Fine gold often has a black coating on it that has to be removed. Mercury can be used but is kind of dangerous so I haven't even tried.
Here area a couple of statements written better than I can about black sands.
http://www.nuggethunters.com/blacksand.htmlBlack sand contains hematite and magnatite as well as other metals. You should first use a magnet to remove the Magnatite.
Black sand concentrates are a combination of minerals in the iron group: Hematite, Fe3o3, with a specific gravity of 5.26, an iron mineral that is non-magnetic and Magnetite, Fe3o4, with a specific gravity of 5.20, is magnetic. These black sands will weigh a third (1/3) to a fourth (1/4) the weight of gold (Au). Gold has a specific gravity of 15 to 19.3. A cubic foot of wet black sand will weigh 225+ pounds or 26.7 pounds per gallon. These heavy concentrates present the major problem in the gold recovery process for the average recreational gold prospector. Gold with a specific gravity of 15 to 19.3 and black sand at 5 to 6, when classified to the same mesh size, will allow the gold contained to be easily recovered. Without classification, gravel three times the size of gold will be recovered with the gold, hence the necessity for proper classification. With the 3 to 1 ratio in mind start by classifying your concentrate to 10 mesh. Run material through the gold wheel and gold contained in cons will be recovered in the 10 to 40 mesh size. Screen concentrate again with a 40 mesh screen and rerun. Your gold wheel should recover any remaining gold in the 40 to 120 mesh class. Beyond this point you must have experience in water pressure and the use of a surfactant to recover any existing microscopic gold.
http://www.angelfire.com/ky/goldpage/HOW TO PROCESS YOUR BLACK SAND CONCENTRATES
The modern day prospector and placer gold miner is becoming aware of the value of the black sand concentrates he finds in his sluice box, rocker box,dredge, dry washer,pan or whatever method used to seperate the gold from the waist rock,sand orgravel. Wher once it was though to be a nuisance and often discarded as of little value,it is now recognized that they may be a major source of the gold available in a placer operation. The old time prospectors threw away fortunes Because they didn't know a large proportion of the gold was in the black sand concentrates.
The practical approach is to mine the gold bearing sand and gravel at the site-sizing,and reducing it down to the black sand concentrates which are then placed in five gallon buckets, coffie cans ,or or what ever type of containers you would like to use to transport it back to your home or where everyour headquarters might be.It is a waist of time to process your cons at the mine site. This is to be done on weekends or in the winter time or other times when you can,t work the mine site.
The Information or medthod presented in this study is not new .Rather with local ,is is except as stander practice by gold prospectors and miners through out the world.the method out lined is recommeded by the Gold Propsectors Ass. of America.
The study is in two parts.The frist deals with the handling of the Black sand and concentrates from a very small pan size operation. The second part discuesses steps ,and nethods and equipment involved in larger operations and quanties of concentrates developed from a pratical two man operation.The principles are the same, the medthods and equipment are adapted to the size of the operation.
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PART 1 SAMPLE SIZE
While the principle is the same in the processing of the black sand, gold concentrates, in small and larger quantities, the method, and equipment is adapted to the quantities involved. Both sample size, and production size, are discussed in this study.
First, let us deal with the small quantity, or pan, sample situation where you have only a limited amount, perhaps the result of a half dozen pans, and where you wind up with approximately a pint of concentrates. This will give us a method and demonstrate the same principles that will be Involved in the larger quantities.
FIRST STEP - MECHANICAL SEPARATION
Assume you have already picked out the nuggets and coarse gold, and have just the black sand and ftne gold remaining. Here is one way to proceed:
1. Spread it all out in your pan, a pie tin, or a plate, and set it in the sun, or on a source of heat such as a radiator or stove to dry.
2. When dry, you can put a small quantity at a time on a piece of stiff cardboard and blow across the material, perhaps tapping the card board a little, gently, and you will ftnd that a good share of the lighter-weight sand will blow off at once. As you stir it around and blow again, you will get rid of a little more, but there will still be a quantity left. That remaining is probably one or more of the iron containing black sands.
3 . Since most of these compounds are magnetic they can be readily picked up with a magnet. Some of the black sand will stick to the magnet in spite of every thing you can do. Fortunately, this can be prevented by wrapping the magnet with a sheet of plastic before using. The black sand will cling to the plastic but will drop off as soon as the magnet is removed.
4. If there is still black sand of a non-magnetic type mixed with the gold, then your next step is to separate the gold with the aid of mercury by a simple process called amalgamation.
