煤矸石和硅藻土对熔模石膏型性能的影响

向石膏中加入不同的耐火填料,在同一水膏比下,分别测试分析石膏浆料的流动性、凝结时间,石膏铸粉的湿强度、焙烧后的强度、线收缩率和显微组织。结果表明,煤矸石和硅藻土同时加入石膏粉中,焙烧后的石膏晶粒间搭接良好、紧密度高、铸型强度高。在煤矸石加入量为20%且硅藻土加入量为10%时,石膏浆料的流动直径为90mm,初凝时间为7min,终凝时间为17min,湿抗折强度为2.02MPa,抗压强度为2.3MPa,焙烧后的抗折强度为0.458MPa,抗压强度为1.07MPa,线收缩率为0.320%。     

Equilibrium moisture content of earth bricks biocomposites stabilized with cement and gypsum

In recent years, energy efficient and ecologically friendly buildings have been important in the housing and construction sector. One of the major barriers to producing good and useful products is the lack of detailed information about natural materials, in particular their moisture related properties, as these materials are hygroscopic and sensitive to moisture. This research aimed to determine the equilibrium moisture content of earth block materials, as an extremely important characteristic variable for all physical simulations. Earth bricks with different compositions were fabricated from cohesive soil, cement, and gypsum combined with two kinds of natural fibers. Wheat and barley straw were used as reinforcing fibers and materials were treated at various temperatures (10–40 °C) and relative humidity (33–95%). The moisture content was considered in dynamic equilibrium with the environmental conditions and the effects of relative humidity and temperature were investigated. The effect of relative humidity was observed more pronounced than that of temperature. The test results are discussed with reference to the relevance of the earth bricks as an ecologically friendly building material that is directly associated with the moisture related properties of buildings. The results also showed significant improvement in the durability.     

A hydration study of various calcium sulfoaluminate cements

The present work studies the hydration process and microstructural features of five calcium sulfoaluminate (CSA) cements and a ternary mixture including also ordinary Portland cement (OPC). The pastes were studied with simultaneous differential thermal-thermogravimetric (DTA-TG) analysis, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and expansion/shrinkage tests. The DTA-TG analysis confirmed the role of the hydration reactions involving the main CSA clinker constituent, tetracalcium trialuminate sulfate, which produced (i) ettringite when combined with lime and calcium sulfate, (ii) ettringite and aluminum hydroxide in the presence of calcium sulfate alone, and (iii) monosulfate and aluminum hydroxide in the absence of both lime and calcium sulfate. The MIP and SEM were able to discriminate between expansive (ternary mixture and CSA cement containing 50% gypsum) and non-expansive cements. Expansive cement pastes had (i) a nearly unimodal pore size distribution shifted toward higher radii and (ii) ettringite crystals smaller in size during the first day of curing. In a SEM image of a hardened paste of the CSA cement containing 50% gypsum, a stellate ettringite cluster was observed.     

Impact of gypsum supersaturated process water on the interactions between silica and zinc sulphide minerals

Flotation recovery and selectivity problems have been reported in the flotation of fine sulphide minerals in gypsum supersaturated process water. In this study, the effect of gypsum supersaturated solution on the interactions between silica and sphalerite (ZnS) minerals was examined by observing deposition behaviour of silica nanoparticles on sphalerite surface using a quartz crystal microbalance with dissipation (QCM-D). Significant deposition of silica nanoparticles on ZnS coated sensor surface was observed in the gypsum supersaturated solution, indicating consequential slime coating of silica fines on sphalerite mineral surface. Substantial deposition of silica nanoparticles on SiO₂ coated surface was also observed suggesting strong homo-aggregation of silica fines in the gypsum supersaturated solution. The interaction behaviour between silica–sphalerite and silica–silica is mainly attributed to the high calcium concentration of the gypsum supersaturated solution. Similar deposition behaviour of silica nanoparticles onto ZnS or SiO₂ coated sensor surface was observed in 800 ppm calcium solution, which is similar to the calcium concentration of the gypsum supersaturated solution. Colloidal force measurement between a silica particle and a fractured sphalerite surface or a silica wafer surface by an atomic force microscopy (AFM) revealed attractive van der Waals force between the mineral particles in both gypsum supersaturated solution and 800 ppm calcium solution. The high calcium concentration of the gypsum supersaturated solution induced the hetero-aggregation between silica and sphalerite, accounting for the observed decrease in flotation selectivity.     

Phase evolution during the low temperature formation of stoichiometric hydroxyapatite-gypsum composites

Both plaster of Paris (CaSO₄·(1/2)H₂O, POP) and bone-like synthetic calcium phosphates (CaP) have been used as bone-like cements. The current study investigated the formation of composites involving POP with each of three types of stoichiometric hydroxyapatites (abbreviated as SHAp, S-SH, and C-SH, each with a Ca/P molar ratio of 1.67). The kinetics, variations in solution chemistry during the formation of these composites and phase compositions of the formed products were investigated over a course of 24 h. Although the presence of gypsum precursors was shown to decrease the alkalinity of the medium involving SHAp formation from its precursors, a delay in the growth kinetics of gypsum was observed. The same behavior was observed in the presence of commercial apatite (C-SH), whereas in the presence of synthetic apatite (S-SH), no delay was observed. A possibility of formation of a calcium sulfate phosphate double salt, as an intermediate, was investigated and confirmed by XRD analysis.     

