CN110760682A - Process for selective recovery of lithium from spent lithium iron phosphate batteries by means of mechanochemical activation - Google Patents

Abstract

The invention provides a process for selectively recovering positive electrode materials of waste lithium iron phosphate batteries, which belongs to the new technology of solid waste recycling in the field of environmental protection and comprehensive utilization of resources. Then, the lithium in the cathode material of the lithium iron phosphate battery is selectively leached into the solution by using the composite leaching agent. At this time, the lithium and iron are completely separated, and the iron and phosphorus enter the leaching residue with the carbon powder in the form of iron phosphate precipitation. In situ recovery of iron and phosphorus is achieved. The process provided by the invention has the characteristics of short process flow, simple operation, low energy consumption, environmental friendliness and no secondary pollution, and has broad application prospects.

Description

Selective recovery of lithium from spent lithium iron phosphate batteries by means of a mechanochemical activation method craft

technical field

The invention relates to a method for the harmless treatment and recovery of valuable elements of waste lithium iron phosphate power batteries, belonging to a new technology of solid waste recycling in the fields of environmental protection and comprehensive utilization of resources, and is especially suitable for lithium in various types of waste lithium-containing batteries. selective recycling.

Background technique

Lithium iron phosphate batteries have the advantages of high specific energy density and good cycle performance, and are widely used in electric vehicles, hybrid electric vehicles and other vehicles as power sources. With the rapid development of the new energy vehicle industry, the limited service life of power batteries has led to the retirement of a large number of waste lithium iron phosphate batteries. Clean recovery of valuable metals, especially strategic metal lithium, has important resources and economic benefits.

At present, the main focus of the treatment of waste lithium iron phosphate batteries is to extract valuable metals such as lithium and iron from the cathode material. The method for separating and recovering valuable metals from the positive electrode sheet is generally to first discharge the waste lithium ion battery, disassemble and pretreat to obtain a positive electrode sheet containing an active material, and then peel off the positive electrode sheet to obtain a lithium-containing positive electrode material. The recovery method of the valuable elements in the positive electrode material is mainly by leaching the positive electrode material with inorganic acid or organic acid, and then precipitating each element step by step, and finally recovering the valuable element as a separate compound, but it is usually used in leaching. Excessive acid and residual acid discharged into the water body will cause serious pollution to the environment and damage to the living environment. In addition, the traditional acid leaching technology has problems such as high recovery cost, long treatment process, poor leaching selectivity, and slow leaching speed. Therefore, it is necessary to find a waste lithium iron phosphate cathode material with low recovery cost, high recovery rate and fast leaching speed. Recycling methods are important.

Since the energy generated during mechanochemical activation can affect the physical and chemical properties of substances, such as in situ enhancement or manipulation of ion diffusion, reducing particle size, increasing specific surface area, causing point defects and dislocations in the crystal structure, reducing reaction activation In recent years, researchers have attracted extensive attention in the field of metal recycling. Using this method to replace the traditional hydrometallurgical process to recover iron and lithium can effectively reduce reagent, energy consumption and secondary Pollution emissions, improve metal recovery rate and recovery selectivity.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the shortcomings of traditional hydrometallurgy process such as slow process, low leaching rate, cumbersome process, high cost, secondary pollution, etc. It realizes the highly selective leaching of lithium, and at the same time recovers phosphorus and iron in situ, and realizes the resource recovery and utilization of the added value of waste lithium iron phosphate batteries. It is characterized in that: by adding a co-grinding agent, relying on the high energy generated by mechanochemical activation to destroy the original crystal phase of the material, changing the physical and chemical properties of the material to induce the chemical reaction of the subsequent leaching agent, leaching lithium with high selectivity, avoiding Problems with traditional hydrometallurgy.

