Gypsum calcination
Camarini et al. (2015) found that the energy consumption of GPW recycling was similar to natural gypsum calcination in diesel kilns. The energy consumption during calcination at 150 °C for 1 h was 447,120 kcal/t and in vertical Kettle was 439,450 kcal/t, which show the energy efficiency of the recycling process.
Gypsum, common sulfate mineral of great commercial importance, composed of hydrated calcium sulfate. It occurs in extensive beds associated with other …
Download scientific diagram | Comparison of model and experimental data from publication: Induced heat transfer from human skin: Its relationship to blood perfusion in the tissue | The present ...The calcination process of gypsum binder was carried out at four different temperatures ranging from 170 to 190 °C. The specimens for testing were prepared on the basis of the obtained raw...Shijin P K. Quantitative analysis of gypsum calcination caused by a fire is of great use in fire investigations. The rate and the depth of calcination through the gypsum board are dictated by the ...May 1, 2021 · The present study compares experimental results of gypsum calcination to the results predicted by a one-dimensional unsteady computational model. Controlled laboratory-scale experiments are ... Calcination is the process of heating a solid material in order to cause chemical separation of its components. The diversity of chemical separation lends calcination to accomplishing a range of objectives, from the removal of chemically bound (crystalline) water, to the volatilization of contaminants from a source material, thermal decomposition, and even …Gypsum is a non-metallic mineral, found in rock form. It is composed of 79.1% calcium sulphate and 20.9% water, by weight. Chemists call it Hydrous Calcium Sulphate, and as there is one molecule of calcium sulphate combined with two molecules of water. It has the chemical formula CaSO 4 2H 2 0. By volume this works out to nearly 50% water in ...
Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are formed and, for technical reasons, are mixed with water to form dihydrate again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated. This …The rate of production of gypsum plaster by a continuous calcination process, in which a mass of gypsum being calcined is maintained in a fluidized condition predominantly by the water vapour evolved during calcination, can be considerably increased and a plaster product of reduced water demand be obtained by introducing an aridizing agent such as calcium chloride along with the gypsum and ... The calcination processes could be divided in two main categories [4]: (i) direct heating processes in which gypsum is dehydrated on contact with flux gases; (ii) …FGD gypsum can also be used as a reducing agent to reduce chromium and vanadium, thereby removing them in the form of precipitation (Fang et al., 2018). The calcination of FGD gypsum is used as a phosphate adsorption material to treat phosphate wastewater. Roasting improves the adsorption performance of FGD gypsum for phosphate.21 hours ago · Raw Materials: Lime (CaO): Limestone, Calcite, Shale, Marl Iron (Fe 2 O 3 ): Clay, Iron ore Silica (SiO 2 ): Clay, Quartz, Shale, Marl, Fly ash Alumina (Al 2 O 3 ): Clay, Shale, Fly, Ash, Aluminium ore Kiln Dehydration Zone (up to 500 or 750 degrees) Calcination Zone (500 to 950 degrees) Free lime (CaO) reacts with silica and aluminum …The invention discloses a calcining process of gypsum. The calcining process includes the steps of taking plaster of paris as a binder, adding coal dust with a particle size smaller than 0.2mm and water, mixing the mixture into sticky coal paste, adding gypsum ore particles with a particle size of 5-10mm into the coal paste with stirring to …
May 10, 2018 · Erbs et al. (2015) evaluated the calcination of gypsum from gypsum plasterboard sheets and commercial gypsum at temperatures of 160 °C, 180 °C and 200 °C for periods of 1, 2, 4, 8, and 24 h. The best results were obtained at 180 °C to the residence period of 24 h in the tests for setting time, axial compressive strength, splitting tensile ... The calcination product has a low strength, but the calcination process requires high energy consumption and can easily cause secondary contamination to the environment . Hemihydrate gypsum is formed through the removal of 1.5 crystal water molecules from dihydrate gypsum under 100 °C to 360 °C [ 22 ].Rotary kiln. Calcination in a rotary kiln is a direct, long-time calcining process. During the process, the phases of the CaSO 4 x H 2 O system can be optimally adjusted. Rotary kilns are used for the calcining natural gypsum. In this process, pre-crushed natural gypsum is calcined in parallel flow with the flue gas.During calcination or calcining, calcium carbonate (CaCO 3) is heated in a cement kiln to form lime, a process that emits CO 2 as a byproduct. The resulting lime reacts in the kiln with silica, aluminum, and iron oxides present in the raw material to produce clinker. Clinker, an intermediate product, is mixed with a small amount of gypsumGypsum is burnt or calcined in the Rotary Kilns at the 630-650º C temperature, and adjusted to remain within half a molecule of water. Calcined gypsum passes ...Another effective method for synthetic gypsum calcining is the use of a horizontal impact calciner. It provides calcination of fine-grained material with high-moisture content. Production is up to 100 tonnes/h. Calcining is conducted in one stage (Gypsum Technik, 2014). 25.2.1.4. Energy consumption and emissions of binders manufacturing
