(School of Chemistry and Environmental Engineering, China University of Mining and Technology (Beijing), Beijing 100083)
The production and application status of heavy calcium carbonate in China are summarized. The present situation and progress of crushing, grading and surface modification technology of heavy calcium carbonate are emphatically summarized. The development trend of its market and technology is prospected.
Heavy calcium carbonate; Production; Application; Processing technology.
About the author: Zheng Shuilin, male, (1956—), professor and doctoral supervisor of School of Chemistry and Environmental Engineering, China University of Mining and Technology (Beijing); Long-term engaged in teaching and research of mineral processing and deep processing of nonmetallic minerals. E-mail :shuilinzh@yahoo.com.cn.
Large-scale production of heavy calcium carbonate in China began in the early 1980s, and most of the original manufacturers were concentrated in Fuyang and Jiande, Zhejiang. After more than 20 years of development, the production scale has increased from the initial annual output of tens of thousands of tons to more than 500× 104t in 2006. The main producing areas have expanded from Jiande and Fuyang in Zhejiang to Anhui, Guangdong, Guangxi, Sichuan, Hunan, Jiangsu, Shandong, Hubei, Jiangxi, Liaoning, Jilin and Heilongjiang. The number of production enterprises has increased from the initial few to more than 300 at present; The product variety has developed from the initial "double fly powder" (200 meshes) and "three fly powder" (325 meshes) to 400 meshes (< 38 microns), 600 meshes (d97 = 20 microns), 800 meshes (d97 = 16 microns) and 1250. Its development speed and scale have surpassed that of light calcium carbonate.
I. Production and Application
In 2006, the total domestic output of heavy calcium carbonate was about 565,438+00× 65,438+004t, an increase of more than 65,438+00% over the previous year, of which 65,438+0,250 mesh (d97 = 65,438+00μ m) superfine heavy calcium carbonate was about 20. The main application fields are plastics, paper making, rubber, coatings, inks, adhesives, daily chemicals and so on. Among them, the main factor to promote the sustained and rapid growth of heavy calcium carbonate output is the significant growth of industrial demand for paper and plastic products.
Plastic products are the largest consumer market of heavy calcium carbonate, and the consumption in 2006 was about 200×104t. t； Especially in 2006, the output of activated calcium carbonate increased greatly, and ultrafine activated calcium carbonate was widely used in plastic profiles, various pipelines, plastic films, cables and other application fields [1]. Paper industry is one of the industries with the fastest growing demand for calcium carbonate. In 2006, the consumption of nonmetallic mineral fillers and pigments in this field was about 500× 104t, of which the heavy calcium carbonate was about 190× 104t, an increase of about 15% over the previous year. About 90× 104t heavy calcium carbonate is used as paper filler, and the rest is used as paper coating [2]. In 2006, the consumption of heavy calcium carbonate in coatings and inks was about 25×104t [3]; Rubber consumption is about15×104t; The consumption of toothpaste is about 30×104t; ; Others are about 40× 104t. In 2006, the domestic export volume of calcium carbonate reached 120878 t, an increase of 46597 t or 62% compared with 2005 (7428 1 t).
Second, the processing technology
(1) crushing and classification
Domestic heavy calcium carbonate production processes mainly include dry method and wet method.
1. Dry method
Dry process equipment mainly includes ball mill, roller mill (including roller mill, ring roller mill, Raymond mill, etc. ) and vibration mill. The combination of ball mill and fine classifier can not only process ultrafine powder of D975 ~ 10μ m, but also adjust it between 325 ~ 2500 meshes according to user's requirements. This processing technology of heavy calcium carbonate has the characteristics of continuous closed-circuit production, multistage classification, large circulating load (300% ~ 500%) and large single-machine production capacity, and is the first choice for large-scale superfine heavy calcium carbonate manufacturers at home and abroad. Roller mill is mainly used to process fine powder with 200 ~ 1000 mesh, and ultrafine powder products with 1250 mesh or more can be processed by fine classifier [4].
Ring roller mill is a small and medium-sized ultrafine grinding equipment widely used in the field of ultrafine heavy calcium carbonate in recent two years. Its characteristics are simple process, large crushing ratio and low energy consumption per unit product. Feed particle size ≤ 20 mm; Built-in grading device, product fineness can be adjusted between d978 ~ 20μ m; The single machine output is 600 ~1800 t/h; Energy consumption (d97 =10 μ m) ≤100 kw h/t
The roller mill is characterized by its large single-machine production capacity, and the GCC output of calcite can reach 5 ~10t/h; And built-in classifier, product fineness can be adjusted between d978 ~ 30μ m. ..
