Research On The Preparation And Properties Of Superfine Precipitated Calcium Carbonate With Ordovician Limestone In Weibei Area

Weibei Ordovician limestone is the most important high quality ore source in Shaanxi province which distributes widely and has a good quality. It has long been used as raw materials for cement production. The capacity of cement production is supply exceeds demand, and the cement industry has been suffering from the problem of less profit and high pollution in China. Therefore, it is of great significance to find and develop new and high additional value products for high quality limestone in Weibei area. In this paper, limestone in Weibei area was used as raw material to prepare superfine precipitated CaCO3 with various morphologies, excellent performance and high additional value by carbonization method,Firstly, the influence of the calcination temperature, particle size of limestone and the calcination time on the preparation of active lime are discussed though the research of the calcination process on the basis of studying the limestone properties. The optimum conditions for the preparation of high active lime are determined as follows: the calcination temperature is 1000 ℃, the particle size of limestone is from 1.6².0 mm and the calcination time is 60 min. It is found that calcination temperature, particle size of limestone and calcination time have great influence on the lime activity. Under the optimal experimental conditions, the lime activity obtained is about 368 m L, which meets the standard of high active lime.Secondly, single factor experimental conditions are used to study the influence of carbonation temperature, diameter of gas distributor, stirring speed, concentration of Ca（OH）₂ emulsion and the flow rate of CO₂ on the particle size, carbonation time, and the morphology of the product which is prepared though the carbonization process. Superfine precipitated CaCO3 with high purity, better whiteness and small particle size is obtained, and the optimum conditions are determined as follows: the carbonization temperature is 20 ℃, the diameter of gas distributor is 0.8 mm. The stirring speed is 1000 r/min, the concentration of Ca（OH）₂ emulsion is 5.6% and the flow rate of CO₂ is 200 m L/min. The product with the calcium oxide content of 56.8%, p H value of 9.0, the iron content of 0.06%, the density of 2.57 g/cm3, the whiteness of 95%, and the average particle size of 0.26 μm is obtained at the optimum conditions. The crystal structure, distribution of particle size, thermal stability and chemical structure are analyzed for the characterization of the products. It is found that the main mineral composition of superfine precipitated CaCO3 is calcite, which conforms to the industry standard indices. The whiteness, particle size and pH value are superior to similar products in market, the development of which has great potential.Finally, the modification of chemical additives to the products is studied, and the influence of the type of chemical additives, addition dosages and addition time on the morphology, particle size of the products and the carbonization time are researched, respectively. The results show that the type of chemical additives has great impacts on the morphology of the products. Chrysanthemum-shaped, flocculent, sphere-liked, rhombohedron with different crystal types and morphologies of superfine precipitated CaCO3 are obtained by adding the chemical additives, such as barium chloride, magnesium sulfate, cetyltrimethy lammonium bromide（CTAB） and sodium laurate. When sodium laurate is used as chemical additive, the addition dosages of sodium laurate and its addition time have great impacts on morphology and particle size of the products. When the addition dosages of sodium laurate is about 1.5 g/L, the obtained superfine precipitated calcium carbonate shows great superiority in particle size, particle size distribution, morphology neat degree and oil absorption value compared with no addition of chemical additives.