The Production of Light Calcium Carbonate from Dicyandiamide Industrial Waste

The Production of Light Calcium Carbonate from Dicyandiamide Industrial Waste

Dicyandiamide industrial waste is a byproduct of chemical production, and about 12 tons of waste are generated for every ton of finished product produced in the dicyandiamide production process. The waste mainly consists of precipitated calcium carbonate, free carbon particles, river sand, and nitrogen-containing organic matter. If not properly disposed of, these wastes will not only occupy a large amount of land resources but also pollute water quality and cause environmental problems.

Using dicyandiamide industrial waste to produce light calcium carbonate is an effective method of waste utilization. Light calcium carbonate is a filler widely used in industries such as rubber, plastics, paper, paint, and decorative and thermal insulation materials. Traditional methods involve removing water, river sand, and nitrogen-containing organic matter from the waste through natural or mechanical dehydration, high-temperature roasting, screening, or air classification, and then producing light calcium carbonate containing carbon. However, this method produces products with free carbon particles, which are gray in color, limiting their application range.

This improved method builds on the above method by further separating free carbon particles through combustion decarbonization. By placing the material in a temperature range above the ignition point of carbon particles (650-700°C) but below the decomposition temperature of calcium carbonate (825-850°C), the free carbon particles will spontaneously combust, oxidize, and volatilize, thus producing high-purity light calcium carbonate. After this process, the purity of precipitated calcium carbonate can reach 99% or above, although trace impurities such as refractory elements may affect the whiteness of the product.

The process includes the following steps: First, the waste sludge from the effluent pool of dicyandiamide production plant is dried naturally or mechanically to reduce its moisture content. Then, the material is crushed, impurities removed, and dried through the steps of initial selection and drying. Next, the dried material is fed into a high-temperature calcination device to burn off free carbon and nitrogen-containing organic matter at an appropriate temperature. Finally, the coarse impurities are removed through screening or air-classification, and a high-purity light calcium carbonate product is obtained.

This method of producing light calcium carbonate from waste sludge of dicyandiamide industry not only effectively treats waste sludge and reduces environmental pollution, but also produces high-quality light calcium carbonate, expanding the application range of the product and improving its utilization value. In addition, the coarse gravel produced in the process can also be used in the construction industry, avoiding secondary pollution and having good social and economic benefits.