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Sep 1, 2020 · With the best calcination temperature of 800 °C, gypsum plaster showed a relatively quick setting and maximum strength with a compact microstructure and low hydration degree due to the large ... Dihydrate gypsum generally has a combined water percentage of about 18 to 20 percent by weight. Three quarters of the combined water is removed through the conversion (i.e., calcination) process. After conversion to alpha-hemihydrate gypsum, the combined water percentage should be about 6 percent by weight.Calcination is the practice of dehydrating gypsum into plaster or stucco through a batch or continuous process which includes heating the gypsum to evaporate the crystalline water. Typically, free water is removed in an initial process at approximately 45℃ and crystalline bound water is removed in a second process at 120-180℃. The present study compares experimental results of gypsum calcination to the results predicted by a one-dimensional unsteady computational model. Controlled laboratory-scale experiments are ...
What is Gypsum? What is gypsum calcination? Gypsum mixtures ... This section is about the history of gypsum, gypsum stone, production of products from gypsum.Sep 30, 2020 · The calcination at low temperatures transforms phosphogypsum (PG) waste in a material with binder properties. This study evaluated two parameters of PG calcination: kiln residence time (1 h, 2 h, and 5 h) and temperature (120 °C, 150 °C, and 200 °C). The main objective was to find adequate calcination conditions considering PG transformation ... Gypsum (CaSO4 ·2H2O) can be calcined and grinded to obtain β-type hemihydrate gypsum (2CaSO4 ·H2O), that is, building gypsum, also known as cooked gypsum or ...The α-hemihydrate gypsum is produced by the autoclaving and salt solution method whereas β-hemihydrate gypsum is obtained through calcination at temperature lower …Dec 1, 2019 · The peaks at 97 ± 11 °C, 146 ± 18 °C, and 156 ± 16 °C were observed for calcium silicate hydrate, ettringite, and the first gypsum calcination step, respectively and the peaks at 163 ± 17 °C, 201 ± 3 °C, 275 ± 7 °C, and 496 ± 26 °C are reported to represent the second gypsum calcination, monosulfate, aluminum hydroxide, and ...The rate of production of gypsum plaster by a continuous calcination process, in which a mass of gypsum being calcined is maintained in a fluidized condition predominantly by the water vapour evolved during calcination, can be considerably increased and a plaster product of reduced water demand be obtained by introducing an aridizing agent such as calcium chloride along with the gypsum and ... Gypsum Maximum reliability combined with efficient operating costs, makes Claudius Peters the ideal partner for your next gypsum project. From stockyard and materials handling systems, calcining mills, flash calciners, and kettle calcining systems to pneumatic conveying, storage, mixing, packing and dispatch systems, gypsum …Coarse natural gypsum or mixtures of natural gypsum and FGD gypsum are ground, dried, calcined, and classified in the MPS vertical roller mill. Product fineness ...gypsum block – sadrový blok · gypsum calcination – pálenie sádrovca · gypsum ... calcined gypsum – pálená sádra · sand-gypsum plaster – pieskosadrová omietka ...Sep 6, 2018 · Gypsum Cement – an α- gypsum plaster or a plaster blend of α- and β- gypsums. α- gypsum – a slurry of pulverised gypsum rock calcined in autoclave conditions to achieve uniform crystal formation. Calcination – the baking of gypsum rock to liberate the bound water of crystallisation. Hydration – the reintegration through setting of ... Gypsum’s calcination occurs with heat transfer to itself, chem-ically and partially dehydrating the molecules. Depending on how the calcination is done, alpha or beta …Gypsum’s calcination occurs with heat transfer to itself, chem-ically and partially dehydrating the molecules. Depending on how the calcination is done, alpha or beta …
Oct 17, 2023 · While calcination is the process mostly used in the oxidation of carbonates, roasting is a method that can be used for converting the sulphide ores. Whereas, during roasting, the non-metallic and moisture impurities in the form of volatile gas are released. The roasting process contains the solid-gas thermal reaction that includes reduction ...
