High-conductivity electrolyte for aluminum electrolysis

Abstract

The invention relates to a high-conductivity electrolyte for aluminum electrolysis, and belongs to the technical field of aluminum electrolysis. According to the invention, an electrolyte is a NaF-LiF-AlF3 electrolyte, and the components of the electrolyte comprise Na3AlF6, LiF, AlF3, Al2O3, CaF2, KF and MgF2; the molecular ratio CR of the electrolyte is 2.60-3.0, the content of LiF in the electrolyte is 4-8wt%, and the content of LiF and the molecular ratio CR of the electrolyte are in positive correlation. The primary crystal temperature of the electrolyte is 920-956 DEG C, the electrolysis temperature is 935-971 DEG C, and the conductivity is 2.51-2.79 s / cm. Compared with the traditional electrolyte, the electrolyte has high conductivity and can ensure a relatively high dissolution rate of aluminum oxide, and the conductivity of the electrolyte is greatly improved, so that the voltage of an electrolytic bath can be reduced, and the energy consumption can be reduced.

Description

Technical Field

[0001] The invention relates to a high-conductivity electrolyte for aluminum electrolysis, belonging to the technical field of aluminum electrolysis. Background Art

[0002] Electrolyte is crucial in the aluminum electrolysis process. It is the reaction medium that dissolves aluminum oxide and realizes electrolytic reduction to metallic aluminum. It also plays the dual role of solvent and electrical conductor. The industrial requirements for electrolytes are, on the one hand, to be able to dissolve aluminum oxide well and have a high solubility, and on the other hand, to have good conductivity and low resistivity, so as to reduce the cell voltage and achieve energy saving. Improving the conductivity of the electrolyte is an effective way to save energy consumption and reduce production costs in the aluminum electrolysis industry, because improving the conductivity of the electrolyte can reduce the working voltage. When the current is stable, the working voltage of the electrolytic cell using a high-conductivity electrolyte will be reduced. When the working voltage is reduced, the heat generated during the electrolysis process will be reduced, thereby reducing heat losses caused by heat dissipation and other reasons, and improving energy utilization; high-conductivity electrolytes can also improve production efficiency. Improving the conductivity of the electrolyte can accelerate the ion migration rate, thereby accelerating the speed of the electrolysis reaction, reducing current loss and waste, and improving current efficiency; improving the conductivity of the electrolyte can also improve the quality of the product. The improvement in conductivity helps to optimize the electric field distribution and melt flow state in the electrolytic cell, making the distribution of the aluminum liquid in the electrolytic cell more uniform, reducing eddy currents and fluctuations in the aluminum liquid, and thus improving the quality of the aluminum liquid.

[0003] There are many ways to improve electrolyte conductivity. For the NaF-AlF 3 For acidic electrolytes, increasing the lithium fluoride content and molecular ratio can achieve the purpose of improving the conductivity of the electrolyte. However, increasing the LiF content in the electrolyte will slow down the dissolution rate of aluminum oxide in the electrolyte molten salt, resulting in more bottom precipitates, causing problems such as increased cell voltage and reduced electrolytic cell life. Adding lithium salts to aluminum electrolytes can effectively improve the conductivity of the electrolyte, but directly adding lithium salts to the electrolyte normally used in aluminum electrolytic plants (molecular ratio of 2.2-2.6) will result in a lower initial crystallization temperature (below 900°C), slower dissolution rate of aluminum oxide, and more bottom precipitates. Summary of the invention

[0004] Aiming at the problem that the solubility of aluminum oxide decreases under the high conductivity of the existing electrolyte, the present invention proposes a NaF-LiF-AlF 3 High conductivity electrolyte, electrolyte molecular ratio CR is 2.60~3.0, LiF content in the electrolyte is 4~8wt%, and LiF content and electrolyte molecular ratio CR are positively correlated. This electrolyte has high conductivity and ensures a faster dissolution rate of alumina, avoiding the formation of bottom precipitation, and realizing energy saving and consumption reduction in the aluminum electrolysis process.

