Smelting process for roasting gold concentrate in two-stage fluidized bed furnace

Abstract

The invention discloses a smelting process for roasting gold concentrate in a two-stage fluidized bed furnace, which comprises the following steps: sequentially carrying out first-stage arsenic removal roasting and second-stage desulfurization roasting on the gold concentrate to obtain roasted sand, then carrying out cyanidation leaching on the roasted sand to obtain gold-containing leachate, adsorbing the gold-containing leachate by adopting activated carbon to obtain gold-loaded carbon, and desorbing the gold-loaded carbon to obtain gold-containing pregnant solution. Electrolyzing the pregnant solution to obtain gold mud, and casting the gold mud to obtain a gold ingot; according to the method, efficient utilization of the low-grade arsenic-containing gold concentrate is achieved through segmented temperature control arsenic removal and desulfurization, sulfur acid making cooperation and whole-process recovery rate optimization, and the recovery rate of gold reaches up to 91.6%.

Description

Technical Field

[0001] This invention belongs to the field of precious metal metallurgy technology, specifically relating to a smelting process for roasting gold concentrate in a two-stage fluidized bed furnace. Background Technology

[0002] Traditional gold concentrate smelting processes typically employ pretreatment techniques such as single roasting, bio-oxidation, or high-pressure leaching to decompose sulfides and release encapsulated gold, followed by cyanide leaching to recover the precious metal. However, existing technologies have significant limitations for complex gold concentrates with low grades (e.g., Au ≤ 20 g / t), high arsenic (As ≥ 2%), and medium to low sulfur (S ≤ 20%).

[0003] 1. The challenge of synergistic removal of arsenic and sulfur: a single-stage roasting process cannot simultaneously meet the differentiated removal needs of arsenic and sulfur. Although high-temperature roasting can efficiently remove sulfur, it easily leads to premature volatilization of arsenic, forming highly toxic As2O3 dust, increasing the cost of flue gas purification; while low-temperature oxygen-controlled roasting can preferentially remove arsenic, low-sulfur ores are difficult to maintain self-heating balance, requiring external fuel supplementation, which is not economical.

[0004] 2. Limited gold recovery rate: Arsenic residues react with cyanide to form stable complexes (such as As(CN)3), significantly increasing cyanide consumption and inhibiting gold dissolution; incompletely oxidized sulfides encapsulate gold particles, reducing the leaching rate. Conventional roasting often results in a gold leaching rate below 80%, leading to significant resource waste.

[0005] 3. The conflict between environmental protection and resource utilization: Traditional SO2 treatment methods often rely on alkaline absorption or direct emission, which not only wastes sulfur resources but also faces stringent environmental regulations. Furthermore, the technology for producing acid from low-concentration SO2 flue gas is technologically demanding, and existing single-stage roasting processes struggle to stably supply gas of suitable concentrations.

[0006] 4. Poor adaptability of low-grade ore: The insufficient calorific value of low-gold and low-sulfur ores leads to instability in the roasting process, requiring the blending of high-grade ore or fuel, which limits the flexibility of raw material sources.

[0007] Traditional gold concentrate smelting processes suffer from significant technical bottlenecks. For example, patent CN201010567569.8, "A Secondary Oxidation Pretreatment Process for Refractory Gold Concentrates Containing Arsenic, Sulfur, and Carbon," describes a process that effectively improves gold recovery, is simple, and has minimal environmental pollution. However, the process is complex and requires biological oxidation and chlorination. The process sequentially includes concentrate regrinding and de-refining, biological oxidation, chlorination oxidation, and cyanide leaching. This process uses biological oxidation to treat the gold concentrate, followed by hypochlorite treatment of the oxidation slag. Chlorination oxidation significantly reduces the harmful effects of carbonaceous matter on fluorination gold extraction.

