The present invention provides a method and apparatus (2a) for producing at least one of
calcium oxide,
magnesium oxide and an
iron oxide from an ore comprising a
carbonate mineral of at least one of
calcium,
magnesium and iron, such as limestone and
siderite ores. The method comprises producing liquid
sodium and
chlorine gas by
electrolysis. The liquid
sodium is oxidised to
sodium oxide and the
chlorine is used to make
hydrochloric acid. The
sodium oxide may be produced in a
redox reaction with an oxide of another
metal to produce the other
metal in elemental form as well. The ore is added to the
hydrochloric acid to dissolve the
carbonate mineral therein, which produces gaseous
carbon dioxide and an
aqueous solution respectively comprising at least one of
calcium chloride,
magnesium chloride and
ferrous chloride. The
carbonate mineral is dissolved in the
hydrochloric acid closed off from their surrounding environment and the
carbon dioxide is captured. The
aqueous solution is reacted with at least some of the
sodium oxide, or
sodium hydroxide derived therefrom, to produce an
aqueous solution of sodium chloride and a precipitate respectively comprising at least one of
calcium hydroxide, magnesium
hydroxide and
ferrous hydroxide. The precipitate is then phase separated from the aqueous solution of sodium chloride and the
hydroxide(s) in the separated precipitate are thermally decomposed to produce water vapour and a
solid end-product comprising the desired oxide(s). Sufficient heat for this
thermal decomposition is transferred to the separated precipitate from at least one of the
electrolysis products, the exothermic processes by which the precipitate is produced, their respective products and the products of the
thermal decomposition itself. Thus the invention consumes no carbonaceous fuel, including any
fossil fuel, and has
electricity as its only
energy requirement. If the
electricity is produced from a source of
renewable energy, it produces no
greenhouse gas emissions. The apparatus (2a) comprises an electrolytic subassembly (10), a
sodium oxide or hydroxide-producing subassembly (13), a hydrochloric acid-producing subassembly (12), a reaction subassembly (14), a
solid-aqueous phase separator (16), a
kiln (20), and a
heat transfer pathway (23) for transferring enough heat to the precipitate in the
kiln (20) to cause the
thermal decomposition from at least one of: a product of the electrolytic subassembly (10), the other subassemblies (12, 13, 14) and their respective products, and a product of the thermal
decomposition. The invention is intended to replace the traditional
calcination process, including for the production of
cement clinker, and can also be used to convert
siderite ores into one or more iron oxides suitable for ironmaking. The captured
carbon dioxide may be reacted with a second portion of the sodium oxide, or with
sodium hydroxide derived therefrom, to produce
sodium carbonate, thereby also providing a replacement for the
Solvay process. In some embodiments, the method can even have a negative
carbon footprint overall.