A lithium phosphate recovery process

Abstract

The present application relates to the technical field of lithium phosphate recovery, and provides a lithium phosphate recovery process, comprising the following steps: S1, a pretreatment module, sewage in an initial adjustment tank is sequentially subjected to precise filtration, pH adjustment, hard-removal adsorption, organic-removal adsorption, and UF filtration; S2, a lithium recovery module, pretreated liquid obtained in step S1 is combined with sodium sulfate and lithium phosphate solution, and is subjected to separation treatment by an electrodialyzer to obtain lithium sulfate solution, dilute lithium phosphate solution, sodium sulfate solution, and sodium phosphate solution; and S3, a phosphorus recovery module, third produced water obtained in step S2 is subjected to nanofiltration filtration process treatment to obtain fourth produced water and nanofiltration concentrated water, the fourth produced water is sent to the nanofiltration filtration process in step S2, and the nanofiltration concentrated water is reused to a separation section of the separation treatment by the electrodialyzer in step S2. The present application solves the problems that the existing lithium phosphate recovery needs multiple desorption-desorption, backwashing processes, the process is complex, and multiple waste water is generated in the recovery process.

Description

Technical Field

[0001] This invention relates to the field of lithium phosphate recovery technology, and more particularly to a lithium phosphate recovery process. Background Technology

[0002] The existing lithium phosphate recovery process consists of a pretreatment module → concentration module → lithium recovery module → phosphorus recovery module. The pretreatment module sequentially includes precision filtration, pH adjustment, hardening adsorption, organic matter removal adsorption, and ultrafiltration (UF). The initial conditioning tank contains raw material wash water, product wash water, and backwash water and desorption liquid from subsequent processes. After precision filtration, the lithium-containing sludge is fed into the subsequent lithium recovery module. The filtrate undergoes pH adjustment with sulfuric acid, hardening adsorption, organic matter removal adsorption, and UF filtration. The filtrate from the pretreatment module then enters the concentration module for further processing. First, it is concentrated by a reverse osmosis (RO) system. The permeate can be reused in the desorption and backwashing stages of the pretreatment module. The concentrated solution then enters an electrodialysis (ED) unit for further concentration. The desalinated water is again concentrated by the RO system. The RO system concentrate is mixed with the ultrafiltration (UF) filtrate, and the permeate can be reused at the upstream stage. The ED concentrate is used for hardening and organic matter removal via adsorption. The desorption and backwashing of the adsorbent follow the same process as in the pretreatment module. The solution obtained in the concentration module mainly contains lithium sulfate, which reacts with added sodium phosphate, resulting in complete precipitation. This precipitate is then filtered through precision to produce lithium-containing sludge, which enters the lithium recovery module's pressure filtration process to produce lithium phosphate sludge. The filtrate undergoes phosphorus removal via adsorption, and the concentrate enters the concentrate discharge tank. The backwash water returns to the initial equalization tank. The desorbed solution after phosphorus removal enters the nanofiltration concentration process, concentrating the sodium phosphate solution before returning it to the upstream lithium recovery module to generate lithium phosphate sludge. The nanofiltration permeate returns to the ED concentration desalination tank in the concentration module for subsequent processes. The entire process involves multiple desorption-desorption and backwashing processes and is complex, generating various types of wastewater during the recovery process. Summary of the Invention

[0003] Therefore, in view of the above problems, the present invention proposes a lithium phosphate recovery process that greatly simplifies the processing, produces less wastewater, has a high recovery rate, and reduces the recovery cost.

[0004] To solve this technical problem, the present invention adopts the following solution: a lithium phosphate recovery process, comprising the following steps:

[0005] S1, Pretreatment Module: The wastewater in the initial equalization tank is sequentially processed through precision filtration, pH adjustment tank, adsorption for hardening, adsorption for organic matter removal, and UF filtration. The lithium-containing sludge after precision filtration is sent to the subsequent lithium recovery module. The filtrate from the precision filtration is sent to the pH adjustment tank to adjust the pH value with sulfuric acid, and then sequentially sent to adsorption for hardening, adsorption for organic matter removal, and UF filtration to obtain the pretreated liquid. The wastewater in the initial equalization tank includes raw material wash water, product wash water, and backwash wastewater and desorption liquid generated from adsorption for hardening and adsorption for organic matter removal.

