A process for preparing dicalcium silicate includes providing a starting material comprising calcium carbonate (CaCO.sub.3) and silicon dioxide (SiO.sub.2), wherein a molar ratio of calcium:silicon (C:S) is from 1.5:1 to 2.5:1. At least one of an inorganic alkali metal salt and an alkaline earth metal salt is added as a mineralizing agent to the starting material in an amount of from 0.5 wt.-% to 20 wt.-%, based on a total weight of the starting material. The starting material is reacted with the mineralizing agent in a gas atmosphere having a CO.sub.2 partial pressure of from 0.05 MPa to 0.2 MPa at a temperature of from 900 C. to 1100 C. so as to obtain a dicalcium silicate product. The dicalcium silicate product comprises a content of an unreacted starting material of <5 wt.-% and a total carbon content of <1.5 wt.-%, each based on a weight of the dicalcium silicate product.

A process for preparing dicalcium silicate includes providing a starting material comprising calcium carbonate (CaCO.sub.3) and silicon dioxide (SiO.sub.2), wherein a molar ratio of calcium:silicon (C:S) is from 1.5:1 to 2.5:1. At least one of an inorganic alkali metal salt and an alkaline earth metal salt is added as a mineralizing agent to the starting material in an amount of from 0.5 wt.-% to 20 wt.-%, based on a total weight of the starting material. The starting material is reacted with the mineralizing agent in a gas atmosphere having a CO.sub.2 partial pressure of from 0.05 MPa to 0.2 MPa at a temperature of from 900 C. to 1100 C. so as to obtain a dicalcium silicate product. The dicalcium silicate product comprises a content of an unreacted starting material of <5 wt.-% and a total carbon content of <1.5 wt.-%, each based on a weight of the dicalcium silicate product.

A method for producing carbon negative supplementary cementitious materials utilizing a carbon mineralization-based direct air capture process. One version of the method comprises pre-treating a mineral feedstock with an alkaline solution, resulting in a pre-treated feedstock and an alkaline solution comprising dissolved alumina or silica. The pre-treated feedstock has enhanced carbonation reactivity in the subsequent carbon mineralization-based direct air capture process. Another version of the method comprises post-treating precipitates yielded from carbon mineralization-based direct air capture process of a mineral feedstock with an alkaline solution, resulting in a residue and an alkaline solution comprising dissolved alumina or silica. The alkaline solutions resulted from the pre- and post-treatments can be directly used as supplementary cementitious materials, or as a sorbent solution for carbon capture.

The invention comprises a method of making lime, dolomitic lime, hydraulic cement such as portland cement clinker and co-products such as pozzolan, acids, alumina, silica and the like while producing reduced amounts of carbon dioxide. The method comprises combining hyaloclastite with a first acid to form a first salt, combining the first salt with a second acid to form a second salt and heating the second salt to form an oxide.

A method for treating limestone comprising raw meal in a cement clinker plant can be improved by first reacting the raw meal with a carboxylic acid (ROOH), thereby producing at least Ca(RCOO).sub.2, wherein the symbol R represents an organic group and subsequently converting the such obtained Ca(ROO).sub.2 into calcined raw meal by thermally decomposing the produced Ca(RCOO).sub.2 and/or Ca(RSO2O).sub.2 to thereby obtain at least CaO, CO.sub.2 and RCOH and/or RCOR.

The invention comprises a method of making lime, dolomitic lime, hydraulic cement such as portland cement clinker and co-products such as pozzolan, acids, alumina, silica and the like while producing reduced amounts of carbon dioxide. The method comprises combining hyaloclastite with a first acid to form a first salt, combining the first salt with a second acid to form a second salt and heating the second salt to form an oxide.

A cement clinker composition incorporates calcium fluoride and iron oxide to reduce firing temperatures and increase strength. High fly ash, aluminum dross, aluminum scrap, high aluminum clays and combinations thereof may also be substituted for bauxite in the cement clinker composition.