How to remove Ferro from silicon carbide powder?

Ferro element is harmful to grinding metal substrate. But Ferro is inevitable in the production process of silicon carbide powder. Following are several methods to remove Ferro and magnetic impurities from silicon carbide powder.

(1) Chemical ferro removal process – acid leaching method

The ferro impurities in silicon carbide powder mainly exist in the form of elemental iron and its oxide ferric oxide. Because the elemental ferro and its ferric oxide can be dissolved in sulfuric acid, nitric acid, hydrochloric acid, etc. The soluble iron salt formed can be removed by washing with water. By comparing the effects of hydrochloric acid concentration and reaction temperature on the ferro removal rate. The ferro removal rate was the highest when the hydrochloric acid concentration was 180g / L and the reaction temperature was 80 ℃.  The ferro removal rate could reach about 93%. Use one or two of sulfuric acid, hydrochloric acid and hydrofluoric acid as the leaching solution. The experimental results show that the solution with a median particle size of 0.5 μ get a good effect. The removal rate of iron impurities in silicon carbide powder can reach 88%.

The mixed acid of hydrochloric acid and hydrofluoric acid with volume ratio of 20% should kept for 3 hours at 70℃.

The high-ferro silicon carbide fine powder obtained by electromagnetic iron removal is first slurried with 80-90 ℃ water in a certain proportion. After stirring the slurry evenly, add a certain amount of sulfuric acid, nitric acid or mixed acid. After immersion for 4-6 hours, the water is washed to neutral. The silicon carbide fine powder is settled at the bottom of the barrel. The Ferro impurities are removed with the cleaning. As a result, the separation of the silicon carbide fine powder and the impurity ferro get done.

The traditional chemical acid addition iron removal method has a high ferro removal rate. However, it is easy to cause groundwater pollution. Moreover, the pickled silicon carbide fine powder is easy to aggregate, which is unfavorable to the further treatment of silicon carbide fine powder. Suspension treatment has to make till the silicon powder to neutral.   Thus, washing will also cause a lot of waste of pure water.

(2) Physical ferro removal process – magnetic separation

Magnetic separation is a method that uses the magnetism of metals and their oxides features. By adding magnetic raw materials around to exert attraction or repulsion force on metal atoms, it can move metal atoms out of silicon carbide powder. We have wet magnetic separation and dry magnetic separation according to the dry and wet of raw materials.

Electromagnetic ferro removal has high efficiency and automation, which meets the needs of industrial production. It can avoid a large number of chemicals, which is in line with the national energy conservation and emission reduction policies. However, for the ferro impurities with high ferro content or weak magnetism, the purity of silicon carbide required by the process cannot be achieved by electromagnetic iron removal alone.

(3) Physical-chemical comprehensive method

Due to the limited iron removal ability of the magnetic separator itself, the silicon carbide fine powder with high iron content may not achieve the expected purpose only by physical method. Therefore, it can make preliminary magnetic separation with the magnetic separation method firstly.  Then make secondary iron removal with the acid leaching method.

A pulsed high gradient electromagnetic magnetic separator is for preliminary magnetic separation. Then four different types of acids, namely sulfuric acid, hydrochloric acid, oxalic acid, and a 1:1 mixed acid of hydrochloric acid and oxalic acid, were added as the leaching solution. The experimental results show that the removal rate of iron impurities in silicon carbide can reach about 95% after the primary magnetic separation of silicon carbide fine powder and the leaching solution of 12% hydrochloric acid and oxalic acid in the ratio of 1:1.

(4) Other Ferro removal processes

Acid leaching and electromagnetic iron removal are the common ferro removal methods in the silicon carbide fine powder industry. However, there are other ferro removal methods and processes in other industries. Here are several processes to provide the theoretical basis for the Ferro removal process of silicon carbide powder.

• Oxidation leaching

The oxidation ferro removal method uses a strong oxidant (sodium hypochlorite, chlorine, etc.) to oxidize water-insoluble Fe into water-soluble Fe2 + in an aqueous medium, thereby removing iron impurities by washing.

•  Reduction leaching

Turn the insoluble trivalent iron ions to divalent iron ions, and then washed with pure water. It can remove ferro impurities.

After Ferro removal, the silicon carbide powder will get higher purity. It will get higher cleanness for making coating and polishing.