Kaolin is a pure fine-grained clay or clay rock, which is mainly composed of kaolinite clay minerals. Kaolinite is named after it was first discovered in Gaoling, Jingdezhen, Jiangxi, China. Kaolinite clay minerals include kaolinite, halloysite, dickite and pearl clay. Other clay minerals and non-clay minerals that constitute kaolin mainly include: clay minerals-hydromica, montmorillonite and chlorite; Non-clay minerals-feldspar and mica. In addition, it also contains a small amount of aluminum oxides and hydroxides, iron minerals (limonite, magnetite, pyrite), titanium oxide, organic matter and so on.

The theoretical chemical composition of kaolinite is: Al2O3 is 39.5%, SiO2 is 46.54%, and H2O is 13.96%. Kaolinite is generally colorless-white fine scale-like, and its single crystal is pseudo-hexagonal flake or book-like, with particle size of 0.5 ~ 2 microns, and individual worm-like crystals can reach several millimeters. Pure kaolin can reach the theoretical composition of kaolinite minerals, generally white or light gray, yellow, rose or gray, black and so on when impurities are contained. The raw ore is in dense lump or loose soil, soft, greasy, pearly or dull, translucent to opaque, with hardness 1 ~ 2.5, less than that of nails, and relative density of 2.2 ~ 2.6.

Pure kaolin has high whiteness, softness, easy dispersion and suspension in water, good plasticity, high cohesiveness and excellent electrical insulation. It has good physical and chemical properties such as acid resistance, low cation exchange capacity and high fire resistance. See table 3-27- 1.

Table 3-27- 1 Physical and Chemical Properties of Kaolin

Two. Ore types and industrial requirements

1. Ore type

According to its quality, plasticity and sand content (grain size of feldspar, mica and other minerals > 50μ m), naturally occurring kaolin can be divided into three industrial types: hard kaolin, soft kaolin and sandy kaolin. Their characteristics are shown in Table 3-27-2.

2. Deposit type

Table 3-27-2 Kaolin Ore Types

There are many genetic types of kaolin deposits in China, including weathering type, hydrothermal alteration type and sedimentary type. Weathered deposits are mainly distributed in Guangdong and Sichuan, sedimentary kaolin deposits are mainly distributed in Shanxi, Hebei, Henan, Shandong and Fujian, and hydrothermal alteration deposits are mainly distributed in Jiangxi and other places. Kaolin produced in northern China mostly belongs to sedimentary deposits, while kaolin produced in southern China mostly belongs to weathering residual type and hydrothermal alteration type. In addition, there are weathered leaching and Quaternary sedimentary kaolin deposits in the north and south. The metallogenic ages of kaolin deposits are mostly Mesozoic and Cenozoic. The types of kaolin deposits in Henan Province are mainly hard kaolin deposited in Carboniferous-Permian coal-bearing formations.

3. General industrial requirements

Different industrial sectors have different requirements for the quality of kaolin. The ceramic industry usually requires kaolin clinker to have high whiteness, low content of coloring and conductive elements such as iron, manganese and titanium, and less impurities and other mechanical inclusions, so that the product is easy to melt and foam during baking, high fire resistance and no deformation after firing. Paper industry requires high whiteness of raw ore, good pulping performance and fine and uniform particles. For example, kaolin with particle size less than 2μm and accounting for more than 80% should be used as raw material for scraper coating; The rubber industry also requires a small particle size to produce a high degree of dispersibility and absorbability, and rarely contains impurities such as Cu and Mn that are easy to harden rubber prematurely. The contents of iron and SO3 must also be low, but there is no specific requirement for whiteness. The basic requirement of refractory industry is refractoriness >1580℃; The white cement industry requires Fe2O3 < 0.7% in the ore, and there is no strict requirement for SiO2 and Al2O3. Therefore, when evaluating kaolin ore, we should comprehensively consider the same and different requirements of various industrial departments, take the minimum industrial requirements as the standard to divide ore and non-ore, and on this basis, divide high-quality ore, and reasonably determine the industrial index of raw ore through mineral resources economics. General industrial indicators can refer to the following standards (Table 3-27-3).

Table 3-27-3 General Industrial Standards for Kaolin Deposits

General mining technical requirements for kaolin deposits: the minimum recoverable thickness of sedimentary hard kaolin: 0.7 ~ 1m for open-pit mining, and 0.7m for open-pit mining; Thickness of stone removal: 0.3~0.5m for open-pit mining and 0.3m for underground mining. Minimum recoverable thickness of other types of kaolin ore: 0.7 ~ 2m for open-pit mining,1m; Used for open-pit mining; Stone removal thickness: open-pit mining 1 ~ 2m, underground mining1m.

