CN108285975A - A method of using PVC pyrolysis lithium is extracted from lepidolite - Google Patents

Abstract

The invention provides a method for extracting lithium from lepidolite by utilizing PVC pyrolysis, comprising the following steps: (1) performing low-temperature pyrolysis on washed and dried PVC plastics under an inert atmosphere to obtain HCl gas and tar; (2) ) mix lepidolite and calcium oxide, grind uniformly and carry out defluorination roasting, obtain defluorinated lepidolite; (3) pass the HCl gas after step (1) into the defluorinated lepidolite after step (2) (4) leaching the clinker after step (3) with water, and obtaining a leachate after solid-liquid separation; (5) adding an alkaline precipitant to the leachate after step (4) , and filtered after the reaction to obtain lithium carbonate solid and filtrate. The method not only provides a new idea for the comprehensive utilization of PVC waste, reduces the pollution of the PVC waste to the environment, but also reduces the production cost of lithium carbonate, realizes the comprehensive utilization of PVC, and produces huge economic benefits.

Description

A kind of method utilizing PVC pyrolysis to extract lithium from lepidolite

technical field

The invention belongs to the field of metallurgy, in particular to a method for extracting lithium from lepidolite by utilizing PVC pyrolysis.

Background technique

Lithium is known as "the energy metal that promotes the progress of the world". As a new energy and strategic resource, lithium is widely used in various fields of the national economy. Not only plays an important role in traditional consumer fields such as glass, ceramics, lubricants, etc., but also promotes the development of high-tech fields such as lithium batteries, nuclear energy, aerospace and other fields, especially in recent years with the new energy automobile industry With the rapid development of electronics industry and the global market demand for lithium is increasing year by year.

China has abundant lepidolite resources, and its Li ₂ O content is generally 3% to 5%. At present, the methods for extracting lithium from lepidolite mainly include limestone method, sulfuric acid method, and chlorination roasting method. The limestone production process has a large material flow and produces a large amount of waste residue. At the same time, the calcination process has high temperature, long cycle, high energy consumption, low lithium recovery rate, high production cost when processing low-grade lepidolite ore, and it is difficult to carry out large-scale production. The sulfuric acid roasting process will produce a large amount of sulfuric acid fumes, which will pollute the atmosphere and have high requirements for the acid corrosion resistance of the equipment. At the same time, a large amount of lye needs to be added to the leaching solution to remove aluminum to adjust the pH value. The remaining acid is difficult to recycle and cause waste. Economically Not dominant. The chlorination roasting method refers to the transformation of some metal components in the ore sample into gas phase or solid phase chlorides under certain conditions and under the action of a chlorinating agent, so that valuable metals can be separated from other components and enriched. The process of collection; commonly used chlorinating agents mainly include gaseous chlorinating agents such as Cl ₂ and HCl and solid chlorinating agents such as sodium chloride, calcium chloride and ammonium chloride. Among them, gaseous chlorinating agents, especially HCl, as chlorinating agents can greatly shorten the chlorination roasting cycle and roasting temperature, and have attracted the attention of many scholars. High pollution and other reasons have greatly limited the application of HCl in chlorination metallurgy, and there are few reports on the use of HCl in lepidolite chlorination to extract lithium. The application in the field of chemical metallurgy is of great significance.

PVC is a high-molecular organic polymer material. Due to its characteristics of flame retardancy, chemical resistance, high mechanical strength and good electrical insulation, its production cost is low, and it is widely used in the production of hard products and films such as pipes, plates, profiles, etc. , wire skin, artificial leather, shoe soles and other soft products, my country’s PVC production capacity has grown rapidly since 2002, and its output has increased significantly. By 2016, PVC output will be close to 16 million tons, and my country’s annual PVC waste that can be effectively recycled accounts for 10% of the output. About 20%, waste PVC that is not recycled will bring huge pollution to the environment, and at the same time bring huge economic pressure to environmental protection. Since PVC molecules contain nearly 60% chlorine, a large amount of HCl gas will be produced during the pyrolysis process, which can be considered as a solid release source of gas chlorinating agent, but direct combustion of PVC in the air is likely to produce carcinogens such as dioxin , Limiting the comprehensive utilization of PVC.

