Preparation of ferrous oxalate and its application in water pollution treatment_Kain Industrial Additive

Background and overview^[1][2]

Iron oxalate, also known as ferrous oxalate, battery-grade ferrous oxalate can be used as the raw material for the battery cathode material lithium iron phosphate. It is one of the main substances for manufacturing lithium iron phosphate, the cathode active material of lithium-ion batteries. Its purity and particle size are critical to the performance of lithium iron phosphate.

Preparation^[1]

1. Preparation method of nanoscale ferrous oxalate

A method for preparing nanoscale ferrous oxalate, including the following steps:

(1) Pretreatment of raw material ferrous sulfate

Put the raw material ferrous sulfate into a stainless steel water washing kettle, fully wash and filter with deionized water, recover the iron powder, and move the ferrous sulfate to the enamel dissolving kettle;

Fully dissolve the ferrous sulfate in the enamel dissolving kettle with deionized water, then add pure iron powder, inhibitors and impurity precipitating agents, adjust the pH value of the solution to 1 to 4, stir thoroughly and let it stand until the solution is clear. , transfer the ferrous sulfate clarified liquid in the upper layer to the enamel synthesis kettle for later use. The amount of iron powder added is 1% to 2% of the mass of ferrous sulfate, and the amount of inhibitor added is 0.5% to 5% of the mass of ferrous sulfate. , the amount of impurity precipitating agent added is 1% to 10% of the mass of ferrous sulfate;

(2) Synthesis of nanoscale ferrous oxalate

Add 100% to 300% of the precipitant’s mass of deionized water to the precipitant, stir and gradually raise the temperature to 70~90°C for later use;

Add the thickener to the ferrous sulfate clarified solution, stir and gradually raise the temperature to 70~90°C. The amount of thickener added is 20%~40% of the mass of ferrous sulfate;

Add precipitant solution to the enamel synthesis kettle. The molar ratio of precipitant to ferrous sulfate is (0.6~1): 1. Keep the temperature constant and stir for 0.5~2h. Let it stand until the precipitation is complete, and then recover the supernatant. liquid, and the resulting precipitate is nanoscale ferrous oxalate;

(3) Washing of nanoscale ferrous oxalate

Add deionized water to the obtained nanoscale ferrous oxalate, stir for 3 to 5 minutes, let it stand, filter and separate, and wash repeatedly until there is no precipitation using a barium chloride solution with a mass fraction of 20% to 30%;

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(4) Drying of nanoscale ferrous oxalate

Dry the washed nanoscale ferrous oxalate to obtain nanoscale ferrous oxalate.

2. Preparation method of special battery grade ferrous oxalate for lithium iron phosphate

A method for preparing special battery grade ferrous oxalate for lithium iron phosphate, including the following process flow:

A. Add pure water to the impurity removal kettle, start stirring, and add ferrous salt solid according to the amount of pure water according to the liquid-solid weight ratio of 0.5 to 5:1, start heating, and the water temperature rises to 80 to 100 ℃, add reduced iron powder with a weight ratio of 0.5 to 3% to the ferrous salt solid, stir at a constant temperature for 1 to 3 hours, control the pH after the reaction = 2 to 4, obtain a ferrous salt solution, and start filtering;

B. Pass the ferrous salt solution produced in step A through a set of automatic pressure-maintaining sealed chamber filter presses to simultaneously filter metal impurities, non-metallic impurities and remove excess reduced iron powder to obtain pure ferrous salt Solution;

C. When the ferrous salt filtrate in step B is clear, open the outlet valve of the filter press and quickly pour the ferrous salt filtrate into the main reaction kettle; when the filter press is completed, control the temperature at 30 to 60°C , take the oxalic acid dihydrate solid in an amount of 1.001 to 1.05 times the mole number of the ferrous salt, and start adding the oxalic acid dihydrate solid. The feeding time is 5 to 60 minutes. After the reaction for 10 to 60 minutes, the reaction temperature is raised to 70 to 100. ℃ constant temperature reaction;

D. Stir the reaction solution obtained in step C thoroughly and keep it warm for 2 to 4 hours for aging to obtain ferrous oxalate slurry;

E. Separate the ferrous oxalate in the ferrous oxalate slurry through a centrifuge, with a rotation speed of 30 to 100 rpm and a centrifugation time of 20 to 60 minutes;

