Lepidolite smelting lithium residue comprehensive utilization method

Abstract

This invention provides a method for the comprehensive utilization of lithium slag from lepidolite smelting, relating to the field of solid waste treatment technology. The method includes the following steps: desalination: mixing the lepidolite smelting lithium slag with an aqueous solution, performing multi-stage washing and pressure filtration at 40-60°C to obtain filter cake and filtrate A; impurity removal; evaporation and salt extraction: treating the high-salt purified liquid using vacuum pervaporation and thermal pervaporation methods respectively to precipitate potassium sulfate and sodium sulfate, obtaining industrial-grade sodium sulfate and potassium sulfate products respectively. This invention enables lithium slag to be desalinated, impurity-removed, and weight-reduced into general solid waste, while obtaining higher purity industrial-grade sodium sulfate and potassium sulfate products, thus improving enterprise efficiency and quality.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, specifically to a method for the comprehensive utilization of lithium slag from lithium mica smelting. Background Technology

[0002] Lithium slag from lepidolite smelting is a residue generated during the sulfuric acid process for producing lithium salts from lepidolite ore. Current lithium salt extraction processes from lepidolite ore produce lithium slag with very fine particles, high salt content, and thallium pollution, impacting the ecological balance of surrounding areas. Therefore, how to achieve resource utilization of lithium slag is an urgent problem to be solved.

[0003] Currently, some lithium slag is used as a raw material in cement production and concrete building materials. However, the high sulfate content in lithium slag leads to a decline in the quality of cement and building materials produced by mixing lithium slag with other materials, affecting the treatment and use of lithium slag. Furthermore, the presence of thallium salts in lithium slag poses environmental risks when used in building materials. Therefore, there is an urgent need to develop a more energy-efficient, effective, and stable lithium slag treatment process. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a method for the comprehensive utilization of lithium slag from lithium mica smelting.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for comprehensive utilization of lithium slag from lepidolite smelting, characterized by comprising the following steps:

[0009] (1) Desalination treatment: The lithium slag from the lithium mica smelting process is mixed and stirred with an aqueous solution, and then subjected to multi-stage washing and pressure filtration to obtain filter cake and filtrate A.

[0010] (2) Impurity removal treatment:

[0011] (21) Add a first alkaline compound to the filtrate A to adjust the pH to 8-11, stir to generate a precipitate, add a flocculant, and then microfilter to obtain the first filtrate.

[0012] (22) Add a second alkaline compound or acidic compound to the first filtrate, adjust the pH of the first filtrate, stir to generate a precipitate, add a flocculant, and ultrafilter to obtain the second filtrate.

[0013] (23) First, add an oxidant to the second filtrate for treatment, then add sodium sulfide and stir to generate a precipitate, then add a flocculant and ultrafilter to obtain filtrate B. Add a chelating agent to filtrate B, stir to generate a precipitate, then add a flocculant and ultrafilter to obtain a high-salt purified liquid.

[0014] (3) Evaporation and salt extraction: The high-salt purification solution was treated by vacuum pervaporation and thermal pervaporation to precipitate potassium sulfate and sodium sulfate, respectively, to obtain industrial-grade sodium sulfate and potassium sulfate products.

[0015] Preferably, in step (1), the multi-stage washing and pressure filtration is a three-stage washing and pressure filtration, specifically including the following steps:

[0016] (1) Primary stirring and pressure filtration: Add primary filtrate water and secondary filtrate water to lithium smelting lepidolite slag, with a solid-liquid mass ratio of 1:(2-4), stir and wash at 40-60℃, add caustic soda and soda ash at a mass ratio of 8:2 to adjust the pH of the slurry to 8.0-8.5, pump it into a vacuum belt filter press for pressure filtration to obtain primary filter cake and primary filtrate. When the sulfate concentration of the primary filtrate is <120g / L, it is returned to the primary filtrate tank; otherwise, it enters the high-salt filtrate storage tank.

[0017] (2) Secondary stirring and filtration: The primary filter cake is added to the tertiary filtrate water at a solid-liquid mass ratio of 1:(2-4), stirred and washed at 40-60°C, and then pumped into a vacuum belt filter press for filtration to obtain a secondary filter cake and a secondary filtrate. The secondary filtrate enters the secondary filtrate tank.

[0018] (3) Three-stage stirring and filtration: Add the secondary filter cake to evaporated water or fresh tap water, with a solid-liquid mass ratio of 1:(2-4), stir and wash at 40-60°C, and pump it into a vacuum belt filter press to obtain a tertiary filter cake and a tertiary filtrate. The tertiary filtrate enters the tertiary filtrate tank.

[0019] The three-stage filter cake is used as a Class I solid waste in general industrial solid waste.

[0020] The filtrate in the high-salt water storage tank is filtrate A.

[0021] Preferably, the vacuum belt filter has a vacuum degree of -0.09MPa to -0.05MPa, an operating speed of 3 to 7m / min, a fabric feeding device frame structure made of 316L stainless steel, an acid and alkali resistant and high temperature resistant EPDM rubber for the belt, and a filter cake layer thickness of 3 to 80mm.

[0022] The vacuum belt filter with three-stage agitation and pressure filtration is equipped with a backwashing device. The backwashing medium is clean water, and the backwashing water pressure is 0.2MPa to 1MPa.

[0023] Preferably, in the method for comprehensive utilization of lithium slag from lithium mica smelting as described in claim 1, in step (2), the flocculant is composed of polyacrylamide, polyaluminum chloride, and polyferric chloride in a mass ratio of (8-10):(1-2):1; in step (21), the amount of flocculant added is 25 mg / L; and in steps (22) and (23), the amount of flocculant added is 10 mg / L.

[0024] Preferably, in step (2), the stirring speed is 50–120 r / min;

[0025] In step (21), sodium hydroxide or potassium hydroxide is added first to adjust the pH to 8-11. Microfiltration for impurity removal specifically includes: using a PCF fiber bundle filter with a filtration speed of 0.3-0.8 m / h and a transmembrane pressure difference of 0.02-0.08 MPa; the impurities include calcium and magnesium ions and iron and copper ions.

