Process for manufacture of particulate LDH adsorbents

Abstract

The invention relates to the field of inorganic adsorbent granulation. A method for manufacturing a particulate lithium dihydroxide aluminum chloride (LDH) adsorbent includes adding metered amounts of LDH powder and a binder to a mixing granulator. After the mixing and the addition of the binder solvent to the mixing granulator, the LDH adsorbent is granulated, the LDH adsorbent is air-degassed and vacuum-degassed, and the resulting granules are unloaded and sieved. The low-boiling-point chlorine carbon compound solvent is used as a binder solvent. According to the invention, the binder solvent is recovered by condensation, in which the stream of the air-vapor mixture is conducted through the following circuits: mixing granulator-dust filtration-condensation of the binder solvent-heating of the air-vapor mixture-mixing granulator. The LDH adsorbent is granulated under the condition that the air-steam mixture in the shell of the mixing granulator is at a temperature of 30-40 DEG C and the air-steam mixture circulates at a volume flow rate of 200-300 times per hour. The method reduces the cost of granulating the LDH adsorbent and recovers the binder solvent evaporated during the granulation.

Description

Technical Field

[0001] The present invention relates to chemical material science, and in particular to a method for granulating an inorganic adsorbent made of aluminum hydroxide, wherein the inorganic adsorbent selectively extracts lithium from natural brine and synthetic lithium-containing chloride salt solutions. Background Art

[0002] In the prior art, inorganic adsorbents made of hydrated composite materials containing the complex LiС1 / А1(ОН)3 (US Patent 6280693) have been proposed for the selective extraction of lithium from brine [1].

[0003] A method for producing a granular adsorbent for extracting lithium from brine by granulating a granular lithium aluminum double hydroxide (LDH) adsorbent with a defect structure is known (Russian Federation Patent No. 2009714), using fluoroplastic as a binder and acetone as a solvent [2].

[0004] A disadvantage of this method is that it uses polytetrafluoroethylene (PTFE) as a binder, which is soluble in acetone. The use of acetone makes the pelletizing process prone to explosion and fire, necessitating appropriate safety measures.

[0005] A method for producing a granular adsorbent for extracting lithium from lithium-containing solutions is known (Russian Federation Patent No. 2455063). The method comprises obtaining lithium aluminum double hydroxide of the chloride type (LiCl∙ 2А1(ОН)3∙ nН2О), drying it, grinding it, and granulating the powder with polyvinyl chloride and dichloromethane (as a solvent), while recovering the volatilized dichloromethane during the granulation process and returning it to the production process. [3].

[0006] Disadvantages of this approach include: - Increased residual solvent levels in the extrudate, leading to higher solvent usage and worsening hygienic conditions during manufacturing; - The initial LDH particles produced by pulverizing the degassed extrudate have reduced mechanical strength due to their irregular shape; Recovery systems based on oil absorption-desorption of dichloromethane vapor and subsequent condensation into a liquid phase are not only bulky and complex to operate, but also present a fire hazard due to the simultaneous use of large amounts of flammable materials in the form of vacuum oil.

[0007] A recognized technology for producing high-strength spherical ceramic granules (Russian Federation Patent No. 2133716) consists in granulating the crushed raw materials by granulation in a pan granulator [4]. The disadvantage of this technology is that the process is multi-stage and the implementation of the technology is complicated.

[0008] A recognized technology for the production of granular adsorbents for the extraction of lithium from lithium-containing brines (Russian Federation Patent No. 2657495) comprises: obtaining lithium double aluminum hydroxide (LDH) powder, separating the LDH powder from the solution, drying it, grinding the powder into particles ≤ 0.10 mm in size, granulating it with the addition of chlorinated polyvinyl chloride and a chlorinated organic solvent, specifically comprising: preparing a paste of the dried and ground DGAL-Cl powder with a pre-prepared solution of chlorinated polyvinyl chloride in a chlorinated organic solvent, extruding the paste through a filter, degassing the extrudate with hot air, degassing it under vacuum, crushing and classifying the extrudate, roller-rolling and packaging the finished particles, compressing and pre-cooling the gas stream containing chlorinated organic solvent vapor, separating the condensed phase, and deep cooling the gas stream to deep condense the chlorinated organic solvent [5]. This method was selected as a prototype of the claimed invention.

[0009] The disadvantages of this method (prototype) are: - In order to achieve uniform distribution of the dry and ground LDH powder, the adhesive must be stirred and mixed for a long time; - The process used to manufacture LDH adsorbent particles consists of multiple stages (extrusion - two-stage degassing - pulverization - granulation); - the high cost of processing the degassing air stream, which is heated (to 120-130°C) to degas the extrudate and then subjected to step-by-step deep cooling (to -15°C) to condense the organochlorine solvent; - To reduce the volume of the gas, the vapor air flow is compressed; - The presence of large amounts of water (solid and liquid) in the condensate requires phase separation and changes the properties of the solvent (e.g., dichloromethane) due to hydrolysis. Summary of the Invention

[0010] The purpose of the present invention is to reduce the cost of LDH adsorbent granulation and binder solvent recovery during the granulation process.

