贾特耶洛奈husband Co., Ltd. is one of North America's largest mining companies to provide arsenic trioxide to the chemical sector. Since 1948 it has become a larger gold producing area. However, before the toxic anti-product arsenic trioxide was sold in large quantities in the near future, it was the cause of losses to varying degrees.
The mine has expanded to its existing production capacity since 1958 and its basic processes have remained unchanged. The increase in gold prices has led to a re-evaluation of waste mines that were once considered uneconomic. Five years ago, when the gold grade was 0.36 ounces/ton of ore, the result was a loss of $1 million. Today, when the ore grade is 0.19 ounces/ton, the situation has greatly improved. This article discusses metallurgical and environmental protection and current issues related to the roasting process for the recovery of arsenic-containing gold ore.
In Jat, the flotation concentrate is self-heating roasting in a two-fluidized combustion chamber, and the discharge of the fluid bed and cyclone dust collector is subjected to conventional cyanide recovery. The exhaust gas is removed by a hot electrostatic precipitator and the arsenic trioxide dust is condensed. The arsenic trioxide dust collected in the bag filter is sold directly or stored in the basement. The dust collection efficiency of the bag filter is 99.8%, and the content of arsenic trioxide is more than 90%. Nowadays, 4,500 short tons of arsenic trioxide (1 short tons = 907.2 kg) are sold every year, and the soot collected by the electrostatic precipitator is treated by batch processing to recover gold.
Foreword The Jat Yellov Mine is located about four kilometers north of Yellowknife City, north of the Great Slave Lake in the northwest. The mine was put into operation in May 1948. At that time, the ore capacity was 250 tons/8. After the process was reformed and expanded, the current processing capacity has reached 1,250 tons/day, and the current ore contains 0.19 ounces/ton of gold.
Jat ore is sericite schist and chlorite containing about 30% quartz, and varying amounts of calcium carbonate, iron, and from about 8 to 10% consisting of metal sulfides. Fine-grained arsenic pyrite and pyrite contain large amounts of sulfides. Also contains variable amounts of stibnite, sphalerite, pyrrhotite, brass and galena ore. Lead, iron and copper sulfonates are also present in small amounts.
It can be seen that there is very little gold. Fine-grained natural gold inclusions are found in the quartz and around the grain boundaries and in the arsenopyrite and stibnite cracks, and appear as small inclusions in the beryllium copper. However, using this as a mineral analysis value to characterize ore is far from sufficient.
Most of the gold is believed to exist in a submicroscopic state in arsenopyrite or even as a solid solution with arsenopyrite. Ore minerals are usually embedded over a relatively wide range.
It is quite obvious that this ore is quite complicated and it is obviously difficult to treat with a single amalgamation and direct cyanidation. In practice, most of the treatment methods used are mixed flotation to enrich sulfide minerals, followed by spontaneous calcination of the concentrate and calcination. The calcined sand produced by most fluidized solid roasters is suitable for cyanidation. In Jat, the purpose of the calcination is to convert the dense sulfide particles into a porous structure such that the gold particles are exposed to the cyanide infusion. The physical state of the calcination is of the utmost importance, for which the thermodynamic conditions of the calciner must be strictly controlled in order to produce a calcine having a satisfactory porosity. Control of the operation of the furnace is impeded when certain minerals are present in the feed to the furnace (e.g., sulphite and sulphonate). Although the exact behavior of these minerals is not fully understood, their presence is indeed detrimental to the extraction of gold.
From the beginning of the calcination, the arsenic contained in the roasting furnace gas should be collected, and the gold in the fine-grained calcined soot mixed with the gas phase of the furnace should be recovered. The fine-grained calcined soot is collected by a general electric dust collector, and gold is extracted from the cyanide solution by using activated carbon. The roasting furnace gas is cooled by the electrostatic precipitator by the introduced thin air, so that the arsenic is condensed by arsenic trioxide and then recovered in the bag filter. The exhaust gas is discharged through the chimney.
At present, the arsenic trioxide dust recovered by the bag filter is transported to the cylinder silo by wind, and then transported by truck to the US market. A few years ago, arsenic trioxide was stored in a silo in a permanent layer.
