The method includes a step of introducing into the reservoir, via a well, a mixture comprising a scale inhibitor, a first scale precursor and a second scale precursor. The first and second scale precursors can react together to form scale. The first scale precursor may be an ammonium salt. The method can further comprise a step of stopping the introduction into the reservoir of the mixture and shutting in the well for 2-24 hours, and a step of introducing into the reservoir a further mixture comprising a scale inhibitor, a first and second scale precursor which can react together to form scale. The steps of stopping and resuming the introduction of mixtures may be repeated at least once. The components of the mixtures may be provided as concentrated solutions and diluted in a stream of water prior to being introduced into the reservoir. The method provides an effective way of generating a barrier to fluid flow in a reservoir. The method may be a method of abandoning an entire well in a reservoir.

Aspects of the invention include a method of producing a cement material comprising step of: first reacting a calcium-bearing starting material with a first acid to produce an aqueous first calcium salt; second reacting the aqueous first calcium salt with a second acid to produce a solid second calcium salt; wherein the second acid is different from the first acid and the second calcium salt is different from the first calcium salt; and thermally treating the second calcium salt to produce a first cement material. Preferably, but not necessarily, during the second reacting step, reaction between the first calcium salt and the second acid regenerates the first acid.

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.

The method includes a step of introducing into the reservoir, via a well, a mixture comprising a scale inhibitor, a first scale precursor and a second scale precursor. The first and second scale precursors can react together to form scale. The first scale precursor may be an ammonium salt. The method can further comprise a step of stopping the introduction into the reservoir of the mixture and shutting in the well for 2-24 hours, and a step of introducing into the reservoir a further mixture comprising a scale inhibitor, a first and second scale precursor which can react together to form scale. The steps of stopping and resuming the introduction of mixtures may be repeated at least once. The components of the mixtures may be provided as concentrated solutions and diluted in a stream of water prior to being introduced into the reservoir. The method provides an effective way of generating a barrier to fluid flow in a reservoir. The method may be a method of abandoning an entire well in a reservoir.

Composition for building materials comprises of fly ash from flue gas desulfurization. The fly ash ( CaSO.sub.4 anhydrite), obtained from circulating fluidized bed flue gas desulfurization, is mixed with binder reactants at a ratio of 9:1. It's mainly used for non-structural cement mortar, bricks for paving walkways, brick wall decors, fire-resistant walls for interior partitions, plasterboards and so on. The binder reactants compose of 70% CaSO.sub.4.H.sub.2O, 10% Na.sub.2SO.sub.4, 10% CaO, 5% NaOH, 05% cement and 05% starch. When the binder reactants are mixed with fly ash and water (30% to 40% of the above total weight), the hydration process of CaSO.sub.4 anhydrite is accelerated.

A method for producing a gypsum plasterboard comprising the steps of providing bundler dust obtained from gypsum plasterboard leftovers of a plasterboard trimming process by a trimming device, in particular by a bundler saw; and adding at least a part of the bundler dust to a gypsum slurry for producing the gypsum plasterboard.

A method of making a gypsum board including: preparing an aqueous slurry including a mixture of: calcium sulfate hemihydrate, water at a weight ratio of water to calcium sulfate hemihydrate of 0.2:1 to 1.2:1, and on a dry basis per 100 parts by weight (pbw) calcium sulfate hemihydrate: 0.2 to 2 pbw siloxane, 0.01 to 2 pbw siloxane polymerization catalyst including magnesium oxide and optionally fly ash, and 0.01 to 0.2 pbw triethanolamine (TEOA); allowing the siloxane to polymerize to polysiloxane; and depositing the slurry on a first cover sheet and covering the slurry with a second cover sheet to shape the slurry, and allowing the shaped slurry to set to form the gypsum board. Also, disclosed is the gypsum board resulting from the method.

The present application describes a process for the continuous production of alpha-calcium sulphate hemihydrate, the process comprising the steps of: providing particulate gypsum; providing water; mixing the particulate gypsum and the water to form a gypsum slurry; and maintaining said gypsum slurry under raised pressure and temperature to convert the particulate gypsum into alpha-calcium sulphate hemihydrate and provide an alpha-calcium sulphate hemihydrate slurry. Additionally, the particulate gypsum comprises a D10 value greater than or equal to 2 ?m, a D90 value smaller than or equal to 90 ?m and a D50 value smaller than or equal to 25 ?m. Particulate gypsum for use in the process is also provided.

The present application describes a process for the continuous production of alpha-calcium sulphate hemihydrate, the process comprising the steps of: providing particulate gypsum; providing water; mixing the particulate gypsum and the water to form a gypsum slurry; and maintaining said gypsum slurry under raised pressure and temperature to convert the particulate gypsum into alpha-calcium sulphate hemihydrate and provide an alpha-calcium sulphate hemihydrate slurry. Additionally, the particulate gypsum comprises a D10 value greater than or equal to 2 ?m, a D90 value smaller than or equal to 90 ?m and a D50 value smaller than or equal to 25 ?m. Particulate gypsum for use in the process is also provided.

A sizing composition including water, a polyvinylpyrrolidone film former, a silane coupling agent, a lubricant, and a surfactant is provided. The polyvinylpyrrolidone film former constitutes from 30 wt. % to 50 wt. % of the dry solids of the sizing composition. Wet use chopped strand glass fibers for use in reinforcing gypsum board are also provided. The wet use chopped strand glass fibers include chopped glass fibers having the sizing composition applied thereto. The sizing composition improves fiber bundle integrity, fiber flow rate, fiber flow rate consistency, and dispersibility of the wet use chopped strand glass fibers in a gypsum matrix or slurry.