The growth of gypsum crystals on barite and calcite

The kinetics of crystallization of calcium sulfate dihydrate on barite and calcite seed materials have been studied at 25°C. The grown solid phases have also been investigated by scanning electron microscopy, specific surface area measurements, and by x-ray diffraction.     

脱硫石膏制备碳酸钙晶体的生长成核过程研究

以脱硫石膏资源化循环利用为目的,碳酸铵、添加剂(二水合柠檬酸三钠、硫酸、十六烷基溴化铵)为原料,在程序搅拌控制条件下制备碳酸钙晶体,利用XRD和微机差热天平对产物的组成、晶型和热稳定性进行分析。添加二水合柠檬酸三钠和十六烷基溴化铵得到的是单一的方解石型碳酸钙;而添加硫酸得到的是方解石、球霰石和文石3种晶型共存的碳酸钙晶体。最佳的程序搅拌方案是实验开始前40 min以450 r/min的速率快速搅拌,提高扩散速率和化学反应速率;然后以350 r/min速率搅拌40 min,为晶型生长成核做准备;最后40 min以250 r/min速率搅拌,促进完整碳酸钙晶型的形成。     

Impact attrition of sodium chloride crystals

Impact attrition of cubic NaCl particles has been studied. The particles are produced by cleaving melt-grown ingots to about 1 mm in size, and standardised by chemical polishing and annealing. They are accelerated in an air eductor, and are impacted onto a target in the velocity range 15 – 30 ms⁻¹. The low velocity impact causes extensive plastic deformation on the impacting corner and removal of thin platelets from the faces adjacent to it. The process may be treated as indentation fracture: the ensuing 〈110〉 cracks resemble closely those produced by quasi-static indentation fracture and can be interpreted in the same way. Formation of platelets is attributed to sub-surface lateral cracks, which follow a pattern similar to impact damage of large targets.     

Tricalcium aluminate hydration in the presence of lime,gypsum or sodium sulfate

The influence of Ca(OH)₂, CaSO₄·2H₂O and Na₂SO₄ on the C₃A hydration was examined in order to study the retardation mechanism of C₃A hydration caused by lime and/or gypsum additions. When C₃A hydrates in the presence of gypsum, the results do not confirm the retardation mechanism based on sulfate ions adsorption or C₄AH_x impervious coating. They substantially confirm the mechanism based on ettringite crystals coating C₃A grains. In the absence of gypsum C₃A hydration is retarded by C₄AH_x formation coating C₃A grains.     

The mechanical breakdown of sodium chloride crystals

Experiments are described of deformation and fracture of melt grown rocksalt crystals (in the form of cubes) under primarily compressive conditions. Specifically these are(i) Indentation, modelling conditions of local contact such as occurs during attrition.(ii) Uniaxial compression, a situation relevant to crushing.It is shown that in all cases extensive plastic flow precedes the initiation of fracture and governs the path of subsequent cracking, which frequently follows irregular surfaces rather than cleavage planes. In experiments of type (ii), fracture is initiated at the compression plates, but cracks do not propagate to final failure: fragmentation occurs progressively from the edges of a plastically deforming core. These effects are discussed in terms of sliding friction at the platens.     

Salts in gypsum and calcined gypsum

Chloride in a number of samples of gypsum and calcined gypsum has been determined by Surkevicius's method and by nephelometry. Results from the former method are confirmed. Sodium was determined by atomic absorption spectroscopy and the content found to be considerably greater than the equivalent of the chloride. Two of the samples appeared to contain close to 0.1% of Na₂SO₄ and it is suggested that standards for the quality of gypsum should specify the determination of sodium as well as that of chloride.     

高钾钠磷石膏生产纸面石膏板工艺控制

用含钾钠高的磷石膏生产纸面石膏板时出现不粘纸现象。通过采用自主开发的抑制剂,使钾钠生成溶解度小的难溶盐;并选用合适的生产工艺,调节一次脱水、二次脱水温度,抑制剂加量等有效的控制方法,实现了用含钾钠高的磷石膏生产出合格纸面石膏板。     

Binding of14C-phosphatidylcholine to sodium chloride crystals

¹⁴C-Phosphatidylcholine in benzene was found to bind to sodium chloride crystals. The magnitude of this binding was greatest when the crystal size was the smallest, namely when the crystals were prepared from frozen and lyophilized aqueous solution.     