Therefore, how to develop an environmentally friendly, efficient and economical method for extracting lithium from lepidolite by using chlorine in PVC is of great significance to my country's lithium industry and comprehensive utilization of PVC.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide an environmentally friendly, economical and efficient method for extracting lithium from lepidolite by utilizing PVC pyrolysis.

In order to solve the problems of the technologies described above, the technical solution proposed by the present invention is:

A method utilizing PVC pyrolysis to extract lithium from lepidolite, comprising the following steps:

(1) Low-temperature pyrolysis treatment is carried out on the cleaned and dried PVC plastic under an inert atmosphere to obtain HCl gas and tar;

(2) mixing lepidolite and calcium oxide, after uniform grinding, defluorination roasting treatment is carried out to obtain defluorinated lepidolite;

(3) passing the HCl gas after the step (1) into the defluorinated lepidolite ore after the step (2), carrying out chlorination and roasting treatment to obtain clinker;

(4) leaching the clinker in step (3) with water, after solid-liquid separation, to obtain the leachate

(5) Add an alkaline precipitating agent to the leachate after step (4), filter after the reaction to obtain lithium carbonate solid and filtrate.

In the above method, preferably, in the step (1), the temperature of the low-temperature pyrolysis treatment is controlled to be 300-450°C, the heating rate is 5-10°C/min, and the time is 1.0-2.0h.

In the above method, preferably, the temperature of the chlorination roasting treatment in the step (3) is 300-450° C., and the time is 1.0-2.0 h.

The above method, preferably, the mass ratio of lepidolite and calcium oxide in the step (2) is 1:0.15 to 1:0.3, and the mass content of _Li2O in the lepidolite is 3% to 5% ; The temperature of the defluorination roasting treatment is 700-800°C, and the time is 0.5h-1.0h.

In the above method, preferably, the temperature of the defluorination roasting treatment in the step (2) is 700-800°C, and the time is 0.5h-1.0h.

In the above method, preferably, the leaching time in the step (4) is 30-60 min, the liquid-solid volume ratio is 1:1-5:1, and the leaching temperature is 10-80°C.

In the above-mentioned method, preferably, in the filtrate obtained after filtering in step (5), _CO gas is introduced, and then the waste heat generated by roasting treatment (comprising defluorination roasting and chlorination roasting) is used to evaporate and concentrate to reduce process energy consumption, After cooling and crystallization, a mixed salt of sodium carbonate and potassium carbonate was precipitated.

In the above method, preferably, the mixed salt is returned to step (5) as an alkaline precipitating agent, and can also be sold as a commercial product. After the crystallized salt is separated out, a mother liquor is also obtained, and the mother liquor contains rubidium and cesium.

Above-mentioned method, preferably, in described step (5), alkaline precipitation agent is sodium carbonate and/or salt of wormwood, has avoided the introduction of new impurity, and purification load is low; The consumption of described alkaline precipitation agent is lepidolite ore Lithium is converted into 110%-130% of the theoretical amount needed for lithium carbonate, and the reaction time in the control step (5) is 1.0-2.5h.

The above-mentioned method, preferably, the inert atmosphere in the step (1) is a nitrogen atmosphere and/or an argon atmosphere; the tar is used as a fuel for pyrolysis treatment, defluorination roasting or chlorination roasting treatment after being recovered by condensation, The condensation method is water cooling; the PVC plastic is PVC waste plastic particles with a particle size of 5-10 mm. .

In the above method, preferably, the low-temperature pyrolysis treatment is carried out in a pyrolysis furnace, the defluorination roasting treatment and the chlorination roasting treatment are carried out in a roasting furnace, and the temperature between the pyrolysis furnace and the roasting furnace is There is a condensation recovery system between them, and the roaster is also connected to the tail gas absorber.

Compared with the prior art, the present invention has the advantages of:

(1) The method of the present invention makes full use of the chlorine element with a content close to 60% in PVC, uses the PVC waste as an HCl release agent, and the HCl produced by the low-temperature pyrolysis treatment of PVC is used for lepidolite chlorination to extract lithium to prepare a higher purity. The raw material of high lithium carbonate, the product tar after PVC pyrolysis can also provide raw material for roasting furnace; On the one hand, the production cost of lithium carbonate is reduced, the comprehensive utilization of PVC is realized, and huge economic benefits are generated.

