Abstract
Clay minerals are one of the most utilized minerals among non-metals. These are hydrous aluminum silicates with a layer (sheet-like) structure. Kaolin is a hydrous aluminosilicate mineral with a thin platelet structure. Kaolin is extensively used in paper, paint, and many other industries. Wet processing of kaolin will not be sustainable over the long term because global freshwater resources are becoming scarce. Hence, a process is necessary that does not consume water during the beneficiation of kaolin. This study developed a dry beneficiation process for low-grade kaolin of 59.6%, with 12% quartz and about 6% titaniferous impurities from Nagar Parkar, Sindh province, Pakistan. To develop a size difference between kaolinite and impurities, steel balls clad with rubber were used as the grinding media in a selective grinding unit. Screens of 60 and 400 mesh were employed to classify the feed of air classifier. Oversize +60 mesh was reground, 400 to 60 mesh fractions were sent to an air classifier, and −400 mesh was considered to be a product with the grade and recovery of 90.6% and 20.5%, respectively. Air classifier experiments were designed using central composite design. An experiment using a fan speed of 1200 revolutions per minute (rpm) and a shutter opening of 4.0 showed optimum results, with maximum kaolinite grade and recovery of 91.5% and 35.9%, respectively. The statistical models developed for grade and recovery predicted the optimum results at a fan speed of 1251 rpm and shutter opening of 3.3 with the maximum kaolinite grade and recovery of 91.1% and 24.7%, respectively. The differences between experimental and predicted grade and recovery were 0.1% and 2.4%, respectively. The characterization results showed the total upgrade of kaolin from 59.6% to 91.2%, with 27.1% recovery during the process. The designed methodology has the potential to improve the yield of the product by focusing on its recovery. Furthermore, the designed process can be improved by using different sized balls in the selective grinding unit. This beneficiation process can utilize more than one air classifier in series to achieve the targeted results.
Highlights
The name “kaolin” is derived from the Chinese term “Kauling”, meaning high ridge.This is the name of a hill near Jauchau Fu, China, where this material was first mined centuries ago for ceramics [1]
Wet processing of kaolin can achieve the brightness grade of 80% to 90% required by the paper industry, 80% to 85% for the filler industry, 85% to 90% for the coating industry [5,14] and potentially 94% for high-specification kaolin products [15]
The aim of this research was to contribute towards replacement of wet processing of kaolin with dry processing, and to examine if dry processing can accomplish the grade and recovery required by different industrial applications
Summary
The name “kaolin” is derived from the Chinese term “Kauling”, meaning high ridge. This is the name of a hill near Jauchau Fu, China, where this material was first mined centuries ago for ceramics [1]. Wet and dry methods are employed to beneficiate crude kaolin to meet the requirements of different industries such as fiberglass and ceramics. Wet methods consist of both physical and chemical processes. Wet processing of kaolin can achieve the brightness grade of 80% to 90% required by the paper industry, 80% to 85% for the filler industry, 85% to 90% for the coating industry [5,14] and potentially 94% for high-specification kaolin products [15]. Bioleaching of iron from kaolin can produce product with a 60% whiteness grade [17] and an 80% brightness grade [18]
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