Gold ore, gold-bearing sand ore and polymetallic ore (gold as a valuable component with collateral recovery) are the main sources of gold production. The roaster is a cylindrical body with an outer dimension of 2640 x 5490 mm lined with 75 mm thick insulating bricks and 225 mm thick refractory bricks. The boiling layer has an inner diameter of 2030 mm and a boiling layer height of 1270 mm. The structure of the hearth is similar to that of the concentrator. During the roasting process, the boiling layer temperature is 700 ° C, which ensures the highest gold recovery. If the boiling layer temperature exceeds 725 ° C, water spray can be used to lower the temperature. The processing capacity of the roaster is 12 to 15 tons of pulp per day and night. At the same time, the feed is stopped at the same time, but the air should be continuously supplied to the furnace for 10 minutes. The purpose is to remove the gas space in the furnace and purify the gaseous compounds of arsenic in the exhaust gas and prevent arsenic from agglomerating in the nozzle. The concentrate slurry is fed into the No. I furnace. 60 tons of concentrate are processed every day and night, and solids in the pulp account for 80%. The flotation concentrate slurry (60% solids) discharged from the concentrator of the concentrator is fed into the intermediate agitation leaching tank by a diaphragm pump. As shown in Fig. 3, the slurry discharged from the leaching tank is fed to the disc filter. The total dust removal rate of the gas is 99% or more. Listed in the table is the composition of the solid product of concentrate and concentrate calcination when obtaining chocolate-colored calcine. The boiling roaster has a diameter of 5 meters and a height of 6 meters. It consists of two chambers, A and B. Depending on the amount of concentrate obtained, the working time of the roaster is between 14 and 16 hours per day and night. Concentrate ore contains 72~78% solids and 22~24% sulfur. The indoor furnace temperature of A is maintained at 588 ° C, and the furnace temperature is controlled by spraying water onto the boiling layer. Room B is mainly used to gradually cool the calcine. The furnace temperature in room B is maintained at 340~450 °C. The maximum allowable content of carbon in the cyanide-raised calcine should not exceed 0.3%. The results of the study prove that the limit content of carbon in the calcine is 0.2%. References cited data from laboratory and semi-industrial tests for two-stage boiling roasting of argillaceous gold-arsenic concentrates directly from the slurry. The main process parameters for the two methods of drying and boiling roasting of refractory gold-containing concentrates in the slurry were determined. The method is characterized by simple equipment construction, stable and long-lasting operation of the roaster, and easy realization of full-disc automation. Conductive Cloth Tape,High Viscosity Conductive Cloth Tape,High Shielding Conductive Cloth Tape,Heat Resistant Cloth Tape Shanghai Huike New Material Technology Co., Ltd. , https://www.shhuike.com
Among the capitalist countries in the world, 85% of the gold reserves that have been identified are from gold ore and gold-bearing sands, and the remaining 15% are from non-ferrous metal composite ores, and the proportion of gold ore in the total metal balance is constantly increasing. increase.
Gold or the free state, or sulfide (mainly with pyrite) closely associated and various compounds present in solid solution. In some ores, gold is mainly present in various compounds and solid solution states. Therefore, it cannot be recovered by conventional cyanidation. This type of ore is considered to be an intractable ore.
The main gold producers in the capitalist world are South Africa, Canada and the United States. Gold production in these countries accounts for 86% of total gold production in industrial and developing countries. In 1874, South Africa's gold production was 780 tons, accounting for 78% of the capitalist world's total gold production, Canada was about 60 tons, accounting for 5%, and the United States was 35 tons, accounting for about 3%. South Africa's gold mining industry is built on the basis of relatively simple, large-scale mining and production where ore is easier to process.
The obvious feature of the Canadian gold mining industry is that there are many small deposits. The composition of the ore in these deposits is very different, some of which are refractory gold-bearing ores. Different processes are used to recover gold for these difficult-to-treat ores. Because small-scale gold vein deposits, the mining and beneficiation plant equipment specifications small, labor productivity is low.