[0006] S2, Lithium Recovery Module: The pretreated liquid obtained in step S1, combined with sodium sulfate and lithium phosphate solution, is separated by an electrodialysis unit to obtain lithium sulfate solution, dilute lithium phosphate solution, sodium sulfate solution, and sodium phosphate solution. The lithium sulfate solution enters an RO system for concentration to obtain first product water and concentrated lithium sulfate solution. The first product water can be reused as the receiving liquid from the electrodialysis unit. The dilute lithium phosphate solution enters an RO system for concentration to obtain second product water and concentrated lithium phosphate solution. The second product water can be reused in the desorption and backwashing stages of the adsorption-hardening and adsorption-organic matter removal processes in step S1. The concentrated lithium phosphate solution... The lithium solution is returned to the separation section of the electrodialysis unit. The sodium sulfate solution and sodium phosphate solution are mixed and then fed into the nanofiltration process to obtain a mixed solution of sodium sulfate and concentrated sodium sulfate and sodium phosphate. The sodium sulfate obtained from the nanofiltration process is returned to the separation section of the electrodialysis unit. The mixed solution of concentrated sodium sulfate and sodium phosphate is mixed with the concentrated lithium sulfate solution and sent to the sedimentation tank. Sodium phosphate and lithium-containing sludge obtained in step S1 are added to the sedimentation tank. After sufficient reaction in the sedimentation tank, lithium phosphate precipitate is generated. The lithium phosphate precipitate in the sedimentation tank is sent to the filter press for filtration to produce lithium phosphate sludge and third-stage permeate.

[0007] S3, Phosphorus Recovery Module: The third permeate obtained in step S2 is treated by nanofiltration to obtain the fourth permeate and nanofiltration concentrate. The fourth permeate is sent to be mixed with the sodium sulfate solution and sodium phosphate solution obtained by electrodialysis in step S2 and then fed into the subsequent process. The nanofiltration concentrate is reused in the separation section of the electrodialysis process in step S2 to complete phosphorus recovery.

[0008] Furthermore, in step S1, the hardening adsorbent and the organic adsorbent that adsorbs and removes organic matter are restored under the action of the desorbent. The hardening adsorbent, the organic adsorbent, and the backwash water from ultrafiltration are returned to the initial conditioning tank. The calcium and magnesium desorption solution that adsorbs and removes hardness is directly sent to the initial conditioning tank, while the organic desorption solution enters the concentrated water discharge tank and the sodium sulfate mixing tank, respectively.

[0009] By adopting the aforementioned technical solution, the beneficial effects of this invention are as follows: The pretreated liquid is sent to a lithium recovery module to recover lithium phosphate sludge. Specifically, the pretreated liquid, along with sodium sulfate and lithium phosphate solution, is separated by an electrodialysis unit to obtain lithium sulfate solution, dilute lithium phosphate solution, sodium sulfate solution, and sodium phosphate solution. These are then concentrated via an RO system, filtered by nanofiltration (NF filtration), and sent to a sedimentation tank for mixing and sedimentation. Finally, they are sent to a filter press for filtration to recover lithium phosphate sludge and third-stage permeate. The third-stage permeate is then sent to the phosphorus recovery module for further treatment. Nanofiltration yields a fourth product water and nanofiltration concentrate. The fourth product water is sent to be mixed with the sodium sulfate solution and sodium phosphate solution obtained from electrodialysis in step S2 and then fed into the subsequent process. The nanofiltration concentrate is reused in the separation section of the electrodialysis process in step S2 to complete phosphorus recovery. The entire lithium phosphate recovery process greatly reduces the use of desorbents and backwash water, significantly reduces water treatment pressure, and lowers process costs. It achieves efficient recovery of lithium resources, greatly simplifies the treatment process, produces less wastewater, has a high recovery rate, and reduces recovery costs, making it widely applicable. Attached Figure Description

[0010] Figure 1 This is a process flow diagram of an embodiment of the present invention. Detailed Implementation

[0011] The present invention will now be further described with reference to the accompanying drawings and specific embodiments. The RO system (i.e., reverse osmosis water treatment system), nanofiltration filter, electrodialysis concentration device, and electrodialyzer are existing devices, which have been disclosed in Chinese patent documents: CN202321664088.8, CN202021364220.X, CN202311197459.0, CN202311028807.1, CN202310824869.7, etc.

[0012] refer to Figure 1 The preferred lithium phosphate recovery process of the present invention includes the following steps:

[0013] S1, Pretreatment Module 1, sequentially processes the wastewater in the initial equalization tank through precision filtration, pH adjustment tank, adsorption for hardening, adsorption for organic matter removal, and UF filtration. The lithium-containing sludge after precision filtration is sent to the subsequent lithium recovery module. The filtrate from precision filtration is sent to the pH adjustment tank to adjust the pH value with sulfuric acid, and then sequentially sent to adsorption for hardening, adsorption for organic matter removal, and UF filtration to obtain the pretreated liquid. The wastewater in the initial equalization tank includes raw material wash water, product wash water, and backwash wastewater and desorption liquid generated from adsorption for hardening and adsorption for organic matter removal. The hardening adsorbent and the organic matter adsorbent for organic matter removal are restored under the action of desorbents. The backwash wastewater from hardening adsorbent, organic matter adsorbent, and ultrafiltration is returned to the initial equalization tank. The calcium and magnesium desorption liquid from adsorption for hardening is directly sent to the initial equalization tank, while the organic matter desorption liquid enters the concentrated water discharge tank and the sodium sulfate mixing tank, respectively.