(2) The method of the present invention carries out defluorination roasting before carrying out chlorination roasting, reduces the generation of hydrogen fluoride in the chlorination roasting process on the one hand, alleviates the corrosion to roasting equipment, on the other hand by pre-roasting, lepidolite ore Reconstruction of the phase of the material can significantly improve the reaction kinetics of the reaction system interface and improve the chlorination efficiency.

(3) The method of the present invention adopts the HCl gas released by PVC pyrolysis as the chlorinating agent, and the traditional chlorination roasting reaction is converted from solid-solid two-phase reaction to gas-solid two-phase reaction, increasing the chlorination roasting The HCl gas concentration in the atmosphere not only reduces the dosage of calcium chloride, but also improves the chlorination efficiency and shortens the chlorination cycle.

(4) Because the chlorinating agent selected in the present invention is the HCl produced by PVC low-temperature pyrolysis, the amount of slag after chlorination and roasting of the clinker after water immersion is small, and the lithium ion concentration is high in the gained leachate, which can be directly used to extract lithium; The whole leaching process does not need to add acid and alkali to adjust the pH, the leaching selectivity is high, the impurity content is low, and the purification and separation process is simple.

(5) method of the present invention, PVC low-temperature pyrolysis and ore sample defluorination roasting and chlorination roasting are carried out in series respectively in two roasting devices, can reduce the productive rate of pyrolysis tar on the one hand, increase the output of HCl, make The ratio between pyrolysis tar and HCl is within a reasonable range. On the other hand, it can prevent PVC pyrolysis product tar from hindering the mass transfer rate of the gas-solid interface, increase the chlorination rate, and shorten the treatment process of clinker after chlorination roasting.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are For some embodiments of the present invention, those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the process flow sheet of the method utilizing PVC pyrolysis to extract lithium from lepidolite in the present invention;

Fig. 2 is a schematic structural view of the device implementing the method of extracting lithium from lepidolite by using PVC pyrolysis in Example 1 of the present invention.

illustration:

1. Pyrolysis furnace; 2. Roasting furnace; 3. Condensation recovery system; 4. Atmosphere supplier; 5. Tail gas absorber.

Detailed ways

In order to facilitate the understanding of the present invention, the invention will be described more comprehensively and in detail below in conjunction with the accompanying drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the protection scope of the present invention.

Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

Example 1:

A method utilizing PVC pyrolysis to extract lithium from lepidolite, its process flow diagram as shown in Figure 1, comprises the following steps:

(1) Under a nitrogen atmosphere, crush the washed and dried PVC waste into plastic particles with a particle size of 5-10mm, and then place it in a pyrolysis furnace for low-temperature pyrolysis, and control the temperature of the pyrolysis treatment to 350°C , the heating rate is 5°C/min, the pyrolysis time is 1.5h, and HCl gas and tar are obtained;

(2) Mix lepidolite with a Li ₂ O content of 3.5% and calcium oxide at a mass ratio of 1:0.2, grind them evenly and place them in a roaster for defluorination and roasting at a controlled temperature of 700°C and roasting time of 30 minutes , to obtain defluorinated lepidolite;

(3) Pass the HCl gas after the step (1) into the defluorinated lepidolite ore after the step (2), carry out chlorination roasting, control the temperature to be 300° C., and the roasting time is 1.5 h to obtain clinker;

(4) leaching the clinker after step (3) with water, the leaching time is 30min, the leaching temperature is 50°C, the liquid-solid volume ratio is 3:1, and the leachate is obtained after solid-liquid separation;

(5) Add sodium carbonate to the leaching solution after step (4), the consumption of sodium carbonate is 120% of the required theoretical amount of lepidolite total lithium into lithium carbonate, stirs and reacts, filters after reacting 1.5h, obtains carbonic acid Lithium solids and filtrates;

(6) In the filtrate, feed _CO gas to carry out acidification, then utilize the residual heat of defluorination roasting or chlorination roasting to carry out evaporation and concentration, cooling crystallization separates out the mixed salt of sodium carbonate and salt of wormwood, mixed salt returns to step (5) as Alkaline precipitant, the mother liquor after precipitation of sodium carbonate and potassium carbonate contains rubidium and cesium, which can be used to extract and separate valuable metals later.

