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What is stuck in the advancement of the precursor

Release date:2018-08-22  source:粉体网  Browse times:788
      The precursor reaction is a complex reaction of salt and alkali neutralization. A certain concentration of salt solution and a certain concentration of alkali solution are continuously added to the reactor at a certain flow rate, and a hydroxide is formed at an appropriate reaction temperature, stirring rate and pH. precipitation.

The process of precursor reaction is a complicated process. The process parameters to be controlled are: the concentration of salt and alkali, the concentration of ammonia, the rate of addition of salt solution and alkali solution to the reaction tank. How do these parameters affect the preparation of the precursor during the preparation of the precursor, how should we control these parameters to ensure good quality of the precursor?

1. Ammonia concentration

In the sulphate system, the addition of a complexing agent such as ammonia will have a great influence on the morphology of the product.

It can be seen from the figure that when no complexing agent is present, the precursor has a looser morphology and a lower tap density. When a complexing agent is present, the precursor becomes dense and the tap density increases accordingly.

In actual production, if a precursor having a tap density higher than 2.0 g·cm-3 is to be prepared, a complexing agent must be added during the reaction.

However, the amount of complexing agent is not as high as possible. When the amount of complexing agent is too large, too much nickel-cobalt ions are complexed in the solution, which may result in incomplete reaction, resulting in nickel, cobalt and manganese in the precursor. The proportion of the deviation from the design value, and the metal ions that are complexed will be discharged with the supernatant, resulting in waste, and the subsequent wastewater treatment workload will also increase.

2, pH value

The pH of the reaction process directly affects the morphology and particle size distribution of the precursor. The relationship between the morphology and particle size distribution of the precursor and the pH is analyzed by the production process.

By adjusting the pH, we can control the morphology of the primary and secondary particles. The pH value is low, which is conducive to the growth of the nucleus, and the primary grain is thicker and larger; the pH value is higher, which is favorable for the formation of the nucleus, and the primary grain is flaky, which is very small. The effect on the secondary particles is that the pH value is low, the secondary particles are prone to agglomeration, and the secondary spheres are shaped; the pH value is high, and the secondary particles are more rounded.

The pH value has an important influence on the growth process of the precursor. The selection of the pH value of the reaction and the stable control of the pH value during the reaction directly affect the particle size distribution of the precursor. If the pH value is out of control during the reaction, if the pH value is too high or too low, the quality of the product will drop sharply and a defective product will be formed.

3. Reaction control of precursors of different components

Due to the different pH values of nickel, cobalt and manganese, the optimal reaction pH of the precursors of different components is different. The main function of the complexing agent is to complex nickel and cobalt and complex the manganese. To be two orders of magnitude lower, the concentration of the desired complexing agent for the different constituent ternary material precursors is also different.

When the tap density and particle size of the precursor are close, the reaction pH and ammonia concentration of the precursors of the different components need to be slightly adjusted.

Since the precursors prepared at different pH values are different, the precursors with different quality and different compositions have different morphology.

4, reaction time

The particle size, tap density and reaction time of the precursor are proportional to each other for a certain period of time. However, the reaction time should not be too long. Too long reaction time will make the precursor particle size too large and adversely affect the quality of the precursor.
5, the reaction atmosphere

The control of the reaction atmosphere has a great influence on the quality of the precursor product, including the influence on the morphology, crystal structure and impurity content of the precursor.

Since the chemical nature of manganese is very active, if the dissolved oxygen in the pure water used in the precursor reaction is not removed, or the reaction slurry is directly in contact with the air during the reaction, the precursor slurry is severely oxidized, and its color is dark brown. Or black. There is also a case where slight oxidation is caused by oxygen entering the reaction system due to various reasons at the end of the reaction or at the end of the reaction.

6, solid content

Solid content refers to the ratio of the solid mass of the precursor slurry to the mass of the liquid during the precursor reaction. At present, the solid content of precursors in most reactors is about 5% to 10%, and different solid contents have certain influence on product performance. In the production practice, it is found that proper increase of solid content can optimize the appearance of the product and increase the tap density of the product.
7. Reaction temperature

It is known from chemical kinetics that temperature is primarily the rate of reaction that affects a chemical reaction. In the actual production process, it is hoped that the chemical reaction rate will be as fast as possible under the premise of ensuring the quality of the precursor, but the temperature should not be too high, and the temperature will be too high, which will cause the precursor to oxidize. If the reaction temperature is too high, the oxidation of the precursor may cause problems such as uncontrollable reaction process and structural change of the precursor.

In the actual production process, it is also critical to control the reaction temperature to be constant and not to fluctuate.

8, traffic

The flow rate mainly refers to the flow rate of the metal salt solution. Flow is directly related to production.
Under the premise of ensuring the quality of the precursor, the larger the flow rate, the better. The maximum flow rate that can be achieved in a reactor is not only related to the reaction process, but also related to the reactor volume, the internal structure of the reactor, and the power of the reactor motor. Reasonable design of the reactor can maximize its production.

9, impurities

It has been found in production practice that a small amount of organic solvent causes a great disturbance to the coprecipitation reaction.

Organic extractants such as 260# solvent oil, P204 and P507 are used in the preparation of nickel sulfate and cobalt sulfate. If the organic extractant remains, it will be carried into the reaction system.
At present, some manufacturers use the method of doping magnesium in the precursor to improve the performance of the finished product. This requires adjustment of the preparation process and control parameters to reflect the precursors with good conformity such as morphology, particle size and tap density.

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