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This study examined the thermal dehydration characteristics of CaSO4∙2H2O in a constant-volume rotary vessel. The experiment used CaSO4∙2H2O particles obtained from the crushed waste gypsum board. The particle size ranged from 850 to 2000 μm, and the experiment was carried out at varying rotation speeds of 1, 10, and 35 rpm, with the vessel temperature heated to 180 °C. Temperature and pressure inside the vessel were measured simultaneously using the thermocouple and the pressure sensor. The XRPD measurement analyzed the transition of CaSO4∙2H2O after the heating of particles. The result showed that the temperature growth rate was similar for high rotation speeds of 10 and 35 rpm, while periodic temperature changes occurred at the low rotation speed of 1 rpm. A distinguishing flow pattern was observed at the low rotation speed, and the particles inside the vessel collapsed periodically downward. This particle behavior was related to the temperature distribution of the rotation speed of 1 rpm. Additionally, the pressure in the vessel increased rapidly at higher rotation speeds. This trend indicates the desorption of the crystal water of CaSO4∙2H2O due to the increasing temperature in the case of high rotation speed. Also, the XRPD measurement results showed the appearance of CaSO4∙0.5H2O under the higher rotation speed conditions, and the mass fraction of CaSO4∙0.5H2O increased with the rotation speed. Overall, the present study suggests that rotation speed plays a crucial role in determining the heat conduction and heat transfer of particles in a constant-volume rotary vessel. [ABSTRACT FROM AUTHOR]

This study examined the thermal dehydration characteristics of CaSO4∙2H2O in a constant-volume rotary vessel. The experiment used CaSO4∙2H2O particles obtained from the crushed waste gypsum board. The particle size ranged from 850 to 2000 μm, and the experiment was carried out at varying rotation speeds of 1, 10, and 35 rpm, with the vessel temperature heated to 180 °C. Temperature and pressure inside the vessel were measured simultaneously using the thermocouple and the pressure sensor. The XRPD measurement analyzed the transition of CaSO4∙2H2O after the heating of particles. The result showed that the temperature growth rate was similar for high rotation speeds of 10 and 35 rpm, while periodic temperature changes occurred at the low rotation speed of 1 rpm. A distinguishing flow pattern was observed at the low rotation speed, and the particles inside the vessel collapsed periodically downward. This particle behavior was related to the temperature distribution of the rotation speed of 1 rpm. Additionally, the pressure in the vessel increased rapidly at higher rotation speeds. This trend indicates the desorption of the crystal water of CaSO4∙2H2O due to the increasing temperature in the case of high rotation speed. Also, the XRPD measurement results showed the appearance of CaSO4∙0.5H2O under the higher rotation speed conditions, and the mass fraction of CaSO4∙0.5H2O increased with the rotation speed. Overall, the present study suggests that rotation speed plays a crucial role in determining the heat conduction and heat transfer of particles in a constant-volume rotary vessel.

The separation of Cu from the CuxO-FexO containing waste (such as copper slag and electroplating sludge) is always intractable by using pyrometallurgy method. The carbothermic reduction methods, as well as the conventional sulfurization technology by using sulfurization agent FeS2, will introduce lots of iron into the prepared Cu–Fe alloy or Cu–Fe–S matte, and this results in the difficulty in further separation of Cu from Fe. In this work, CaS is utilized as the new sulfurization agent, and the iron content of prepared Cu–Fe–S matte is lower than 5%, while the copper grade is improved to about 76–79%. Such products could be used as the raw materials for producing metallic copper. According to the experimental results, at 1450 °C, the copper oxides in CuO–Fe2O3–SiO2–CaO system is selectively sulfurized by CaS, and Cu2S dominated product is formed and separated from slags. The recovery extent of copper reaches 98% when the CaS addition is 1.15 times (1.15CaS) of the stoichiometric quantity required. However, the increase of CaS addition (1.6CaS) will lead to the sulfurization of iron oxides, and make the iron content in Cu–Fe–S matte increase to 15%. Besides, when the Cu/Fe ratio (in mass) of synthetic waste is 0.5, part of the CaS is oxidized by Fe2O3, which results in the recovery extent of Cu to only about 73.30%. However, the copper recovery extent could be improved to 97% by adding extra reductant carbon.