In the gold mining industry in the United States, gold is mainly recovered when dealing with non-ferrous metal ore (this part of the gold production accounts for about 40% of the total US gold production). There are many gold deposits in the United States that are also like Canada-like tough ore.
A large number of scientific research work and production practices have proved that it is technically and economically reasonable to carry out oxidative roasting of refractory gold-bearing ores and concentrates and to prepare oxidative roasting as ore before cyanidation. The gold-containing materials that are difficult to handle are: copper products, arsenic products, and pyrite concentrates containing fine-grained gold. If cyanidation of these materials is carried out directly without calcination, the recovery of gold does not exceed 60 to 70%.
The results show that after the oxidative calcination, the refractory gold-containing material can obtain the porous calcine containing a large amount of fine grain exposure gold. In this way, the cyanide solution can enter the interior of the golden fruit, making the process of recovering gold easier. After pre-oxidation roasting, and then treating the ore with cyanidation, the recovery of gold can be increased to 95~97.5%.
Oxidative roasting of refractory gold-containing arsenic materials is quite complicated. Arsenic and sulfur must be removed during the roasting process. In order to remove arsenic, it is necessary to remove arsenic into arsenic trioxide in a weak oxidizing atmosphere and at a lower temperature (450 to 500 ° C, or to make arsenic in a reducing atmosphere and at a high temperature (760 to 800 ° C). The change to arsenic trisulfide is eliminated. At a temperature of 750 to 850 ° C and a large excess of air, the sulfur in the sulfide is burned out at a suitable rate (ie, desulfurized) to minimize the amount of sulfate produced. Therefore, two-stage calcination is used to treat these gold-containing materials for one-stage calcination.
The method of --boiling roasting of gold-arsenic materials was first adopted by the Canadian company Dow in 1946 at the concentrator. They calcined the slurry containing Au 200 g/t, S 15%, As 5% arsenic pyrite concentrate. The solids content of the pulp is 80%. The Liyu spray gun feeder directly feeds the slurry into the boiling layer of the roaster. The roaster is cylindrical, 5.4 meters high and 2.64 meters inside. The diameter of the furnace in the boiling zone is reduced to 2.04 meters because of the refractory brick lining in the furnace. At the top of the furnace, refractory bricks are built in the flue and cylinder. The bottom of the furnace is a steel plate lined with refractory cement. The steel plate has 120 disc-shaped holes and a corundum ball with a diameter of 6 mm. These corundum balls act as distribution valves and retaining devices when air is fed in to prevent the sand from falling into the furnace.
The height of the boiling layer is 1525 mm. When the air supply is stopped, the height is reduced to 1200 mm. The baking temperature is 640 to 650 °C. The temperature inside the furnace is adjusted by a water sprayer. Increasing the calcination temperature is highly undesirable because in this case the material is melted, which reduces the gold recovery of the calcine during the leaching process. During the roasting process, about-half (which contains 57% of the total gold) of the calcine is discharged through the furnace door. About 40% of the calcine (with a gold content of 37%) was trapped in the first cylinder. The remaining calcine (containing 6% gold) was trapped in the second cylinder.
According to the data in the reference, the roaster has not been overhauled for 14 years. Only repaired the refractory brick substrate at the bottom of the furnace. Later, due to the improvement of the grade of talc in the concentrate and the formation of the furnace bottom (furnace knot) at the bottom of the furnace, it was stopped. Later, the position of the gun feeder was changed to the upper part of the furnace top, and the slurry was fed into the furnace in a fan-shaped line. Thus the slurry can be evenly distributed on the surface of the boiling layer. With this method of adding concentrate, most of the water can be removed when the concentrate falls. Changing the installation position of the gun feeder can also avoid the phenomenon of stopping the furnace due to the destruction of the boiling layer.
