Method for selectively removing trace impurity elements in phosphorus-iron slag

Abstract

This invention discloses a method for selectively removing trace impurity elements from ferrophosphate slag, belonging to the technical field of hydrometallurgy and comprehensive utilization of secondary resources. The method includes the following steps: S1. Crushing the ferrophosphate slag to -150 mesh, oxidizing and roasting it at 500-600℃ for 1.5-2.5 hours in air or an oxygen-enriched atmosphere to volatilize some arsenic, which is then absorbed by an alkaline solution; S2. Adjusting the roasted slag into a slurry with a liquid-to-solid ratio of 3:1-6:1, adding sulfuric acid to adjust the pH to 1.0-2.0, and controlling the H2SO4 mass concentration to 3%-8%; S3. Adding NaCl to make Cl... ‑ With a concentration of 0.3~1.0 mol / L, hydrogen peroxide or sodium hypochlorite (dosage 1.5%~4.0%) is added, and the oxidation-reduction potential (ORP) is controlled at +350~+500 mV. Leaching is carried out at 30~60℃ for 1~3 hours. After three solid-phase washings (S4), purified phosphorus-iron concentrate is obtained. The filtrates are combined and the pH is adjusted to 8~9 with lime milk to precipitate and recover lead and arsenic. This invention employs a combined process of roasting pre-arsenic removal and acidic complexation oxidation, solving the problem of high-arsenic material processing. It achieves efficient and selective removal and resource recovery of lead and arsenic, with low main iron and phosphorus loss rates, stable process, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgy and comprehensive utilization of secondary resources, specifically a method for the selective removal of trace impurity elements from iron phosphate slag. Specifically, it relates to a method for selectively removing trace harmful elements such as lead (Pb) and arsenic (As) from iron phosphate slag in an acidic system using a complexation-oxidation synergistic effect. Background Technology

[0002] Iron phosphate slag is the main solid waste discharged during the production of yellow phosphorus. With the rapid development of my country's phosphate chemical industry, the annual stockpile of iron phosphate slag has reached millions of tons. Traditional methods of treating iron phosphate slag mainly involve simple stockpiling or use as a low-grade steelmaking coolant. This not only results in a huge waste of iron and phosphorus resources but also occupies a large amount of land and poses environmental risks.

[0003] In recent years, with the explosive growth of the new energy industry, the preparation of battery-grade iron phosphate (FePO4) or lithium iron phosphate (LiFePO4) precursors using iron phosphate slag has become an important direction for the high-value utilization of resources. However, this high-value utilization path places extremely high demands on the purity of the raw materials.

[0004] Some phosphorus slag (especially slag from small and medium-sized yellow phosphorus plants using low-grade phosphate rock) contains trace amounts of heavy metal impurities, such as lead (Pb, 50~500ppm) and arsenic (As, 20~200ppm).

[0005] Lead is difficult to remove from the lithium iron phosphate lattice. If the content exceeds the standard (usually required to be <50ppm or even lower), it will seriously damage the electrochemical stability of the battery material, leading to an increase in the battery's self-discharge rate and even causing safety hazards.

[0006] Arsenic is not only a highly toxic element with extremely strict environmental emission standards, but it also easily volatilizes during high-temperature sintering, corroding kiln equipment and polluting the production environment.

[0007] Existing technologies mainly include strong acid leaching and high-temperature roasting, but all have obvious limitations: 1) High-concentration sulfuric acid or hydrochloric acid is typically used for leaching at high temperatures. While this method can remove lead and arsenic, it is a non-selective dissolution process, resulting in a large amount of iron (Fe) and phosphorus (P) from the phosphate slag also dissolving into the solution. This not only causes the loss of the main metal resources (iron loss is usually >10%), but also leads to a huge load on subsequent wastewater treatment, a large amount of neutralization slag, and poor economic benefits.

[0008] 2) Although the volatility of arsenic can be used for removal, the removal effect on lead is limited (lead has a high boiling point and is difficult to volatilize), and the high-temperature process has extremely high energy consumption, easily generates arsenic-containing flue gas, imposes stringent requirements on exhaust gas treatment equipment, and poses a risk of secondary pollution.

[0009] 3) Current conventional mineral processing or physical separation methods cannot effectively separate chemically derived lead and arsenic with extremely fine particle sizes.

[0010] In summary, how to achieve highly selective removal of trace amounts of lead and arsenic from phosphorus-iron slag under mild conditions, while retaining the main iron and phosphorus components to the greatest extent possible without dissolution, is a technical challenge that urgently needs to be solved in the field of solid waste resource utilization in the phosphorus chemical industry. Summary of the Invention

[0011] To address the aforementioned problems, this invention provides a method for the selective removal of trace impurity elements from phosphorus-iron slag.

