Monthly Archives: October 2012

Process Electrowinning For Gold Mining

Electrowinning is an electrochemical process used to reduce the metal cations to the cathode surface of an aqueous solution derived from the chemical leaching proces. Electrowinning or often referred to as electroextraction is the electrodeposition of metals from ore minerals that have dissolved into the liquid and will be processed using Electrorefining to remove impurities from the metal. Electrowinning an electrolytic process that is very old in the mining industry. The English chemist Humphry Davy first obtained sodium metal in the form of the element in 1807 by electrolysis of molten sodium hydroxide. And then in 1847 Maximilian, Duke of Leuchtenberg first to show an experiment about Electrorefining copper. Then James Elkington patented a commercial process in 1865 and successfully opened the first factory in Pembrey, Wales in 1870. The first commercial plant in the United States is Balbach and Sons Refining and smelting Company in Newark, New Jersey in 1883
     Electrowinning is applied to a variety of chemical solutions that are found in large mining industry. This process involves the use of alkaline cyanide solution as an electrolyte in a cell as the anode and cathode, among others, can use:

     ( – )   
99,99 %

( + )

Cell reaction that occurs is: Merkury dicoating Copper, Lead, Iron, Aluminum
Anode: 2OH-→ O2 + H2O + 2e-
Cathode: 2Au (CN) 2 – + 2e-→ 2Au + 4CN-
Overall: 2Au (CN) 2 – + 2OH-→ 2Au + O2 + H2O + 4CN-

         Metals most often processed in electrowinning techniques are copper, gold and silver. Most metals occur in nature in the form of oxidized ore and thus should be reduced to form a pure metal. Ore is dissolved into some preprocessing in aqueous electrolyte or in the molten salt and the resulting solution is electrolysis. Then deposited on the cathode metal (whether in solid or in liquid form), while the anodic reaction is usually oxygen evolution. Some metals are naturally present as metal sulfides; These include silver, tin, molybdenum, cadmium, nickel, silver, cobalt, and zinc. In addition, gold and platinum group metals associated with sulfidic base metal ores. Most metal sulfide or its salts, are electrically conductive and this allows for efficient electrochemical redox reaction occurs in the liquid state or in aqueous solution.Some metals, including arsenic and nickel did not come out, but still electrolyze the electrolyte solution. This is then reduced by a chemical reaction to improve the metal. Other metals, the metals during the processing of the target has been reduced but not deposited on the cathode, sank to the bottom of the electrolytic cell, where they form a substance called the anode anode mud or slime. Metals in the sludge can be removed with standard pyrorefining method.

         For practical purposes, the extent to which metals can be recovered by electrowinning depending on its position in the electromotive series. In general, metals that have a more positive electrode plate is the standard potential is more easily compared with less positive potentials. As an illustration, the metals are more noble, such as silver anda gold, can be removed from the solution to less than 1 mg / l by using a cathode while the flat plate with copper and tin, the concentration in the range of 0.5 to 1 g / L or more required to deposit a homogeneous metal. Electrowinning This applies mainly to remove metal from a solution containing high concentrations of metal ions moderate (> 3000 mg / l). Under 1,000 to 2,000 mg / l of metal, the process of conventional electrowinning become very inefficient but otherwise the benefit is in recovering the precious metals that would otherwise be converted into a metal hydroxide sludge by the waste water treatment system. In the electrowinning process will release gases create H + pH down so risky mengasilkan HCN gas. This gas is extremely dangerous and corrosive to the anode, to the alkaline cyanide solution must be maintained at pH 12.5.

Activation Over potential For The Evolution Of Selected Gases On Various Electrode Materials At 25 °C


Platinum ( Platinized )
    – 0.07 V    + 0.77 V   + 0.08 V    
– 0.07 V + 0.93 V
– 0.09 V + 1.02 V
Iron – 0.15 V + 0.75 V
Platinum ( Shiny )
– 0.16 V + 0.95 V
Silver – 0.22 V + 0.91 V
Nickel – 0.28 V + 0.56 V
Graphite – 0.62 V + 0.95 V + 0.12 V
Lead – 0.71 V + 0.81 V
Zinc – 0.77 V

Mercury -0.85 V
      In elektrowinning, the current is passed from inert anode through a liquid solution containing the metal absorption so that the metal is extracted and then stored in the electroplating process to the cathode. In electrorefining, the anode consists of a metal that is not pure, and will then pass a current through the anode which corroded acid electrolyte into the solution so that the electroplating process deposits refined pure metal to the cathode. Electrowinning is different from other recovery technologies (eg, evaporation, ion exchange) in a metal element that recovered than metal bearing solutions. Metals recovered are usually not pure enough for use as an anode material in a plating process. Because metal deposition rates associated with the available surface area, the cathode must be able to work and this is very important. Two types of flat plate and reticulated cathodes are used, each having its own advantages. Flat-plate cathode can be cleaned and reused, recovered and plated metal. Reticulated cathode has a higher deposition rate compared to the flat-plate cathode. However, they are not reusable and must be sent for recycling. Alternatively, the cathode starter from a pre-refined metals can be used, which became an integral part of the metal so it is ready for rolling or further processed.

