Method for recovering metal ions in lithium iron phosphate waste through solid-phase electrolysisTechnical Field
The invention belongs to the technical field of lithium ion battery recovery, and particularly relates to a method for recovering metal ions in lithium iron phosphate waste through solid-phase electrolysis.
Background
Among various lithium ion batteries at present, lithium iron phosphate batteries are widely applied due to the characteristics of rich raw materials, low cost, good safety performance and the like, and a large number of lithium iron phosphate batteries enter a scrapping stage in the future. The lithium iron phosphate battery can be recycled, so that the pollution of waste batteries to the environment can be solved, nonferrous metals in the lithium iron phosphate waste can be recycled, the shortage of resources can be effectively relieved, and certain economic benefit can be brought.
The existing method for recycling and treating the lithium iron phosphate waste mainly comprises hydrometallurgy and pyrometallurgy. The binder and carbon black of the anode are removed by a pyrogenic recovery method, and the lithium iron phosphate is repaired to achieve secondary utilization. In the aspect of hydrometallurgy, the treatment mode of the lithium iron phosphate battery anode material is to leach iron and lithium and then separate the iron and lithium by acid leaching and adding an oxidant.
The invention patent with application number 201710317300.6 discloses a method for selectively recovering lithium from lithium iron phosphate waste, which comprises the steps of adding the lithium iron phosphate waste into an aqueous solution, adding an oxidant and stirring, reacting the lithium iron phosphate with the oxidant to generate iron phosphate, allowing lithium ions to enter the solution, and filtering to obtain a pure lithium-containing solution. The lithium-containing solution can be used to prepare battery grade lithium products. However, the method needs to add an oxidant to generate gas, so that potential safety hazards exist and the cost is high.
According to the invention patent with the application number of 201711285262.7, lithium iron phosphate powder, ternary positive electrode material powder, inorganic acid and water are mixed, the mixture is stirred and filtered, and the filtrate is enriched to obtain a high-concentration lithium-containing solution, so that lithium can be selectively leached at a high leaching rate and concentration, and the ternary battery positive electrode material powder is used for replacing a common strong oxidant, so that the reaction is mild, and the advantages of low cost, environmental protection and safety are achieved. However, the anode material of the ternary battery contains noble metals such as cobalt, nickel and the like, and has high recovery value, the noble metals in the anode material cannot be recovered by using the method as an oxidant, the potential cost is very high, a large amount of mixed salt wastewater is generated, and the treatment difficulty is high.
Disclosure of Invention
In view of the above defects or improvement needs in the prior art, an object of the present invention is to provide a method for recovering metal ions from lithium iron phosphate waste by solid-phase electrolysis, wherein the overall process flow of the method is controlled, an electrochemical method is used to replace adding an oxidant to dissolve out lithium in lithium iron phosphate (of course, iron element is also dissolved out), and the problems of large medicament usage amount, high wastewater treatment difficulty and high treatment cost of the existing method for recovering lithium iron phosphate waste can be effectively solved. The invention realizes the solid-phase electrolysis recovery of metal ions in the lithium iron phosphate waste for the first time, and solves the problems of using a large amount of reagents and generating mixed salt wastewater in the existing wet recovery process.
In order to achieve the above object, according to the present invention, there is provided a method for recovering metal ions from a lithium iron phosphate waste material by solid-phase electrolysis, comprising the steps of:
(1) preparing the grinded lithium iron phosphate waste, mixing the grinded lithium iron phosphate waste with water, and then carrying out ultrasonic oscillation and mechanical oscillation treatment to prepare uniform slurry;
(2) preparing an electrode substrate, attaching the slurry to the electrode substrate, and drying to prepare an anode;
(3) preparing an acid-resistant metal plate, and applying direct current to electrolyze by using the acid-resistant metal plate as a cathode and a phosphoric acid solution as an electrolyte to dissolve lithium ions and iron ions on an anode to obtain an acid solution;
(4) adjusting the acid solution to enable the pH value of the solution to be 1.5-2, then heating and refluxing for 3-8 h, and separating out crude iron phosphate; then, drying the rough ferric phosphate, and then calcining at 700-1000 ℃ to obtain anhydrous ferric phosphate;
(5) and (5) adding alkali liquor into the solution after the crude iron phosphate is separated out in the step (4) to adjust the pH value of the solution to 8-9, and separating out lithium phosphate to obtain a lithium phosphate product.