[0026] Preferably, in step (22), ultrafiltration specifically includes: using hollow fiber modules, the ultrafiltration membrane module having a tubular structure, a transmembrane pressure difference of 0.01 to 0.045 MPa, an operating pressure of 0.1 to 0.5 MPa, shear cross-flow filtration, a membrane surface water velocity of 0.05 to 0.25 m / s, a feed temperature of 40 to 60°C, external pressure ultrafiltration, a reflux ratio R = reflux flow rate / permeate flow rate of 0.3 to 2, a water flux of 0.3 to 0.6 NWP, an influent turbidity of less than 50 NTU, suspended particulate matter of less than 100 μm, and COD of less than 50 mg / L.

[0027] Preferably, in step (23), the oxidant is selected from any one of ozone, sodium peroxide, potassium peroxide, or hydrogen peroxide; the ultrafiltration adopts a plate and frame structure with dead-end filtration, the ultrafiltration membrane material is polyvinylidene fluoride, the shell material is rigid polyvinyl chloride, the operating pressure is 0.1-0.3 MPa, the feed temperature is 40-60℃, the water flux is 0.5-0.8 NWP, and the water turbidity is less than 15 NTU; the deep ultrafiltration adopts a plate and frame structure with dead-end filtration, the ultrafiltration membrane material is polyvinylidene fluoride, the shell material is rigid polyvinyl chloride, the operating pressure is 0.1-0.3 MPa, the feed temperature is 40-60℃, and the water flux is 0.5-0.8 NWP.

[0028] Preferably, in step (3), potassium sulfate and sodium sulfate are precipitated from the high-salt purification solution using vacuum pervaporation and thermal pervaporation methods, respectively, specifically including:

[0029] When the potassium content in the high-salt purified solution is greater than 96% sodium, the solution is heated to 40°C in the first heater, then concentrated in a vacuum permeation membrane evaporator until the solubility in sodium sulfate brine is <29.8% wt and the solid content is 10-60%, precipitating potassium sulfate. The concentrated solution is then kept at 40°C in the first insulator, further concentrated in the first thickener, and then separated in the first centrifuge to obtain potassium sulfate product. The sodium-rich mother liquor from the first thickener and first centrifuge is heated to 100-105°C in the second heater, then evaporated and concentrated in a thermal permeation membrane evaporator until the solubility in potassium sulfate brine is <19.4% wt and the solid content is 10-60%, precipitating potassium sulfate. Sodium sulfate is first heated to 100°C in a second insulator, then further concentrated in a second thickener before entering a second centrifuge for separation to obtain sodium sulfate product. The mother liquor from the second thickener and centrifuge is returned to the potassium-rich feed point, heated to 40°C in a first heater, and then concentrated in a vacuum permeate membrane evaporator until the solubility in the sodium sulfate solution is <29.8%wt and the solid content is 10-60%, precipitating potassium sulfate. The concentrated solution is then heated to 40°C in a first insulator, further concentrated in a first thickener before entering a first centrifuge for separation to obtain potassium sulfate product. The sodium-rich mother liquor from the first thickener and centrifuge is returned to the potassium-rich feed point.

[0030] Preferably, in step (3), potassium sulfate and sodium sulfate are precipitated from the high-salt purification solution using vacuum pervaporation and thermal pervaporation methods, respectively, specifically including:

[0031] When the potassium ion content in the purified solution is <96% sodium, the high-salt purified solution is heated to 100-105°C in the second heater, and then concentrated by evaporation in a thermal permeation membrane evaporator until the solubility in potassium sulfate brine is <19.4% wt and the solid content is 10%-60%, precipitating sodium sulfate. The concentrated solution is then kept at 100°C in the second insulator, and then further concentrated in the second thickener before entering the second centrifuge for separation to obtain sodium sulfate product. The mother liquor from the second thickener and the second centrifuge is returned to the potassium-rich feed point. After being heated to 40°C in the first heater, the solution is concentrated by vacuum permeation membrane evaporator until the solubility in sodium sulfate brine is <29.8% wt and the solid content is 10-60%, precipitating potassium sulfate. The concentrated solution is then kept at 40°C in the first insulator, and then further concentrated in the first thickener before entering the first centrifuge for separation to obtain potassium sulfate product. The sodium-rich mother liquor from the first thickener and the first centrifuge enters the sodium-rich feed point.

[0032] Preferably, in step (3), the vacuum pervaporation method uses a water ring vacuum pump to draw a vacuum, with an absolute pressure of 50 kPa to 150 kPa, a pressure difference of 1.5 kPa to 5 kPa across the membrane, the pervaporation membrane material is polytetrafluoroethylene, the structure is tubular, the operating pressure is external pressure, the structural components are 2205 duplex stainless steel, and the vacuum pump vacuum degree is -0.095 to -0.065 MPa; the thermal pervaporation method uses a slight negative pressure operation at the condensing end, with a pressure difference of 1.5 kPa to 3 kPa between the hot end and the condensing end, the pervaporation membrane material is polytetrafluoroethylene, the structure is tubular, the operating pressure is external pressure, and the structural components are titanium.

[0033] (III) Beneficial Effects

[0034] This invention provides a method for the comprehensive utilization of lithium slag from lepidolite smelting. Compared with existing technologies, it has the following advantages:

[0035] The method for comprehensive utilization of lithium slag from lithium mica smelting in this invention includes the following steps: (1) Desalination treatment: the lithium slag raw material is mixed with an aqueous solution and subjected to multi-stage stirring and filtration treatment; (2) Impurity removal treatment: the first stage is to perform preliminary microfiltration to remove impurities by adjusting the pH; the second stage is to take the filtrate from the first stage, add sodium carbonate and flocculant for ultrafiltration to remove calcium, magnesium and other metal ions; the third stage is to take the filtrate from the second stage, add an oxidant for thallium removal pretreatment, and then add sodium sulfide, chelating agent and flocculant for two-step deep ultrafiltration to remove thallium; (3) take the high-salt purified liquid, and use the pervaporation process to perform vacuum pervaporation to precipitate potassium sulfate, and thermal pervaporation to precipitate sodium sulfate, to obtain industrial-grade sodium sulfate and potassium sulfate products; under the above process, this invention not only realizes that lithium slag becomes general solid waste after desalination, impurity removal and weight removal, but also obtains higher purity industrial-grade sodium sulfate and potassium sulfate products, thereby improving the quality and efficiency of enterprises. Attached Figure Description

[0036] 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 these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the desalination process of the present invention.

