How is synthetic diamond purified

September 23,2024

Diamond purification is the process of removing residual catalyst alloy, graphite, and pyrophyllite fragments from synthetic blocks to obtain pure diamonds.

The key steps in diamond purification include acid treatment, electrolytic removal of metals, chemical removal of graphite, and high-temperature or low-temperature alkali melting removal of pyrophyllite. ‌

Acid treatment:

The raw material of diamond powder stone contains a small amount of impurities such as graphite, catalytic metals, and pyrophyllite. Acid treatment can remove most of the metal impurities, as well as impurities such as graphite. The operation method of acid treatment includes weighing a certain amount of diamond abrasive, placing it in an acid resistant and high-temperature resistant container, adding an appropriate amount of acid solution, heating until the reaction is completely stopped, then washing with water until neutral, and entering the classification process.

Electrolytic removal of metals:

Metal catalysts are removed by electrolysis, and the synthesized blocks are crushed and placed in an anode cloth bag for electrolysis. The electrolyte dissolves the metal into ions and enters the electrolyte, which is then discharged and reduced to metal on the cathode plate. The remaining graphite and diamond are further processed and separated. This method can effectively separate metal catalysts, but there are many drawbacks due to immature and unreasonable process flows.

Chemical removal of graphite:

using perchloric acid to remove metal impurities and residual graphite, and hydrofluoric acid to remove silicates. The operation steps include heating the diamond micro powder raw materials in nitric acid, perchloric acid, hydrofluoric acid and other acids in sequence until boiling, dissolving various impurities adsorbed on the diamond surface, rinsing with high-purity water to remove residual acids and various impurities, and drying to obtain high-purity diamond micro powder.

High temperature or low temperature alkali melting method for removing pyrophyllite:

The removal of pyrophyllite by high temperature or low temperature alkali melting method requires precise control of operating conditions to ensure purification efficiency, environmental protection and safety.