The present invention refers to a process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate and its uses.

In a preferred embodiment, the invention relates to a process of sequestering carbon dioxide. The process comprises the steps of: (a) reacting a metal silicate with a caustic alkali-metal hydroxide to produce a hydroxide of the metal formerly contained in the silicate; (b) reacting carbon dioxide with at least one of a caustic alkali-metal hydroxide and an alkali-metal silicate to produce at least one of an alkali-metal carbonate and an alkali-metal bicarbonate; and (c) reacting the metal hydroxide product of step (a) with at least one of the alkali-metal carbonate and the alkali-metal bicarbonate produced in step (b) to produce a carbonate of the metal formerly contained in the metal silicate of step (a).

In this disclosure, a process of recycling acid, base and the salt reagents required in the Li recovery process is introduced. A membrane electrolysis cell which incorporates an oxygen depolarized cathode is implemented to generate the required chemicals onsite. The system can utilize a portion of the salar brine or other lithium-containing brine or solid waste to generate hydrochloric or sulfuric acid, sodium hydroxide and carbonate salts. Simultaneous generation of acid and base allows for taking advantage of both chemicals during the conventional Li recovery from brines and mineral rocks. The desalinated water can also be used for the washing steps on the recovery process or returned into the evaporation ponds. The method also can be used for the direct conversion of lithium salts to the high value LiOH product. The method does not produce any solid effluent which makes it easy-to-adopt for use in existing industrial Li recovery plants.

A method for preparing lithium concentrate from natural lithium-bearing brines was developed. The brine is first subjected to purification from the suspended solids, then filtered through a static layer of a granulated sorbent based on LiCl.2Al(OH).sub.3.mH.sub.2O, where m=3-5, to obtain a primary lithium concentrate. The process is carried out in sorption-desorption units consisting of 4 columns, two of which are in the process of sorption of lithium chloride from the brine, one column is in the process of washing the sorbent saturated with lithium chloride from the brine, and one column is in the process of lithium chloride desorption. The primary lithium concentrate is converted to a secondary lithium concentrate by concentration in evaporative pools or reverse osmotic concentration-desalination. The secondary lithium concentrate is used for further production of lithium chloride or lithium carbonate.

A process for recovering alkali from power boiler ash is provided. The power boiler ash is first contacted with Na.sub.2CO.sub.3 to produce a mixture containing settling and non-settling solid particles. A fraction of the settling particles is then separated from the mixture to produce a first clarified alkaline solution. The first clarified alkaline solution contains species such as NaOH and KOH depending upon the power boiler ash characteristics. The non-settling solid particles may optionally be further separated from the first clarified alkaline solution to obtain a second clarified alkaline solution. This process is also applicable for the extraction of alkali from other oxide/hydroxide containing materials.

The present invention provides a method for manufacturing a composite carbonate in a semi-dry manner by using combustion ash and, more specifically, provides a method for manufacturing a composite carbonate in a semi-dry manner by using combustion ash, the method comprising a step of adding a small amount of water to combustion ash containing calcium ions in an atmosphere of carbon dioxide. According to the present invention, carbon mineralization is carried out in a semi-dry manner by the manufacturing method, so that the composite carbonate can be efficiently produced. In addition, the composite carbonate can be utilized as a component for a concrete composition.

The present invention discloses the systems of producing calcium and magnesium carbonate from the Ca/Mg containing solution leached by a CO.sub.2-based hydrometallurgical process which includes: a precipitation reactor that the Ca/Mg containing leached solution is continuously added and fully mixed with the alkaline reagent at specific mole ratio into the precipitation reactor and the reactor also comprises a CO.sub.2 bubbling module where CO.sub.2 is captured and recirculated from the thermal decomposition process as needed; a solid-liquid separation unit that the treated slurry is treated by the solid-liquid separation unit to produce precipitated calcium and magnesium carbonate products where the recirculating water is recycled back into the precipitation reactor; a thermal decomposition unit that the calcium and magnesium carbonate products is calcined by the thermal decomposition unit to produce an alkaline reagent and the alkaline reagent is recycled back into the precipitation reactor for the next batch of reaction.

Provided are a method for producing calcium carbonate having a controlled size and a method for growing crystals in order to produce calcium carbonate having a controlled size. A method for producing a calcium carbonate comprises the steps of reducing the pH of an aqueous calcium carbonate dispersion to 9.0 or less and then increasing the pH of the aqueous calcium carbonate dispersion to grow calcium carbonate particles.

A method for ship ballasting includes receiving, at a carbon negative energy storage system, input comprising calcium oxide and water and reacting, within a reaction chamber of the carbon negative energy storage system, the calcium oxide and water to release energy and generate calcium hydroxide. The method includes directing, by the carbon negative energy storage system, the released energy to a requesting end user and providing, by the carbon negative energy storage system, the calcium hydroxide to a marine vessel ballasting system. The method includes releasing a mixture of the calcium hydroxide and ballast water from the marine vessel ballasting system into the ocean to sequester atmospheric CO.sub.2.

To produce a calcium carbonate in a controlled form while carbon dioxide gas is efficiently used. A method for producing a calcium carbonate comprises a carbon dioxide gas absorption step of allowing an aqueous sodium hydroxide solution at a concentration of 5 to 21% to absorb carbon dioxide gas to give an aqueous sodium carbonate solution at a concentration of 4 to 24%; a hydration step of reacting calcium oxide with an aqueous sodium hydroxide solution at a concentration of 0 to less than 6% to give a lime milk that is a suspension of calcium hydroxide having a BET specific surface area of 5 to 40 m.sup.2/g; and a carbonation step of adding the aqueous sodium carbonate solution to the lime milk and performing reaction.