石膏矿采空区稳定性主要影响因素正交试验研究

采用房柱法开采的石膏矿山,采空区稳定性的主要影响因素为矿柱和护顶层。基于Bieniawski矿柱强度公式和＂伏萨尔梁＂概念对矿柱的安全系数和护顶层抗压缩破坏安全系数进行了计算,并采用正交试验方法,对影响矿柱及护顶层稳定性的各因子进行了敏感度分析。结果表明：矿柱稳定性的主要影响因子为矿柱尺寸,其次为上覆岩层厚度;石膏护顶...     

高温水泥浆体系研究与应用

针对土库曼斯坦南约洛坦气田膏盐层固井对高温抗盐水泥浆性能的要求,研究了高温缓凝剂GHN和高温抗盐降失水剂GFL.GHN由有机膦酸钠盐、有机酸组成,对水泥浆其它性能无不利影响,对水质和水泥品种适应性强,其加量与稠化时间具有良好的线性.GFL为单磺酸四元共聚物AA-AM-VP-AMPS,抗温达180℃,抗欠饱和盐水.为提高固井质量,在高温水泥浆中还使用了硅粉、稳定剂及微膨胀剂.该高温水泥浆性能优越,应用温度范围为100～180℃,失水量在100mL以内,在土库曼的7口井中进行了试验,现场施工顺利,固井质量合格率为100％,解决了该气田高温盐膏层固井技术难题及高压、多气层固井过程中井漏与气侵并存的问题.     

脱硫石膏用于自流平地坪的应用研究

以脱硫石膏煅烧而成的α型半水石膏为基料,掺加石英砂以及减水剂、缓凝剂、消泡剂等外加剂,成功研制了一种石膏基自流平砂浆;30 min流动度损失＜3mm,抗折、抗压强度达到10.4 MPa和32.3 MPa,拉伸粘结强度达到1.50 MPa,主要技术性能指标均达到JC/T 1023-2007《石膏基自流平砂浆》标准要求,可...     

Impact of gypsum supersaturated solution on surface properties of silica and sphalerite minerals

In some sulphide mineral flotation operations, the process water contains high concentrations of calcium and sulphate ions that exceed the solubility limit of gypsum. It has been speculated that the gypsum supersaturated process water would lead to precipitation of gypsum which could coat on mineral surfaces by either nucleation or coagulation, resulting in reduced flotation recovery and selectivity. In this study, a laboratory prepared gypsum supersaturated solution is used to represent the gypsum supersaturated process water, the effect of gypsum supersaturated solution on the surface properties of silica and sphalerite minerals was investigated using zeta potential distribution measurements, scanning electron microscope (SEM), X-ray photon spectroscopy (XPS), Auger electron spectroscopy (AES), and quartz crystal microbalance with dissipation (QCM-D). Our results show that silica and sphalerite minerals carry identical surface charge (−10 mV of zeta potential) in the gypsum supersaturated solution at pH 10 although they are charged differently in simple electrolyte solution at the same pH. Needle shape gypsum precipitates are found in both silica and sphalerite minerals systems conditioned with gypsum supersaturated solution. The gypsum precipitates do not grow on the minerals surfaces but form in the bulk gypsum supersaturated solution. The heterocoagulation between the examined minerals and gypsum particles is insignificant in the gypsum supersaturated solution. It is the high calcium concentration in the gypsum supersaturated solution that has significant effect on the surface properties of silica and sphalerite minerals. The zeta potentials of silica and sphalerite in a 800 ppm calcium solution (similar to the calcium concentration in the gypsum supersaturated solution) are similar to those measured in the gypsum supersaturated solutions. Both silica and sphalerite minerals surfaces are indiscriminately coated with calcium. The surface coating of calcium results in the identical surfaces between silica and sphalerite minerals, and ultimately causes problems for the flotation separation of silica and sphalerite.     

Effects of Process Parameters on Gypsum Scale Formation in Pipes

Scaling often leads to a series of technical and economical problems in industrial plants and equipments by blocking water flow in pipes or limiting heat transfer in heat exchangers. While most contemporary studies are focusing on crystallization at heat‐exchanger surfaces and scaling on nanofilters in desalination plants, very little work has been done investigating scale formation on pipe and vessel walls. A comprehensive investigation of the effects of various process parameters in controlling the formation of calcium sulfate scale in pipes was undertaken. Supersaturation ratio, run time, and operational hydrodynamics were altered systematically to determine their influence on the scale growth rate. The results confirmed that the deposition of gypsum on pipe walls was significantly affected by these process parameters.