A method and supporting equipment for low-temperature oxidation roasting pretreatment of gold-bearing pyrite.

Abstract

This invention relates to a low-temperature oxidative roasting pretreatment method and supporting equipment for gold-bearing pyrite. The method includes: raw material preparation; humidification and cooling; low-temperature oxygen-enriched roasting; and roasted sand collection. The supporting equipment includes a batching bin, the bin outlet of which is connected to the feed hopper inlet via an elevator, and the feed hopper outlet connected to the fluidized bed furnace inlet via a conveyor belt. A spraying device is mounted on the conveyor belt. Atomized temperature-regulating and water-replenishing device and a temperature sensor are installed in the upper and middle combustion spaces of the fluidized bed furnace. An online oxygen analyzer is installed on the flue gas duct at the top of the fluidized bed furnace, and is sequentially connected to a waste heat boiler, a cyclone dust collector, an electrostatic precipitator, and an acid production system. The air inlet at the bottom of the fluidized bed furnace is connected to a blower via an air duct. This invention achieves full oxidation of gold-bearing pyrite under low-temperature, oxygen-enriched, and low-gas-velocity conditions, resulting in loose and porous roasted sand and a significantly increased gold and silver exposure rate, providing important technical support for the comprehensive utilization of the valuable components of gold-bearing pyrite.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing technology, specifically relating to a low-temperature oxidative roasting pretreatment method and supporting equipment for gold-bearing pyrite, which is particularly suitable for low-temperature controllable oxidative roasting of pyrite with sulfur content of 30% to 45% and fine gold inclusions under drying-free conditions. Background Technology

[0002] In pyrite-bearing gold ores, the gold and silver particles are finely embedded and closely associated with / encapsulated pyrite. Industrially, a common process is "fluidized bed oxidative roasting – flue gas acid production – roasted slag cyanide extraction." The roasting stage aims to oxidize pyrite and other sulfide minerals into a loosely porous roasting slag (hematite or magnetite), breaking the physical encapsulation of gold and silver, and converting sulfur and arsenic into SO2 and As2O3 for removal. This creates favorable conditions for the subsequent efficient and comprehensive recovery of gold, silver, copper, iron, and sulfur.

[0003] However, current fluidized bed oxidation roasting methods mostly involve high-temperature roasting (above 900℃), which presents the following prominent problems: (1) Thermal runaway and overburning: The sulfur content of pyrite gold ore is relatively high (generally 40% to 45%), and the heat release during combustion is concentrated, and the furnace temperature is prone to rise sharply; at high temperature, Fe2O3 forms insoluble ferrates (MFe2O4) with Cu, Co, etc., and causes the surface of the roasted sand to vitrify, and secondary coating of gold and silver, resulting in a decrease in cyanide leaching rate.

[0004] (2) Increase in partial pressure of SO3: Temperature↑→SO2+½O2⇌SO3 equilibrium shifts to the right. Although the increase in partial pressure of SO3 is beneficial to metal sulfation, excessively high SO3 is prone to react with CaO, Al2O3 and other substances to form low-melting-point sulfates, causing material to stick to the furnace wall and form rings, which affects continuous operation.

[0005] (3) Under-burning and short circuit: The raw material has a fine particle size (more than 60% of which are -0.074 mm). Under high gas velocity (1.0 m / s, hot state), it is easy to be directly carried out of the furnace. The residence time is less than 30 min, the oxidation is insufficient, and the residual sulfide encapsulates the gold, reducing the leaching rate.

[0006] (4) Large temperature fluctuations: The sulfur content of the raw materials fluctuates by ±5%, the existing cooling coil area is insufficient, the heat transfer capacity is limited, the furnace temperature fluctuation can reach ±60 ℃, and the quality of roasted sand is unstable.

[0007] (5) High energy consumption: Before entering the fluidized bed furnace, a pre-drying process is required to reduce the water content of the pyrite, which is complicated and increases costs.

[0008] Therefore, there is an urgent need for a new roasting method and supporting equipment that can achieve full oxidation, avoid over-burning and under-burning, and improve the gold and silver exposure rate under the conditions of "low temperature (≤700 ℃), oxygen-rich, slightly acidic, and low gas velocity" to take into account the comprehensive recovery of multiple elements and energy saving and consumption reduction. Summary of the Invention

[0009] This invention provides a low-temperature oxidation roasting pretreatment method and supporting equipment for gold-bearing pyrite. Through the system integration innovation of "dry-free furnace feeding - humidification and heat transfer - combined temperature control of expanded coil and atomized water supply - low-temperature oxygen enrichment", it achieves deep oxidation and efficient recovery of multiple elements of gold-bearing pyrite under low temperature conditions of 680-700 ℃, solving the problems of thermal runaway, over-burning, under-burning and high energy consumption in traditional processes.