[0014] S2, Lithium Recovery Module 2: The pretreated liquid obtained in step S1 is sent to the raw liquid chamber of the electrodialysis unit, while the sodium sulfate solution and lithium phosphate solution are sent to the recovery chamber and replenishment chamber of the electrodialysis unit, respectively. The electrodialysis unit separates and processes the liquid to obtain lithium sulfate solution, dilute lithium phosphate solution, sodium sulfate solution, and sodium phosphate solution. The lithium sulfate solution enters the RO system for concentration to obtain first product water and concentrated lithium sulfate solution. The first product water can be reused as the receiving liquid from the electrodialysis unit. The dilute lithium phosphate solution enters the RO system for concentration to obtain second product water and concentrated lithium phosphate solution. The second product water can be reused from the desorption / desorption processes of adsorption for hardening and organic matter removal in step S1. In the absorption and backwashing water stage, the concentrated lithium phosphate solution is returned to the separation section of the electrodialysis unit. The sodium sulfate solution and sodium phosphate solution are mixed and then enter the nanofiltration process to obtain a mixed solution of sodium sulfate and concentrated sodium sulfate and sodium phosphate. The sodium sulfate obtained from the nanofiltration process is returned to the separation section of the electrodialysis unit. The mixed solution of concentrated sodium sulfate and sodium phosphate is mixed with the concentrated lithium sulfate solution and sent to the sedimentation tank. Sodium phosphate and lithium-containing sludge obtained in step S1 are added to the sedimentation tank. After sufficient reaction in the sedimentation tank, lithium phosphate precipitate is generated. The lithium phosphate precipitate in the sedimentation tank is sent to the filter press for filtration to produce lithium phosphate sludge and third permeate.

[0015] S3, Phosphorus Recovery Module 3, processes the third permeate obtained in step S2 using nanofiltration to obtain the fourth permeate and nanofiltration concentrate. The fourth permeate is sent to be mixed with the sodium sulfate solution and sodium phosphate solution obtained in step S2 through electrodialysis and then fed into the subsequent process. The nanofiltration concentrate is reused in the separation section of the electrodialysis process in step S2 to complete phosphorus recovery.

[0016] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A lithium phosphate recovery process, characterized in that: Includes the following steps: S1, Pretreatment Module: The wastewater in the initial equalization tank is sequentially processed through precision filtration, pH adjustment tank, adsorption for hardening, adsorption for organic matter removal, and UF filtration. The lithium-containing sludge after precision filtration is sent to the subsequent lithium recovery module. The filtrate from the precision filtration is sent to the pH adjustment tank to adjust the pH value with sulfuric acid, and then sequentially sent to adsorption for hardening, adsorption for organic matter removal, and UF filtration to obtain the pretreated liquid. The wastewater in the initial equalization tank includes raw material wash water, product wash water, and backwash wastewater and desorption liquid generated from adsorption for hardening and adsorption for organic matter removal. S2, Lithium Recovery Module: The pretreated liquid obtained in step S1, combined with sodium sulfate and lithium phosphate solution, is separated by an electrodialysis unit to obtain lithium sulfate solution, dilute lithium phosphate solution, sodium sulfate solution, and sodium phosphate solution. The lithium sulfate solution enters an RO system for concentration to obtain first product water and concentrated lithium sulfate solution. The first product water can be reused as the receiving liquid from the electrodialysis unit. The dilute lithium phosphate solution enters an RO system for concentration to obtain second product water and concentrated lithium phosphate solution. The second product water can be reused in the desorption and backwashing stages of the adsorption-hardening and adsorption-organic matter removal processes in step S1. The concentrated lithium phosphate solution... The lithium solution is returned to the separation section of the electrodialysis unit. The sodium sulfate solution and sodium phosphate solution are mixed and then fed into the nanofiltration process to obtain a mixed solution of sodium sulfate and concentrated sodium sulfate and sodium phosphate. The sodium sulfate obtained from the nanofiltration process is returned to the separation section of the electrodialysis unit. The mixed solution of concentrated sodium sulfate and sodium phosphate is mixed with the concentrated lithium sulfate solution and sent to the sedimentation tank. Sodium phosphate and lithium-containing sludge obtained in step S1 are added to the sedimentation tank. After sufficient reaction in the sedimentation tank, lithium phosphate precipitate is generated. The lithium phosphate precipitate in the sedimentation tank is sent to the filter press for filtration to produce lithium phosphate sludge and third-stage permeate. S3, Phosphorus Recovery Module: The third permeate obtained in step S2 is treated by nanofiltration to obtain the fourth permeate and nanofiltration concentrate. The fourth permeate is sent to be mixed with the sodium sulfate solution and sodium phosphate solution obtained by electrodialysis in step S2 and then fed into the subsequent process. The nanofiltration concentrate is reused in the separation section of the electrodialysis process in step S2 to complete phosphorus recovery.

2. The lithium phosphate recovery process according to claim 1, characterized in that: In step S1, the hardening adsorbent and the organic matter adsorbent are restored under the action of the desorbent. The hardening adsorbent, the organic matter adsorbent, and the backwash water from ultrafiltration are returned to the initial conditioning tank. The calcium and magnesium desorption solution for hardening is sent directly to the initial conditioning tank, while the organic matter desorption solution enters the concentrated water discharge tank and the sodium sulfate mixing tank, respectively.

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