Salt-melting pre-coated ore particle suspension roasting system and method for clay type lithium ore

Abstract

The invention provides a salt-melting pre-coated ore particle suspension roasting system and method for clay type lithium ore, and belongs to the field of lithium ore smelting and extraction. The system comprises a mixer, a preheating furnace, a dispersion dryer, a first cyclone separator, a cyclone preheater, a suspension roaster, a second cyclone separator, a cyclone cooler, an air cooler, a cloth bag or an electric precipitator, a tail gas treatment device, an induced draft fan, a first spiral feeder and a second spiral feeder. The method comprises the following steps: uniformly stirring and mixing clay type lithium ore powder with mixed salt of alkali metal sulfate and nitrate; preheating at the temperature of 300-400 DEG C to obtain salt melting pre-coated mineral powder; the method comprises the following steps: dispersing and drying mineral powder, feeding into a cyclone preheater, preheating at 500-600 DEG C, feeding into a suspension roaster, and performing suspension roasting at 600-700 DEG C; and after gas-solid separation, cooling to obtain roasted clinker. According to the method, the advantages of salt-adding roasting of the clay type lithium ore can be played, suspension fluidized roasting after salt mixing of the lithium ore can be achieved, and efficient selective leaching of low-grade lithium in the clay lithium ore is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ore smelting and extraction, and in particular relates to a system and method for suspended roasting of salt-melting pre-coated ore particles of clay-type lithium ore. Background Art

[0002] As an unconventional lithium resource, clay-type lithium ore has received increasing attention in recent years. At present, the methods for extracting lithium from clay-type lithium ore mainly include sulfuric acid method and sulfate mixed roasting method, which are similar to the current treatment methods of hard rock lithium ore. Chinese patent CN 103849761A discloses a method for extracting lithium from low-grade lithium-containing clay ore. The lithium-containing clay ore is ground to 2 mm, mixed according to the mass ratio of lithium-containing clay ore: calcium sulfate: calcium fluoride: sodium sulfate = 1:0.7:0.2:0.5, roasted at 800℃ for 2-3h, and then the roasted sand is granulated and heap leached, with a lithium leaching rate of up to 91.78%. The technical process is complex, the roasting temperature is high, and the energy consumption is high. Chinese patent CN 114892024A discloses a method for extracting lithium from lithium-containing clay ore by low-temperature roasting. After 98% concentrated sulfuric acid and lithium-containing clay ore are evenly mixed at an acid-ore ratio of 0.5:1 to 1:2, they are roasted at 180-250°C, and the resulting roasted product is leached in water to obtain a lithium-containing solution with a lithium leaching rate of 89.32%. The lithium-containing leaching solution obtained by this technology has a high acidity, a complex solution composition, and a complicated subsequent purification and impurity removal process, resulting in a high lithium extraction cost. Chinese patent CN 113104867A discloses a method for preparing lithium carbonate by composite sulfate acidification and roasting of lithium mica. The lithium mica ore powder is mixed with at least two of the sulfates such as potassium sulfate, sodium sulfate, calcium sulfate, barium sulfate, and iron sulfate, as well as additives such as barium carbonate and calcium carbonate, in a mass ratio of lithium mica ore powder: composite sulfate: additive = 1: 0.39-0.64: ​​0.03-0.09, and then placed in a high-performance ball mill for mechanical activation treatment, and then 1-4% of concentrated sulfuric acid is added to mix, and then placed in a rotary kiln for roasting at 830-880°C. The roasted product is crushed, soaked in water, and impurities are removed to prepare lithium carbonate products. This technology uses a large amount of composite sulfate, and high-performance ball mill equipment is required for mechanical activation after mixing. The process is complicated, and the energy consumption of 830-880°C rotary kiln roasting is high. Zhu Lingyan et al. (Zhu Lingyan, Liang Xianzhi, Liu Yuelong et al. Na2SO4-H2SO4 mixed roasting process for lithium extraction from low-grade lepidolite. Nonferrous Metals Engineering, 2021, 11(11): 48-55.) disclosed a Na2SO4-H2SO4 mixed roasting process for lithium extraction from low-grade lepidolite, comprising the following steps: weighing a certain amount of lepidolite ore, adding it to a pre-prepared sulfuric acid solution in a mass ratio of 1:1, then adding a certain mass of sodium sulfate, mixing well, and then roasting it in a muffle furnace at 280°C for 2h, and then heating it to 800-1000°C in a muffle furnace for 2h after the roasting sand is crushed, and then leaching it with hot water after the roasting sand is cooled. The lithium leaching rate can reach 90%, but due to the two-stage roasting, the process is complicated and the energy consumption is high. Chinese patent CN 116790911 A discloses a method for lithium extraction from clay-type lithium ore.Clay-type lithium ore powder, sulfate (sodium sulfate and / or potassium sulfate), and concentrated sulfuric acid are mixed evenly in a mass ratio of 1:0.03-0.25:0.18-0.6, and then roasted at 480-750℃ for 2-8h. The roasted sand is ground and soaked in water to obtain a lithium leachate. This technology uses less sulfate and concentrated sulfuric acid, has a low roasting temperature, low energy consumption, low acidity of the leachate, and a lithium leaching rate of up to 90%. From the above analysis, it can be seen that during the roasting process of clay-type lithium ore, highly active sulfates (such as sodium sulfate, etc.) are mixed in, and the alkali metal ions at high temperature have the characteristics of destroying the silicate crystal structure of clay minerals and affecting the amorphous phase transformation temperature of the material, which can achieve effective decomposition of fine-grained lithium minerals wrapped by clay minerals such as kaolinite and illite at low temperatures. In addition, the roasted sand obtained after salt roasting can be used for simple water leaching of lithium. Compared with the traditional sulfuric acid method for lithium extraction, the obtained lithium leaching solution has low acidity and simple solution composition, which is easy for subsequent solution purification and impurity removal and preparation of high-purity lithium carbonate products.