[0005] A high-conductivity electrolyte for aluminum electrolysis, the electrolyte being NaF-LiF-AlF 3 The electrolyte, the components of the electrolyte including Na 3 AlF 6 , LiF, AlF 3 , Al 2 O 3 , CaF 2 , KF, MgF 2 ; The molecular ratio CR of the electrolyte is 2.60 to 3.0, and the LiF content in the electrolyte is 4 to 8 wt%.

[0006] Preferably, the Al 2 O 3 content in the electrolyte is 1.5 to 2.5 wt%, the CaF 2 content is 3 to 5 wt%, the KF content is 1 to 2 wt%, the MgF 2 content is 1 to 2 wt%, the excess AlF 3 content is 0 to 5.12 wt%, and the Na 3 AlF 6 content is 82.46 to 86 wt%.

[0007] The LiF content in the electrolyte and the molecular ratio CR of the electrolyte have a positive correlation relationship. Specifically: When the LiF content is 8 - 7 wt%, the molecular ratio CR of the electrolyte is 3.0 - 2.9; When the LiF content is 7 - 6 wt%, the molecular ratio CR of the electrolyte is 2.9 - 2.8; When the LiF content is 6 - 5 wt%, the molecular ratio CR of the electrolyte is 2.8 - 2.7; When the LiF content is 5 - 4 wt%, the molecular ratio CR of the electrolyte is 2.7 - 2.6.

[0008] The primary crystallization temperature of the electrolyte is 920 to 956 °C, the electrolysis temperature is 935 to 971 °C, and the conductivity is 2.51 - 2.79 s / cm.

[0009] The calculation formula for the molecular ratio CR of the electrolyte is: (1) In the formula , are the mole fractions of NaF and AlF 3 in the electrolyte respectively.

[0010] The beneficial effects of the present invention are: (1) The electrolyte of the present invention effectively improves the conductivity of the electrolyte. By different component ratios, the content of LiF in the electrolyte and the molecular ratio of the electrolyte are controlled to be relatively high, so that the primary crystallization temperature is increased (920 °C - 956 °C). At the same time, a relatively high alumina solubility and a relatively fast alumina dissolution rate are maintained, and it is not easy to generate bottom deposits in the cell. (2) Compared with traditional electrolytes, the electrolyte of the present invention can ensure a relatively fast alumina dissolution rate while having high conductivity. Since the conductivity of the electrolyte is greatly improved, the voltage of the electrolytic cell can be reduced, and the energy consumption can be reduced. Specific Embodiments

[0011] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0012] Example 1: A high-conductivity electrolyte for aluminum electrolysis. The electrolyte components are: LiF is 4 wt%, CaF 2 is 3 wt%, Al 2 O 3 is 1.5 wt%, MgF 2 is 1 wt%, KF is 1 wt%, excess AlF 3 is 5.12 wt%, Na 3 AlF 6 is 84.31 wt%. The molecular ratio of NaF to AlF 3 in the electrolyte is 2.60. Under this system, the primary crystallization temperature of the electrolyte is 956 °C, and the conductivity of the electrolyte is 2.51 s / cm at the electrolysis temperature of 971 °C.

[0013] Example 2: A high-conductivity electrolyte for aluminum electrolysis. The electrolyte components are: LiF is 4.5 wt%, CaF 2 is 3 wt%, Al 2 O 3 is 1.5 wt%, MgF 2 is 1.5 wt%, KF is 1.8 wt%, excess AlF 3 is 4.4 wt%, Na 3 AlF 6 is 83.3 wt%. The molecular ratio of NaF to AlF 3 in the electrolyte is 2.65. Under this system, the primary crystallization temperature of the electrolyte is 953 °C, and the conductivity of the electrolyte is 2.52 s / cm at the electrolysis temperature of 968 °C.

