Research on Post-Processing Production Techniques for Rutile Titanium Dioxide

Abstract: Currently, the domestic production of rutile-type titanium dioxide predominates, offering limited profit margins, while there is a severe shortage of rutile titanium dioxide, leading to heavy reliance on imports. In theory, with minor investments and suitable improvements in the existing technological conditions, it is possible to produce rutile-type titanium dioxide from the anatase-type titanium dioxide production line. Such improvements in production processes are of significant practical importance for advancing the titanium dioxide industry in China and enhancing its overall competitiveness. This article provides a brief overview of the sulfuric acid method for producing rutile titanium dioxide and focuses on describing the production techniques for post-processing.

Rutile, also known as Rutile Titanium Dioxide, is a relatively pure form of titanium dioxide, typically containing over 95% titanium dioxide, making it a crucial mineral resource for titanium extraction. However, rutile reserves in the Earth's crust are limited. Chemical composition: TiO2, Ti 60%, and sometimes contains Fe, Nb, Ta, Cr, Sn, and others.

Currently, the primary methods for producing rutile titanium dioxide are the sulfuric acid method and the chloride method. Regardless of whether it is the sulfuric acid method or the chloride method, both processes involve two stages: the production of crude titanium dioxide and post-processing. The primary purpose of producing crude titanium dioxide is to convert the effective components in titanium ore or titanium slag into easily purified sulfuric acid oxided titanium or titanium tetrachloride. This is done through strict control to minimize the content of harmful impurities and ensure good particle size, particle size distribution, and thorough crystalline transformation of the crude titanium dioxide. The sulfuric acid method production process is relatively complex and can be summarized in three steps: acid dissolution, hydrolysis, and calcination. Post-processing involves surface treatment and processing of the crude product to rectify inherent defects, such as photocatalytic activity, and further improve properties such as anti-settling and dispersibility, to meet user requirements.

Post-Processing Production TechniquesThe core of post-processing rutile titanium dioxide lies in surface treatment, commonly known as coating, achieved by applying a special coating to the surface of the coarse particles.

1.1. Slurry DispersionThis process involves taking the raw material of coarse rutile titanium dioxide and mixing it with a sodium hexametaphosphate solution through roller grinding. The mixture is then dispersed through a dispersion machine, directed into a tank, and stirred to create a relatively uniform and stable slurry.

1.2. Wet GrindingThe uniformly dispersed rutile titanium dioxide slurry is further ground to the required fineness through a sand mill, with zirconium oxide beads as the grinding medium, followed by separation.

1.3. CoatingCoating is carried out in a coating tank under specific temperature and stirring speed conditions. A special coating is applied to the surface of the particles, allowing specific chemical substances to adhere to the surface of TiO2 particles in a 'film' form.

1.4. WashingWashing is performed using filtration and water rinsing to remove dispersants, water-soluble salts, and reaction by-products from the coated rutile titanium dioxide slurry to ensure product performance.

1.5. DryingBefore micro-pulverization, the rutile titanium dioxide undergoes a drying process to reduce water content to meet usage requirements.

1.6. Ultrafine GrindingTo ensure properties such as dispersibility, gloss, coloring power, and resistance to aging in the final product, the post-processed product undergoes additional grinding to separate coagulated particles.

Research on Post-Processing Production Techniques2.1. Coating Process ImprovementThe wet automatic coating process using a large coating tank should be adopted, making full use of large coating tanks and highly automated processes. For instance, a 120m3 large coating tank should be equipped with steam heating coils to maintain the coating process temperature. Furthermore, the system should include stirring devices meeting process requirements, along with an online analysis and detection system to automatically monitor and transmit the detected data, ensuring that various indicators meet the required values. The system should also incorporate a linkage device that stops the feeding pump when the coating parameters exceed the requirements. This improved coating process ensures that, once the coating process parameters are set, the entire production process can be completed automatically, effectively ensuring product quality stability. When switching to different products, adjusting the parameter values on the computer is sufficient. This approach not only achieves product quality stability but also enables large-scale production with multiple varieties.

2.2. Washing Process ImprovementCurrently, titanium dioxide post-processing devices primarily use leaf filters for washing. This method has a simple process flow and equipment structure, is easy to operate, and requires a small investment. However, it consumes a significant amount of water, increasing water-related costs and not being conducive to subsequent washing. The ultimate drawback is an increase in production costs. Membrane filter presses provide a better solution for washing. This approach boasts high automation, low water consumption, and shorter filtration operation time. After the feeding is complete, compressed air is used for cake blowing to reduce the cake moisture content, and high-pressure water squeezing is employed to enhance dewatering efficiency. The membrane filter press washing can achieve a solid content of around 70% in the washed cake, effectively reducing energy consumption in subsequent processes.

2.3. Drying Process ImprovementCommon post-processing drying techniques for titanium dioxide include belt drying, spray drying, and flash evaporation drying. Belt drying employs direct steam heating, leading to lower thermal efficiency and relatively long drying times, resulting in larger agglomerate diameters in the output material, which is not favorable for subsequent processing. Spray drying uses hot air as the heat source, offering high thermal efficiency, but the material needs to be made into a slurry. Flash evaporation drying is a combination of drying, crushing, and screening in one machine, enabling continuous drying and uniform drying. This method is particularly suitable for materials with high solid content.

ConclusionIn summary, research on post-processing production techniques for rutile titanium dioxide, with improvements in the coating process, enhanced operational procedures, the adoption of membrane filter presses for washing, and the use of flash evaporation drying machines, allows for the production of various grades of rutile titanium dioxide, significantly reducing water content and saving energy, thereby lowering production costs. The application of post-processing production techniques for titanium dioxide in industrial production has brought about substantial economic and societal benefits.