Direct mineral carbonation (MC) is used to mitigate carbon dioxide (CO2) emissions. This method has the great advantages of reducing the amount of industrial residues and creating valuable materials by incorporating CO2. Waste gypsum, industrial waste including flue gas desulfurization (FGD) gypsum (25.27–53.40 wt% of CaO), and phosphogypsum (30.50–39.06 wt% of CaO) can be used for direct MC (conversion rate up to 96%). Mineral carbonation converts waste gypsum into calcium carbonate (CaCO3), which can be recycled during desulfurization. Furthermore, ammonium sulfate ((NH4)2SO4), which is used as a fertilizer, can be prepared as a by-product when the carbonation reaction is performed using ammonia (NH3) as a base. In this study, recent progress in the carbonation kinetics and preparation of CaCO3 using FGD gypsum and phosphogypsum with NH3 was investigated. Temperature, CO2 partial pressure, CO2 flow rate, and NH3 concentration were reviewed as factors affecting carbonation kinetics and efficiency. The factors influencing the polymorphs of the prepared CaCO3 were also reviewed and summarized. A state-of-the-art bench-scale plant study was also proposed. In addition, economic feasibility was investigated based on a bench-scale study to analyze the future applicability of this technology. [ABSTRACT FROM AUTHOR]

Herein, we have attempted to recycle the waste gypsum to be used as filler material in polymer composite. In this regard, aqueous dispersion of gypsum was ultrasonicated for varying time duration (10, 30, and 60 min), dried and used as fillers to develop corresponding EPDM composites. As per the mechanical performance (i.e., tensile strength and elongation at break), the gypsum obtained after ultrasonication for 60 min (i.e., U-60 gypsum) was found best performing filler material compared to the other ultrasonicated gypsum samples, commercial carbon black, and another surface treated gypsum sample. The decreased particle size and enhanced surface area of U-60 gypsum are supposed to be responsible for improving the mechanical property of the composite. Corresponding particle size, surface area, and morphology of all the gypsum samples were thoroughly examined to conclude the reason behind such observation. [ABSTRACT FROM AUTHOR]

This study employed a Gypsum-derived CaO catalyst with 10 wt% MgCO 3 to convert palm oil into biofuel via pyrolysis in a continuous packed-bed reactor at atmospheric pressure without purge gas. The reaction occurred within the 500–550 °C temperature range, with varying catalyst calcination temperatures. ASTM D86 distillation to separate the pyrolytic oil into biogasoline (75–150 °C), biokerosene (150–250 °C), and biodiesel (250–330 °C) was conducted. The physical and chemical properties of products and catalysts using various techniques were determined. Notably, calcination temperature changes minimally affected the final oxygen content in the product but significantly influenced the textural properties of the catalyst. At a reaction temperature of 525 °C, the 10% MgCO 3 catalyst calcined at 850 °C yielded the highest volume of distilled product distilled from pyrolytic oil, accounting for 100% of pyrolytic oil (equivalent to 66.44 vol% of palm oil). It implies that 100% of pyrolytic oil could be converted to distilled oil completely by the distillation process. The primary constituents of the pyrolytic oil were aliphatic and olefinic compounds, with a notable presence of ketones, mainly in the C5 to C33 range. C17 ketones were prominent, constituting approximately 5 wt% of the pyrolytic oil (equivalent to 2.92 wt% of palm oil). These ketones likely resulted from the decarboxylation of carboxylic acids and aldol condensation reactions facilitated by CaO or MgO catalysts. CaO decarboxylation was confirmed by the presence of CaCO 3 in the spent catalyst. Additionally, the pyrolytic oil exhibited an acidity of approximately 5.72 mg KOH/g, primarily attributed to phenolic compounds, confirmed through GCxGC-FID, GCxGC-TOFMS, and 1H NMR spectroscopy. [Display omitted] • The main products over alkaline catalyst were aliphatic and olefinic compounds. • The aliphatic and olefinic compounds were more than 50% in pyrolytic oil. • The ketone compound was formed about 31% via ketonization mechanism. • The major carbon number of alkanes was C 8 – C 15. • The decarboxylation was confirmed by the CaCO 3 compound in the spent catalyst. [ABSTRACT FROM AUTHOR]