In the process of using such a roaster, the occurrence of strontium in the concentrate is adversely affected by the recovery of gold, especially when the grade of the crucible exceeds 0.5%. The adverse effects are more obvious. In this case, melting of the gold particles and formation of a layer on the surface thereof are difficult to be cyanide; the dissolved film occurs. This results in a significant reduction in gold recovery.
(KoxHHoyp B aulahc) The use of boiling roasting in the concentrator greatly improved the gold recovery rate during the cyanidation process.
The ore processing capacity of the Canadian concentrator is 500 tons / day and night. In 1951, a boiling roaster was put into operation. The treated concentrate contained Au 76 g/ton; S 18.8%; As 11.04%; Sb 0.42% and Fe 27.8%.
The flotation concentrate from the concentrator was fed into a concentrator with a diameter of 3.7 m and fed into a rotary vacuum filter. The material is thus fed into a tank of 1830 x 1830 mm. The slurry (80% solids) is pumped into the feeder and fed into the gun feeder (the position is opposite the discharge hood and 610 mm above the boiling level of the roaster). The flow of the entire roaster is shown in the figure. [next] 
The furnace is running stably. Only shut down three times in 10 years. The purpose of the shutdown is to perform inspections and minor repairs to the lining.
The concentrate having a calcination at the beginning of the operation of the calciner has a particle size of 60% to 325 mesh. Later, the ore dressing plant installed an auxiliary grinding machine to achieve a grinding fineness of 87%-325 mesh. Reducing the size of the concentrate increases the dust yield from 40% to 50%, resulting in blockage of the discharge tube of the precipitator.
When processing fine concentrates, the heat reserve in the boiling layer is less than when the coarse concentrate is processed. This situation is particularly noticeable when the furnace is shut down. The fine-grained concentrate layer cools much faster than the coarse-grained concentrate layer. When calcining the coarse concentrate, the time to lower the layer temperature lasts for 36 hours. Then the furnace can start working without the need for an auxiliary oven. When the fine material is fired, the temperature drop is stopped for more than 12 hours. This requires an auxiliary oven to make the furnace work better.
Calcination of concentrates can increase gold recovery rates prior to cyanidation in the concentrator.
A Canadian company commissioned a boiling roaster in 1949. The mixed flotation concentrate for calcination contains Au 230 g/ton, S 24%, As 6.5%, Sb 0.43 %, Ni 0.33%, and Fe 29%.
The boiling roaster was also designed by Dow. The roaster is a cylindrical furnace body with a diameter of 5 meters and a height of 7 meters. The bottom of the furnace is equipped with a steel strip screen (or furnace) with a thickness of 16 mm. A layer of 100 mm thick refractory cement was placed on the hearth. The boiling layer height is 1625 mm. The furnace is built with 230 mm thick refractory bricks. The height of the refractory brick lining is the same as the height of the boiling layer.
The upper part of the roaster casing is made of 115 mm thick refractory bricks. The flotation concentrate containing 78-80% solids is directly pumped from the thickener into the upper part of the furnace (through the intermediate slurry tank).
The roaster can handle 75 tons of concentrate every day and night.
The calcination temperature is 565 ° C. The calcin contains As: 2.3 to 2.9%, and S: 0.7 to 0.8%. The exhaust gas passes through the dust collector and is discharged into the air through a 38-meter-high chimney.
The boiling recovery of the flotation concentrate prior to cyanidation increases the gold recovery from 80% to 90.2%.
After several laboratory tests, two stages of roasting were applied to the flotation concentrate in 1955. As a result, arsenic can be completely eliminated.
The contact diagram of the two-stage roasting equipment is shown in Figure 2. After the No. I roaster installed in 1949, it was changed to two-stage roasting. The direct boiling zone (due to the refractory bricks) was reduced to 3.36 meters. The boiling layer height has not changed and is still 1625 mm. The bottom of the furnace is equipped with 20 nozzles with spherical valves. The air is sent to the furnace with an air compressor. The adjustment of the air compressor production capacity is carried out remotely through the control room. [next]
The temperature fluctuation of the boiling layer in the No. 1 furnace is between 560 and 590 °C. The furnace temperature is adjusted by changing the feed rate.
