The present invention relates to processes employing water produced from wells that, after suitable purification steps, is processed to recover resources that can be used to treat other waste streams, such as flue gases and ashes from combustion of fossil fuels.

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.

A method for removing a target substance from a gas is provided. The method comprises providing a capture medium comprising an alkaline aqueous solution for dissolving the target substance comprised in the gas to form a target ion in the capture medium, contacting the target substance comprised in the gas with the capture medium to form a target ion in the capture medium, and transporting the target ion comprised in the capture medium to a process medium via an ion transport mechanism, wherein the process medium comprises an aqueous solution comprising an ion having an electric charge opposite to that of the target ion, and which interacts with the target ion to form a compound in the process medium, wherein the ion transport mechanism is adapted to allow a flow of ions between the capture medium and the process medium to maintain charge balance. An apparatus for removing a target substance from a gas, and use of the method and apparatus disclosed herein in treatment of industrial exhaust gas or air are also provided.

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 process to produce high purity strontium sulfate and strontium carbonate from subterranean brines. The present disclosure also relates to chemical precipitations of subterranean brines to isolate strontium from divalent cations, such as calcium and barium. Such precipitations include the use of sulfate and subsequent solids separations and washing of the precipitate. In a latter step in the strontium carbonate process, a metathesis reaction with a carbonate is performed upon the strontium sulfate to produce strontium carbonate while allowing optional recycling of the sulfate. An additional rinse with acid or water of the strontium sulfate may be performed prior to metathesis to increase the purity of the resulting strontium carbonate.