Gold processing methods with the Carbon in pulp are often used in large-scale gold mining processing, where the active carbon in pulp method used for recovery of gold ore minerals in the washing tank. Tanks that are used are usually equipped with an agitator and air bubbles equipment and tools are designed to maintain solids in suspension in the slurry, and the achievement of leaching. In the process adsorption ore minerals in the soil material condition of the tank should be good enough to form a slurry that can flow under gravity or when pumped. To form a slurry, mineral ore in the mix with water and the reagent was added to the tank to get the gold leaching reaction
How to work the gold extraction process with carbon adsorption in the pulp can be explained by the following system
Preparation of mineral ore from mines that have been destroyed to obtain a smaller rock with crushing and grinding like a stone or Jaws Crusher Crusher which later can reduce the particle size and liberate gold ore for leaching processes.
Mineral ore that has undergone a process of destruction and into the refining process by machine Ball Mill to get Ø200 mesh. In the process of natural mineral processing, the size of a Raw materials will greatly influence the outcome and recovery at the end of the process. The more subtle the higher raw material recovery in the can due to leaching in the chlorination process will be the maximum
Transportation of mineral ore into the first tank made to form a slurry which will be ready at the pump to tank leaching. The use of agitators and H2O in minerals carried out to form a slurry, for pulp which has a density of 1.5 g / cm 3 was diluted to give a pulp that has a density of 1.17. Gold content of about 2 ppm aqueous pulp but obviously fluctuate. Ores containing free gold recovery can not produce high enough to use a single cyanide leaching process, since a very long time for the dissolution of large gold particles.Gold ore containing gold bearing minerals associated with sulphide or carbon require additional treatment, other than size reduction, prior to gold recovery. The addition of cyanide reagents used in the first stage and the pH of the slurry is raised to pH 10 -11 uses chalk, in order to ensure that when cyanide is added, hydrogen cyanide gas is generated and stored in a cyanide solution to dissolve the gold. To create alkaline conditions with pH 10-11 using lime as a pH modifier. Active lime or calcium oxide (CaO) is more reactive raise the pH so it needs a little. However superficial Hydroksida (CaOH) can also be used. pH Modifier others are Coustic Soda or Sodium Hydroxide (NaOH) or Soda Ash (Na2CO3).The concentration of cyanide which is used in a variety of practice 300-500 mg / l (0.03 to 0.05% as NaCN) depending on the ore minerals. Gold was discovered by way of either heap leaching or agitated pulp leaching.
Results from the first slurry tank at the pump to the tank and leaching. The use of oxygen or peroxygen compound instead of air as an oxidant increases infiltration rates and reduce the consumption of cyanide, because the inactivation of some species consume cyanide present in the slurry. Oxygen gas is often injected under stirring or into the vat to get the desired level of dissolved gases, several base metals plant sulfur dioxide may be sometimes necessary. The addition of chemical reagents for cyanide leaching process is still being done and the ph of the slurry also remain on guard until the pH of 10-11. If the pH is too high will cause the cyanidation process was slow, this is because the cyanide to be too stable in the pulp. Additionally, with too low or too high will cause other metals will dissolve in cyanide compounds that form the complex that also absorbed by activated carbon
Alkaline conditions (high pH) during the cyanidation process largely determines the success of the process of cyanidation. The use of alkaline such as calcium oxide, will prevent the decomposition of cyanide in solution to form gaseous hydrogen cyanide (HCN.) If the pH is too low / acid can produce volatile HCN gas due to the hydrolysis process, so the concentration cyanide reduced.
CN-(aq) + H + (aq) → HCN (g)
Make sure the pH of 10-11 to anticipate that NaCN does not turn into a very dangerous HCN gas (60 mg of HCN can kill people). Where the conditions of pH 9.3, the concentration of cyanide can be reduced by about 50% since evaporated into a gas HCN, even to 99% changed cyanide HCN at pH 7. In addition to this very dangerous gas would reduce the amount of NaCN dissolved in the slurry so that its ability to dissolve gold is also reduced.
Oxygen from air is the oxidizing agent to separate the gold in a cyanide solution. Oxygen plays an important role in the process of leaching. In general the higher the oxygen, the reaction is also faster. The use of hydrogen peroxide (H2O2) in a solution of cyanide have been detected in which gold can be separated quickly, and this observation suggests that some gold possible through a separate pair of reactions involving first the formation of hydrogen peroxide:
2Au + 4CN-+ O2 + H2O → 2 [Au (CN) 2] - + 2OH-+ H2O2
Then hydrogen peroxide reacts with some gold and cyanide.
2Au + 4CN-+ H2O2 → 2 [Au (CN) 2] - + 2OH-
Then hydrogen peroxide reacts with some gold and cyanide.
2Au + 4CN-+ H2O2 → 2 [Au (CN) 2] - + 2OH-
Then carbon for gold in the uptake of metals added to the tank leaching. Activated carbon of good quality gold production greatly determines the results obtained. Activated carbon is good to have: the structure of the natural pores, a high level of resistance to friction, high hardness levels and form a uniform and have a fairly high CTC. For if the use of activated carbon which has a low CTC, the gold that has been in the activated carbon adsorption will be more easily dislodged during the washing process carbon. CTC is recommended preferably 50% -60%. To produce high-carbon CTC should use a rotating kiln and flat and accurate temperature control. Carbon that has not been through the process kilns typically have only CTC 10-20%. Usually in the CIP method using granular activated carbon with a size of 6x12 or 6x16 mesh, while the size of 6x16 or 12x30 mesh used in the method of CIC. The concentration of carbon in the use of CIP method is 10-25 grams per liter of pulp (0.5 to 1.2% carbon by volume)
Gold adsorbs onto the surface of the carbon and then passed through a column of carbon and carbon is then filtered by using the screening, the screening of carbon will settle and fine tailings liquid (-100 mesh) will come out through the screen into the tank, which is generally located in step mode , so that the overflow of the highest gravity field which will flow to the next column. Carbon loaded periodically from the column, and then sent to the stripping in place. Carbon pregnant solution is generally heated (200 degrees to 250 degrees F) of (1%) and sodium hydroxide (0.1%) and gold cyanide is re-dissolved and removed from the carbon surface. At this point, a solution of NaOH / CN sent to electrowinning cells, where it will stick to the gold-plated stainless steel cathode. Gold is removed from the cathode by using either high pressure water spray, sometimes shaking the cathode, and in some cases, placed in a stainless steel cathode melting furnace and heated to 2,000 degrees F, to melt the gold from the cathode. Stainless steel cathode, of course, does not melt at this temperature, but this temperature reduces the life of the cathode, and most will wash the gold "sponge" from the cathode. Gold from the powder and then melted until melted and subsequently poured into gold bullion
Once the carbon has been revoked, it can be reused after charging in the kiln, by heating to about 1300 degrees F. carbon is then cooled, filtered and ready for reuse. Generally, various sizes of carbon is 10 mesh to 16 mesh and is almost always no better than 20 mesh. Carbon from coconut shell carbon shell is generally preferred for use in recovering gold from leach solutions.
To obtain optimum results, the processing of gold in rocks oxydis usually quite effective with the mill at 65 mesh and leaching with NaCN 0.05% for 4-24 hours at a density of 50% solids. While rock sulfide require up to 325 mesh refinement and leaching with 0.1% NaCN for 10-72 hours at a density 40% solids. (Weiss 1985)
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