[0008] Patent CN202311284213.7, "A New Green and Efficient Smelting Process for Gold Concentrate," describes a direct cyanidation method for gold extraction after ultrafine grinding, with the final tailings being finely ground to produce cement additives. While this process boasts high recovery rates and is green and environmentally friendly, it directly extracts gold through cyanidation without roasting, making it impossible to treat impurities such as arsenic and sulfur in the concentrate.

[0009] Patent CN202410809848.2, "A Two-Stage Roasting Process for Gold Recovery from Arsenic-Containing Gold Concentrate," employs a two-stage roasting and pressurized pretreatment process, combined with an activator, to effectively remove harmful impurities such as arsenic, carbon, and sulfur, creating favorable conditions for chemical leaching. The gold concentrate processed in this process has a gold grade of 73 g / t, and the arsenic impurity content is only 0.6%. Furthermore, it specifically recovers copper from the roasted ore, making it unsuitable for gold concentrates with low-grade gold and high impurity content.

[0010] Patent CN100404708C, "Production Process for Recovering Au, Ag, Cu, As, and S from Arsenic-Containing Carbon Gold Concentrate by Two-Stage Roasting," employs a two-stage roasting process to recover Au, Ag, Cu, As, and S from arsenic-containing carbon gold concentrate. After the gold concentrate is treated with an activator and roasted in two stages, arsenic, carbon, and sulfur enter the flue gas in gaseous form. For copper impurities that enter the roasted sand in the form of CuSO4 and CuO, a copper extraction process of acid leaching-extraction-electrowinning is used to recover cathode copper. Finally, a cyanidation process is used to recover precious metal products such as gold and silver from the acid leaching residue. This patent requires strict ore blending and the addition of activators, resulting in high operating costs. Furthermore, the boundaries for arsenic and sulfur removal are unclear, leading to problems such as low arsenic recovery rate and high sulfuric acid impurity content.

[0011] The patented process involves gold concentrate that requires blending and also contains copper, using a process of roasted sand acid leaching, extraction, and electrolytic copper extraction. This patent, however, processes low-grade gold concentrate that does not contain copper. The patented process uses cyanide leaching, zinc powder replacement, and hydrometallurgy to produce finished gold and silver products. This patent, on the other hand, uses cyanide leaching, carbon adsorption, desorption, electrolysis, and casting to obtain gold ingots.

[0012] Patent CN110306066B, entitled "A Multi-stage Gold Extraction Method for Difficult-to-Treat Arsenic-Containing Gold Tailings," discloses a multi-stage gold extraction method for difficult-to-treat arsenic-containing gold tailings, including steps such as acidification, primary acidification slag alkali leaching, roasting, roasted sand acid leaching, secondary acidification slag alkali leaching, and secondary alkali leaching filter cake cyanidation. This patented process is complex and costly. Summary of the Invention

[0013] To address the problems existing in the prior art, the purpose of this invention is to provide a smelting process for gold concentrate roasting using a two-stage fluidized bed furnace. This invention employs a "two-stage fluidized bed furnace roasting" process, which achieves the cascade removal and resource utilization of arsenic and sulfur through precise segmented temperature control, oxygen control, and airflow guidance. This fundamentally solves the problem of efficient smelting of low-grade complex gold concentrate, and has both economic and environmental advantages. It is especially suitable for the resource utilization of complex gold concentrate with a gold grade ≤20g / t, arsenic content ≥2%, and sulfur content ≥20%.

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] This invention provides a smelting process for roasting gold concentrate in a fluidized bed furnace. The gold concentrate is subjected to a first-stage arsenic removal roasting and a second-stage desulfurization roasting to obtain roasted sand. The roasted sand is then subjected to cyanide leaching to obtain a gold-containing leachate. Activated carbon is used to adsorb the gold-containing leachate to obtain gold-loaded carbon. The gold-loaded carbon is then desorbed to obtain a gold-containing precious solution. The gold-containing precious solution is then electrolyzed to obtain gold mud. The gold mud is then smelted and cast to obtain gold ingots.

