Evolution and Application of Sealing Ability of Gypsum Caprocks under Temperature-Pressure Coupling:An Example of the ZS5 Well in the Tazhong Area of the Tarim Basin

Gypsum caprocks'sealing ability is affected by temperature-pressure coupling.Due to the limitations of experimental conditions,there is still a lack of triaxial stress-strain experiments that simultaneously consider changes in temperature and pressure conditions,which limits the accuracy of the comprehensive evaluation of the brittle plastic evolution and sealing ability of gypsum rocks using temperature pressure coupling.Triaxial stress-strain tests were utilized to investigate the differences in the evolution of the confinement capacity of gypsum rocks under coupled temperaturepressure action and isothermal-variable pressure action on the basis of sample feasibility analysis.According to research,the gypsum rock's peak and residual strengths decrease under simultaneous increases in temperature and pressure over isothermal pressurization experimental conditions,and it becomes more ductile.This reduces the amount of time it takes for the rock to transition from brittle to plastic.When temperature is taken into account,both the brittle–plastic transformation's depth limit and the lithological transformation of gypsum rocks become shallower,and the evolution of gypsum rocks under variable temperature and pressure conditions is more complicated than that under isothermal pressurization.The sealing ability under the temperature-pressure coupling is more in line with the actual geological context when the application results of the Well#ZS5 are compared.This provides a theoretical basis for precisely determining the process of hydrocarbon accumulation and explains why the early hydrocarbon were not well preserved.

Gypsum-based Silica Gel Humidity-controlling Composite Materials:Preparation,Characterization,and Performance

Gypsum was used as substrate,and silica gel was mixed into substrate at a certain mass ratio to prepare humidity-controlling composites;moreover,the moisture absorption and desorption properties of gypsum-based composites were compared with adding different silica gel particle size and proportion.The morphological characteristics,the isothermal equilibrium moisture content curve,moisture absorption and desorption rate,moisture absorption and desorption stability,and humidity-conditioning performance were tested and analyzed.The experimental results show that,compared with pure-gypsum,the surface structure of the gypsum-based composites is relatively loose,the quantity,density and aperture of the pores in the structure increase.The absorption and desorption capacity increase along with the increase of silica gel particle size and silica gel proportion.When 3 mm silica gel particle size is added with a mass ratio of 40%,the maximum equilibrium moisture content of humidity-controlling composites is 0.161 g/g at 98% relative humidity(RH),3.22 times that of pure-gypsum.The moisture absorption and desorption rates are increased,the equilibrium moisture absorption and desorption rates are 2.68 times and 1.61 times that of pure-gypsum at 58.5% RH,respectively.The gypsum-based composites have a good stability,which has better timely response to dynamic humidity changes and can effectively regulate indoor humidity under natural conditions.

Preparation of α-High Strength Gypsum from Flue Gas Desulfurization Gypsum Pretreated by Hydrothermal-aging Method

The synthesis of α-calcium sulfate hemihydrate (α-CSH) from flue gas desulfurization (FGD)gypsum is a good way to realize the comprehensive utilization of FGD gypsum. To obtainα-CSH with the satisfactory performances, a facile hydrothermal-aging pretreatment process for FGD gypsum raw materials was proposed, where FGD gypsum was firstly hydrothermally converted to α-CSH whiskers, and α-CSH whiskers were further hydrated to synthesize CaSO4·2H2O (CSD) by aging under the regulation of N,N'-methylenebisacrylamide (MBA). The effects of aging time, MBA addition, aging temperature, and pH on the morphology of the synthesized CSD were investigated. The synthesized CSD crystals exhibit highly uniform prismatic morphology with the length of ca 100μm and the whiteness of 91.56%. The regulation mechanism of MBA was also illustrated. The synthesized CSD crystals with prismatic morphology were further used as raw materials to synthesize the short columnar α-CSH. The absolute dry compressive strength of paste prepared from the short columnar α-CSH is 40.85 MPa, which reaches α40 strength grade.