Roasting The initial flotation concentrate was calcined in an Allls Chalmers type of roaster with a total area of ​​approximately 3,800 square feet of treated concentrate of 40 tons per day.
In early 1952, in order to expand the processing capacity of the roaster, a two-stage fluidized solid roaster was installed. This type of furnace has been modified several times (because it was not tested during installation). It comprises a cylindrical roasting chamber which is divided into two different chambers by partition walls, and the bellows are also separated, so that the air volume supplied to each chamber can be separately adjusted. The calcine flows uniformly from the first chamber (i.e., the first stage) through the three transfer ports in the partition wall into the second-stage firing chamber where the firing is completed in an oxidizing atmosphere. A portion of the calcined dust is collected by three cyclones in series. The rear duct of the cyclone extends through the top of the roasting chamber and is embedded in a fluid bed in the second stage roasting chamber. One section of the firing chamber has an area of ​​about 105 square feet and the second section of the firing chamber has an area of ​​only 35 square feet. The transfer port of the duct has a large corner, and even then, the corners formed by the barrel of the roasting chamber and the partition wall are difficult to maintain fluidization. There is a dead space here, which gradually expands outwards and hinders the transfer of the material at the rear of the transfer port and the cyclone. Enlarging the transfer port means that the two-stage roasting atmosphere is out of control due to the mixing of the gases.
In order to further improve the processing capacity of Gongguang, a larger; two-stage fluidized solid roaster was installed in 1958. The furnace is also composed of two separate fluidized roasters. The flow bed of a section of the calciner has an inner diameter of 13 feet and is about 5 feet higher than the second stage roaster.
The flotation concentrate is metered by a Monu type pump (concentrate concentration is 76% in the horizontal body), and the material enters the first stage roaster through the spray gun. The level of its fluid bed is kept in the wind. Five feet above the mouth. The flow bed overflows the calcine into the flushal transfer valve, which is a U-shaped tube with a small fluidized injector at the bottom and a small auxiliary air injector on the discharge side. In order to lift the calcine to the feed tube of the two-stage roaster. The wind pressure in the two injectors was 20 psi, at which time the air flow was 14-20 cubic feet per minute. [next]
The air is sent to the bellows of the first firing chamber at 4 gauge psig through a 3700 cubic feet per minute Spencer turbo compressor and then enters the fluidized bed through the tuyere. There are 193 winds in the 10 inch tuyere. The mouth has six 3/16-inch air holes for each tuyere. The dust-containing gas enters the second stage free plate from the first stage.
The calcine of the first stage roaster enters the second stage roaster from the fluidized bed surface. The two-stage roaster has an inner diameter of 9.5 feet and has 100 plum heads on the center of the 10-inch.
Air was supplied at 4 gauge pounds per square inch through two 2100 cubic feet per minute Spencer turbine compressors. The fluid bed overflow tube is 5 feet above the tuyere, and the roasting sand that overflows from the fluid bed directly enters a quenching tank. All quenched roasting products are pumped to the calcine washing system and sent to cyanidation.
The first stage of calcination is commonly referred to as the arsenic removal stage. Here, the temperature is controlled at 925 o F and the oxygen supply is controlled to the lowest value. In order to ensure the removal of arsenic in the form of trivalent god, it is usually kept in the reduced state at the beginning of the calcination, because the presence of excess oxygen promotes the oxidation of the third-order arsenic to pentavalent arsenic, which is arsenic of ferric iron. The surface morphology of the acid salt remains on the calcine, thereby delaying or hindering further volatilization of arsenic and affecting the leaching of gold in the calcine.
The second stage of calcination is referred to as oxidative roasting. The material calcined in the fluidized bed is further oxidized under active oxidizing conditions, and the sulfur is further removed. However, it is impossible to achieve or hope to cause dead roasting because the complete removal of sulfur tends to promote the continued oxidation of iron into a magnet. The ore remains in the micropores of the calcine, thereby preventing the permeation of the cyanide solution.