In the production of heavy calcium carbonate, especially in the production of superfine heavy calcium carbonate, fine classification equipment is one of the essential process equipment. Its purpose is: ① to control the fineness and particle size distribution of products. (2) separating qualified fine-grained products in time to prevent over-grinding and improve crushing efficiency; The latter point is very important for ball mills. It is precisely because of the fine particle classifier that qualified fine particle products are separated in time, which significantly improves the grinding and crushing efficiency of the ball mill, which makes the ball mill widely used in this field.
At present, the main industrial classifiers in China are QF-5A micro classifier, FQZ ultra-fine classifier, MSS fine classifier, ATP single-wheel classifier and ATP multi-wheel classifier. These classifiers are basically used in conjunction with pulverizers, and their grading granularity can be adjusted within the range of d973~20μm ... The production capacity of a single classifier varies from several hundred kilograms per hour to 5,000kg per hour.
Since 1985, the dry classification technology has made remarkable progress. The product fineness d97 of the most advanced fine classifier in 1985 is less than10μ m; 1992, d97 < 6 microns; In 2000, the d97 was less than 3.5 microns; In 2002, D97 < 2.5μ m, and the production capacity (d97≤ 10μm, GCC). 1985 single machine production capacity of 500 kg/hour; 1990, 1000 kg/hour; 1995,2000 kg/hour; In 2000, 4,000 kg/hour; In 2005, it was 7000kg/h, and domestic large-scale fine classifier includes LHB turbine fine classifier and FJW500×6 ultra-fine classifier.
2. Wet method
The wet production process of heavy calcium carbonate in China was put into production after 1993, which was mainly used to produce paper coated products with d60≤2μm, d90≤2μm and d97≤2μm; The grinding equipment mainly includes a stirring mill, a sand mill and a grinding stripper [5].
Before 2000, the domestic 80 ~ 500 L BP mill and other stirring mills were mainly used in this field. Around 2002, with the rapid growth of the demand for superfine calcium carbonate slurry in the domestic paper industry, 1500 L stirred mill was put into industrial application. In 2003, 3000 L vertical stirring mill was adopted; In 2005, 3500~5000 L stirring mill was used. The single machine production capacity (d90≤2μm dry weight) increased from 65438+300 kg/h in 0995, 500 kg/h in 2000, and 1000 kg/h in 2003 to over 2000 kg/h in 2005. The energy consumption in 1995 was 250kw h/t, in 2000180kw h/t, in 2003120kw h/t and in 2005/90kw h/t.
At present, there are CYM, LXJM and MB-5000L large vertical stirring mills with a capacity of more than 3000 L which are applied in the processing field of superfine calcium carbonate slurry in China.
The important progress in the processing technology of superfine calcium carbonate slurry is also reflected in the fineness and viscosity of the product: high-quality special surface-coated finely ground calcium carbonate GCC is produced, and the solid content of the slurry is 75% ~ 78%; The viscosity is less than 350 MPa·s；; ; The maximum particle size is 3 ~ 5 microns, the content of -2μm is ≥97%, and the content of 1μm is ≥ 75%; The average particle size is 0.3 ~ 0.5 μ m.
(2) Surface modification
Heavy calcium carbonate is the largest amount of inorganic filler in polymer-based composites at present. The main advantages of calcium carbonate filler are wide source of raw materials, low price and non-toxicity. According to statistics, about 70% of inorganic fillers in plastic products industry are calcium carbonate, including light or precipitated calcium carbonate (PCC) and heavy or finely ground calcium carbonate (GCC). Because calcium carbonate filler is inorganic powder, its compatibility with organic polymer is poor, and it is difficult to disperse evenly when it is directly added to polymer materials, which will also affect the processability and mechanical properties of the materials. Therefore, it is generally necessary to modify the surface of polymer materials before filling them. At present, surface modification technology has become one of the most important and necessary deep processing technologies for calcium carbonate (including light calcium carbonate and heavy calcium carbonate), and the annual output of activated calcium carbonate powder with different fineness reaches 150× 104t or more [6].
1. surface modification method
At present, the surface modification methods of calcium carbonate are mainly chemical coating, supplemented by mechanochemistry; The surface modifiers used are stearic acid (salt), titanate coupling agent, aluminate coupling agent and so on. There are two kinds of surface modification processes: dry method and wet method.
Stearic acid (salt) is the most commonly used surface modifier for calcium carbonate. The modification process can be dry or wet. Generally, stearate, such as sodium stearate, is used in the wet process. In addition to stearic acid (salt), other fatty acids (esters), such as phosphate and sulfonate, can also be used for surface modification of calcium carbonate. After surface modification of calcium carbonate with special structure of polyphosphonate (ADDP), the surface of calcium carbonate particles is hydrophobic and lipophilic, and the average aggregate size in oil decreases. Filling modified calcium carbonate into PVC plastic system can significantly improve the processability and mechanical properties of plastics. It is reported that the mixed use of stearic acid and sodium dodecyl benzene sulfonate can improve the surface modification effect of light calcium carbonate.
