Fire Assay". we will additionally inspect an previous "sourdough" method that may be very helpful.
 
Aqua regina
In this method a weighed quantity of the ground sample is roofed with concerning 2-3 volumes of turquoise regina and heated for a such that time. The cooled sample is then filtered and the remaining solids washed three times with dilute acid. All the liquid is pooled and gaseous by gentle heating until only a awfully bit is left. Then, acid is additional and the evaporation continual. This Hydrochloric reduction is continual three times to make sure that every one of the chemical element is gone. now you have got the values during a answer of focused acid. now add concerning two volumes of water. If there was silver in the ore it will precipitate as a white cloud of silver chloride. The silver is removed.

At now there area unit several choices as to however the next step is accomplished, but the same old is to extract the gold chloride into an organic solvent, make it up to an exact volume and put it into an instrument known as an atomic absorption spectroscope that measures the gold content.
 
Fire Assay
In this form of assay ore is ground and a weighed quantity, usually thirty or 40 grams is mixed with an assay flux. we will go into fluxes later. The ore and flux is placed during a clay vessel and heated at concerning 1100 C or 1850 F for concerning an hour or until it is a thick, homogenized liquid. This soften is then poured into a cone formed mildew. This cone will contains a bottom piece of lead with all the values dissolved as an amalgam. This cone of lead is termed a "pill". the top or wide finish of the cone will contains a lump of glass containing all varieties of impurities.

The lead is separated from the glass by merely smashing it with a hammer. The lead is additional pounded into a cube. This cube is weighed. The lead cube containing the values is now put into a kind of a cup with a awfully thick bottom, made from bone ash or cement. This cup is termed a bone-ash cup. that is Q-ple not cup-l. If you drop this info at a party you would’t want to mis-pronounce it.

The bone-ash cup with the lead is placed back into the furnace and heated at a thousand degrees close to. The door to the furnace is sometimes left open a crack in order that air can enter. At this temperature the lead quickly combines with the chemical element in the air and is regenerate back into lead oxide. You see, another oxidoreduction reaction. first it was reduced from lead oxide to golden lead and now it is being oxidized back to guide oxide. I’ll make a case for this higher when we get to fluxes.

The liquified lead oxide now soaks into the bone-ash cup. Don’t ask why, it’s just the nature of the beast. bone ash or cement will absorb large quantities of lead oxide. when all of the lead oxide has soaked in you will be left with a awfully tiny sphere of metal. This sphere contains all of the precious metals apart from atomic number 76. in the trade they say, "if you'll bone-ash cup it, you'll sell it". something that is still when cupeling is precious metal.

Now this small lump is weighed. Next it is flattened by smashing it with a hammer. this is often to increase the extent. keep in mind concerning surface area? The flat metal piece is put into a small ceramic ware dish and treated with 500th nitric acid until there is no additional reaction. The remaining piece of metal is dried and weighed.

The reason for consideration before and when the nitric acid treatment is that you just most likely want to understand what quantity silver you had in the sample. Since the nitric acid removes the silver the difference between the first consideration and the second is the quantity of silver that was in the sample. The metals remaining when this acid treatment area unit gold and the noble metal metals.
 

How they do that
The issue that creates a fireplace assay work is the flux. what is a flux anyhow? Why can we would like it? A flux is (usually) a combination of common chemicals that react to supply a desired result on the metal of interest. It can cut back it or it can oxidize it. we have a tendency to should use fluxes as a result of it is imperative to provide the right setting for the precious metals to be recovered for no matter purpose we have a tendency to desire.

For example, If we have a tendency to area unit assaying a sample of ore for gold we have a tendency to should first divide all the ore still as potential by grinding it. Usually, thirty grams of this ore is mixed with the flux. The flux is composed of a calculated quantity of silica (white sand), lead oxide (red lead or litharge), sal soda (washing soda), and flour, cornmeal, or amylum. that is not an error. All the ingredients including the sample area unit mixed thoroughly and put into a clay vessel. The vessel is put into a muffle furnace and heated at 1100 C or 1850 F until everything is liquified and could be a thick liquid.