As a further preferred of the present invention, the method further comprises the steps of:
(6) and (4) evaporating and crystallizing the solution after the lithium phosphate is precipitated in the step (5) to obtain phosphate.
As a further preferable mode of the present invention, in the step (1), the lithium iron phosphate waste is derived from scrap generated in a lithium iron phosphate battery production process or a cathode material obtained by disassembling a lithium iron phosphate battery.
In a further preferable mode of the invention, in the step (1), the liquid-solid ratio of the lithium iron phosphate waste to the water is 5-10: 1, the ultrasonic oscillation time is 0.5-3 hours, and the mechanical oscillation treatment time is 1-5 hours.
As a further preferred aspect of the present invention, in the step (2), the electrode substrate is made of a porous conductive material; and attaching the slurry to the electrode substrate, specifically, immersing the electrode substrate into the slurry, and taking out the electrode substrate after the electrode substrate is fully immersed.
As a further optimization of the invention, in the step (2), the drying temperature is 80-105 ℃, and the drying time is 2-3 h.
In a further preferred embodiment of the present invention, in the step (3), the acid-resistant metal plate is made of stainless steel, titanium metal, or platinum metal.
In a further preferred embodiment of the present invention, in the step (3), the concentration of the phosphoric acid solution is 0.2 to 1.0mol/L, and the voltage used for electrolysis is 1V to 3V.
In a further preferred embodiment of the present invention, in the step (4), the temperature of the heating reflux is 60 to 90 ℃.
As a further preferable mode of the invention, in the step (4), the acidic solution is adjusted to have a pH of 1.5-2, specifically, an alkali solution is added to the acidic solution to adjust the pH of the solution to 1.5-2; the alkali liquor is sodium hydroxide solution or ammonia water;
in the step (5), the alkali liquor is sodium hydroxide solution or ammonia water.
Compared with the prior art, the lithium and iron are directly transferred into the electrolyte from the lithium iron phosphate through solid-phase electrolysis by the technical scheme of the invention, and the lithium ion transfer rate can reach more than 90% without adding other oxidants. Because the electrolyte used by the method is a phosphoric acid solution which is the same as the anions of the lithium iron phosphate material, the residual wastewater component after the lithium phosphate product is recovered by precipitation is single phosphate, and the treatment is easy.
The invention realizes the control of the oxidation-reduction potential of the system through the electrolysis process, and considering the extremely poor conductivity of the lithium iron phosphate solid, if the lithium iron phosphate solid is directly used as a working electrode, the current density is small, and the time-space yield of electrolysis is very low, therefore, the invention grinds the lithium iron phosphate and adds water to prepare the slurry, and the slurry is attached to the electrode substrate, and can be particularly dispersed into the porous conductive material, so that the contact area between the lithium iron phosphate and the electrode is enlarged, thereby increasing the current density and improving the time-space yield of electrolysis.
By careful consideration, the invention selects phosphoric acid solution as electrolyte, and the recovered lithium-containing target product is lithium phosphate. Lithium carbonate is generally used as a lithium source in domestic lithium iron phosphate production, so the recovery target product of the lithium iron phosphate waste treatment process is lithium carbonate. However, the process for recovering lithium carbonate introduces excessive carbonate into the leaching solution, thereby generating mixed wastewater of a plurality of acid radicals. By using the wet recovery process of leaching phosphoric acid and then precipitating lithium phosphate, the by-product is only phosphate, and the recovery process is cleaner.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Generally speaking, the method for recovering metal ions in lithium iron phosphate waste material by solid-phase electrolysis in the invention is that firstly, water is added into the ground lithium iron phosphate waste material, the ground lithium iron phosphate waste material is pasted and coated on an electrode substrate (such as a porous conductive material) to be dried to be used as an anode, an acid-resistant metal plate is used as a cathode, dilute phosphoric acid is used as an electrolyte, direct current is applied, lithium iron phosphate on the anode is oxidized, lithium ions and iron ions enter the electrolyte, the pH of the electrolyte is adjusted by using an alkali solution, and crude iron phosphate and lithium phosphate are respectively precipitated under different pH values. Preferably, after filtering the obtained lithium phosphate, the electrolyte can be evaporated and crystallized to obtain the phosphate.