[0011] This object is achieved by implementing the method for producing a granular LDH adsorbent as proposed below, wherein in the method: granulation is performed using a mixer granulator having a rotor, wherein the rotor forms a vortex field of a mixture of material particles and steam-air inside a mixer granulator housing; LDH powder, a binder and a measured binder solvent are mixed in the mixer granulator housing; the obtained granular LDH adsorbent is then air-degassed and vacuum-degassed in the mixer granulator housing; the binder solvent is metered after the LDH powder and the binder are mixed in the mixer granulator housing; the LDH adsorbent is air-degassed in the mixer granulator housing while the housing and the rotor are rotating; and the binder solvent is metered. air degassing after the binder is added to the mixer granulator housing; air degassing is performed while the LDH adsorbent is being granulated; air degassing is performed on the LDH adsorbent by circulating the steam-air mixture in a closed loop (mixer granulator housing - binder solvent condensation - steam-air mixture heating - mixer granulator housing); the binder solvent is condensed after the steam-air mixture is filtered out from the LDH adsorbent dust; after air degassing, the LDH adsorbent is vacuum degassed while the mixer granulator housing is rotating and the mixer granulator housing is under a residual pressure in the housing of 0.1 atm; the LDH adsorbent is granulated at a steam-air mixture temperature in the mixer granulator housing of 300°C and a steam-air mixture circulation rate of 200-300 times / hour.

[0012] The use of a rotary mixer-granulator with a high-speed rotor enhances the particle formation process by creating a vortex field within the mixer-granulator housing that swirls the powder material and vapor gas mixture. The mixer-granulator performs several functions: intensive mixing of the initial components, granulation of the adsorbent, and removal of the binder solvent from the adsorbent particles.

[0013] The air degassing process occurs in a closed loop where the vapor-gas mixture circulates: mixer-granulator – aerosol filter – heat exchanger – dichloromethane vapor condenser – vapor-gas mixture heater – mixer-granulator.

[0014] Compared to the prototype (Russian Federation Patent No. 2657495), air deaeration of the granulated LDH adsorbent in the mixer-granulator housing reduces the amount of vapor-air mixture that enters the condensate during the removal of the binder solvent from the LDH adsorbent.

[0015] At the end of the air degassing process, the granulated LDH adsorbent was vacuum degassed with the rotating mixer-granulator housing at a residual pressure of 0.1 atm.

[0016] The adsorbent particles from the granulator were sieved and the target fraction (particles in the range of 0.5 mm to 3.0 mm) was separated.

[0017] The remaining recycled sorbent particles (sorbent particles with a particle size less than 0.5 mm and sorbent particles with a particle size greater than 3.0 mm) can be returned to the mixer granulator for further processing.

[0018] The LDH powder is mixed with the binder and the binder solvent is added into the mixing granulator housing under the condition that the rotating housing and the rotor form a high-intensity vortex field. Firstly, a high mixing uniformity is quickly achieved, and then a uniform adhesive is quickly produced when the binder solvent is added for the subsequent formation of adsorbent particles.

[0019] The use of low boiling point organochlorine solvents as binder solvents enables efficient degassing of the particles without requiring significant heating of the vapor-air mixture.

[0020] The binder solvent was added to the mixer-granulator housing after the LDH powder was mixed with the binder to ensure that the solvent came into contact with the fresh, homogeneous mixture.

[0021] Due to the details of the manufacturing process of the LDH adsorbent using a binder, which requires the removal of the binder solvent from the resulting particles, the simultaneous pelletizing and degassing of the LDH adsorbent reduces the time required to manufacture the adsorbent.

[0022] During the degassing of the LDH adsorbent, the steam-air mixture is circulated in a closed loop (mixer-granulator housing - dust filtration - binder solvent condensation - steam-air mixture heating - mixer-granulator housing) to first remove the binder solvent vapor from the adsorbent surface. Then, the adsorbent dust from the steam-air mixture flow prevents the heat exchange surface from interfering with adsorbent deposits. The adsorbent vapor is extracted from the steam-air mixture by condensation and the adsorbent is removed from the system. The adsorbent-depleted steam-air mixture is heated to stabilize the temperature during the adsorbent degassing process because the evaporation of the low-boiling point binder solvent is accompanied by a decrease in the adsorbent surface temperature. Circulating the steam-air mixture in a closed loop enhances the condensation of the adsorbent vapor, thereby improving the efficiency of the condensation by reducing the amount of steam-air mixture.

