Precipitation Of CaSO4 Research Articles

Leaching characteristics and mechanism of copper flotation tailings in sulfuric acid solution

The copper deposit in Yangla zone of China is large, and its recovery is low only using flotation process. Therefore, the copper in the flotation tailings is leached by sulfuric acid can improve copper recovery. The factors affecting leaching process and the leaching mechanism were investigated in this study. Copper is leached at a rate of 53.8% when initial H2SO4 concentration is 0.428 mol/L, leaching temperature is 348 K, liquid-to-solid ratio is 3: 1, stirring speed is 300 r/min and leaching time is 60 min. Through combine the acid leaching process of tailings with the flotation process of raw ore, copper comprehensive recovery has been improved. Kinetics results show that the leaching process is controlled by internal diffusion with an activation energy of 9.796 kJ/mol. To characterize the mechanism of acid leaching, chemical analysis, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were used. The results indicate that the fine size of copper minerals and CaSO4 precipitation which generated during acid leaching process affected the leaching of copper minerals.

Effect of temperature and calcium ion concentration on permeability reduction due to composite barium and calcium sulfate precipitation in porous media

In the oil industry, water injection is used as a secondary recovery technique for pressure maintenance and efficient oil and gas production. Injected water may be incompatible with water that occurs naturally within the pores of reservoir rock. When these two incompatible waters mix, inorganic scales precipitate within porous media. Many studies have been conducted to investigate the effect of scale formation on the ability of reservoir rock to transmit fluids. Most of these studies have focused on single salt precipitation. This paper is intended to investigate the permeability reduction of porous media due to composite BaSO4–CaSO4 precipitation. Since pure BaSO4 scaling tendency decreases with increasing temperature, while pure CaSO4 scale formation potential increases with increasing temperature, the effect of temperature on the co-precipitation of BaSO4 and CaSO4 was questionable. This paper presents the results of an experimental study which performed by injection of two incompatible solutions into the pack of glass beads at temperatures of 50 and 70 °C to exhibit the effect of temperature on the composite BaSO4–CaSO4 scaling potential. The experimental results and Scanning Electron Microscopy images indicated that even minute amounts of calcium ions combined with barium ions clearly affected the scale nature, morphology, particle size and intensity of scale formation.

Study on Calcium Scales Inhibition Performance in the Presence of Double-Hydrophilic Copolymer

Novel double-hydrophilic block copolymers, acrylic acid (AA)-2-acrylamido-2-methyl-propane sulfonate (AMPS)-oxalic acid-allypolyethoxy carboxylate (APEM) was specially designed and synthesized from allyloxy polyethoxy ether (APEG) to inhibit the precipitation of CaCO3 and CaSO4. The structure of the copolymer was characterized by FT-IR and H1-NMR. Using the static experiment method, the scale inhibition efficiencies for CaCO3 and CaSO4 scale were investigated. It was shown that AA-AMPS-APEM exhibited excellent ability to control inorganic minerals scales, with approximately 97.1% CaSO4 inhibition and displayed significant ability to prevent the formation of CaCO3 scales. The synthesized AA-AMPS-APEM was also compared with that of current commercial inhibitors. The effect of the copolymer addition on the crystals of CaCO3 and CaSO4 scales morphology and structures were examined through scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction studies (XRD). It proved that great changes in the size and morphology of the calcium scales took place under the influence of AA-AMPS-APEM. The proposed inhibition mechanism suggests the formation of complexes between the side-chain carboxyl groups of AA-AMPS-APEM and calcium ions on the surface of inorganic minerals, and the excellent solubility of complexes resulted from a number of hydrophilic polyethylene glycol (PEG) and sulfonic group (-SO3H) group.

Synthesis, solution properties and scale‐inhibiting behaviour of a diallylammonium/sulfur dioxide cyclocopolymer bearing phospho‐ and sulfopropyl pendents

