Method for recovering selenium and mercury from acid mud in acid making

Abstract

The invention discloses a method for recovering selenium and mercury from acid-making acid mud, and relates to the field of non-ferrous metal metallurgy. The method comprises the following steps: slurrying acid mud produced in a purification process in a sulfuric acid production process and concentrated sulfuric acid, roasting at low temperature to realize preliminary separation of mercury and selenium, distilling roasting residues to realize recovery of mercury in the acid mud, and returning distillation residues to a lead system to recover lead in the acid mud. The method can realize efficient separation of mercury and selenium in acid-making acid mud, has the characteristics of echelon recovery of selenium, mercury and lead, environmental friendliness and the like, is simple to operate, and has good economic benefits.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of non-ferrous metal smelting, and particularly relates to a method for recovering selenium and mercury from acid sludge. BACKGROUND

[0002] In the process of non-ferrous metal smelting, flue gas containing a large amount of sulfur dioxide is sent to an acid production process to produce sulfuric acid. The by-products or hazardous waste produced in the acid production process is acid sludge, which is complex in composition and includes unreacted sulfides, heavy metals (such as lead, zinc, copper, selenium, mercury, etc.), sulfates, and acidic liquids, and has corrosive and potential toxic properties, and needs to be properly treated to avoid environmental pollution.

[0003] Currently, the treatment methods of acid sludge include fire process, wet process and neutralization and solidification. The fire process mainly uses calcium addition and selenium fixation roasting to remove mercury, and recovers mercury, selenium, lead and the like in stages. The main advantage of this process is high mercury removal efficiency and large treatment capacity, but the disadvantage is large equipment investment, and a large amount of lime needs to be added during the roasting process. In the process of selenium recovery, a large amount of lead-containing calcium sulfate slag is produced, and the treatment of lead-containing calcium sulfate still requires a cost. There are many research processes for wet treatment of acid sludge, mainly including "sulfuric acid + hydrochloric acid + oxidizing agent" leaching system, "hydrochloric acid + oxidizing agent" leaching system, "sulfuric acid + oxidizing agent" leaching system, and sodium sulfite leaching system. Selenium, mercury and other elements are first leached into the solution, and then mercury, selenium and other elements are recovered by precipitation. The main advantage of this process is less mercury pollution on site, but the disadvantage is large amount of wastewater, and the treatment of chlorine-containing mixed acid wastewater is difficult, the corrosion resistance requirement of on-site equipment is high, and the treatment cost is high. The neutralization and solidification method mainly adds calcium oxide and solidifying agent to the acid sludge to solidify it, so that the solidified body has a structure similar to that of ceramics, and has chemical stability and high strength characteristics. This process only considers harmless treatment, and does not recover rare metals such as mercury and selenium.

[0004] The invention patent with publication number CN115341097A relates to a method for treating high-arsenic low-mercury selenium acid sludge by wet process, which comprises: (1) chlorination leaching, high-arsenic low-mercury selenium acid sludge is subjected to oxidative leaching in a hydrochloric acid system; (2) selenium reduction removal, a reducing agent is added to the obtained leaching solution to reduce selenium; (3) sulfidation and precipitation of mercury and copper, a sulfidation agent is added to the deselenized solution to precipitate and enrich mercury and copper, and after sufficient reaction, solid-liquid separation is performed to obtain mercury and copper enriched material and mercury and copper removed solution; (4) arsenic and bismuth removal, the sulfidation method or lime neutralization method is used to remove arsenic and bismuth, and after sufficient reaction, solid-liquid separation is performed to obtain high-arsenic slag and purified filtrate. The invention uses a wet process to treat high-arsenic mercury selenium acid sludge and stepwise recovers selenium and mercury therein. The invention has a long process when treating acid sludge, has high requirements for corrosion resistance of equipment and plant, generates toxic gases such as hydrogen sulfide when performing steps such as sulfidation and copper precipitation, has a large amount of wastewater, and has high treatment cost; the invention patent with publication number CN112795774A relates to a method for separating and recovering copper, selenium, mercury and lead containing multi-metal acid sludge, which comprises: (1) roasting and volatilization, the acid sludge is mixed with sodium carbonate and sodium nitrate and then is subjected to roasting, and mercury is recovered after condensation of roasting flue gas; (2) water leaching and selenium separation, the roasted sand is subjected to water leaching, the leaching residue is sent to a copper and lead recovery system, and the leaching solution is used for separating and recovering selenium; (3) reduction and selenium precipitation, the water leaching solution is adjusted in acidity and then is subjected to reduction by blowing SO2 gas to obtain selenium powder; (4) acid leaching and copper separation, the water leaching residue is subjected to sulfuric acid leaching, copper enters the solution and is concentrated and crystallized to obtain copper sulfate product, and lead is retained in the residue as lead smelting raw material. The invention uses oxidative roasting to treat copper, selenium, mercury and lead acid sludge and stepwise recovers selenium, mercury, lead and copper therein. The invention uses a combination of oxidative roasting and wet process, has a long process, needs to add sodium carbonate and sodium nitrate during roasting, and has high production cost. The invention patent uses low-temperature acidification roasting, only adds low-cost sulfuric acid as additive, controls roasting temperature, enriches most of mercury in roasting residue, and mainly recovers selenium in the form of selenium dioxide in flue gas, reduces crude selenium in a selenium absorption tower, and recovers mercury in the roasting residue by vacuum distillation.

