Gold extraction by nitric acid pre-oxidation method - Arseno immersion gold process

A Xinnuo Mining Company Arseno process is successfully developed a low temperature and pressure oxidation leaching technology, simply carried out at 100 deg.] C and 700 kPa oxygen pressure leaching of sulfide can not make full decomposition 15min. Therefore, it is easy to promote the application in industrial production. The Arseno process is another variant of the nitric acid oxidation process. The leaching process plays a major role in nitrous acid rather than nitric acid. The corresponding equilibrium is:

2N0 ₂ +H ₂ 0 ==== HNO ₂ +HN0 ₃

3HN0 ₂ ==== HN0 ₃ +2N0+H ₂ 0

Since the oxidation rate is fast and the leaching time is short, a large amount of precipitate is not formed. All of the iron , arsenic and sulphate are in solution, which enriches the gold and is advantageous for subsequent cyanidation leaching.
The slurry is discharged from the reactor into a gas separator to recover the gas generated during the reaction. This gas can be returned to the reactor as a raw material for the catalyst. It has been determined that more than 99% of the nitrate reagent can still be recycled to the process for recycling. The nitrate concentration in the solution varies between 0.2 and 3 mol/L.
The slurry discharged from the gas separator is a solid residue containing gold and a solution containing soluble iron, sulfur and arsenic. This solution can be neutralized by the addition of limestone and lime when processing the ore. Calcium and rock can reach a neutralization rate of about 80%, and then lime is used to achieve complete neutralization. The neutralized pulp may be recovered by a conventional method such as a carbon slurry method.
When the concentrate is treated in this way, the slurry discharged from the gas separator is first subjected to solid-liquid separation. The mass of the solid residue obtained from the concentrate leaching process usually accounts for only 10% to 20% of the ore quality, so the scale of the factory gold recovery process is small.
The comparative test results for ores and concentrates using the Arseno process are shown in the table below.

The leaching speed of gold is generally high, so the residence time is preferably less than 12h. The solution obtained by the solid-liquid separation step is treated with lime to control the content of impurities. The precipitate formed at this time contains calcium sulfate, hematite and iron arsenate. The stability of these precipitates has been tested and the results show that they are suitable for stacking in tailings ponds.
Arseno Mining and Metallurgy has tested gold ore in many deposits around the world, including gold-bearing ores in which gold is encased in pyrite, pyrite or arsenopyrite, and has achieved good results, proving this It is a cost-effective new process for dealing with difficult gold mines. The Arseno process is characterized by low pressure oxidation and requires a short processing time. Compared with several other processes, it has the following advantages:
1 This process is less sensitive to the sulfur content of the material. Good results have been obtained when testing various materials containing 1% to 50% sulfur in this way. Since the sulphide ore is dissolved, the gold contained in the sulphide ore can be recovered in the next cyanidation treatment. For a wide variety of materials tested, the extraction rate of gold can reach more than 95%.
2 Compared with the traditional roasting process, the Arseno process can save the recovery of gold and eliminate the process of processing SO ₂ gas and As ₂ 0 ₃ products. The sulfur in the ore or concentrate is oxidized to sulfate, and in the next step, it can be precipitated as calcium sulfate, the arsenic present in the material is oxidized to arsenate, and iron can be precipitated as iron arsenate.
3 The high pressure oxidation leaching method needs to be carried out under the conditions of a pressure of 1000 to 1200 kPa and a temperature of 200 ° C (leaching time of about 90 min). When the process is used, it is only required to be carried out at a temperature of about 100 ° C and about 700 kPa, and the leaching speed is fast (the sulfide can be completely decomposed in less than 15 minutes), which is easy to achieve in industrial production.
4Arseno method can achieve high recovery rate of silver without adding auxiliary processes. Since no precipitate of jarosite is formed during the leaching process, all dissolved silver is easily recovered from the solution.
The Arseno process has been extensively studied by Bacon, Donaldson & Associates of Vancouver, Canada, and the Hazen Institute of Colorado, USA, confirming many of the benefits of the process, the Arseno method has There are factory production examples. In recent years, gold ore containing arsenic has been found in many parts of China, and it is urgent to be developed and utilized. Therefore, exploring and formulating new technologies for arsenic removal and gold extraction has become an urgent task for China's gold production and scientific research. At present, the ore is treated at home and abroad, and the arsenic is widely used in the roasting of concentrates, and then the cyanidation of the slag is carried out, which is very serious to the environment.
In the autumn of 1987, a continuously operating semi-industrial pilot plant was commissioned. This intermediate pilot plant has a processing capacity of 1 t/d when dealing with low grade sulphide ore. Tests that have been completed demonstrate that this process is capable of continuous operation and is easily extended to industrial scale. The intermediate test tests the samples of the two deposits. The results of the oxidation of the sulfide ore and the recovery of the next gold are better.
According to reports, the investment and production costs of the Arseno process, the total equipment cost of the factory processing 25t concentrate is 3.5 million Canadian dollars, the daily processing 100t concentrate is 8 million Canadian dollars, the design and transfer fee is 250,000 Canadian dollars. . The economic benefit of this Arseno process, the direct processing cost of concentrates is 1.54 Canadian dollars / t concentrate, of which 31.5% of pharmaceutical costs, 22% of hydropower, maintenance management accounted for 15.4%, and wages accounted for 26.1%.
It is also reported that City Resources Canada has decided to invest $110 million to develop its Cinola gold mine in Charlotte, Queensland (the largest gold mine in British Columbia). The construction work was rolled out in 1988 and officially put into operation in October 1989. Mining ore day 6 600 t, the grade of mineral stone 2.5g / t. Because the ore contains pyrite and iron ore, it is a difficult ore. It is difficult to recover gold by the conventional cyanidation method, so it was decided to adopt the Arseno process under low temperature and low pressure conditions. The production cost of gold for the first two years is expected to be $7.3/g ($207/oz).
Practice has proved that the Arseno method is a good method for pretreating gold ores and concentrates that are difficult to leach.

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