F. Wash the separated ferrous oxalate with water and dry it to obtain the finished product of ferrous oxalate.

Apply ^[3]

1. Use ferrous oxalate to activate the persulfate system to repair organic polluted water

CN201610482121.3 provides a method of using ferrous oxalate (FeC₂O₄·2H₂O) to activate persulfate (PS ) system method for remediating water bodies polluted by organic matter. This method solves the problems that Fe(III) is easy to precipitate in the Fe(II)-excited persulfate system, and Fe(III)/Fe(II) is difficult to circulate and cannot be recycled and reused.And it can improve the remediation efficiency, and its use in the remediation of organic polluted water has the advantages of high efficiency, non-selectivity, environmental friendliness, and no secondary pollution. The technical solution is: a method of using ferrous oxalate to activate the persulfate (PS) system to repair organic matter-contaminated water, which is characterized in that: adding ferrous oxalate and persulfate substances to the organic matter-contaminated water to be repaired, and carrying out the organic matter-contaminated water body of repair. The ferrous oxalate is a substance that is difficult to dissolve in water, and the size is not limited; the molar ratio of the ferrous oxalate to persulfate is 1:10 to 2:1.

2. Preparation of lithium ferrous phosphate using ferrous oxalate

A method for preparing lithium ferrous phosphate using ferrous oxalate, comprising the following steps:

In the first step, weigh x moles of ferrous ammonium sulfate and (1-x) moles of oxalate according to the molecular formula LiFe1-xMxPO4/C, where x is 0-0.01, M is Cu, Co, Ca, Zn, Mg, Ni, Ti, V or Mo are put into an excess oxalic acid solution with a concentration of 0.1mol/L-0.7mol/L, heated to 60°C-90°C, and stirred to obtain ferrous oxalate crystals. The acid salt is copper oxalate, cobalt oxalate, calcium oxalate, zinc oxalate, magnesium oxalate, nickel oxalate, titanium oxalate, vanadium oxalate or molybdenum oxalate.

In the second step, phosphate, ferrous oxalate crystals, lithium salt, and carbon source are ball milled respectively. The ball milling particle size of phosphate and ferrous oxalate is 8 μm-20 μm, and the ball milling particle size of lithium salt and carbon source is 2 μm-10 μm.

The phosphate is diammonium hydrogen phosphate, ammonium dihydrogen phosphate or ammonium phosphate, the lithium salt is lithium acetate, lithium carbonate, lithium hydroxide, lithium oxalate or lithium citrate, the carbon source It is sucrose, glucose, fructose, polyisoglycol or acetylene black,

The third step is to weigh the phosphate, ferrous oxalate crystals, lithium salt and carbon source that were ball-milled in the second step. The molar ratio of phosphate, ferrous oxalate crystals and lithium salt is 1:1:1; carbon source The amount is to make the carbon content in the prepared lithium iron phosphate cathode material reach 2% to 6%,

The fourth step is to put the material weighed in the third step into the mixer. After mixing for 2 to 4 hours, the material is discharged and put into the ball mill for ball milling. The ball milling time is 20 to 30 hours. After the ball milling, the material will naturally Dry and pass through a 100 mesh sieve.

The balls used for ball milling are agate balls with diameters of half Φ30 and half Φ10. The ratio of ball weight to powder weight is 4:1. The ball milling medium is alcohol or acetone. The ratio of medium weight to powder weight is 1:1;

In the fifth step, the material prepared in the fourth step is fired in two stages, low temperature and high temperature, under the protection of nitrogen. The low temperature stage is selected at 200~400℃ and kept for 5~20 hours, and the high temperature stage is selected at 600~800 ℃, keep it warm for 10 to 30 hours, with a heating rate of 0.5°C/min-3°C/min. After cooling to room temperature, pass it through a 300-mesh screen to make lithium iron phosphate.

Because this method uses ferrous oxalate raw materials and simple raw material pretreatment, it solves the problems of uneven multi-phase mixing of lithium ferrous phosphate raw materials and narrow process margins, and the prepared material has enhanced coating properties. It has good processing performance, stable structure, good thermal stability and excellent cycle performance.

Main reference materials

[1] CN201310321418.8 Preparation method of nanoscale ferrous oxalate

[2] CN201110396502.7 Preparation method of special battery grade ferrous oxalate for lithium iron phosphate

[3] CN201610482121.3 A method of using ferrous oxalate to activate persulfate system to repair water polluted by organic matter