Efficacy of borneol-gypsum in skin regeneration and pain control in toxic epidermal necrolysis:A case report

BACKGROUND Toxic epidermal necrolysis(TEN)is a life-threatening dermatological emergency mainly induced by drug hypersensitivity reactions.Standard management includes discontinuation of culprit drug and application of immunomodulatory therapy.However,mortality remains high due to complications like septic shock and multiorgan failures.Innovative approaches for skin care are crucial.This report introduces borneol-gypsum,a traditional Chinese drug but a novel dressing serving as an adjuvant of TEN therapy,might significantly improve skin conditions and patient outcomes in TEN.CASE SUMMARY A 38-year-old woman diagnosed with eosinophilic granulomatosis with polyangiitis experienced gangrenous complications and motor nerve involvement.After initial treatment of high-dose corticosteroids and cyclophosphamide,symptom of foot drop improved,absolute eosinophil counts decreased,while limb pain sustained.Duloxetine was added to alleviate her symptom.Subsequently,TEN developed.Additional topical application of borneol-gypsum dressing not only protected the skin lesions from infection but also significantly eased localized pain.This approach demonstrated its merit in TEN management by promoting skin healing and potentially reducing infection risks.CONCLUSION Borneol-gypsum dressing is a promising adjuvant that could significantly improve TEN management,skin regeneration,and patient comfort.

New Data on Coal, Gypsum, Iron and Silica Sand Deposits and Geochemical Exploration (Pakistan): Revision of 25 Years History of Dinosaur Discoveries from Pakistan

Discoveries of many coal seams at depths by drilling carried by Geological Survey of Pakistan in Sor Range and Harnai Gochina, extended the coal seams at depth which is challenge for mine owners to exploit feasibly. Bed to bed gypsum samplings (and their chemical analyses) of huge gypsum deposits from Sulaiman foldbelt is a base for industrialist and also planers to develop cement and gypsum industries to increase export and foreign exchange for the development of area and Pakistan. Low and high grade sedimentary iron deposits, silica sand and uranium host rocks and their extensions in Sulaiman and Kirthar foldbelts are presented. Anomalies of a few base metals arise as a result of geochemical exploration carried at part of Loralai District of Balochistan. Theropod dinosaurs were frequent in India, while Poripuchian titanosaurs (Sauropoda, Dinosauria) were frequent in Pakistan. Besides some ichnotaxa, many bone taxa such as 1 titanosauriform, 14 titanosaurian sauropod (including one new titanosaur), and 3 theropod dinosaurs are established from Pakistan. Among these 12 titanosaur species and 3 theropod species are named in about 10 km2 area of Vitakri dome and 2 titanosaur species are named in about a few hundred square meter area of Mari Bohri (Kachi Bohri) which is about 10 km westward from Vitakri dome. Pakistan is a unique country which discoverd 14 diversified titanosaurs in a short area and also in a short period (67 - 66 million years ago/Ma). About 400 bones found from a few meter thick upper part of upper shale horizon of latest Maastrichtian Vitakri Formation which is base for titanosaur taxa. Cranial material is in low fraction (but include significant diverse snouts), caudal vertebrae are prominent, the cervicals, dorsals and sacrals have significant numbers, forelimb and hind limb bones have balanced fraction. Humeri, femora and tibiae are most common. To know the position of Pakistani titanosaurs among titanosaurs and sauropods, there is a need to extend list of characters for phylogenetic analyses. This broad feature list should include main characters of titanosaurs from Pakistan and also from global world.

Environmental risk assessment of industrial byproduct gypsum utilized for flling abandoned mines

In response to the basic policy of green and low-carbon circular development to solve resource,environmental and ecological problems,gypsum is considered to be a flling material for mine backflling.To explore the potential risks of gypsum to the groundwater environment due to the backflling of abandoned mines,a sequential batch leaching experiment was carried out in this paper,which used three types of industrial waste gypsum,namely,phosphorus gypsum(PG),titanium gypsum(TG)and fue gas desulfurization gypsum(FGDG).COMSOL Multiphysics 5.4 software was used to simulate and solve the migration process of the leached metal elements in the mine foor when these three gypsum types were used as flling materials to observe the concentration distributions and difusion distances of the metal elements from these three gypsum types in the mine foor.The results show that(1)during repeated contact of the three types of industrial waste gypsum with the leaching medium,the pH levels changed,and the changes in pH afected the leaching patterns for the heavy metal elements in the gypsum.(2)Based on the concentrations of the metal elements that were leached from the three types of gypsum,it can be determined that these three types of gypsum are not classifed as hazardous solid wastes,but they cannot be ruled out with regard to their risk to the groundwater environment when they are used as mine flling materials.(3)When the three types of gypsum are used as flling materials,the concentration distributions of the metal elements and their migration distances all exhibit signifcant changes over time.The concentration distributions,difusion rates and migration distances of the metal elements from the diferent gypsum types are afected by their initial concentrations in the leachate.The maximum migration distances of Zn in the foor from the PG,FGDG and TG are 8.2,8.1 and 7.5 m,respectively.

