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It can be seen from the above that the research on early cyanidation and the use of potassium cyanide in industrial production are mainly derived from the practice of the electroplating industry. Later experiments showed that the leaching rate of sodium cyanide to gold and silver was higher than that of potassium cyanide, and the supply of sodium cyanide was wide and the price was also cheap. Therefore, the recent cyanidation method uses sodium cyanide (even calcium cyanide) almost without exception. Aqueous solution.
The cyanidation process was applied to the gold extraction industry at the end of the 19th century. After the first leaching of gold from ore with a cyanide solution in 1887, the cyanidation method was quickly applied to gold and silver mines around the world, and human gold was introduced to a new stage. The characteristics of this new stage are: from the main gold mining to the main focus of mining gold, expanding the gold resources; gold production increased rapidly, it is estimated that human production of 116,000 tons, after 1901 reached 10.5 Ten thousand tons, or 90% of the gold, is produced after the application of the cyanidation process. According to statistics, 161 of the 191 large-scale gold selection plants in China use cyanide gold extraction technology. Since 1965, China has built a number of highly mechanized mixing cyanide plants. Gold mud cyanide and carbon pulp plants are also used in industrial production, and have achieved good technical and economic effects.
The recovery rate of cyanide gold extraction is very high, and it can realize the real estate gold, avoiding the various drawbacks of long-distance transportation of gold concentrate, which is conducive to improving the economic benefits of enterprises. However, its shortcoming is that cyanide is a highly toxic agent, the process flow is long, and the extraction speed of gold is slow.
Both the re-election method and the amalgamation method are ancient methods of gold extraction, and they are only suitable for extracting coarse gold from ore. But most gold ore, in addition to coarse gold, contains a large amount, and sometimes even all, fine gold. Gold extraction from these ores must be by means of hydrometallurgy. Cyanide metal extraction in hydrometallurgical process is a modern technology for direct gold extraction from gold-bearing ores. The cyanidation gold extraction technology mainly includes the following two steps:
The first step is "leaching" - the transfer of gold from the ore into the solution by solvent;
The second step is "deposition" - gold is extracted from the leachate by displacement.
That is, the cyanidation process is a process in which gold in the ore is leached by using an alkali metal cyanide (KCN or NaCN) aqueous solution as a solvent; and then gold is replaced from the leaching solution by a ruthenium metal (such as zinc wire). [next]
In order to adapt to different types of gold-bearing ores, improve the recovery rate of gold and reduce costs, the cyanidation process is constantly innovating. At the beginning, the method of continuous leaching, dewatering and filtration of large quantities of ore has not been developed due to the high cost of ore fine grinding. Therefore, the first stage of development of the cyanidation process is percolation leaching (or immersion). The percolation leaching is only suitable for the treatment of coarse-grained ore, and it is not allowed to have fine particles such as clay and slime in the material. Therefore, the finely divided ore is classified (panning) before the leaching, the slime is separated, and the coarse mud product (sand) is placed in the immersion tank and cyanated by diafiltration.
With the improvement of hydrometallurgical equipment, slurry agitation tanks, filters, thickeners, etc. have been continuously developed. In addition to the leaching of ore by percolation, the separated slime products can be cyanated with a stirred tank. Due to advances and improvements in grinding, concentration and filtration techniques, the cyanide leaching diverts gold from the fine-grained gold ore and begins to finely grind all the ore and then leaching in a strongly stirred tank. This method is called the "full mud cyanidation" method. It has the advantages of high recovery rate, fast immersion speed and short gold extraction period, so it is quickly promoted and applied.
In the whole mud cyanidation, the amount of slurry is large and often causes difficulties in sedimentation and filtration. In order to overcome this difficulty, in the late 1970s, there was a carbon slurry method (CIP) - adsorption of gold from cyanide pulp with activated carbon; carbon leaching (CIL) - addition of activated carbon while cyanide leaching; Resin slurry method (RIP) - the use of ion exchange resins instead of activated carbon to adsorb gold from cyanide pulp.
Modern, most gold-raising companies are operating in the above-mentioned whole mud cyanidation process. Of course, coarse gold is still mainly recycled by re-election. The diafiltration cyanidation process has lost its original status, but it is still used to treat small or poor ore that are not worthy of building a mixing plant.
The heap leaching method that has been rapidly promoted in the past decade can be regarded as the development of leaching and leaching. Due to the large amount of processing, the process equipment is simple, the investment is low, and the cost is low. It is especially suitable for the treatment of fine-grained, low-grade gold-bearing ores which cannot be economically profitable by Other methods.
In summary, the basic process of the pool leaching (diafiltration leaching) method and the stirring method for gold extraction is consistent, so it is collectively referred to as the cyanidation method. The process of the carbon slurry method and the resin (pulp) method has undergone major improvements and will be introduced in the next two chapters. The heap leaching method is currently undergoing large-scale development, and its gold extraction process is adapted to local conditions and varies greatly. The above different processes are often used, so it will be discussed separately.
Cyanide method
The cyanidation method is the most economical and simple method for extracting gold and silver directly from ore, concentrate or tailings. It has the advantages of low cost, high recovery rate and wide adaptability to ore type. . Gold and silver are soluble in cyanide solution, which was discovered by Western alchemists in the 18th century and was first used for electroplating. In the 1880s, the main progress in the study of cyanidation was: In 1884, AP Price successfully recovered the residual gold from the concentrated potassium cyanide electroplating bath with metal zinc ; in 1886, FW&W. Forrest (Forrest Brothers) invented the method of leaching gold from ore with concentrated potassium cyanide solution and replacing the precipitated gold from the immersion liquid with zinc blocks; an improved method for JS MacArthur research at the Glasgow Laboratory, UK Medium, leaching gold with a very low concentration of potassium cyanide solution (No. 47 patent in 1888), zinc in the form of zinc chips to replace precipitated gold (No. 74 patent in 1889) and zinc powder in advance to soak lead acetate solution It formed a zinc-lead battery and was used to replace the precipitated gold (patented in 1894). These are the main contents of the MacArthur-Forrest method.