Example 1
Provides the waste materials in the production process of the lithium iron phosphate battery (such as unqualified materials eliminated in the production process of the lithium iron phosphate battery)Wherein the purity of the lithium iron phosphate raw material is high, the impurities are mainly a small amount of binder such as PVDF and the like, water is added after grinding (the size of the ground particles is not strictly required, and the subsequent carbon felt attached with the particles is dried and then does not fall off), the liquid-solid ratio (namely the mass ratio of liquid to solid) is 5:1, and after 30min of ultrasonic oscillation, the mixture is mechanically stirred for 1h to obtain uniform slurry. And (3) immersing a graphite felt of 1cm by 2cm by 3cm into the slurry, taking out after full infiltration, drying for 3 hours at 105 ℃ to prepare an anode, and weighing the mass of the anode loaded with lithium iron phosphate. 30ml of 0.6mol/L phosphoric acid solution is used as electrolyte, stainless steel is used as a cathode, 2.5V potential is applied to the electrolyte in an electrolytic tank, and the time is 1h, so that lithium and iron in an anode are transferred into the electrolyte to form lithium-containing solution. After the experiment is finished, the content of lithium in the lithium-containing solution is detected, and the concentration of lithium in the lithium-containing solution is 100mg/L (by taking Li+Measured), the lithium migration rate can reach 94 percent.
Concentrating the lithium-containing solution to a concentration of 1g/L (in terms of Li)+And (2) adding ammonia water into the solution, adjusting the pH value to be 2, heating and refluxing the solution at 90 ℃ for 8h, carrying out solid-liquid separation to obtain a crude iron phosphate precipitate and a filtrate, washing the crude iron phosphate twice by deionized water according to the liquid-solid ratio of 3:1, and calcining the washed crude iron phosphate at 900 ℃ for 2h to obtain an iron phosphate product with the purity of a battery level.
And continuously adding ammonia water into the filtrate to adjust the pH value to 9, carrying out solid-liquid separation to obtain a lithium phosphate precipitate and an ammonium phosphate solution, washing the lithium phosphate precipitate twice with deionized water according to the liquid-solid ratio of 3:1, and drying at 105 ℃ to obtain a lithium phosphate product with the purity of a battery grade.
And evaporating the ammonium phosphate solution to dryness to obtain an ammonium phosphate product.
Example 2
Providing a positive electrode material obtained after the lithium iron phosphate battery is disassembled (namely, the positive electrode material obtained after the scrapped lithium iron phosphate battery is disassembled), grinding, adding water, wherein the liquid-solid ratio is 7:1, and mechanically stirring for 3 hours after ultrasonic oscillation is carried out for 60 minutes to obtain uniform slurry. And (3) immersing a graphite felt of 1cm by 2cm by 3cm into the slurry, taking out after full infiltration, drying for 2 hours at 105 ℃ to prepare an anode, and weighing the mass of the anode loaded with lithium iron phosphate. 30ml of 0.6mol/L phosphoric acid solution is used as electrolyte, a platinum sheet is used as a cathode, 2V potential is applied to the electrolyte in an electrolytic tank, and the time is 1h, so that lithium and iron in an anode are transferred into the electrolyte to form lithium-containing solution. And after the experiment is finished, detecting the lithium content in the lithium-containing solution, wherein the lithium concentration in the lithium-containing solution is 80mg/L, and the migration rate of lithium can reach 91%.
Concentrating the lithium-containing solution to a solution with the concentration of 1g/L, adding ammonia water into the solution to adjust the pH to 2, heating and refluxing the solution for 5 hours at 90 ℃, carrying out solid-liquid separation to obtain a crude iron phosphate precipitate and a filtrate, washing the crude iron phosphate twice by deionized water according to the liquid-solid ratio of 3:1, and calcining the crude iron phosphate at 850 ℃ for 2 hours to obtain an iron phosphate product with the purity of a battery level.
