A method of treating a sulphate-bearing stream which includes the steps of hydrolysing aluminium sulphate to produce a chemically-reactive aluminium trihydroxide and sulphuric acid, adding lime to immobilize the sulphuric acid as gypsum and using the aluminium trihydroxide to remove sulphate from the sulphate-bearing stream without interference of sulphate derived from the aluminium sulphate used as an aluminium source in the hydrolysis step.

The disclosure discloses a production method for producing cement and co-producing sulfuric acid from phosphogypsum. The method includes: pretreating and purifying the phosphogypsum to reduce insoluble phosphorus, water-soluble phosphorus impurities, and most free water in the phosphogypsum, directly feeding the materials kneaded and granulated with a reducing agent into a reduction and decomposition integrated rotary kiln with a fluidized preheating function, and controlling to carry out step-by-step heating, drying, dehydration, reduction and decomposition in a gas phase atmosphere under pulverized coal combustion; using sulfur dioxide gas generated after reduction and decomposition to produce the sulfuric acid after dust removal and purification; making the materials after reduction and decomposition enter an oxidation calcining kiln for sintering a cement clinker, and controlling to heat, mineralize and sinter the cement clinker in the gas phase atmosphere under the pulverized coal combustion.

A carbonized brick of recycled concrete powders and a preparation method thereof are provided, belonging to the field of concrete materials. The preparation method includes: adding composition A to a liquid storage tank; introducing composition B into the liquid storage tank to react with a solid waste solution to generate calcium bicarbonate solution; filling recycled powders into a molding die, decomposing the calcium bicarbonate solution by heat, reacting generated carbon dioxide with calcium ions leached from a C—S—H gel in the recycled powders to produce calcium carbonate, and precipitating, crystallizing and cementing in the molding die together with calcium carbonate produced by decomposing calcium bicarbonate solution, and resulting in strength of the recycled powders.

Gypsum derived from waste gypsum boards is calcined and converted into gypsum granules including hemihydrate and/or anhydrous type III gypsum. The calcined gypsum granules are dropped into water to prepare a gypsum slurry. Then, dihydrate gypsum particles are crystalized in the slurry. The temperature of the gypsum granules just before being dropped into the water is 90 C. or higher.

A method of processing plasterboards or plasterboard for recover a calcium sulphate source for producing a hydraulic binder, includes comminuting plasterboards or a gypsum fraction thereof so as to obtain plasterboard particles and, thereafter, subjecting the plasterboard particles to a heat treatment at an elevated temperature so as to volatilize and/or decompose organic components present in the plasterboard particles.

Gypsum derived from waste gypsum boards is calcined and converted into gypsum granules including hemihydrate and/or anhydrous type III gypsum. The calcined gypsum granules are dropped into water to prepare a gypsum slurry. Then, dihydrate gypsum particles are crystalized in the slurry. The temperature of the gypsum granules just before being dropped into the water is 90 C. or higher.

A low-cost four-element system cementitious material, a preparation method and an application thereof are provided by the present disclosure, and the cementitious material is used in the fields of mine cementing filling and building materials. The four-element system cementitious material includes the following raw materials in percentage by mass: 20-60% of water-quenched blast furnace slag, 10-40% of waste incineration bottom ash, 20% of pretreated waste incineration fly ash and the balance of desulfurization gypsum. The low-cost four-element system cementitious material is used to replace cement to prepare mine cementing filling materials, and is also used to prepare concrete materials for construction industry.

Wasted gypsum boards are crushed and calcined to gypsum granular solid, and the gypsum granular solid is mixed with water to form gypsum slurry. Gypsum particles are deposited from the gypsum slurry in a crystallization tank. Heated steam is blown into the gypsum slurry at a height from surface of the gypsum slurry and down to upper ? of the gypsum slurry to heat the gypsum slurry and to eliminate foam on the gypsum slurry.

In general, the present invention is directed to a method of making a gypsum board. The method comprises: applying a phosphorus containing compound to a first gypsum composition to provide a phosphorus modified gypsum composition; calcining the phosphorus modified gypsum composition to provide a calcined gypsum composition; preparing a gypsum slurry by combining water and the calcined gypsum composition; depositing the gypsum slurry on a first facing material; providing a second facing material on the gypsum slurry; and allowing the calcined gypsum to convert to calcium sulfate dihydrate.

A drying-type joint compound and related methods, the drying-type joint compound having a lowered friction coefficient and formulated with chloride-containing flue-gas-desulfurization (FGD) gypsum powder having the median particle size (D50) of at least about 20 m, preferably the chloride-containing FGD gypsum powder having a D10 greater than 5 m, wherein the drying-type joint compound further comprises a binder; one or more clays; a cellulosic thickener; and an additive.