Elemental iron is harmful for grinding metal substrates. However, iron is unavoidable in the production process of silicon carbide micro powder. The following are several methods for removing iron and magnetic impurities from silicon carbide powders.
Chemical iron removal process – acid leaching method
The iron impurities in silicon carbide micro powder exist mainly in the form of singlet iron and its oxide ferric oxide. Because the monomeric iron and its iron trioxide are soluble in sulfuric acid, nitric acid, hydrochloric acid, etc., generating soluble iron salts can be removed by washing with water. By comparing the effect of hydrochloric acid concentration and reaction temperature on the iron removal rate, we finally obtained the highest iron removal rate with hydrochloric acid concentration at 180g/L and reaction temperature at 80℃, and the iron removal rate can reach about 93% under this condition. The experimental results show that for silicon carbide micro powder with a median particle size of 0.5 μm, the removal rate of iron impurities from silicon carbide micronized powder can reach 88% by using a mixture of 20% hydrochloric acid and 10% hydrofluoric acid by volume and holding at 70°C for three hours.
The high iron silicon carbide micronized powder obtained by electromagnetic iron removal is first slurried with water at 80-90°C. After the slurry is stirred, a certain amount of sulfuric acid, nitric acid, or mixed acid is added, and after 4-6 h of immersion, the water is washed to neutral, and the silicon carbide micronized powder sinks to the bottom of the barrel, while the iron impurities are removed with the washing, thus achieving the separation of silicon carbide micro powder from iron impurities.
The traditional chemical acid removal method has a high iron removal rate. However, the acid water produced by the iron removal needs to be treated before discharge, which can easily cause groundwater pollution if not properly treated. And after acid washing of silicon carbide micro powder is easy to produce aggregation, which is not conducive to further processing of silicon carbide micro powder, acid washing of silicon carbide micro powder needs to be washed to neutral, so washing will also cause a lot of pure water waste.
Physical iron removal process – magnetic separation method
Magnetic separation method is the use of the magnetic properties of metals and their oxides, around the addition of magnetic materials to the metal atoms to exert an attractive or repulsive force to move the metal atoms out of the silicon carbide powder method. According to the wet and dry raw materials can be divided into: wet magnetic separation method and dry magnetic separation method two.
Electromagnetic iron removal efficiency, high degree of automation, in line with the needs of industrial production, while avoiding the use of a large number of chemicals, in line with the national energy-saving, emission reduction policy. However, for iron impurities with high iron content or weak magnetic properties, the use of electromagnetic removal alone does not achieve the purity of silicon carbide required by the process.
Physical – chemical integrated method
Due to the limited iron removal capacity of the magnetic separator itself, for high iron content of silicon carbide micro powder just through the physical method, the obtained silicon carbide micro powder may not be able to achieve the desired purpose. So you can first use the magnetic separation method for preliminary magnetic separation, and then through the acid leaching method for secondary iron removal method.
Firstly, the magnetic separation is carried out using a pulsating electromagnetic magnetic separator, and then four different types of acids, namely sulfuric acid, hydrochloric acid, oxalic acid, and a 1:1 mixture of hydrochloric acid and oxalic acid, are added as leaching solution. The experimental results show that: after the primary magnetic separation of silicon carbide powder, and then through the acid concentration of 12% of hydrochloric acid and oxalic acid 1:1 ratio of mixed acid as the leaching solution for iron removal, the final removal rate of iron impurities in silicon carbide can reach about 95%.
Other iron removal processes
Acid leaching method and electromagnetic iron removal is the current silicon carbide powder industry is commonly used to remove iron. However, there are other iron removal methods and processes in other industries, and some of them are listed to provide theoretical basis for the iron removal process of silicon carbide powder.
Leaching by oxidation
The oxidation method of iron removal uses strong oxidizing agents (sodium hypochlorite, chlorine, etc.) to oxidize insoluble Fe into water-soluble Fe2+ in aqueous media, thereby removing the iron impurities through washing.
The water-insoluble trivalent iron ions are reduced to divalent iron ions, and then washed by adding pure water, thus achieving the removal of iron impurities.