[0014] Example 3: A high-conductivity electrolyte for aluminum electrolysis. The electrolyte components are: LiF is 5.5 wt%, CaF 2 is 3.6 wt%, Al 2 O 3is 1.6 wt%, MgF 2 is 1.2 wt%, KF is 1.3 wt%, excess AlF 3 is 3.43 wt%, Na 3 AlF 6 is 83.37 wt%, the molecular ratio of NaF to AlF in the electrolyte 3 is 2.72, the primary crystallization temperature of the electrolyte under this system is 941 °C, and the conductivity of the electrolyte at the electrolysis temperature of 956 °C is 2.57 s / cm.

[0015] Example 4: A high-conductivity electrolyte for aluminum electrolysis, the electrolyte composition: LiF is 7 wt%, CaF 2 is 3 wt%, Al 2 O 3 is 1.5 wt%, MgF 2 is 1 wt%, KF is 1 wt%, excess AlF 3 is 0.58 wt%, Na 3 AlF 6 is 85.92 wt%, the molecular ratio of NaF to AlF in the electrolyte 3 is 2.95, the primary crystallization temperature of the electrolyte under this system is 932 °C, and the conductivity of the electrolyte at the electrolysis temperature of 947 °C is 2.76 s / cm.

[0016] Example 5: A high-conductivity electrolyte for aluminum electrolysis, the electrolyte composition: LiF is 5 wt%, CaF 2 is 5 wt%, Al 2 O 3 is 1.5 wt%, MgF 2 is 1 wt%, KF is 1.4 wt%, excess AlF 3 is 3 wt%, Na 3 AlF 6 is 83.08 wt%, the molecular ratio of NaF to AlF in the electrolyte 3 is 2.75, the primary crystallization temperature of the electrolyte under this system is 944 °C, and the conductivity of the electrolyte at the electrolysis temperature of 959 °C is 2.56 s / cm.

[0017] Example 6: A high-conductivity electrolyte for aluminum electrolysis, the electrolyte composition: LiF is 6.1 wt%, CaF 2 is 3.2 wt%, Al 2 O 3 is 1.7 wt%, MgF 2 is 2 wt%, KF is 1.6 wt%, excess AlF 3 is 1.76 wt%, Na 3 AlF 6is 83.64 wt%, and the molecular ratio of NaF to AlF in the electrolyte is 2.85. The primary crystallization temperature of the electrolyte under this system is 938 °C, and the conductivity of the electrolyte at the electrolysis temperature of 953 °C is 2.62 s / cm. 3 The primary crystallization temperature of the electrolyte under this system is 938 °C, and the conductivity of the electrolyte at the electrolysis temperature of 953 °C is 2.62 s / cm.

[0018] Example 7: A high-conductivity electrolyte for aluminum electrolysis. The electrolyte composition: LiF is 7 wt%, CaF 2 is 4.5 wt%, Al 2 O 3 is 1.8 wt%, MgF 2 is 1.1 wt%, KF is 2 wt%, excess AlF 3 is 1.14 wt%, Na 3 AlF 6 is 82.46 wt%, and the molecular ratio of NaF to AlF in the electrolyte is 2.9. The primary crystallization temperature of the electrolyte under this system is 926 °C, and the conductivity of the electrolyte at the electrolysis temperature of 941 °C is 2.67 s / cm. 3 The primary crystallization temperature of the electrolyte under this system is 926 °C, and the conductivity of the electrolyte at the electrolysis temperature of 941 °C is 2.67 s / cm.

[0019] Example 8: A high-conductivity electrolyte for aluminum electrolysis. The electrolyte composition: LiF is 6.2 wt%, CaF 2 is 3.3 wt%, Al 2 O 3 is 1.6 wt%, MgF 2 is 1.3 wt%, KF is 1.3 wt%, excess AlF 3 is 2.15 wt%, Na 3 AlF 6 84.15 wt%, and the molecular ratio of NaF to AlF in the electrolyte is 2.82. The primary crystallization temperature of the electrolyte under this system is 938 °C, and the conductivity of the electrolyte at the electrolysis temperature of 953 °C is 2.64 s / cm. 3 The primary crystallization temperature of the electrolyte under this system is 938 °C, and the conductivity of the electrolyte at the electrolysis temperature of 953 °C is 2.64 s / cm.

