Light calcium carbonate is a widely used industrial filler, mainly used in plastics, paper, rubber, paint and other industries. Light calcium carbonate, also known as precipitated calcium carbonate (PCC for short), is made by chemical processing methods. Because its sedimentation volume (2.4mL/g～2.8mL/g) is larger than that of heavy calcium carbonate produced by mechanical methods (1.1mL/g～1.9mL/g), it is called light calcium carbonate.
1. Preparation of light calcium carbonate from phosphogypsum
Phosphogypsum is an industrial waste residue produced during the production of wet-process phosphoric acid. It has large emissions, occupies a lot of land, and has serious environmental pollution. The preparation of light calcium carbonate using phosphogypsum can solve the problem of comprehensive treatment of phosphogypsum.
Step I: Wash the phosphogypsum with 42°C hot water, grind it with deionized water and add it to the reactor, set the stirring speed of the electric stirrer to 350r/min, then slowly add ammonium carbonate dropwise, the reaction temperature is 125°C, constant temperature After 1 hour of reaction, after the reaction is completed, the filtrate and the precipitate are filtered, the filtrate is cooled and crystallized, and then filtered, and the crystal is dried to obtain ammonium sulfate;
Step II: Take the precipitate in step I, add deionized water grinding slurry, place it in the reactor, set the electric stirrer stirring speed to 150r/min, pass in carbon dioxide, carbon dioxide flow rate is 250mL/min, react for 2h, filter, The recovered filtrate is heated to a temperature of 95°C and reacted for 2 hours. The carbon dioxide generated is reused. After the reaction is completed, it is filtered. The filtrate is recovered and returned to the reactor for a secondary reaction. Light calcium carbonate is obtained.
2. Preparation of light calcium carbonate by-product from soda production
In the process of producing soda ash by ammonia-alkali method, by-product calcium chloride solution and crude hydrazine hydrate solution are used as raw materials to prepare high-quality light calcium carbonate.
When feeding, first add a certain amount of crude hydrazine hydrate solution (hydrazine hydrate temperature 60℃～80℃, sodium carbonate concentration 100g/L～160g/L), start stirring and then add calcium chloride solution to the kettle.
Calcium chloride concentration is controlled at about 30% to 50% (high calcium chloride concentration not only reduces the dilution of hydrazine hydrate, but also is the optimal concentration of the reaction), and the feed rate is 15% of the amount of hydrazine hydrate solution every 10 minutes. 30%, the total feed of calcium chloride and sodium carbonate (the molar equivalent ratio) is 1.05 to 1.15. After the addition of calcium chloride solution is completed, the reaction takes 20 min to 60 min, and the specific reaction time depends on the content of sodium carbonate in the crude hydrazine hydrate. After the reaction of the crude hydrazine solution is completed, after solid-liquid separation, the liquid enters the evaporative rectification system for rectification treatment, and the solid is light calcium carbonate.
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