[0016] During the arsenic removal roasting process, the O2 concentration is controlled to be ≤10wt.% and the temperature is 450-550℃.

[0017] During the second-stage desulfurization roasting, the O2 concentration is controlled to be ≥15wt.% and the temperature is 650-750℃.

[0018] The fluidized bed roasting process for gold concentrate of this invention employs a two-stage fluidized bed roasting process. The first stage involves low-temperature arsenic removal roasting, using a weak oxidizing atmosphere to suppress Fe3O4 formation and promote selective As volatilization, oxidizing As to As2O3 gaseous form for removal, achieving an arsenic removal rate ≥95%. The second stage involves desulfurization roasting using a strong oxidizing atmosphere to ensure the directional conversion of sulfur to SO2 (concentration >8%), which is directly fed into the sulfuric acid production system, achieving a sulfur utilization rate ≥96%. Simultaneously, it produces highly porosity roasted sand (porosity >35%), which facilitates leaching. This sand undergoes cyanide leaching and carbon adsorption to obtain gold-loaded carbon. Further desorption and electrolysis yield sponge gold, which is then melted and cast to obtain gold ingots.

[0019] In this invention, by optimizing the roasting temperature and atmosphere, firstly, sufficient energy is provided to completely destroy the crystal structure of minerals such as pyrite, allowing microcracks to fully expand and thus fully release the encapsulated gold; secondly, it promotes the preferential conversion of sulfides into loose and porous magnetite (Fe3O4), which not only ensures that the original inclusions are destroyed, but also creates a good channel for the fluid, thus solving the problems of encapsulation and passivation.

[0020] In a preferred embodiment, the gold concentrate has a gold grade of ≤20g / t, an arsenic content of ≥2wt.%, and a sulfur content of 18-22wt.%.

[0021] In a preferred embodiment, gold concentrate is slurried to form a slurry, which is then fed into a fluidized bed furnace for two-stage roasting. The concentration of the slurry is 30-50 wt%. Experiments have shown that controlling the slurry concentration within this range yields optimal performance. If the concentration is too low, the reaction is difficult to control and resources are wasted; if the concentration is too high, the reaction is incomplete and the gold inclusions cannot be fully destroyed.

[0022] In a preferred embodiment, during the first stage of arsenic removal roasting, the oxygen concentration is controlled at 5-10%, the temperature at 500-550℃, and the roasting time is 0.5-2h, preferably 30-40min.

[0023] During the two-stage desulfurization roasting, the oxygen concentration is controlled at 15-25%, the temperature at 650-700℃, and the roasting time is 0.2-4h, preferably 20-60min.

[0024] The optimal performance is achieved by controlling the oxygen concentration in the first-stage arsenic removal roasting and the second-stage desulfurization roasting within this preferred range. If the oxygen concentration in the first-stage roasting is too low, arsenic will not be fully converted into As2O3, resulting in some arsenic entering the gold leaching process. If the oxygen concentration in the second-stage desulfurization roasting is too high, FeS2 will generate the most stable hematite (Fe2O3). The dense structure of hematite will form a hard "eggshell" that encapsulates unreacted sulfides or exposed gold, causing severe physical passivation.

[0025] In a preferred embodiment, after the two-stage desulfurization roasting is completed, the resulting roasted product is immediately transferred to cooling water and rapidly cooled to below 80°C, and then ball-milled until the content of 400 mesh is >90%. In this invention, the rapid cooling of the roasted product can effectively destroy the gold-encapsulated structure. When the high-temperature roasted sand is rapidly cooled, huge thermal stress is generated inside and between different mineral phases (such as hematite, magnetite, and unreacted minerals), causing a large number of microcracks to be generated inside the roasted sand particles, which greatly increases the porosity of the roasted sand. The cyanide leaching reagent (cyanide and oxygen) provides a channel, making it easier for it to contact the encapsulated gold particles.

[0026] In a preferred embodiment, the As2O3 flue gas generated during the first stage of arsenic removal roasting is rapidly cooled and then recovered through a baghouse dust collection system.