[0012] Includes the following steps: S1 Oxidative Roasting Pre-arsenic Removal: The phosphorus iron slag is crushed to -150 mesh (≤106μm) and oxidized and roasted at 500~600℃ for 1.5~2.5 hours in air or oxygen-enriched atmosphere, so that some arsenic volatilizes into the gas phase. The arsenic-containing flue gas is absorbed by dust collection and alkaline spraying to obtain roasted slag. S2 Slurry preparation and acidification: The roasted slag obtained from S1 is mixed with water at a liquid-to-solid mass ratio of 3:1 to 6:1; sulfuric acid is added to adjust the pH of the slurry to 1.0 to 2.0, and the H2SO4 mass concentration in the slurry is controlled at 3% to 8%; S3 Acidic Chlorination Complex Oxidative Leaching: NaCl is added to the acidic slurry obtained from S2 to reduce the Cl concentration in the slurry system. - The concentration reaches 0.3~1.0 mol / L; 30% industrial-grade hydrogen peroxide or sodium hypochlorite is added as an oxidant, with an addition amount of 1.5%~4.0% of the slurry mass; the redox potential (ORP) of the system is controlled at +350~+500mV (vs Ag / AgCl), and the leaching is carried out by stirring at a temperature of 30~60℃ for 1~3 hours, so that lead and residual arsenic enter the liquid phase in a soluble form; S4 Solid-Liquid Separation and Precipitation Recovery: After leaching, solid-liquid separation is performed. The obtained solid phase is washed three times (the solid-to-wash mass ratio is 2:1 each time) to obtain purified phosphorus iron concentrate. The filtrate and washing liquid are combined, and the pH is adjusted to 8-9 with lime milk to precipitate and recover lead and arsenic.

[0013] Specifically, in S1, the preferred oxidative calcination temperature is 550°C, and the preferred calcination time is 2 hours.

[0014] Specifically, in step S3, the leaching temperature is preferably 50°C, and the leaching time is preferably 2 hours.

[0015] Specifically, in S3, when hydrogen peroxide is used as an oxidant, its dosage is preferably 3% of the slurry mass.

[0016] Specifically, the initial lead content in the phosphorus-iron slag is 50-500 ppm, and the initial arsenic content is 20-500 ppm.

[0017] It has the following beneficial effects: (1) Staged removal and balanced load: Most of the arsenic is removed in advance by oxidative roasting (especially for high arsenic phosphorus iron slag, where As>500ppm), which reduces the processing pressure of the subsequent wet process system and avoids the enrichment of arsenic in the circulating acid.

[0018] (2) High selectivity and high efficiency: By strictly controlling the ORP in the range of +350~+500mV, the complexation dissolution of lead and the oxidative dissolution of arsenic are guaranteed, while the dissolution of iron and phosphorus is effectively inhibited.

[0019] (3) Under the conditions of the embodiments, the present invention can achieve a lead removal rate of ≥85%, a residual arsenic removal rate of ≥80%, and a purified phosphorus iron concentrate with Pb <50ppm and As <20ppm, which fully meets the raw material purity requirements of battery-grade lithium iron phosphate precursor. At the same time, the main iron loss rate is ≤3% and the phosphorus loss rate is ≤5%, resulting in high resource utilization.

[0020] (4) After the wet leachate is neutralized by lime milk, the effluent can meet the discharge standards, and the precipitate can be further refined, thus realizing the resource utilization of waste. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 This is a flowchart of the steps of a method for selectively removing trace impurity elements from phosphorus-iron slag according to the present invention. Detailed Implementation

[0023] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0024] The following detailed description of the implementation method of the present invention is in conjunction with the accompanying drawings. The description is only a partial embodiment and not all embodiments. For clarity, representations and descriptions unrelated to the present invention are omitted in the drawings and description.

[0025] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the following detailed description of the technical solution is provided. Obviously, the described embodiments are only a portion of the embodiments of this invention, not all of them, and should not be construed as limiting the scope of implementation of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0026] Example 1 This embodiment is a specific implementation of a method for selectively removing trace impurity elements from phosphorus-iron slag according to the present invention.

[0027] In this embodiment, 500g of phosphorus-iron slag (As 650ppm, Pb 200ppm) was taken and crushed to -150 mesh.

[0028] In this embodiment, the material is placed in a muffle furnace and calcined at 550°C for 2 hours in an air atmosphere. In this embodiment, the flue gas is absorbed by an alkaline solution to obtain a Na3AsO4 solution. The calcined residue is cooled and stored for later use.