[0010] To achieve the above objectives, the present invention provides a low-temperature oxidative roasting pretreatment method for gold-bearing pyrite, comprising the following steps: (1) Raw material preparation: Gold-containing pyrite and low-sulfur roasted sand are mixed at an effective sulfur mass fraction of 35% to 38% to obtain mixed furnace charge; This step, using low-sulfur roasted slag as a remixing diluent, achieves three main benefits: ① It stabilizes the sulfur content of the furnace charge within a narrow range of 35%–38%, resolving large furnace temperature fluctuations caused by large fluctuations in raw material sulfur content; ② The stable sulfur content in the furnace charge ensures more stable exothermic heating efficiency of sulfur, facilitating better control of the roasting temperature; ③ It prioritizes the use of low-quality roasted slag due to operational anomalies, enabling resource recycling of slag. Compared to the traditional method of directly reducing the feed rate, this approach solves the problem of fine particles failing to form a stable boiling layer while avoiding loss of processing capacity.

[0011] (2) Humidification and cooling: The mixed furnace material is pre-humidified on the conveyor belt. The moisture content of the material is increased by 10% to 15% by spraying atomized water. The latent heat of water evaporation is used to remove part of the combustion heat, so that the wet material can be directly fed into the furnace. At the same time, atomized temperature regulation and water replenishment devices are set in the upper and middle combustion space of the fluidized bed furnace as a means of temperature regulation. The furnace roasting temperature is stabilized by adjusting the amount of water sprayed. It pioneered a dual liquid water heat transfer mechanism of "pre-humidification before the furnace and in-furnace atomization temperature control": ① Before the mixed furnace charge enters the fluidized bed furnace, it is humidified by spraying atomized water (the atomized water droplet size is <100 μm to ensure uniform wetting without agglomeration). For every 10% increase in moisture, the evaporation of moisture during calcination can remove about 5% of the combustion heat, allowing wet materials (water content >10%) to be directly fed into the furnace, eliminating the traditional drying process and effectively reducing calcination energy consumption; ② In-furnace atomization is used as a fine-tuning method. A dual-flow atomizing nozzle is used with a water spray rate of 0.5 to 2.0 t / h. It responds quickly when the temperature rise at the furnace top or in the furnace is >5℃, solving the problem of lag in temperature control by a single cooling plate.

[0012] (3) Low-temperature oxygen-enriched roasting: The humidified mixed furnace charge is continuously added to the fluidized bed furnace and roasted at a temperature of 680-700 ℃. The reaction is enhanced and the local reduction is inhibited through a four-in-one deep oxidation system of "low gas velocity - thick bed - high residual oxygen - full bottom air". By increasing the total orifice area of ​​the air cap and reducing the gas velocity of the air cap orifice, the residence time of the material in the fluidized bed is extended by more than 50%. The operating gas velocity is controlled from the conventional 1.0-1.2 m / s to 0.90-0.95 m / s (hot state), so that the fluidized bed of the material is thickened by 20%-30%. The feed rate is adjusted according to the residual oxygen volume fraction of the flue gas ≥2.5% to stabilize the gas-to-material ratio at 2.5-2.9. m³ / kg (containing gold pyrite) to enhance oxygen-enriched roasting and suppress localized reducing atmosphere; eliminate tertiary air supply and avoid using secondary air unless necessary, with all air volume supplied by primary air from the furnace bottom, so that the combustion zone moves down to the furnace bottom and middle, thereby advancing the oxidation reaction and effectively extending the reaction time, avoiding furnace top supplementary combustion and equipment overheating and coking caused by traditional secondary / tertiary air; This step constructs a four-in-one deep oxidation system of "low gas velocity - thick bed layer - full bottom air - high residual oxygen", achieving reaction enhancement and local reduction inhibition: ① Adjusting the wind cap structure to extend the residence time: After the air velocity in the small holes of the wind cap is reduced, the entrainment capacity of the airflow in the furnace for mineral particles is greatly weakened. The height of the mineral particles being blown up is reduced, the rising rate is slowed down, and the falling back flow speed is accelerated. The circulation and discharge rhythm of materials in the furnace are slowed down accordingly. At the same time, the low air velocity will aggravate the back mixing in the furnace. The disorderly collision and backflow of mineral particles in the boiling zone are more frequent, further extending the time for a single particle to complete the reaction and be discharged from the furnace.

[0013] ② Reduce operating gas velocity to thicken the boiling layer: The higher the operating gas velocity (hot state), the stronger the airflow lifting force, the higher the mineral particles are suspended and the more dispersed their distribution, resulting in a thin and sparse boiling layer; when the operating gas velocity is reduced, the airflow lifting force is insufficient, and the mineral particles are difficult to rise to a high position, and they will accumulate in the lower boiling section of the furnace, resulting in a thick and dense boiling layer.

[0014] ③ High residual oxygen and oxygen-enriched synergistic enhanced oxidation: By synergistically controlling the residual oxygen volume fraction of flue gas ≥2.5% and the gas-to-material ratio of 2.5~2.9m³ / kg, the oxygen partial pressure is increased by 30% compared with the conventional method. At a low temperature of 680~700 ℃, the driving force of the FeS2→Fe2O3 reaction is still maintained, the formation of magnetic iron (Fe3O4) is suppressed, and the surface oxidation artifact is solved.