[0038] Figure 2 This is a schematic diagram of the impurity removal process of the present invention.

[0039] Figure 3 This is a schematic diagram of the evaporation and salt extraction process of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0042] Example 1

[0043] This embodiment provides a method for the comprehensive treatment of lithium slag from lepidolite smelting, including the following steps:

[0044] (1) Multi-stage water washing and desalination treatment

[0045] The lithium slag raw material is mixed and stirred with an aqueous solution, and then subjected to multi-stage washing and pressure filtration at 40°C. The solid-liquid ratio of the washing solution is 1:3. The process includes the following steps.

[0046] a. Primary washing and filter press: Add primary filtrate water and secondary filtrate water to the lithium slag raw material, control the solid-liquid mass ratio to 1:3, add soda ash to adjust the pH of the slurry to between 8.0 and 8.5, pump it into the filter press, and obtain primary filter cake and primary filtrate through vacuum belt filter press. When the sulfate concentration of the primary filtrate is <120g / L, it is returned to the primary filtrate tank; otherwise, it enters the high-salt filtrate storage tank.

[0047] b. Secondary washing and pressure filtration: Add the primary filter cake to the tertiary filtrate water, control the solid-liquid mass ratio to 1:3, add soda ash to adjust the pH of the slurry to between 7.0 and 8.0, pump it into the filter press, and obtain the secondary filter cake and secondary filtrate through vacuum belt filtration. The secondary filtrate enters the secondary filtrate tank.

[0048] c. Three-stage washing and pressure filtration: Add evaporating water or fresh tap water to the secondary filter cake, control the solid-liquid mass ratio to 1:3, add soda ash to adjust the pH of the slurry to between 7.0 and 8.0, pump it into the filter press, and obtain the tertiary filter cake and tertiary filtrate through vacuum belt filtration. The tertiary filtrate enters the tertiary filtrate tank. The tertiary filter cake is backwashed using the backwashing device on the belt filter to control the moisture content of the tertiary filter cake to below 25% and the soluble sulfate content to <0.6%.

[0049] d. The three-stage filter cake is transferred to the solid waste warehouse for use as building material raw material. The sulfate content of the filtrate in the high-salt filtrate storage tank is >120g / L, and it enters the multi-stage impurity removal treatment.

[0050] The filter press used is a vacuum belt filter with a vacuum degree of -0.1MPa to -0.08MPa. The filter cake thickness is 20-30mm, and the operating speed is 4-5m / min. The filter cloth device is made of 316L stainless steel. The three-stage vacuum belt filter is equipped with a backwashing device, using clean water as the washing medium, with an operating water pressure of 0.2MPa to 1MPa. The belt material is made of acid- and alkali-resistant, high-temperature-resistant EPDM rubber.

[0051] (2) Multi-stage impurity removal

[0052] The flocculant is a mixture of polyacrylamide, polyaluminum chloride, and polyferric chloride in a mass ratio of 9:1.5:1. The flocculant dosage is 25 mg / L in the first stage of sedimentation and separation, and 10 mg / L in the second and third stages of flocculation and sedimentation. The stirring speed in the reactor is continuously 100 r / min.

[0053] Multi-stage impurity removal consists of the following steps:

[0054] In the first stage, the sulfate filtrate enriched in the first step is first adjusted to pH 8-9 with sodium hydroxide, and then 25 mg / L of flocculant is added to remove some calcium, magnesium, iron, copper and other metal ions. Flocculation and precipitation are carried out using a micro-flocculator, and the supernatant enters the microfiltration system. The microfiltration uses a PCF fiber bundle filter with a filtration rate of 0.3-0.4 m / h and a transmembrane pressure difference of 0.02-0.04 MPa.

[0055] The second stage involves adjusting the pH of the filtrate filtered by the PCF fiber bundle filter to 9-10 by adding sodium carbonate or sulfuric acid. After stirring for 25-35 minutes, 10 mg / L of flocculant is added. The ultrafiltration uses hollow fiber modules with a membrane pressure difference of 0.01-0.015 MPa, an operating pressure of 0.1-0.2 MPa, shear cross-flow filtration, a membrane surface water velocity of 0.05-0.1 m / s, a feed temperature of 40-50℃, and external pressure ultrafiltration. The reflux ratio R = reflux flow rate / permeate flow rate is 1, the water flux is 0.3-0.4 NWP, and the influent turbidity is less than 35 NTU.

[0056] In the third stage, the filtrate from the second stage is taken and 1.5 g / L of 3% hydrogen peroxide is added. The mixture is stirred and reacted for 60 minutes to perform thallium removal pretreatment. The pretreated brine is then treated with 500 mg / L sodium sulfide. After stirring to form a precipitate, 10 mg / L flocculant is added, and the thallium and other heavy metal ions are removed by ultrafiltration at 25–60 °C. In the second step of the third stage, the filtrate from the first stage is taken, and 150 mg / L of thallium removal chelating agent is added. After stirring to form a precipitate, 10 mg / L flocculant is added, and the thallium is removed by deep ultrafiltration to obtain a high-salt purified solution.

