The breakthrough in light transmittance of marble tiles lies in the refined control of iron removal processes in raw materials. Iron, a common impurity in natural minerals, exists in raw materials such as kaolin and quartz sand in the form of iron oxide and iron sulfide, significantly reducing the light transmittance of tiles. In marble tile production, iron impurities not only cause defects such as black spots and yellow patches after firing, but also disrupt the light transmission path, drastically reducing the overall light transmittance of the tiles. Therefore, the iron removal process in raw materials is a crucial step in improving light transmittance, and its technical approach must be integrated throughout the entire process of raw material selection, processing, and production.
In the raw material selection stage, iron content must be controlled from the source. The occurrence state of iron in natural mineral raw materials directly affects the difficulty of iron removal. For example, iron in kaolin may be embedded in the mineral structure in the form of a crystal lattice, while iron in quartz sand is mostly attached to the particle surface. During production, mineral sources with lower iron content should be prioritized, and visible iron impurities should be removed manually. Simultaneously, chemical composition analysis of the raw materials should be performed to assess the occurrence form of iron, providing a basis for subsequent iron removal processes. The rigorous screening at this stage significantly reduces the burden of subsequent processing, laying the foundation for improved light transmittance.
Physical iron removal processes separate iron impurities through magnetic fields. In raw materials such as kaolin, strongly magnetic minerals like magnetite can be removed using high-gradient magnetic separators, while weakly magnetic minerals like hematite require roasting to enhance their magnetism. During magnetic separation, parameters such as slurry flow rate and magnetic field strength must be precisely controlled to ensure complete adsorption of iron impurities. Furthermore, ultrasonic technology can peel off secondary iron minerals adhering to the particle surface, and through cavitation, disrupt the bond between iron impurities and the mineral surface, further improving the iron removal effect. The advantage of physical iron removal processes is that they do not introduce chemical impurities, making them suitable for large-scale industrial production.
Chemical iron removal processes remove iron impurities through dissolution or chelation. For iron elements embedded in the mineral lattice, acid leaching can effectively dissolve iron oxides. For example, sulfuric acid or oxalic acid solutions react with iron impurities under heating conditions to generate soluble iron salts, which are then removed by washing with water. Chemical iron removal requires strict control of solution concentration, temperature, and reaction time to avoid excessive corrosion of the mineral structure. Furthermore, microbial leaching technology utilizes the metabolic activity of microorganisms such as *Thiobacillus ferrooxidans* to convert ferrous iron into ferric iron and dissolve it, offering advantages such as environmental friendliness and high efficiency. Chemical iron removal processes can deeply remove iron impurities that are difficult to separate using physical methods, significantly improving the whiteness and transmittance of raw materials.
Combined iron removal processes combine physical and chemical methods to achieve full-chain removal of iron impurities. In actual production, single iron removal methods often fail to achieve ideal results, requiring multi-stage treatment to achieve precise control of iron content. For example, magnetic separation is first used to remove strongly magnetic minerals, followed by ultrasonic stripping of the surface iron film, and finally acid leaching to dissolve residual iron impurities. Composite processes can tailor solutions for different forms of iron impurities, minimizing iron content. In addition, online monitoring technology can detect the iron content in the slurry in real time, adjusting process parameters through feedback to ensure the stability of iron removal efficiency.
Raw material homogenization and aging processes have a significant impact on iron removal efficiency. Due to differences in formation conditions, the chemical composition and mineral composition of natural mineral raw materials fluctuate. Homogenization ensures uniform mixing of different batches of raw materials, preventing quality defects caused by excessively high local iron content. The aging process, through prolonged settling, allows moisture and minerals in the raw materials to fully react, promoting the migration and aggregation of iron impurities, facilitating subsequent iron removal. The combination of homogenization and aging enhances the stability of the raw materials, ensuring breakthroughs in light transmittance.
A breakthrough in light transmittance requires the coordinated advancement of process innovation and equipment upgrades. With the development of industrial technology, intelligent iron removal systems are gradually being applied to marble tile production. By integrating equipment such as laser particle size analyzers and online quality indicators, a closed-loop control system of "detection-adjustment-feedback" can be constructed, enabling dynamic optimization of the iron removal process. Furthermore, the development of modules such as high-pressure air knives and vibrating feeders has solved the problem of moisture-laden raw material adhesion, improving iron removal efficiency. This collaborative innovation in process and equipment has propelled marble tile light transmittance to higher levels, meeting the stringent performance requirements of the high-end market.