In this embodiment, the structural schematic diagram of the device for implementing the above method is shown in Figure 2. As can be seen from the figure, the pyrolysis furnace 1 and the roasting furnace 2 operate in series, and a condensation recovery system 3 is arranged between the pyrolysis furnace 1 and the roasting furnace 2 , the tar and HCl gas produced by the pyrolysis of PVC in the pyrolysis furnace 1 are separated by the condensation recovery system 3, and the tar is used as fuel for pyrolysis treatment, defluorination roasting treatment or chlorination roasting treatment after recovery, and the HCl gas continues to be in the form of gas Pass in the roasting furnace 2; The pyrolysis furnace 1 is connected with the atmosphere supplier 4 so that keep an inert atmosphere in the pyrolysis furnace 1, and the roasting furnace 2 is connected with the tail gas absorber 5 to prevent the roasting tail gas from polluting the air.

In this embodiment, the recovery rate of lithium in lepidolite ore is 96.4%.

Example 2:

A method utilizing PVC pyrolysis to extract lithium from lepidolite, its process flow diagram as shown in Figure 1, comprises the following steps:

(1) Under an argon atmosphere, place the cleaned and dried PVC plastic particles in a pyrolysis furnace for low-temperature pyrolysis. The temperature of the pyrolysis treatment is controlled at 400°C, and the heating rate is 5°C/min. For 2h, HCl gas and tar were obtained;

(2) Mix lepidolite with a Li ₂ O content of 3.8% and calcium oxide at a mass ratio of 1:0.3, grind them evenly and place them in a roaster for defluorination and roasting at a temperature of 800°C and a roasting time of 30 minutes , to obtain defluorinated lepidolite;

(3) Pass the HCl gas after the step (1) into the defluorinated lepidolite ore after the step (2), carry out chlorination roasting, control the temperature to be 350° C., and the roasting time is 2 hours to obtain clinker;

(4) leaching the clinker in step (3) with water, the leaching time is 20min, the leaching temperature is 30°C, the liquid-solid volume ratio is 4:1, and the leachate is obtained after solid-liquid separation;

(5) add sodium carbonate in the leaching liquid after step (4), the consumption of sodium carbonate is 125% of the required theoretical amount of lithium carbonate that lepidolite total lithium is converted into, stirs and reacts, filters after reacting 1h, obtains lithium carbonate solids and filtrates;

(6) In the filtrate, feed _CO gas to carry out acidification, then utilize the residual heat of defluorination roasting or chlorination roasting to carry out evaporation and concentration, cooling crystallization separates out the mixed salt of sodium carbonate and salt of wormwood, mixed salt returns to step (5) as Alkaline precipitant, the mother liquor after precipitation of sodium carbonate and potassium carbonate contains rubidium and cesium, which can be used to extract and separate valuable metals later.

In this embodiment, the recovery rate of lithium in lepidolite ore is 94.4%.

Example 3:

A method utilizing PVC pyrolysis to extract lithium from lepidolite, its process flow diagram as shown in Figure 1, comprises the following steps:

(1) Under a nitrogen atmosphere, put the cleaned and dried PVC plastic particles in a pyrolysis furnace for low-temperature pyrolysis. The temperature of the pyrolysis treatment is controlled at 350°C, the heating rate is 8°C/min, and the pyrolysis time is 1h, get HCl gas and tar;

(2) Mix lepidolite with a Li ₂ O content of 4.5% and calcium oxide at a mass ratio of 1:0.25, grind them evenly and place them in a roaster for defluorination and roasting at a controlled temperature of 750°C and roasting time of 30 minutes , to obtain defluorinated lepidolite;

(3) Pass the HCl gas after the step (1) into the defluorinated lepidolite ore after the step (2), carry out chlorination roasting, control the temperature to be 450°C, and the roasting time is 1h to obtain clinker;