[0003] Suspension roasting is a new energy-saving and efficient roasting technology. Compared with traditional rotary kiln roasting processes, it can achieve efficient decomposition of difficult-to-decompose minerals at a lower temperature and faster speed, reducing roasting costs. Chinese patent CN 107739847 A discloses a crystal transformation method for natural spodumene by suspension roasting. After natural α-spodumene is ground to a certain particle size, it is put into a secondary suspension roasting furnace, and the high-temperature tail gas separated from the primary cyclone dust collector is used for fluidized drying and preheating, and then the dried and preheated spodumene powder is passed into the secondary cyclone dust collector with the high-temperature tail gas for gas-solid separation. After the separated tail gas is separated by the dust collector for gas-solid separation, the collected spodumene powder and the preheated spodumene powder separated in the secondary cyclone dust collector are introduced into the primary suspension roasting furnace, and suspended roasting is performed using high-temperature gas to make the spodumene powder undergo preliminary crystal transformation. After separation by the primary cyclone dust collector, the obtained high-temperature mineral powder is kept in an insulation tank for a certain period of time to complete the crystal transformation, and finally transferred to a cooler for cooling to obtain β-spodumene. Compared with the traditional rotary kiln roasting spodumene crystal transformation, this technology has the advantages of low energy consumption, large processing capacity, easy control of crystal transformation temperature, and more complete crystal transformation. Chinese patent CN 108034839 B discloses a method for defluorination of lithium mica by suspended roasting. The crushed lithium mica is sent into a suspended roasting furnace, mixed with the hot gas generated by the combustion at the bottom of the furnace and the water vapor introduced by the preheating steam recovery system for rapid roasting and defluorination. After roasting, the hot gas carries the mineral powder into the cyclone separator for gas-solid separation, and the mineral powder is transferred to the insulation tank for further residence and defluorination. After defluorination, the mineral powder enters the cooler for cooling to obtain the finished product of defluorinated lithium mica. Compared with the traditional rotary kiln roasting and defluorination, the invention has low energy consumption, short residence time of lithium mica mineral powder in the equipment, large mineral powder processing capacity per unit time, uniform temperature control in the suspended roasting furnace, and stable and thorough defluorination effect. Chinese patent CN 111439762 A discloses a method for extracting lithium by suspended roasting of spodumene. The spodumene concentrate is ground and introduced into the suspended roasting furnace, and the mixed gas is introduced into the bottom of the suspended roasting furnace to heat the suspended roasting furnace to 1000-1100 ℃. The ore powder is suspended and heated under the action of airflow, and the crystal form is transformed to generate roasted clinker. The roasted product is ground and mixed with sulfuric acid solution, and then acid-roasted at 190-220 ℃ in an acid kiln. The product after acid-roasting is water-leached, and then the filtrate is filtered, neutralized, purified, and lithium is precipitated to obtain a lithium carbonate product. Compared with the traditional rotary kiln crystal rotation roasting, this technology has low energy consumption, easy control of the temperature field in the furnace, large equipment processing capacity, and high lithium leaching rate. Chinese patent CN 114349031 A discloses a method for suspended roasting of spodumene concentrate. The suspension roasting technology is used to roast spodumene. Compared with conventional rotary kiln or tunnel kiln roasting, the suspension roasting can accurately control the roasting temperature and temperature field distribution in the furnace, with high heat and mass transfer efficiency, and can quickly, efficiently and completely transform spodumene from α phase to β phase.The suspension roasting process has low energy consumption, greatly shortened reaction time, and large equipment processing capacity per unit time. In addition, since the crystal conversion adopts the suspension roasting technology, the conversion rate is high, so no excessive sulfuric acid is required during the subsequent acidification roasting, which reduces the reaction time and equipment corrosion. Chinese patent CN114812179 A discloses a spodumene ore powder suspension roasting furnace device and roasting method. The device includes a dispersion dryer, a first separator, a cyclone preheater, a suspension roasting furnace, a second separator, a phase change reactor, a cyclone cooler, a powder waste heat boiler, an exhaust gas purifier and an induced draft fan. After the spodumene is ground into a certain particle size ore powder, it is continuously fed into the dispersion dryer, and after dispersion drying, it enters the first separator and cyclone preheater, and after heat exchange with hot air, it enters the suspension roasting furnace, and the suspension heating generates pre-phase change ore powder, and then enters the second separator and phase change reactor, and fluidized air is introduced to generate full phase change ore powder. The mineral powder is sent into the cyclone cooler along with the air, and the pre-cooled mineral powder enters the powder waste heat boiler to generate low-temperature mineral powder for discharge. This technology has a fast reaction speed, high roasting and crystal conversion efficiency, full use of waste heat, low heat consumption, large equipment processing capacity per unit time, and low roasting cost.

[0004] From the above disclosed suspension roasting technology, suspension roasting has obvious advantages over traditional rotary kiln and other kiln roasting processes. However, the current suspension roasting process is mostly only used for direct oxidation roasting of lithium ore powder, and cannot be coupled with the salt roasting process of clay-type lithium ore. Due to the large difference in the physicochemical properties between clay-type lithium ore powder and salt particles such as sulfate, even if the clay-type lithium ore powder is mixed with salt particles such as sulfate before suspension roasting, it is difficult to achieve effective contact in a suspended state after the mixture of the two solid materials enters the suspension roasting furnace. Because the solid-solid phase reaction is difficult to carry out, the added sulfate cannot react with the clay-type lithium ore particles, and cannot achieve the effect of salt roasting clay-type lithium ore particles in traditional kilns. Summary of the invention

[0005] In order to solve the above problems, the present invention aims to provide a system and method for suspended roasting of salt-melting pre-coated ore particles of clay-type lithium ore, so as to achieve the effect of static roasting in traditional kilns such as rotary kilns during the suspended roasting process, and better play the advantages of salt-adding roasting clay-type lithium ore to extract lithium. In order to achieve this purpose, the present invention realizes the above purpose and method through the following technical solutions:

[0006] A salt melting pre-coated ore particle suspension roasting system for clay-type lithium ore, the system comprising a mixer, a preheating furnace, a dispersion dryer, a first cyclone separator, a cyclone preheater, a suspension roasting furnace, a second cyclone separator, a cyclone cooler, an air cooler, a bag or an electric precipitator, an exhaust gas treatment device, an induced draft fan, a first screw feeder and a second screw feeder, wherein:

[0007] The mixer is used to mix the mineral powder and the mixed salt. The upper part of the mixer is provided with a feed port for the mineral powder and the mixed salt of alkali metal sulfate and nitrate; the lower discharge port of the mixer is connected with the feed port of the preheating furnace through the first screw feeder;

[0008] The preheating furnace is used to preheat the mixture output by the mixer to obtain the salt-molten pre-coated mineral powder, and the discharge port of the preheating furnace is connected to the feed port of the dispersion dryer through the second screw feeder;

[0009] The dispersion dryer uses the hot air from the cyclone cooler to disperse and dry the mineral powder output from the preheating furnace. The air inlet of the dispersion dryer is connected to the air outlet of the cyclone cooler through a pipeline; the discharge port of the dispersion dryer is connected to the feed port of the first cyclone separator;

[0010] The first cyclone separator is used to perform gas-solid separation on the discharge of the dispersion dryer, and the air outlet of the first cyclone separator is connected to the air inlet of the preheating furnace; the discharge port of the first cyclone separator is connected to the air outlet pipe of the second cyclone separator through the feed pipe, and is connected to the feed port of the cyclone preheater;

