Provided herein are zero carbon dioxide (CO.sub.2) emission processes and systems to carry out the processes, comprising a) calcining limestone in a cement plant in an electric kiln to form a mixture comprising calcium oxide and a first gaseous stream comprising clean carbon dioxide, wherein the clean carbon dioxide comprises no gaseous or non-gaseous components from combustion of fuel; b) treating the mixture comprising calcium oxide with a N-containing salt solution under one or more dissolution conditions to produce a first aqueous solution comprising calcium salt; and c) contacting the first aqueous solution with the first gaseous stream comprising clean carbon dioxide under one or more precipitation conditions to produce a precipitation material comprising vaterite, aragonite, calcite, or combinations thereof.

Provided herein are zero carbon dioxide (CO.sub.2) emission processes and systems to carry out the processes, comprising a) calcining limestone in a cement plant in an electric kiln to form a mixture comprising calcium oxide and a first gaseous stream comprising clean carbon dioxide, wherein the clean carbon dioxide comprises no gaseous or non-gaseous components from combustion of fuel; b) treating the mixture comprising calcium oxide with a N-containing salt solution under one or more dissolution conditions to produce a first aqueous solution comprising calcium salt; and c) contacting the first aqueous solution with the first gaseous stream comprising clean carbon dioxide under one or more precipitation conditions to produce a precipitation material comprising vaterite, aragonite, calcite, or combinations thereof.

Provided herein are zero carbon dioxide (CO.sub.2) emission processes and systems to carry out the processes, comprising a) calcining limestone in a cement plant in an electric kiln to form a mixture comprising calcium oxide and a first gaseous stream comprising clean carbon dioxide, wherein the clean carbon dioxide comprises no gaseous or non-gaseous components from combustion of fuel; b) treating the mixture comprising calcium oxide with a N-containing salt solution under one or more dissolution conditions to produce a first aqueous solution comprising calcium salt; and c) contacting the first aqueous solution with the first gaseous stream comprising clean carbon dioxide under one or more precipitation conditions to produce a precipitation material comprising vaterite, aragonite, calcite, or combinations thereof.

According to one embodiment, a magnesium-recycling hydrogen generation system includes: a by-product acquisition unit that separates a by-product from a post-reaction solution, which is a solution after reacting with a hydrogen generation material containing a hydrogen-containing magnesium compound that generates hydrogen via a reaction with the solution, to acquire the by-product including more than one type of oxygen-containing magnesium compound that contains oxygen produced by the reaction, a raw material production unit that reacts the by-product with a halogen-containing substance containing halogen and other atoms than the halogen to produce a raw material containing magnesium halide, a hydrogen generation material production unit that reduces the raw material with plasma containing hydrogen to produce the hydrogen generation material, and a hydrogen generator that reacts the hydrogen generation material with the solution to generate hydrogen.

Provided herein are methods comprising a) calcining limestone in a cement plant to form carbon dioxide and calcium compound selected from calcium oxide, calcium hydroxide, or combination thereof; b) treating the calcium compound with N-containing salt in water to produce an aqueous solution comprising calcium salt and N-containing salt; and c) contacting the aqueous solution with the carbon dioxide under one or more precipitation conditions to produce a precipitation material comprising calcium carbonate and a supernatant aqueous solution wherein the calcium carbonate comprises vaterite.

The present invention relates to processes employing water produced from wells that, after suitable purification steps, is processed to recover resources that can be used to treat other waste streams, such as flue gases and ashes from combustion of fossil fuels.

Provided herein is a process for producing one or more products from a lignocellulosic feedstock. The process comprises treating the lignocellulosic feedstock by contacting the feedstock at least sulfur dioxide, sulfurous acid, or a combination thereof to produce a pretreated feedstock comprising one or more sulfonic acids. A process stream comprising one or more sulfonic acids is subsequently treated in a wet oxidation step to produce a stream comprising at least soluble oxidized phenolic compounds. The soluble oxidized phenolic compounds are then fed to an anaerobic digestion to produce methane. Optionally, hydrogen sulfide is produced during the anaerobic digestion. The hydrogen sulfide may then be converted to an acid selected from sulfur dioxide, sulfurous acid or a combination thereof in one or more steps. The acid may then be re-used in treatment as desired.

According to one embodiment, a magnesium-recycling hydrogen generation system includes: a by-product acquisition unit that separates a by-product from a post-reaction solution, which is a solution after reacting with a hydrogen generation material containing a hydrogen-containing magnesium compound that generates hydrogen via a reaction with the solution, to acquire the by-product including more than one type of oxygen-containing magnesium compound that contains oxygen produced by the reaction, a raw material production unit that reacts the by-product with a halogen-containing substance containing halogen and other atoms than the halogen to produce a raw material containing magnesium halide, a hydrogen generation material production unit that reduces the raw material with plasma containing hydrogen to produce the hydrogen generation material, and a hydrogen generator that reacts the hydrogen generation material with the solution to generate hydrogen.

Provided herein are methods comprising a) calcining limestone in a cement plant to form carbon dioxide and calcium compound selected from calcium oxide, calcium hydroxide, or combination thereof; b) treating the calcium compound with N-containing salt in water to produce an aqueous solution comprising calcium salt and N-containing salt; and c) contacting the aqueous solution with the carbon dioxide under one or more precipitation conditions to produce a precipitation material comprising calcium carbonate and a supernatant aqueous solution wherein the calcium carbonate comprises vaterite.

A process for producing one or more products from a lignocellulosic feedstock comprising treating the lignocellulosic feedstock to produce sugar in one or more stages comprising addition of acid, base or a combination thereof and introduction of heat. The addition of the acid, base, or a combination thereof produces a salt. The sugar is fermented to produce a fermentation product and the fermentation product is recovered. A stream comprising the salt is treated by wet oxidation with the introduction of heat. A stream comprising salt resulting from the wet oxidation is provided for use as a salt product or a process chemical for introduction within the process. Heat from the wet oxidation may be supplied to any stage of the process in which heat is introduced.