Growth inhibition in calcium sulfate crystal using a copolymer in oil fields: theoretical study and experimental evaluations

Insights into mechanism of electric field regulating calcium sulfate crystal structure and crystallization: A study by DFT calculation and experiment

Effect of chemical and physical factors on the crystallization of calcium sulfate in seawater reverse osmosis brine

Morphologies and elemental compositions of calcium crystals in phyllodes and branchlets of Acacia robeorum (Leguminosae: Mimosoideae).

Understanding the mechanisms of growth and inhibition during crystallization of calcium sulfate is of primary importance for many industrial applications. For instance, inhibition of the crystallization process may be required to prevent scale formation in pipes, boilers, heat exchangers, reactors, reverse osmosis membrane surfaces, cooling water systems, secondary oil recovery utilizing water flooding techniques and desalination evaporators, etc. On the other hand, control growth and morphology of gypsum crystals is desired in achieving higher filtration rate and higher productivity of phosphoric acid from phosphate rocks. In this regard, this basic study is carried out to understand effect of Aminotris (methylenephosphonic acid (ATMP) on calcium sulfate dihydrate (gypsum) crystallization. The time elapsed between the achievement of supersaturation and the appearance of a solid phase (termed as induction time) is measured under different supersaturation ratios ranging from 1.018 to 1.979. The data are used to calculate the surface energy, critical nucleus size, and crystal growth rates of gypsum under different conditions. The results show that, the induction time decreases exponentially with increasing the supersaturation ratio. In addition, the surface energy decreases with ATMP compared to the baseline (without ATMP). Interestingly, with addition of the ATMP, the crystals mean and median diameters are found to decrease. The inhibition efficiency ranges from 16% to 59% depending on supersaturation ratio.

The presence of suspended particles in solutions significantly affects the crystallization rate. This study investigates the effects of calcium sulphate (crystallizing) particles and alumina (noncrystallizing) particles on calcium sulphate crystallization fouling in a plate heat exchanger. Calcium sulphate particles are formed during the preparation of calcium sulphate solution due to breakage of calcium sulphate crystals growing on the heat transfer surface. These suspended particles settle on the heat transfer surface and act as nuclei. The availability of extra nucleation sites increases the crystallization rate significantly. These particles can be removed with a filter, and the removal of the particles prevents this extra assistance available for crystallization. Therefore, the crystallization rate is reduced markedly. Alumina particles were purposely added during the preparation of calcium sulphate solutions. These particles attach loosely to the heat transfer surface compared with crystalline deposits which adhere strongly. Therefore, calcium sulphate crystals growing on these particles are removed easily. Also, alumina particles settling on the growth faces of calcium sulphate crystals may act as a distorting agent. This slows down the growth of the crystals.

Calcium sulfate crystals with microrod morphology have been synthesized by a simple hydrothermal process using calcium oxide and sodium sulfate as the raw materials. X-ray diffraction, scanning electron microscopy and infra-red spectrum have been used to characterize the calcium sulfate crystals with microrod morphology. The calcium sulfate crystals with microrod morphology possess orthorhombic CaSO4 phase and the diameter and length are 500 nm-10 μm and 10-100 μm, respectively. The hydrothermal temperature and reaction time play essential roles on the formation and size of the calcium sulfate crystals with microrod morphology. The nucleation and crystalline growth process are proposed to explain the formation and growth of the calcium sulfate crystals with microrod morphology. Keywords: Calcium sulfate crystals, microrods, growth conditions, electron microscopy, biomineralization, microemulsion, diffractometer, monochromatized, hydrothermal process, submicroscale particles, metastable, microrod powders, hydrothermal conditions, hydroxylate, IR