The general detection items of kaolin deposits include: basic chemical analysis of Al2O3, Fe2O3 and TiO2; ; Combined analysis of SiO2 _ 2, MgO, CaO, Na2O, K2O and TSO3 _ 3 (sulfur-bearing gangue): ③ Physical properties: particle size composition, whiteness, plasticity, drying shrinkage, fire resistance, etc.

Three. Overview of kaolin mineral resources

According to the estimation of the US Bureau of Mines (1985), the total proven kaolin mineral resources in the world are117.94 million t, which are distributed in more than 50 countries and regions, mainly in Europe (5.443 billion t) and North America (3.77./kloc-0.90 billion t), followed by. Among them: US 3.538 billion tons, former Soviet Union 2.268 billion tons, UK 1 .81.400 million tons, Czech Republic1100 million tons, and China about 330 million tons. The annual output of kaolin in the world exceeds 23 million tons (1994), including about100000 tons in the United States, over 2 million tons in Britain and North Korea, and over100000 tons in Brazil, Germany, China and the Czech Republic. Kaolin price (1998): paper coating grade 100 ~ 180 USD/ton, filler grade 75 ~ 100 USD/ton, ceramic grade 60 ~ 120 USD/ton.

China is rich in kaolin resources and the deposits are widely distributed. There are 16 provinces in China, but they are mainly distributed in the southeast coastal areas. The proven reserves in East China and Central South China account for 80% of the total reserves in China, mainly distributed in Jiangsu, Zhejiang, Fujian, Jiangxi, Hunan and Guangdong provinces, but also distributed in Sichuan, Guizhou, Yunnan, Shanxi, Hebei, Liaoning, Shandong and Henan provinces. There are more than 200 kaolin deposits in China, including ceramic clay, but there are few large deposits, mostly small and medium-sized ones. The main deposits are: Suzhou in Jiangsu, Xuyong in Sichuan, Dandong in Liaoning, Wenzhou in Zhejiang, Chaoan in Guangdong, Maoming, Zhanjiang, Yongchun in Fujian, Minqing, Tongan, Liling in Hunan, Hengyang, Hengshan, Datong in Shanxi, Jingdezhen in Jiangxi, Luonan in Shaanxi, Zibo in Shandong and Yangbajing in Tibet.

Henan province is rich in kaolin resources. The work in recent years has proved that the reserves rank among the top in China. However, due to historical reasons, the degree of exploration, development and utilization is very low. The main reasons are as follows: firstly, the coal-series kaolin widely distributed in our province was recognized late, and used to be explored, evaluated, developed and utilized as a refractory clay deposit in the past; Second, because the development of kaolin in China was mainly concentrated in the southeast coastal areas in the past, a relatively mature development and processing process was formed. The main deposit type in this area is weathering residual type, and the development and processing technology of hard kaolin in northern coal measures has only made breakthroughs and applications in recent years.

The genetic type of kaolin deposits in our province is mainly coal-bearing sedimentary type, followed by hydrothermal alteration type and weathering leaching type. The main mineral deposits are Shendong in Yuxian, Zhong Ling in Gongxian, Aibo Jiufen, Ligou in Yiyang, Fengxue Temple in Linru, Sansan in Yuxian, Zhutun in Yuxian, Liangwa in Lushan, Donghuangdao in Jiaxian, Jing Ke in Jiyuan, Zhenyuan in Jiyuan, Babaoshan in Lushi and Prince Temple in Xichuan 10. The accumulated proven reserves are about 6.5438+million tons (kaolin and ceramic soil) (654.38+0998 ended), and the annual output is about 60,000 tons (654.38+0998).

