Gold--arsenic raw material treatment and environmental protection issues

The importance of addressing the arsenic-containing materials with dwindling reserves of gold ore and gold sand single metal and concentrates, the composition of the metallurgical complex in gold is also growing. Many of the gold deposits that are being discovered and mined in the Soviet Union, Kazakhstan, Central Asia and Siberia are classified as intractable gold ore. Due to the presence of arsenic compounds in these ores, it is not only difficult to extract gold from them, but also poses a great threat to the surrounding environment.
Some Gold - Concentrate arsenic treatment process is very complex, due to the carbonaceous substance which is present in the concentrate, and the leaching of gold fine particles was closely associated with the state and arsenic pyrite and other minerals.
For many gold - arsenic concentrates, there is still no reasonable treatment to date. Some of these concentrates can be mixed with other metal concentrates, and some concentrates are simply unavailable.
The most common method of handling gold-containing materials is cyanidation. However , when gold - arsenic concentrate is treated by this method , the recovery rate of gold can only reach 45-80% .
Gold - arsenic concentrates can also be smelted together with the charge from copper smelters or lead smelters, but the results are not ideal. The trapped magazines are distributed among various products, complicating the next processing process, especially the refining operation of the main metal, increasing the cost of refining, and causing serious pollution of the surrounding environment due to the generation of highly toxic arsenic trioxide during the smelting process. And worsening working conditions. In addition, when the gold - arsenic concentrate containing no copper or lead is treated by the fire method , since the main metal is greatly lost with the slag, it is economically uneconomical.
In foreign and Soviet production practices. When arsenic and gold are recovered from gold - arsenic concentrates, the most widely used method is oxidative roasting of sulphide concentrates, followed by cyanidation of slag or slag and copper smelters or lead smelters. from a smelting furnace charge.
Arsenic is mainly present in the form of arsenic pyrite in sulfide concentrates. When arsenic pyrite is oxidized, volatile arsenic trioxide and iron oxides are formed. A part of arsenic becomes arsenate of iron, lead and other metals, and enters the next stage of processing together with the slag, resulting in a reduction in the gold recovery rate of the cyanidation operation and contamination of the smelted product. For some gold - arsenic concentrates, arsenic in the slag cannot be completely removed even after two stages of calcination.
Generated during roasting arsenic trioxide condensed compounds difficult, especially steam coal is particularly the case for strong gas mixture Dilute. This is also the case when boiling roasting of gold - arsenic concentrates. In order to capture and eliminate the highly toxic compounds such as arsenic trioxide in the gas, special and expensive devices need to be installed.
Due to the limited use of arsenic dioxide, most of the arsenic trioxide obtained during the roasting of polymetallic concentrates must be stored in a dedicated storage yard filled with concrete. The cost of storage yards such as buildings sometimes exceeds the cost of major smelting operations. Therefore, solving the problem of rational treatment of gold - arsenic concentrate is still an extremely important economic and ecological task in modern metallurgy.
With the continuous improvement of oxidative roasting and further recovery of gold from slag, new methods for separating gold and arsenic from sulfide raw materials have been developed, such as chlorination metallurgy, bacterial leaching, adsorption and extraction, direct Hydrometallurgy and so on. Vacuum high temperature separation is one of them. In this way, arsenic can be removed from the sulphide concentrate containing arsenic pyrite at the beginning of the smelting operation, making it a non-toxic volatile state.
Heating in a neutral atmosphere or in a vacuum, the arsenic pyrite is decomposed to form a vaporizable metal and a solid ladder of pyrite. In the process of heat treatment of arsenic-containing pyrite concentrate. The vacuum method not only prevents the oxidation of arsenic, but also lowers the calcination temperature (this is especially important when processing easily-smelted concentrates) and improves the condensation conditions of hard-to-dilute steam. The main advantage of the vacuum heat treatment method for arsenic-containing ores and concentrates is that arsenic can be effectively removed during a process and is independent of the original content of arsenic, which means that the method is somewhat versatile and can be obtained non-toxic. Volatile.
Had various Kazakhstan, Central Asia and Siberia different Gold - Concentrate arsenic (arsenic wherein 0.6 to 34%; 4 to 32% of sulfur; 11% to 35% iron; 5 to 53.7% of silica; alumina 2.4~11% ; carbon 0~22% ; calcium oxide 1~18.7% ; copper 0~6% ; gold 25~ 70 grams / ton) conducted laboratory tests and expanded experimental studies, the results proved: at a temperature of 650~ 700 °C The pressure of the remaining gas is 5~ 10mm Under mercury column, within 10 to 15 minutes can cause more than 95% of the arsenic from the thin volatilize or pseudo liquefied layer. The ratio of arsenic pyrite and pyrite in the original material is different. The volatiles contained 64 to 99% arsenic and 34.1% sulfur . The reason for the large change in the composition of the volatiles is that the arsenic and sulfur which are discharged during the thermal decomposition of the arsenic pyrite and pyrite interact to form sulfides in the condensate. When the pure arsenic pyrite ore and its concentrate are subjected to vacuum heat treatment, the volatile matter itself contains about 1% impurity subordinate arsenic. The obtained mixed volatiles of metal arsenic and arsenic sulfide can be easily dissolved in a neutral medium and made into a block which is easy to transport and preserve. [next]
In order to recover gold from the slag, the slag containing 0.1 to 0.3% arsenic should be sent to the pyrometallurgical or hydrometallurgical section and treated by known methods. The direct cyanidation of the calcined slag after vacuum heat treatment only results in a high gold recovery from the low-iron, carbon-free material. For most concentrates, the acid-treated residue should be subjected to a combined acid treatment to leach the iron compound prior to cyanidation. When the residue contains carbonaceous rock sheets, oxidative roasting should be performed to remove carbon. According to this scheme, even if it is difficult to treat concentrates like gold - arsenic carbon concentrate, the gold recovery rate can reach 97~98% . The easiest way to do this is to smelt the slag together with the charge from a copper smelter or lead smelter.