[0015] ④ Optimize the reaction zone distribution with bottom air: Eliminate tertiary air supply and avoid using secondary air unless necessary. The total air volume is provided by the primary air at the bottom of the furnace, which moves the combustion zone down to the bottom and middle of the furnace. This allows 90% of the oxidation reaction to be completed from the bottom to the middle of the furnace, avoiding the furnace top supplementary combustion and equipment overheating and coking caused by traditional secondary / tertiary air, and effectively extending the reaction time.

[0016] (4) Collection of roasted sand: The roasted sand discharged with the flue gas is collected in sequence by the waste heat boiler, cyclone dust collector and electrostatic precipitator, and then combined with the roasted sand overflowing from the fluidized bed furnace and sent to the leaching and purification system for recovery. The residual flue gas is sent to the acid production system.

[0017] The obtained calcined sand is loose and porous, with a particle size of -0.045 mm accounting for >70% and a specific surface area >5 m² / g. A three-stage dust collection system achieves segmented collection of particle sizes: a waste heat boiler collects coarse calcined sand (+0.074 mm), a cyclone collector collects medium-sized particles (0.045–0.074 mm), and an electrostatic precipitator collects fine particles (-0.045 mm). This allows for on-demand diversion and utilization of the calcined sand, improving the recovery rate of gold, silver, and copper.

[0018] Furthermore, the sulfur content of the low-sulfur calcined sand in step (1) is 0.2% to 1%, and low-quality calcined sand produced due to abnormal operation is preferred as re-burning material.

[0019] Furthermore, in step (3), the control of the roasting temperature is mainly based on expanding the total heat exchange area of ​​the cooling coils in the furnace, supplemented by the atomized temperature regulation and water replenishment device. This combined temperature control of expanding the total heat exchange area of ​​the cooling coils and humidification can achieve furnace temperature fluctuations of <±15℃.

[0020] Furthermore, the formula for calculating the total heat exchange area of ​​the cooling coil in step (3) is as follows: (1) (2) Where F is the total heat exchange area of ​​the required cooling coil, in meters. 2 Q represents the excess heat removed to maintain the calcination temperature, in W; k is the thermal conductivity coefficient, taken as 290 W / (m²). 2 .K); Δt is the logarithmic mean temperature difference, K; T is the furnace control temperature, 680~700℃; t1 is the cooling water inlet temperature of the cooling coil, ≤20 ℃; t2 is the cooling water outlet temperature of the cooling coil, ≤45 ℃.

[0021] Furthermore, the total heat exchange area of ​​the cooling coils can be increased by increasing the number of cooling coils or increasing the heat exchange area of ​​a single cooling coil, or a combination of both. The cooling coils absorb heat from the furnace in the form of steam, thereby reducing the furnace temperature.

[0022] Furthermore, the increase in the total area of ​​the small holes in the wind cap in step (3) can be achieved by increasing the number of wind caps, increasing the number of holes in a single cap, or expanding the area of ​​a single hole, or by any one or more combinations thereof.

[0023] Furthermore, the method for adjusting the gas-to-material ratio in step (3) is as follows: monitor the residual oxygen volume fraction of the flue gas at the top of the furnace in real time. When the residual oxygen is <2.5%, reduce the amount of feed proportionally to stabilize the gas-to-material ratio at 2.5 to 2.9 m³ / kg.

[0024] To achieve the above objectives, the present invention also provides supporting equipment for the above-mentioned low-temperature oxidative roasting pretreatment method for gold-bearing pyrite, including a batching bin, the discharge port of which is connected to the feed hopper inlet via an elevator, and the feed hopper discharge port connected to the fluidized bed furnace inlet via a conveyor belt (with built-in weighing function); a spraying device is mounted on the conveyor belt for spraying water to humidify the material; atomizing temperature regulation and water replenishment devices and temperature sensors are installed in the upper and middle combustion spaces of the fluidized bed furnace for furnace temperature control; an online oxygen analyzer is installed on the flue gas duct at the top of the fluidized bed furnace, and a waste heat boiler, a cyclone dust collector, an electrostatic precipitator, and an acid production system are connected in sequence; the air inlet at the bottom of the fluidized bed furnace is connected to a blower via an air duct (eliminating the need for secondary / tertiary air supply ducts).

[0025] Furthermore, both the spraying device and the atomizing temperature-regulating water supply device consist of a variable frequency booster water pump, water pipes, and several atomizing nozzles.

[0026] Furthermore, an online moisture detector is also installed on the conveyor belt to detect the moisture content of the material being humidified by the water spray, thereby controlling the amount of water sprayed by the spraying device.