How to metal gold testing

        The testing process gold from gold bouillon is very necessary, in which the gold content so that the results we obtain can be seen the most of what percentage of karat or purity levels of the value contained in the gold metal. How to do metal gold testing, In the process of testing the gold, there are several methods that can be used, ranging from gold assay methods in a simple way to use chemical solutions to using digital tools. Several types of testing processes such as methods Touchstone testing, Acid testing kits, Electronic gold testers.
      Touchstone testing is the testing of gold by using a textured black stone and is very light or even with the slate. In testing this gold requires an acid to see references from the gold content being tested. The way the test is to rub a gold metal on black stone, so it will look a yellowish colored scratches scratches from gold or small deposit of gold on the surface of the touch stone then do the same with a known gold item, apply a small drop of the test acid to each mark and observe – compare the reaction of the acid and repeat the test with a different Karat acid until a match is observed. Remember to test a fresh portion of the mark as you don’t wont to cross contaminate the test acids. This method is best suited for known items of gold that are not hallmarked and you just really need to determine the Karat or purity of the gold. Touchstone testing compares how gold alloys of known and unknown fineness react to acid. For gold, the test is based on the fact that 24K gold resists all but the strongest acids. The purer the gold (the higher the karatage), the stronger the acid required to change its character or to dissolve it.
         Acid test kit is a method of testing by placing a small drop of acid to the surface of the item, sometimes it is required that you scratch the test surface in an inconspicuous place to be sure your not testing a gold plated item, this can be done with a pocket knife or small file. By breaking the surface of the metal the acid will give a more accurate result. Place a small drop of acid directly on the scratch starting with theAcid gold test lowest Karat acid first e.g.9kt. Observe the reaction and compare to a colour reference chart that is usually included, repeat the test with a higher value Karat acid if necessary until a colour match is found. Genuine or solid gold will usually leave a brown stain and non gold items will leave a green stain on the metal or react by bubbling and sizzling indicating that the item is either gold plated or contains copper as a base metal. Rinse the test item in clean water to remove any excess test fluid, any light staining left behind can be easily removed with a pencil eraser or buffing wheel. Always exercise caution when using Acid Testing Kits and be sure to read all safety information provided with your kit, acid is very corrosive and toxic. Acid testing is probably the most widely used of all the gold testing methods. A selection of different Karat acids are formulated to react in different ways when they come into contact with genuine gold items of a certain Karat
       The electronic gold tester is a relatively new addition for the scrap gold dealers toolbox, briefly it consists of an electronic circuit and a test plate of reference gold all housed in a neat desktop size box. Electronic Gold this assay is very easy to use in testing gold, quickly and efficiently detects karat value of the gold from 6 to 18 karats. Also detects platinum and separates solid gold items from gold plated ones. Provides a numeric reading on the LCD display that corresponds to the karat table.

Gold Panning For Identify Minerals Gold Alluvial

           There may be some of the less know how panning eluvial gold ore found on the path of the river or the prospect area which contains metallic gold ore, and how to identify alluvial gold in river to obtain a suitable sample of gold ore. The place to look for gold eluvial including creeks and ditches along the sides of hills and in depressions between the hills. Alluvial deposits occur on the hillsides and in the hollows between the hills. Then we tried along the river, which at the start of a bend in the curve of the river downstream side or bend in the river because it is usually gold ore are often stuck in there. And we can try to take a few handfuls of sand sediment and then washed with a platter.

           By using equipment made ​​from plastic pots or metal we can do an analysis of eluvial gold ore. And we also need to separate magnetic metal with a gold metal content of iron ore. Before you use these pans equipment wash with soap to remove any residual oil from the sometimes still tied at the bottom of the pan.

Step in gold panning:
Look for areas in the bend of the river that have a prospect of the gold mineral ore. Then fill the pot you use for gold panning with sand, soil and gravel that you think have gold content of ore minerals. 
        To begin the next step place the pan on the bottom of the water and gently shake pan and rotate them. Then tilt the pan for some materials rough stone are in a position above the rough and then you throw rocks slowly by hand. Indirectly mineral ore will be under because of the force of gravity, and gravity of gold metallic minerals and rocks
Now turn and shake the pan back gold from side to side and pull it backwards, while partially submerging under the water pan. While such set up a tidal wave This allows each particle of gold is not out of the pot but was trapped at the bottom of the pan.

Tilt the pot of gold with the tip away from you slightly under water. While your hands are still shaking while positions remain as they are side to side, sink, lift and out of the water and tilted back, allowing it to form a wave. Tip forward again, letting the waves travel ahead to take out of the pan. Next turn back the pan from side to side again so that the metal back on the bottom of the pan

      Some of the previous steps should be repeated until the only remaining approximately one tablespoon of the remaining fine material. This action is necessary to gently wash the used amount of dirt remaining. Eventually will be seen a few grains of fine gold ore at the bottom of the pan but still there are some impurities. To eliminate some black dirt that is most likely iron ore sand, we can use a magnetic metal to take it. Place a magnetic metal in a plastic bag so that the black sand collected on the outside of the magnetic metal for iron ore can be easily retrieved from a magnetic metal.

To eliminate some black dirt that is most likely iron ore sand, we can use a magnetic metal to take it. Place a magnetic metal in a plastic bag for iron ore can be easily retrieved from a magnetic metal. then enter a magnetic metal into a pot which contained gold ore, then iron ore will stick to the magnetic metal, while gold ore will be fixed and does not stick

Gold spots can then be collected with wet fingers and placed in sample bottles filled with water. A teaspoon is useful to collect the gold when present in large numbers