The method of selecting a reasonable method for recovering gold from the residue after vacuum heat treatment requires various compositions according to various specific conditions (for example, whether or not non-ferrous metals, carbonaceous shale and iron sulfides are present in the raw materials), and fineness. The characteristics of the mining area (distance from the fire smelter and whether there is industrial water) are solved.
For all gold - arsenic concentrates, removing arsenic from concentrates in advance is a common and most complex process.
In order to achieve vacuum heat treatment of granular materials, the Kazakh Soviet Socialist Republic Academy of Sciences Institute of Metallurgy and Mineral Processing jointly. National Institute of non-ferrous metals science and Central Asia Institute developed into a vacuum vibration apparatus for continuous operation. The main body of such a device is a vertical closed heating vibration transporter. The results of the expanded semi-industrial test prove that the working capacity of this equipment is reached when used for a long time. 700 °C . These devices are currently being retrofitted to increase processing power and improve product quality. In the vibrator, the material dummy layer formed by the directional vibration has high heat exchange and mass exchange (the thermal conductivity in the vibration layer is 15-20 times of the thermal conductivity in the fixed layer ), thereby enabling the device Maintain a high unit handling capacity of 5 to 7 tons / m 2 evaporation surface every day and night .
When the gold - arsenic concentrate of a mining area in Kazakhstan was subjected to vacuum heat treatment and arsenic semi-industrial test, the equipment used was an industrial vibration vacuum heat treatment device, which has a processing capacity of 5 tons per day and night . The test results prove that the main indicators of the whole heat treatment process are correct and reliable.
At a temperature of 650~ 670 °C The remaining pressure is 30~ 50 mm · Under the condition of mercury column, after vacuum heat treatment for 5-7 minutes, it contains 6.2% As and SiO 2 24% . Al 2 O 3 8.8% , Fel 6.55% , Au 80.7 grams The arsenic volatilized in the concentrate per ton is 95~97% (the arsenic content in the slag is 0.2~0.3% ). The volatiles were earth sulfide with 6 ~ 68% of a mixture of arsenic, and the orange-yellow powder fall down from the condenser wall. Dust loss of 7.4%, per unit processing ability of the circadian 2.5 to 4 t / m 2, the power consumption per ton of concentrate of 350 kW time. 99.5% of the gold, 94% of the silver is accumulated in the slag and the returned dust. According to the test results, the original data was prepared for the design of a continuous action vibration vacuum heat treatment device with a day and night processing capacity of 10 tons of concentrate. The Soviet Union’s Ministry of Nonferrous Metallurgy and the Kazakh Academy of Social Sciences have taken many measures to manufacture such equipment at a factory in Kazakhstan.
Manufacture and use of industrial vacuum heat treatment equipment not only to solve the problem of arsenic removal and to expand the base of gold-containing raw materials, but also to remove arsenic and to develop non-condensed tin - arsenic concentrate, tin-arsenic - copper concentrate, tungsten - arsenic concentrate and The comprehensive utilization process of other concentrates is necessary, because for this type of concentrate, there is still no reasonable treatment process until now. It is technically or economically important to remove arsenic from the multi-metal raw material in advance to make it non-toxic.
At present, it is ideal for manufacturing vacuum heat treatment equipment that processes several tons of bulk materials. The practical use of steam jet pumps, high-power mechanical pumps and booster pumps enables the task of rapidly manufacturing large-volume vacuum equipment to be successfully solved. It is now possible to manufacture a wide range of parts for vacuum systems in batches, as well as a variety of special steels.
Researching and adopting new processes and equipment to reduce the levels of arsenic, mercury and sulphur dioxide in exhaust gases is not only a social issue, but also of great economic importance. At present, many experts in relevant fields are studying this issue in depth and carefully. This will greatly accelerate the resolution of the arsenic removal problem involved in all environmental protection work. It is also very important for the relevant enterprises to realize that it is necessary to study and solve this problem as soon as possible, but it does not provide direct economic benefits, but it is also of close interest to the company to improve the working conditions and the surrounding environment. Resolving these problems quickly and correctly will, to a large extent, determine the duration of the actual application and whether vacuum high temperature separation can be used to treat arsenic-containing polymetallic materials.

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