[0027] During operation, the online signals of the aforementioned supporting equipment are all connected to the DCS control system. After the gold-bearing pyrite and low-sulfur roasted sand are precisely proportioned in the batching silo, they are transferred by an elevator to the feed hopper for storage, and then conveyed to the fluidized bed furnace by a conveyor belt. During the conveying process, a spray device performs pre-humidification, and an online moisture detector provides feedback on the moisture content to adjust the spray volume. The total area of ​​the cooling coils, the total orifice area of ​​the air caps, and the operating air velocity of the fluidized bed furnace are pre-configured based on the heat removal, the residence time of the fluidized bed, and the thickness requirements, respectively. All airflow within the furnace is supplied by a blower through the furnace bottom duct, eliminating secondary / tertiary air supply pipes and shifting the combustion zone to the furnace bottom and middle. Simultaneously, an online oxygen analyzer monitors residual oxygen in the flue gas in real time (range 0–5%, accuracy ±0.1%). When residual oxygen <2.5%, the DCS system interlocks to reduce the feed rate via the conveyor belt, maintaining the gas-to-material ratio at 2.5–2.9 m³ / kg, ensuring a 30% increase in oxygen partial pressure compared to conventional methods. This allows for the full reaction of FeS2→Fe2O3 even at low temperatures of 680–700 ℃. Furnace temperature is controlled primarily by cooling coils with expanded heat exchange area, supplemented by an atomized temperature control and water supply device. When the temperature sensor detects a temperature rise >5 ℃ at the furnace top or center, the DCS automatically activates a variable frequency booster water pump to spray water, instantly vaporizing and absorbing heat to achieve rapid and precise temperature control, keeping furnace temperature fluctuations within ±10℃. Within ℃; most of the roasted sand produced by roasting is discharged from the overflow port of the fluidized bed furnace, and a small portion is discharged with the flue gas and collected by a three-stage dust collection system of waste heat boiler, cyclone dust collector and electrostatic precipitator. All of it is sent to subsequent leaching and purification, and the remaining flue gas is sent to the acid production system to achieve deep oxidation and multi-element recovery.

[0028] The beneficial effects of this invention are as follows: This invention achieves full oxidation of gold-bearing pyrite under low-temperature, oxygen-enriched conditions through a deep oxidation system of "mixed sulfur control - humidification and heat transfer - combined temperature control with expanded coils and atomized water supply - low-temperature oxygen enrichment." This solves the problems of thermal runaway in traditional high-temperature roasting, over-burning gold encapsulation and resealing, under-burning of fine particles, and large temperature fluctuations. The resulting roasted sand is loose and porous, with a significantly improved gold and silver exposure rate. The gold recovery rate is stable at over 85%, the silver recovery rate is over 50%, and the copper and sulfur recovery rates are ≥85% and ≥99%, respectively. Simultaneously, high-quality iron concentrate is obtained, achieving a dual breakthrough in the efficient comprehensive utilization of valuable components in gold-bearing pyrite and energy conservation and emission reduction. Specific details are as follows: (1) By precisely mixing gold-containing pyrite with low-sulfur roasted sand, the effective sulfur content of the material fed into the furnace is kept within a relatively narrow range, effectively avoiding furnace temperature runaway caused by excessive fluctuations in raw material sulfur.

[0029] (2) By pre-humidifying the material entering the furnace, wet material can be directly put into the furnace without drying, which can significantly reduce energy consumption and cost compared with traditional drying. At the same time, the latent heat of water evaporation is used to remove the heat of combustion, which optimizes the heat balance in the furnace and is more conducive to the realization of low-temperature roasting, reducing the investment in heat dissipation in the furnace.

[0030] (3) Through the coordinated control of multiple parameters in the furnace, the stability and continuous operation cycle of the low-temperature roasting process have been greatly improved, eliminating phenomena such as overheat coking and short-circuit belt, and the quality of roasted sand has been significantly improved. Attached Figure Description

[0031] Figure 1 This is a flowchart of a low-temperature oxidation roasting pretreatment method for gold-bearing pyrite according to the present invention; Figure 2 This is a diagram showing the associated equipment for a low-temperature oxidative roasting pretreatment method for gold-bearing pyrite according to the present invention. In the diagram: 1-Battery bin, 2-Elevator, 3-Feed hopper, 4-Conveyor belt, 5-Fluidized bed furnace, 6-Spraying device, 7-Atomizing temperature control and water supply device, 8-Temperature sensor, 9-Online oxygen analyzer, 10-Waste heat boiler, 11-Cyclone dust collector, 12-Electrostatic precipitator, 13-Acid production system, 14-Fan, 15-Online moisture analyzer, 16-Cooling coil, 17-Wind cap. Detailed Implementation

[0032] To make the technical problems and solutions solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. Example 1

[0033] A gold-bearing pyrite, with the following main elements and their contents: gold 2-4 g / t, silver 20-50 g / t, iron 40%-45%, copper 0.1%-0.2%, and sulfur 40%-45%. The main elements recovered are Au, Ag, S, Fe, and Cu. The gold-bearing pyrite is mainly pyrite, with trace amounts of arsenopyrite, chalcopyrite, galena, and sphalerite; the gangue minerals are mainly quartz, feldspar, and calcite.