Construction technology in the twenty-first century is on the peak yet developing countries of the world still dream for shelter in bad weather conditions and apply old traditional techniques for construction of their houses. The reason is the increasing cost of construction materials due to energy crises, poor economic conditions, and sometimes the love of people toward earthen architecture culture. The world will prefer low energy alternatives to conventional construction. Some alternatives regarding conventional construction like mud block masonry are part of this research paper to avoid shrinking natural resources and take control of the energy crisis. This research work focuses on the compressive strength of the mud block by stabilizing it with additives like waste gypsum. The study also intended to investigate the rapid hardening of the masonry block. Finally, study the morphology of the stabilized blocks by using scanning electron microscopy and energy dispersive X-ray microanalysis (EDXMA). This research found that the compressive strength of waste gypsum-stabilized mud block at 7 days and 14 days increases with the increasing rate of waste gypsum from 0 to 20%. This research will help the poor community by reducing the economy and energy consumed in the construction of houses. Besides, this research will play a role by minimizing the consumption of natural resources, encourage people to reuse waste gypsum in construction without compromising on environmental pollution. [ABSTRACT FROM AUTHOR]

Mineral carbonation using natural minerals or industrial wastes is a safe and promising strategy for CO 2 sequestration. Application of industrial wastes for this purpose has significant ecological and environmental value, which is one of the key green technologies in the global carbon mitigation. This review summarizes the current research status of CO 2 mineralization by industrial wastes. This work surveys the mechanisms and capacities of CO 2 mineralization using different industrial wastes (mainly steel slags, blast furnace slags, coal fly ash, waste gypsum, and red mud), evaluates the influence of carbonation pathways and process parameters on the CO 2 sequestration capacity, and analyzes the current industrial application status of CO 2 sequestration using industrial wastes. Direct aqueous carbonation and indirect carbonation are the two most studied and promising mineralization routes. The leaching-mineralization cycle process has great potential for industrial application, especially for the treatment of coal fly ash, steel slag and other wastes containing calcium oxide, owing to the stable cycle performance of the absorbers. Researchers pay more attention to CO 2 mineralization by steel slag compared to other wastes, and the capacity of CO 2 mineralization varies greatly for different wastes. Several reports already reported carbonation effectiveness up to 100%. A CO 2 sequestration capacity reached 536 g/kg for steel slag and 361 g/kg of blast furnace slag, revealing superior properties of these materials. CO 2 sequestration using industrial wastes benefits CO 2 emission reduction and comprehensive utilization of industrial wastes. To overcome the problem of the high energy consumption for regeneration of absorbent, a novel integrated CO 2 absorption-mineralization process is currently widely studied. A possibility of co-production of value-added products - like different types of zeolite or lithium orthosilicate based adsorbents was highlighted, improving the economic balance of the overall process. More studies on pilot scale should be performed, to fully confirm the feasibility of developed technologies. Application of these developments is still faced with significant issues, including low carbonation efficiency, poor product quality, high process cost, and insufficient mass and heat transfer. In future studies, it is necessary to investigate the mechanisms of CO 2 sequestration, the optimization of process parameters, the exploration of ways to accelerate carbonation, and the generation of value-added products or effective by-product utilization. [Display omitted] • CO 2 sequestration by industrial wastes through mineral carbonation was summarized. • Indirect carbonation can yield high-purity carbonated products. • Improvement of mass transfer, solvent regeneration, leaching agents is needed. • The production of value-added byproducts is helpful to increase the process economic feasiblity. [ABSTRACT FROM AUTHOR]

• Disposal of Waste gypsum board is difficult due to the evolution of hydrogen sulfide. • High SO 3 clinker using waste gypsum board has a important implications. • The mineral composition of the high-SO 3 clinker was investigated. • The result indicate that gypsum was decomposed stably to clinker minerals. Portland-cement clinker with a SO 3 content up to 3.4% was produced in a cement kiln using waste gypsum board, and the influence of SO 3 content on the clinker mineral was investigated. Formation of anhydrite (CaSO 4) in the clinker with over 1.6%-SO 3 was attributed to a thermodynamic effect but not to the residual waste gypsum board. The mineral composition with a higher SO 3 content exhibited a similar trend to those found in the previous studies. The measured alite and belite contents in the clinker agreed with the calculated values derived from modified Bogue's equation which considers the substitution of sulfur and aluminum by silicon in belite. This substitution increased the lattice parameters of belite. The M1 phase in the alite increased with an increase in SO 3 content in the clinker. These characteristics of the high-SO 3 clinker indicates that the waste gypsum was decomposed stably to clinker minerals in the cement kiln. [ABSTRACT FROM AUTHOR]