[0020] Example 9: A high-conductivity electrolyte for aluminum electrolysis. The electrolyte composition: LiF is 6.8 wt%, CaF 2 is 3 wt%, Al 2 O 3 is 2.5 wt%, MgF 2 is 1 wt%, KF is 1 wt%, excess AlF 3 is 1.43 wt%, Na 3 AlF 6 is 86.07 wt%, and the molecular ratio of NaF to AlF in the electrolyte is 2.88. The primary crystallization temperature of the electrolyte under this system is 928 °C, and the conductivity of the electrolyte at the electrolysis temperature of 943 °C is 2.64 s / cm. 3 The primary crystallization temperature of the electrolyte under this system is 928 °C, and the conductivity of the electrolyte at the electrolysis temperature of 943 °C is 2.64 s / cm.

[0021] Example 10: A high conductivity electrolyte for aluminum electrolysis, electrolyte composition: LiF is 8wt%, CaF 2 4wt%,Al 2 O 3 1.5wt%,MgF 2 is 1.2wt%, KF is 1.1wt%, and the excess AlF 3 0.91wt%, Na 3 AlF 6 The electrolyte contains NaF and AlF. 3 The molecular ratio is 2.92. The initial crystallization temperature of the electrolyte in this system is 920°C, and the conductivity of the electrolyte is 2.72s / cm at an electrolysis temperature of 935°C.

[0022] Example 11: A high conductivity electrolyte for aluminum electrolysis, electrolyte composition: LiF 5.3wt%, CaF 2 3wt%,Al 2 O 3 2wt%,MgF 2 1.4wt%, KF 1wt%, excess AlF 3 3.71wt%, Na 3 AlF 6 The electrolyte contains NaF and AlF. 3 The molecular ratio is 2.7. The initial crystallization temperature of the electrolyte in this system is 944°C, and the conductivity of the electrolyte is 2.53s / cm at an electrolysis temperature of 959°C.

[0023] Example 12: A high conductivity electrolyte for aluminum electrolysis, electrolyte composition: LiF 7.5wt%, CaF 2 3wt%,Al 2 O 3 1.5wt%,MgF 2 1wt%, KF 1wt%, excess AlF 3 is 0wt%, Na 3 AlF 6 The electrolyte contains NaF and AlF 3 The molecular ratio is 3, the initial crystallization temperature of the electrolyte in this system is 926°C, and the conductivity of the electrolyte is 2.79s / cm at an electrolysis temperature of 959°C.

[0024] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A high conductivity electrolyte for aluminum electrolysis, characterized in that: The electrolyte is NaF-LiF-AlF3 electrolyte, and the components of the electrolyte include Na3AlF6, LiF, AlF3, Al2O3, CaF2, KF, and MgF2; The electrolyte molecular ratio CR is 2.60-3.0, and the LiF content in the electrolyte is 4-8wt%.

2. The high-conductivity electrolyte for aluminum electrolysis according to claim 1, characterized in that: The LiF content and electrolyte molecular ratio CR are positively correlated, specifically: When the LiF content is 8-7wt%, the electrolyte molecular ratio CR is 3.0-2.9; When the LiF content is 7-6wt%, the electrolyte molecular ratio CR is 2.9-2.8; When the LiF content is 6-5wt%, the electrolyte molecular ratio CR is 2.8-2.7; When the LiF content is 5-4wt%, the electrolyte molecular ratio CR is 2.7-2.

6.

3. The high conductivity electrolyte for aluminum electrolysis according to claim 1, characterized in that: The crystallization temperature of the electrolyte is 920~956℃, the electrolysis temperature is 935~971℃, and the conductivity is 2.51-2.79s / cm.