CLEANING THE CONCENTRATE
Before proceeding to the second step of separating the gold from the black sands, the concentrate must be thoroughly cleaned. The necessity for this preliminary step before amalgamation is attempted cannot be overemphasized. In discussing the amalgamating powers of mercury in a placer gold washing plant with a consulting engineer recently, I was surprised when he said, "from my experience, the amount of fine gold crossing a mercurycoated plate that is actually recovered is comparatively small - perhaps 10 to 15 percent. He explained the reason the percentage is so low is that practically all placer gold has a protective coating of some kind, perhaps pine oil, if in a mountain country. Unfortunately, gold is often coated with various substances, such as iron sulfide, magnesium, rust, or other inorganic amalgamation. Explaining further he said, the answer is to treat the sand containing the gold with a cleaning substance before it comes into contact with mercury." This is extremely valuable Information and has to do with the over-all recovery ratefrom any placer gold recovery system or operation.There are other ways of cleaning gold, but one very simple method employs the use of nitric acid. First,place the concentrated, gold-bearing sands into a plastic gold pan or other container that will not be affected by strong acids. Cover the concentrates with about a half inch of water and add the acid in small amounts until a slight boiling action occurs. This boiling begins when about a 90 percent concentration is reached. In some cases, no dilution is necessary. Add straight acid. Mix the acid solution around for several minutes, making sure all the material is well saturated. Even better, let it stand a while. The acid solution is then poured off and the concentrate rinsed by dipping- the pan in the stream. The gold is now ready for amalgamation.
SECOND STEP - SEPARATION BY AMALGAMATION
Amalgamation is one of the oldest and simplest methods for recovering free gold from the black sand concentrates from placer mining. When clean particles of gold are brought into contact with mercury, they unite, or merge, into a single new substance known as amalgam.
Amalgamation takes place when the two metals are brought into contact with each other by mldng or blending, and even the smallest particles of flour gold is gathered up and absorbed by the mercury. This special affinity for gold makes mercury an invaluable aid in separating the gold from the black sands.
It takes only a few drops of mercury to gather the gold in the black sand found in an average pan of sample. The mercury should be agitated with the concentrate under water until every portion has been contacted and all the slall globules and BBs of mercury absorbed by the one ball of amalgam. It now contains all the flne, and flour gold that would otherwise have been lost.
Part # 1: Quite frequently, more mercury win be applied than is required for the amount of gold to be absorbed, in which case the ball of "amalgam' will actually be a mixture offree mercury and the amalgamated substance. In fact, it is desirable that an excess of mercury be used to assure that all the free gold in the sample is absorbed. However, in the interest of economy, and the conservation of mercury, a preliminary step is required before beginning the separation of the gold from the amalgam. This consists of removing as much of the free mercury from the amalgam as possible. This can be accomplished in several ways.
Historically, the mcrcury-amalgam mixture was squeezed through a piece of chamois skin, or a sflk cloth, but this created problems. More recently, a syringe, with a thin, cotton pad in front of the plunger head, is being used with great success. The mercuryamalgam mixture is placed in the syringe and, upon pressure, the mercury is squeezed through the cotton pad into a container, leaving the small, round, cake or wafer of amalgam in the syringe. The cake of amalgam is now ready for further treatment.
PART #2: The next step is to be conducted out-of-doors, as toxic fumes are produced. It is suggested that you set up a stool, chair or small table in your back yard, or other open area, then place an electric hot plate, with a long extension cord attached, on the table. Place a Pyrex dish 2/3 full of 25 to 65 percent nitric acid on the hot plate. Ordinary glass will break upon heating, so the dish must by Pyrex, which is made to withstand heat.
You are now ready to place the cake of amalgam in the solution. Almost at once, you will note a reaction taking place as fumes begin to rise. These fumes may not be fatal, but are toidc and, ifinhaled, may make you sick andcause damage to your lungs, so stay away from them. Take no chances. Next, you turn the current on to the hot plate, and let the solution boil for 5* minutes. What is the mercury from the amalgam is being taking place is, absorbed, or taken into solution by the nitric acid an leaving the free gold in a natural form. At the end of 5 minutes, turn off the current and, after the dish has cooled and no more fumes coming off, walk over and inspect your cake Of gold- Pick it out of the solution with and drop it into a cup Of water with a pair of pliers natc of soda in it to neutralize the acid on ordinarybicarbo r, or cake, of gold is not solid, it. you will note the little wafer but rather looks like a sponge After the mercury was absorbed by the nitric acid, it left empty spaces where the mercury had been, giving the remaining gold a sponge-like appearance, drab and rusty or. In fact, it'-s calledtsponge gold and is ready to be in col melted down into a bar, or used for any purpose desired. Heating the sponge blowtorch temperature will bring out the natural, bright gold color. Incidentally, you should have a half gallon or more of water and bicarbonate of soda mixture available in case you get some of the acid on your hands and clothes. If you should get acid on your hands, dip them in the soda water immediately.
Part #3: The remaining nitric acid solution now contains the small amount of mercury which came from the amalgam. This mercury can be recovered by placing a small sheet or bar of copper in the solution. The mercury will collect on the copper and can be scrapped off and saved for future use.
The used nitric acid solution should be diluted and neutralized by adding soda water then flushed away.Itmust not be put through the plumbing system unless diluted and neutralized. The acid solution can be saved and re-used again, but nitric acid is not so costly that this seems necessary.Boil gently; don't deplete the quantity of acid more than a third. Put a Pyrex dish 2/3 full of 25 to 65 per cent nitric acid on a table in your back yard, or other open area. The fumes are very toxic-take no chances.