[0034] The conventional oxidation roasting method was used for pretreatment. The main parameters of the fluidized bed furnace were as follows: furnace area 70 m²; 4500 air caps, each cap with 6 holes and a hole diameter of 4 mm, for a total small hole area of ​​0.339 m²; 5 sets of cooling coils, each with a heat exchange area of ​​12.5 m², for a total heat exchange area of ​​62.5 m². The roasting temperature was 900℃, the operating gas velocity was 1.14 m / s, the residual oxygen volume fraction in the flue gas was 1.5%, and the gold and silver leaching rates of the roasted sand were 70% and 28%, respectively.

[0035] Pre-processing using the method and supporting equipment described in this invention, such as... Figure 1-2 As shown, the specific steps are as follows: (1) Raw material preparation: In the batching bin 1, the gold-bearing pyrite and the bottom roasted sand are mixed once by a loader, and then mixed twice by a grab bucket. The effective sulfur grade of the mixed furnace charge is detected to be 35%±0.5%, forming a furnace material with stable sulfur content. The processing capacity is 31.25 t / h (dry basis). The mixed furnace charge is transferred to the feed hopper 3 by the elevator 2 for storage and later use. (2) Humidification and cooling: When the mixed furnace charge (originally containing about 12% water) is conveyed by the conveyor belt 4, atomized water is sprayed through the spray device 6 installed above the belt to pre-humidify it, thereby increasing the moisture content of the material by 10% and the total moisture content by about 22%. Based on the fact that every 10% of moisture evaporation can remove about 5% of the heat, the humidified furnace charge can remove about 11% of the heat of sulfurization combustion.

[0036] (3) Low-temperature oxygen-enriched calcination: The humidified furnace charge is directly fed into fluidized bed furnace 5, where a four-in-one deep oxidation system of "low gas velocity - thick bed - high residual oxygen - full bottom air" is used to achieve reaction enhancement and local reduction inhibition. ① Temperature control: The roasting temperature is controlled at 700 ℃±10 ℃, mainly by expanding the total heat exchange area of ​​the cooling coil 16, and supplemented by the temperature adjustment of the atomized temperature adjustment and water replenishment device 7.

[0037] Based on heat balance, processing 1 kg of gold-bearing pyrite with 35% available sulfur releases approximately 4872.03 KJ of chemical heat. The actual processing capacity in this embodiment is 36.29 t / h (dry basis). The heat released by sulfidation oxidation is approximately 176805.97 GJ / h. After deducting the sensible heat from flue gas and roasted sand (approximately 45%), heat loss from moisture evaporation (approximately 11%), and heat loss from the furnace body (approximately 4%), 70762.39 GJ / h (the remaining 40%) needs to be removed by the cooling coil.

[0038] Q = 176805.97 × 40% = 70762.39 GJ / h Calculate using the formula F=Q / (k·Δt): k = 290 w / (m²·K)

[0039]

[0040] Therefore, the number of cooling coils needs to be increased from 5 to 8, or the heat exchange area of ​​a single coil needs to be increased from 12.5㎡ to 20.4㎡ without changing the number of cooling coils (still 5), so as to ensure that the total heat exchange area reaches 102㎡.

[0041] In addition, the atomizing temperature regulating and water replenishment device 7 added to the upper and middle parts of the fluidized bed furnace 5 serves as an auxiliary device. When the temperature rise at the top or middle of the furnace exceeds 5°C, the atomizing temperature regulating and water replenishment device 7 automatically sprays atomized water to evaporate the latent heat and assist in cooling, ensuring that the bed temperature is maintained at 700°C ± 10°C.

[0042] ② Air velocity and residence time: Total area of ​​small holes in the vent cap = number of vent caps × number of holes per cap × area of ​​a single hole, area of ​​a single hole = π × r² Orifice velocity = Air volume / Total orifice area of ​​the vent cap Cold operating air velocity = air volume / 3600 / furnace area Hot operating gas velocity = Cold operating gas velocity × (273 + calcination temperature) / 273 With the air volume remaining constant (i.e., 67000 Nm) 3 / h), the orifice diameter is increased from 4mm to 4.8mm, the number of holes in a single wind cap is increased from 6 to 8, and the total area of ​​the orifices in the wind cap needs to be increased from 0.339m². 2 Increasing the diameter to 0.651 m², the gas velocity in the small hole decreased from 54.90 m / s to 28.59 m / s, a reduction of approximately 48%, thereby extending the material residence time from 28 min to 45 min.

[0043] Cold operating gas velocity = 67000 / 3600 / 70 = 0.27 m / s Hot operating gas velocity (900℃) = 0.27 × (273 + 900) / 273 = 1.14 m / s Hot operating gas velocity (700℃) = 0.27 × (273 + 700) / 273 = 0.95 m / s Meanwhile, by reducing the hot operating gas velocity from 1.14 m / s to 0.95 m / s, the thickness of the boiling layer was increased from 0.9 m to 1.2 m.