[0057] The first step of the third stage ultrafiltration uses a plate and frame structure with dead-end filtration. The ultrafiltration membrane is made of polyvinylidene fluoride (PVDF), and the shell material is made of rigid polyvinyl chloride (PVC). The operating pressure is 0.1–0.3 MPa, the feed temperature is 40–60°C, the water flux is 0.5–0.8 NWP, and the water turbidity is 12 NTU. The second step of the third stage ultrafiltration also uses a plate and frame structure with dead-end filtration. The ultrafiltration membrane is made of PVDF, and the shell material is made of rigid PVC. The operating pressure is 0.1–0.2 MPa, the feed temperature is 40–60°C, and the water flux is 0.5–0.55 NWP.

[0058] (3) Salt extraction by percolation evaporation

[0059] Since the purified solution has a high sodium content and low potassium content, sodium sulfate is first precipitated by thermal pervaporation, and then potassium sulfate is precipitated by vacuum pervaporation.

[0060] The specific steps are as follows:

[0061] When the potassium sulfate content in the purified solution is 36.5 g / L and the sodium sulfate content is 88.5 g / L, the potassium content in the purified solution is less than 96% sodium. The high-salt purified solution is then heated to 100–105°C in the second heater, and then concentrated by a thermal osmosis membrane evaporator until the potassium sulfate solution has a solubility of 18.8% wt and a solid content of 43.4%, precipitating sodium sulfate. The concentrated solution is then kept at 100°C in the second insulator, and further concentrated in the second thickener before entering the second centrifuge for separation to obtain the sodium sulfate product. The mother liquor from the second thickener and the second centrifuge is returned to the potassium-rich feed point. After cooling, the potassium-rich mother liquor is heated to 40°C in the first heater, then concentrated in a vacuum permeate membrane evaporator until the solubility in sodium sulfate brine is 26.0% wt and the solid content is 32.1%, precipitating potassium sulfate. The concentrated solution is then kept at 40°C in the first insulator, further concentrated in the first thickener, and then separated in the first centrifuge to obtain the potassium sulfate product. The mother liquor from the first thickener and the first centrifuge enters the sodium-rich feed point.

[0062] Vacuum pervaporation is performed using a water ring vacuum pump to achieve an absolute pressure of 60 kPa and a pressure difference of 2 kPa across the pervaporation membrane. The pervaporation membrane is made of polytetrafluoroethylene (PTFE) and has a tubular, externally pressurized structure. The structural components are made of 2205 duplex stainless steel, and the vacuum pump has a vacuum level of -0.09 MPa.

[0063] The thermal pervaporation condenser operates under slight negative pressure, with a pressure difference of 1.5 kPa to 3 kPa between the hot end and the condenser. The pervaporation membrane is made of polytetrafluoroethylene, and the structure is tubular with titanium components.

[0064] Based on the salt extraction process described in the above embodiments, lithium slag produced by lithium carbonate production enterprises was treated and experiments were conducted.

[0065] The main components of lithium slag are: Al2O3, SiO2, Na, K, and SO4. 2- Li2O, Ca, etc.

[0066] Using ion chromatography, atomic absorption spectrometry, and EDTA titration, the soluble ion content and leaching content of the heavy metal thallium in the raw materials and filter cake were determined in the above embodiments. The content of each ion in the purified solution was also determined. The results are shown in Table 1 below:

[0067] Table 1. Ion content in raw materials and filter cake, thallium leaching amount, and ion content in purified solution.

[0068]

[0069] According to the standards "Industrial Anhydrous Sodium Sulfate" (GBT 6009-2014) and "Agricultural Potassium Sulfate" (GBT 20406-2017), the sodium sulfate and potassium sulfate (calculated as potassium oxide) were determined under the treatment process of Example 1, and the results are shown in Table 2 below:

[0070] Table 2. Test results of sodium sulfate and potassium sulfate (potassium oxide meter)

[0071]

[0072] Example 2

[0073] This embodiment provides a method for the comprehensive treatment of lithium slag from lepidolite smelting, including the following steps:

[0074] (1) In the multi-stage water washing and desalination process, the lithium slag raw material is mixed and stirred with the aqueous solution, and multi-stage washing and pressure filtration are carried out at 40°C, with a solid-liquid mass ratio of 1:2.

[0075] a. Primary washing and pressure filtration: Add strong sodium oxide and soda ash to adjust the pH of the slurry to between 8.0 and 8.5. When the sulfate concentration of the primary filtrate is <100g / L, return it to the primary filtrate tank; otherwise, it enters the high-salt filtrate storage tank. Other steps and operating conditions are the same as in Example 1.

[0076] b. Secondary washing and filtration: Add soda ash to adjust the pH of the slurry to between 7.5 and 8.0. Other steps and operating conditions are the same as in Example 1.

[0077] c. Three-stage washing and pressure filtration: Add soda ash to adjust the pH of the slurry to between 7.5 and 8.0, backwash the filter cake, and control the moisture content of the three-stage filter cake to <25% and the soluble sulfate content to <0.5%;

[0078] The vacuum belt filter operates at a vacuum level of -0.1MPa to -0.05MPa, a filter cake layer thickness of 15 to 25mm, and a belt filter operating speed of 4 to 6m / min. Other steps and operating conditions are the same as in Example 1.

[0079] (2) In the multi-stage impurity removal step, the flocculant is a mixture of polyacrylamide, polyaluminum chloride and polyferric chloride in a mass ratio of 9:2:1, and the amount of flocculant added is the same as in Example 1.

[0080] Multi-stage impurity removal consists of the following steps:

[0081] In the first stage, sodium hydroxide is added to the sulfate filtrate enriched in the first step to adjust the pH to 9-10. The PCF fiber bundle filter has a filtration rate of 0.35-0.4 m / h and a transmembrane pressure difference of 0.03-0.04 MPa. Other aspects are the same as in Example 1.

[0082] After filtration through the second stage filter, sodium carbonate or sulfuric acid is added to adjust the pH to 9.5-10, and the rest is the same as in Example 1.

[0083] In the third stage, 1.5 L / h of ozone was added to the filtrate from the second stage, and the mixture was stirred for 60 minutes to perform thallium removal pretreatment. After pretreatment, 0.5 g / L of sodium sulfide was added to the saline solution, and after stirring to form a precipitate, 10 mg / L of flocculant was added. The solution was then subjected to ultrafiltration at 45–60 °C to remove thallium and other heavy metal ions. The other steps were the same as in Example 1.

