Gold mining was first carried out in alluvial areas, namely in watersheds that have a mineral content of the ore deposits of gold, where gold is mined by a very simple way by using the tools of a pan. This processing method gold panning is very simple, the separation between the gold ore minerals is done by shaking the pan to follow the movement of the hand that spins in the flow of water while hand is vibrated so that the gold ore will drop down, then slowly poured the water in the pan out as the flow of sea water waves , so that the sand which is above the exit wasted, while the gold ore would remain at the bottom. The separation between the gold ore with other minerals in the alluvial deposits then developed with gold mining wave table, and then followed by a gravity separation
method using the process of merging with the capture of mercury
. Gold exploration in the lower layers of soil to get the primary sediment deposits began in 1860 with gold using a cyanide treatment system. And in 1960 the method of processing low-grade gold began being applied, which carried out the processing system through leaching heap, this process is basically developed from gold processing system using cyanidation. Economic climate that developed during the decade of 60-70s also forced more and more advanced processing technology so that the plague of gold exploration gold mining began to flourish around the world. And during this decade found several technologies that can improve the recovery of gold recovery even for low-grade gold. This development was influenced by the development of chemical technology.
Some of the advanced and economical technology used in the processing of gold mining is
Carbon in Pulp (CIP)
Carbon in pulp process or CIP was developed in the early 70’s. In the process, the leaching of gold ore mineral rocks through the stages of cyanidation process, then the particles of gold in gold-rich solution is absorbed by the pores of the carbon. Carbon containing gold is then washed and the electrolysis to produce metallic gold bullion.
Heap leach is a method developed by Henin and Lindstrom to process low grade ore with large scale and small production costs, so that the lowest levels of mineral ore can still be economical. This is a process heap leach gold leaching low-grade rocks are stockpiled, then the solution containing the metal particles are screened and separated by electrolysis. Heap leach done repeatedly and on a large scale.
Ore is refractory gold ore that can not be processed by simple cyanidation because it wrapped up by other minerals, such as sulfide or telluroid. But this can be in cyanidation ore after roasting for wrapping wet mineral particles of gold. This ore can be treated by chlorination followed by cyanidation and zinc precipitation or with CIP and electrowinning.
Of all the gold mineral processing must go through several stages in all these stages it is absolutely live to get the desired results, as for some stages it can be underlined by the diagram below
CRUSHING / MILLING
Phase diagram of the processing of gold :
* Destruction of rocks minerals
Mineral rocks from the mining area was then taken into the area of destruction, and destruction of rock do to get smaller sized rocks. Size obtained is usually ± 20mm. machine used is a machine or Stone Crusher Hammer Mill or Crusher Jaws. After going through the process of destruction, and entered into the refining process using a machine Ball Mill to get Ø200 mesh. In the process of natural mineral processing, the size of a mineral material will greatly affect the outcome and recovery at the end of the process. The finer the mineral material will be higher and further that the maximum recovery can result in the leaching process
* The Processing Of Gold
Once the size of the ore is reduced, the process is then performed by separating the mineral concentration process gold from mineral impurities, consisting of several kinds of processing techniques:
- PROCESS GRAVITY CONCENTRATION : Gravity concentration is the separation of valuable materials and worthless in a mineral due to the forces within the fluid by / depending on the difference in density, shape and size. Concentration / separation by gravity methods exploit differences in the density of gold with a density of other minerals in the rocks
- AMALGAMATION PROCESS : Amalgamation is a process of binding of mineral ore by mercury and form an amalgam form of Au (gold) with Hg (mercury). And the process of amalgamation is the process of chemical physics, if the results of the amalgam is heated, it will break down into elements, namely mercury and gold bullion. Amalgam can be decomposed by heating in a retort, the mercury will evaporate and can be recovered from the condensation of mercury vapor. While Au – Ag still remained in the retort as a form of mineral ores.
- FLOTATION PROCESS : Flotation can be interpreted as a separation of a substance from other substances in a liquid or a solution based on differences in surface properties of the substance to be separated, where the substances that remain hydrophilic aqueous phase while hydrophobic substances that are air bubbles will be bound by and will be brought to the surface solution and form bubbles which can then be separated from the liquid, where flotation process aims to separate and produce a metal concentrate. This process produces metals from ore concentrates at the mine by separating valuable minerals from impurities that cover it.
- LEACHING PROCESS : leaching is the extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). Process Leaching Cyanide This process aims to take the gold extraction is formed in the chlorination process and transformed into a compound Dicyano Aurrat (Au (CN) 2). Because the compound that would be absorbed in the pores of activated carbon. Cyanidation process consists of two important phases, namely the dissolution process and the process of separating gold from the solution. Solvents commonly used in the process cyanidasi is NaCN, KCN, Ca (CN) 2, or a mixture of all three. The most commonly used solvent is NaCN, being able to dissolve gold is better than other solvents. In general, Au and Ag dissolution reactions are as follows:
4Au 8CN-+ + O2 + 2 H2O = 4Au (CN) 2 – + 4OH-
4Ag 8CN-+ + O2 + 2 H2O = 4Ag (CN) 2 – + 4OH–
* Gold Concentrate
From the stage of the process will then be obtained concentrate processing ores containing various metals. And the concentrate will be processed in order to obtain the value of gold in high purity chemical process. And a few stages of the treatment process through a process
- SMELTING : Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes production of silver, iron, copper and other base metals from their ores. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gasses or slag and leaving just the metal behind.
- PARTING: Parting is the separation of gold by using nitric acid or HNO3. In this process the gold is only separated from the metals copper and silver by nitric acid. Dissolved copper in the form of copper and silver nitride is dissolved by nitric acid in the form of silver nitride, so that only gold is left in this process.
- AQUA REGIA : Aqua regia is a solution made from a mixture of concentrated hydrochloric acid and concentrated nitric acid. This solution is highly corrosive, issued a yellow vapor. This is the only solution capable of dissolving gold and platinum (metal-metal of the most noble in the series Volta), which concentrated hydrochloric acid and concentrated nitric acid separately had no effect on gold, but a mixture of two acids react with gold dramatically.
* Bars Gold : The results of the concentrate that has been processed, then used a metal rod that is ready to be marketed in accordance with the price of gold on the market.