Coal-bearing sedimentary kaolin is mainly produced in Carboniferous-Permian sedimentary rock series, and the ore-bearing strata include Carboniferous benxi formation, Taiyuan Formation and Permian Xiashihezi Formation. The thickness of hard kaolin deposits in benxi formation varies greatly, which is generally 1m ~ nm thick, and often coexists with iron ore, bauxite and refractory clay. Main characteristics: high iron content, rich in organic matter, gray-black. This layer was once evaluated as a refractory clay layer. According to recent research, it can be used in layers, one part is refractory clay, and the other part of high-quality ore can be used as kaolin for ceramics or paper making. The natural whiteness of coal seam is low, which can reach above 90% after calcination, and the content of kaolinite is generally above 90%. The overall quality in the north of the Yellow River is good. For example, the Jiufufen ceramic clay mine in Boai is located in benxi formation stratum, with a thickness of 0.45 ~ 2.78 m, generally 0.75 ~1.65m. The main mineral composition is kaolinite, and the main chemical composition is 35.63% ~ 38.65% Al2O3 and 44.05% ~ 45.79 SiO2. The content of TiO2 is 0.40% ~ 1.8%, the loss on ignition is 7.94% ~ 8.76%, and the plasticity index is 8.43 ~1.81. Benxi formation Kaolin Mine in Jiyuan Well contains 93% ~ 99% kaolinite, and benxi formation Kaolin Mine in Jiyuan Yuan Shao contains more than 95% kaolinite, including al2o 3 38.94%, SiO 2 45. 14%, fe2o 3 0.25% and TiO 2 0.38%. The ore quality is close to the theoretical chemical composition of kaolinite.

The hard kaolin deposits of Permian Xiashihezi Formation are mainly distributed in the south of the Yellow River, and the thickness of the deposits is generally large, ranging from several meters to more than ten meters, located in the lower part of Xiashihezi Formation. Main characteristics: low organic matter content, high natural whiteness, generally gray-blue-gray, high iron content. But it can be used in layers, with high iron content as refractory clay and low iron content as ceramic clay or clay for paper making. The quality of the high-quality part of the seam is good, the natural whiteness is above 85%, the quality is pure and delicate, and the kaolinite content is high, which is very close to pure kaolinite. In recent years, with the re-understanding of non-metallic minerals, the research, development and utilization of this layer have been strengthened. Representative mines, such as Zhong Ling ceramic clay mine in Gongxian county, can be divided into three layers according to quality: the lower layer is 1.28m thick, which can be used as ceramic raw materials locally; The middle seam is the main seam, with a thickness of 1.5 ~ 8.5m, generally 3 ~ 5m, dark gray and blue gray thick layer, fine texture, cleavage development and conchoidal fracture; The upper seam thickness is 1 ~ 2. 14m, and the maximum thickness exceeds 13m, which is yellowish brown thin-layer bauxite shale containing kaolin. Proved reserves1658,000 t, chemical composition of main coal seam is: al2o 3 39.8%, SiO 2 43.5 1%, Fe2O3 less than 3%, plasticity index 5.8% ~ 19.97%. Lushan Liangwa clay mine, with a thickness of 2. 1 ~ 15.28 m and a reserve of more than 8 million tons, was mainly used as refractory clay in the past. Research in recent years shows that high-quality seams can be separated, with kaolinite content of 90% ~ 98%, natural whiteness of 85% and iron content less than 0.8%. The exploration of Donghuangdao Kaolin Mine in Jiaxian County began in 1990s, with a submitted reserve of 424,400 tons and a prospective reserve of nearly one million tons. The thickness of main seam is 2.0~2.2m, the natural whiteness is 76.6%, Al2O3 is 36.72% ~ 38.79%, SiO2 is 42.56% ~ 45.11%,and Fe2O3 is 0%. In addition, Jiaozuo and Jiyuan also have high-quality ore beds, in which the main ore bed of Shaoyuan Fengou in Jiyuan is pure and grayish white with a thickness of 1.8m, with kaolinite content of 80% ~ 95%, Al2O3 of 38.08% ~ 38.52%, SiO2 of 45.20% ~ 45.38% and Fe2O3 of 0.30%.

Hydrothermal altered kaolin deposits are not widely distributed in our province, and the representative mine is Lushi Babaoshan ceramic clay mine. It is formed by hydrothermal alteration of K-feldspar granite porphyry. There are two types of ores: kaolinite and strongly kaolinized potash feldspar granite porphyry. White, massive, mainly kaolinite, with high iron content (average 1.5% ~ 2.5%). After washing, it can be used as raw material for ceramic industry and high alkali glass. The proven reserves of kaolin are 1.34 million tons, and the reserves of high-alkali glass raw materials are 7 1 10,000 tons.

Weathered leached kaolin deposits are only found in Miaogou, Taishan Mountain, Xichuan. The ore bed is located at the sedimentary contact interface between Sinian dolomite limestone and Cambrian siliceous rock and near it, and belongs to weathered residual kaolin deposit. The ore type is illite-kaolinite (including dickite) clay, which is divided into high-quality kaolin and ordinary kaolin. High-quality kaolin is clean and white, oily and shiny, slippery and plastic after wetting. After drying, it is fragile into powder, mainly kaolinite, with trace amounts of timely and chlorite, and the iron content ranges from zero to trace. Kaolin ore here used to be used as raw material for refractories. Since 1970s, it has been used as a raw material for ceramics, mainly for electric ceramics and sanitary ceramics.

