Spent Claus catalyst having a high alumina content is used as an ingredient in the manufacture of Portland cements in place of all or a portion of a conventional source of alumina. The spent Claus catalyst is preferably of a small particle size and can be ground to the desired fineness before mixing with the other ingredients that are heated in a conventional kiln to produce the cement composition. Finely ground spent Claus catalyst can also be used as an additive at levels of 0.1% to 2% by weight to increase the thickening time of shallow casing cement slurries.

A method for preparing low-background cement includes: uniformly mixing a seed crystal of cement, C.sub.4AF whiskers, and high-magnesium raw material to yield a first mixture, calcining the first mixture at 1400-1500? C., to yield a low-background clinker, the first mixture including 1.0-5.0 wt. % of the seed crystal of cement, 1.0-5.0 wt. % of the C.sub.4AF whiskers, and the balance is the high-magnesium raw material; and grinding a second mixture of the low-background clinker and gypsum, to yield low-background cement. The seed crystal of cement is a high-magnesium and low hydration heat clinker, has a specific activity of Ra-226 radioactive nuclides within 50 Bq/kg, and the MgO content of the clinker is between 4.0 wt. % and 5.0 wt. %, with 50 wt. %?C.sub.3S?55.0 wt. %; and the high-magnesium raw material has a MgO content between 2.5 wt. % and 3.0 wt. %.

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.

The invention comprises a method of making a hydraulic cement clinker. The method comprises delivering a natural calcium-iron-aluminosilicate mineral from one or more of hyaloclastite, lava, scoria, volcanic glass, volcanic ash, or any other mineral of a basaltic or intermediate basaltic chemical composition and blending it in ground form with limestone, calcium oxide or calcium hydroxide. The blended mixture is calcined in a portland cement clinker kiln at an elevated temperature and for a time sufficient to form a hydraulic cement clinker.

A method for industrial refining of coal ash created in power plants and carbonaceous ashes produced in other combustion processes by separating coal from said ashes and returning it to use and by recovering a substantially coal-free ash fraction obtained in the refining. In the method, coal ash and at least one ash fraction created by gasification technique in combustion plants are carefully proportioned in relation to one another and formed into a slurry mixture by means of an efficient dispersion technique, the slurry being then led to a flotation step, where a fraction rich in coal and a siliceous fraction poor in coal and a fraction dissolving in the process water are separated by flotation. The coal ash is arranged to have the highest proportion in the mixture to be taken to flotation, the ashes from combustion plants being dosed into said mixture in an amount that does not cause the maximum amounts of harmful substances to be exceeded in the qualities of the carbonaceous product and the silicate product poor in coal to be obtained.

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.

Methods and composition are provided for deriving cement and/or supplementary cementitious materials, such as pozzolans, from one or more non-limestone materials, such as one or more non-limestone rocks and/or minerals. The non-limestone materials, e.g., non-limestone rocks and/or minerals, are processed in a manner that a desired product, e.g., cement and/or supplementary cementitious material, is produced.

A method for producing a pozzolanic product by hydrothermal treatment of a feedstock including silicate, aluminate, and/or aluminosilicate materials, and a source of calcium ions, wherein the feedstock has a molar ratio of Ca:(Si+Al) from 0.4 to 1.2 and a maximum content of hydrated cement paste of 10 wt.-%, to provide a hydrate product, and subsequent carbonation of the hydrate product to provide a pozzolanic product including calcium carbonate and silica gel, alumina gel and/or silica-alumina gel. A pozzolanic product is obtainable by the method. The pozzolanic product is used as a supplementary cementitious material for manufacturing a composite cement including the pozzolanic product and a hydraulic cement.

A method of making building materials includes precipitating calcium salts from an aqueous solution by increasing a pH of the aqueous solution, and mixing the calcium salts with a first material including silicon to form a mixture. The mixture is then heated to form cement clinker.

A method for industrial refining of coal ash created in power plants and carbonaceous ashes produced in other combustion processes by separating coal from said ashes and returning it to use and by recovering a substantially coal-free ash fraction obtained in the refining. In the method, coal ash and at least one ash fraction created by gasification technique in combustion plants are carefully proportioned in relation to one another and formed into a slurry mixture by means of an efficient dispersion technique, the slurry being then led to a flotation step, where a fraction rich in coal and a siliceous fraction poor in coal and a fraction dissolving in the process water are separated by flotation. The coal ash is arranged to have the highest proportion in the mixture to be taken to flotation, the ashes from combustion plants being dosed into said mixture in an amount that does not cause the maximum amounts of harmful substances to be exceeded in the qualities of the carbonaceous product and the silicate product poor in coal to be obtained.