Rapid and stable calcium-looping solar thermochemical energy storage via co-doping binary sulfate and Al–Mn–Fe oxides

Solar thermochemical energy storage based on calcium looping(CaL)process is a promising technology for next-generation concentrated solar power(CSP)systems.However,conventional calcium carbonate(CaCO_(3))pellets suffer from slow reaction kinetics,poor stability,and low solar absorptance.Here,we successfully realized high power density and highly stable solar thermochemical energy storage/release by synergistically accelerating energy storage/release via binary sulfate and promoting cycle stability,mechanical strength,and solar absorptance via Al–Mn–Fe oxides.The energy storage density of proposed CaCO_(3)pellets is still as high as 1455 kJ kg^(-1)with only a slight decay rate of 4.91%over 100 cycles,which is higher than that of state-of-the-art pellets in the literature,in stark contrast to 69.9%of pure CaCO_(3)pellets over 35 cycles.Compared with pure CaCO_(3),the energy storage power density or decomposition rate is improved by 120%due to lower activation energy and promotion of Ca^(2+)diffusion by binary sulfate.The energy release or carbonation rate rises by 10%because of high O^(2-)transport ability of molten binary sulfate.Benefiting from fast energy storage/release rate and high solar absorptance,thermochemical energy storage efficiency is enhanced by more than 50%under direct solar irradiation.This work paves the way for application of direct solar thermochemical energy storage techniques via achieving fast energy storage/release rate,high energy density,good cyclic stability,and high solar absorptance simultaneously.

Effects of Foliar Spraying of Magnesiumpotassium Sulfate Fertilizer on Absorption of Magnesium, Potassium and Calcium in Differentposition Tobacco Leaves

[Objective] ln the Mg-deficient （exchangeable Ca/Mg ratio ＆gt; 20） tobacco-growing areas in Qujing City of Yunnan Province, the ratio of Ca/Mg was adjusted by applying Mg fertilizer in soil and spraying Mg fertilizer on tobacco leaves. ln ad-dition, the effects of Mg fertilization on the absorption of K, Ca and Mg in flue-cured tobacco leaves were investigated, providing theoretical basis and production guidance for the balanced fertilization technology in the Mg-deficient flue-cured to-bacco-growing areas in Qujing City of Yunnan Province. [Method] The field plot test and randomized complete block design were adopted in this research. The group without Mg fertilization was treated as control. There were 3 treatment groups for foliar spraying of magnesium-potassium sulfate fertilizer and 2 treatment groups for soil application ＋ foliar spraying of magnesium-potassium sulfate fertilizer. The tobac-co roots, stems, lower leaves, middle leaves and upper leaves were dried and weighed. They were grinded for the determination of K, Ca and Mg content. The total K, Ca and Mg content in upper （B2F）, middle （C3F） and lower （X2F） flue-cured tobacco leaves in each plot was measured. [Result] The foliar spraying and soil application ＋ foliar spraying al increased the absorption of Mg and K in middle and lower tobacco leaves and the absorption of Ca in lower tobacco leaves, but de-creased the absorption of Mg, K and Ca in upper leaves and the absorption of Ca in middle leaves. Among the positions, the accumulated distribution of Mg, K and Ca ranked as middle leaves ＆gt; lower leaves ＆gt; upper leaves. With the application of Mg fertilizer, the Ca/Mg ratio and K/Mg ratio al decreased in middle and upper to-bacco leaves; while the Ca/Mg ratio increased in the lower tobacco leaves, and the K/Mg ratio showed no significant difference among treatment groups. [Conclusion] The foliar spraying and soil application ＋ foliar spraying of magnesium-potassium sulfate fertilizer affected the Ca/Mg ratio and K/Mg ratio in tobacco leaves mainly through affecting the absorption of Mg.