Fourth, the main uses of kaolin

Kaolin is the main raw material for ceramic production because of its plasticity, cohesiveness, certain drying strength, sinterability and whiteness after firing. Excellent technological properties such as whiteness, softness, high dispersibility, absorbability and chemical inertness make it widely used in paper industry. In addition, kaolin is also widely used in rubber, plastics, refractories, petroleum refining and other industrial fields, as well as cutting-edge technology fields of agriculture and national defense. See table 3-27-4.

Table 3-27-4 Main Uses of Kaolin

Five, the main industrial and technical indicators of products

1. Product quality requirements

The application fields of kaolin are different, and its quality requirements are completely different. In terms of chemical composition, the contents of Al2O3 and SiO2 in kaolin are required to be close to the theoretical values of kaolinite in paper coatings, radio ceramics and refractory crucibles. The fillers of daily-use ceramics, building sanitary ceramics, white cement raw materials and rubber plastics can appropriately reduce the Al2O3 content of kaolin, and the SiO2 content can be appropriately higher. The allowable contents of harmful components such as Fe2O3, TiO2 and SO3 are also different, and the allowable values of CaO, MgO, K2O and Na2O are also different in different applications. In terms of physical properties, the emphasis of various application fields is more obvious. Paper coatings mainly require high whiteness, low viscosity and fine particle size; Ceramic industry requires good plasticity, formability and firing whiteness; Refractory materials require high fire resistance; The enamel industry requires good suspension and so on. This determines the diversity of kaolin product specifications and brands.

Table 3-27-5 General Standard for Kaolin (JC88-82)

2. Product quality standards

China's current kaolin product standard was revised by the National Building Materials Bureau in 1982. According to the chemical composition and physical properties, the general standard of kaolin (JC88-82) was established, as shown in Table 3-27-5. At the same time, according to the purpose, three special standards of kaolin for paper, kaolin for enamel and kaolin for rubber have been formulated, as shown in Table 3-27-6, Table 3-27-7 and Table 3-27-8.

Table 3-27-6 Kaolin Standard for Paper Industry (JC3 18-82)

Table 3-27-7 Kaolin Standard for Enamel Industry (JC3 19-82)

Table 3-27-8 Kaolin Standard for Rubber Industry (JC320-82)

Six, kaolin mineral processing method and process flow

1. Mineral processing method

In order to separate non-clay minerals and organic substances such as quartz, feldspar, mica, iron minerals and titanium minerals from kaolin, and produce kaolin products that can meet the needs of various application fields. Gravity separation, flotation, magnetic separation, chemical treatment and other processing methods to improve the quality of kaolin have been applied to the processing of kaolin. According to the characteristics of deposited kaolin in our province, two mineral processing schemes have been put forward by relevant scientific research units after years of research and experiments. One is to improve the whiteness by roasting to remove water and decarbonize, and the other is to improve the whiteness by superfine grinding and chemical bleaching, so as to reach the quality standard of coating grade kaolin. These two technical routes have matured and been applied. The main processing methods of kaolin are shown in Table 3-27-9.

Table 3-27-9 Main Mineral Processing Methods of Kaolin

sequential

2. Process flow

The technological process of kaolin mineral processing generally includes three parts: preparation, separation and product treatment. The preparation part includes crushing, beating and other operations; The sorting part includes sorting, bleaching, peeling and other operations; The product treatment part includes concentration, filtration, drying and packaging. Because of different ore types and product indexes, the beneficiation process is also different. See table 3-27- 10 for the main process flow of each ore type.

Table 3-27- 10 kaolin mineral processing flow

The key links of producing high value-added fine kaolin products are ultra-fine grinding and fine classification. Through superfine grinding and fine classification (including stripping process), the content ratio of kaolinite powder with particle size less than 2 microns in the product can be increased (up to more than 80%), and the fine products of coating grade kaolin can be produced, which greatly improves the gloss and opacity of paper. Chemical bleaching is a traditional process for removing variegated iron compounds in kaolin industry. Its purpose is to remove impurities such as iron and titanium and improve the whiteness of products. High gradient magnetic separation and selective flocculation are also effective methods to remove impurities and improve whiteness. When selecting the processing flow, the characteristics of ore types and compositions should be fully considered to produce high value-added products and create high economic benefits, which can be comprehensively utilized in various ways.