[0011] The cyclone preheater uses the exhaust gas of the second cyclone separator as a heat source to preheat the ore powder output by the first cyclone separator to obtain preheated ore powder. The solid phase discharge port of the cyclone preheater is connected to the feed port of the suspension roasting furnace; the air outlet of the cyclone preheater is connected to the inlet of the bag or electric precipitator;

[0012] The bag or electrostatic precipitator is used to separate the gas phase discharge of the cyclone preheater into gas and solid, and transport the separated solid phase product back to the cyclone preheater. The lower outlet of the bag or electrostatic precipitator is connected to the feed inlet of the cyclone preheater; the upper gas outlet of the bag or electrostatic precipitator is connected to the gas inlet of the tail gas treatment device;

[0013] The tail gas treatment device is used to treat the gas phase discharge of the cyclone preheater and the bag or electric precipitator, and the induced draft fan is used to discharge the waste gas generated by the tail gas treatment device, and the air outlet of the tail gas treatment device is connected to the air inlet of the induced draft fan;

[0014] The suspension roasting furnace is used to roast the solid phase discharge from the cyclone preheater, the mineral powder is in a fluidized suspension state in the suspension roasting furnace, and the discharge port of the suspension roasting furnace is connected to the feed port of the second cyclone separator; a fuel inlet is provided at the bottom of the suspension roasting furnace for introducing fuel;

[0015] The second cyclone separator is used to perform gas-solid separation on the discharge of the suspension roasting furnace, and the discharge port of the second cyclone separator is connected to the feed port of the cyclone cooler;

[0016] The cyclone cooler is used to cool the solid phase discharge of the second cyclone separator and perform gas-solid separation, and the discharge port of the cyclone cooler is connected to the feed port of the air cooler; the air outlet of the cyclone cooler is connected to the air inlet of the dispersion dryer through a pipeline;

[0017] The air cooler is used to further cool the solid phase discharge from the cyclone cooler and introduce the separated hot air into the suspension roasting furnace as combustion air; the air inlet of the suspension roasting furnace is connected to the air outlet of the air cooler through a pipeline, and a roasting clinker discharge port is provided below the air cooler.

[0018] The present invention also provides a method for suspension roasting using the system, comprising the following steps:

[0019] (1) grinding clay-type lithium ore or its concentrate into ore powder, and mixing it with a mixed salt of alkali metal sulfate and nitrate in a mixer to obtain a mixture;

[0020] (2) feeding the mixture obtained in step (1) into a preheating furnace by means of a first screw feeder, and preheating and keeping the mixture warm at a temperature in the range of 300 to 400° C. by means of waste heat from the tail gas of the first cyclone separator, to obtain salt-molten pre-coated ore powder;

[0021] (3) introducing air into the air inlets of the cyclone cooler and the air cooler, and conveying the salt melt pre-coated ore powder obtained in step (2) to the dispersion dryer by a second screw feeder; introducing hot air at 300-400°C from the air outlet of the cyclone cooler into the air inlet at the bottom of the dispersion dryer, and mixing the hot air with the ore powder to disperse and dry the ore powder; the dried ore powder is discharged from the outlet of the dispersion dryer along with the hot air, enters the first cyclone separator, and is separated from the gas in the first cyclone separator; under the condition of starting the induced draft fan, the dried ore powder enters the cyclone preheater in front of the suspension roasting furnace along with the hot air at 500-600°C from the air outlet of the second cyclone separator;

[0022] (4) exchanging heat between the dried ore powder obtained in step (3) and the tail gas at 500-600°C from the outlet of the second cyclone separator in a cyclone preheater to form preheated ore powder, which is discharged from the outlet of the cyclone preheater and enters the suspension roasting furnace;

[0023] (5) hot air from an air cooler is introduced into the air inlet at the bottom of the suspension roasting furnace, and fuel is introduced into the fuel inlet of the burner at the bottom of the suspension roasting furnace. The fuel is burned in the furnace of the suspension roasting furnace to further heat the preheated ore powder from step (4) to a temperature in the range of 600 to 700° C. The ore powder is subjected to the action of the airflow in the suspension roasting furnace in a fluidized suspended state for roasting;

[0024] (6) The ore powder obtained after suspension roasting in step (5) is transported by hot air flow into a second cyclone separator connected to the suspension roasting furnace for gas-solid separation. The obtained ore powder is transported into a cyclone cooler for air cooling and gas-solid separation. The ore powder is discharged from the discharge port at the bottom of the cyclone cooler and sent to an air cooler for further air cooling to obtain roasted clinker. The preheated air in the air cooler is introduced into the bottom burner of the suspension roasting furnace as combustion air.

[0025] (7) The tail gas at a temperature of 500 to 600° C. obtained by the second cyclone separator in step (6) is introduced into the cyclone preheater in step (4) as heating gas to preheat the mineral powder; the tail gas of the cyclone preheater passes through a bag filter or an electrostatic precipitator, and then enters an exhaust gas treatment device for treatment to meet the standards and then is discharged; the mineral powder collected by the bag filter or the electrostatic precipitator is returned to the cyclone preheater and re-sent to the suspension roasting furnace for further roasting.

[0026] Furthermore, in the mineral powder of step (1), the part with a particle size of -0.074 mm accounts for 60-90% of the total mass of the mineral powder, and preferably the mass percentage of Li2O in the clay-type lithium ore is 0.4-0.5%; the mass percentage of Li2O in the clay-type lithium ore concentrate is 0.6-1.0%. The weight percentage of water in the clay-type lithium ore or its concentrate is 1-5%.

[0027] Furthermore, in step (1), the alkali metal sulfate added is sodium sulfate and / or potassium sulfate, the alkali metal nitrate added is sodium nitrate and / or potassium nitrate, the mass ratio of the clay-type lithium ore powder to the mixed salt (i.e., alkali metal sulfate and nitrate) is 1:0.05 to 1:0.3, and the mass ratio of sulfate to nitrate in the mixed salt of alkali metal sulfate and nitrate is 2:1 to 1:2. Since the melting point of nitrate is relatively low, it is preferentially softened and melted when heated and kept warm at 300 to 400°C in the preheating furnace. After the nitrate melts and softens, the erosion of the surface of the ore particles helps the high-melting-point sulfate to embed into the layered lattice of the ore particles, thereby forming a pre-coating of the ore particles. When the subsequent salt-melted pre-coated ore particles enter the cyclone preheater and are preheated at 500 to 600°C, the nitrate on the surface will completely decompose and volatilize, preventing the nitrate from entering the suspension roasting furnace and affecting the suspension roasting reaction. Therefore, the mass ratio of sulfate to nitrate needs to be controlled within the above range. If the amount of nitrate added is too small, the added sulfate cannot effectively pre-coat the ore particles, and the sulfate and the ore particles are still in a state where they cannot be combined. If the amount of nitrate added is too large, the nitrate cannot be completely decomposed and volatilized in the cyclone preheater, affecting the subsequent suspension roasting reaction.