If the composition of the gas phase can be controlled in the furnace No. I, the arsenic can be completely discharged. This will fully dissociate the gold, and after the next cyanidation, the recovery rate of gold can be greatly improved.
The calcine discharged from the weir of the No. 1 roaster was passed along the calcine discharge pipe and fed into the No. II roaster by a spray gun feeder. The dusty gas in the No. I furnace enters the dust collector and is then fed into the No. II furnace.
The outer size of the No. II roaster is 4.27 x 4.88 meters, the boiling zone is 2.7 meters in diameter, and the boiling layer height is 915 mm. The bottom of the furnace is equipped with 90 nozzles with ball valves.
The temperature of the boiling layer in the No. II furnace is 650~760 °C. In order to make the temperature in the No. 2 furnace not exceed 760 °C, water should be sprayed into the furnace regularly. The No. II furnace is shut down once a year. The shutdown time is 36 hours for inspection.
The dust-containing gas discharged from the No. II furnace was fed into three dust collectors. After the gas is purified by the dust collector, it is discharged into the atmosphere through a chimney of 42.3 meters high and built-in refractory bricks.
The dust discharged from the dust collector is fed into the fire extinguishing tank below. The calcine in the No. II furnace and the dust in the precipitator should also be subjected to cyanidation after being subjected to a cyanidation process after extinguishing the fire.
When re-using the roaster after a long period of shutdown, the petroleum burner should be switched on first to bring the boiling layer temperature to the working limit. Then feed into the No. 1 furnace and gradually increase the temperature of the boiling layer. The calcine discharged through the weir is fed into the No. II furnace. In general, it takes about 36 hours to feed and bring the two furnaces to the specified height. When the flotation concentrate enters the No. 2 furnace from the No. 1 furnace, the arsenic content in the calcine can be reduced to 1.5 to 1.6%. This ensures that the gold recovery rate during cyanidation is increased to 97.5%.
Canadian companies use a two-stage boiling roaster with a capacity of 200 tons per day and night.
US concentrator began in 1951 to carry out flotation concentrate sulfur tellurium - segment roasting. The concentrate contains 310 g/ton of Au, 22 to 25% of S and 22 to 24% of Fe. The roasting equipment flow is shown in Figure 3. Gold is in the form of telluride in these concentrates (the telluride is closely symbiotic with pyrite), and a small amount of gold is in a free state. [next]
The filter cake containing 84~88% solids is fed into the slurry tank, diluted with water to a solid content of 78-80%, and then fed into the 1800×1800 mm stirred leaching tank by gravity.
The slurry is fed from the feed tank into the Dow type roaster using a disk pump. The concentrate slurry enters the roaster through the feed pipe. The feeding tube is mounted in the opposite direction to the discharge opening and is 150 mm higher than the boiling level. The feed tube has a diameter of 38 mm and its end is flattened and twisted downward to an angle of 30° into the furnace. In order to allow the concentrate to be uniformly fed into the furnace and to cool the tube during shutdown, a small amount of compressed air is fed through the dedicated tube.
This boiling roaster has a cylindrical casing 5 meters high and 5 meters in diameter. The outside of the furnace body is made of 6 mm thick steel plate with a 150 mm thick insulation layer and a 220 mm thick refractory brick lining.
The lining is placed at a height of 1.5 meters at the bottom of the furnace, that is, it is built into the hollow discharge hole. The total thickness of the insulating layer and the refractory brick lining on the upper portion of the calcining discharge hole is 125 mm.
The bottom of the furnace is made of 22 mm thick steel plates with 134 holes. The distance between the centers of the holes is 300 mm.