Now, so as to understand what is happening it is necessary to review very well the things that area unit going down during this awful mixture. Guys, we have a tendency to area unit getting to get inside a liquified, boiling mixture that will cut back something. as the dry mixture melts, some very fascinating things begin to happen. first let ME say that the carbonate is in the flux merely to stay the ph on the alkaline  (basic) side in order that you can’t lose your gold as a vapor of gold chloride. The sand (quartz) is there to make the soften liquid in order that it is poured into a mildew and to create a glass with impurities that may be removed when running.

Are you continue to with me?? It ain’t physics, but it is pretty sensible chemistry. excluding the sand and carbonate, that area unit kind of inert ingredients, what can we have left? Well, we've got the precious metals, the flour, and an outsized quantity of lead oxide. what is happening to those?

Of course you keep in mind the other pages wherever we have a tendency to talked concerning oxidoreduction (oxidation/reduction). you furthermore mght keep in mind that I told you that if you were to understand something concerning metallurgy/chemistry you had to have an inspiration of oxidoreduction. If you forgot, go back and skim it once more.

O.K., as our mixture starts to urge hot the flour starts to undertake to burn but it can’t. Why not? Well, there just ain’t no chemical element offered. At the melting temperatures of those materials there is no air (oxygen) in the furnace. At these temperatures, the flour is crying to burn. therefore what will it do? It’s desperate. It finds the only chemical element offered to that. That is, the chemical element that is contained in the lead oxide (PbO). The flour becomes a reducer. In different words it strips the chemical element from the lead oxide and burns to carbon dioxide. Well, that leaves the lead with no chemical element. The lead has been reduced to golden lead rather than the salt, lead oxide.

This is a rather traumatic modification for the lead. One minute it was contented } contented salt of lead, a paint pigment. now it is an important metal. As a metal it is now heavier than any of the quartz or carbonate therefore it has no choice, it heads for rock bottom of the vessel. now the lead was reduced in very small droplets that now kind of "rain" down through the soften. As they withstand the thick, viscous soften they amalgamate with any gold, silver, or noble metal metals that they encounter.

The lead/precious metals area unit now in the bottom of the vessel with the sand/carbonate/impurities "glass" floating on top. This mixture is poured into a mildew and allowed to chill. You now have a lead "pill" containing all the precious metals. The pill is cupeled as delineate on top of to see the precious metal content.

WOW! I arrived, is anyone still with me? If not, take a break, have a brewage, scan it once more, that’s what I’m gonna do. After all, If you're getting to be a Basement Chemist you gotta be willing to suffer somewhat bit.

Twice in my life I have encountered statements that left ME speechless. many years ago while inspecting a replacement automotive then known as an "economy car"; I told the salesman that i assumed the price was a bit steep for the rather shoddy workmanship. With a incommunicative face he replied "sir", if you wish an economy automotive, you need to to be willing to buy it". What do you inform a naked lady? It’s like this site, if you wish to understand what is happening, you gotta be willing to suffer just somewhat. unfold it out, it won’t hurt so much.
 
Assay Fluxes
There area unit definitely additional fluxes than there area unit individuals mistreatment them. Why? Well, you have got to have over one flux. The composition of the ore sample determines the composition of the flux. That is, the flux should be "tailored" to the sample to be run. If the sample contains scores of oxidizing agents then your flux should contain additional reducer (flour) than usual. keep in mind that the oxidation/reduction system should balance out. In distinction, if your sample contains scores of reducing minerals you will would like less reducer. Well however the hell will anyone ever understand what reasonably flux to use? you will before long understand. You understand that from this one website you will have enough data that you just won't be ready to "drop" all of it at cocktail parties for the remainder of your life.