[0029] In this embodiment, 2.0L of water was added to the roasted residue (containing approximately 150ppm of residual As) to make a slurry, and concentrated sulfuric acid was added to adjust the pH to 1.5 (with an H2SO4 concentration of approximately 4%).

[0030] In this embodiment, 120g of NaCl (Cl) was added. - Add 15 mL of 30% H2O2 (concentration 0.8 mol / L). Control the ORP at +400 mV and stir the reaction at 50 °C for 2 hours.

[0031] In this embodiment, filtration was performed, and the filter cake was washed three times (600 mL × 3). The filter cake analysis showed: Pb 18 ppm, As 12 ppm. The filtrate was adjusted to pH 8.5 with lime milk to precipitate lead and arsenic.

[0032] In this embodiment, the solid phase analysis after purification showed that Pb decreased to 22 ppm (removal rate 87.8%), and As decreased to 16 ppm (removal rate 83.2%). TFe was 48.1% (loss 1.1%), and P was 19.9% ​​(loss 4.3%).

[0033] In this embodiment, if the As content is extremely high (>500ppm), a roasting pre-oxidation-water leaching process is recommended. That is, roasting in air at 500~600℃ causes As2O3 to volatilize into the gas phase. The gas phase is then cleaned and washed to recover As2O3. The roasted residue is then subjected to wet Pb removal.

[0034] In this embodiment, ozonated air can be used instead of hydrogen peroxide as the oxidant, which is suitable for large-scale continuous operation, but requires an ozone generator and exhaust gas treatment device.

[0035] Example 2 This embodiment is an alternative to Embodiment 1.

[0036] In this embodiment, CaCl2 can be used instead of NaCl as the complexing agent, which is cheaper, but it should be noted that Ca... 2+ The impact on subsequent iron phosphate preparation is introduced.

[0037] In this embodiment, sulfide precipitation (adding Na2S or FeS) can be used instead of lime neutralization for waste liquid treatment. Lead and arsenic precipitate in the form of PbS / As2S3, and the precipitate has a lower impurity content, which can be further refined and recovered.

[0038] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for selectively removing trace impurity elements from phosphorus-iron slag, characterized in that, Includes the following steps: S1 Oxidative Roasting Pre-arsenic Removal: The phosphorus iron slag is crushed to -150 mesh (≤106μm) and oxidized and roasted at 500~600℃ for 1.5~2.5 hours in air or oxygen-enriched atmosphere, so that some arsenic volatilizes into the gas phase. The arsenic-containing flue gas is absorbed by dust collection and alkaline spraying to obtain roasted slag. S2 Slurry preparation and acidification: The roasted slag obtained from S1 is mixed with water at a liquid-to-solid mass ratio of 3:1 to 6:1; sulfuric acid is added to adjust the pH of the slurry to 1.0 to 2.0, and the H2SO4 mass concentration in the slurry is controlled at 3% to 8%; S3 Acidic Chlorination Complex Oxidative Leaching: NaCl is added to the acidic slurry obtained from S2 to reduce the Cl concentration in the slurry system. - The concentration reaches 0.3~1.0 mol / L; 30% industrial-grade hydrogen peroxide or sodium hypochlorite is added as an oxidant, with an addition amount of 1.5%~4.0% of the slurry mass; the redox potential (ORP) of the system is controlled at +350~+500mV (vs Ag / AgCl), and the leaching is carried out by stirring at a temperature of 30~60℃ for 1~3 hours, so that lead and residual arsenic enter the liquid phase in a soluble form; S4 Solid-Liquid Separation and Precipitation Recovery: After leaching, solid-liquid separation is performed. The obtained solid phase is washed three times (the solid-to-wash mass ratio is 2:1 each time) to obtain purified phosphorus iron concentrate. The filtrate and washing liquid are combined, and the pH is adjusted to 8-9 with lime milk to precipitate and recover lead and arsenic.

2. The method for selectively removing trace impurity elements from phosphorus-iron slag according to claim 1, characterized in that: In step S1, the preferred oxidative calcination temperature is 550°C, and the preferred calcination time is 2 hours.

3. The method for selectively removing trace impurity elements from phosphorus-iron slag according to claim 1, characterized in that: In step S3, the leaching temperature is preferably 50°C, and the leaching time is preferably 2 hours.

4. The method for selectively removing trace impurity elements from phosphorus-iron slag according to claim 1, characterized in that: In S3, when hydrogen peroxide is used as an oxidant, its dosage is preferably 3% of the slurry mass.

5. The method for selectively removing trace impurity elements from phosphorus-iron slag according to claim 1, characterized in that: The initial lead content in the phosphorus-iron slag is 50-500 ppm, and the initial arsenic content is 20-500 ppm.

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