There is a threaded pipe in each hole. The threaded pipe is screwed with a stainless steel semi-circular top cover with a diameter of 25 mm and a length of 228 mm. At the upper end of the semi-circular top cover is a steel sheet with a diameter of 75 mm and a thickness of 6.5 mm. There are four circular holes of equal diameter and 6.5 mm in diameter on the wall of the lower part of the steel sheet. The bottom of the roaster is covered with two layers of refractory bricks, each with a thickness of 75 mm. At the time of baking, the temperature of the boiling layer was 620 °C.
The acupuncture gold ore is dissociated during the roasting process and the fine metal gold is separated. This metal gold is easily dissolved during cyanidation.
The pyrite is oxidized to form porous iron oxide particles. Thus, the cyanide solution can easily penetrate into the gold particles and dissolve it.
In the first six months after the calciner was put into production, it was calcined under conditions of excess air (from 50% to 100%). The resulting calcine is bright red. The gold recovery from this calcination is not high during the cyanidation process.
The roasting method was later changed. Initially, the calcination is carried out under conditions of a small excess of air and an exhaust gas having an oxygen content of about 1%. As a result, the obtained calcine was chocolate color. Under this calcination condition, the gold content in the residue after the blasting of the calcine is low.
The "KapaTOH" concentrator believes that if there is a large excess of air in the space above the boiling level of the roaster, then the air flow makes the fine concentrate concentrate in suspension. As a result, a temperature much higher than the temperature of the boiling layer can be formed on the surface of these particles. Therefore, the calcine particles (dust) are melted. This has an adverse effect on the gold recovery rate in the next-step cyanidation treatment. Therefore, the excess oxygen remaining in the upper portion of the boiling layer during calcination cannot melt the calcine. This is an essential condition for increasing the gold recovery rate during cyanidation. [next]
It is quite obvious that when the calcine is chocolate, the gold recovery rate is the highest and the chemical consumption is also the least.
It is also obvious that the two-stage roasting effect is the best. This is because the amphoteric gold ore can be decomposed in a reducing atmosphere under two-stage calcination conditions, and the sulfur-containing hot calcined sand is re-fired in an atmosphere containing excess air until reddish brown baking is obtained.
The processing capacity of the roaster for every day and night was originally set at 60 to 70 tons of concentrate, which actually only reached 30 to 35 tons of concentrate, and only worked 14 to 16 hours per day and night. When the furnace is shut down, the material layer can maintain its original temperature for a long time. This eliminates the need for an auxiliary oven for the roaster prior to furnace opening. It is certain that the calciner can be maintained for 36 hours without the need for an oven.
When the roaster is in operation, about 60% of the material is discharged through the furnace door, and about 40% is taken away from the furnace.
The exhaust gas dedusting system consists of two 1100 mm diameter dust collectors, a 600 mm diameter double tube cyclone and an electric precipitator.
Concentrate and composition of its roasting products
Material Au(g/t) SiO 4 (%) Si(%) Fe 2+ (%) Fe 3+ (%) Insoluble residue (%)
Raw concentrate 215 - 22.90 - 22.40 44.70
Calcined 140 0.80 0.20 2.60 11.90 70.00
Dust
No. 1 dust collector 485 0.50 0.80 11.30 29.40 31.40
No. 2 dust collector 560 0.40 1.00 14.50 24.50 32.30
Cyclone dust collector 560 0.50 0.70 9.30 23.40 40.20
Electric precipitator 231 0.70 0.10 2.90 29.90 36.20
The gold recovery rate during cyanidation was 97.5%, and the gold grade in cyanide leach residue was 5.1 g/ton.
The US concentrator is one of the few foreign exchange companies in the world. The plant directly calcined the gold-arsenic ore with a boiling roaster at a capacity of 75 tons per hour.
The ore contained in the furnace contained As 2.85%, S 3.6%, Fe 3.2%, Sb 0.1% and Au 7 g/ton. The boiling furnace has a diameter of 4.8 meters and is fueled by petroleum. The calcination temperature is 590 to 650 °C. The exhaust gas discharged from the furnace is cooled to 175 to 200 ° C, and as a result, a large amount of arsenic is condensed. The residual arsenic in the gas is collected into the scrubber during the wet purification process.