The possibilities of the application of waste gypsum (citrogypsum, nitrogyosum and sulphogypsum), fly ash and bottom ash in construction: for production of gypsum binders (a-calcium sulphate hemihydrate, b-calcium sulphata hemihydrate and b-anhydrite), for obtaining construction products (bricks and blocks) and as component materials for road layers were presented in this work. Also, the possibilities of the application of sulphogypsum (or FGD gypsum) for solidification and stabilization of fly ash were presented. The obtained results could have great importance in both ecological and economic views (elimination of important pollutants of water, air and soil, replacement of natural by waste materials, reduction of waste disposal cost).

• The increase of the acidity of the reaction medium can increase the length to diameter ratio and the crystallinity of α-HH. • With the increase in pH value, the overall reaction rate is accelerated to a certain extent. • The preparation of recycled α-HH from WG can be achieved by atmospheric hydrothermal process. Phosphogypsum (PG) is a typical solid waste in the phosphorus chemical industry, which restricts the sustainable development of the phosphorus chemical industry. From the perspective of green manufacturing in the whole life cycle, this paper puts forward the hydrothermal recycling and utilization of waste gypsum (WG) from αlpha-hemihydrate phosphogypsum (α-PGHH). It is revealed that the raw material characteristics of WG will lead to the crystal fine fragmentation of the product, which will lead to the significant deterioration of the strength and filtration performance of the hardened paste. The increase of the acidity of the reaction medium is proposed to weaken the negative effect of the crystal modifier on crystal phase transition, so as to obtain recycled αlpha-hemihydrate gypsum (α-HH) with better crystal integrity and macroscopic performance. It was proved that when the pH value was controlled at 4.5, the comprehensive properties of the product were good, and the 2 h bending strength and 3 d compressive strength were 4.1 MPa and 29.2 MPa, respectively. The preparation of recycled α-HH from WG produced by α-PGHH can be achieved through the atmospheric hydrothermal process. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high value-added recycling path of waste gypsum board was designed to prepare the 3D printing powder with high-precision. • The waste gypsum board was firstly recycled to product α-hemihydrate gypsum of high strength. • A synergistic strategy was proposed to optimize the morphology of α-hemihydrate crystal particles recycled from waste gypsum. • The 3D printability of the recycled α-hemihydrate powder was improved obviously. A large number of waste gypsum was reused of low-value or landfilled which caused serious waste of resources. In this study, a high value-added recycling scheme for waste building gypsum to synthesize a 3D printable material with high-precision was designed. The α-hemihydrate gypsum (α-HH) was synthesized from waste plasterboard by the salt solution hydrothermal method. A synergistic optimization strategy was proposed involving the effect of sodium succinate and pH on the morphology and mechanical strength of α-HH. The properties of recycled α-HH were modified to meet the requirements of 3D printing, including fluidity, setting time and green strength. When the modifier dosage is 0.05 wt% and the pH is 5, the best morphology of α-HH crystals with an average aspect ratio of 1.07 (length of 10 μm) are synthesized. The converted product has close interlocking and intergrowth after hydration, which exhibits excellent mechanical strength (25.5 MPa). The 3D printing materials prepared by the composite modification of recycled α gypsum powder has proven to achieve good printable. The print errors smaller than 4% for pore objects larger than 4.0 mm, and satisfactory results are shown in terms of the strength and resolution of printing high detail cavity structures. This work provides a high value-added upcycling scheme for waste building gypsum that has great potentiality for future industrial application. [ABSTRACT FROM AUTHOR]

