Hafnium wire, produced by hafnium metal drawing. In nature, hafnium and zirconium often symbiosis, zirconium containing minerals are hafnium, hafnium and zirconium is similar to the quality, hafnium mainly occurs in zirconium quartz. Zircons used for industrial use contain 0.5-2% HfO2. Beryllium zircon in secondary zirconium ores may contain up to 15% HfO2. There is also a metamorphic zircon with a content of more than 5% HfO2. The latter two minerals are scarce and have not yet been used industrially. Hafnium is recovered mainly from the process of producing zirconium.
Hafnium smelting and zirconium is basically the same, generally divided into five steps. The first step is the decomposition of the ore by three methods: Zircon chlorination (Zr,Hf)Cl4. When zircon is fused with NaOH at 600℃, more than 90% (Zr,Hf)O2 is converted into Na2(Zr,Hf)O3, and SiO2 is dissolved in water. Na2(Zr,Hf)O3 can be used as the original solution for zirconium and hafnium separation after being dissolved in HNO3. However, due to the presence of SiO2 colloid, the solvent extraction separation is difficult. Sintering with K2SiF6, water immersion K2(Zr,Hf)F6 solution. Zirconium and hafnium can be separated from the solution by fractional crystallization. The second step is the separation of zirconium and hafnium by solvent extraction with hydrochloric acid-MiBK (methyl isobutyl ketone) system and HNO3-TBP(tributyl phosphate) system. The technology of multistage fractionation under high pressure (higher than 20 atmospheres) using the difference between the vapor pressure of HfCl4 and ZrCl4 melts has long been studied, which can save the secondary chlorination process and reduce the cost. However, due to the corrosion problems of (Zr, Hf)Cl4 and HCl, it is not easy to find suitable fractionating column material, and the quality of ZrCl4 and HfCl4 will be reduced and the purification cost will be increased. The third step is the secondary chlorination of HfO2 to prepare crude HfCl4 for reduction. The fourth step is the purification and reduction of HfCl4 by adding magnesium. The process is the same as the purification and reduction of ZrCl4, and the semi-finished product is the crude hafnium sponge. The fifth step is vacuum distillation of crude hafnium sponge to remove MgCl2 and recover excess magnesium, and the resulting product is hafnium sponge metal. If the reducing agent does not use magnesium but sodium, the fifth step should be water immersion.
Extreme care should be taken when removing the sponge from the crucible to avoid spontaneous combustion. Large pieces of hafnium sponge are broken into small pieces of a certain size so that they can be pressed into consumable electrodes and then fused into ingots. Spontaneous combustion should also be prevented when broken. The hafnium sponge is further purified by the iodide thermal decomposition method, as is the case with titanium and zirconium. The control conditions are slightly different from zirconium. The hafnium sponge around the iodized tank is kept at 600 ° C, while the hot wire in the center is kept at 1600 ° C, higher than the 1300 ° C when the zirconium is made from the "crystal rod". Hafnium processing includes forging, extrusion, tube drawing and other steps, the same as processing zirconium.