After the laboratory study in the South Rhodesia mine, a test device for the boiling roaster was established to treat the gold-containing arsenopyrite concentrate. The processing capacity of the device is 100 tons / day and night.
The industrial plant was commissioned in 1952 with a processing capacity of 600 tons/day and night. The flow of the device is shown in Figure 4. [next]
The arsenic grade in the calcine is 1.4%, sulfur 1%, and gold 120-150 g/ton.
The Soviet Union has not widely used boiling roasting to treat various refractory gold-bearing concentrates. However, a lot of research has been done on the calcination parameters of different ore materials in various deposits; from 1956 to 1957, the Irkutsk branch of the National Institute of Rare Metals conducted the first two-stage boiling roasting laboratory test in the Soviet Union. . The calcined raw material used is the arsenopyrite concentrate of the Dalazon Concentrator. The concentrate contains S 23.5%; As 9.55%; Fe 23.3%; Cu l.13%; Pb 0.6%; Au 18.4 g/ton; Ag 6.2 g/ton.
For the test, two laboratory-scale boiling roasters were designed and installed. The first and second stages of baking were sequentially carried out using the two calcining furnaces.
According to the results of the study, the optimum conditions for the first stage of roasting to exclude arsenic and retain sulfur in the calcine were as follows:
Calcination temperature, °C 450~480
Unit processing capacity, tons / (m 2 / day and night) 4.5~5.5
Unit consumption of air, m 2 / (m 2 / min) 3.5~4.0
Line speed of air, cm/sec 8
It has been determined that in the first stage roasting, when the air consumption is 85-90% theoretically necessary for the combustion of sulfur and arsenic, the arsenic can be excluded by 85-90% (ie, the arsenic content in the calcine is reduced to 1.3~). 1.9%), and the sulfur in the sulfide is actually all left in the calcine.
The calcined calcined in the first stage is calcined in the second stage roasting furnace. The best conditions selected according to the test results are as follows:
Calcination temperature, °C 580~620
Unit processing capacity, tons / meter 2 • day and night 3.0~4.0
Unit consumption of air, m 3 / m 2 • minute 5.5~6.0
Line speed of air, cm / sec 8.5 ~ 9.5
Gold recovery rate in calcination during cyanidation% 92~93
At the same time as the laboratory research, the Soviet Nonferrous Metallurgy Design Institute developed a preliminary design of the test furnace and roasting workshop for the boiling roasting of the arsenic pyrite concentrate in Dalazon.
The rectangular double-chamber roaster designed has a total area of ​​4.2 m 2 (1.7 x 2.5) and a day and night processing capacity of 18 tons. In 1960, the Dalazon mine was built in advance, and a two-stage roasting device for flotation concentrate was installed and the test was started. According to the research results, the calcination conditions originally selected under laboratory conditions were used. The arsenic-containing concentrate used for the test contained S 30.6%; As 9.6%; Cu 2.4%; Pb l.1%; Fe 27.0%; Au 60 g/ton.
The fineness of the concentrate is 60%-0.074 mm and the humidity is 4~7%.
During the test, the device was found to have many structural disadvantages and many difficulties in the operation. However, as the researchers have demonstrated, satisfactory results have been obtained in the preferential oxidation of arsenopyrite. These results also confirm that the previous laboratory study data is correct.
According to the metal balance meter, the process recovery rate of gold obtained from the calcined material was 97%.
The device was later modified. The calciner was changed to a single chamber furnace in place of the boiling roasting method instead of the calcination in a mechanical roaster. The equipment for industrial testing is shown in Figure 5.
The basic task of roasting is to remove arsenic from the concentrate and to obtain arsenic trioxide for industrial use. Obtaining arsenic dioxide is very difficult. This is because there are no similar examples of industrial production at home and abroad.
