The present invention provides a process for preparing a precipitated calcium carbonate product comprising the steps of: (a) preparing an aqueous suspension of precipitated calcium carbonate seeds by carbonating a suspension of Ca(OH).sub.2 in the presence of 0.005 to 0.030 moles of Sr, in the form of Sr(OH).sub.2, per mole of Ca(OH).sub.2, (b) dewatering and dispersing the precipitated calcium carbonate seeds prepared in step (a) to obtain an aqueous suspension of precipitated calcium carbonate seeds having a d.sub.50 of less than or equal to 0.1 to 0.3 m and a BET specific surface area of 10 to 30 m.sup.2/g, and (c) forming an aqueous suspension of a precipitated calcium carbonate product by carbonating a slurry of Ca(OH).sub.2 in the presence of 0.5 to 5% by dry weight of the precipitated calcium carbonate seeds obtained in step (b), wherein the precipitated calcium carbonate seeds have a d.sub.50 that is less than the d.sub.50 of the precipitated calcium carbonate product and the precipitated calcium carbonate seeds have an aragonitic polymorph content greater than or equal to the precipitated calcium carbonate product obtained in step (c) characterized in that the dewatering of step (b) is carried out by the use of a tube press.

The present invention relates to a method and a process of preparing precipitated calcium carbonate of high purity by extracting calcium ion contained in an alkali ion-containing inorganic material such as mineral, steelmaking slag and waste concrete with the use of an acidic aqueous solution, separating other metal ions from the extracted solution, preparing an alkaline earth metal hydroxide using an alkaline aqueous solution and then contacting the same with carbon dioxide.

Compositions comprising highly reflective microcrystalline/amorphous materials are provided. In some instances, the highly reflective materials are microcrystalline or amorphous carbonate materials, which may include calcium and/or magnesium carbonate. In some instances, the materials are CO.sub.2 sequestering materials. Also provided are methods of making and using the compositions, e.g., to increase the albedo of a surface, to mitigate urban heat island effects, etc.

A method for promoting the rapid precipitation of travertine crystals by algae is disclosed. Microalgae is added to a body of water having a calcium ion concentration of 100-500 mg/L and stirred. The amount of microalgae is 0.1-8?10.sup.8 cells/L. The invention adopts a method for promoting the rapid precipitation of travertine crystals by algae, which significantly improves the sedimentation rate of travertine crystals. At the same time, there are pseudomonas in the calcified water body of algae, which can be used for algae-lysing bacteria isolation and purification.

A dual-pathway system for CO.sub.2 capture in both acidified and basified streams is provided. The system may be embodied in an off-shore stand-alone facility to allow for the operation of oceanic CO.sub.2 capture to be more efficient and cost effective. Systems maintain high environmental standards by containing all intermediate acidic and alkaline solutions in a closed system so that the effluent discharged back into the ocean is at the similar pH and salinity as the feed oceanwater, with only CO.sub.2 removed. Acid and base produced by an electrodialyzer unit is used to achieve oceanwater decarbonization via gaseous CO.sub.2 removal and solid CaCO.sub.3 precipitates removal. The system is configured to require the processing of a very small fraction of the total oceanwater intake for the acid-base generation process.

Provided is a calcium carbonate that comprises crystals having a particular shape and structure and has a nano-order average particle size. Provided are a method for producing a calcium carbonate that comprises crystals having a particular shape and structure and has an average particle size in a particular range and a crystal growth method. The calcium carbonate has the calcite structure, has a BET specific surface area of 2 to 50 m.sup.2/g, has a number-based average particle size of 30 nm to 1.0 ?m as determined by electron microscopy, and partially comprises substantially ring-like particles.

The present invention relates to a process for preparing amorphous calcium carbonate, the amorphous calcium carbonate obtainable by the process, its use as well as a product comprising the amorphous calcium carbonate and the use of a spray dryer for the preparation of amorphous calcium carbonate.

A method of coating a calcium carbonate film. In one aspect, the method includes preparing a calcium aqueous solution by adding a calcium-containing material to distilled water; forming a calcium carbonate film on a surface of the calcium aqueous solution by leaving the calcium aqueous solution; placing the calcium carbonate film on a substrate; and forming a calcium carbonate coating film by leaving the calcium carbonate film on the substrate.

A pigment particle composition which comprises calcium carbonate particles and pigment particles, its method of manufacture and its use. According to the present invention, the calcium carbonate particles are carbonated so that they bind to each other, in which case calcium carbonate structures are generated, which comprise pigment particles and which form essentially opaque and stable pigment-calcium carbonate aggregates. It is possible to manufacture the composition by atomizing calcium hydroxide-bearing pigment slurry into a carbon dioxide-bearing gas, in which case the calcium hydroxide is carbonated in order to precipitate the calcium hydroxide particles to be attached to each other and the carbonation is continued until essentially all of the calcium hydroxide has been converted into calcium carbonate. The composition is suitable for use, among others, in paints, coating materials, fillers, polymers and printing inks.

Disclosed is a carbonation device including: a storage tank storing a carbonation subject solution; a droplet spray unit spraying the carbonation subject solution from the storage tank as droplets; a carbonation reaction tank disposed with the droplet spray unit and filled with a carbonation gas under a predetermined pressure to provide a slurry by a carbonation reaction of the droplet-sprayed carbonation subject solution with the filled carbonation gas; a carbonation gas supply unit supplying the carbonation gas into the carbonation reaction tank to maintain the carbonation gas in the carbonation reaction tank under the predetermined pressure; and a slurry outlet unit ejecting the slurry from the carbonation reaction tank to maintain the slurry formed in the carbonation reaction tank within a predetermined level, and a method of carbonation using the same.