[0023] Granulation of the LDH adsorbent in a mixer granulator at a steam-air mixture temperature of 30°C to 40°C and a steam-air mixture circulation rate of 200-300 times / hour produced a target portion of adsorbent particles in an amount of 65% to 70% of the mass of the loaded LDH powder, binder, and recycled mixture.

[0024] The volumetric circulation rate of the steam-air mixture (times / hour) is defined as the flow rate of the steam-air mixture circulating (m 3 / h) and the volume of the mixing granulator shell (m 3 ) and characterizes the gas exchange in the mixer granulator housing.

[0025] The achievement of technical results is confirmed by way of example by a method for producing a granular LDH adsorbent.

[0026] List of tables. Table 1. Characteristics of the vortex mixer granulator.

[0027] Table 2. Process parameters for LDH adsorbent granulation in a mixer granulator.

[0028] Table 3. Particle size distribution of the obtained LDH adsorbent particles.

[0029] Table 4. Yields of target granule fractions and recycled mixtures in the mixer granulator.

[0030] Example. The synthesized LDH blocks were crushed using a CW-60C+ grinder and finely divided on a sieve mill.

[0031] The apparatus for producing LDH adsorbent particles includes a vortex mixer granulator, an aerosol filter, a rotary flow meter, a condenser, a condensate cylinder, a circulation pump, a gas heater, and a cryostat. The characteristics of the mixer granulator are shown in Table 1.

[0032] Table 1 - Characteristics of Vortex Mixer Granulators feature value type OVP (granulation type, vortex type, batch type) Operation Mode Periodicity Shell volume 6 L Shell speed 70 rpm rotor speed 0–3,000 rpm Powder loading Max 1 kg The vortex mixer granulator was operated in a periodic mode. Calculated amounts of LDH powder and chlorinated polyvinyl chloride resin were loaded into the mixer granulator housing through an opening. An aerosol filter was then installed on the mixer granulator.

[0033] When the mixer-granulator is started, the housing rotates first, followed by the rotor. The rotor speed is set using a frequency converter in the control unit. The mixer-granulator housing rotates at a constant speed of 70 rpm. The rotation of the housing and rotor (the housing and rotor rotate in opposite directions) creates a strong vortex of the loaded material along the bottom and walls of the housing. The mixing time is 5 minutes.

[0034] Then, a required amount of a binder solvent for granulation is introduced into the mixing granulator housing through a liquid phase supply unit, wherein dichloromethane (a low-boiling-point organic chlorine solvent) is used as the binder solvent.

[0035] The dichloromethane enters the moving layer of material where repeated collisions of the wet particles with each other, with the mixing elements and with the housing walls result in the formation of the desired spherical adsorbent particles during distillation of the dichloromethane in the eddy flow field.

[0036] Since dichloromethane is an expensive reagent, it is recovered by condensation on a cooling surface.

[0037] While the granules are being formed, they are degassed (distilled from dichloromethane). To this end, the air circulation pump is switched on while the housing and rotor are rotating. This creates a vacuum in the suction line and an overpressure in the supply line. The vacuum in the suction line draws the vapor-air mixture from the mixer-granulator housing into the dichloromethane condensation system, while the overpressure in the supply line returns the gas flow to the mixer-granulator housing.

[0038] The steam-air mixture containing suspended LDH adsorbent particles and dichloromethane vapor enters the aerosol filter from the mixing granulator housing, where the LDH adsorbent dust particles are separated.

[0039] Next, the vapor-air mixture is sent to a condenser where it is cooled and the dichloromethane is condensed on a surface cooled by a cryostat through a cooling liquid (TOSOL-40).

[0040] The mixture of condensed dichloromethane and residual gas enters the condensate receiver where phase separation occurs. To reduce dichloromethane losses, the condensate cylinder is cooled by a cryostat using a TOSOL-40.

[0041] The steam-air mixture is then added to the inlet of the air circulation pump and from the outlet reaches the steam-air mixture heater where it is heated to 30°C and then fed into the mixer-granulator housing.

[0042] The circulation of the steam-air mixture in a closed loop (mixer-granulator housing - dust filtration - binder solvent condensation - steam-air mixture heating - mixer-granulator housing) allows the recovery of dichloromethane used in the production of LDH adsorbent granules from LDH adsorbent powder.

[0043] At the end of the air degassing process (dichloromethane distillation), the mixer granulator rotor stopped rotating and vacuum degassing was carried out while the mixer granulator housing rotated at a residual pressure of 0.1 atm, after which the material was unloaded. The unloaded material was finely divided using a set of screens.

[0044] Table 2 presents the process characteristics of the LDH adsorbent particles for several experiments.