Original: Jul 3, 2016. Gypsum is a naturally occurring stone, a metallic salt of calcium. It commonly forms as an evaporite from the dissolution of limestone by exposure to sulphuric acid from volcanic activity. Under certain conditions, continual cycles of dissolution and evaporation will agglomerate into a "primary" deposit of gypsum.Gypsum is burnt or calcined in the Rotary Kilns at the 630-650º C temperature, and adjusted to remain within half a molecule of water. Calcined gypsum passes ...operating gypsum panel manufacturing plants in the United States was about 34.1 billion square feet1 per year. Total ... Employment, mine and calcining plant, numbere 4,500 4,500 4,500 4,500 4,500 Net import reliance5 as a percentage of apparent consumption 10 …Calcination is the essential factor for high-quality further processing of gypsum. Grenzebach’s calcining technologies ensure utmost precision in grinding, drying, calcining and classifying the gypsum. Contact Gypsum From raw material to stucco or high-fired plaster – with precisely matched technology TAILORED TO YOUR NEEDS What is Calcination Gypsum? Solution Calcination: The process in which solids are heated to a very high temperature to remove any volatile substance present and also to …Examples of calcination reactions. The conversion of calcium carbonate to calcium oxide is a common calcination process. Limestone calcination – entails the breakdown of carbonate ores and the removal of carbon dioxide. Calcination of bauxite and gypsum – requires the elimination of water vapour from crystallisation.How Tiger Boards are made [Tiger Board manufadtacturing process] "Gypsum" is baked in a furnace and made into "calcined plaster" which will solidify when it reacts with water. Calcined “gypsum” is mixed with water to make a slurry (muddy state). Then, the slurry is poured into a line (belt) where board liners are flowing down, thus ...Due to the vast scale of production, its high energy demands and the significant CO 2 footprint of gypsum calcination (ca. 76 kg of CO 2 per ton of gypsum …May 20, 2020 · Calcination can not only remove impurities such as soluble phosphorus, soluble fluorine and organic matter in PG, and it is observed that during the heating process of PG at high temperature, the P 2 O 5 occluded in the gypsum crystals (CaHPO 4 ·2H 2 O) can convert into calcium pyrophosphate (CaP 2 O 7) which is water insoluble and harmless ...
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May 1, 2021 · The present study compares experimental results of gypsum calcination to the results predicted by a one-dimensional unsteady computational model. Controlled laboratory-scale experiments are ... Mar 21, 2023 · Quantitative analysis of gypsum calcination caused by a fire is of great use in fire investigations. The rate and the depth of calcination through the gypsum board are dictated by the heat and ... Rotary kiln. Calcination in a rotary kiln is a direct, long-time calcining process. During the process, the phases of the CaSO 4 x H 2 O system can be optimally adjusted. Rotary kilns are used for the calcining natural gypsum. In this process, pre-crushed natural gypsum is calcined in parallel flow with the flue gas.The rate of production of gypsum plaster by a continuous calcination process, in which a mass of gypsum being calcined is maintained in a fluidized condition predominantly by the water vapour evolved during calcination, can be considerably increased and a plaster product of reduced water demand be obtained by introducing an aridizing agent such as calcium chloride along with the gypsum and ... Calcination can not only remove impurities such as soluble phosphorus, soluble fluorine and organic matter in PG, and it is observed that during the heating process of PG at high temperature, the P 2 O 5 occluded in the gypsum crystals (CaHPO 4 ·2H 2 O) can convert into calcium pyrophosphate (CaP 2 O 7) which is water insoluble and harmless ...industry. Part of this Gypsum, however, is used as a filter aid to remove complex trace metals. It has a blue colour due to absorption of Ferric Hexacyanoferrate complexes which can only be removed by high temperature calcination producing Anhydrite (usable by the cement industry). D. FluoroanhydriteJul 31, 2023 · Gypsum plaster is a versatile building material that has been used for thousands of years in construction projects around the world. Welcome to our Minerals Company ZME_Zohdy_Minerals_Egypt. Call Us: +20-1222125268. sun - Fri: 9:00 am - 07.00pm. Home; Aboutus. Single Service; Minerals. Limestone; calcium carbonate; …The paper assesses the influence