The present relates to a method for producing calcium sulfate solid crystals and hydrochloric acid (HCl) from a calcium chloride solution comprising the steps of feeding a continuous stirred-tank reactor with a calcium chloride solution, sulfuric acid and water; mixing the calcium chloride solution, sulfuric acid and water in the reactor; and maintaining the reactor a temperature of less than about 70° C., converting the calcium chloride solution, sulfuric acid and water into HCl and calcium sulfate solid crystals. The method described herein can be incorporated as a means for regenerating HCl from CaCl.sub.2 solutions which are generated in the metallurgical industry when processing calcium-bearing ores for recovering metals like rare earth elements.

Hydrometallurgical systems, methods, and compositions are described in which amine-based lixiviants are utilized in substoichiometric amounts to recover alkaline earths from raw or waste materials. The lixiviant can be regenerated and recycled for use in subsequent iterations of the process or returned to a reactor in a continuous process. Extraction of the alkaline earth from the raw material and precipitation of the extracted alkaline earth is performed in the same reactor and essentially simultaneously.

Hydrometallurgical systems, methods, and compositions are described in which amine-based lixiviants are utilized in substoichiometric amounts to recover alkaline earths from raw or waste materials. The lixiviant can be regenerated and recycled for use in subsequent iterations of the process or returned to a reactor in a continuous process. Extraction of the alkaline earth from the raw material and precipitation of the extracted alkaline earth is performed in the same reactor and essentially simultaneously.

The present invention is a CO.sub.2 based hydrometallurgical multistage reaction and separation system comprising: a pre-washing device configured to fully mix the feedstock, such as industrial solid waste, mineral and mine tailings with auxiliary reagents and water at specific ratio, a reactor configured to treat the washed slurry with CO.sub.2 bubbling and discharge the treated slurry to the next stage, multistage separators configured to separate solid particles from treated slurry and recycle the unreacted solids back into the pre-washing device, a by-product preparation device configured to generate calcium and magnesium based products from filtrate containing target elements, a water recirculating device configured to recycle the remaining liquor back to the system. The present invention ensures the whole system is able to continuously and consistently react at maximum capacity through continuous slurry feeding and CO.sub.2 bubbling into the reactors which also enables multistage circulating reaction.

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.

The invention relates to processes for the extraction of products from titanium-bearing materials or a composition produced in a process for the production of titanium dioxide, and more particularly, although not exclusively, extracting titanium dioxide and/or one or more other products from iron making slag.

The present invention concerns a process for producing calcium carbonate from a calcium-containing alkaline slag material, the process containing the steps of extracting the alkaline slag material in a series of extraction steps, including at least 2 extraction steps, using extraction solvent(s) containing salt in an aqueous solution, whereby a calcium-containing filtrate and a residual slag is formed in each extraction step, separating the residual slag from the filtrate after each extraction step, carrying each residual slag to the following extraction in the series of extractions, to be used as raw material in said following extraction, and discarding the residual slag separated from the last extraction, carrying each filtrate to the previous extraction in the series of extractions, to be used as extraction solvent in said previous extraction, and carrying the first filtrate, separated from the first extraction step, to a carbonating step, carbonating calcium as calcium carbonate from the first filtrate, the first filtrate also used as the carbonation solvent, and using a carbonation gas, whereby calcium carbonate precipitates, separating and recovering the calcium carbonate from the remaining carbonation solvent, and recycling the remaining carbonation solvent to the last extraction step in the series of extraction steps, to be used as extraction solvent.

The present invention concerns a process for producing calcium carbonate from a calcium-containing alkaline slag material, the process containing the steps of extracting the alkaline slag material in a series of extraction steps, including at least 2 extraction steps, using extraction solvent(s) containing salt in an aqueous solution, whereby a calcium-containing filtrate and a residual slag is formed in each extraction step, separating the residual slag from the filtrate after each extraction step, carrying each residual slag to the following extraction in the series of extractions, to be used as raw material in said following extraction, and discarding the residual slag separated from the last extraction, carrying each filtrate to the previous extraction in the series of extractions, to be used as extraction solvent in said previous extraction, and carrying the first filtrate, separated from the first extraction step, to a carbonating step, carbonating calcium as calcium carbonate from the first filtrate, the first filtrate also used as the carbonation solvent, and using a carbonation gas, whereby calcium carbonate precipitates, separating and recovering the calcium carbonate from the remaining carbonation solvent, and recycling the remaining carbonation solvent to the last extraction step in the series of extraction steps, to be used as extraction solvent.

Weak acid lixiviants are used to selectively extract calcium from various sources (e.g., steel slag, impure lime, dolomite). Preferably, non-amine weak acids (e.g., weak acids that do not include an amine) as lixiviants are used. Such lixiviants can be used in stoichiometric quantities relative to calcium content of the calcium source material.

Weak acid lixiviants are used to selectively extract calcium from various sources (e.g., steel slag, impure lime, dolomite). Preferably, non-amine weak acids (e.g., weak acids that do not include an amine) as lixiviants are used. Such lixiviants can be used in stoichiometric quantities relative to calcium content of the calcium source material.