(4) leaching the clinker after step (3) with water, the leaching time is 60min, the leaching temperature is 70°C, the liquid-solid volume ratio is 5:1, and the leachate is obtained after solid-liquid separation;

(5) Add sodium carbonate to the leaching solution after step (4), the consumption of sodium carbonate is 130% of the required theoretical amount of lithium carbonate for lepidolite total lithium, stirs and reacts, filters after reacting 2.5h, obtains carbonic acid Lithium solids and filtrates;

(6) In the filtrate, feed _CO gas to carry out acidification, then utilize the residual heat of defluorination roasting or chlorination roasting to carry out evaporation and concentration, cooling crystallization separates out the mixed salt of sodium carbonate and salt of wormwood, mixed salt returns to step (5) as Alkaline precipitant, the mother liquor after precipitation of sodium carbonate and potassium carbonate contains rubidium and cesium, which can be used to extract and separate valuable metals later. In this embodiment, the recovery rate of lithium in lepidolite ore is 98.4%.

Example 4:

A method utilizing PVC pyrolysis to extract lithium from lepidolite, its process flow diagram as shown in Figure 1, comprises the following steps:

(1) Under a nitrogen atmosphere, put the cleaned and dried PVC plastic particles in a pyrolysis furnace for low-temperature pyrolysis. The temperature of the pyrolysis treatment is controlled at 450°C, the heating rate is 10°C/min, and the pyrolysis time is 2h, get HCl gas and tar;

(2) Mix lepidolite with a Li ₂ O content of 3.0% and calcium oxide at a mass ratio of 1:0.15, grind them evenly and place them in a roaster for defluorination and roasting at a controlled temperature of 800°C and roasting time of 30 minutes , to obtain defluorinated lepidolite;

(3) Pass the HCl gas after the step (1) into the defluorinated lepidolite ore after the step (2), carry out chlorination roasting, control the temperature to be 400° C., and the roasting time is 2 hours to obtain clinker;

(4) leaching the clinker after step (3) with water, the leaching time is 50min, the leaching temperature is 60°C, the liquid-solid volume ratio is 2:1, and the leachate is obtained after solid-liquid separation;

(5) Add sodium carbonate to the leaching solution after step (4), the consumption of sodium carbonate is 110% of the required theoretical amount of lepidolite total lithium into lithium carbonate, stirs and reacts, filters after reacting 2.0h, obtains carbonic acid Lithium solids and filtrates;

(6) In the filtrate, feed _CO gas to carry out acidification, then utilize the residual heat of defluorination roasting or chlorination roasting to carry out evaporation and concentration, cooling crystallization separates out the mixed salt of sodium carbonate and salt of wormwood, mixed salt returns to step (5) as Alkaline precipitant, the mother liquor after precipitation of sodium carbonate and potassium carbonate contains rubidium and cesium, which can be used to extract and separate valuable metals later. In this embodiment, the recovery rate of lithium in lepidolite ore is 95.4%.

Example 5:

A method utilizing PVC pyrolysis to extract lithium from lepidolite, its process flow diagram as shown in Figure 1, comprises the following steps:

(1) Under a nitrogen atmosphere, put the cleaned and dried PVC plastic particles in a pyrolysis furnace for low-temperature pyrolysis. The temperature of the pyrolysis treatment is controlled at 400°C, the heating rate is 5°C/min, and the pyrolysis time is 2h, get HCl gas and tar;

(2) Mix lepidolite with a Li ₂ O content of 4% and calcium oxide at a mass ratio of 1:0.3, grind them evenly and place them in a roaster for defluorination and roasting at a controlled temperature of 800°C and roasting time of 30 minutes , to obtain defluorinated lepidolite;

(3) Pass the HCl gas after the step (1) into the defluorinated lepidolite ore after the step (2), carry out chlorination roasting, control the temperature to be 400° C., and the roasting time is 2 hours to obtain clinker;

(4) leaching the clinker after step (3) with water, the leaching time is 60min, the leaching temperature is 80°C, the liquid-solid volume ratio is 4:1, and the leachate is obtained after solid-liquid separation;