[0028] Furthermore, in step (2), the mixture is preheated for a holding time of 0.5 to 2 hours.

[0029] Furthermore, in step (2), the mixture obtained in step (1) is fed into a preheating furnace by a first screw feeder, and the mixture obtained in step (1) is preheated and kept warm for a certain period of time at a temperature range of 300-400°C by using the waste heat of the tail gas from the first cyclone separator, with the purpose of pre-melting and softening the nitric-sulfur mixed salt in the range of 300-400°C. Since the melting point of sodium nitrate is 307°C, the boiling point is 380°C, and the decomposition temperature is 380°C, the melting point of sodium sulfate is 884°C, the boiling point is 1404°C, and the decomposition temperature is 1100°C; while the melting point of potassium nitrate is 334°C, the boiling point is 400°C, and the decomposition temperature is 670°C, and the melting point of potassium sulfate is 1067°C, the decomposition temperature is 1067°C, and the boiling point is 1689°C, the melting point of nitrate is lower than that of sulfate, and nitrate will be softened and melted first. The erosion of the surface of the mineral particles by the nitrate after melting and softening helps the high-melting-point sulfate to embed into the layered lattice of the mineral particles for pre-encapsulation.

[0030] Furthermore, in step (3), the salt-molten pre-coated ore powder obtained in step (2) is conveyed to a dispersion dryer by a second screw feeder, and hot air at 300 to 400° C. is introduced into the air inlet at the bottom of the dispersion dryer. The purpose is to mix the hot air with the ore powder, disperse and dry the ore powder, and prevent the nitrate on the surface of the ore particles from being melted and softened and adhering to the ore particles, which is not conducive to the particle size requirement of the ore powder entering the subsequent suspension roasting furnace.

[0031] Furthermore, the dispersion dryer in step (3) is a venturi dryer, a flash dryer or a drying and dispersing machine.

[0032] Furthermore, in step (4), the dried ore powder obtained in step (3) is heat exchanged with 500-600°C hot air from the second cyclone separator in a cyclone preheater, the purpose of which is to further increase the temperature to the range of 500-600°C, promote the further decomposition and volatilization of the nitrate on the surface pre-coated by the salt melt, and obtain ore particles with sulfate coated on the surface, so as to facilitate the subsequent suspension roasting process. The sulfate enters the interior of the ore particle lattice and opens the layered lattice to wrap the fine-grained lithium mineral.

[0033] Furthermore, in step (5), the preheated ore powder from step (4) is heated in a suspension roasting furnace at a temperature in the range of 600 to 700°C, and the ore powder is subjected to the action of the airflow in a fluidized suspension state for roasting in the suspension roasting furnace, the purpose of which is to cause the sodium sulfate and / or potassium sulfate wrapped on the surface of the clay mineral to corrode and destroy the interlayer structure of clay minerals such as kaolinite and illite, and to utilize the alkali metal ions in the sulfate to corrode and destroy the aluminosilicate crystal structure in the clay mineral, thereby releasing the fine lithium minerals "bound" in the layered lattice structure and exposing them, reacting with the sodium salt and / or potassium salt, and decomposing and converting them into water-soluble lithium sulfate salts, so as to facilitate the subsequent neutral water leaching to effectively leach out and improve the lithium leaching yield.

[0034] Furthermore, in step (5), the residence time of the mineral powder in the suspension roasting furnace is 10 to 30 min, and the ventilation rate per kilogram of mineral powder is 500 to 800 mL / min.

[0035] Furthermore, in step (5), the fuel used in the burner of the suspension roasting furnace is an alkane fuel, including but not limited to one or more of heavy oil, natural gas, liquefied gas or water gas.

[0036] Furthermore, in step (6), the cyclone cooler separates the exhaust gas at a temperature in the range of 300-400°C, and in step (3), the second cyclone separator separates the exhaust gas at a temperature in the range of 500-600°C.

[0037] Furthermore, in order to test the effect of suspended roasting, the roasted clinker obtained in step (6) is ground to a particle size of -0.074 mm, which accounts for 60 to 90% of the total mass, to prepare a roasted powder; the roasted powder is mixed with water at a solid-liquid mass ratio of 1:3 to 1:4, and stirred and soaked in water at 20 to 100° C. for 0.5 to 2 h to obtain a soaked material; the soaked material is filtered and separated to obtain a lithium-containing leaching solution and a filter residue; and the lithium-containing leaching solution and the filter residue are sampled and sent for analysis to detect the lithium content therein.

[0038] The method of the present invention adopts the fluidized suspension roasting principle of powdered minerals, can process clay lithium ore powder with a particle size of 0.074 to 0.08 mm, has a short roasting time, precise temperature control, high roasting efficiency, stable roasting product quality, full use of waste heat, low energy consumption, and low process cost.

[0039] Compared with other disclosed technical solutions, the present invention has the following beneficial effects:

[0040] (1) The new method can give full play to the advantages of salt roasting of clay-type lithium ore: within a certain temperature range, it can effectively remove the hydroxyl groups that connect the basic units of aluminum oxygen octahedron and silicon oxygen tetrahedron in clay minerals kaolinite and illite, destroy the basic structure of clay mineral layered silicates, and dissociate the fine-grained lithium minerals "bound" in the silicate layered structure and react with sulfate to convert into soluble sulfate.

[0041] (2) The new method can also take advantage of the suspended roasting method: precisely control the dissociation, mineral phase transformation and decomposition behavior of clay minerals and lithium-containing mineral aggregates at the microscopic scale during the roasting process; and achieve efficient decomposition of fine-grained lithium ore embedded in the clay mineral lattice at a relatively low temperature and at a relatively fast speed. Compared with traditional kiln roasting methods such as rotary kilns and tunnel kilns, the new method has low energy consumption, low roasting cost, large processing capacity, and uniform temperature field control in the suspended roasting furnace, stable roasting effect and thorough roasting.