The present invention is completed according to the following steps:

Pre-treatment process: First, the waste lithium iron phosphate battery is soaked in sodium chloride solution for 24 hours for discharge, and then manually disassembled, classified and recycled. The negative electrode sheet is peeled off and then the copper foil and carbon powder are recovered. The separation of aluminum foil and cathode material was achieved after calcination at 360 °C for 2 h in a medium nitrogen atmosphere;

Mechanochemical activation process: take the above-mentioned peeled positive electrode material, place it in a zirconia ball mill jar with 3-10ml of water added, add a co-grinding agent, and the molar ratio of the co-grinding agent and the positive electrode material is 1:1, and after sealing, At a speed of 600rpm, grind clockwise and counterclockwise for 15 minutes each, and set a ball milling gap of 2 minutes to dissipate the heat generated during ball milling;

Leaching process: The ball-milled material was washed three times with deionized water and then transferred to a conical flask, adding 1vol.%-6vol.% hydrogen peroxide, turning on the magnetic stirrer, stirring and leaching at the set temperature, and the temperature was set. The fixed range is 25℃-80℃, the leaching time is set at 10min-60min, and the leaching speed is fixed at 400rpm;

Precipitation process: after the above-mentioned leaching reaction finishes, carry out vacuum filtration to separate leaching residue and leaching solution, dry leaching residue, measure the pH value of leaching solution, add sodium hydroxide solution to adjust pH value between 11-13, then add stoichiometric ratio as Lithium was recovered by precipitation with sodium phosphate in a molar ratio of 1.05:1.

This process has the following characteristics:

The cathode material used in this process does not introduce impurities such as aluminum and copper after roasting and stripping, so as to avoid the loss of lithium, and the gas generated in the roasting process is treated with alkaline solution, which does not cause atmospheric pollution;

The traditional hydrometallurgical leaching of valuable metals in waste lithium iron phosphate batteries produces a large amount of acidic waste liquid, causing secondary pollution. This process has the characteristics of low reaction temperature, simple operation and high added value of products, which can effectively Avoid secondary pollution;

The mechanochemical activation method adopted in the present invention can effectively reduce the dosage of reagents, lithium can be completely leached, lithium and iron are completely separated, lithium is recovered in the form of lithium phosphate, and iron is recovered in the form of iron phosphate, both of which can be used for iron phosphate Re-preparation of lithium cathode materials;

The invention realizes the harmless treatment of waste and old lithium iron phosphate batteries and the recovery of valuable metals in a green and environment-friendly manner, thereby realizing the reuse of secondary resources.

Description of drawings

In order to further understand the present invention, the following describes the process flow of the present invention, the phase of the leaching residue, and the phase of the lithium precipitate with the accompanying drawings.

Fig. 1 is the process flow chart of the harmless treatment of waste lithium iron phosphate batteries and the recovery of valuable metals.

Fig. 2 is the phase diagram of the leaching residue of mechanochemical activation of the cathode material of waste lithium iron phosphate battery.

FIG. 3 is a phase diagram of the mechanochemically activated leachate precipitate of the cathode material of waste lithium iron phosphate battery.

Detailed ways

The preparation method of the present invention will be further described below through specific examples, but the present invention is not limited to these examples.

Example 1

According to the flow chart in Figure 1, the positive electrode sheet is collected after the waste lithium iron phosphate battery is discharged, and the positive electrode sheet is cut into small strips of 4*2cm with scissors and placed in a tube furnace under nitrogen atmosphere at 360 °C for 2 hours. Positive electrode material: Take positive electrode material LiFePO ₄ as raw material, add an appropriate amount of water and a stoichiometric ratio of co-grinding agent for mechanochemical activation treatment, grind at 600 rpm for 30 min, transfer to a round-bottomed conical flask, add 4 vol.% leaching agent After leaching for 60 min, solid-liquid separation was performed to collect the leaching solution and leaching residue (Fig. 2); the leaching solution was evaporated at 105 °C for an hour, and the remaining appropriate amount of lithium-containing solution was moved to a water bath with a water temperature of 85 °C for magnetic stirring. After the lithium content, an appropriate amount of sodium phosphate was added, and the solid and liquid were separated after stirring for two hours, and the precipitate was recovered (Figure 3). .

