A grout composition includes a grout binder comprising calcium sulfate, the grout binder constituting from about 25.0 weight percent to about 99.0 weight percent of the grout composition, and at least one thermal conductivity additive comprising graphite. A grout formed from the grout composition has a thermal conductivity greater than about 1.0 W/m.Math.K. Related grout slurries formed from the grout composition, grouts, and methods of grouting a wellbore are also disclosed.

Wasted gypsum boards are crushed and heated to convert semi-hydrated gypsum and/or anhydrous type III gypsum, and the obtained semi-hydrated gypsum and/or anhydrous type III gypsum is mixed with gypsum slurry. The gypsum slurry is solid/liquid separated by a filtration device into gypsum particles and filtrate which has passed through the filter cloth of the filtration device. The filtrate is returned into the gypsum slurry. The solid/liquid separation is performed such that the concentration of the suspended solid in the filtrate that has passed through the filter cloth and consists of gypsum granules and inorganic impurities derived from wasted gypsum boards is made 1000 to 8000 mass ppm. The clogging of the filter cloth is reduced.

Wasted gypsum boards are crushed and heated to convert semi-hydrated gypsum and/or anhydrous type III gypsum, and the obtained semi-hydrated gypsum and/or anhydrous type III gypsum is mixed with gypsum slurry. The gypsum slurry is solid/liquid separated by a filtration device into gypsum particles and filtrate which has passed through the filter cloth of the filtration device. The filtrate is returned into the gypsum slurry. The solid/liquid separation is performed such that the concentration of the suspended solid in the filtrate that has passed through the filter cloth and consists of gypsum granules and inorganic impurities derived from wasted gypsum boards is made 1000 to 8000 mass ppm. The clogging of the filter cloth is reduced.

According to the present invention. there is provided a method of manufacturing a plasterboard, the method comprising combining at least one recycled calcium sulphate material and at least one non-recycled calcium sulphate material to form a mixture of particles, combining at least the mixture of particles and water to form a settable slurry, and drying the settable slurry to form a plasterboard, wherein the ratio of the recycled calcium sulphate material to the non-recycled calcium sulphate material in the mixture of particles is at least 1:1, wherein the method further comprises calcining the mixture of particles before the mixture of particles is combined with water to form a settable slurry. A plasterboard is also provided.

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.

A process for the calcination of raw gypsum in a heatable extruder, wherein the raw gypsum is feed into the extruder and heated to a temperature of from 150 C. to 350 C. to thereby convert the raw gypsum to calcined gypsum with a content of calcium hemihydrate of at least 50 wt.-%. By using a heatable extruder for the calcination, calcined gypsum with a high content of calcium sulphate hemihydrate and low residual amounts of the respective dihydrate and anhydrite can be obtained. The present invention further concerns a system, which is adapted to such preparation of calcined gypsum and includes an appropriate heatable extruder and the use of a heatable extruder for the calcination of raw gypsum.

A process for the calcination of raw gypsum in a heatable extruder, wherein the raw gypsum is feed into the extruder and heated to a temperature of from 150 C. to 350 C. to thereby convert the raw gypsum to calcined gypsum with a content of calcium hemihydrate of at least 50 wt.-%. By using a heatable extruder for the calcination, calcined gypsum with a high content of calcium sulphate hemihydrate and low residual amounts of the respective dihydrate and anhydrite can be obtained. The present invention further concerns a system, which is adapted to such preparation of calcined gypsum and includes an appropriate heatable extruder and the use of a heatable extruder for the calcination of raw gypsum.

An extruder, preferably for calcining and extruding raw gypsum, including a calcination zone and a mixing zone, wherein the extruder is optionally configured to capture and/or retain water liberated in the calcination zone, apparatuses and processes employing such extruders and respective uses.

An extruder, preferably for calcining and extruding raw gypsum, including a calcination zone and a mixing zone, wherein the extruder is optionally configured to capture and/or retain water liberated in the calcination zone, apparatuses and processes employing such extruders and respective uses.

The present disclosure belongs to the technical field of harmless treatment of phosphogypsum and building materials, and particularly provides a phosphogypsum-based building material, and preparation and use thereof. The method includes: adding a pretreated phosphogypsum premix having a temperature above 60 C., a free water content 10% and an organic matter content of 5-20 wt % into a ceramsite at a temperature above 800 C., continuing mixed calcination after combustion by using residual heat of the ceramsite, separating out ceramsite coarse aggregate to obtain a residual material, and performing post-treatment on the residual material to obtain the phosphogypsum-based building material. The method of the present disclosure not only fully utilizes phosphogypsum solid waste, but also simultaneously achieves harmless treatment of phosphogypsum. More importantly, the method achieves a synergistic enhancement between the ceramsite and phosphogypsum, resulting in the prepared phosphogypsum-based building material with higher strength, a more uniform structure and a wider application range.