[0042] (3) The new method organically integrates the advantages of static kiln salt roasting and dynamic suspension roasting. The roasting temperature of the suspended dynamic roasting is precisely controlled, and the roasting temperature fluctuates within ±5°C. Compared with the traditional kiln static roasting, it can better control the overburning phenomenon, which is conducive to regulating the changes in the mineral phase structure during the roasting process, so that the selective leaching effect of lithium in the subsequent roasted sand is better. After the roasted sand is roasted with salt suspension by the new process, it can achieve efficient selective leaching of low-grade lithium in clay-type lithium ore and effective suppression of impurity elements by direct neutral water leaching, and the burden of subsequent purification and impurity removal is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those skilled in the art, other related drawings can also be obtained based on these drawings without creative work.

[0044] Figure 1 It is a structural schematic diagram of a system for suspended roasting of salt-melt pre-coated ore particles of a clay-type lithium ore according to the present invention;

[0045] In the figure, 1, mixer; 2, preheating furnace; 3, dispersion dryer; 4, first cyclone separator; 5, cyclone preheater; 6, suspension roasting furnace; 7, second cyclone separator; 8, cyclone cooler; 9, air cooler; 10, bag or electric precipitator; 11, tail gas treatment device; 12, induced draft fan; 13, first screw feeder; 14, second screw feeder;

[0046] A. Clay-type lithium ore or its concentrate powder; B. Mixed salt of alkali metal sulfate and nitrate; C. Fuel; D. Roasted clinker; E. Air; F. Waste gas. DETAILED DESCRIPTION

[0047] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0048] Example 1

[0049] A salt melting pre-coated ore particle suspension roasting system for clay-type lithium ore, the structure of which is shown in the figure Figure 1 The system includes a mixer 1, a preheating furnace 2, a dispersion dryer 3, a first cyclone separator 4, a cyclone preheater 5, a suspension roasting furnace 6, a second cyclone separator 7, a cyclone cooler 8, an air cooler 9, a bag or electric dust collector 10, an exhaust gas treatment device 11, an induced draft fan 12, a first screw feeder 13 and a second screw feeder 14, wherein:

[0050] The upper part of the mixer 1 is provided with a feed port for mineral powder A and a mixed salt B of alkali metal sulfate and nitrate; the lower discharge port of the mixer 1 is connected to the feed port of the preheating furnace 2 through the first screw feeder 13; the discharge port of the preheating furnace 2 is connected to the feed port of the dispersion dryer 3 through the second screw feeder 14; the air inlet of the dispersion dryer 3 is connected to the air outlet of the cyclone cooler 8 through a pipeline; the discharge port of the dispersion dryer 3 is connected to the feed port of the first cyclone separator 4; the air outlet of the first cyclone separator 4 is connected to the air inlet of the preheating furnace 2; the discharge port of the first cyclone separator 4 is connected to the air outlet pipeline of the second cyclone separator 7 through a feed pipeline, and is connected to the feed port of the cyclone preheater 5;

[0051] The solid phase discharge port of the cyclone preheater 5 is connected to the feed port of the suspension roasting furnace 6; the air outlet of the cyclone preheater 5 is connected to the inlet of the bag or electric precipitator 10; the lower outlet of the bag or electric precipitator 10 is connected to the feed port of the cyclone preheater 5; the upper air outlet of the bag or electric precipitator 10 is connected to the air inlet of the exhaust gas treatment device 11; the air outlet of the exhaust gas treatment device 11 is connected to the air inlet of the induced draft fan 12, and the exhaust gas F is discharged from the air outlet of the induced draft fan 12;

[0052] The discharge port of the suspension roasting furnace 6 is connected with the feed port of the second cyclone separator 7; a fuel inlet is provided at the bottom of the suspension roasting furnace 6 for introducing fuel C; the discharge port of the second cyclone separator 7 is connected with the feed port of the cyclone cooler 8; the discharge port of the cyclone cooler 8 is connected with the feed port of the air cooler 9; the air outlet of the cyclone cooler 8 is connected with the air inlet of the dispersion dryer 3 through a pipeline; the air inlet of the suspension roasting furnace 6 is connected with the air outlet of the air cooler 9 through a pipeline, and a discharge port for roasted clinker D is provided below the air cooler 9. Air E is introduced into the air inlets of the cyclone cooler and the air cooler.

[0053] The method for using the system to carry out suspension roasting of salt-melt pre-coated ore particles of clay-type lithium ore is as follows:

[0054] (1) Grind 1000 kg of clay-type lithium ore (the mass percentage of Li2O in the ore is 0.4% and the weight percentage of water is 5%) to a particle size of -0.074 mm, which accounts for 90% of the total mass, to prepare ore powder, and stir it evenly with a mixed salt of sodium sulfate and sodium nitrate in a mixer 1 to obtain a mixture. The mass ratio of the clay-type lithium ore powder to the mixed salt of sodium sulfate and sodium nitrate is 1:0.3, and the mass ratio of sodium sulfate to sodium nitrate is 2:1;

[0055] (2) The mixture obtained in step (1) is fed into the preheating furnace 2 by the first screw feeder 13, and the mixture obtained in step (1) is preheated at a temperature of 300-400° C. by using the waste heat of the tail gas from the first cyclone separator 4 and kept warm for 2 hours to obtain salt-molten pre-coated mineral powder;

[0056] (3) The salt melt pre-coated ore powder obtained in step (2) is conveyed to the dispersion dryer 3 by the second screw feeder 14, and the tail gas at 300-400°C from the outlet of the cyclone cooler 7 is introduced into the air inlet at the bottom of the dispersion dryer, and the tail gas is mixed with the ore powder to disperse and dry the ore powder; the dried ore powder is discharged from the outlet of the dispersion dryer 3 along with the hot air, enters the first cyclone separator 4, and is separated from the gas in the first cyclone separator 4; under the condition of starting the induced draft fan 12, the dried ore powder enters the cyclone preheater 5 in front of the suspension roasting furnace 6 along with the 500-600°C hot air from the outlet of the second cyclone separator 7;

[0057] (4) The dried mineral powder obtained in step (3) is heat exchanged with the 500-600°C tail gas from the outlet of the second cyclone separator 7 in the cyclone preheater 5 to form preheated mineral powder, which is discharged from the outlet of the cyclone preheater 5 and enters the suspension roasting furnace 6;

[0058] (5) The hot air from the air cooler 9 is introduced into the air inlet at the bottom of the suspension roasting furnace 6, and the natural gas is introduced into the fuel inlet of the burner at the bottom of the suspension roasting furnace 6. The natural gas is burned in the furnace of the suspension roasting furnace 6 to further heat the preheated mineral powder from step (4) to a temperature in the range of 600-700°C. The mineral powder is subjected to the action of the airflow in the suspension roasting furnace and is in a fluidized suspension state for roasting. The residence time of the mineral powder in the suspension roasting furnace is 10 min, and the ventilation rate per kg of mineral powder is 500 mL / min.