Heavy calcium carbonate treated with titanate coupling agent has good compatibility with polymer molecules. At the same time, titanate coupling agent can form a molecular bridge between calcium carbonate molecules and polymer molecules, which can enhance the interaction between organic polymers or resins and calcium carbonate and improve the mechanical properties of thermoplastic filled composites, such as impact strength, tensile strength, bending strength and elongation.
Aluminate coupling agents are also widely used in the surface treatment of heavy calcium carbonate and the processing of filled plastic products, such as PVC, PP, PE and filled masterbatch. After aluminate treatment, the viscosity of CaCO3- liquid paraffin mixed system decreased significantly, and the modified CaCO3 had good dispersibility in organic media. In addition, the surface modified activated heavy calcium carbonate can significantly improve the mechanical properties of CaCO3 and PP (polypropylene) * * * mixed system, such as impact strength and toughness.
Surface modification of heavy calcium carbonate by polymers can improve the stability of heavy calcium carbonate in organic or inorganic phases (systems). These polymers include oligomers, polymers and water-soluble polymers, such as polymethylmethacrylate (PMMA), polyethylene glycol, polyvinyl alcohol, polymaleic acid, polyacrylic acid, alkoxy styrene-styrene sulfonic acid, polypropylene and polyethylene.
The process of coating modified calcium carbonate on polymer surface can be divided into two types: one is to adsorb polymer monomer on the surface of calcium carbonate and then initiate its polymerization, thus forming a polymer coating on its surface; Secondly, the polymer is dissolved in a suitable solvent, and then the surface of calcium carbonate is modified. When the polymer is gradually adsorbed on the surface of calcium carbonate particles, the solvent is removed and a coating is formed. These polymers are directionally adsorbed on the surface of calcium carbonate particles to form physical and chemical adsorption layers, which can prevent calcium carbonate particles from agglomerating, improve dispersibility and make calcium carbonate have better dispersion stability in application.
In the process of superfine grinding, the surface of calcium carbonate powder can also be modified by mechanochemistry. In the process of superfine grinding of calcium carbonate, due to the action of mechanical force, on the one hand, the particle size becomes smaller; At the same time, a part of mechanical energy accumulates in the particles, which causes the changes of surface structure and properties and enhances the interaction between calcium carbonate surface and surface modifier. Therefore, the surface chemical coating modification of calcium carbonate can be completed at the same time by adding surface modifiers and additives during ultrafine grinding.
2. Surface modification equipment
Surface modification equipment of heavy calcium carbonate can be divided into dry method and wet method. At present, the commonly used dry surface modification equipment includes SLG continuous powder surface modifier, high-speed heating mixer, PSC powder surface modifier (Figure 1) and vortex mill. Among them, SLG type continuous powder surface modifier, PSC type powder surface modifier and vortex mill are continuous powder surface modifiers. High-speed heating mixer is an intermittent surface modification equipment. Commonly used wet surface modification equipment is controllable temperature reaction kettle and reaction kettle.
SLG continuous powder surface modification machine is currently dominant in dry continuous surface modification of ultrafine calcium carbonate, and it is a continuous surface modification equipment with independent intellectual property rights in China. At present, more than 100 equipment has been used for surface modification of ultrafine calcium carbonate powder, with an annual output of about 80× 104t [6].
Third, the development trend
The main raw materials of heavy calcium carbonate are calcite, marble, chalk and high-quality limestone. Rich in raw materials and low in market price; This product is a non-metallic mineral powder material, which has a wide range of applications and a large amount of consumption. Its relatively low price and wide applicability determine that it has a good development prospect in the inorganic filler and pigment market. With the rapid development of domestic paper-making, plastics, coatings, printing ink and rubber industries, it is predicted that the annual demand of domestic heavy calcium carbonate will increase by about 10% during the 11th Five-Year Plan period, and will reach about 850× 104t in 20 10, and the production capacity will reach about 900× 104t.
In terms of processing technology, improving crushing and classification efficiency, reducing energy consumption and wear, optimizing surface modification effect and reducing modification cost will be the main development trends.
Figure 1 dry surface modification equipment
1- feeding device; 2- drug delivery device; 3-SLG continuous powder modifier; 4- cyclone collector; 5— Dust catcher
Due to the increasing demand of users, in order to supply products with stable quality, it will be the main development trend of heavy calcium carbonate grinding technology in the future to enlarge the existing grinding equipment and its supporting subdivision equipment. In order to reduce energy consumption, in addition to large equipment, the existing crushing and grading equipment will be improved to improve the efficiency of crushing and grading equipment; In order to reduce wear, in addition to optimizing the crushing process, the material of equipment in contact with materials will also be improved.