of the calcination temperature of synthetic gypsum binder 14 on the binding properties of innovative gypsum pastes, as well as on masonry and plastering mortars.Original: Jul 3, 2016. Gypsum is a naturally occurring stone, a metallic salt of calcium. It commonly forms as an evaporite from the dissolution of limestone by exposure to sulphuric acid from volcanic activity. Under certain conditions, continual cycles of dissolution and evaporation will agglomerate into a "primary" deposit of gypsum.Finally, analyzing the results obtained for recycled gypsum (powder), a predominance of the calcination phase can be seen in most of the impact categories studied (Fig. 8), reaching, for example, 82.12% of the total impacts of global warming. The milling and separation phase predominated in four of the categories, while the packaging and ...May 10, 2018 · Erbs et al. (2015) evaluated the calcination of gypsum from gypsum plasterboard sheets and commercial gypsum at temperatures of 160 °C, 180 °C and 200 °C for periods of 1, 2, 4, 8, and 24 h. The best results were obtained at 180 °C to the residence period of 24 h in the tests for setting time, axial compressive strength, splitting tensile ... Take advantage of our know-how with raw materials and our experience with gypsum processing to ensure your success. We will be happy to advise you fully on gypsum plaster production. +49 6621 81-3000. [email protected]. From pre-crushing of the raw material to calcination and bagging, Grenzebach supplies customized production technologies ... ….
Rotary kiln. Calcination in a rotary kiln is a direct, long-time calcining process. During the process, the phases of the CaSO 4 x H 2 O system can be optimally adjusted. Rotary kilns are used for the calcining natural gypsum. In this process, pre-crushed natural gypsum is calcined in parallel flow with the flue gas.Calcination is the thermal process by which gypsum is dehydrated. The material is calcined at a temperature range of 140–160 °C, so that 75% of the crystalized water is removed from the structure to obtain the hemihydrate (Barbosa et al. 2014 ).Feb 20, 2018 · Gypsum lath is of smaller dimensions, 4 feet long, 16 inches wide, and 3/8 to 1/2 inch thick. It is available either plain or with aluminum foil cemented on the back side for insulation. Gypsum sheathing is made with water-repellent paper and is wind resistant. It is available in sheets 1/2 inch thick, 2 feet wide, and 8 feet long. Gypsum Cement – an α- gypsum plaster or a plaster blend of α- and β- gypsums. α- gypsum – a slurry of pulverised gypsum rock calcined in autoclave conditions to achieve uniform crystal formation. Calcination – the baking of gypsum rock to liberate the bound water of crystallisation. Hydration – the reintegration through setting of ...The FGD gypsum was firstly calcined in the DRY-36 high-temperature industrial furnace at 800 °C for 1 h, and then cooled to room temperature within the furnace. The effect of calcination on the fineness and chemical composition was evaluated. As shown in Figure 1, the calcination tends to reduce the particle size. More than 47% of calcined FGD ...The calcination of the dolomite stone (CaMg(CO 3) 2) for the production of sintered dolomite (CaO and MgO), is a high-temperature energy-intensive process accompanied by a significant CO 2 emission.In dentistry, gypsum is mainly used to produce study or diagnostic models, and working or master models as well [6]. Study models are used to assess clinical cases requiring prostheses or orthodontic devices, while working models are the models of arches on which wax-ups of prosthetic frameworks or orthodontic devices are made.Gypsum’s calcination occurs with heat transfer to itself, chem-ically and partially dehydrating the molecules. Depending on how the calcination is done, alpha or beta …Introduction. Gypsum is one of the natural minerals that contain calcium, hydrogen, water, and sulfur, known as calcium sulfate dihydrate (CaSO 4.2H 2 O). 