[0059] (6) The ore powder obtained after suspension roasting in step (5) is transported by hot air flow into the second cyclone separator 7 connected to the suspension roasting furnace 6 for gas-solid separation. The obtained ore powder is transported into the cyclone cooler 8 for air cooling and gas-solid separation. The ore powder is discharged from the bottom discharge port of the cyclone cooler 8 and sent to the air cooler 9 for further air cooling to obtain roasted clinker. The preheated air in the air cooler 9 is introduced into the bottom burner of the suspension roasting furnace 6 as combustion air.

[0060] (7) The exhaust gas at 500° C. to 600° C. separated by the second cyclone separator 7 in step (6) is introduced into the cyclone preheater 5 in step (4) as heating gas to preheat the mineral powder; the exhaust gas from the cyclone preheater 5 passes through the bag filter 10 and enters the exhaust gas treatment device 11 for treatment to meet the standards before being discharged; the mineral powder collected by the bag filter 10 is returned to the cyclone preheater 5 and re-sent to the suspension roasting furnace 6 for further roasting.

[0061] In order to test the effect of suspended roasting, the roasted clinker obtained in step (6) was ground to a particle size of -0.074 mm accounting for 90% of the total mass to prepare a roasted powder; the roasted powder was mixed with water at a solid-liquid mass ratio of 1:3, and stirred and soaked in water at 20°C for 2 h to obtain a soaked material; the soaked material was filtered and separated to obtain a lithium-containing leachate and a filter residue; the lithium concentration in the lithium-containing leachate was analyzed and detected to be 1.08 g / L; the filter residue was dried and weighed, and the mass percentage of Li2O was analyzed and detected to be 0.03% and the lithium leaching rate was 93.1%.

[0062] Example 2

[0063] The structure of the suspension roasting system is the same as that of Example 1. The suspension roasting method is:

[0064] (1) 600 kg of clay-type lithium ore concentrate (the mass percentage of Li2O in the concentrate is 0.83%, and the weight percentage of water is 3%) is ground to a particle size of -0.074 mm, which accounts for 60% of the total mass, to prepare ore powder, and the ore powder is mixed with a mixed salt of sodium sulfate and sodium nitrate in a mixer 1. The mass ratio of the clay-type lithium ore concentrate powder to the mixed salt of sodium sulfate and sodium nitrate is 1:0.05, and the mass ratio of sodium sulfate to sodium nitrate is 1:2;

[0065] (2) The mixture obtained in step (1) is fed into the preheating furnace 2 by the first screw feeder 13, and the mixture obtained in step (1) is preheated at a temperature in the range of 300-400° C. by utilizing the waste heat of the tail gas from the first cyclone separator 4 and kept warm for 0.5 h to obtain the salt-molten pre-coated ore powder;

[0066] (3) The salt melt pre-coated ore powder obtained in step (2) is conveyed to the dispersion dryer 3 by the second screw feeder 14, and the tail gas at 300-400°C from the outlet of the cyclone cooler 7 is introduced into the air inlet at the bottom of the dispersion dryer, and the tail gas is mixed with the ore powder to disperse and dry the ore powder; the dried ore powder is discharged from the outlet of the dispersion dryer 3 along with the hot air, enters the first cyclone separator 4, and is separated from the gas in the first cyclone separator 4; under the condition of starting the induced draft fan 12, the dried ore powder enters the cyclone preheater 5 in front of the suspension roasting furnace 6 along with the 500-600°C hot air from the outlet of the second cyclone separator 7;

[0067] (4) The dried mineral powder obtained in step (3) is heat exchanged with the 500-600°C tail gas from the outlet of the second cyclone separator 7 in the cyclone preheater 5 to form preheated mineral powder, which is discharged from the outlet of the cyclone preheater 5 and enters the suspension roasting furnace 6;

[0068] (5) hot air from the air cooler 9 is introduced into the bottom air inlet of the suspension roasting furnace, and a mixed gas of natural gas and water gas is introduced into the fuel inlet of the bottom burner of the suspension roasting furnace 6. The mixed gas of natural gas and water gas is burned in the furnace of the suspension roasting furnace 6 to further heat the preheated mineral powder from step (4) to a temperature in the range of 600-700°C. The mineral powder is subjected to the action of the airflow in the suspension roasting furnace and is in a fluidized suspension state for roasting. The residence time of the mineral powder in the suspension roasting furnace is 30 min, and the ventilation rate per kg of mineral powder is 800 mL / min.

[0069] (6) The ore powder obtained after suspension roasting in step (5) is transported by hot air flow into the second cyclone separator 7 connected to the suspension roasting furnace 6 for gas-solid separation. The obtained ore powder is transported into the cyclone cooler 8 for air cooling and gas-solid separation. The ore powder is discharged from the bottom discharge port of the cyclone cooler 8 and sent to the air cooler 9 for further air cooling to obtain roasted clinker. The preheated air in the air cooler 9 is introduced into the bottom burner of the suspension roasting furnace 6 as combustion air.

[0070] (7) The exhaust gas at 500° C. to 600° C. separated by the second cyclone separator 7 in step (6) is introduced into the cyclone preheater 5 in step (4) as heating gas to preheat the mineral powder; the exhaust gas from the cyclone preheater 5 passes through the bag filter 10 and enters the exhaust gas treatment device 11 for treatment to meet the standards before being discharged; the mineral powder collected by the bag filter 10 is returned to the cyclone preheater 5 and re-sent to the suspension roasting furnace 6 for further roasting.

[0071] In order to test the effect of suspended roasting, the roasted clinker obtained in step (6) was ground to a particle size of -0.074 mm accounting for 60% of the total mass to prepare a roasted powder; the roasted powder was mixed with water at a solid-liquid mass ratio of 1:4, and stirred and soaked in water at 90°C for 0.5 h to obtain a soaked material; the soaked material was filtered and separated to obtain a lithium-containing leachate and a filter residue; the lithium concentration in the lithium-containing leachate was analyzed and detected to be 1.03 g / L; the filter residue was dried and weighed, and the mass percentage of Li2O was analyzed and detected to be 0.05%, and the lithium leaching rate was 95.1%.

