Preparation method of silicon particles by inert anode molten salt electrolysis

Abstract

The invention relates to a preparation method of silicon particles by inert anode molten salt electrolysis. The method comprises the following steps of: carrying out cathodic electrolysis by using a cryolite molten salt system as the electrolyte, molten aluminum or Al-Si alloy as the cathode and silicon dioxide or silicate as electrolysis raw materials to prepare a liquid Al-Si alloy and carryingout condensation treatment to obtain the silicon particles with purity more than 99.72wt%. According to the invention, NiFe2O4-based cermet or Cu-Ni-Fe alloy is used as the inert anode, thus reducingthe boron, phosphorus and other impurities in the cathode caused by anode consumption; the liquid Al-Si alloy is used as the actual cathode, thus avoiding the poor electrical conductivity of electrolytic cell caused by solid silicon deposition on the cathode, easily taking out the cathode product from the electrolytic cell and maintaining electrolysis continuity; and the electrolysis temperature is low, thus reducing the pollution of the electrolyte and the wall material of the electrolytic cell to the cathode product. The process method provided by the invention is simple and convenient to operate and environmentally-friendly, has the advantages of long anode life, low electrolysis temperature, high purity of electrolysis product and low production cost and, and is suitable for industrial application.

Description

technical field [0001] The invention relates to a method for preparing silicon particles by electrolysis of an inert anode molten salt, in particular to the use of NiFe 2 o 4 The invention relates to a method for preparing Al-Si alloy and extracting silicon particles through directional condensation by using a molten salt silicon electrolysis process as an anode, belonging to the field of electrochemical technology. technical background [0002] The molten salt electrolysis of elemental silicon has a history of more than 150 years. Since the 1980s, researchers have begun to study the use of this method to prepare solar-grade silicon materials. The content of impurities such as boron and phosphorus in silicon is an indicator that they are very concerned about. Stubergh uses silicate as raw material, cryolite melt as electrolyte, and carbon material as anode, at an electrolysis temperature of 1000°C and a current density of 0.5A / cm 2 Under the conditions of electrolysis, the...

AI Technical Summary

Problems solved by technology

In the three-layer electrolysis process, the anode of the lower layer can be made of Si-Cu alloy with higher density, and the middle layer is made of CaO-MgO-SiO 2 The upper layer is the prepared high-purity silicon, and the electrolysis temperature is 1500°C. However, during the electrolysis process, a certain density difference must be maintained between the melts of each layer to ensure that the melts of each layer are in a stable state during electrolysis. At the same time, due to electrolyte inclusions, electrolyte and electrolytic tank wall contamination, laboratory tests can only produce 4N grade silicon

[0004] At present, the main technical difficulty in preparing silicon by molten salt electrolysis is that when silicate or silicon dioxide is used as the electrolytic raw material and consumable carbon material is used as the anode for electrolysis, the consumption of the anode simultaneously brings a certain amount of impurities such as boron and phosphorus into the electrolyte. , and then increase the content of boron and phosphorus in the cathode silicon, which increases the difficulty for the subsequent physical or chemical silicon purification; Periodically stop the tank to take out silicon, affecting the continuity of electrolysis

When the three-layer liquid refining method is used to prepare high-purity silicon, the electrolysis temperature is too high, and it is difficult to avoid the contamination of the cathode liquid silicon by the electrolyte and the wall material of the electrolytic cell, and the silicon purity cannot reach the technical standard of solar-grade polysilicon materials.