Name | Tons/day | Au (ounces per ton) | Fe | S | As | Sb |
Grinder feeding | 1250 | 0.19 | 6.60 | 2.2 | 0.85 | 0.04 |
Flotation concentrate | 130 | 1.60 | 23.00 | 17.5 | 7.6 | 0.18 |
Calcination | 100 | 2.00 | 27.80 | 2.5 | 1.0 | 0.13 |
Electrostatic dust collector dust | twenty two | 1.43 | 18.00 | 2.75 | 2.29 | 0.30 |
Bag dust collector dust | 15 | 0.12 | 1.75 | 0.50 | 70.00 | 0.50 |
First stage roasting room | Second stage roasting chamber | |
Bed temperature | 925 o F | 1000 o F |
Free plate temperature | 825 o F | 880 o F |
Flow (standard cubic feet per minute) | 2500 | 950 |
Bellows pressure (pounds per square inch) | 3.9 | - |
Water spray | no | 1.91 US gallons per minute |
Feed rate (ton / hour) | 5.6 | - |
Concentration (g/L) | 2250 | - |
Arsenic removal rate | 91.6% | - |
Desulfurization rate | 87.9% | - |
The temperature of the gas evolved in the roaster | 880 o F | - |
A Brief History of Gas cleaning operations Jat mine gas purification first in October 1951 Curt McConnell built a low-temperature type electrostatic precipitators for dust collector calcine and condensate from gas exports Edward roaster down the arsenic trioxide . At the beginning of 1952, the first fluidized, roasting furnace, a 9-foot-tall, 150-foot-tall brick chimney was installed, along with a booster auxiliary fan and an expanded flue system. It is hoped that this better control of ventilation and air temperature and improved operation of the electrostatic precipitator. However, due to the expansion of the production capacity of the roaster, the dust collection efficiency of this electric precipitator has dropped by 10%.
It appears that in terms of gold extraction, the first stage of the fluidized roaster is strictly controlled air to maintain operation under a moderate reducing atmosphere, so that the furnace outlet gas contains a high concentration of sulfur dioxide (substantially not trioxide) sulfur). When the temperature of the electrostatic precipitator is still gas at SO 2 and SO 3 is close to the condensation temperature, the surface of the non-conductive arsenic dust particles adsorbs SO 3 , which causes the suspended dust to become electrically conductive and be recovered. The amount of SO 3 in the outlet gas of the roaster is not high, so that the non-conductive dust particles of the condensed arsenic are discharged from the chimney through the electric precipitator. [next]
In 1955, a second Cotnel-type high-temperature electrostatic precipitator was built. It was used to selectively recover the impurities contained in the roasting dust before the arsenic condensed in the original low-temperature electrostatic precipitator was collected. gold. The two (hot and cold) electrostatic precipitators operate in tandem to increase the efficiency of the dust collection, but the condensed arsenic particles are not sufficiently conductive for recycling in low temperature electrostatic precipitators. Attempts to increase the amount of sulfur trioxide in the exit gas of the roaster have not been successful. Finally, the mixed recovery of As 2 O 3 and the baking dust is reduced to 60%, which makes it necessary to operate the two electrostatic precipitators at low temperatures.
In 1957, a small bag filter was tested on a portion of the roaster gas. The results show that the arsenic capture efficiency of this device is as high as 99%, and the service life of the bag is satisfactory.
An enlarged two-stage fluidized solid roaster was installed in 1958. At the same time, a standard 30-Draco bag filter with 8 compartments was put into operation. It was used to capture the roasting dust in the furnace gas and the condensed dioxide. After the new fluidized solid roaster was in good condition, the Cotnel electrostatic precipitator acted as a high temperature electrostatic precipitator to propel the flue gas. From this, selective collection of gold-containing roasting dust and condensed arsenic trioxide is put into practice. In the spring of 1962, the original low-temperature Cotnel electrostatic precipitator was modified, and it is currently operating in parallel with a high-temperature electrostatic precipitator.
Gas Purification and Calcination Dust Recovery The mixed furnace gas escaped from the second stage roaster passes through two Dukang cyclone dust collectors installed in series, and each cyclone dust collector removes all the collected bake dust. Into a separate quench tank. The quenched calcined product is pumped to the calcine scrubbing system. The remaining roasting dust and cyclone dust collector gas is 880 o F, and is adjusted to 700 o F with air before entering the electrostatic precipitator.