[0072] Example 3

[0073] The structure of the suspension roasting system is the same as that of Example 1, and the suspension roasting method is as follows:

[0074] (1) Grind 1200 kg of clay-type lithium ore (the mass percentage of Li2O in the concentrate is 0.5%, and the weight percentage of water is 3%) to a particle size of -0.074 mm, which accounts for 80% of the total mass, to make ore powder, and mix it with a mixed salt of potassium sulfate and potassium nitrate in a mixer 1. The mass ratio of the clay-type lithium ore powder to the mixed salt of potassium sulfate and potassium nitrate is 1:0.1, and the mass ratio of potassium sulfate to potassium nitrate is 1:1;

[0075] (2) The mixture obtained in step (1) is fed into the preheating furnace 2 by the first screw feeder 13, and the mixture obtained in step (1) is preheated at a temperature in the range of 300-400° C. by utilizing the waste heat of the tail gas from the first cyclone separator 4 and kept warm for 1 h to obtain salt-molten pre-coated ore powder;

[0076] (3) The salt melt pre-coated ore powder obtained in step (2) is conveyed to the dispersion dryer 3 by the second screw feeder 14, and the tail gas at 300-400°C from the outlet of the cyclone cooler 7 is introduced into the air inlet at the bottom of the dispersion dryer, and the tail gas is mixed with the ore powder to disperse and dry the ore powder; the dried ore powder is discharged from the outlet of the dispersion dryer 3 along with the hot air, enters the first cyclone separator 4, and is separated from the gas in the first cyclone separator 4; under the condition of starting the induced draft fan 12, the dried ore powder enters the cyclone preheater 5 in front of the suspension roasting furnace 6 along with the 500-600°C hot air from the outlet of the second cyclone separator 7;

[0077] (4) The dried mineral powder obtained in step (3) is heat exchanged with the 500-600°C tail gas from the outlet of the second cyclone separator 7 in the cyclone preheater 5 to form preheated mineral powder, which is discharged from the outlet of the cyclone preheater 5 and enters the suspension roasting furnace 6;

[0078] (5) hot air from the air cooler 9 is introduced into the air inlet at the bottom of the suspension roasting furnace, and heavy oil is introduced into the fuel inlet of the burner at the bottom of the suspension roasting furnace 6. The heavy oil is burned in the furnace of the suspension roasting furnace 6 to further heat the preheated mineral powder from step (4) to a temperature in the range of 600-700°C. The mineral powder is subjected to the action of the airflow in the suspension roasting furnace and is in a fluidized suspension state for roasting. The residence time of the mineral powder in the suspension roasting furnace is 20 min, and the ventilation rate per kg of mineral powder is 700 mL / min.

[0079] (6) The ore powder obtained after suspension roasting in step (5) is transported by hot air flow into the second cyclone separator 7 connected to the suspension roasting furnace 6 for gas-solid separation. The obtained ore powder is transported into the cyclone cooler 8 for air cooling and gas-solid separation. The ore powder is discharged from the bottom discharge port of the cyclone cooler 8 and sent to the air cooler 9 for further air cooling to obtain roasted clinker. The preheated air in the air cooler 9 is introduced into the bottom burner of the suspension roasting furnace 6 as combustion air.

[0080] (7) The tail gas at 500° C. to 600° C. separated by the second cyclone separator 7 in step (6) is introduced into the cyclone preheater 5 in step (4) as heating gas to preheat the mineral powder; the tail gas of the cyclone preheater 5 passes through the electrostatic precipitator 10 and then enters the tail gas treatment device 11 for treatment to meet the standards and then is discharged; the mineral powder collected by the electrostatic precipitator 10 is returned to the cyclone preheater 5 and re-sent to the suspension roasting furnace 6 for further roasting.

[0081] In order to test the effect of suspended roasting, the roasted clinker obtained in step (6) was ground to a particle size of -0.074 mm accounting for 80% of the total mass to prepare a roasted powder; the roasted powder was mixed with water at a solid-liquid mass ratio of 1:4, and stirred and soaked in water at 70°C for 1 h to obtain a soaked material; the soaked material was filtered and separated to obtain a lithium-containing leachate and a filter residue; the lithium concentration in the lithium-containing leachate was analyzed and detected to be 0.82 g / L; the filter residue was dried and weighed, and the mass percentage of Li2O was analyzed and detected to be 0.06%, and the lithium leaching rate was 89.8%.

[0082] Comparative Example 1

[0083] The structure of the suspension roasting system is the same as that of Example 1, and the suspension roasting method is as follows:

[0084] (1) 1000 kg of raw clay-type lithium ore (the raw ore has a Li2O mass percentage of 0.4% and a water mass percentage of 5%) is ground to a particle size of -0.074 mm, which accounts for 90% of the total mass, to prepare ore powder, which is then mixed evenly with sodium sulfate in a mixer 1 to obtain a mixture. The mass ratio of the raw clay-type lithium ore powder to sodium sulfate is 1:0.3.

[0085] Steps (2) to (7) are the same as in Example 1.

[0086] In order to test the effect of suspended roasting, the roasted clinker obtained in step (6) was ground to a particle size of -0.074 mm, which accounted for 90% of the total mass, to prepare a roasted powder; the roasted powder was mixed with water at a solid-liquid mass ratio of 1:3, and stirred and soaked in water at 20 °C for 2 h to obtain a water-soaked material; the water-soaked material was filtered and separated to obtain a lithium-containing leaching solution and a filter residue; the lithium concentration in the lithium-containing leaching solution was analyzed and detected to be 0.13 g / L, the filter residue was dried and weighed, and the mass percentage of Li2O was analyzed and detected to be 0.42%, and the lithium leaching rate was only 6.5%. The results show that when no nitrate is added, only sulfate is added to the clay-type lithium ore powder and then suspended roasted, and the implementation effect of the present invention cannot be obtained.

[0087] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A salt melting pre-coated ore particle suspension roasting system for clay-type lithium ore, characterized in that: The system includes a mixer, a preheating furnace, a dispersion dryer, a first cyclone separator, a cyclone preheater, a suspension roasting furnace, a second cyclone separator, a cyclone cooler, an air cooler, a bag or electric precipitator, an exhaust gas treatment device, an induced draft fan, a first screw feeder and a second screw feeder, wherein: The upper part of the mixer is provided with a feed port for mineral powder and a mixed salt of alkali metal sulfate and nitrate; the lower discharge port of the mixer is connected with the feed port of the preheating furnace through a first screw feeder; the discharge port of the preheating furnace is connected with the feed port of the dispersion dryer through a second screw feeder; the air inlet of the dispersion dryer is connected with the air outlet of the cyclone cooler through a pipeline; the discharge port of the dispersion dryer is connected with the feed port of the first cyclone separator; The air outlet of the first cyclone separator is connected to the air inlet of the preheating furnace; the material outlet of the first cyclone separator is connected to the air outlet pipeline of the second cyclone separator through the feed pipeline, and is connected to the feed port of the cyclone preheater; the solid phase material outlet of the cyclone preheater is connected to the feed port of the suspension roasting furnace; the air outlet of the cyclone preheater is connected to the inlet of the bag or electrostatic precipitator; the lower outlet of the bag or electrostatic precipitator is connected to the feed port of the cyclone preheater; the upper air outlet of the bag or electrostatic precipitator is connected to the air inlet of the exhaust gas treatment device; the air outlet of the exhaust gas treatment device is connected to the air inlet of the induced draft fan; The discharge port of the suspension roasting furnace is connected with the feed port of the second cyclone separator; a fuel inlet is provided at the lower part of the suspension roasting furnace for introducing fuel; the discharge port of the second cyclone separator is connected with the feed port of the cyclone cooler; the discharge port of the cyclone cooler is connected with the feed port of the air cooler; the air outlet of the cyclone cooler is connected with the air inlet of the dispersion dryer through a pipeline; the air inlet of the suspension roasting furnace is connected with the air outlet of the air cooler through a pipeline, and a roasting clinker discharge port is provided below the air cooler.