The flux is calculated to contain enough lead oxide (litharge) in order that if it is utterly reduced, it will manufacture a pill consideration (usually) 25-28 grams. however do i do know what quantity that is? I’m getting to tell you. Ain’t gonna be no additional igerunt prospectors out there. Litharge is composed of one atom of lead and one atom of chemical element. we have a tendency to represent it as PbO. metal being lead and O being chemical element. Lead incorporates a molecular weight of 207 and chemical element 16. Since they are combined the molecular weight of PbO is 223 (see link for Periodic chart of elements). In different words pbO Is ninety eight.2% lead. If we have a tendency to cut back it to golden lead then for every one hundred gr of pbO we will be left with ninety eight.2 gr of pure lead. will that help? Well, it helps ME as a result of i do know something that you just don’t. i do know that we would like a pill of around 25-28 gr. therefore i am getting to put 26 gr of PbO in my flux. when this PbO is all reduced by the flour/ore it will manufacture a lead pill of 25.79 gr. that is lots close enough for government work. If we have a tendency to get a pill that only weighs eighteen grams, we know that a number of the flour should are worn-out in reducing, not the litharge, but the sample. There wasn’t enough flour to cut back each the sample and the PbO. So, what is done to fix this problem? easy, we have a tendency to run the sample Again and now we have a tendency to put during a very little additional flour. what quantity more? I’m getting to get thereto but straight away my parapsychology tells ME that some brains out there {are|ar|area unit|square MEasure} setting out to overheat and some folks area unit thinking unhealthy thoughts concerning me and why they ever started reading this to start with. i think there area unit two things that we have a tendency to should accomplish. we have a tendency to should calm down the brain cells and we should regulate the angle of the reader. I feel this will best be accomplished by one action. Take a trip to the refrigerator and recover another (or two) of those cool, soothing, foamy, unguents that i do know you have got squirreled away. Hey guys, we have a tendency to ain’t taking part in now. this is often "Jet Airline" stuff.

Now that things area unit back to traditional (do I hear muttering out there?), I’m getting to provide you with a instruction for a flux that will, with minor changes, work most of the time. i do know you aren’t getting to established an assay laboratory but this is often what happens once you send in a sample to be assayed.

This is an honest beginning flux for quartz or "neutral" ore samples.

Ground sample -----------30 gr
Litharge (PbO) ---------- thirty gr
Soda (Na2CO3) -------- thirty gr
Flour --------------------- two gr
Silica Sand -------------- ten gr

The amounts used don't seem to be correct for all ores. If your pill is just too tiny, add additional flour. I happen to understand that 1 gr of flour will manufacture concerning twelve gr of lead from the litharge. So, if your pill is ten gr too lightweight you should add another gram of flour to the next assay. It’ll be close enough. Another issue that may go wrong is that sometimes the ore produces a soften that is too thick and viscous to pour properly. could most likely add additional sand or, more practical, would be to feature a couple of grams of borax. borax produces a diluent, additional liquid soften. If borax is used you should bear in mind that it attacks the clay vessel therefore don’t use so much that you just get a hole in it.

I ought to additionally mention that liquified Litharge will dissolve the vessel and the firebricks that line the furnace. that is another excuse for the quartz sand in the flux. It protects the vessel.

So, in reality, the business of fire Assay is some science, some art, some patience and somewhat luck.

I ne'er meant to make assay chemists of you. This page is meant to, hopefully, provide you with somewhat insight as to what goes on in those mysterious back rooms that you just ne'er get to see at the assay laboratory.
 
 Smelting
I think plenty of oldsters get confused between assaying and smelting. In fact, smelting is kind of the other of assaying. They each area unit administered at high temperatures. I think, perhaps this is often wherever the confusion begins. In an assay soften, as I have explained, the setting that is created in the soften is reducing. In fact, it will cut back nearly something illustrious to science.

In a smelting soften we have a tendency to accomplish just the other. we would like to oxidize everything except the precious metals. As all the base metal salts area unit attacked or oxidized by the smelting flux they dissolve in the flux wherever they continue to be until the soften is poured into a mildew. These base metals will end up in the dross or glass that floats on top of the gold. As in assaying, the flux depends to an outsized degree on the composition of the material to be smelted.

The term "smelt" seems to mean various things to different individuals. to many the word brings up visions of smoking, boiling, caldrons of metal. To others it refers to any purification which ends in the separation of the gold from most of the contaminating materials. The gold that almost all folks are going to be operating with is in pretty good shape to start with. Sure, it most likely contains some black sand and perhaps a few different minor contaminants but not 500th black sand etc..

Furnace smelting is sometimes administered using a vessel made from black lead (a crystal style of carbon). in fact I don’t need to tell a basement chemist why we have a tendency to favor to use black lead, except for any casual visitor I ought to make a case for that at high temperatures the black lead (carbon) becomes a reducer that helps keep gold and noble metal metals in their reduced or golden forms. Some silica sand or ground glass is sometimes additional in order that there will be a glass matrix that floats on top of the metal. Some soda niter (Chilean nitrate or Saltpeter) is additional. This nitrate could be a rather sturdy oxidizer. when hot it will oxidize nearly any metal, apart from gold and the noble metal metals, to its nitrate salt. These salts mix with the liquified sand. usually some borax is additional to skinny the viscous, liquified glass.