The two electrostatic precipitators are K-type Ketterner dust collectors with a bar wind barrier. Each dust collector consists of two sets of parallel-arranged devices. Enter into two intervals arranged in series. Each section contains 882 to 1/8 inch (diameter) electrode and 272 3/16 inch square wire discharge electrodes. The trap electrodes are arranged in 18 wind barriers (8 feet long and 12 feet high) with an 8-inch conduit between the wind barriers. This discharge electrode forms 17 wind barriers and is located in an 8 inch conduit. This dust collector housing is of mild steel construction and is sufficiently insulated.
In order to strike the soot from the electrode, the number of times the top hammer hits the trapping electrode and the discharge electrode frame must be controlled. The calcine dust is shaken down into the V-shaped bin and sent to the quenching tank. The gas flow rate and its distribution through the electrostatic precipitator are regulated by a multi-directional vane air lock installed in the inlet and outlet of each dust collector. Today only two of the four sets of devices are working, while the remaining two are used as backups. When a group of devices experiences a severe short circuit or other failure, they stop their work and put another set of equipment into service until the equipment is repaired.
High-voltage direct current is generated by a transformer, which is raised from a low voltage of 500 volts to a high voltage of 500 volts. High-potential alternating current is converted to high-voltage direct current by using a mechanical rectifier. The negatively charged discharge electrode ionizes the surrounding gas, thereby causing the conductive baking dust to carry a charge, and the charged dust particles are attracted and deposited on the grounded collecting electrode. The dust remaining on the trapping electrode is removed until it is shaken by the top hammer.
The maximum voltage that does not generate an arc allows the electrostatic precipitator to achieve the highest capture yield. The operating voltage is related to the composition of the gas, the temperature and the concentration of the dust, all of which are a function of the operating parameters of the furnace.
The voltage and current on the primary side of the transformer can be monitored to show the interruption of the discharge of the collector electrode and the short circuit due to contamination of the insulator or increased dust between the wind barriers. In order to overcome an accident when installing such equipment, it must be installed and inspected according to a detailed project comparison table. Projects that seem less important, such as damage to the air duct and outer casing insulation, can cause cold spots, and the presence of cold spots promotes the formation of hard crucibles and calcined dust aggregates. These aggregates can cause damage or short circuit to the hopper screw conveyor. Air leakage near the inlet is sufficient to condense the arsenic trioxide out of the gas and contaminate the captured roasting dust.
The electrostatic capture rate of this electrostatic precipitator is 94.5% on average (in terms of the amount of gold in the cyclone exhaust).
Inlet temperature | 700 o F |
output temperature | 600 o F |
Primary voltage | 550 volts |
Secondary voltage | 50,000 volts |
Au | Fe | S | As | Sb |
1.43 | 18,00 | 2.75 | 2.29 | 0.30 |
(oz/ton) | (weight%) | (weight%) | (weight%) | (weight%) |
The exhaust of the gas-cooled electrostatic precipitator is cooled to 220 o F by adding conditioned air drawn by a hybrid fan outside the furnace. The As 2 O 3 contained in the gas phase condenses into a fine dust in an enlarged chamber located below the hybrid fan. The temperature of the baghouse is maintained at 220 o F using a pneumatically controlled damper mounted on a hybrid fan to adjust the air inlet. The damper is automatically positioned by a thermocouple and temperature controller.
The electrostatic precipitator produces approximately 6500 standard cubic feet per minute of gas at a temperature of 600 o F. The gas is air conditioned to a flow rate of approximately 3,500 standard cubic feet per minute and a temperature of 220 o F. The condensed arsenic trioxide is recovered from the gas discharged from the cooled calciner in a 300-type Draco bag collection chamber of eight compartments. Each compartment is fitted with 300 pockets of 5 inches in diameter and 10 feet in length, Draylon 32, rated at 60,000 cubic feet per minute, 230 o F. The device was designed to have a air to filter cloth ratio of 1.9 cubic feet per square foot and a minimum capture yield of 99.8%. Initially, such equipment was equipped with a time striking device to remove soot from the bag. Each of the two compartments is equipped with a V-shaped silo and a screw conveyor for collecting and transporting arsenic trioxide. A horizontal conveyor transports arsenic trioxide dust into the Fuller-Jinyu type pneumatic feed pump.