[0045] experiment# LDH powder weight, g LDH powder size, μm Binder weighing weight, g Maximum volume, ml Mixing time, min Maximum addition time, min Particle formation and maximum removal time, min 1 460 > 100 40 350 5 2 12 2 460 > 100 40 350 5 2 10 3 460 100–160 40 350 5 2 11 4 460 160–250 40 350 5 2 11 Table 3 shows the particle size distribution of the LDH adsorbent produced in the mixer granulator.

[0046] Table 3 - Particle size distribution of the resulting LDH adsorbent particles.

[0047]

[0048] The output of the target granule fraction and the recirculated mixture in the mixer granulator was calculated based on Table 3. The calculation results are presented in Table 4.

[0049] Table 4 – Yields of target granule fractions and recirculated mixture in the mixer granulator.

[0050]

[0051] When implementing the claimed method for manufacturing granular LDH adsorbent in a mixer granulator, the observed conditional granulation yield was greater than 76% wt.

[0052] In order to test the adsorption characteristics of the granular LDH adsorbent obtained according to this method, brine with a composition similar to that of the Qarhan Lake (g / dm 3 ) Similar simulated brine: LiC1 3.71; MgC12 -450.

[0053] The exchange capacity of the adsorbent produced using calcium hydride as the base agent was practically identical to the exchange capacity value of the LDH adsorbent example produced according to the prototype.

[0054] References 1. U.S. Patent 6280693 C01D 15 / 00. Composition for the recovery of lithium values from brine and process of making / using said composition / William C. Bauman John L. Burba. Filed September 20, 1996, published August 28, 2001.

[0055] 2. Russian Federation Patent No. 2009714. B 01 J 20 / 00. Process of manufacturing pelletized sorbing material for lithium recovery from salt brines / Menzheres LT, Kotsupalo NP, Orlova LB, Isupov VP, filed on January 27, 1992, published on March 30, 1994. Publication No. 9.

[0056] 3. Russian Federation Patent 2455063. B 01 J 20 / 30, B 01 J 20 / 02. Method of producing granular sorbent for extracting lithium from lithium-containing brine / Rjabtsev ADTitarenko, NP Kotsupalo et al. Filed on October 13, 2010, published on July 10, 2012. Publication No. 19.

[0057] 4. Russian Federation Patent No. 2133716. C04B 20 / 04, 20 / 10, 35 / 16, E 21 B 43 / 267. Method for producing high-strength spherical ceramic pellets / Migal VP, Mozhzherin VA, Novikov AN et al. Filed November 10, 1997, published July 27, 1999. Publication No. 21.

[0058] 5. Russian Federation Patent No. 2657495. B 01 J 20 / 30, B 01 J 20 / 02, B 01 J 20 / 08. Method for obtaining a granular sorbent for lithium recovery from lithium-containing brines under conditions of production of commercial lithium products / Rjabtsev AD Titarenko, NP Kotsupalo et al. Filed on September 25, 2017, published on June 14, 2018. Publication No. 17.

Claims

1. A method for producing a granular LDH adsorbent, comprising batching LDH powder and a binder for granulation, mixing, metering a binder solvent, granulating, air degassing and vacuum degassing, and screening the resulting LDH adsorbent particles, and recovering the binder solvent by condensation, wherein: Granulation is carried out in a mixing granulator having a rotor, wherein the rotor forms a vortex field of a mixture of material particles and steam-air inside the housing of the mixing granulator; LDH powder, a binder and an added binder solvent are mixed in the housing of the mixing granulator; and the obtained granular LDH adsorbent is then degassed with air and vacuum in the housing of the mixing granulator.

2. The method according to claim 1, characterized in that After the LDH powder and the binder are mixed in the mixer-granulator housing, the binder solvent is added.

3. The method according to claim 1, characterized in that The air degassing of the LDH adsorbent is performed in the mixer-granulator housing while both the housing and the rotor are rotating.

4. The method according to claim 3, characterized in that After the addition of the binder solvent into the mixer granulator housing is completed, the LDH adsorbent is subjected to the air degassing.

5. The method according to claim 3, characterized in that While the LDH adsorbent is being granulated, the air degassing is performed on the LDH adsorbent.

6. The method according to claim 3, characterized in that The air degassing of the LDH adsorbent is performed by circulating the steam-air mixture in a closed loop, wherein the closed loop is: mixing granulator housing-condensation of binder solvent-heating of the steam-air mixture-mixing granulator housing.

7. The method according to claim 6, characterized in that After filtering the vapor-air mixture to remove LDH adsorbent dust, the binder solvent is condensed.

8. The method according to claim 1, wherein After the air degassing process, the LDH adsorbent was vacuum degassed while the mixer granulator housing was rotating and the residual pressure in the housing was 0.1 atm.

9. The method according to claim 1, wherein The LDH adsorbent was granulated under the conditions that the temperature of the steam-air mixture in the mixing granulator shell was 30-40° C. and the volume circulation rate of the air flow mixture was 200-300 times / hour.

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