(5) Add sodium carbonate to the leaching solution after step (4), the consumption of sodium carbonate is 125% of the required theoretical amount of lepidolite total lithium into lithium carbonate, stirs and reacts, filters after reacting 2.5h, obtains carbonic acid Lithium solids and filtrates;

(6) In the filtrate, feed _CO gas to carry out acidification, then utilize the residual heat of defluorination roasting or chlorination roasting to carry out evaporation and concentration, cooling crystallization separates out the mixed salt of sodium carbonate and salt of wormwood, mixed salt returns to step (5) as Alkaline precipitant, the mother liquor after precipitation of sodium carbonate and potassium carbonate contains rubidium and cesium, which can be used to extract and separate valuable metals later. In this embodiment, the recovery rate of lithium in lepidolite ore is 98.7%.

Claims (10)

1. a method utilizing PVC pyrolysis to extract lithium from lepidolite, is characterized in that, may further comprise the steps: (1) Low-temperature pyrolysis treatment is carried out on the cleaned and dried PVC plastic under an inert atmosphere to obtain HCl gas and tar; (2) mixing lepidolite and calcium oxide, after uniform grinding, defluorination roasting treatment is carried out to obtain defluorinated lepidolite; (3) passing the HCl gas after the step (1) into the defluorinated lepidolite ore after the step (2), carrying out chlorination and roasting treatment to obtain clinker; (4) leaching the clinker after the step (3) with water, and obtaining the leachate after solid-liquid separation; (5) Add an alkaline precipitating agent to the leachate after the step (4), filter after the reaction to obtain lithium carbonate solid and filtrate. 2. The method according to claim 1, characterized in that, in the step (1), the temperature of the controlled low-temperature pyrolysis treatment is 300-450° C., the heating rate is 5-10° C./min, and the time is 1.0-2.0° C. h. 3. The method according to claim 1 or 2, characterized in that the temperature of the chlorination roasting treatment in the step (3) is 300-450° C., and the time is 1.0-2.0 h. 4. The method according to claim 1 or 2, characterized in that, in the step (2), the mass ratio of lepidolite and calcium oxide is 1:0.15～1:0.3, and _Li in the lepidolite The mass content of O is 3%-5%; the temperature of the defluorination roasting treatment is 700-800° C., and the time is 0.5h-1.0h. 5. The method according to claim 1 or 2, characterized in that, the time of the leaching process in the step (4) is 30 to 60 minutes, the liquid-solid volume ratio is 1:1-5:1, and the leaching temperature is 10 ~80°C. 6. The method according to claim 1 or 2, characterized in that, in the filtrate obtained after filtering in step (5), feed _CO gas, then utilize the waste heat generated by roasting to carry out evaporation and concentration, and precipitate after cooling and crystallization Mixed salt of sodium carbonate and potassium carbonate. 7. method according to claim 6, is characterized in that, described mixed salt returns step (5) and is used as alkaline precipitant, also obtains the mother liquor after extracting sodium, potassium after separating out described mixed salt, described The mother liquor contains rubidium and cesium. 8. according to the method for claim 1 and 2, it is characterized in that, in described step (5), alkaline precipitation agent is sodium carbonate and/or salt of wormwood, and the consumption of described alkaline precipitation agent is in lepidolite ore Lithium is converted into 110%-130% of the theoretical amount needed for lithium carbonate, and the reaction time in the control step (5) is 1.0-2.5h. 9. The method according to claim 1 or 2, characterized in that, the inert atmosphere in the step (1) is a nitrogen atmosphere and/or an argon atmosphere; the tar is used as pyrolysis treatment, degassing after condensation recovery For the fuel processed by fluorine roasting or chlorination roasting, the condensation method is water cooling; the PVC plastic is PVC waste plastic particles with a particle size of 5-10 mm. 10. The method according to claim 1 or 2, characterized in that, the low-temperature pyrolysis treatment is carried out in a pyrolysis furnace, and the defluorination roasting treatment and the chlorination roasting treatment are carried out in a roasting furnace, so that A condensation recovery system is provided between the pyrolysis furnace and the roasting furnace, the pyrolysis furnace is also connected to an atmosphere supplier, and the roasting furnace is also connected to a tail gas absorber.