[0044] ③ Residual oxygen and gas-to-material ratio: Install an online oxygen analyzer 9 on the flue gas outlet pipe and interlock it with the conveyor belt 4 (which has a built-in weighing function) to monitor the residual oxygen in the flue gas in real time. When the residual oxygen is <2.5%, reduce the feed rate proportionally to maintain the gas-to-material ratio at 2.5 to 2.9 m³ / kg.

[0045] ④ The tertiary air supply is cancelled, the secondary air supply is normally closed, and the total air volume (approximately 67,000 Nm³) is reduced. 3 The furnace bottom blower 14 provides the material for combustion at the bottom and middle of the furnace, thereby increasing the roasting time and making the oxidation more complete and thorough.

[0046] (4) Collection of roasted sand: The roasted sand discharged with the flue gas is collected in sequence by the waste heat boiler 10, the cyclone dust collector 11, and the electrostatic precipitator 12, and is combined with the roasted sand overflowing from the fluidized bed furnace 5 and sent to the leaching and purification system for recovery. The residual flue gas is sent to the acid production system 13.

[0047] The gold and silver leaching rates of roasted ore were increased to 89% and 54% respectively, the sulfur recovery rate reached 99.28%, and the copper recovery rate reached 80.26%. This achieved low-temperature, oxygen-rich, slightly acidic, and low-gas-velocity roasting of gold-bearing pyrite, realizing comprehensive resource recovery and utilization. Example 2

[0048] A gold-bearing pyrite has the following main elements and contents: gold 3-4 g / t, silver 30-40 g / t, iron 35%-42%, copper 0.2%-0.5%, and sulfur 36%-44%. The main elements recovered are Au, Ag, S, Fe, and Cu. The gold-bearing pyrite is mainly pyrite, with trace amounts of arsenopyrite, chalcopyrite, galena, and sphalerite; the gangue minerals are mainly quartz, feldspar, and calcite.

[0049] The pretreatment was performed using a conventional oxidation roasting method. The main parameters of the fluidized bed furnace were: furnace area 38㎡; 2530 air caps, each with 4 holes and a diameter of 4×4.8mm; 8 sets of cooling coils, each with a heat exchange area of ​​4㎡, for a total heat exchange area of ​​32㎡. Low-sulfur roasted sand was uniformly blended to reduce the sulfur content of the furnace charge (approximately 38%). The roasting temperature was 900℃, the hot operating gas velocity was 1.13 m / s, the residual oxygen volume fraction in the flue gas was 1.0%, and the gold and silver leaching rates of the roasted sand were 66.21% and 36.78%, respectively.

[0050] Pre-processing using the method and supporting equipment described in this invention, such as... Figure 1-2 As shown, the specific steps are as follows: (1) Raw material preparation: In the batching bin 1, the gold-bearing pyrite and the bottom roasted sand are mixed once by a loader, and then mixed twice by a grab bucket. The effective sulfur grade of the mixed furnace charge is detected to be 38%±0.5%, forming a furnace charge with stable sulfur content. The processing capacity is 15.29t / h (dry basis). The mixed furnace charge is transferred to the feed hopper 3 by the elevator 2 for storage and later use. (2) Humidification and cooling: When the mixed furnace charge (originally containing about 8% water) is conveyed by the conveyor belt 4, atomized water is sprayed through the spray device 6 installed above the belt to pre-humidify it, thereby increasing the moisture content of the material by 12% and the total moisture content by about 20%. Based on the fact that every 10% of moisture evaporation can remove about 5% of the heat, the humidified furnace charge can remove about 10% of the heat of sulfurization combustion.

[0051] (3) Low-temperature oxygen-enriched calcination: The humidified furnace charge is directly fed into fluidized bed furnace 5, where a four-in-one deep oxidation system of "low gas velocity - thick bed - high residual oxygen - full bottom air" is used to achieve reaction enhancement and local reduction inhibition. ① Temperature control: The roasting temperature is controlled at 680 ℃±10 ℃, mainly by expanding the total heat exchange area of ​​the cooling coil 16, and supplemented by the temperature adjustment of the atomized temperature adjustment and water replenishment device 7.

[0052] Based on heat balance, processing 1 kg of gold-bearing pyrite with 38% available sulfur releases approximately 5186.34 KJ of chemical heat. The actual processing capacity in this embodiment is 15.29 t / h (dry basis). The heat released by sulfidation oxidation is approximately 79300.06 GJ / h. After deducting the sensible heat from flue gas and roasted sand (approximately 45%), heat loss from moisture evaporation (approximately 10%), and heat loss from the furnace body (approximately 4%), 31720.02 GJ / h (the remaining 41%) needs to be removed by the cooling coil.

[0053] Q = 79300.06 × 41% = 32513.02 GJ / h Calculate using the formula F=Q / (k·Δt): k = 290 w / (m²·K)

[0054]

[0055] Therefore, the number of cooling coils needs to be increased from 8 to 12, or the heat exchange area of ​​a single coil can be increased from 4㎡ to 6㎡ without changing the number of cooling coils (still 8), so as to ensure that the total heat exchange area reaches 48㎡.