[0027] In a preferred embodiment, the SO2 generated by the two-stage desulfurization roasting is directly fed into the sulfuric acid production system. In this invention, the sulfuric acid production system includes flue gas purification and conversion absorption processes, with an SO2 conversion rate ≥99.5%, and exhaust emissions meeting national environmental protection standards.

[0028] In a preferred embodiment, the waste heat generated during the first-stage arsenic removal roasting and the second-stage desulfurization roasting processes is recovered through a waste heat boiler for power generation or heating.

[0029] In a preferred embodiment, calcined sand is placed in a sodium cyanide solution to obtain a slurry for cyanide leaching. The pH of the cyanide leaching is 10-12, the mass fraction of sodium cyanide in the sodium cyanide solution is 0.05-0.2%, the liquid-solid mass ratio of the sodium cyanide solution to the calcined sand is 2.5-3.5:1, and the cyanide leaching time is 24-36 hours.

[0030] In a preferred embodiment, lime is used to adjust the pH of the slurry, and mechanical stirring or aeration is used to enhance cyanide leaching.

[0031] In the preferred embodiment, when using activated carbon to adsorb gold-containing leachate, a countercurrent adsorption process is employed, with a flow rate of 5-10 m / s within the adsorption tower. 3 / h·m 2 The activated carbon has a particle size of 1-3 mm. Under the above parameters, gold adsorption is achieved with an adsorption rate of ≥98% and a gold loading of 6000 g / t.

[0032] In this invention, the desorption of gold-loaded carbon can be performed using either the conventional "Zadera process" or its improved "AARL process".

[0033] In a preferred embodiment, the desorption process of gold-loaded carbon is as follows: gold-loaded carbon is loaded into a desorption column, preheated desorption liquid is pumped into the column from the bottom, and gold-containing solution is obtained from the top of the column. The desorption liquid is a mixed solution composed of sodium cyanide (NaCN) and sodium hydroxide (NaOH), wherein the mass fraction of sodium cyanide in the mixed solution is 0.1% - 1%, and the mass fraction of sodium hydroxide is 1% - 2%.

[0034] In the preferred embodiment, during electrolysis, a gold-containing precious liquid is used as the electrolyte, a stainless steel plate is used as the cathode, and the current density is controlled at 10-30 A / m. 2 In the electrolyte, Au≥50g / L, gold mud is obtained.

[0035] In a preferred embodiment, the gold mud is washed with hydrochloric acid, dried, and then smelted to obtain gold ingots. In this invention, the gold mud is smelted using a high-temperature pyrometallurgical process to obtain gold ingots with a purity ≥99.95%.

[0036] Beneficial effects

[0037] Two-stage roasting with synergistic control: The first stage uses low temperature and weak oxygen to inhibit the formation of Fe3O4 and promote the selective volatilization of As; the second stage uses high temperature and strong oxygen to ensure the directional conversion of sulfur into SO2 (concentration >8%), which is then directly fed into the sulfuric acid production system, with a sulfur utilization rate of ≥96%.

[0038] Pre-treatment for calcination activation: After two-stage calcination, the sand is rapidly cooled to below 80°C and then ball-milled to a 400 mesh size of >90% to destroy the gold-encapsulated structure;

[0039] Environmentally friendly integrated design: As2O3 flue gas is recovered through quenching + bag dust collection system, with As fixation rate >99%; cyanide tail liquid is degraded by SO2 / air method, with total cyanide degradation rate ≥99.5%.