1 Gypsum products are available in the form of a fine white powder which has undergone calcination or heating at a temperature of 110‒130°C in the open air.Nov 1, 2021 · Calcining Flue gas desulfurization gypsum Crystal modifier Strength 1. Introduction Flue gas desulfurization (FGD) gypsum is an inevitable industrial solid waste originated from the process of calcium-based wet flue gas desulfurization in thermal power plants and some chemical plants in order to reduce the emission of SO 2 pollution gas [1], [2]. Gypsum calcination, Calcination: The process in which solids are heated to a very high temperature to remove any volatile substance present and also to oxidize a substance is called Calcination. Calcination of Gypsum: When the gypsum is heated in a controlled environment, it partially loses its water of crystalization and converts into plaster or stucco is called ..., Calcination occurs at approximately 120 to 150°C (250 to 300°F), and 0.908 megagrams (Mg) (1 ton) of gypsum calcines to about 0.77 Mg (0.85 ton) of stucco. ... Gypsum and stucco are usually transferred from one process to another by means of screw conveyors or bucket elevators. Storage bins or silos are normally located downstream of roller mills, ©Skilled at managing lab operation with tasks including test and analysis of Raw materials and finished products<br>©:Apply and enhance my academic background skills , experience and carrier through working in creative and productive Team that aims to meet the Company 's Customer requirements and satisfaction.<br>©: Validation of both chemical and …, When gypsum is heated, it undergoes a process called calcination, during which it loses some or all of its water content, depending on the temperature and duration of heating. This results in the formation of different gypsum products with varying properties, such as plaster of Paris, stucco, and gypsum board., The calcination of phosphogypsum (PG) was employed to produce gypsum plaster to achieve its recovery and utilization. Although previous studies have indicated the possibility of producing hemihydrate and anhydrous gypsum, the influence mechanism of the impurities in calcined PG (CPG) on the properties of plaster is unclear. Herein, the …, Calcination of Gypsum. Gypsum or calcium sulfate dihydrate (CaSo 4.2H 2 O) is a mineral of calcium that is mined in various parts of the world. It is also formed as a by-product of flue gas desulphurization in some coal-fired electric power plants. There are different kinds of Gypsum, and they are listed below:, Calcination is a process of heating a substance under controlled temperature and in a controlled environment. This process is known to improve the chroma, tinctorial strength, pigmentary texture, weather stability, light-fastness and thermal stability of pigment whereas it has adverse effect on the dispersibility of pigments., Jul 31, 2023 · Gypsum plaster is a versatile building material that has been used for thousands of years in construction projects around the world. Welcome to our Minerals Company ZME_Zohdy_Minerals_Egypt. Call Us: +20-1222125268. sun - Fri: 9:00 am - 07.00pm. Home; Aboutus. Single Service; Minerals. Limestone; calcium carbonate; …, Jun 21, 2018 · SETTING OF GYPSUM PRODUCTS The reaction between gypsum products and water produces solid gypsum, and the heat evolved in the exothermic reaction is equivalent to the heat used originally for calcination. Set gypsum products probably never attain 100% conversion unless they are exposed to high humidity for a long time. Therefore, there are ... , The calcination of gypsum is completed at ∼150 °C. The temperature of the hemihydrate transition for LPdce-08 is 151.7 °C at a DTA value of ‐37.567 μV with a heat change of about ‐179.2 μV/mg and the temperature of the hemihydrate transition for LPdce-10 is 148.8 °C at a DTA value of ‐37.544 μV with a heat change of about ‐133.3 ..., The calcination of gypsum, under a pressure of 320 to 380 mbar in an atmosphere saturated with water, gives the plaster mechanical characteristics and ..., Mar 11, 2015 · CN102500223A Equipment for performing wet-method flue gas desulfurization and producing gypsum by discarded carbide slag : 06/13/2012: CN102491662A Natural anhydrous gypsum-made bonding material ..., Calcination process 2. A not-for-profit trade association founded in 1930, promoting the use of gypsum while advancing the development, growth, and general welfare of the gypsum industry in the United States and Canada on behalf of its member companies. , Rotary kiln. Calcination in a rotary kiln is a direct, long-time calcining process. During the process, the phases of the CaSO 4 x H 2 O system can be optimally adjusted. Rotary kilns are used for the calcining natural gypsum. In this process, pre-crushed natural gypsum is calcined in parallel flow with the flue gas., The reaction of gaseous CO2 with the CaS slurry leads to the stripping of sulphide to form H2S gas and the precipitation of CaCO3. The H2S generated was then reacted with SO2 in the PIPco ..., The present study aimed to optimize the calcination process parameters (viz., temperature, time, and particles size) for the extraction of aluminum from Ethiopian kaolinite. The kaolinite calcination