Research on the Performance of Titanium Gypsum Concrete Based on Calcium-Silicon-Sulfur Ratio

Based on the high sulfur content in titanium gypsum,the concept of the calcium-silicon-sulfur(Ca/Si/S)ratio was proposed.The Ca/Si/S ratio of concrete was adjusted by changing the titanium gypsum,fly ash,and cement con-tent.The effects of different Ca/Si/S ratios on the mechanical properties,hydration products,and concrete micro-structure were investigated by nuclear magnetic resonance,uniaxial compression,and scanning electron microscopy.The result shows:(1)The compressive strength of concrete mixed with titanium gypsum increases first and then decreases with the Ca/Si/S ratio decrease.When the Ca/Si/S ratio is 1:0.85:0.10,the strength reaches the peak and is lower than the blank group.(2)The microstructure indicates the addition of titanium gypsum can effectively stimulate the activity of fly ash.Still,too much or too little titanium gypsum will hamper concrete strength development.(3)Titanium gypsum concrete’s nuclear magnetic resonance T2 spectrum has two characteristic peaks.With the Ca/Si/S ratio decreasing,the micropores in the concrete expand towards the macropores.The compressive strength is negatively correlated with the proportion of macropores and is positively correlated with the proportion of no-capillary pores.

Fluoride Ion Adsorption Effect and Adsorption Mechanism of Self-Supported Adsorbent Materials Based on Desulfurization Gypsum-Aluminate Cement

The adsorption method has the advantages of low cost,high efficiency,and environmental friendliness in treating fluorinated wastewater,and the adsorbent material is the key.This study combines the inherent anion-exchange adsorption properties of layered double hydroxides(LDHs).Self-supported porous adsorbent materials loaded with AFm and AFt were prepared from a composite cementitious system consisting of calcium aluminate cement(CAC)and flue gas desulfurization gypsum(FGDG)by chemical foaming technique.The mineral composition of the adsorbent material was characterized by X-ray diffraction(XRD)and Scanning electron microscopy(SEM).Through the static adsorption experiment,the adsorption effect of the mineral composition of the adsorbent on fluoride ions was deeply analyzed,and the adsorption mechanism was revealed.XRD and SEM showed that the main hydration phases of the composite cementitious system consisting of CAC and FGDG are AFm,AFt,AH_(3),and CaSO_(4)·2H_(2)O.FGDG accelerates the hydration process of CAC and inhibits the transformation of AFt to AFm.The AFt content increased,and the AFm content decreased or even disappeared as the amount of FGDG increased.Static adsorption experiment results showed that AFm and AFt in adsorbent materials could significantly enhance the adsorption of fluoride ions.The adsorption of F^(−)in aqueous solution by PAG tends more towards monolayer adsorption with a theoretical maximum capacity of 108.70 mg/g and is similar to the measured value of 112.77 mg/g.

Tensile and tear-type fracture toughness of gypsum material:Direct and indirect testing methods

In this context,four specimens,i.e.(i)circumferentially notched cylindrical torsion(CNCT),(ii)circum-ferentially notched cylindrical direct tension(CNCDT),(iii)edge notch disc bend(ENDB)and(iv)three-point bend beam(3PBB),were utilized to measure the modesⅠandⅢfracture toughness values of gypsum.While the CNCT specimen provides pure modeⅢloading in a direct manner,this pure mode condition is indirectly produced by the ENDB specimen.The ENDB specimen provided lower KⅢc and a non-coplanar(i.e.twisted)fracture surface compared with the CNCT specimen,which showed a planar modeⅢfracture surface.The ENDB specimen is also employed for conducting pure modeⅠ(with different crack depths)and mixed modeⅠ/Ⅲtests.KIc value was independent of the notch depth,and it was consistent with the RILEM and ASTM standard methods.But the modeⅢfracture results were highly sensitive to the notch depth.While the fracture resistance against modeⅢwas significantly lower than that of modeⅠ,the greater work of fracture under modeⅢwas noticeable.

