I. Introduction
Full mud cyanide leaching is an ancient and reliable gold extraction process that is still widely used in production. Conventional cyanide leaching is more adaptable to minerals with a simple composition of minerals, low impurity content and high oxidation rate. The cyanide consumption is generally 500 to 1200 g/t, and the leaching rate is 90% to 95%. While for high copper-containing, arsenic, sulfur and other harmful impurities, the oxidation rate is low, high sulfide gold ore, using conventional cyanide leaching, cyanide consumption which must be at 2500 ~ 3000g / t, and the leaching rate Not very ideal, generally about 90%.
In recent years, in order to increase gold production, gold mines have increased their economic benefits and increased the application of the whole mud cyanide leaching process. In order to further meet the requirements of gold production development, the whole mud cyanidation process is more perfect and more adaptable. We have carried out a large number of experimental research work on pre-dip pretreatment for different types of gold ore with high impurity content. There are many pretreatment methods, such as alkali treatment before immersion, stirring with air, adding various oxidants, and the like. Higher impurity paper introduces copper sulfide, arsenic, sulfur and the sulfide gold ore secondary lead nitrate was added before the immersion pretreatment.
Second, the nature of the ore
Several pretreated ores, material composition and gold embedding characteristics are summarized below.
The mineral composition and content are shown in Table 1.
Table 1 Mineral composition and content
The main elements of the ore are analyzed in Table 2. The phase analysis is shown in Table 3, Table 4, and Table 5.
Table 2 Main element content of ore (%)
Table 3 Analysis of arsenic phase of sulfide gold 2 arsenic ore (%)
Table 4 Analysis of arsenic and cobalt phases of sulfide gold 2 arsenic and cobalt ore (%)
Table 5 High sulfide pyrrhotite type 2 gold copper ores, copper, iron phase analysis (%)
From the mineral composition and phase analysis, it is known that the content of primary sulfide and secondary sulfide in each ore is high, and the content of soluble copper oxide, secondary copper, arsenic sulfide, cobalt sulfide and pyrrhotite is high. From the multi-element analysis, it is seen that the gold content of each ore is the main object of recovery, and the content of harmful cyanide impurities such as copper, arsenic and sulfur is relatively high.
The embedding grain size of gold in various ores is mostly medium and fine grain gold, and the gold occurrence state is mainly composed of intergranular gold and fissure gold. This kind of embedded state is conducive to cyanide leaching, but all kinds of ore still contain a small amount of fine-grained gold, which will have a certain impact on the leaching rate of gold. The results of the ore material composition study show that each ore type belongs to the hard-to-dip gold ore, which consumes a large amount of cyanide during cyanide leaching and affects the gold leaching rate.
Third, pre-dip pretreatment test
The conventional cyanidation leaching process is used for medium and high sulfide type gold ore containing more harmful impurities such as copper, arsenic and sulfur, which not only consumes a large amount of cyanide, but also has a low leaching rate. Pre-treatment by adding lead nitrate before immersion can reduce the consumption of cyanide and increase the leaching rate.
In the cyanidation leaching process, in addition to the dissolution of gold to form gold cyanide complexes need to consume cyanide, the soluble metal ions in the ore and cyanide to form various metal complexes, also need to consume a large amount of cyanide. For example, the two gold ores in Heilongjiang Province are medium-sulfide gold 2 arsenic ores, and the contents of sulfur and arsenic are 3.30% to 4.90% and 0.11% to 0.37%, respectively, and contain certain secondary copper minerals and cobalt minerals. The amount of sodium cyanide used in the leaching process is 2500-3000 g/t, and the leaching rate is 87%-92%. In a gold mine in Hubei Province, the ore type is a high-sulfide magnetic yellow iron-type gold 2 copper ore. During the cyanide leaching process, the consumption of sodium cyanide reaches 3000g/t, and the leaching rate is 92%.
The addition of lead nitrate prior to immersion reduces the amount of soluble metal ions in the slurry, thus reducing the consumption of sodium cyanide. As the amount of interfering ions in the pulp decreases, the chances of gold and cyano complex formation increase, and the probability of increasing the leaching rate of gold increases. For example, in a gold mine in Hubei Province, the ore type is high-magnetic pyrite-type gold 2 copper ore, and the pyrrhotite content is 23130%. In the molecular structure of pyrrhotite, there is a sulfur atom that is not well-bonded. Oxidation produces soluble sulfides, which consumes a large amount of cyanide during cyanide leaching. Prolonging the pretreatment time and adding lead nitrate can reduce the presence of sulfur ions in the slurry and precipitate some soluble sulfides, thus reducing the consumption of sodium cyanide. The leaching rate has increased. The test procedure and optimal test conditions and results of several different types of gold ore pre-dip pretreatment are described below.
Whole mud cyanidation pretreatment principle flow chart
Table 6 Pre-dip pretreatment test results
It can be seen from the test results that when three different types of gold ore are not pretreated, the amount of sodium cyanide is 2500-3000 g/t, and the leaching rate is 87%-92%. After pretreatment, the sodium cyanide is greatly reduced, and the leaching rate of gold cyanide is also improved.
Fourth, the conclusion
For refractory gold ore with high harmful impurities such as copper, arsenic and sulfur, the consumption of sodium cyanide by conventional cyanidation leaching is high, and the leaching rate is low. Adding 300-600g/t lead nitrate to the ore before pre-treatment for 2~3h, the sodium cyanide consumption can be reduced to 1200-1500g/t, that is, the dosage can be reduced by 40%-60%. The gold leaching rate can reach 92%-96%, which is 2%~4% higher than that before pretreatment. It can be seen that it is feasible to pretreat some medium and high sulfide gold ore with high oxidation rate and low oxidation rate. To make some gold ore that is not suitable for flotation and other processes and costly cyanide to be developed and utilized, and to obtain better economic and social benefits.
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