The ability of charcoal to adsorb, separate and purify certain substances from the gas phase and the liquid phase has been recognized by humans in ancient times and applied to the fields of life and production. The solution from the carbon adsorption properties of noble metal, is M · Lazo Chomsky (Lazowski) 1848 put forward the. In 1880, WNDavis successfully recovered and recovered gold from charcoal leaching gold solution using charcoal and obtained a patent. In 1894, WD Johnston used an activated carbon-filled filter to extract gold and silver from the potassium cyanide leaching solution through a filter, and then smelted the activated carbon for recovery. In 1934, TGChapman successfully added activated carbon directly into the cyanide leaching slurry to successfully absorb and recover gold. He took the first step in the development of the carbon slurry method. This "carbon slurry method" was applied to the Gittel mine in Nevada, USA in the 1940s. Although it successfully adsorbed gold from the slurry, the whole process proved to be uneconomical. Because the gold recovered from it must be burned and smelted. In 1950, JBZadra successfully desorbed gold from gold-loaded charcoal using a mixture of sodium sulfide and sodium hydroxide, but this method is not suitable for recovering silver from gold-loaded charcoal. It was not until 1952 that Zadra and others successfully studied the simultaneous desorption of gold and silver from gold-loaded charcoal with hot sodium cyanide and sodium hydroxide mixtures, thus laying the foundation for the modern carbon slurry method.
The core of the carbon extraction process or carbon leaching gold extraction process is the adsorption of gold on the cyanide solution by activated carbon. The advantages and disadvantages of the adsorption of gold on activated carbon will directly affect the recovery rate of gold in the process. Therefore, the mastery and selection of the physical and chemical properties of activated carbon is the key to gold extraction by carbon slurry.
1. Activated carbon 1) Crystal structure of activated carbon According to x-ray diffraction studies, the typical structure of activated carbon is similar to the typical structure of graphite . Activated carbon belongs to amorphous carbon or microcrystalline carbon. Its structure is similar to that of graphite. It is a layered lattice composed of polycyclic aromatic rings, as shown in Figure 1.
Figure 2 is a schematic view of a typical structure of graphite and activated carbon. It can be seen from the figure that graphite is composed of a layer of carbon atoms bonded into a hexagon, and the layers are maintained by a Van der Waals force at a distance of about 0.335 nm, and the carbon atoms in any one plane are in Below the upper part of the hexagonal middle section. Activated carbon is not regularly arranged like graphite. Many of its hexagonal carbon rings have been broken, and its overall structure is disordered. [next]
The structure of microcrystalline carbon is less than the integrity of graphite. There are two different structures in microcrystalline carbon. One is a binary structure similar to graphite. The plane of the network is parallel and forms equal intervals. The plane is incompletely oriented in the vertical direction, and the arrangement between the layers is also irregular. This is the so-called chaotic structure, see Figure 3. The carbon having a disordered structure is arranged in a unit called a basic crystal, and the size of this basic crystal varies depending on the carbonization temperature. The shift between the basic crystals forms pores, which are the sites of adsorption. The other is composed of a space lattice formed by carbon hexagonal irregular cross-connections, and the graphite layer has a skew in the plane. This structure can be thought of as a result of intrusion of different atoms like oxygen. The existence of such different atoms has a great influence on the chemisorption and catalysis of activated carbon.
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Carbon materials other than diamond can be classified into easily graphitizable carbon and non-graphitizable carbon, as shown in Fig. 4. In the figure, (a) is soft and (b) is hard. It is believed that the easily graphitizable carbon may be composed of a disordered layer structure, and the non-graphitizable carbon may be composed of a lattice structure having cross-links. Based on the soft and hard differences of microcrystalline carbon, it can be inferred that there are two types of mixed structures of microcrystalline carbon such as activated carbon.
The size and length of the basic crystals of activated carbon vary with the starting materials and activation conditions. It can be divided into a soft structure like carbon black and a hard structure like charcoal. The soft structure is easy to oxidize and decompose because the crystallization is formed by a relatively simple interlocking assembly; the hard structure is formed because the crystals cross each other and are difficult to oxidize. Zinc chloride, activated carbon, carbon black, metal-like structure more, and to steam activated carbon charcoal structure places more, especially granular activated carbon is more inclined to such structures.
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