| 摘要 |
The embodiment of kaolin quality improvement includes a chemical, heating method for processing kaolin to high brightness levels and lower viscosities. This permits addition of natural titania for greater opacity in commercial paper coating. Mechanism of brightness improvement includes removal of iron oxides and iron sequestered by natural organic acids. Viscosity is improved by removal of organic and at least partial decomposition of expandable clay, such as montmorillonite. Kaolin crude is dispersed preferably with Calgon at minimum level. Classification to desired particle size is followed by adding 0.2 percent sodium sulfate decahydrate. After raising pH to 8.5 with dilute sodium hydroxide the slip is heated to 65 to 70 degrees centigrade for 5 to 60 minutes. Cooled to at least 40 degrees centigrade, the slip is bleached with sodium hydrosulfite. Time of bleach is 20 minutes at pH 3 to 3.5. Efficient filtration and rinsing is critical, a 2:1 ratio of water to dry clay rinse preferable.
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