[0040] In summary, the innovations of this process are: ① Two-stage roasting removes arsenic and sulfur in stages, avoiding interference from impurities in the cyanidation reaction and simultaneously realizing sulfur resource utilization; ② Optimizes roasting temperature and atmosphere to suppress gold encapsulation and sulfide passivation effects; ③ Integrates efficient processing of low-grade ore with environmentally friendly emission reduction, suitable for low-grade gold concentrate, with high overall recovery rate and low cost, and has significant industrial application value. Attached Figure Description

[0041] Figure 1 The process flow diagram of this invention. Detailed Implementation

[0042] The following describes preferred embodiments of the present invention, and the specific details of these embodiments further illustrate the above-mentioned content of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

[0043] Example 1

[0044] Raw material: Gold concentrate produced by a gold mine beneficiation plant (slurry feed, slurry concentration 20%), composition: Au 20.3g / t, As 2.15%, S 19.8%, with 90% of the particles being 200 mesh.

[0045] Implementation steps

[0046] (1) Pretreatment

[0047] The slurry is dewatered by a thickener until the slurry concentration reaches 50%, and then continuously conveyed to a first-stage fluidized bed roaster by a screw feeder.

[0048] (2) Low-temperature boiling roasting stage (arsenic removal stage)

[0049] Furnace temperature: 530±10℃ (controlled by adjusting the amount of supplemental natural gas), O2 concentration controlled at 10wt.%.

[0050] Duration of stay: 35 minutes.

[0051] Output:

[0052] Flue gas: Contains As2O3 dust (concentration 8.2 g / Nm³), and arsenic ash (purity >92%) is recovered after electrostatic precipitator + quench tower treatment.

[0053] Calcium ore: Contains 0.18% As.

[0054] (3) Two-stage high-temperature enhanced roasting (desulfurization stage)

[0055] The roasted sand is transported to the second-stage fluidized bed furnace.

[0056] Furnace temperature: 700±10℃ (using oxygen-enriched air, oxygen concentration 25%).

[0057] Duration of stay: 25 minutes.

[0058] After the second-stage roasting is completed, the resulting roasted product is immediately transferred to cooling water and rapidly cooled to below 80°C, and then ball-milled to a density of >90% at 400 mesh.

[0059] Output:

[0060] Flue gas: SO2 concentration 7.6%, directly connected to the acid production system;

[0061] Calcium sand: contains 4.3% sulfur and has a specific surface area of ​​12.5 m² / g.

[0062] (4) Cyanide leaching

[0063] The calcined sand was slurry adjusted to a concentration of 40%, and 0.3 g / t of NaCN (pH=10.5) was added.

[0064] Leaching time: 36 hours, gold leaching rate: 92.7%.

[0065] (5) Activated carbon adsorption and electrolysis

[0066] The countercurrent adsorption process is adopted, the flow rate in the adsorption tower is 5-10 m³ / h·m², and the particle size of the activated carbon is 1-3 mm.

[0067] Gold-loaded carbon capacity: 8.2 kg / t

[0068] The electrolyte has an Au concentration of 120 g / L and a current efficiency of 94.5%.

[0069] (6) Melting and casting

[0070] Electrolytic gold mud is smelted in an electric arc furnace (1250℃) to produce gold ingots with a purity of 99.96%.

[0071]

[0072] Example 2

[0073] Raw material: Low-sulfur, high-arsenic ore containing 3.2% As, 15.4% S, and 18.7 g / t Au.

[0074] All other conditions are the same as in Example 1, except that the following parameters are adjusted:

[0075] The roasting temperature was increased to 610℃, and the dwell time was extended to 45 minutes.

[0076] The second-stage roasting process switches to an oxygen-deficient mode (oxygen concentration 10%) to suppress sulfate formation.

[0077] result:

[0078] Arsenic removal rate was 95.8%, and sulfur oxidation rate was 73.4% (SO2 concentration was 6.9%).

[0079] The gold leaching rate reached 88.3%.