And continuously adding ammonia water into the filtrate to adjust the pH value to 9, carrying out solid-liquid separation to obtain a lithium phosphate precipitate and an ammonium phosphate solution, washing the precipitate twice with deionized water according to the liquid-solid ratio of 3:1 after separation, and drying at 105 ℃ to obtain a lithium phosphate product with the purity of a battery grade.
Example 3
Providing a cathode material obtained after the lithium iron phosphate battery is disassembled, grinding the cathode material, adding water, wherein the liquid-solid ratio is 10:1, and mechanically stirring the cathode material for 5 hours after ultrasonic oscillation is carried out for 3 hours to obtain uniform slurry. And (3) immersing a graphite felt of 1cm by 2cm by 3cm into the slurry, taking out after full infiltration, drying for 3 hours at 105 ℃ to prepare an anode, and weighing the mass of the anode loaded with lithium iron phosphate. 30ml of 1.0mol/L phosphoric acid solution is taken as electrolyte, a titanium sheet is taken as a cathode, 3V potential is applied to the electrolyte in an electrolytic tank, and the time is 1h, so that lithium and iron in an anode are transferred into the electrolyte to form lithium-containing solution. And after the experiment is finished, detecting the lithium content in the lithium-containing solution, wherein the lithium concentration in the lithium-containing solution is 86mg/L, and the migration rate of lithium can reach 92%.
Concentrating the lithium-containing solution to a solution with the concentration of 1g/L, adding ammonia water into the solution to adjust the pH to 2, heating and refluxing the solution at 90 ℃ for 8 hours, carrying out solid-liquid separation to obtain a crude iron phosphate precipitate and a filtrate, washing the crude iron phosphate twice with deionized water according to the liquid-solid ratio of 3:1, and calcining the crude iron phosphate at 1000 ℃ for 2 hours to obtain an iron phosphate product with the purity of a battery level.
And continuously adding ammonia water into the filtrate to adjust the pH value to 9, carrying out solid-liquid separation to obtain a lithium phosphate precipitate and an ammonium phosphate solution, washing the precipitate twice with deionized water according to the liquid-solid ratio of 3:1 after separation, and drying at 105 ℃ to obtain a lithium phosphate product with the purity of a battery grade.
Example 4
Providing the waste material of the lithium iron phosphate battery, grinding, adding water with a liquid-solid ratio of 5:1, carrying out ultrasonic oscillation for 30min, and mechanically stirring for 1h to obtain uniform slurry. And (3) immersing a graphite felt of 1cm by 2cm by 3cm into the slurry, taking out after full infiltration, drying for 2 hours at 80 ℃ to prepare an anode, and weighing the mass of the anode loaded with lithium iron phosphate. 30ml of 0.2mol/L phosphoric acid solution is used as electrolyte, a platinum sheet is used as a cathode, 1V potential is applied to the electrolyte in an electrolytic tank, and the time is 1h, so that lithium and iron in an anode are transferred into the electrolyte to form lithium-containing solution. And after the experiment is finished, detecting the lithium content in the lithium-containing solution, wherein the lithium concentration in the lithium-containing solution is 67mg/L, and the migration rate of lithium can reach 65%.
Concentrating the lithium-containing solution to a solution with the concentration of 1g/L, adding ammonia water into the solution to adjust the pH value to 1.5, heating and refluxing the solution for 3h at 90 ℃, carrying out solid-liquid separation to obtain a crude iron phosphate precipitate and a filtrate, washing the crude iron phosphate twice with deionized water according to the liquid-solid ratio of 3:1, and calcining the crude iron phosphate at 700 ℃ for 2h to obtain an iron phosphate product with the purity of a battery level.
And continuously adding ammonia water into the filtrate to adjust the pH value to 8, carrying out solid-liquid separation to obtain a lithium phosphate precipitate and an ammonium phosphate solution, washing the precipitate twice with deionized water according to the liquid-solid ratio of 3:1 after separation, and drying at 105 ℃ to obtain a lithium phosphate product with the purity of a battery grade.
The electrode of the present invention may be made of other materials in addition to the above-described embodiments; and when the electrode substrate made of non-porous materials is used as the anode base material, the slurry can be coated on the electrode substrate and dried to prepare the anode.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.