1. Raw Material Preparation.
Mineral Processing: Zirconium in nature is mainly found in ores such as zircon sand (ZrSiO4). The first step is to process these ores to separate the useful zirconium minerals from other impurities, increasing the zirconium content. Methods such as gravity separation, flotation, and magnetic separation are used to separate the zircon sand from associated minerals like quartz and feldspar, obtaining a concentrate.
Enrichment: The concentrate obtained after mineral processing may not have a high enough zirconium content and requires further enrichment. This step uses chemical or physical methods to increase the zirconium content, preparing for subsequent extraction.
2. Decomposition of Zircon Sand.
Alkali Fusion Method: Zircon sand is mixed with a strong alkali such as sodium hydroxide and reacted at high temperature. This converts the zirconium element in the zircon sand into water-soluble compounds such as sodium zirconate, while impurities such as silicon form insoluble silicate precipitates. After the reaction, water leaching is performed to obtain a sodium zirconate solution, separating it from the insoluble residue. Acid dissolution method: Strong acids such as sulfuric acid and hydrochloric acid react with zircon sand, converting zirconium into soluble zirconium salts that enter the solution. However, this process is complex because different acids produce different reaction conditions and products. Furthermore, careful control of reaction temperature, time, and acid concentration is crucial to ensure effective dissolution and purity of the zirconium.
3. Solution purification.
Impurification: The solution obtained after decomposition contains many other impurity ions besides zirconium salts, such as iron, aluminum, and titanium. These impurities need to be removed using chemical methods. For example, adding precipitants allows the impurity ions to precipitate and separate from the solution; or using ion exchange resins, utilizing the different adsorption capacities of the resin for different ions, can separate zirconium ions from impurity ions, resulting in a relatively pure zirconium-containing solution.
4. Preparation of zirconium compounds.
Precipitation: A precipitant is added to the pure zirconium-containing solution to precipitate the zirconium ions. Commonly used precipitants include ammonia and oxalic acid, and the resulting precipitate may be zirconium hydroxide, zirconium oxalate, etc. These precipitates, after filtration and washing, yield relatively pure zirconium compounds.
Calcination: The obtained zirconium compound precipitates are calcined at high temperatures to allow them to decompose or transform, yielding zirconium oxide products such as zirconium dioxide (ZrO). Different zirconium compounds require different calcination conditions; temperature and time must be carefully controlled to ensure product quality.
5. Preparation of Metallic Zirconium
Reduction of Zirconium Compounds: To obtain metallic zirconium, zirconium compounds such as zirconium dioxide need to be reduced. A common method is to reduce zirconium dioxide with reactive metals such as magnesium and calcium at high temperatures, resulting in metallic zirconium and the corresponding metal oxides. This process is generally carried out in a vacuum or inert gas protected environment to prevent oxidation of the metallic zirconium.
Refining: The purity of the metallic zirconium obtained through reduction is not high enough and further refining is required. There are many refining methods, such as iodination and electron beam melting. Taking the iodination method as an example, crude zirconium reacts with iodine at a certain temperature to produce volatile zirconium iodide. Then, the zirconium iodide is heated and decomposed to obtain high-purity metallic zirconium.