[0005] The acid sludge is a high-value hazardous solid waste containing metals such as selenium and mercury, and unreasonable treatment can easily pollute the environment and waste rare and high-value mineral resources. Therefore, there is an urgent need for a method for efficiently recovering high-value rare metals such as selenium and mercury. SUMMARY

[0006] Based on the problems in the background art, the invention overcomes the deficiencies in the prior art and provides a method for recovering selenium and mercury from acid sludge. The acid sludge produced in the purification process of the sulfuric acid production process is slurried with concentrated sulfuric acid and subjected to low-temperature roasting to preliminarily separate mercury and selenium, the roasting residue is subjected to a distillation process to recover mercury in the acid sludge, and the distillation residue is returned to a lead system to recover lead in the acid sludge.

[0007] The application is realized by the following technical scheme: a method for recovering selenium and mercury from acid sludge in sulfuric acid production, and the specific steps are as follows: (1) Slurry: the acid sludge produced by the purification system in the sulfuric acid production process is slurried with concentrated sulfuric acid at a certain ratio, the mass and volume ratio of the acid sludge and the concentrated sulfuric acid is controlled at 1:0.15~0.3, the slurry time is controlled at 1~2h, and then the slurry is transferred to a roasting furnace; (2) Roasting: the slurry is sent into a roasting furnace for low-temperature acidification roasting, the roasting temperature is controlled at 340~440℃, the roasting time is controlled at 10~20h, the negative pressure in the furnace during the roasting process is controlled at-50~-1000Pa, the roasting flue gas is sent into a selenium absorption tower to recover crude selenium, and the roasting residue is sent into a distillation process; (3) Distillation: the roasting residue is sent into a distillation furnace for distillation, the distillation temperature is controlled at 450~800℃, the distillation time is controlled at 1~2h, the outlet temperature of the condenser needs to be less than 30℃, the flue gas is recovered after passing through the condenser, the distillation residue is returned to a lead smelting system to recover lead, gold, silver and other metals; Preferably, in the roasting process of step (2), the roasting furnace can be a muffle furnace, a rotary kiln, a steel belt furnace or other forms of roasting furnace. Preferably, in the distillation process of step (3), the distillation method can be atmospheric distillation, reduced pressure distillation or vacuum distillation.

[0008] The main mechanism involved in the method for recovering selenium and mercury from acid sludge in sulfuric acid production is as follows: In the acid sludge produced by the purification process in the sulfuric acid production process, mercury mainly exists in the form of mercury sulfide and mercury selenide, selenium exists in the form of elemental selenium and mercury selenide, and lead exists in the form of lead sulfate. During low-temperature acidification roasting, mercury sulfide and mercury selenide react with sulfuric acid to generate sulfur dioxide, selenious acid and mercury sulfate, and selenium reacts with sulfuric acid to generate selenious acid and sulfur dioxide; at a roasting temperature of 340~440℃, mercury sulfate does not decompose and remains in the roasting residue, and selenious acid decomposes into selenium dioxide and water vapor into the flue gas, in the selenium absorption tower, the selenium dioxide in the flue gas dissolves in water and is reduced to crude selenium by SO2 in the flue gas, thereby realizing the separation of selenium and mercury.

[0009] (1) Low-temperature acidification roasting reaction process:

[0010] (2) Dissolution of selenium dioxide in water and reduction reaction process:

[0011] After low-temperature roasting, the mercury in the acid sludge is in the form of mercury sulfate in the roasting slag, and when the roasting slag is distilled at a temperature above 450 DEG C, the mercury sulfate decomposes into mercury vapor, sulfur dioxide and oxygen into the flue gas, and the mercury in the flue gas is converted from gas to liquid after the flue gas passes through the condenser, realizing the recovery of mercury.

[0012] (3) roasting slag distillation reaction process:

[0013] The beneficial effects of the present application are: (1) The process has the characteristics of good selenium and mercury separation effect, more than 90% of the mercury is enriched in the roasting slag, and more than 93% of the selenium is enriched in the crude selenium, realizing efficient separation of selenium and mercury in the acid sludge; (2) The process can realize the step-by-step recovery of valuable elements such as selenium, mercury, lead and silver in the acid sludge, and has high resource utilization level and high utilization degree; (3) The process has high automation level, and the production process is easy to realize, only needs to be transformed on the basis of existing production equipment, is simple to operate, and has low production cost. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is the process flow chart of the present application. DETAILED DESCRIPTION

[0015] The present application will be further described below in combination with the drawings and specific embodiments. EMBODIMENT