Exploration of As(Ⅲ)/As(V) Uptake from Aqueous Solution by Synthesized Calcium Sulfate Whisker

Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction between modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As(Ⅲ)/As(V) from aqueous solutions by calcium sulfate whisker(CSW, dihydrate or anhydrite) synthesized through a cooling recrystallization method was explored. A series of batch experiments were conducted to examine the effect of p H, reaction time, whisker dosage, and initial As concentration. X-ray diffraction(XRD) and scanning electron microscopy(SEM) were used to characterize the samples prepared. The results showed that p H of the aqueous solution was an important parameter for As(Ⅲ)/As(V) uptake, and an excellent removal efficiency could be achieved under strongly alkaline condition. The data from batch experiments for reaction of As(V) with calcium sulfate dihydrate whisker(CSDW) and calcium sulfate anhydrous whisker(CSAW) were well described with extended Langmuir EXT1 model, from which theoretic maximum adsorption capacity of 46.57 mg As(V)·(g CSDW)-1and 39.18 mg As(V)·(g CSAW)-1were obtained. Some calcium arsenate solids products,such as Ca As O3(OH)(weilite, syn), Ca3(As O4)2(calcium arsenate), Ca O–As2O5, Ca–As–O, Ca5(As O4)3OH·x H2O(calcium arsenate hydroxide hydrate), and Ca H(As O4)·2H2O(hydrogen calcium arsenic oxide hydrate), were detected at p H = 12.5 through XRD analysis. This indicates that the interaction mechanism between As(V) and CSW is a complex adsorption process combined with surface dissolution and chemical precipitation.

Effects of Magnesium and Ferric Ions on Crystallization of Calcium Sulfate Dihydrate Under the Simulated Conditions of Wet Flue-gas Desulfurization

The influences of magnesium and ferric ions in their different ratios on the rate of gypsum crystallization were studied under the conditions similar to those of wet flue-gas desulfurization（WFGD）. The results show that addition of both Mg^2＋ and Fe^3＋ increased induction time and decreased the growth efficiency up to 50% compared with the baseline（without impurities） depending on the concentration and the type of impurity. The effects of Mg^2＋ and Fe^3＋ on the surface energy and the rate of nucleation were estimated by employing the classical nucleation theory. The surface energy decreased by 8% and 14% with the addition of 0.02 mol/L magnesium or ferric ions, respectively, compared to the baseline. Mg^2＋ and Fe^3＋ made the growth rate of the （020）, （021） and （040） faces of gypsum crystal a much greater reduction, which leads to the formation of needle crystals compared to the baseline which favors the formation of plate or flakes. Furthermore, an edge detection program was developed to quantify the effects of impurities on the filtration rate of gypsum product. The results show that the inhibition efficiency of the presence of 0.02 mol/L Mg^2＋ and Fe^3＋ on the filtration rate of gypsum crystal ranges from 22% to 39%.

Preparation, Characterization, and Formation Mechanism of Calcium Sulfate Hemihydrate Whiskers

Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials’ ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio(L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.

Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement(CSA), ordinary Portland cement(OPC), and calcium sulfate(CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength(UCS), splitting tensile strength(STS), and volume change of fiber-added expansive mixtures were determined at different time periods(i.e. the strengths on the 28 th day, and the volume changes on the 1 st, 7 th, 14 th, 21 st, and 28 th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.

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.

Thermodynamic Stability of Sulfate Ions on Calcium Aluminosilicate Hydrate Microstructure

The thermodynamic stability of sulfate ions on synthesized calcium aluminosilicate hydrate（C-A-S-H） microstructure with different Ca/Si ratios and Al/Si ratios was investigated by XRD, SEM-EDS, 29 Si and 27 Al nuclear magnetic resonance（NMR） and thermodynamic modeling. The results indicate that sulfate attack leads to both decalcification and dealumination for C-A-S-H gels, and the amount of corrosion products（gypsum and ettringite） decreased gradually with decreasing Ca/Si ratios of C-A-S-H. Sulfate ions can also promote the polymerization degree of C-A-S-H gels, improving its resistance to sulfate attack. Moreover, the 4-coordination aluminum（Al[4]） in C-A-S-H, 5-coordination aluminum（Al[5]）, 6-ccordination aluminum（Al[6]） in TAH（third aluminum hydrate） and Al[6] in monosulfate or C-A-H（calcium aluminate hydrate） can be transformed into Al[6] in ettringite by sulfate attack. Furthermore, through thermodynamic calculation, the decrease of Ca/Si ratios and increase of Al/Si ratios can improve the thermodynamic stability of C-A-S-H gels under sulfate attack, which agrees well with the experiment results.

