Reaction schemes involving acids and bases; reactors comprising spatially varying chemical composition gradients (e.g., spatially varying pH gradients), and associated systems and methods, are generally described.

Reaction schemes involving acids and bases; reactors comprising spatially varying chemical composition gradients (e.g., spatially varying pH gradients), and associated systems and methods, are generally described.

Chemical reaction devices involving acid and/or base, and related systems and methods, are generally described.

Chemical reaction devices involving acid and/or base, and related systems and methods, are generally described.

Reaction schemes involving acids and bases; reactors comprising spatially varying chemical composition gradients (e.g., spatially varying pH gradients), and associated systems and methods, are generally described.

Reaction schemes involving acids and bases; reactors comprising spatially varying chemical composition gradients (e.g., spatially varying pH gradients), and associated systems and methods, are generally described.

Reaction schemes involving acids and bases; reactors comprising spatially varying chemical composition gradients (e.g., spatially varying pH gradients), and associated systems and methods, are generally described.

Reaction schemes involving acids and bases; reactors comprising spatially varying chemical composition gradients (e.g., spatially varying pH gradients), and associated systems and methods, are generally described.

Reaction schemes involving acids and bases; reactors comprising spatially varying chemical composition gradients (e.g., spatially varying pH gradients), and associated systems and methods, are generally described.

Methods and apparatuses for converting metal carbonate salts to metal hydroxides are disclosed. The methods involve electrochemical production of hydrogen ions (H.sup.+) for decarbonating the metal carbonate salt to generate metal ions in a chemical compartment of the electrochemical cell. The metal ions are transported to a cathode compartment where they combine with hydroxide (OH.sup.) to form metal hydroxides. The methods and apparatus may be applied to produce calcium hydroxide which may be used as a precursor for cement clinker. In some embodiments electrochemically produced hydrogen and oxygen are burned to produce heat for production of cement clinker.