2. A method for suspended roasting of salt-melt pre-coated ore particles of clay-type lithium ore, characterized in that: Using the system of claim 1, comprising the following steps: (1) grinding clay-type lithium ore or its concentrate into ore powder, and mixing it with a mixed salt of alkali metal sulfate and nitrate in a mixer to obtain a mixture; (2) feeding the mixture obtained in step (1) into a preheating furnace by means of a first screw feeder, and preheating and keeping the mixture warm at a temperature in the range of 300 to 400° C. by means of waste heat from the tail gas of the first cyclone separator, to obtain salt-molten pre-coated ore powder; (3) introducing air into the air inlets of the cyclone cooler and the air cooler, and conveying the salt melt pre-coated ore powder obtained in step (2) to the dispersion dryer by a second screw feeder; introducing hot air at 300-400°C from the air outlet of the cyclone cooler into the air inlet at the bottom of the dispersion dryer, and mixing the hot air with the ore powder to disperse and dry the ore powder; the dried ore powder is discharged from the outlet of the dispersion dryer along with the hot air, enters the first cyclone separator, and is separated from the gas in the first cyclone separator; under the condition of starting the induced draft fan, the dried ore powder enters the cyclone preheater in front of the suspension roasting furnace along with the hot air at 500-600°C from the air outlet of the second cyclone separator; (4) exchanging heat between the dried ore powder obtained in step (3) and the tail gas at 500-600°C from the outlet of the second cyclone separator in a cyclone preheater to form preheated ore powder, which is discharged from the outlet of the cyclone preheater and enters the suspension roasting furnace; (5) hot air from an air cooler is introduced into the air inlet at the bottom of the suspension roasting furnace, and fuel is introduced into the fuel inlet of the burner at the bottom of the suspension roasting furnace. The fuel is burned in the furnace of the suspension roasting furnace to further heat the preheated ore powder from step (4) to a temperature in the range of 600 to 700° C. The ore powder is subjected to the action of the airflow in the suspension roasting furnace in a fluidized suspended state for roasting; (6) The ore powder obtained after suspension roasting in step (5) is transported by hot air flow into a second cyclone separator connected to the suspension roasting furnace for gas-solid separation. The obtained ore powder is transported into a cyclone cooler for air cooling and gas-solid separation. The ore powder is discharged from the discharge port at the bottom of the cyclone cooler and sent to an air cooler for further air cooling to obtain roasted clinker. The preheated air in the air cooler is introduced into the bottom burner of the suspension roasting furnace as combustion air. (7) The tail gas at a temperature of 500 to 600° C. obtained by the second cyclone separator in step (6) is introduced into the cyclone preheater in step (4) as heating gas to preheat the mineral powder; the tail gas of the cyclone preheater passes through a bag filter or an electrostatic precipitator, and then enters an exhaust gas treatment device for treatment to meet the standards and then is discharged; the mineral powder collected by the bag filter or the electrostatic precipitator is returned to the cyclone preheater and re-sent to the suspension roasting furnace for further roasting.

3. The method for suspended roasting of salt-melt pre-coated ore particles of clay-type lithium ore according to claim 2, characterized in that: In the mineral powder of step (1), the part with a particle size of -0.074 mm accounts for 60-90% of the total mass of the mineral powder.

4. The method for suspended roasting of salt-melt pre-coated ore particles of clay-type lithium ore according to claim 2, characterized in that: The mass percentage of Li2O in the clay-type lithium ore of step (1) is 0.4-0.5%; the mass percentage of Li2O in the clay-type lithium ore concentrate is 0.6-1.0%, and the weight percentage of water in the clay-type lithium ore or its concentrate is 1-5%.

5. The method for suspended roasting of salt-melt pre-coated ore particles of clay-type lithium ore according to claim 2, characterized in that: In step (1), the alkali metal sulfate added is sodium sulfate and / or potassium sulfate, the alkali metal nitrate added is sodium nitrate and / or potassium nitrate, the mass ratio of the clay-type lithium ore powder to the mixed salt is 1:0.05 to 1:0.3, and the mass ratio of the sulfate to the nitrate in the mixed salt of the alkali metal sulfate and nitrate is 2:1 to 1:

2.

6. The method for suspended roasting of salt-melt pre-coated ore particles of clay-type lithium ore according to claim 2, characterized in that: In step (2), the mixture is preheated for a holding time of 0.5 to 2 hours.

7. The method for suspended roasting of salt-melt pre-coated ore particles of clay-type lithium ore according to claim 2, characterized in that: The dispersion dryer in step (3) is a venturi dryer, a flash dryer or a drying and dispersing machine.

8. The method for suspended roasting of salt-melt pre-coated ore particles of clay-type lithium ore according to claim 2, characterized in that: In step (5), the residence time of the mineral powder in the suspension roasting furnace is 10 to 30 min, and the ventilation rate per kilogram of mineral powder is 500 to 800 mL / min.

9. The method for suspended roasting of salt-melt pre-coated ore particles of clay-type lithium ore according to claim 2, characterized in that: In step (5), the fuel used in the burner of the suspension roasting furnace is an alkane fuel, including one or more of heavy oil, natural gas, liquefied gas or water gas.

10. The method for suspended roasting of salt-melt pre-coated ore particles of clay-type lithium ore according to claim 2, characterized in that: In order to test the effect of suspended roasting, the roasted clinker obtained in step (6) is ground to a particle size of -0.074 mm, which accounts for 60 to 90% of the total mass, to prepare a roasted powder; the roasted powder is mixed with water at a solid-liquid mass ratio of 1:3 to 1:4, and stirred and soaked in water at 20 to 100° C. for 0.5 to 2 h to obtain a soaked material; the soaked material is filtered and separated to obtain a lithium-containing leaching solution and a filter residue; and the lithium-containing leaching solution and the filter residue are sampled and sent for analysis to detect the lithium content therein.

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