The modified calciner has a rectangular cross section. Its bottom area is 3.4 m 2 and its height is 1 m. The height from the bottom of the furnace to the top of the furnace is 6 meters. Lined with clay brick in the roaster. The bottom of the furnace is made of heat-resistant concrete and has a dome-shaped nozzle. The effective section of the nozzle is 0.8% of the area of ​​the bottom of the furnace.
The exhaust gas discharged from the furnace is purified in a UH-15 type dust remover and a BYI-2.4 type electric dust collector which are sequentially arranged. The dust collector, flue and electric precipitator can be insulated to prevent condensation of arsenic trioxide vapor. In order to condense and collect the arsenic trioxide vapor, a crystallization chamber is installed after the electric precipitator. The purified gas is discharged from the crystallization chamber to the atmosphere through a chimney 800 meters away from the workshop.
The concentrate after drying (to reach 4 to 5% moisture) is sent to a baking furnace for baking. This type of baking furnace is different from similar devices in foreign countries. Its main feature is the roasting of the pulp. The roasting of the concentrate slurry with this device is eliminated due to the need to obtain arsenic trioxide.
This device has been tested with two concentrate roasting systems: complete oxidation of sulfides and volatilization of arsenic into the gas phase.
When the amount of oxygen is insufficient to completely oxidize the sulfide, the arsenic has the highest volatilization rate.
When the air consumption is equal to 130~135% of the theoretical consumption and the temperature is 750~850 °C, the system for completely oxidizing the sulfide can be guaranteed. When sulphide is completely oxidized (Institution A) and arsenic is preferentially volatilized (System 6), the process parameters for boiling roasting are as follows: [next]
Institution A
Air consumption is the theoretical consumption of 130~135 80~90
Roaster unit processing capacity, t / m 2 • day and night 3.5~4.5 6.5~7.5
The temperature of the boiling layer, °C 750~850 550~580
The content of the calcined from the furnace, %
S total 0.4~0.6 12~20
Ss 0.1~0.2 7.2~15.0
As 1~1.5 0.35~0.65
Arsenic recovery rate transferred to the gas phase, % 65~75 80~85
In order to use the roaster frequently, a system of preferential arsenic arsenic should be used.
The working system of the roaster was tested under conditions of insufficient oxygen and calcination temperature of 500-850 ° C (the selected optimum temperature was 550-550 ° C). It is proved that this-roasting system can guarantee the temperature conditions necessary for the electrostatic precipitator and the entire gas pipe. Under the above-mentioned calcination temperature and air consumption (80-90% of its theoretical consumption), the oxygen content in the gas in the lower part of the furnace top fluctuates between 0 and 1.5%, and the content of SO 2 is 10 to 12%.
The amount of dust blown out in the baking furnace is 20% of the concentrate. Under the conditions of long-term operation of the electrostatic precipitator, qualified industrial arsenic anhydride containing 92~99% As 2 O 3 can be obtained. The gold grade in arsenic anhydride is 1~2 g/ton. If the dust in the gas before the electrostatic precipitator does not exceed 5-8 g/ m2 , the effect is best. The actual recovery of gold in the calcine is 96.1~97%. However, if the effective utilization factor of the electrostatic precipitator is increased and the mechanical loss is eliminated, the recovery rate of gold can be improved.
Gold enrichment in the calcine often occurs in the hearth during the roasting process, particularly at the bottom of the furnace. This has happened in factories abroad. After long-term work in the roaster, the grade of gold in the calcine of the bottom of the furnace can exceed 2~3 kg/ton or even higher. The reason for this is that free gold in the concentrate and gold that is dissociated during the oxidation of the sulfide precipitate in the gas stream.
The test device of the Dalazon Mining Bureau is the first device used by the Bureau to boil the roasting of the gold-containing arsenopyrite concentrate. It was officially put into industrial production in 1967.