[0084] (3) In the percolation evaporation salt extraction step

[0085] Since the purified solution has a high potassium content and low sodium content, potassium sulfate is first precipitated by vacuum pervaporation, and then sodium sulfate is precipitated by thermal pervaporation.

[0086] When the purified solution contains 64.5 g / L potassium sulfate and 58.5 g / L sodium sulfate, and the potassium ion content is greater than 96% sodium ion content, the purified solution is heated to 40°C in the first heater, then concentrated in a vacuum permeation membrane evaporator until the solubility in the sodium sulfate brine is 27.8% wt and the solid content is 33%, causing potassium sulfate to precipitate. The concentrated solution is then kept at 40°C in the first insulator, further concentrated in the first thickener, and then separated in the first centrifuge to obtain the potassium sulfate product. The sodium-rich mother liquor from the first thickener and the first centrifuge is heated to 100–105°C in the second heater, then evaporated and concentrated in a thermal permeation membrane evaporator until the solubility in the potassium sulfate brine is 19.4% wt and the solid content is 46%, causing sodium sulfate to precipitate. The concentrated solution is then kept at 100°C in the second insulator, further concentrated in the second thickener, and then separated in the second centrifuge to obtain the sodium sulfate product. The mother liquor from the second thickener and the second centrifuge is returned to the potassium-rich feed point. After being cooled to 40°C by the first heater, it is concentrated in a vacuum permeate membrane evaporator until the solubility in sodium sulfate brine is 27.8% wt and the solid content is 33%, precipitating potassium sulfate. The concentrated solution is then kept at 40°C by the first insulator and further concentrated in the first thickener before entering the first centrifuge for separation to obtain the potassium sulfate product. The sodium-rich mother liquor from the first thickener and the first centrifuge is returned to the potassium-rich feed point.

[0087] The vacuum pervaporation operation and equipment are the same as in Example 1.

[0088] Based on the salt extraction process described in the above embodiments, lithium slag produced by lithium carbonate production enterprises was treated and experiments were conducted. The same analytical methods as in Example 1 were used, and the results are shown in Table 3 below:

[0089] Table 3. Ion content in raw materials and filter cake, thallium leaching amount, and ion content in purified solution.

[0090]

[0091] According to the standards "Industrial Anhydrous Sodium Sulfate" (GBT 6009-2014) and "Agricultural Potassium Sulfate" (GBT 20406-2017), the sodium sulfate and potassium sulfate (calculated as potassium oxide) were determined under the treatment process of Example 2, and the results are shown in Table 4 below.

[0092] Table 4. Test results of sodium sulfate and potassium sulfate (potassium oxide meter)

[0093]

[0094] Example 3

[0095] This embodiment provides a method for the comprehensive treatment of lithium slag from lepidolite smelting, including the following steps:

[0096] (1) Multi-stage water washing and desalination treatment

[0097] The lithium slag raw material is mixed and stirred with an aqueous solution, and then subjected to multi-stage washing and pressure filtration at 40°C. The solid-liquid ratio of the washing solution is 1:4. The process includes the following steps.

[0098] a. Primary washing and filtration: Add the lithium slag raw material to the primary filtrate water and the secondary filtrate water, control the solid-liquid mass ratio to 1:4, pump it into the filter press, and obtain the primary filter cake and primary filtrate through vacuum belt filtration. When the sulfate concentration of the primary filtrate is <90g / L, it is returned to the primary filtrate tank; otherwise, it is sent to the high-salt filtrate storage tank.

[0099] b. Secondary agitation and pressure filtration:

[0100] The solid-liquid mass ratio was controlled at 1:4, and other steps and operating conditions were the same as in Example 1.

[0101] c. Three-stage washing and pressure filtration: Add evaporated water or fresh tap water to the secondary filter cake, control the solid-liquid mass ratio to 1:4, and obtain the tertiary filter cake and tertiary filtrate through vacuum belt pressure filtration. The tertiary filtrate enters the tertiary filtrate tank. The tertiary filter cake is backwashed using the backwashing device on the belt filter to control the moisture content of the tertiary filter cake to below 25% and the soluble sulfate content to <0.4%.

[0102] d. The three-stage filter cake is transferred to the solid waste warehouse for use as building material raw material. The sulfate content of the filtrate in the high-salt filtrate storage tank is >120g / L, and it enters the multi-stage impurity removal treatment.

[0103] The vacuum belt filter has a vacuum level of -0.1MPa to -0.06MPa and a filter cake layer thickness of 20 to 25mm. Other operating conditions and equipment are the same as in Example 1.

[0104] (3) Multi-stage impurity removal

[0105] The flocculant is a mixture of polyacrylamide, polyaluminum chloride, and polyferric chloride in a mass ratio of 8:2:1; wherein, the amount of flocculant added in the first stage of precipitation separation is 20 mg / L, and the other steps and operating conditions are the same as in Example 1.

[0106] Multi-stage impurity removal consists of the following steps:

[0107] In the first stage, sodium hydroxide is added to the sulfate filtrate enriched in the first step to adjust the pH to 9-10, and 20 mg / L of flocculant is added. The microfiltration rate is 0.2-0.4 m / h, and the transmembrane pressure difference is 0.01-0.04 MPa.

[0108] In the second stage, sodium carbonate or sulfuric acid is added to the filtrate filtered through the PCF fiber bundle filter to adjust the pH to 8-9. After flocculation, ultrafiltration is performed with a reflux ratio R of 1.5. Other steps and operating conditions are the same as in Example 1.

[0109] In the third stage, 0.1 g / L of sodium peroxide was added to the filtrate from the second stage for pretreatment. Then, 0.4 g / L of sodium sulfide was added, followed by flocculant. After filtration, 0.15 g / L of thallium removal chelating agent was added and stirred to generate a precipitate. Then, flocculant 1 was added. The other steps and operating conditions were the same as in Example 1. Thallium was removed by deep ultrafiltration to obtain a high-salt purified solution.