Roles of gypsum/salt-bearing sequence in hydrocarbon accumulation and storage

Gypsum/salt beds are widely developed in petroliferous basins across the world.Most basins with gypsum/salt beds have been proven to host abundant hydrocarbon resources.Previous studies on the effects of gypsum/salt beds on hydrocarbon reservoirs primarily focused on their excellent sealing property as cap rocks.However,an increasing number of exploration discoveries have shown that gypsum/salt beds have the potential to promote the formation of high-quality source rocks and hydrocarbon reservoirs.Gypsum/salt beds influence the generation,preservation and accumulation of hydrocarbons.Based on the systematic analysis of the generation of hydrocarbons in global gypsum/saltbearing sequences,the study discussed the control of gypsum/salt beds on play elements,and explore the relationship between the development of gypsum/salt beds and global large-and medium-scale hydrocarbon reservoirs.Furthermore,we analyzed the correlation between typical gypsum/saltbearing sequences and their hydrocarbon generation potentials in China.In-depth analysis shows three patterns in terms of the spatial superimposition of gypsum/salt beds and source rocks,that is,postsalt pattern,inter-salt pattern and pre-salt pattern.Among others,the source rocks of the inter-salt pattern are widely developed in salt basins and of great potential for hydrocarbon exploration.

Evaluation of Cobalt Application Combined with Gypsum and Compost as a Regulator of Cabbage Plant Tolerance to Soil Salinity

In response to the global food crisis and the imperative to address soil degradation, the international agricultural policy is actively working to alleviate the adverse impacts of soil salinity. As part of this initiative, a field trial spanning two consecutive seasons (2019/20-2020/21) was conducted under saline conditions. The primary objective was to evaluate the influence of various compost sources, including vermicompost at a rate of 0.5 ton·fed-1 and plant residues compost at a rate of 5.0 ton·fed-1, as main plots. Subplots were established by applying agricultural gypsum, both in the presence and absence of gypsum requirements. Additionally, sub-subplots were created by externally applying cobalt at a rate of 10.0 mg·L-1, with one sub-subplot receiving foliar cobalt application and the other not. The trial sought to assess the growth performance, chemical composition, enzymatic antioxidants, yield, and quality of cabbage plants (Brassica oleracea var. capitata L.) cultivated in saline soil. According to the findings, cabbage plants exhibited the most favorable response in terms of plant height, chlorophyll content, carotene levels, leaf area, nitrogen (N), phosphorus (P), potassium (K), head yield, vitamin C, and total dissolved solids (TDS) when treated with vermicompost, followed by plant compost. Conversely, plants grown without compost exhibited the least improvement in performance. Cabbage treated with agricultural gypsum requirements showed better performance than those without gypsum amendment. Moreover, plants subjected to cobalt spray demonstrated the highest growth, yield, and quality parameters compared to those without cobalt foliar application. In contrast, the control group (plants without the studied treatments) displayed the highest levels of enzymatic antioxidants, specifically catalase and peroxidase. This indicates that soil salinity stress led to an increase in catalase and peroxidase production in cabbage plants as a defense against the harmful impact of reactive oxygen species (ROS) resulting from soil salinity stress. The applied treatments (compost, gypsum, and cobalt) led to a reduction in the cabbage plant’s inherent production of catalase and peroxidase. Generally, the combined treatment of vermicompost × gypsum requirements × cobalt proved effective in mitigating the detrimental effects of soil salinity on cabbage plants. These findings hold significance for farmers and policymakers aiming to enhance agricultural productivity in regions affected by soil salinity. Additionally, further research can explore the long-term effects of these treatments on soil health and crop sustainability.

Evolution of Biofilm and Its Effect on Microstructure of Mortar Surfaces in Simulated Seawater

To explore the role of biofilm formation on the corrosion of marine concrete structures, we investigated the attachment of biofilm on mortar surfaces in simulated seawater and the influence of biofilm on the microstructure of mortar surfaces. The results show that the evolution of biofilm on mortar surfaces in simulated seawater is closely related to the corrosion suffered by the mortar, and the process of biofilm attachment and shedding is continuous and cyclical. It is found that the specimens in the absence of biofilm attachment are more severely eroded internally by the corrosive medium in simulated seawater than those in the presence of biofilm attachment. For the specimens without biofilm attachment, after 60 days, gypsum forms,and after 120 days, the number of pores in the mortar is reduced. In contrast, for the specimens in the presence of biofilm attachment, gypsum could only be detected after 90 days, and fewer pores are filled. Therefore, the formation of biofilm could delay the invasion of the corrosive medium into the interior of mortar during the evolution of biofilm on mortar surfaces, mitigating the corrosion of mortars in seawater.

