A method of preparing alkali-activated cement by stepwise calcination with sodium chloride includes the following steps. (1) Sodium chloride, a silicate and a carbonate are mixed and finely ground to obtain a raw material powder. (2) The raw material powder is calcined sequentially at 850-1050? C. and 1240? C. or more, and cooled to obtain a clinker. (3) The clinker is mixed with at least one of sodium hydroxide and potassium hydroxide, and ground finely to produce a cement powder.

A method for preparing a general-purpose cement is provided. Raw materials containing all of SiO.sub.2, Al.sub.2O.sub.3, CaO, MgO and Na.sub.2O (or K.sub.2O) are mixed to obtain a raw meal, which is dried and ground into a raw meal powder. The raw meal powder is oxidatively calcined at no less than 1210 C. to reach a stable phase state, and rapidly cooled to obtain a clinker predominated by glass phase. The clinker is mixed with NaOH, KOH or a combination thereof and ground to obtain the general-purpose cement. Alternatively, the clinker is ground to obtain a clinker powder, which is mixed with an aqueous NaOH solution, an aqueous KOH solution or a combination thereof for use. The NaOH and/or KOH is/are added such that a weight ratio of NaOH+0.713KOH to the clinker powder is 0-0.03:1.

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

A method of making a composition of matter comprising calcium hydroxide. The method includes the steps of contacting a calcium-containing molecule with an aqueous solution of a water-soluble salt having ammonium cation and a counter-anion, under conditions effective to yield a compound containing calcium and the counter-anion; and reacting the compound comprising calcium and the counter-anion with ammonia and water under conditions to yield calcium hydroxide.

This invention discloses a rare earth energy-saving admixture and its preparation method for cement kilns, involving the field of energy saving and emission reduction technology for cement kilns. The invention, without changing or minimally changing existing hardware equipment, reduces the thermal consumption of the production system and sulfur-nitrogen and sulfur emissions by conducting a thermodynamic diagnosis and calculating the amount of rare earth energy-saving admixture to be added, thereby saving the cost of retrofitting large hardware equipment.

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.

Provided is a method for controlling a free lime content of a clinker by regulating the free lime content. Here the amount of sulfur trioxide resulting from fuel and the used amount of a fluorine-based mineralizer are regulated using the following Formulas (1) to (3), thereby controlling the free lime content (f.CaO) of the clinker.
f.CaO=0.29e.sup.(0.65A)(A=aSO.sub.3+b)(1)
a=0.0001F+9.2t0.18HM9.2(2)
b=0.0005F32.8t2.9HM+28.4(3) SO.sub.3 is an amount of sulfur trioxide in the clinker; a is a coefficient satisfying Formula (2); b is a coefficient satisfying Formula (3); F is an amount of fluorine in the clinker; when a burning temperature is X C., t=X/1450; and HM is a hydraulic modulus.

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.