[0110] The equipment and ultrafiltration operating conditions for the third stage are the same as in Example 1.

[0111] (3) Salt extraction by percolation evaporation

[0112] Since the purified solution has a high sodium content and low potassium content, sodium sulfate is first precipitated by thermal pervaporation, and then potassium sulfate is precipitated by vacuum pervaporation.

[0113] The specific steps are as follows:

[0114] When the potassium sulfate content in the purified solution is 44.5 g / L and the sodium sulfate content is 79.5 g / L, the potassium content in the purified solution is less than 96% sodium. The high-salt purified solution is then heated to 100-105°C in the second heater, and then concentrated by a thermal osmosis membrane evaporator until the solubility in the potassium sulfate brine is 16.6% wt and the solid content is 19.4%, precipitating sodium sulfate. The concentrated solution is then kept at 100°C in the second insulator, and further concentrated in the second thickener before entering the second centrifuge for separation, yielding the sodium sulfate product. The mother liquor from the second thickener and the second centrifuge is returned to the potassium-rich feed point. Alternatively, after being heated to 40°C in the first heater, the solution is concentrated by a vacuum osmosis membrane evaporator until the solubility in the sodium sulfate brine is 22.0% wt and the solid content is 39.4%, precipitating potassium sulfate. The concentrated solution is then kept at 40°C in the first insulator, and further concentrated in the first thickener before entering the first centrifuge for separation, yielding the potassium sulfate product. The mother liquor from the first thickener and the first centrifuge enters the sodium-rich feed point.

[0115] The pervaporation equipment and vacuum operating conditions and procedures are the same as in Example 1.

[0116] Based on the salt extraction process described in the above embodiments, lithium slag produced by lithium carbonate production enterprises was treated and experiments were conducted. The same analytical methods as in Example 1 were used, and the results are shown in Table 5 below.

[0117] Table 5. Ion content in raw materials and filter cake, thallium leaching amount, and ion content in purified solution.

[0118]

[0119] According to the standards "Industrial Anhydrous Sodium Sulfate" (GBT 6009-2014) and "Agricultural Potassium Sulfate" (GBT 20406-2017), the sodium sulfate and potassium sulfate (calculated as potassium oxide) were determined under the treatment process of Example 3, and the results are shown in Table 6 below:

[0120] Table 6. Test results of sodium sulfate and potassium sulfate (potassium oxide meter)

[0121]

[0122] Example 4

[0123] In the multi-stage water washing and desalination process, the lithium slag raw material is mixed and stirred with the aqueous solution, and then subjected to multi-stage washing and pressure filtration at 40°C, with a solid-liquid mass ratio of 1:2.5.

[0124] a. Primary washing and pressure filtration: Add strong sodium oxide and soda ash to adjust the pH of the slurry to between 8.0 and 8.5. When the sulfate concentration of the primary filtrate is <110g / L, return it to the primary filtrate tank; otherwise, it enters the high-salt filtrate storage tank. Other steps and operating conditions are the same as in Example 1.

[0125] b. Secondary stirring and filtration: Add soda ash to adjust the pH of the slurry to between 8 and 8.5. Other steps and operating conditions are the same as in Example 1.

[0126] c. Three-stage washing and pressure filtration: Add soda ash to adjust the pH of the slurry to between 8.0 and 8.5, backwash the filter cake, and control the moisture content of the three-stage filter cake to be <23% and the soluble sulfate content to be <0.55%. Other steps and operating conditions are the same as in Example 1.

[0127] The operating conditions for the vacuum belt filter are the same as in Example 1.

[0128] (3) In the multi-stage impurity removal step, the flocculant is a mixture of polyacrylamide, polyaluminum chloride and polyferric chloride in a mass ratio of 9:1.5:1, and the amount of flocculant added is the same as in Example 1.

[0129] Multi-stage impurity removal consists of the following steps:

[0130] In the first step, sodium hydroxide is added to the sulfate filtrate enriched in the first step to adjust the pH to 9-10. Other steps and operating conditions are the same as in Example 1.

[0131] After filtration through the second stage filter, sodium carbonate or sulfuric acid is added to adjust the pH to 8-9. Other steps and operating conditions are the same as in Example 1.

[0132] In the third stage, 0.15 g / L of potassium peroxide was added to the filtrate from the second stage for thallium removal pretreatment. Then, 0.35 g / L of sodium sulfide was added to the pretreated brine, and after stirring to form a precipitate, flocculant was added. The thallium and other heavy metal ions were removed by ultrafiltration. Other steps and operating conditions were the same as in Example 1.

[0133] (3) In the percolation evaporation salt extraction step

[0134] Since the purified solution has a high potassium content and low sodium content, sodium sulfate is first precipitated by thermal pervaporation, and then potassium sulfate is precipitated by vacuum pervaporation.

[0135] When the purified solution contains 78.5 g / L potassium sulfate and 48.5 g / L sodium sulfate, and the potassium ion content is greater than 96% sodium ion content, the purified solution is heated to 40°C in the first heater, then concentrated in a vacuum permeation membrane evaporator until the solubility in the sodium sulfate brine is 28% wt and the solid content is 45%, precipitating potassium sulfate. The concentrated solution is then kept at 40°C in the first insulator, further concentrated in the first thickener, and then separated in the first centrifuge to obtain the potassium sulfate product. The sodium-rich mother liquor from the first thickener and the first centrifuge is heated to 100–105°C in the second heater, then evaporated and concentrated in a thermal permeation membrane evaporator until the solubility in the potassium sulfate brine is 18.8% wt and the solid content is 25%, precipitating sodium sulfate. The concentrated solution is then kept at 100°C in the second insulator, further concentrated in the second thickener, and then separated in the second centrifuge to obtain the sodium sulfate product. The mother liquor from the second thickener and the second centrifuge is returned to the potassium-rich feed point. After being heated to 40°C by the first heater, it is concentrated in a vacuum permeate membrane evaporator until the solubility in sodium sulfate brine is 28% wt and the solid content is 45%, precipitating potassium sulfate. The concentrated solution is then kept at 40°C by the first insulator and further concentrated in the first thickener before entering the first centrifuge for separation to obtain the potassium sulfate product. The sodium-rich mother liquor from the first thickener and the first centrifuge is returned to the potassium-rich feed point.

