Gold is a metal that people are very familiar with and has been known since ancient times. It is one of the earliest metals discovered by mankind. This copper , tin , lead , iron and zinc are all early.
Gold is the element of Group IB of the periodic table, atomic weight 196.9665 , density
   The appearance of gold is golden yellow, and the gloss is strong and soft. It is malleable and can be drawn into very fine (thin than hair) filaments or pressed into very thin sheets.
Gold is a good conductor of heat and electricity, and its heat transfer and conductivity are second only to silver and copper.
Gold is chemically stable with valences of 1 and 3 . At any temperature, air or oxygen has no effect on gold. This quot;?. True gold fears fire. "This saying is based on the ancient science of gold still has thousands of years, but still glittering separate acid, such as hydrochloric acid, nitric acid, sulfuric acid, etc. There was no gold. Role. But Wang Shui can dissolve gold.
　　 Au+4HCl+HNO 3 +HAuCl 4 +NO↑+2H 2 O
Gold can also be dissolved in the cyanide solution in the presence of oxygen.
　　 4Au+8NaCN+2H 2 O+O 2 =4NaOH+4NaAu ( CN ) 2
Gold can also be oxidized by peroxides to metabasic acid salts.
　　 2KO 2 +2Au=2KAuO 2
　　 3Na 2 O 2 +2Au=2NaAuO 2 +2 Na 2 O
Gold also dissolved chlorine, bromine water, an aqueous solution of manganese chloride high state (or cobalt, nickel), ether solution.
　　 2Au+3Cl 2 =2AuCl 3
　　 2Au+3MnCl 4 =2 AuCl 3 +3 MnCl 2
When some metals (such as iron, manganese, bismuth) to participate in higher-order oxide, hydroiodic acid can be generated with gold iodide, gold effect.
　　 2Au+Fe 2 O 3 +4HI=2AuI+ FeI 2 + FeO+2H 2 O
At high temperatures, gold can also form halides with compounds such as fluorine and bromine, but too high a temperature will cause it to decompose again. In addition, molten sodium nitrate and sodium hydroxide can be combined with gold.
Gold is often used as an ornament. For example, gold Buddha is used to decorate Buddha statues and works of art. The crown is made of gold wire, and the jade pieces are twisted into gold and jade clothes with gold wire. In the past, gold was still the international currency. The gold reserves of a country can measure the economic power of a country to a certain extent.
Gold is an important industrial raw material. In the IC industry, gold is used in large quantities. Gold salt is also the raw material for electroplating gold.
Gold is not too small in the earth's crust, accounting for 5 × 10 -7 % of the total weight of the earth's crust , but it is very scattered, almost all in the state of sound quality (natural gold). There are two kinds of natural gold, one is that the particles are scattered in the rock, called rock gold or vein gold; the other is in the form of particles in the gravel, called impact gold or gold. The density of gold and sand is very different. People use this feature to wash gold-containing sand with water. This is the so-called “sand goldâ€, which is similar to Taomi. At present, gold is mostly derived from rock gold. Natural gold often contains different amounts of silver, and sometimes contains platinum , palladium , rhodium , mercury , copper, lead and the like.
There is also a lot of gold in the ocean. This is because the rain continues to flow from the land to the sea. It will dissolve many substances, and it will accumulate in billions of years. It is estimated that there are 6×10 6 ~12×10 6 tons in total. gold! But relative to the amount of sea water 13.6 ×
There are many ways to extract gold from nature.
People often use the re-election method to extract gold from the gold mine. The specific equipment includes gold pan, chute, jig, shaker, centrifugal concentrator (spiral chute and Nielsen concentrator).
Mercury amalgamation is also a very effective way to extract gold. It uses gold to form an alloy - gold amalgam characteristic with mercury at room temperature . The obtained gold amalgam is further heated to distill off mercury to obtain a merging gold.
The most important method for extracting gold from ore is the cyanidation process, the principle of which is the chemical reaction described above. Among the commonly used processes are cyanide - zinc powder replacement process, cyanide - carbon slurry process ( CIP process), and heap leaching process.
There are also methods such as sea wave dissolved gold, thiourea dissolved gold, chlorine water soluble gold, bromine water soluble gold, biosoluble gold, etc., but they are not popularized by cyanidation method because of imperfect technology or economic irrationality or equipment.
With the vigorous exploitation of gold and the depletion of conventional resources, people began to study the gold resources that could not be effectively extracted by conventional methods. The so-called difficult to choose yellow ore. Refractory gold ore refers arsenic compound, quartz inclusions, even though the finely ground ore, gold will not be exposed, since the particle size is much smaller than the size of the gold ore particles, which can not be extracted with reselection Gold is planted, and the cyanide does not come into contact with gold, nor can it extract gold. In short, the conventional method cannot extract gold. In order to extract this kind of gold, people have developed a number of methods. Such as fine grinding, ultra-fine grinding technology, alkali and oxygen pre-oxidation of insoluble arsenic sulfur compound technology, pressurized warm acid pre-oxidation (arsenic sulfur compound) technology, pressurized warming alkaline pre-oxidation (arsenic sulfur compound) technology , warming nitric acid pre-oxidation (arsenic sulfur compound) technology, heating pressurized sulfuric acid (mixed with a small amount of nitric acid) pre-oxidation (arsenic sulfur compound) technology, biological pre-oxidation technology, roasting thermal decomposition (arsenic sulfur compound) technology. Among them, bio-preoxidation technology and high-pressure high-temperature pre-oxidation technology and roasting decomposition technology have been industrially applied for many years and are very effective. The widespread use of these technologies will allow gold resources to be fully utilized and gold production to hit new highs.
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