The basis of production of extraction phosphoric acid is two simultaneous processes: dissolving phosphate raw material in a mixture of sulfuric and phosphoric (formed in the process) acids and crystallization of calcium sulfate (phosphogypsum). Phosphogypsum is an inevitable large-tonnage and cumbersome waste at sulfuric acid processing of apatite, which is of interest not only as a source of building gypsum, but also as an alternative rare earth raw material does not have a natural activity and containing rare-earth elements as a cerium and yttrium groups. As a raw material for the production of rare earth elements, calcium sulfate of three types has been used: phosphogypsum from a sludge accumulator, calcium phosphate phospho-hemihydrate and calcium sulfate phosphate dihydrate from a carousel filter produced by extraction phosphoric acid at JSC "PhosAgro-Cherepovets". The extraction of rare-earth elements from phosphogypsum from a sludge accumulator by leaching (percolation) with inorganic acids with subsequent sorption on cation-exchange resins is considered. As an adsorbent for extracting REE from leach solutions, cationite "Purolite" S-150 is used. A static exchange capacitance of cation exchanger is found that is the capacity of the resin when equilibrium is reached with a solution of a certain volume and composition. The static capacity of cation exchanger for rare-earth elements is 1.57%, which indicates a good absorbing capacity. Desorption of rare-earth elements from the cation exchanger is carried out with a solution of ammonium nitrate. The optimal solution for leaching was found to be sulfuric acid with a concentration of 5% by weight. The degree of extraction of rare-earth elements from phosphogypsum with sulfuric acid is about 82%.Forcitation:Artamonov A.V., Smirnova D.N., Smirnov N.N., Ilyin A.P. Extraction of rare earth elements from solid waste of production of phosphoric acid followed by sorption on cation exchange resins. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 10. P. 87-93

Simulate the production of phosphoric acid by wet process is conducted in batch experiments facilities by adopting phosphorus concentrate as raw material from Wengfu, Dazhou city, with a view to study sulfuric acid concentration, reaction time, crystallization temperature of calcium sulfate, active additive, the influence of seed crystal on the size and shape of calcium sulfate crystal under conditions of Wet process phosphoric acid productive process. The research results show that under the conditions of the liquid-solid ratio of 4:1, the sulfate acid stoichiometric ratio of 1.1, phosphoric acid mass fraction of 21%, the crystallization temperature of 75&degC, crystallization time of 120 min, when (NH4)2SO4 taken as active additives, Mg-doped calcium sulphate crystal as crystal seed can obtain rodlike crystallization of stability, thickness, uniformity.

The state of water in calcium chloride and sodium sulfate solutions, as well as during the crystallization of calcium sulfate from solutions with concentrations of 0.68–7.08 g dm–3 was studied by the differential scanning calorimetry. One clearly detectable endothermic peak was revealed in the DSC curves of ice melting of CaCl2 and Na2SO4 solutions. An increase in the concentration of these solutions does not lead to the appearance of any additional peaks or “shoulders” on the DSC curves. Thermograms for sodium sulfate and calcium chloride mixed solutions change their patterns: a low-temperature peak appears and peaks with asymmetric shoulders or splitted principal peak are registered. These changes are presumably related to the water structuring by the surface of forming calcium sulfate crystals.

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

The influence of surfactants on the crystallization of calcium sulfate was investigated in both batch and continuous systems. The investigation was performed at the following conditions: 343 °K, 28% P2O5 and with a sulfate level of 2.0%. At concentrations of 5 and 200 µg/g, respectively, dodecylbenzenesulfonic acid (DBSH) and sodium diisooctilsulfosuccinate (SSNa) promoted both an increase in the size and a reduction in the length/width (L/W) ratio of the calcium sulfate hydrates produced in the batch and continuous crystallizers. Unique effects were observed in the batch system at higher DBSH concentrations. At 10 µg/g, the precipitation of hemihydrate crystals with a distinct morphology and texture occurred under conditions where dihydrate precipitation was expected. Above 50 °g/g, the precipitation of calcium sulfate hydrates was completely inhibited.