[0016] The composition of the acid sludge in the sulfuric acid production process is as follows: Acid sludge composition Name Pb (%) Se (%) Hg (%) Cu (%) Zn (%) As (%) S（%） Au (g / t) Ag (g / t) Acid sludge 41.44 10.13 3.12 0.13 0.018 0.57 6.81 0.20 644.7 The acid sludge is mixed with 98% concentrated sulfuric acid at a mass to volume ratio of 1:0.3, and is slurried for 2 hours, then is transferred into a roasting furnace for roasting, the negative pressure is controlled at-600Pa, the roasting temperature is controlled at 380 DEG C, and the roasting time is controlled at 20 hours, during the roasting process, the flue gas is absorbed into the selenium fourth-stage absorption tower, after the roasting is completed, the crude selenium is discharged from the bottom of the selenium absorption tower, and the roasting slag is transferred into a vacuum distillation furnace.

[0017] The roasting slag transferred into the vacuum distillation furnace is distilled, the distillation temperature is controlled at 500 DEG C, the distillation furnace pressure is controlled at 50~80Pa, the condenser outlet temperature is controlled at 30 DEG C, the distillation time is 2h, after the distillation is completed, the crude mercury is discharged from the bottom of the condenser, and the distillation residue is returned to the lead system for lead recovery. Roasting slag composition Name Pb (%) Se (%) Hg (%) Cu (%) Zn (%) Roasted slag 51.36 0.66 3.21 0.15 0.02 Distillation residue composition Name Pb (%) Se (%) Hg (%) Cu (%) Zn (%) Distillation residue 54.08 0.036 0.011 0.16 0.02 Example

[0018] The acid sludge composition in the sulfuric acid production process is as follows: Acid sludge composition Name Pb (%) Se (%) Hg (%) Cu (%) Zn (%) As (%) S（%） Au (g / t) Ag (g / t) Acid sludge 42.53 5.98 2.14 0.16 0.012 0.32 8.82 1.70 598.8 The acid sludge is mixed with 98% concentrated sulfuric acid at a mass to volume ratio of 1:0.2, and is slurried for 2 hours, and then is transferred into a roasting furnace for roasting. During the roasting process, the negative pressure is controlled at -300 Pa, the roasting temperature is controlled at 400°C, and the roasting time is controlled at 16 hours. During the roasting process, the flue gas is introduced into a selenium fourth-stage absorption tower for absorption. After the roasting is completed, crude selenium is discharged from the bottom of the selenium absorption tower, and the roasting residue is transferred into a vacuum distillation furnace.

[0019] The roasting residue transferred into the vacuum distillation furnace is distilled. The distillation temperature is controlled at 550°C, the distillation furnace pressure is controlled at 50-80 Pa, the condenser outlet temperature is controlled at 25-28°C, the distillation time is 1.5 hours, and after the distillation is completed, crude mercury is discharged from the bottom of the condenser, and the distillation residue is returned to the lead system for lead recovery. During the low-temperature acidizing roasting and vacuum distillation process, the roasting residue and the distillation residue are sampled and tested, and the test results are as follows: Roasting residue composition Name Pb (%) Se (%) Hg (%) Cu (%) Zn (%) Roasted slag 52.61 0.32 2.20 0.19 0.01 Distillation residue composition Name Pb (%) Se (%) Hg (%) Cu (%) Zn (%) Distillation residue 55.37 0.03 0.01 0.20 0.01

Claims

1. A method for recovering selenium and mercury from acid sludge, characterized in that... The specific steps are as follows: (1) Pulping: The acid sludge produced by the purification system during the sulfuric acid production process is pulverized with concentrated sulfuric acid in a certain proportion. The mass and volume ratio of acid sludge to concentrated sulfuric acid is controlled at 1:0.15~0.3, and the pulverization time is controlled at 1~2h. After pulverization, it is transferred to the roasting furnace. (2) Roasting: The slurry acid mud is sent into the roasting furnace for low-temperature acid roasting. The roasting temperature is controlled at 340~440℃ and the roasting time is controlled at 10~20h. During the roasting process, the negative pressure in the furnace is controlled at -50~-1000Pa. The roasting flue gas is sent into the selenium absorption tower to recover crude selenium, and the roasting residue is sent into the distillation process. (3) Distillation: The roasted residue is sent into the distillation furnace for distillation. The distillation temperature is controlled at 450~800℃ and the distillation time is controlled at 1~2h. The condenser outlet temperature must be less than 30℃. After the flue gas passes through the condenser, crude mercury is recovered. The distillation residue is returned to the lead smelting system to recover lead, gold, silver and other metals.

2. The method for recovering selenium and mercury from acid sludge according to claim 1, characterized in that: In step (2), the roasting process can be carried out in a roasting furnace such as a muffle furnace, rotary kiln, or steel belt furnace.

3. The method for recovering selenium and mercury from acid sludge according to claim 1, characterized in that: In step (3), the distillation process can be carried out by atmospheric distillation, vacuum distillation, or vacuum distillation.

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