In 1978 the federal government announced a gold roaster chimney God's emission standard, specified as 15 mg / Scm. During this period, the dust efficiency was improved by improving the operating conditions of the main baghouse.
Bag Cleaning Room Temperature In order to increase the percentage of arsenic trioxide condensed from the gas phase to the solid phase, the working temperature of the bag filter is reduced from 230 o F to 220 o F. Further lowering the temperature is considered to be impractical because the temperature must be kept at a dew point of SO 2 above.
Bag vibration period
The bag filter was initially used to shock dust from the bag through a time-shake device. At the Jat mine, the shock period is one week per 45 minutes. A total of 32 weeks per day. Studies have shown that when the bag is subjected to vibration operations, its collection efficiency is the lowest. This is presumably due to the vibration of the bag, causing some fine-grained arsenic trioxide dust to penetrate the micropores of the filter cloth, so that the amount of As 2 O 3 discharged from the chimney is increased.
Working system | Before 1977 | Currently |
temperature | 230 o F | 220 o F |
Bag vibration period | Timing vibration every 45 minutes | Vibration when pressure is reduced |
Vibration frequency | 32 weeks / day | 4 weeks / day |
Filter media | Oryo Full Fiber Bag | De Lei Long 32 bags |
Chimney arsenic emissions (mg/Scm) | 75~25 | 6~10 |
Arsenic (lbs/day) | 273~760 | 16~20 |
As | As 2 O 3 | Fe | Sb | Au (ounces per ton) |
65~72 | 85~95 | 1.0~2.5 | 0.3~0.7 | 0.10~0.15 |
The ratio of bag air collector to filter cloth is 1.9 cubic feet per minute • square feet is considered low. The vibration mechanism of today's bags is working when the pressure drop across the baghouse reaches 2 inches of water. The direct result is that the vibration frequency is reduced from 32 weeks to 4 weeks per day. At present, arsenic trioxide dust is concentrated on the side of the bag, and can be collected as a filter medium. The combination of the filtering effect of the dust and the vibration frequency makes the collection efficiency of the bag dust collector significantly improved.
The filter media bag filter was originally made of Oryo (a synthetic fiber made of acrylonitrile polymer) as a filter medium, but after extensive research using filter bags made of various materials, the splash was selected. Portrtts and Spencer's De's Dragon 32 filter media, this bag has proven to be very reliable.
A variable-speed pneumatic exhaust fan delivers the exhaust of the purified baghouse into a chimney 9 feet in diameter and 150 feet high. The standard analysis results of chimney gas are as follows:
1.25% SO 2 , 19.9% ​​O 2 , 78.5% N 2 and 0.1% C0 2 .
Treatment of recycled arsenic trioxide:
The bag filter collects an average of 15 tons of soot per working day. The typical analysis result of this bag dust is (% by weight): 85~95As 2 0 3 , 0.3~0.7Sb and 0.1~0.15Au (oz/ton).
In the past few years, bag dust has been transported by pneumatic transport to specialized underground warehouses in permafrost, which are used to store As 2 O 3 dust. After the excavation of the silo is completed, a concrete partition is installed to prevent any stored material from being removed from the silo. Before the bag dust is placed in the silo, some of the dust may be returned to the ground through the formation. Use a pneumatic conveyor to press the wind to bring the dust from the underground into the dust collector inlet duct.
Today, the market for arsenic trioxide in North America has improved, and arsenic trioxide products have turned from loss to profit.
At present, bag dust is transported by wind to a 15,000-cubic-foot cylinder silo, which is then transported to a refinery in the southeastern United States with a 1,500-cubic-foot car. In order to prevent dust leakage during loading into the cylinder silo and loading into the car, the silo and the car's charging are operated under negative pressure (loading) behind the belt dust collector population duct.
Conclusion Due to the continuous development of gold production, in order to meet the requirements of metallurgical and environmental protection, Jatylo Nef Mine Co., Ltd. has made progress in the combined use of sulfide ore concentrate roasting and flue gas purification systems. The efficiency of the gas purification system has been improved by retrofitting existing equipment. At present, the market for arsenic trioxide in North America has expanded, making the treatment of bag dust have turned from loss to profit.
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