Heavy calcium carbonate is a calcium carbonate powder material produced by mechanical crushing using calcite, chalk, marble and other minerals as raw materials. It has the characteristics of wide raw material sources, high whiteness, low oil absorption value, good applicability and low price. It is currently the most widely used and largest inorganic non-metallic mineral powder product.
At present, the production technology of heavy calcium carbonate is mainly based on grinding and surface modification, in order to process products that meet the fineness requirements of different application fields, including fine powder, ultrafine powder, surface modified (active) powder and ultrafine pulp for papermaking, etc. There are more than ten kinds of special heavy calcium carbonate products with different fineness and surface modification activation.
1. Heavy calcium carbonate production process and equipment
Taking heavy calcium carbonate for coating industry as an example, its production process mainly includes: cleaning and impurity removal, coarse crushing, fine crushing, screening, grinding and grading, material collection, surface treatment, packaging, etc.
2. Heavy calcium carbonate grinding technology and equipment
At present, heavy calcium carbonate with d97≥5μm is mainly produced by dry method, and the equipment includes improved Raymond mill (suspension roller mill or pendulum mill), roller mill (including pressure roller mill/vertical mill, ring roller mill, etc.) and ball mill, etc.
Ultrafine heavy calcium carbonate with d97＜5μm generally adopts dry production process, and some adopts wet grinding + drying process. Dry production mainly adopts cylindrical ball mill + classifier, roller mill (including ring roller mill with internal classification, vertical mill/pressure roller mill), dry stirring mill + classifier, etc.
The ball mill + classifier production line is mainly used to produce heavy calcium carbonate fine powder and ultrafine powder with d97=5～43μm. It is characterized by continuous closed-circuit production, multi-stage classification, large circulation load (300%～500%), and large single-machine production capacity.
Ring roller mill is the most widely used fine grinding and ultrafine grinding equipment in the field of heavy calcium carbonate in China in the past decade. It is characterized by a large crushing ratio and low energy consumption per unit product. Internal or external fine classifiers can produce ultrafine products with d97≤10μm, and the product fineness can be adjusted between d97=5～40μm; the most suitable product particle size range is d97=10～30μm.
Roller mill (vertical roller mill/roller mill) is one of the main large-scale equipment for fine grinding and ultrafine grinding of heavy calcium carbonate. Its characteristics are large crushing ratio, the most suitable product particle size range is d97=15~45μm, and after external fine classifier, ultrafine products with d97≤10μm can be produced; the product has good particle shape and low oil absorption value, which is particularly suitable for the production of heavy calcium carbonate filler for unsaturated polyester-based composite materials (artificial stone), and the unit product energy consumption and wear are low.
3. Heavy calcium carbonate surface modification technology and equipment
The surface modification of heavy calcium carbonate mainly adopts organic coating and composite modification methods.
Organic coating modification is a method of coating and modifying heavy calcium carbonate powder with organic substances such as stearic acid and its salts, aluminate coupling agents, titanate coupling agents, water-soluble polymers, etc. as surface coating/modifiers.
Composite modification is a surface modification method that uses physical or chemical methods to evenly mix in heavy calcium carbonate or ultrafine heavy calcium carbonate powder or coat another inorganic powder on the surface of the particles.
At present, dry modification is the mainstream process for heavy calcium carbonate. Unless wet ultrafine grinding is used, wet modification is rarely used.
Common surface modification equipment for heavy calcium carbonate includes SLG continuous powder surface modifier, HEM high-efficiency hybrid modifier, high-speed heating mixer, vortex mill, nail disc mill, etc. Some heavy calcium carbonate surface modification is also carried out simultaneously with fine grinding or ultrafine grinding, that is, surface modifiers are added during fine grinding and ultrafine grinding, and fine grinding/ultrafine grinding and surface modification of heavy calcium carbonate are completed in the same equipment.