层状结晶二硅酸钠的合成与改性

以工业水玻璃和氢氧化钠为原料制得层状结晶二硅酸钠并进行改性,以提高其水热稳定性。利用FT-IR,WXRD和SEM对层状结晶二硅酸钠的结构和形态进行表征,并对其基本性能进行了研究,探讨了煅烧温度、煅烧时间、改性剂种类和加入量对该层状结晶二硅酸钠性能的影响。最佳工艺条件:煅烧温度为725℃、煅烧时间为30 min。层状结晶二硅酸钠的钙镁交换容量分别为363 mg/g和434 mg/g,抗酸能力为9.32 mmol/g。改性的效果以采用十六烷基三甲基溴化铵(CTMAB)和铝盐复合改性为最佳,其最佳加入量分别为层硅理论产量的1%和2%(以上均为质量分数),经复合改性后明显提高了产品的水热稳定性。     

Impact of gypsum on flotation of scheelite and fluorite using sodium oleate as collector

ABSTRACT

In this study, effect of calcium and gypsum on scheelite and fluorite was investigated using sodium oleate as collector. Micro-flotation and contact angle results showed that the adsorption of calcium could inhibit the hydrophobicity of scheelite and fluorite. Moreover, sulfate could enhance the inhibition. FT-IR results showed that calcium could be priori precipitated into calcium oleate and adsorb on mineral surface. The adsorption of calcium could increase the scheelite potential to IEP, while it showed limited effect on fluorite potential. However, the interaction of calcium on scheelite and fluorite in gypsum solution was more complex than that in calcium solution.     

晶态层状结构二硅酸钠机理性能研究

阐述了新型助洗剂－晶态层状结构二硅酸钠的物化性能与特征,它具有室温快速软化水能力、碱性缓冲能力、去污能力、抗再沉积能力等功能特点,它是粉状洗涤剂中功能好、不污染环境、价格低廉的新一代助洗剂。     

Properties and antimicrobial activities of starch–sodium alginate composite films incorporated with sodium dehydroacetate or rosemary extract

Antimicrobial films were prepared with oxidized and acetylated corn starch–sodium alginate by incorporating sodium dehydroacetate or rosemary extract. Films incorporated with sodium dehydroacetate ≥ 0.1% or rosemary extract ≥ 0.3% had an anti‐Escherichia coli effect. Aspergillus niger could be effectively inhibited by the incorporation of sodium dehydroacetate ≥ 0.3%. Rosemary extract showed no inhibitory effect on Aspergillus niger. Sodium dehydroacetate and rosemary extract reduced the tensile strength and elongation at break, and increased the water vapor permeability of the films. Sodium dehydroacetate made the films more greenish–yellow with the increase of sodium dehydroacetate concentration. The color of the films became darker and more reddish–yellow as rosemary extract was increased. Fourier transform infrared (FTIR) spectra analysis revealed that sodium dehydroacetate and rosemary extract reduced starch crystallinity. The surface of the films became rougher as a result of an addition of sodium dehydroacetate and rosemary extract. These findings had potential applications in prolonging food shelf life based on different needs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

石膏及石膏制品中锶含量测定方法的研究

锶是石膏及石膏制品中常见的杂质元素,锶的同位素中锶85、锶89和锶90等都具有放射性且半衰期较长,对人体有较大危害。传统的测定锶含量方法不适宜石膏及石膏制品中锶含量的测定;采用电感耦合等离子原子发射光谱(ICP-AES)法来测定石膏及制品中锶含量,具有快速、准确、重现性好的特点,符合检验检疫行业要求。     

Factors affecting the solubility of gypsum: II. Effect of sodium hydroxide under various conditions

A quantitative estimation of the effect of sodium hydroxide on the solubility of gypsum in the presence of lime at 30, 60 and 100°C is given. At 30°C the solubility of gypsum was promoted by a 0.0146M solution of sodium hydroxide which at a concentration as low as 0.0029M raised the sulphate ion concentration at 60 and 100°C. At the three temperatures studied the solubility curves of gypsum first rose slowly then more rapidly around 0.02 to 0.08M NaOH. In the range 0.08 to 1M NaOH solution, a constant value of the sulphate ion concentration was measured which corresponded to the complete dissolution of gypsum, even in the presence of lime. The solubility curve of gypsum was lowered slightly at 30°C in a supersaturated lime solution and was depressed by concentrations lower than or equal to 0.02M NaOH solutions at 60 and 100°C.     

