The invention pertains to a method for providing a succinic acid solution, comprising the steps of providing a first magnesium succinate containing medium with a magnesium succinate concentration of 18-23 wt. % to a first acidification reactor where it is contacted with hydrogen chloride to form a solution of succinic acid, magnesium chloride and hydrogen chloride, providing a second magnesium succinate containing medium with a magnesium succinate concentration of 25-50 wt. %, and contacting it in a second acidification reactor with the solution of succinic acid, magnesium chloride and hydrogen chloride withdrawn from the first acidification reactor, to form an aqueous mixture comprising magnesium chloride and succinic acid with a succinic acid concentration of at least 18 wt. %. The method according to the invention makes it possible to obtain a solution comprising succinic acid and magnesium 20 chloride with an increased succinic acid concentration.

The invention is a method for coproducing Hydrogen and certain metals by reducing a metal oxide(s) with MgH.sub.2 or with metal and water, wherein the non-water oxides used in the method include SiO.sub.2, Cr.sub.2O.sub.3, TiO.sub.2, SnO.sub.2, ZrO.sub.2, CuO, ZnO, WO.sub.3, Ta.sub.2O.sub.5, Cs.sub.2Cr.sub.2O.sub.7 or CsOH. The method reacts the MgH.sub.2 with a metal oxide or directly uses metal and water instead of a hydride, and initiates a reaction with the metal oxide. The reaction releases Hydrogen and reduces the subject oxide to metal.

The invention is a method for coproducing Hydrogen and certain metals by reducing a metal oxide(s) with MgH.sub.2 or with metal and water, wherein the non-water oxides used in the method include SiO.sub.2, Cr.sub.2O.sub.3, TiO.sub.2, SnO.sub.2, ZrO.sub.2, CuO, ZnO, WO.sub.3, Ta.sub.2O.sub.5, Cs.sub.2Cr.sub.2O.sub.7 or CsOH. The method reacts the MgH.sub.2 with a metal oxide or directly uses metal and water instead of a hydride, and initiates a reaction with the metal oxide. The reaction releases Hydrogen and reduces the subject oxide to metal.

The present application pertains to methods for making metal oxides and/or citric acid. In one embodiment, the application pertains to a process for producing calcium oxide, magnesium oxide, or both from a material comprising calcium and magnesium. The process may include reacting a material comprising calcium carbonate and magnesium carbonate. Separating, concentrating, and calcining may lead to the production of oxides such as calcium oxide or magnesium oxide. In other embodiments the application pertains to methods for producing an alkaline-earth oxide and a carboxylic acid from an alkaline earth cation-carboxylic acid anion salt. Such processes may include, for example, reacting an alkaline-earth cation-carboxylic acid anion salt with aqueous sulfur dioxide to produce aqueous alkaline-earth-bisulfite and aqueous carboxylic acid solution. Other useful steps may include desorbing, separating, and/or calcining.

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.

Embodiments relate to systems and methods directed towards arrangements of a preheater, a heat exchanger, a plasma recovery system, and at least one processing stage configured to use steam output of a calciner for heating incoming wastewater that is being processed.

Embodiments relate to systems and methods directed towards arrangements of a preheater, a heat exchanger, a plasma recovery system, and at least one processing stage configured to use steam output of a calciner for heating incoming wastewater that is being processed.

A process for producing magnesia can include contacting CO2-containing emissions with a magnesium-containing material to produce magnesium carbonate; subjecting the magnesium carbonate to calcination to produce a CO2 by-product and magnesia; and recycling at least a portion of the CO.sub.2 by-product for contacting the magnesium-containing material to produce the magnesium carbonate. The magnesium-containing material can include mining residues, such as phyllosilicate or chrysotile mining residue, and the magnesium carbonate produced can include precipitated nesquehonite that is subjected to calcination to produce the magnesia.

A process for producing magnesia can include contacting CO2-containing emissions with a magnesium-containing material to produce magnesium carbonate; subjecting the magnesium carbonate to calcination to produce a CO2 by-product and magnesia; and recycling at least a portion of the CO.sub.2 by-product for contacting the magnesium-containing material to produce the magnesium carbonate. The magnesium-containing material can include mining residues, such as phyllosilicate or chrysotile mining residue, and the magnesium carbonate produced can include precipitated nesquehonite that is subjected to calcination to produce the magnesia.

The present invention provides a process for producing high purity hydromagnesite from a source of magnesium chloride. The process involves preparation of a magnesium chloride brine of a specific concentration and reacting with sodium carbonate, while maintaining the reaction at a specific temperature range to form a hydromagnesite precipitate. The product can be calcined to generate high purity magnesium oxide compounds.