The Irkutsk branch of the National Institute of Rare Metals and the National Science Institute of Non-ferrous Metals have studied the oxidative roasting of the Mugong gold-bearing concentrate in boiling roasting under laboratory conditions. In 1966, the All-Sugar Nonferrous Metals Research Institute conducted a semi-industrial test on the two-stage roasting of argillaceous gold-bearing concentrates from a deposit in Kazakhstan. This concentrate is characterized by the absence of free gold. All gold in the concentrate is symbiotic with arsenic pyrite.
When the first stage calcination temperature is low (500~559 °C) and in a weak oxygen atmosphere, arsenic is volatilized. During the second stage of calcination, sulfur and carbon are completely oxidized after excess air and increased calcination temperature.
The optimum process conditions for two-stage roasting of concentrates are as follows:
The first stage of roasting The second stage of roasting Unit processing capacity, tons / m 2 • Day and night 6.0~6.5 2.5~5.0
Calcination temperature, °C;
Within the layer 500~550 650~670
Under the layer 450~470 no less than 560
The coefficient of excess air 0.5 1.5~1.8
Line speed of air in airflow, m/s 0.1 0.1
Vacuum, mm mercury column lower portion of the furnace roof 3 2 ~ 3 2 ~
It is certain that calcination is the only beneficial calcination product for the subsequent cyanidation of argillaceous concentrates. The dust in the precipitator and the electric precipitator contains a lot of activated carbon during the roasting process. After pre-granulation, it should be returned to the first stage roaster and then calcined.
The results of the study prove that when the baking temperature exceeds 670 °C. The loss of gold with cyanide slag is greatly increased. This is due to the result of thermal purification of gold (Figure 7). If the calcination temperature is lower than 635 ° C, the gold grade in the cyanide slag is sharply increased due to the adsorption of unremoved carbon ( FIG. 8 ). [next]
It is also certain that some of the arsenic pyrite that is not completely oxidized in the calcine and dust is responsible for the large loss of gold during cyanidation (Fig. 9). An optimum process condition was established for the two-stage roasting of argillaceous gold-bearing concentrates, thereby increasing gold recovery and ensuring acceptable arsenic trioxide.
It must be pointed out that there is very little information on this aspect of the major gold producing countries in the world. In recent years, there have been few reports on the practice of deduction treatment of all gold-containing materials, especially for difficult-to-select gold-containing materials.
After analyzing and summarizing the existing data in the literature for laboratory, semi-industrial, industrial test and industrial applications of boiling roasting refractory gold-containing materials, it can be seen that the refractory gold-containing materials are subjected to boiling roasting before cyanidation. The method will be more widely used. But this method, whether it is the Soviet Union or in foreign countries, is still not the main method of gold mining companies. Bed-type roasters are still used in many countries, such as Canada, Australia, South Africa, Ghana, and the United States. There are about 50 such devices in Australia alone, which can be fired every day and night - more than a thousand tons of refractory gold-containing materials.
Since the boiling roasting method has many advantages, why is the speed of promotion so slow? And what is the vitality of the bed roasting method? The reason is that most gold mining companies are small in scale and have little processing ore. The cost of roasting-ton of gold-containing materials in these companies is 50 to 90 cents, and in some cases 20 to 25 cents. However, the cost of treating the same material using boiling roasting is a few dollars. For example, the US boiling plant's boiling roaster has a processing capacity of 40 tons/day and night, and the cost of processing-ton gold concentrate is $3.9.
Despite this, the bed type roasting method has its disadvantages, for example, the calcining furnace has a low processing ability, the surface temperature distribution of the calcined material is uneven, and the furnace temperature and gas conditions are difficult to control. Therefore, the boiling roasting method should be promoted continuously in gold enterprises.
Especially after the merger of many small businesses and the need to expand the processing capacity and scale of the company, it is necessary to replace the bed roasting method with boiling boiling. In this case, a large number of small bed type roasting apparatuses are not suitable.
In recent years, in the Soviet Union and abroad, it has been studied to carry out chlorination of gold-containing materials in a boiling roaster. According to the reference, this method can more comprehensively recover various useful components.