Estimation of number of surface crystals on sodium fluoride mother crystal in crystallization

A simple model was developed to explain the surface crystals found on the clear mother crystal face. The surface crystals on the mother crystal in the reaction crystallization of sodium were mathematically estimated by using a model based on two-dimensional secondary nucleation and two-step growth mechanisms. The model predicted that the surface crystals found on the mother crystal would be sensitive to the reactant concentration and agitation speed due to their influence on the interfacial supersaturation in the crystal growth. As the bulk supersaturation increased and the molecular transport was facilitated, the number of surface crystals on the mother crystal also increased, because the interfacial supersaturation built up on the mother crystal surface was enhanced. The prediction of the number of the surface crystals on the mother crystal appeared to be consistently comparable with experimental results.     

Use of gypsum/brucite mixed precipitate instead of gypsum in Portland cement

The possibility of replacing the natural gypsum used in cement production by a chemical precipitate consisting of gypsum (CaSO₄ ·2H₂O) and brucite (Mg(OH)₂), was investigated. This precipitate is a by‐product of a new hydrometallurgical process, which was developed in order to treat economically low‐grade nickel oxide ores. More specifically, it is obtained by hydrolytic precipitation of magnesium at temperatures not exceeding 80 °C, from sulfate solutions which result from heap leaching of nickel oxide ores with dilute sulfuric acid at ambient temperature, using calcium hydroxide as a neutralizing agent. The mixture generally consists of 20–30% non‐fibrous magnesium hydroxide, 60–75% gypsum and any excess of calcium hydroxide, depending on the precipitation conditions. In the present work, a mixture was produced by hydrolytic precipitation at 25 °C, using 1.1 times the stoichiometric quantity of Ca(OH)₂ required to precipitate all of the magnesium. The possibility of using the above precipitate as a substitute for gypsum in cement was examined by testing four different cement mixtures, one reference sample, containing 4.5% gypsum and 0.5% anhydrite ((PC)_Ref) and another three with 4.1%, 5.2% and 6.3% of gypsum/brucite mixed precipitate ((PC)_B/G), in the place of gypsum. All samples were tested by determining the grindability, setting time, expansion and compressive strength. The results of the physico‐mechanical tests showed that the replacement of natural gypsum by the above precipitate did not affect negatively the quality of the produced cements. Copyright © 2005 Society of Chemical Industry     

脱硫石膏完全代替天然石膏作水泥缓凝剂的应用经验

<正>我公司是年生产能力20万t的水泥粉磨站,有2条由MB2275管磨机和NHX600高效转子式选粉机组成的闭路水泥生产线。2008年3月份开始,我公司     

Synthesis of large plate-like gypsum dihydrate from waste gypsum board

This paper reports the synthesis of large plate-like gypsum (calcium sulfate) dihydrate generated from waste gypsum board via a wet process. Gypsum hemihydrate was formed by dehydrating waste gypsum board in a sodium sulfate solution at 100 °C for 1 h to form needle-like crystals. The large gypsum dihydrate was formed by lowering the temperature of the gypsum hemihydrate suspension below 80 °C. The large plate-like gypsum dihydrate was obtained by adding seed crystals to a suspension cooled at 80 °C. When 40 μm seed crystals were added at 0.5 mass%, the large plate-like gypsum dihydrate crystals obtained from waste gypsum board had average dimensions of 250 μm length × 100 μm width × 35 μm thickness.     

脱硫石膏制备半水石膏晶须的研究

脱硫石膏是电厂湿法烟气脱硫的固体废弃物,不仅造成资源浪费,还会对环境产生污染。为提高脱硫石膏的附加值,以脱硫石膏为原料,采用盐溶液法制备半水石膏晶须,研究了氯化钠浓度、温度、液固比、pH对转化率的影响,并研究了柠檬酸的含量对形貌的影响。采用傅立叶变换红外光谱仪（FTIR）、X射线衍射仪（XRD）、扫描电子显微镜（SEM）等对制备的半水石膏晶须做了表征,并研究了柠檬酸对形貌影响的机理。研究表明：当氯化钠质量分数为20%、反应温度为100 ℃、液固比为5∶1、反应时间为2 h、柠檬酸的质量分数为0.25% 时,可制备出长度为50～100 μm、长径比为（30～50）∶1的半水石膏晶须。