was done in the temperature of 600–700°C, time of 120–180 min, and particles size of …, This dehydration of gypsum by heat is called as calcination. The calcination results in a covering over the materials that stop it to undergo combustion and allow the material near them to maintain a lower safer temperature. Even after complete calcination of water crystals, the residue would behave like an insulating layer till it gets ..., Apr 6, 2019 · Gypsum Calcining. Gypsum is the crystalline chemical compound CaSO4·2H2O. A close chemical relation – and frequently occurring with Gypsum – is Anhydrite which is CaSO4. Gypsun has wide commercial use because relatively simple heat processing reduces it to Plaster of Paris. While Anhydrite can be converted to Gypsum and thence to Plaster ... , Oct 18, 2023 · gypsum calcination calculations calcination system input --> system output presentation of calculations to our customer, showing the importance of…, Oct 22, 2020 · The goal of the proposed research is to develop a reliable predictive tool for the analysis of gypsum calcination. Gypsum plasterboards are commonly used in building construction due to their fire-resistant properties. Gypsum undergoes calcination when exposed to fire. This leaves fire patterns on the gypsum board and most forensic fire investigations rely on it. , Known as dihydrate in construction chemistry, gypsum is a water-containing calcium sulfate (CaSO 4 • 2 H 2 O). In various calcination processes, some of the water of crystallization is removed ..., Key words: calcination, structural, traditional, gypsum, oven construction. Influencia del proceso de calcinación del yeso trasicional para uso estructural., Gypsum is a non-metallic mineral, found in rock form. It is composed of 79.1% calcium sulphate and 20.9% water, by weight. Chemists call it Hydrous Calcium Sulphate, and as there is one molecule of calcium sulphate combined with two molecules of water. It has the chemical formula CaSO 4 2H 2 0. By volume this works out to nearly 50% water in ... , Calcination is the thermal process by which gypsum is dehydrated. The material is calcined at a temperature range of 140–160 °C, so that 75% of the crystalized water is removed from the structure to obtain the hemihydrate (Barbosa et al. 2014 )., Calcination and Phase Transformations. G.L. Messing, in Encyclopedia of Materials: Science and Technology, 2001 8 Summary. Calcination and phase transformations are of critical importance for ceramics, since almost all ceramic powders are produced by such processes. The formation of powders of small size, phase purity and without aggregates …, Ferhat Abbas University of Setif. calcination is a heat treatment at a temperature where all phase transformations are carried out. on the other hand, sintering is a thermal treatment of a product ..., Moreover, Geraldo et al [35] studied the effect of calcination time (1t o6h) on gypsum strength under a calcination temperature of 150 ° C and concluded that the maximum strength was achieved ..., Coarse natural gypsum or mixtures of natural gypsum and FGD gypsum are ground, dried, calcined, and classified in the MPS vertical roller mill. Product fineness ..., 1000 tpd gypsum calcination kiln is going to one of ongoing projects in Turkey, for Erciyes Alci. by IPS… Liked by Carlos Munoz. Gypsum factory Gypsum Plasters Production design, engineering ..., Method and apparatus for calcining gypsum in a kettle (10) in which the calcined mass is fluidized. Heat for the calcination is supplied by heating rods (46) which are immersed in said bed. Said heating rods (46) supply about 1 British Thermal Unit (Btu) of heat per minute per square inch of surface area of rod. Heat is also supplied to the calcined mass by a …, The calcination process at high temperature is expected to have an important impact on physical properties and the microstructure of the cement-based material. The FTIR spectra of cement samples CS1, CS2, CS3, CS4, CS5, and CS6, after calcination at a temperature of 600°C, are illustrated in Figure 2 . , Calcination process 2. A not-for-profit trade association founded in 1930, promoting the use of gypsum while advancing the development, growth, and general welfare of the gypsum industry in the United States and Canada on behalf of its member companies., industry. Part of this Gypsum, however, is used as a filter aid to remove complex trace metals. It has a blue colour due to absorption of Ferric Hexacyanoferrate complexes which can only be removed by high temperature calcination producing Anhydrite (usable by the cement industry). D. Fluoroanhydrite