Claims

1. A smelting process for roasting gold concentrate in a two-stage fluidized bed furnace, characterized in that, The gold concentrate is subjected to a first-stage arsenic removal roasting and a second-stage desulfurization roasting to obtain roasted sand. The roasted sand is then subjected to cyanide leaching to obtain a gold-containing leachate. The gold-containing leachate is adsorbed by activated carbon to obtain gold-loaded carbon. The gold-loaded carbon is desorbed to obtain a gold-containing precious solution. The gold-containing precious solution is electrolyzed to obtain gold mud. The gold mud is then melted and cast to obtain gold ingots. During the arsenic removal roasting process, the O2 concentration is controlled to be ≤10wt.% and the temperature is 450-550℃. During the second-stage desulfurization roasting, the O2 concentration is controlled to be ≥15wt.% and the temperature is 650-750℃.

2. The smelting process for roasting gold concentrate in a two-stage fluidized bed furnace according to claim 1, characterized in that, The gold concentrate has a gold grade of ≤20g / t, an arsenic content of ≥2wt.%, and a sulfur content of 18-22wt.%.

3. The smelting process for roasting gold concentrate in a two-stage fluidized bed furnace according to claim 1, characterized in that, The gold concentrate is slurryed to form a slurry, which is then fed into a fluidized bed furnace for two-stage roasting. The concentration of the slurry is 30-50 wt%.

4. The smelting process for roasting gold concentrate in a two-stage fluidized bed furnace according to claim 1, characterized in that: During the first stage of arsenic removal roasting, the oxygen concentration is controlled at 5-10%, the temperature at 500-550℃, and the roasting time at 0.5-2 hours. During the second-stage arsenic removal roasting, the oxygen concentration is controlled at 15-25%, the temperature at 650-700℃, and the roasting time at 0.2-4h.

5. The smelting process for roasting gold concentrate in a fluidized bed furnace according to claim 1, characterized in that: The As2O3 flue gas generated by the first stage of arsenic removal roasting is rapidly cooled and then recovered through a bag filter dust collection system. The SO2 produced by the second-stage desulfurization roasting is directly fed into the sulfuric acid production system. The waste heat generated during the first-stage arsenic removal roasting and the second-stage desulfurization roasting processes is recovered through a waste heat boiler for power generation or heating.

6. The smelting process for roasting gold concentrate in a two-stage fluidized bed furnace according to claim 1, characterized in that: The calcined sand is placed in a sodium cyanide solution to obtain a slurry for cyanide leaching. The pH of the cyanide leaching is 10-12, the mass fraction of sodium cyanide in the sodium cyanide solution is 0.05-0.2%, the liquid-solid mass ratio of the sodium cyanide solution to the calcined sand is 2.5-3.5:1, and the cyanide leaching time is 24-36 hours.

7. The smelting process for roasting gold concentrate in a two-stage fluidized bed furnace according to claim 5, characterized in that: The pH of the slurry was adjusted with lime, and mechanical or aerated stirring was used to enhance cyanide leaching.

8. The smelting process for roasting gold concentrate in a two-stage fluidized bed furnace according to claim 1, characterized in that: When using activated carbon to adsorb gold-containing leachate, a countercurrent adsorption process is adopted, with a flow rate of 5-10 m³ / h·m² in the adsorption tower and a particle size of 1-3 mm for the activated carbon.

9. The smelting process for roasting gold concentrate in a two-stage fluidized bed furnace according to claim 1, characterized in that: The process of desorbing gold-loaded carbon is as follows: gold-loaded carbon is loaded into a desorption column, preheated desorption liquid is pumped into the column from the bottom, and gold-containing solution is obtained from the top of the column. The desorption liquid is a mixed solution composed of sodium cyanide and sodium hydroxide, wherein the mass fraction of sodium cyanide in the mixed solution is 0.1% - 1% and the mass fraction of sodium hydroxide is 1% - 2%. During electrolysis, a gold-containing precious liquid is used as the electrolyte, a stainless steel plate is used as the cathode, and the current density is controlled at 10-30 A / m. 2 In the electrolyte, Au≥50g / L, gold mud is obtained.

10. The smelting process for roasting gold concentrate in a two-stage fluidized bed furnace according to claim 1, characterized in that: The gold mud was washed with hydrochloric acid, dried, and then melted and cast.

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