Hydrothermal synthesis of calcium sulfate whisker from flue gas desulfurization gypsum

Plenty of flue gas desulfurization(FGD) gypsum generated from coal-fired power plants for sulfur dioxide sequestration caused many environmental issues. Preparing calcium sulfate whisker(CSW) from FGD gypsum by hydrothermal synthesis is considered to be a promising approach to solve this troublesome problem and utilize calcium sulfate in a high-value-added way. The effects of particle size of FGD gypsum, slurry concentration,and additives on CSW were investigated in this work. The results indicated that fine particle size of FGD gypsum and moderately high slurry concentration were beneficial for crystal nucleation and growth. Three additives of magnesium chloride, citric acid, and sodium dodecyl benzene sulfonate(SDBS) were employed in this study. It was found that mean length and aspect ratio of CSW were both decreased by the usage of magnesium chloride,while a small quantity of citric acid or SDBS could improve the CSW morphology. When multi-additives of citric acid-SDBS were employed, the mean length and aspect ratio increased more than 20%. Moreover, surface morphology of CSW went better, and the particle size and crystal shape became more uniform.

Removal and utilization of calcite existed in scheelite by preparation of calcium sulfate whiskers

In order to eliminate the effect of calcite associated with scheelite on the scheelite flotation, hydrochloric acid was used to dissolve the calcite, and the soaking solution was used to prepare CaSO_4 whiskers by hydrothermal reaction with sulfuric acid at ambient pressure. First, the condition experiments of preparing CaSO_4 whiskers by using CaCl_2 and H_2SO_4 were carried out to optimize reaction parameters of the crystallization process. The optimal conditions were: at 102 ℃ reaction temperature, 0,5 mol/L reactant concentration and 60 min reaction time. Then based on the condition experiments and considering keeping acid concentration stable for achieving HCl recycling, Calcium sulfate whiskers with the average diameter of 1.41 μm and the average aspect ratio of 109 were prepared by the soaking solution after evaporating to half of its volume and 1.0 mol/L H_2SO_4 at 102 ℃ for 60 min: After ion exchange processing,the filtrate could be used as HCl in the process of HCl dissolution.

Comparative study on simultaneous removal of calcium and sulfate ions from flotation recycling water by aluminum hydroxide

Due to the environmental policies and economic reasons,the water used in some flotation operations of complex sulfide ores is recirculated,causing the ion concentration of some species to increase over time,affecting the flotation of the minerals of interest.In this work,an experimental and thermodynamic analysis of the synthetic solutions was presented with a high content of calcium and sulfate ions.The study focused on evaluating the use of two aluminum compounds for the precipitation of Ca^(2+)and SO_(4)^(2−)in the form of ettringite.The amorphous aluminum hydroxide was found to be more efficient than the crystalline one,giving rise to 83%calcium and 91%sulfate removal.The XRD analysis of the solids showed the main reaction product of ettringite,accompanied by small amounts of calcite,due to the absorption of atmospheric carbon dioxide.The final solution after the chemical treatment showed residual calcium and sulfate concentrations below 200 mg/L.Finally,the kinetics of calcium removal appeared to correspond to a second order reaction with respect to calcium concentration,with an apparent activation energy of 53.48 kJ/mol,which may suggest that the ettringite precipitation process is governed by the chemical reaction.

Inhibition of the Crystal Growth and Aggregation of Calcium Oxalate by Algae Sulfated Polysaccharide In-vitro

The influence of sulfated polysaccharide （SPS） isolated from marine algae Sargassum fusiforme on the morphology and phase compositions of urinary crystal calcium oxalate was investigated in vitro by means of scanning electron microscopy and X-ray diffraction. SPS maybe is a potential inhibitor to CaOxa urinary stones by inhibiting the growth of calcium oxalate monohydrate （COM）, preventing the aggregation of COM, and inducing the formation of calcium oxalate dihydrate （COD） crystals.