Crystallization of calcium sulfate in concentrated phosphoric acid

Calcium sulfate scale is a typical deposit on the equipment pieces or pipes of an industrial water system. Scale inhibitors could obviously reduce the precipitation of calcium sulfate crystal. The development and research of late-model environmentally friendly polymer inhibitors are often urgent problems to be addressed. A water-soluble poly(ethylenediaminetetraacetic acid-diethanolamine) (PEDTA-DEA) was successfully synthesized by thermal polycondensation of ethylenediaminetetraacetic acid (EDTA) with diethanolamine (DEA). The polymer product was characterized by Fourier infrared spectrum (FTIR) and the molecular weight was measured by gel chromatography, which confirms the polymerization of the two monomers. The inhibition effect of the polymer against calcium sulfate deposition was studied by static scale inhibition tests. When the Ca2+ concentration is 3000 mg/L, and the dosage of the polymer inhibitor is 10 mg/L, the inhibition effect exceeds 90%. The results show that PEDTA-DEA can inhibit the precipitation of calcium sulfate and reduce the deposition of calcium sulfate scale. The precipitate of calcium sulfate collected from the static scale inhibition test solution was analyzed by FTIR, scanning electron microscope (SEM) and X-ray diffraction (XRD). The results revealed that the addition of the polymer significantly changes the calcium sulfate crystal’s growth shape. Therefore, PEDTA-DEA is a potential calcium sulfate precipitation inhibitor for the industrial water system.

The results of a study of the composition of solid halite waste (halite dump and quarry salt) from potash production were presented in the work. The form of calcium sulfate and its localization in solid halite waste have been determined. It was established that in the quarry salt calcium sulfate was presented in the form of anhydrite and dihydrate, and in the halite dump the impurity was only in the form of anhydrite. Photomicroscopic photography of the surface of large halite crystals showed that calcium sulfate in the halite dump was localized mainly on the surface of halite, and on particles of quarry salt. Calcium sulfate crystals were pressed into the crystalline surface of halite due to the processes of dissolution - crystallization occurring under the influence of atmospheric precipitation and changes temperatures. An assessment of the influence of ultrasonic and hydromechanical effects on the treated aqueous suspension of halite waste for purification of calcium sulfate impurities was presented. The possibility of removing most of the CaSO4 without additional reagent treatment of the halite suspension has been proven. The optimal technological parameters for the duration and intensity of ultrasonic and hydromechanical effects on the treated environment have been found. It was found that ultrasonic treatment of halite in a saturated salt brine of sodium chloride at a ratio of L:S = 5:1 for 6 min with a frequency of 22 kHz, intensity of 9.4 W/cm2, amplitude of ultrasonic vibrations of 80 μm and intensive stirring allows to achieve 80% extraction of calcium sulfate from both quarry salt and halite dump. Based on the results obtained, the feasibility of using ultrasonic treatment was demonstrated and an effective technology was proposed for the preparation of sodium chloride and (or) technical salt brines with a residual calcium sulfate impurity content of less than 0.5 wt.%, which can subsequently be used in various industries.

Perennial rhizomatous grasses are regarded as leading energy crops due to their environmental benefits and their suitability to regions with adverse conditions. In this paper, two different experiments were carried out in order to study the salinity (S) and water stress (WS) effects on biomass production in giant reed (Arundo donax L.). In Experiment 1, eight clones of giant reed were subjected to four salinity (S) and water stress (WS) treatments: (1) well watered with non-saline solution, (2) water stress with non-saline solution, (3) well watered with saline solution and 4) water stress with saline solution. In Experiment 2, five clones of giant reed were subjected to increasing S levels in two locations: University of Catania (UNICT-Italy) (1) well watered with non-saline solution and (2) well watered with mild saline solution; and University of Barcelona (UB-Spain) (3) well watered with non-saline solution and (4) well watered with severe saline solution. Photosynthetic and physiological parameters as well as biomass production were measured in these plants. According to our data, giant reed seems to be more tolerant to S than WS. Both stresses mainly affected stomatal closure to prevent dehydration of the plant, eventually decreasing the photosynthetic rate. The differential performance of the giant reed clones was ranked according to their tolerance to S and WS by using the Stress Susceptibility Index. ‘Agrigento’ was the most WS resistant clone and ‘Martinensis’ was the most S resistant. ‘Martinensis’ and ‘Piccoplant’ were found to be the most suitable clones for growing under both stress conditions. Moreover, ‘Fondachello’, ‘Cefalu’ and ‘Licata’ were the most resistant clones to increasing S levels.