[0136] The vacuum pervaporation operation and equipment are the same as in Example 1.

[0137] Based on the salt extraction process described in the above embodiments, lithium slag produced by lithium carbonate production enterprises was treated and experiments were conducted. The same analytical methods as in Example 1 were used, and the results are shown in Table 7 below:

[0138] Table 7. Ion content in raw materials and filter cake, thallium leaching amount, and ion content in purified solution.

[0139]

[0140] According to the standards for "Industrial Anhydrous Sodium Sulfate" (GBT 6009-2014) and "Agricultural Potassium Sulfate" (GBT 20406-2017), the sodium sulfate and potassium sulfate (calculated as potassium oxide) were determined under the treatment process of Example 4, and the results are shown in Table 8 below:

[0141] Table 8. Test results of sodium sulfate and potassium sulfate (potassium oxide meter)

[0142]

[0143] As demonstrated by the above embodiments, after treatment, the thallium in the lithium slag from lepidolite smelting is effectively removed, and the salt in the slag is utilized as a resource. The comprehensively treated lithium slag will be better suited for use in building materials, yielding sodium sulfate with a purity of over 90% and potassium sulfate (based on potassium oxide) with a purity of over 48%. This indicates that the present invention employs a combination of thermal and cooling methods to precipitate potassium sulfate, as well as a high-temperature thermal method to precipitate sodium sulfate. By controlling the precipitation temperatures of sodium and potassium salts and setting different precipitation sequences based on the different sodium and potassium contents, it is beneficial to achieve effective separation of sodium and potassium salts, resulting in higher value-added potassium sulfate and sodium sulfate products.

[0144] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0145] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Any aspects of the present invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for comprehensive utilization of lithium slag from lepidolite smelting, characterized in that, Includes the following steps: (1) Desalination treatment: The lithium slag from the lithium mica smelting process is mixed and stirred with an aqueous solution, and then subjected to multi-stage washing and pressure filtration to obtain filter cake and filtrate A. (2) Impurity removal treatment: (21) Add a first alkaline compound to the filtrate A to adjust the pH to 8-11, stir to generate a precipitate, add a flocculant, and then microfilter to obtain the first filtrate. (22) Add a second alkaline compound or acidic compound to the first filtrate, adjust the pH of the first filtrate, stir to generate a precipitate, add a flocculant, and ultrafilter to obtain the second filtrate. (23) First, add an oxidant to the second filtrate for treatment, then add sodium sulfide and stir to generate a precipitate, then add a flocculant and ultrafilter to obtain filtrate B. Add a chelating agent to filtrate B, stir to generate a precipitate, then add a flocculant and ultrafilter to obtain a high-salt purified liquid. (3) Evaporation and salt extraction: The high-salt purification solution was treated by vacuum pervaporation and thermal pervaporation to precipitate potassium sulfate and sodium sulfate, respectively, to obtain industrial-grade sodium sulfate and potassium sulfate products.

2. The method for comprehensive utilization of lithium slag from lepidolite smelting as described in claim 1, characterized in that, In step (1), the multi-stage washing and pressure filtration is a three-stage washing and pressure filtration, specifically including the following steps: (1) Primary stirring and pressure filtration: Add primary filtrate water and secondary filtrate water to lithium smelting lepidolite slag, with a solid-liquid mass ratio of 1:(2-4), stir and wash at 40-60℃, add caustic soda and soda ash at a mass ratio of 8:2 to adjust the pH of the slurry to 8.0-8.5, pump it into a vacuum belt filter press for pressure filtration to obtain primary filter cake and primary filtrate. When the sulfate concentration of the primary filtrate is <120g / L, it is returned to the primary filtrate tank; otherwise, it enters the high-salt filtrate storage tank. (2) Secondary stirring and filtration: The primary filter cake is added to the tertiary filtrate water at a solid-liquid mass ratio of 1:(2-4), stirred and washed at 40-60°C, and then pumped into a vacuum belt filter press for filtration to obtain a secondary filter cake and a secondary filtrate. The secondary filtrate enters the secondary filtrate tank. (3) Three-stage stirring and filtration: Add the secondary filter cake to evaporated water or fresh tap water, with a solid-liquid mass ratio of 1:(2-4), stir and wash at 40-60°C, and pump it into a vacuum belt filter press to obtain a tertiary filter cake and a tertiary filtrate. The tertiary filtrate enters the tertiary filtrate tank. The three-stage filter cake is used as a Class I solid waste in general industrial solid waste. The filtrate in the high-salt water storage tank is filtrate A.

3. The method for comprehensive utilization of lithium slag from lepidolite smelting as described in claim 2, characterized in that, The vacuum belt filter has a vacuum degree of -0.09MPa to -0.05MPa, an operating speed of 3 to 7m / min, a cloth feeding device frame structure made of 316L stainless steel, a belt material made of acid and alkali resistant and high temperature resistant EPDM rubber, and a filter cake layer thickness of 3 to 80mm. The vacuum belt filter with three-stage agitation and pressure filtration is equipped with a backwashing device. The backwashing medium is clean water, and the backwashing water pressure is 0.2MPa to 1MPa.

4. The method for comprehensive utilization of lithium slag from lepidolite smelting as described in claim 1, characterized in that, In step (2), the flocculant is a mixture of polyacrylamide, polyaluminum chloride and polyferric chloride in a mass ratio of (8-10):(1-2):1; in step (21), the amount of flocculant added is 25 mg / L; in steps (22) and (23), the amount of flocculant added is 10 mg / L.

