How do the Kroll process and the Hunter process differ?

The primary difference between the Hunter process and the Kroll process lies in the reducing agent used to convert titanium tetrachloride (${\text{TiCl}}_4$) into metallic titanium.1

• Hunter Process: This method utilizes sodium as the reducing agent.1
• Kroll Process: This method utilizes magnesium as the reducing agent.1

Both processes are conducted in sealed steel vessels at high temperatures (approximately 800 to 1,000 °C) within an inert argon atmosphere to prevent contamination from air or moisture. Each method results in the production of a highly porous material known as titanium sponge, which contains entrapped salts—either sodium chloride ($\text{NaCl}$) in the Hunter process or magnesium chloride (${\text{MgCl}}_2$) in the Kroll process. These salts are subsequently removed through acid leaching or vacuum distillation to isolate the titanium metal.1