[0056] In addition, the atomizing temperature regulating and water replenishment device 7 added to the upper and middle parts of the fluidized bed furnace 5 serves as an auxiliary device. When the temperature rise at the top or middle of the furnace exceeds 5°C, the atomizing temperature regulating and water replenishment device 7 automatically sprays atomized water to evaporate the latent heat and assist in cooling, ensuring that the bed temperature is maintained at 680°C ± 10°C.

[0057] ② Air velocity and residence time: Under the condition of constant air volume (i.e., 36000 Nm) 3 / h), increasing the diameter of the 2530 wind cap orifices from 4×4.8mm to 8×4.8mm doubles the total cross-sectional area of ​​the orifices, requiring the total area of ​​the small orifices in the wind cap to increase from 0.183m². 2 Increasing the diameter to 0.366 m², the gas velocity in the small hole decreased from 54.64 m / s to 27.32 m / s, a reduction of approximately 50%, thereby extending the material residence time from 30 min to 55 min.

[0058] Cold operating gas velocity = 36000 / 3600 / 38 = 0.26 m / s Hot operating gas velocity (900℃) = 0.26 × (273 + 900) / 273 = 1.13 m / s Hot operating gas velocity (680℃) = 0.26 × (273 + 680) / 273 = 0.92 m / s Meanwhile, by reducing the hot operating gas velocity from 1.13 m / s to 0.92 m / s and increasing the boiling layer thickness from 1.1 m to 1.4 m, the residence time was extended by approximately 30%. Additionally, by appropriately increasing the density of air caps below the feed inlet based on spatial distribution to reduce the accumulation rate, the gas velocity through the small holes was reduced by half after the technical modification.

[0059] ③ Residual oxygen and gas-to-material ratio: Install an online oxygen analyzer 9 on the flue gas outlet pipe and interlock it with the conveyor belt 4 (which has a built-in weighing function) to monitor the residual oxygen in the flue gas in real time. When the residual oxygen is <2.5%, reduce the feed rate proportionally to maintain the gas-to-material ratio at 2.5 to 2.9 m³ / kg.

[0060] ④ The tertiary air supply is cancelled, the secondary air supply is normally closed, and the total air volume (approximately 36,000 Nm³) is reduced. 3 The furnace bottom blower 14 provides the material for combustion at the bottom and middle of the furnace, thereby increasing the roasting time and making the oxidation more complete and thorough.

[0061] (4) Collection of roasted sand: The roasted sand discharged with the flue gas is collected in sequence by the waste heat boiler 10, the cyclone dust collector 11, and the electrostatic precipitator 12, and is combined with the roasted sand overflowing from the fluidized bed furnace 5 and sent to the leaching and purification system for recovery. The residual flue gas is sent to the acid production system 13.

[0062] The gold and silver leaching rates of roasted ore were increased to 88.12% and 52.15% respectively, the sulfur recovery rate reached 99.4%, and the copper recovery rate reached 82%. This achieved low-temperature, oxygen-rich, slightly acidic, and low-gas-velocity roasting of gold-bearing pyrite, realizing comprehensive resource recovery and utilization.

[0063] As can be seen from the two embodiments, the present invention achieves full oxidation roasting of gold-bearing pyrite under low temperature, oxygen-rich, and low gas velocity conditions through a series of measures including "mixed sulfur control - humidification and heat transfer into the furnace - combined temperature control with expanded coil and atomized water supply - reduced gas velocity - elimination of back air". The roasted sand is loose and porous, and the gold and silver exposure rate is significantly improved. The gold recovery rate is stable at over 85%, the silver recovery rate is over 50%, and the copper and sulfur recovery rates are ≥80% and ≥99%, respectively. At the same time, high-quality iron concentrate is obtained, with strong comprehensive recovery and processing capabilities and stable production indicators.

[0064] The present invention has been described in detail above through specific and preferred embodiments. However, those skilled in the art should understand that the present invention is not limited to the embodiments described above. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for low temperature oxidative roasting pretreatment of gold-containing pyrite, characterized in that, Includes the following steps: (1) Raw material preparation: Gold-containing pyrite and low-sulfur roasted sand are mixed at an effective sulfur mass fraction of 35% to 38% to obtain mixed furnace charge; (2) Humidification and cooling: The mixed furnace material is pre-humidified on the conveyor belt. The moisture content of the material is increased by 10% to 15% by spraying atomized water. The latent heat of water evaporation is used to remove part of the combustion heat, so that the wet material can be directly fed into the furnace. At the same time, atomized temperature regulation and water replenishment devices are set in the upper and middle combustion space of the fluidized bed furnace as a means of temperature regulation. The furnace roasting temperature is stabilized by adjusting the amount of water sprayed. (3) Low-temperature oxygen-enriched roasting: The humidified mixed furnace charge is continuously added to the fluidized bed furnace and roasted at a low-temperature oxygen-enriched temperature of 680-700 ℃. The reaction is enhanced and the local reduction is inhibited through a four-in-one deep oxidation system of "low gas velocity - thick bed - high residual oxygen - full bottom air": by increasing the total orifice area of ​​the air cap and reducing the gas velocity of the air cap orifice, the residence time of the material in the fluidized bed is extended by more than 50%; the operating gas velocity is controlled from the conventional 1.0-1.2 m / s to 0.90-0.95 m / s, so that the fluidized bed of the material is thickened by 20%-30%; the feed rate is adjusted according to the residual oxygen volume fraction of the flue gas ≥2.5% to stabilize the gas-to-material ratio at 2.5-2.