5. The method for comprehensive utilization of lithium slag from lepidolite smelting as described in claim 1, characterized in that, In step (2), the stirring speed is 50–120 r / min; In step (21), sodium hydroxide or potassium hydroxide is added first to adjust the pH to 8-11. Microfiltration for impurity removal specifically includes: using a PCF fiber bundle filter with a filtration speed of 0.3-0.8 m / h and a transmembrane pressure difference of 0.02-0.08 MPa; impurities include calcium and magnesium ions and iron and copper ions.

6. The method for comprehensive utilization of lithium slag from lepidolite smelting as described in claim 1, characterized in that, In step (22), ultrafiltration specifically includes: using hollow fiber modules, the ultrafiltration membrane module having a tubular structure, a transmembrane pressure difference of 0.01 to 0.045 MPa, an operating pressure of 0.1 to 0.5 MPa, shear cross-flow filtration, a membrane surface water velocity of 0.05 to 0.25 m / s, a feed temperature of 40 to 60°C, external pressure ultrafiltration, a reflux ratio R = reflux flow rate / permeate flow rate of 0.3 to 2, a water flux of 0.3 to 0.6 NWP, an influent turbidity of less than 50 NTU, suspended particulate matter of less than 100 μm, and COD of less than 50 mg / L.

7. The method for comprehensive utilization of lithium slag from lepidolite smelting as described in claim 1, characterized in that, In step (23), the oxidant is selected from ozone, sodium peroxide, potassium peroxide, or hydrogen peroxide; the ultrafiltration adopts a plate and frame structure, dead-end filtration, the ultrafiltration membrane material is polyvinylidene fluoride, the shell material is rigid polyvinyl chloride, the operating pressure is 0.1-0.3 MPa, the feed temperature is 40-60℃, the water flux is 0.5-0.8 NWP, and the water turbidity is less than 15 NTU; the deep ultrafiltration adopts a plate and frame structure, dead-end filtration, the ultrafiltration membrane material is polyvinylidene fluoride, the shell material is rigid polyvinyl chloride, the operating pressure is 0.1-0.3 MPa, the feed temperature is 40-60℃, and the water flux is 0.5-0.8 NWP.

8. The method for comprehensive utilization of lithium slag from lepidolite smelting as described in claim 1, characterized in that, In step (3), potassium sulfate and sodium sulfate are precipitated from the high-salt purification solution using vacuum pervaporation and thermal pervaporation methods, respectively. Specifically, this includes: When the potassium content in the high-salt purified solution is greater than 96% sodium, the solution is heated to 40°C in the first heater, then concentrated in a vacuum permeation membrane evaporator until the solubility in sodium sulfate brine is <29.8% wt and the solid content is 10-60%, precipitating potassium sulfate. The concentrated solution is then kept at 40°C in the first insulator, further concentrated in the first thickener, and then separated in the first centrifuge to obtain potassium sulfate product. The sodium-rich mother liquor from the first thickener and first centrifuge is heated to 100-105°C in the second heater, then evaporated and concentrated in a thermal permeation membrane evaporator until the solubility in potassium sulfate brine is <19.4% wt and the solid content is 10-60%, precipitating potassium sulfate. Sodium sulfate is first heated to 100°C in a second insulator, then further concentrated in a second thickener before entering a second centrifuge for separation to obtain sodium sulfate product. The mother liquor from the second thickener and centrifuge is returned to the potassium-rich feed point, heated to 40°C in a first heater, and then concentrated in a vacuum permeate membrane evaporator until the solubility in the sodium sulfate solution is <29.8%wt and the solid content is 10-60%, precipitating potassium sulfate. The concentrated solution is then heated to 40°C in a first insulator, further concentrated in a first thickener before entering a first centrifuge for separation to obtain potassium sulfate product. The sodium-rich mother liquor from the first thickener and centrifuge is returned to the potassium-rich feed point.

9. The method for comprehensive utilization of lithium slag from lepidolite smelting as described in claim 1, characterized in that, In step (3), potassium sulfate and sodium sulfate are precipitated from the high-salt purification solution using vacuum pervaporation and thermal pervaporation methods, respectively. Specifically, this includes: When the potassium ion content in the purified solution is <96% sodium, the high-salt purified solution is heated to 100-105°C in the second heater, and then concentrated by evaporation in a thermal permeation membrane evaporator until the solubility in potassium sulfate brine is <19.4% wt and the solid content is 10%-60%, precipitating sodium sulfate. The concentrated solution is then kept at 100°C in the second insulator, and then further concentrated in the second thickener before entering the second centrifuge for separation to obtain sodium sulfate product. The mother liquor from the second thickener and the second centrifuge is returned to the potassium-rich feed point. After being heated to 40°C in the first heater, the solution is concentrated by vacuum permeation membrane evaporator until the solubility in sodium sulfate brine is <29.8% wt and the solid content is 10-60%, precipitating potassium sulfate. The concentrated solution is then kept at 40°C in the first insulator, and then further concentrated in the first thickener before entering the first centrifuge for separation to obtain potassium sulfate product. The sodium-rich mother liquor from the first thickener and the first centrifuge enters the sodium-rich feed point.

10. The method for comprehensive utilization of lithium slag from lepidolite smelting as described in claim 1, characterized in that, In step (3), the vacuum pervaporation method uses a water ring vacuum pump to draw a vacuum, with an absolute pressure of 50 kPa to 150 kPa and a pressure difference of 1.5 kPa to 5 kPa across the membrane. The pervaporation membrane is made of polytetrafluoroethylene (PTFE), has a tubular structure, operates under external pressure, and its structural components are made of 2205 duplex stainless steel. The vacuum pump has a vacuum degree of -0.095 to -0.065 MPa. The thermal pervaporation method uses a slight negative pressure operation at the condensing end, with a pressure difference of 1.5 kPa to 3 kPa between the hot and condensing ends. The pervaporation membrane is made of PTFE, has a tubular structure, operates under external pressure, and its structural components are made of titanium.

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