This study experimentally examined the drying characteristics of the waste gypsum powder using a permeation of heated air. The powder used was the waste gypsum which the particle diameter was classified into three kinds. As the experimental conditions, the particle diameter of dehydrate gypsum, the heating temperature, the initial mass of powder, the heating time and the mass flux of heated air were varied. When the initial mass of powder was an identical, it is found that the decrease in the time of change from the dehydrate gypsum to the hemihydrate gypsum depends on the increase in the particle diameter and the heating temperature. As the analysis of X-ray diffraction pattern, it can be confirmed a permeation test of heated air was an effectiveness for the evaluation of the change to hemihydrate gypsum. In addition, an effective thermal conductivity and heat flux of the packing bed of gypsum were estimated. It is found that a particle Reynolds number influenced to an effective thermal conductivity in the packing bed of waste gypsum. Also, an effective thermal conductivity including the flow of heated air was high in the case of large particle diameter. Furthermore, it is inferred that a high heat flux acting on the packing bed of gypsum influenced the time of change from the dehydrate gypsum to the hemihydrate gypsum. [ABSTRACT FROM AUTHOR]

Belite-barium calcium sulfoaluminate (CBA$) cement was belite-rich cement containing CBA$ mineral of 9 mass%. Due to the differences in dissolution velocity and element sulfur content, the effects of citro-, phosphor- and FGD gypsum on the setting and early mechanical properties of belite-CBA$ cement were investigated. The experimental results showed that citrogypsum had the fastest dissolution velocity among all the waste gypsum. This resulted in the short initial and final setting time of belite-CBA$ cement with citrogypsum. Moreover, the early compressive strength of belite-CBA$ cement with citrogypsum was high, owing to that much content of AFt and C-S-H gel was formed at an early age. In summary, the later compressive strength of belite-CBA$ cement with any type of waste gypsum was superior to that of cement with reference natural gypsum. Also, the early compressive strength of cement with any type of waste gypsum was comparable to that of cement with reference gypsum. Therefore, citro-, phosphor- and FGD gypsum all could replace natural gypsum as an adjusting agent of belite-CBA$ cement. [ABSTRACT FROM AUTHOR]

The recovery of better quality waste gypsum during acid mine drainage (AMD) neutralization is one step closer to achieving downstream waste gypsum beneficiation for recovery of valuable materials. This can facilitate recovery of treatment costs and prevention of environmental pollution from gypsum waste-dumps. Thermal reduction using rotary kilns to recover valuable materials from waste gypsum remains a critical and controversial process because of waste gypsum handling problems, environmental pollution due to dust and gaseous emissions and poor conversion yields. In order to mitigate these problems and improve waste gypsum conversion yields, pelletization of waste gypsum in the presence of binders (starch and cellulose) was investigated. A laboratory-scale disc pelletizer was used to produce pellets from a mixture of coal and commercial gypsum or waste gypsum, generated during AMD neutralization, with starch and micro-crystalline cellulose used as binders. The pellets were subjected to high-temperature thermal treatment in a tube furnace to generate calcium sulphide (CaS), an important intermediate for waste gypsum beneficiation. The kinetics of thermal conversion of pelletized waste gypsum to CaS were found to be highly dependent on furnace temperature. Results also showed that pelletization affords improved handling of waste gypsum while use of binders as additives significantly improved the CaS yield, with starch giving the better yield compared to cellulose. [ABSTRACT FROM AUTHOR]

The thermochemical conversion of abundant renewable resources through pyrolytic catalysis cracking (PCC) is one of the most promising technologies for producing green biofuels. In this study, the pyrolysis of palm oil was investigated over a sustainable CaO-based catalyst derived from waste gypsum. PCC was conducted in a continuous packed-bed reactor under atmospheric pressure without purge gas. The effects of Mg doping and reaction temperature were also examined. A wet ball milling process was used to prepare the well-mixed catalysts and to subsequently form a heterojunction structure between the CaO and MgO particles. CaO was synthesized using the Ca(OH) 2 derived from the reaction between gypsum and sodium hydroxide. The pyrolytic oil was separated from the crude oil to remove water and other impurities. The pyrolytic oil was then distilled following ASTM D86 , and the three separated products were classified as bio-gasoline, bio-kerosene, and bio-diesel. The highest renewable light fuel volume (bio-gasoline and bio-kerosene) of about 75% (74 %wt.) was obtained at a reaction temperature of 525 °C with 10% MgCO 3 content. The percent volume of light fuel increased with increasing reaction temperature. Renewable light fuel production over the Mg-doped CaO-based catalyst was related to both the Mg content and reaction temperature. [Display omitted] • Biofuels were produced over CaO-based catalysts derived from waste gypsum. • Catalytic cracking can convert palm oil to biofuel oil under atmospheric pressure. • Deoxygenation in a packed bed reactor can reduce the acidity of biofuel. • The 10% MgCO 3 catalyst was the most suitable for high light biofuel production. [ABSTRACT FROM AUTHOR]