The optimization of surface modification effect will mainly start from three aspects: surface modification method, modification equipment and modifier formula: ① surface modification method and process improve the dispersibility and equality of mutual contact or action opportunities of calcium carbonate powder and surface modifier in the modification process according to the preparation process of powder and the types of surface modifiers; (2) Selecting surface modification equipment which can make the powder and surface modifier disperse well, contact with each other or have equal opportunities in the modification process; (3) According to the types and application requirements of the resin substrate, surface modifiers and modification additives are selected.
Reducing the cost of surface modification will mainly start from the aspects of surface modifier, energy consumption of surface modification and surface modification process. Surface modifier is one of the main cost components of surface modification of calcium carbonate. In order to reduce the dosage of surface modifier, the dispersibility of surface modifier will be improved and it will be coated on the surface of calcium carbonate particles as much as possible. Surface modification is mostly an operation requiring heating, which consumes electric energy and heat energy. In order to reduce the energy consumption in the modification process, in addition to simplifying the process, the surface modification equipment or device will be improved. The loss of powder materials in the modification process not only increases the production cost of modified products, but also pollutes the workshop environment. Therefore, continuous and closed surface modification equipment will be used as much as possible to minimize the transportation links and distances of powder materials.
Four. conclusion
In 2006, the domestic output of heavy calcium carbonate was about 5 10× 104t, an increase of 10% over the previous year. Among them, superfine heavy calcium carbonate with 1250 mesh (d97 = 10μ m) is about 200× 104t, accounting for about 40% of the total output.
Plastic products are the largest consumer market of heavy calcium carbonate, and the consumption in 2006 was about 200×104t. t； Paper industry is one of the industries with the fastest growing demand for heavy calcium carbonate. In 2006, the consumption in this field was about190×104t. In 2006, the consumption of heavy calcium carbonate in paint, ink, rubber and toothpaste was about110×104t; In 2006, the domestic export volume of calcium carbonate was120878 t.
Since 2000, the crushing and classification technology of heavy calcium carbonate in China has made remarkable progress. Large-scale heavy calcium carbonate production plants mainly adopt ball milling and classification combined process and roller grinding production process, while small and medium-sized ultra-fine heavy calcium carbonate production plants mainly adopt roller mill; Wet ultrafine calcium carbonate slurry mainly uses a large stirring mill with a capacity of more than 3000 L.
Surface modification is one of the most important processing technologies of heavy calcium carbonate. At present, surface organic coating modification methods are mainly used, such as stearate, aluminate coupling agent, titanate coupling agent and other surface modifiers. The main modification equipment includes SLG continuous powder surface modifier, high-speed heating mixer, vortex mill and so on.
During the 11th Five-Year Plan period, it is estimated that the annual domestic demand for heavy calcium carbonate will increase at a rate of about 10%, and it will reach about 850× 104t in 20 10, with a production capacity of about 900× 104t and an export volume of 30× 104.
Improving crushing and classification efficiency, reducing energy consumption and wear, optimizing surface modification effect and reducing modification cost will be the main development trends.
refer to
Liu Yingjun. Several problems in the application of calcium carbonate in plastics. China nonmetallic mineral industry guide, 2007(3), 3-7.
[2] Song Baoxiang, Yan Wang, consumption status and development trend of non-metallic mineral materials for papermaking. China nonmetallic mineral industry guide, 2007( 1), 10- 14.
Zhou Ming, Hou Cuihong. Research status and development trend of calcium carbonate for coatings. China nonmetallic mineral industry guide, 2006(2), 3-6.
Zheng shuilin, zu zhanliang. Present situation of non-metallic mineral crushing processing technology. China nonmetallic mineral industry guide, 2006 (supplement), pp. 3-8.
Zheng shuilin. Non-metallic mineral materials. Beijing: Chemical Industry Press, 2007,92-130.
Zheng shuilin. Present situation and development trend of surface modification technology of calcium carbonate powder. China nonmetallic mineral industry guide, 2007(2), 3-6.
Production and Development of Heavy Calcium Carbonate in China
Zheng shuilin
(School of Chemistry and Environmental Engineering, China University of Mining and Technology (Beijing Campus), Beijing 100083)
Abstract: The production and application of heavy calcium carbonate in China are summarized, especially the grinding technology and equipment, classification technology and equipment and surface modification technology in the production of heavy calcium carbonate. The development trend of heavy calcium carbonate market and processing technology is prospected.
Key words: heavy calcium carbonate, production, application and processing technology.