Hollow calcium carbonate microspheres prepared in the presence of polyoxyethylene(20) sorbitan monolaurate and sodium dodecyl sulfate

Hollow calcium carbonate （ CaCO3 ） microspheres were prepared in aqueous solution with the presence of polyoxyethylene （20） sorbitan monolaurate （ Tween20 ） and sodium dodecyl sulfate （SDS）. The microspheres were characterized with X-ray diffraction （XRD） , scanning electron microscopy （SEM） and transmission electron microscope （TEM）. The X-ray diffraction data showed that the hollow CaCO3 microsphere consisted of calcite crystals. The influence of Tween20 and SDS concentrations on the morphology of CaCO3 crystals was investigated. The results suggested that the ＂core-shell model＂ of Tween20/SDS micelle aggregated as templates, which could control the growth of hollow CaCO3 microspheres. The interaction between mixed surfactants and calcium ions played a critical role in organizing calcium carbonate in microscopic level.

Thermodynamic and experimental studies on removal of calcium and sulfate ions from recycling water of complex sulfide flotation operations

A chemical method for removing calcium sulfate saturated solutions(0.016 mol/L CaSO_(4))using barium chloride(BaCl_(2)∙2H_(2)O)and sodium phosphate(Na_(3)PO_(4))was experimentally studied.The main interest is to remove these ions from the solution through the precipitation of two solid species:sulfate(SO_(4)^(2−))as barite(BaSO4),and calcium(Ca^(2+))as hydroxyapatite(Ca_(5)(PO_(4))_(3)OH).Additionally,a solid/liquid separation method(i.e.,flotation)was explored,using oleic acid and dodecylamine as collectors.The results show that,the chemical treatment of saturated solutions at 60℃,pH 11.5 and using 3.9 g/L BaCl_(2)·2H_(2)O and 1.6 g/L Na_(3)PO_(4),promotes the precipitation of barium sulfate and calcium-deficient hydroxyapatite(Ca_(10−x)(HPO_(4))_(x)(PO_(4))_(6−x)(OH)_(2−x)),with residual concentrations of calcium and sulfate below 0.10 and 5 mg/L,respectively.The residual calcium concentration increases to 28 mg/L when using the same amount of reactants,at temperature and pH values below those quoted.The highest flotation recovery of hydroxyapatite with oleic acid at pH 9.5 was about 80%,while that of barite floated with dodecylamine at pH 6.5 was about 90%.

Effect of Compounding of Sodium Tripolyphosphate and Super Plasticizers on the Hydration of α-calcium Sulfate Hemihydrate

The inhibition and its mechanism of sodium tripolyphosphate （STP） composited with super plasticizers （SPs） on hydration of α-calcium sulfate hemihydrate were studied by setting time, strength, hydration heat, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, electronic probe micro analysis （EPMA）, scanning electron microscopy （SEM） and differential scanning calorimeter （DSC） measurements. The experimental results show that compared with STP addition, compositing STP with polycarboxylate （PC） plasticizer, the final setting time is prolonged from 0.5h to 2hs. While formulating STP with naphthalene-based plasticizer （NAP） or sulfonate melamine formaldehyde plasticizer （SMF）, the final setting time is reduced to quarter of an hour. Similar changes can also be found in the rate of exothermic hydration and hydration degree. Formulating STP with suitable addition of PC can enhance the strength, while compositing STP and NAP or SMF weakens the strength. Besides, adding STP or STP and SMF, obvious movement （more than 1ev） of binding energy of Ca2p1/2 and Ca2p3/2 is detected. Compared with STP addition, content of the characteristic element （P） of STP is cut down form 1.1% to 0.49% by compositing STP with SMF. Furthermore, as hydration age increases, hydration inhibition in the presence of admixtures weakens and even disappears within 56 h.