This mixture is heated until the soften becomes "quiet" with no bubbles, foam, or lumps in it. the precious metals area unit now poured into a mildew and the glass or different "gangue" is removed. The black sand that was in our soften was oxidized to iron nitrate by the soda niter and is now dissolved in the glass that we have a tendency to discard. Your gold, at his purpose won't be 100% pure. It most likely contains tiny amounts of copper, silver, tellurium, etc.. the great news is that it's like gold and may be of fairly top quality. lots good enough to sell.
 

A field assay that you just can do!
The previous prospectors might need illustrious a few things that we have a tendency to don’t usually give them credit for. They knew concerning fine gold and that they knew that it was value even as very much like coarse or nugget gold. They additionally had a awfully easy method of decisive concerning what quantity of this fine gold that was in the ore that they were presently interested in. I have no plan wherever they learned a way to try this assay, United Nations agency told them concerning it, or wherever the procedure originated. I ne'er hear of anyone mistreatment this method anymore. Don’t understand why. If you scan my page on halide action you know that solutions of Iodine will dissolve fine gold very quickly. Well, the previous sour-dough’s knew this too. And, somehow they devised the subsequent method for mistreatment it as an assay tool.

All you wish to try to to this assay is get some "Lugol’s Iodine". this is often merely Iodine dissolved during a answer of sodium iodide. you'll get this from any pharmacy. just make sure that it is in water, not "tincture of Iodine", that is in alcohol answer. you'll make it yourself (see page on Halides). you will additionally would like somewhat dilute nitric acid, two traditional close to.

Now, just take some material that you just suppose might contain a major quantity of fine gold and grind it, pound it with a rock or a hammer, or no matter until it is as fine as you'll get onto. Take a measured quantity of the sample and put it in some convenient vessel like an outsized tube, a small baby food jar, or other. you'll use no matter measure is convenient for you. 5 level tablespoons, one low scoop, etc.. you do want to use constant quantity each time in order that you will have some plan of the quantity of gold in the ore. at least you will be ready to say that this ore has over that one.

Now, your ore is in the jar. Pour in the Iodine answer in order that the ore is well lined. Shake it often for some time, perhaps ½ to 1 hour. now you need to remove the ore. {you can|you'll|you'll be able to} let it settle and pour off the Iodine containing the gold or you can filter it with a small funnel and some coffee filter paper. the concept is to urge the answer as clear as potential. now you add a small clump of mercury and shake. At some purpose the answer will lose it's red-brown Iodine color and become a (usually) clear yellow liquid with sediment of serious floured mercury in the bottom of the jar/test tube. enable this to settle for a few minutes and then rigorously pour off the liquid. Add some water to the mercury, shake, enable it to settle, and pour off. Don’t throw the liquids away. now you have got your precious metals amalgamated in the floured mercury. now you simply add some nitric acid (not over 50/50 with water) and dissolve the mercury. when the mercury is all dissolved you will be left with a black or brown material that you just cannot dissolve. this is often your precious metals. Don’t throw the chemical element answer away. now take an honest inspect the black sediment. try to get a sympathize with what quantity there is in order that you will have a comparative plan of what quantity you have got. you'll get, from chemical supply companies, a graduated, round shape tube. If you run the assay during this you'll merely scan off the amount of precious metals on the dimensions inscribed on the tube. It’s a nicety that the previous timers didn’t have but it is convenient.

The reason I told you to save lots of all the liquids is simple, we have a tendency to area unit getting to recover all your Iodine and mercury. the answer that contained Iodine is treated with a few drops of Clorox. The Iodine will settle to rock bottom. The liquid is poured off and then you add somewhat lye water until the answer becomes clear and colorless. Your Iodine is in answer ready to use once more (see the page on Halides). The nitric acid answer of mercury is treated by your favorite method to recover the mercury (see the mercury page).

You see, now that you just became a basement chemist, you don’t need to keep in the basement, you'll take it right out into the field with you.

O.K. now we know a few things that the old-timers knew one hundred fifty years ago. The question is what percentage of you knew concerning or have used this method? give it a attempt, it works.