The recovery of calcium carbonate from waste gypsum (a waste product of the reverse osmosis (RO) desalination process) was tested using sodium carbonate. Batch recovery of calcium carbonate from waste gypsum slurries by reacting with sodium carbonate under ambient conditions was used to assess the technical feasibility of CaCO3 recovery and its use for pre-treatment of acid mine drainage (AMD) from coal mines. The effect of key process parameters, such as the slurry concentration (%) and the molar ratio of sodium carbonate to gypsum were considered. It was observed that batch waste gypsum conversion significantly increased with decrease in the slurry concentration or increase in the molar ratio of sodium carbonate to gypsum. The CaCO3 recovered from the benchscale batch reactor demonstrated effective neutralization ability during AMD pre-treatment compared with commercial laboratory grade CaCO3. [ABSTRACT FROM AUTHOR]

Abstract: The performance and water resistance of binders 30–50% blast furnace slag and hemihydrate from waste gypsum were investigated. Mortars of various aggregate:binder ratios were prepared with granulated BFS and silica sand. The cements with 50% slag were the best in terms of strength; higher aggregate loads reduced the strength. The solidification of mortars by the formation of an initial gypsum framework was indicated by the very fast setting, low 1 day strength and high non-evaporable water. Further strength development was due to the slag reactions. The microstructures of polished samples were dense and conformed by gypsum crystals surrounded by C–S–H. The use of BFS sand was more efficient, in terms of strength, than silica sand; this was due to the participation of the slag aggregate in the hydration reactions, improving the bonding in the interfacial zone. The lower density of the former makes them potentially more insulating efficient. [Copyright &y& Elsevier]

• Reactive MgO-activated slag (MAS) binders modified by waste gypsum (WG) used in CPB. • Appropriate WG incorporation significantly enhanced the 28 d strengths of MAS-WG-CPB. • Long-term strengths of MAS-WG-CPB were stable regardless of WG content. • Hydration products of MAS-WG-CPB were CaSO 4 ·2H 2 O, ettringite and C-S-H/M-S-H gels. • Leaching solution pH of CPB decreased and trended to stable with WG content increase. In this study, the basic properties of waste gypsum (WG), WG and reactive MgO-activated slag (MAS-WG) binders were experimentally explored. The effects of WG content in MAS-WG binders on the unconfined compressive strength (UCS) development of cemented paste backfill (CPB) from sulphide-rich mine tailings were investigated as well. The corresponding stabilization mechanisms were assessed through mineralogical and micro-structure analysis and leaching tests. The results showed that when the content of citric acid exceeded 0.15 wt% of WG content, the initial setting time and 28 d UCS of the WG plaster of 180 mm slump were over 1 h and 15.5 MPa, respectively. The appropriate WG incorporation improved the particle gradation of MAS-WG and MAS-WG-CPB mixtures. The main hydration products of MAS-WG plaster and MAS-WG-CPB from sulphide-rich tailings were crystalline CaSO 4 ·2H 2 O, ettringite (AFt) and amorphous hydrated products (C-S-H/M-S-H). The proper WG incorporation in the MAS-WG binder also significantly enhanced the early age (14 d and 28 d) UCSs of MAS-WG plaster and MAS-WG-CPB, in which the reason is that appropriate WG incorporation accelerated the hydration process of GGBS in the alkaline solution by forming ettringite (AFt) and enhanced amorphous phase development resulting in the denser microstructure. A lot of WG incorporation made the 28 d UCSs of MAS-WG-CPB decrease due to the loose micro-structure resulted from the decrease of amorphous hydration products. However, the long-stage UCSs of MAS-WG-CPB after 120 d of curing were all stable (i.e., no strength loss) regardless of WG incorporation content, which were attributed to the low-alkalinity solution in MAS-WG-CPB preventing the secondary expansive hydration product formation. The long-stage (180 d) UCS of MAS-WG-CPB had positive correlations with the refined pore structure and the alkalinity of the leaching solution. [ABSTRACT FROM AUTHOR]