Preparation of High Percentage α-Calcium Sulfate Hemihydrate via a Hydrothermal Method

α-calcium sulfate hemihydrate (α-HH) is known to be suitable for application as bone void filler. High percentage of α-HH is obviously needed for medical applications, especially for implantation. Three commercially available calcium sulfate dihydrates (DH, CaSO4·2H2O) with different sizes and surface morphologies were used as starting materials to synthesize high percentage α-HH via a hydrothermal method. The median particle sizes of the three types of DH were 946.7 μm, 162.4 μm and 62.4 μm, respectively. They were named as DH-L, DH-M and DH-S in this paper. The particle size distribution, morphology and phase composition of the raw materials were evaluated before synthesis. SEM results revealed that DH-L consisted of irregular large particles, while DH-M and DH-S were composed of plate-like particles with some small ones. High percentage HH can be obtained with proper synthesis parameters by hydrothermal method, specifically, 105 °C/90 min for DH-L (achieving 98.8% HH), 105°C/30 min for DH-M (achieving 96.7% HH) and 100°C/45 min for DH-S (achieving 98.4% HH). All the synthesized HH were hexagonal columns, demonstrating that they were α-phase HH. The particle size and morphology of starting material (DH) have significant influences on not only the rate of phase transition but also the morphology of the synthesized α-HH. Calcium sulfate dihydrate cements were prepared by the synthesized α-HH. The highest compressive strength of calcium sulfate dihydrate cement was 17.2 MPa. The results show that the preparation of high percentage α-HH is feasible via a hydrothermal method and the process can be further scaled up to industrial scale production.

The Effect of Additives on Calcium Sulfate Dihydrate Crystallization Kinetics in Gypsum Type Brine System

1 Introduction There exist calcium and sulfate ions outside sodium chloride in solution mining for calcium sulfate brine.The calcium and sulfate ions not only affect the purity of the vacuum salt products,but also increase the scaling of vacuum evaporation tanks and brine reusing pipes.Additives have certain impacts on the crystallization dynamics(Randolph et al.,1971).The crystallization

Crystallization Process of Calcium Sulfate Dihydrate in Gypsum Type Brine System

1 Introduction Calcium sulfate deposition is one of the most important and serious problems faced by heat transfer equipment during operation(Pavlos et al.,1999;Liu et al.,1996).The crystallization of calcium sulfate is known as a major

Research on Preparation and Influencing Fctors of High Calcium High Sulfate Ash to Autoclaved Aerated Concrete

In this paper, a high calcium high sulfate ash as the main material, adding fly ash, lime, cement, gypsum and some modifiers to prepare autoclaved aerated concrete. The products complies with the technical requirements of GB/T11968-2006. This paper also studies the influence of the physical methods and water ratio on autoclaved aerated concrete by high calcium high sulfate ash aerated concrete. The best ratio of water and Grinding time were found in practice study.

Comparison of Fusion Rates between Autologous Iliac Bone Graft and Calcium Sulfate with Laminectomy Bone Chips in Multilevel Posterolateral Spine Fusion

Multilevel lumbar fusion usually requires a large quantity of iliac crest bone graft but the supply is usually insufficient, so an alternative bone graft substitute for autograft is needed. This prospective study investigated the efficacy of calcium sulfate by comparing the fusion rates between the experimental material (calcium sulfate pellets with bone chips from laminectomy) and autologous iliac bone graft in long segment (three-or four-level) lumbar and lumbosacral posterolateral fusion. Forty-five patients with degenerative scoliosis or spondylolisthesis received multilevel spine fusion and decompression. The experimental material of calcium sulfate pellets with decompression bone chips was placed on the experimental side and the iliac crest bone graft was placed on the control side. The fusion status was assessed radiographically at three-month intervals, and solid fusion was defined as a clear continuous intertransverse bony bridge at all levels. The average follow-up period was 34.4 months. Twenty-nine (64.4%) patients showed solid fusion on the experimental side and 39 (86.7%) patients on the control side. The overall fusion rate was 86.7%. A statistically significant relation was found between the two sides with the Kappa coefficient of agreement of 0.436. Compared to the control side, the fusion rate of experimental side is significantly reduced (p = 0.014). The fusion ability of autograft is higher than the experimental material in multilevel lumbar posterolateral fusion. However, the overall fusion rate of calcium sulfate pellets is improved, compared with previously reported rates, which suggested that such material may be considered as an acceptable bone graft extender.