内蒙古露天煤矿排土场盐碱化土壤脱硫石膏改良研究

鉴于露天煤矿排土场存在土壤盐碱化、瘠薄化等问题,以煤矿区发电厂废弃物脱硫石膏(flue gas desulphurization gypsum,FGD gypsum)为土壤改良剂,以露天煤矿排土场土壤为盐碱化土壤基质,以内蒙古半干旱区本地植物斜茎黄芪(Astragalus adsurgens)为试验对象,设置两组试验——土壤柱淋溶试验和盆栽试验,探讨不同添加量(0、1、2、3、4 kg/m^(2))的脱硫石膏对排土场盐碱化土壤理化性质改良及土壤肥力提升的效果。结果发现:施加脱硫石膏后,两组试验中的土壤pH值均显著降低,表明脱硫石膏可通过中和作用有效降低土壤碱性;脱硫石膏添加量小于2 kg/m^(2)时,两组试验土壤中Na^(+)、HCO_(3)^(-)含量均随脱硫石膏添加量的增加而降低,说明适量施加脱硫石膏可以提高土壤离子交换作用的活跃程度,使大量的Na^(+)、HCO_(3)^(-)析出到土壤表面,从而降低土壤盐度,即脱硫石膏对盐碱化土壤的改良效果显著;脱硫石膏添加量小于2 kg/m^(2)时,两组试验土壤中速效氮(AN)、速效钾(AK)的含量均随脱硫石膏添加量的增加而显著增加,说明适量施加脱硫石膏可显著增加土壤有效营养元素含量,有利于缓解土壤瘠薄化,提升盐碱化土壤的肥力水平;脱硫石膏添加量为2 kg/m^(2)时,盆栽试验中斜茎黄芪的种子发芽率、株高、根长、生物量、根量及碳氮比均达到最大值,幼苗成活率接近最大值,表明脱硫石膏改良露天煤矿排土场盐碱化土壤效果显著,2 kg/m^(2)是脱硫石膏的最适宜添加量。

熟料含量对矿井充填胶固粉质量影响研究

为了减少对自然环境的破坏,保证充填体强度,节约充填胶固粉生产成本,对胶固粉配比进行优化试验。通过调整胶固粉中辅料与矿渣配比以及辅料中熟料与石膏的配比,测试不同熟料含量的充填体试块3,7,28 d抗压强度,研究熟料含量对胶固粉、充填体试块的性能影响。试验结果表明,适当降低熟料含量能提高胶固粉前期抗压强度,并对后期强度影响较小;当石膏含量提升至17.4%、16.8%,熟料含量降低至1.2%、1.8%时,充填试块的前期强度达到最优值;在相同养护龄期下,辅料与矿渣配比为20∶80,熟料掺量为1.8%的充填体试块整体抗压强度最优,可使胶固粉单位生产成本降低约3元。

Modification of FGD gypsum in hydrothermal mixed salt solution

A novel utilization way of the sludge from wet calcium-based flue gas desulfurization （FGD） processes has been developed in this paper. This study focused on the conversion of the FGD gypsum into α-hemihydrate calcium sulfate by a hydrothermal salt solution method at atmospheric pressure. Experimental study has been carried out in a batch reactor. Qualitative and quantitative analyses were made by DSC/TG thermal analysis, SEM, XRD, metalloscope and chemical analysis. The experimental results showed that the modification of FGD gypsum was controlled by the dissolution and recrystallization mechanisms. With the introduction of FGD gypsum the salt solution was supersaturated, then crystal nucleus of α-hemihydrate calcium sulfate were produced in the solution. With the submicroscopic structure of FGD gypsum crystal changed, the crystal nucleus grew up into α-hemihydrate calcium sulfate crystals. Thus ,the modification of FGD gypsum was fulfilled.

Experimental study on cracking behaviour of moulded gypsum containing two non-parallel overlapping flaws under uniaxial compression

Failure of rock mass that is subjected to compressive loads occurs from initiation, propagation, and linkage of new cracks from preexisting fissures. Our research investigates the cracking behaviour and coalescence process in a brittle material with two non-parallel overlapping flaws using a high-speed camera. The coalescence tensile crack and tensile wing cracks were the first cracks to occur from the preexisting flaws. The initiation stresses of the primary cracks at the two tips of each flaw were simultaneous and decreased with reduced flaw inclination angle. The following types of coalescence cracks were identified between the flaws: primary tensile coalescence crack, tensile crack linkage, shear crack linkage, mixed tensile-shear crack, and indirect crack coalescence. Coalescence through tensile linkage occurred mostly at pre-peak stress. In contrast, coalescence through shear or mixed tensile-shear cracks occurred at higher stress. Overall, this study indicates that the geometry of preexisting flaws affect crack initiation and coalescence behaviour.