Example 2

According to the flow chart in Figure 1, the positive electrode sheet is collected after the waste lithium iron phosphate battery is discharged, and the positive electrode sheet is cut into small strips of 4*2cm with scissors and placed in a tube furnace under nitrogen atmosphere at 360 °C for 2 hours. Positive electrode material; take positive electrode material LiFePO ₄ as raw material, add an appropriate amount of water and a stoichiometric ratio of compound co-grinding agent for mechanochemical activation treatment, wherein the molar ratio of lithium iron phosphate and co-grinding agent is 1:0.5:0.5, at 600rpm After grinding for 30 minutes at the rotating speed, transfer it to a round-bottomed conical flask, add 4 vol.% leaching agent solution, and carry out solid-liquid separation after leaching for 60 minutes to collect the leaching solution and the leaching residue; the leaching solution is evaporated at 105 ° C for a few hours, and an appropriate amount of lithium-containing solution remains. Move to a water bath with a water temperature of 85°C for magnetic stirring, add an appropriate amount of sodium phosphate after measuring the lithium content, separate the solid and liquid after stirring for two hours, and recover the precipitate; the analysis results show that the lithium leaching rate during the leaching process is higher than 99.80% , the recovery rate of iron is 100% and lithium is about 89.50%.

The above examples are only for illustrating the applicability of the present invention, and are not intended to limit the implementation. Waste lithium-ion batteries can be selected from lithium manganate, lithium cobaltate and other lithium batteries. The present invention is not limited to the above-mentioned implementation cases, and the content can be implemented with good effects.

Claims (5)

1. The process for selectively recovering lithium in the waste lithium iron phosphate batteries by means of a mechanochemical activation method is characterized by comprising the following steps:

(1) soaking the waste lithium iron phosphate battery in saturated saline water for 24 hours for discharging, then disassembling and separating to obtain a shell, a diaphragm, a negative plate and a positive plate, wherein the positive plate of the battery is a required experimental raw material, and the negative plate and the diaphragm are uniformly recovered for resource treatment;

(2) baking the obtained positive plateBurning and separating the anode material and the aluminum foil to obtain the anode material LiFePO₄；

(3) And (3) mixing the positive electrode material and the grinding aid in a weight ratio of 1:1, adding the mixture into a ball milling tank, then adding water, wherein the weight of the water is equal to the sum of the weights of the grinding aid and the anode material, and grinding for 15min clockwise and anticlockwise respectively at the rotating speed of 600 rpm;

(4) washing the sample subjected to mechanochemical activation for 2 times by using deionized water, adding a leaching agent, leaching for 1h to obtain a lithium-containing solution and leaching residues containing iron, phosphorus and carbon powder, and combining the phosphorus and the iron into an iron phosphate precipitate;

(5) adjusting the pH value of the lithium-containing solution to 11-13 by using 1.5M sodium hydroxide, then adding sodium phosphate into the solution, wherein the adding amount of the sodium phosphate is 1/3 which is equivalent to the mole number of lithium ions in the solution, then heating and stirring the solution at 90 ℃ for about 2 hours, and filtering the solution to obtain a precipitate, namely the product lithium phosphate.

2. The process as set forth in claim 1, characterized in that: in the step (2), the roasting atmosphere is nitrogen, the temperature is 360 ℃, and the time is 2 h.

3. The process as set forth in claim 1, characterized in that: the grinding aid in the step (2) is a mixture of two or more of ferrous sulfide, sodium sulfate, ammonium chloride, ferrous chloride, sodium phosphate, ammonium ferric phosphate and ammonium phosphate.

4. The process as set forth in claim 1, characterized in that: in the step (4), the leaching agent is a mixture of two or more of sodium thiosulfate, sodium bicarbonate, hydrogen peroxide, sodium hypochlorite, sodium pyrophosphate and ferric chloride.

5. The process as set forth in claim 1, characterized in that: the adding amount of the leaching agent in the step (4) is calculated according to the mole number of lithium ions in the solution, the leaching temperature is 80 ℃, and the leaching solid-liquid ratio is 50 g: 1000mL, leaching time 50 min.

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