9. m³ / kg to enhance oxygen-enriched roasting and suppress localized reducing atmosphere; eliminate tertiary air supply and avoid using secondary air unless necessary, with all air volume supplied by primary air from the furnace bottom, so that the combustion zone moves down to the furnace bottom and middle, thereby advancing the oxidation reaction and effectively extending the reaction time, avoiding furnace top supplementary combustion and equipment overheating and coking caused by traditional secondary / tertiary air; (4) Collection of roasted sand: The roasted sand produced by roasting is collected by the waste heat boiler, cyclone dust collector and electrostatic precipitator in sequence with the flue gas and then sent to the leaching and purification system for recovery, while the remaining flue gas is sent to the acid production system.

2. A method for low temperature oxidative roasting pretreatment of gold bearing pyrite according to claim 1, characterized in that, The sulfur content of the low-sulfur calcined sand in step (1) is 0.2% to 1%, and low-quality calcined sand produced due to abnormal operation is preferred as re-burning material.

3. A method for low temperature oxidative roasting pretreatment of gold bearing pyrite according to claim 1, characterized in that, Step (3) The main measure to control the roasting temperature is to increase the total heat exchange area of ​​the cooling coil in the furnace, supplemented by the atomized temperature regulation and water replenishment device.

4. The method according to claim 3, wherein the gold-containing pyrite is pre- treated by low-temperature oxidation roasting. The formula for calculating the total heat exchange area of ​​the cooling coil in step (3) is as follows: (1) (2) Wherein, F is the total heat exchange area of the required cooling coil, m 2 ; Q is the excess heat removed to maintain the roasting temperature, W; k is the thermal conductivity coefficient, the value is 290 W / (m 2 .K); Δt is the logarithmic mean temperature difference, K; T is the control temperature in the furnace, 680-700℃; t1 is the cooling coil cooling water inlet temperature, ≤20℃; t2 is the cooling coil cooling water outlet temperature, ≤45℃.

5. A method of low temperature oxidative roasting pretreatment of gold bearing pyrite according to claim 3, characterized in that, The increase in the total heat exchange area of ​​the cooling coil can be achieved by increasing the number of cooling coils or increasing the heat exchange area of ​​a single cooling coil, or a combination of both.

6. A method for low temperature oxidative roasting pretreatment of gold bearing pyrite according to claim 1, characterized in that, In step (3), the increase in the total area of ​​the small holes in the wind cap can be achieved by increasing the number of wind caps, increasing the number of holes in a single cap, or expanding the area of ​​a single hole, or any one or more combinations thereof.

7. The method of low temperature oxidative roasting pretreatment of gold bearing pyrite according to claim 1, characterized in that, The method for adjusting the gas-to-material ratio in step (3) is as follows: monitor the residual oxygen volume fraction of the flue gas at the top of the furnace in real time. When the residual oxygen is <2.5%, reduce the amount of feed according to the proportion so that the gas-to-material ratio is stable at 2.5 to 2.9 m³ / kg.

8. A complete set of equipment for a low-temperature oxidative roasting pretreatment method of gold-containing pyrite according to any one of claims 1-7, characterized in that, The system includes a batching bin (1), the discharge port of which is connected to the feed hopper (3) via an elevator (2), and the discharge port of the feed hopper (3) is connected to the feed inlet of the fluidized bed furnace (5) via a conveyor belt (4); a spraying device (6) is mounted on the conveyor belt (4) for spraying water to humidify the material; the upper and middle combustion spaces of the fluidized bed furnace (5) are equipped with an atomizing temperature regulating and water replenishing device (7) and a temperature sensor (8) for controlling the temperature inside the furnace; an online oxygen analyzer (9) is installed on the flue gas duct at the top of the fluidized bed furnace (5), and a waste heat boiler (10), a cyclone dust collector (11), an electrostatic precipitator (12) and an acid production system (13) are connected in sequence; the air inlet at the bottom of the fluidized bed furnace (5) is connected to a blower (14) via an air duct.

9. The complete set of equipment for the low-temperature oxidative roasting pretreatment method of gold-containing pyrite according to claim 8, characterized in that, Both the spray device (6) and the atomizing temperature-regulating water supply device (7) consist of a variable frequency booster water pump, water pipes and several atomizing nozzles.

10. The complete set of equipment for the low-temperature oxidative roasting pretreatment method of gold-containing pyrite according to claim 8, characterized in that, An online moisture detector (15) is also installed on the conveyor belt (4) to detect the moisture content of the material being sprayed with water for humidification, thereby controlling the amount of water sprayed by the spraying device (6).

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