Fertility and biochemical activity in sodic soils 17 years after reclamation with flue gas desulfurization gypsum

Previous studies have mainly focused on changes in soil physical and chemical properties to evaluate the reclamation of sodic soils using flue gas desulfurization(FGD)gypsum.However,information on the effects of this reclamation method on microbial-based indicators of soil quality is limited,particularly after many years of FGD gypsum application.This study aimed to investigate the long-term effects of FGD gypsum on soil organic carbon(SOC),nutrients,microbial biomass and enzyme activity.Data were collected from soils of three exchangeable sodium percentage(ESP)classes(i.e.,low-,middle-and hjgh-ESP classes of 6.1-20,20-30 and 30-78.4%,respectively)17 years after FGD gypsum treatment in Inner Mongolia,China.Averaged across the three ESP classes,FGD gypsum application increased the SOC contents at the 0-20 and 20-40-cm soil depths by 18 and 35%,respectively,and increased available potassium at the 0-20-cm soil depth by 51%compared with the no-gypsum controls.The microbial biomass carbon and microbial biomass nitrogen contents at the 20-40-cm soil depth increased by 69 and 194%,respectively,under FGD gypsum.Except in the high-ESP class,urease activities in the 0-40 cm soil profile were significantly higher in the FGD gypsum treatments than in the controls.A significant increase in alkaline phosphatase activity was concentrated in the 20-40 cm soil layer;few classes showed significant increases in catalase and invertase activities in the 0-20 cm soil layer.Pearson correlation analysis showed that increases in soil fertility and biological activity could be attributed to reductions in electrical conductivity,pH and ESP caused by FGD gypsum application.These results confirm that FGD gypsum application is a viable strategy for reclaiming sodic soils due to its positive effects on soil fertility and biochemistry and that it may contribute to soil ecosystem sustainability.

Calcium sulfate whisker prepared by flue gas desulfurization gypsum:A physical–chemical coupling production process

In this paper,the solid waste desulfurization gypsum produced by coal-fired power plants was used as a raw material to prepare calcium sulfate whiskers with high application prospects.Calcium sulfate whiskers with uniform morphology and high aspect ratio can be prepared by hydrothermal method in sulfuric acid solution.A new process of desulfurization gypsum activated by high-energy grinding to reduce the reaction temperature and sulfuric acid concentration was developed.Through the comparison of product morphology,the best grinding time was determined to be 3.5 h.The mechanism of desulfurization gypsum through physical–chemical coupling to reduce energy consumption was clarified.The activation of desulfurization gypsum by grinding and the acidic environment provided by the sulfuric acid solution made the calcium sulfate solution reached rapid saturation and accelerated the nucleation rate.By calculating the conversion and crystallization rate of calcium sulfate whiskers,it was found that there were obvious"autocatalytic"kinetic characteristics during the crystallization process.

Formation Mechanism and Microstructure of High-Strength Gypsum

The microstructure, phase composition, and thermal characteristics of various natural gypsums and the high-strength gypsum──the converted product of natural one are analysed.The formation mecbanism of high-strength gypsum is further discussed. It is found that the high-streugth gypsum is of hollow irregular hexagonal prism structure, which is almost free from tbe (010) and (100) cleavages and can form clustered fibrous crystals with high-strength.

Gypsum crystallization and potassium chloride regeneration by reaction of calcium chloride solution with potassium sulfate solution or solid

Gypsum crystallization along with the simultaneous regeneration of KCl was investigated by the reaction of CaCl2 solution with K2SO4.Well developed sheet structure gypsum crystals were produced when K2SO4 solution was added into the CaCl2 solution by slow titration or in multiple stages over 2-8 h followed by 2 h equilibration.In order to regenerate KCl solution as concentrated as possible,K2SO4 solid was added into the given CaCl2 solution instead of K2SO4 solution,obtaining gypsum crystals with almost the same quality by multistage addition with[SO4 2-]/[Ca 2+]molar ratio no larger than 0.8.However,impurity of K2SO4·CaSO4·H2O was detected by XRD and was further confirmed by SEM-EDS in the produced crystals when the[SO4 2-]/[Ca 2+] ratio increased to 1.1.It is proved that appearance of the double sulfate is attributed to the relatively high concentration of K2SO4.So,it is essential to properly control the[SO4 2-]/[Ca 2+]ratio and make sure[Ca 2+ ]in excess to suppress the solubility of CaSO4 even at the expense of low calcium removal rate.