Zwitterion (Z) monomer 3‐[diallyl{3‐(diethoxyphosphoryl)propyl}ammonio]propane‐1‐sulfonate underwent cyclocopolymerization with sulfur dioxide to give a new alternating copolymer poly(Z‐alt‐SO2) in excellent yield (ca 90%). The polyzwitterion (±) (PZ) (i.e. poly(Z‐alt‐SO2), bearing a diethylphosphonate as well as a sulfonate functionality in each repeat unit, upon ester hydrolysis gave its corresponding pH‐responsive polyzwitterionic acid (±) (PZA). The pH‐induced equilibrations (+) cationic polyelectrolyte ⇌ (±) PZA ⇌ polyzwitterion/anion (± −) (PZAN) ⇌ polyzwitterion/dianion (± =) (PZDAN) permitted us to examine the effects of charge types and their densities on the interesting solubility and viscosity behaviours. The apparent protonation constants of the basic functionalities &tbond;N±PO32− in (± =) PZDAN and &tbond;N±PO3H1− in (± −) PZAN in salt‐free water and 0.1 mol L−1 NaCl were determined using potentiometric titrations. (±) PZA at a meagre concentration of 20 ppm was found to be an effective antiscalant to inhibit the precipitation of CaSO4 from its supersaturated solution: after 500 and 800 min, the respective scale inhibitions of 86 and 98% indicated its potential use as an effective antiscalant in reverse osmosis plant. © 2014 Society of Chemical Industry

Ca2+ as an Air Impurity in Polymer Electrolyte Membrane Fuel Cells

Cationic contamination is known to cause performance degradation and reduced lifetime in polymer electrolyte based electrochemical systems. Calcium is an important cationic impurity due to its prevalence in roadside particulates and as an airborne contaminant. The role of calcium ion (Ca2+) is investigated in-situ by injecting a solution of calcium sulfate (CaSO4) in deionized (DI) water into the cathode of a polymer electrolyte membrane (PEM) fuel cell through a nebulizer. Stability tests are conducted to determine the effects at various current densities with various Ca2+ concentrations. It is found that 5 parts per million (ppm, molar ratio) eq. Ca2+ in air is sufficient to lead to high cell performance loss at 1 A/cm2 as well as severe membrane degradation. Precipitation of CaSO4 is found at the contact regions between the gas diffusion layers (GDL) and bipolar plates of the cathode at all test conditions. The amount of precipitation becomes sufficient to cause mass transport issues.

Mechanism and numerical simulation of multicomponent solute transport in sodic soils reclaimed by calcium sulfate

The mechanism for reclaiming sodic soils using calcium sulfate (CaSO4) could provide a theoretical basis for the field application of CaSO4 substitutes, including the by-products of flue gas desulfurization (BFGD), fly ash, and phosphorus gypsum. In this study, Ca2+ application experiment was conducted to analyze the dynamic changes of the cations in the reclamation of sodic soils with CaSO4. A multicomponent solute transport model (UNSATCHEM) that considers ion adsorption exchange and dynamic changes in the soil’s hydraulic conductivity was subsequently used to simulate and predict the movement of ions. The Ca2+ application experiment consisted of four treatments with four CaSO4 concentrations (0.5, 1, 1.5, and 2 g L−1). When the Ca2+ concentrations in the supplied water were 14.71, 22.06, and 29.41 mmol L−1, Ca2+ achieved penetration, and this process was faster when the Ca2+ concentration in the supplied water was higher. Ca2+ did not achieve penetration when the Ca2+ concentration was 7.35 mmol L−1. UNSATCHEM was able to simulate the transportation mechanism of Ca2+ and Na+ in the soil solution in the Ca2+ application experiment, the adsorption and exchange between the Na+ in the soil colloid and Ca2+ in the soil solution, and the precipitation and dissolution of CaSO4 with a high degree of accuracy. Sodic soil reclamation with CaSO4 was not a short-term process. Compared with applying CaSO4 only once, applying CaSO4 in batches decreased the accumulation of soil salts and promoted its dissolution.

Effect of groundwater chemistry on the swelling behavior of a Ca-bentonite for deep geological repository

The swelling properties of buffer material for high level radioactive waste repository in a near-field environment are of particular importance for achieving the low permeability sealing function. In this study, the free swelling behavior of a potential buffer material Zhisin clay is evaluated under simulated groundwater conditions such as immersion in NaCl, CaCl2, and Na2SO4 solutions at various concentrations. Experimental results indicate that Zhisin clay, being a Ca-bentonite, exhibits reduced swelling strain in salt solutions. The amount of decrease in swelling strain upon saline water intrusion is affected by both the type and concentration of electrolyte. At the same concentration, the swelling strains in CaCl2 solution are lower than those in NaCl solution due to the quasi-crystals formed in the presence of calcium ions. Also, the swells in Na2SO4 solution are found to be lower than those in NaCl solution. This is attributed to the precipitation of CaSO4, which acts as binding agent and results in aggregation of clay particles.

Further treatment of ion exchange brine with dynamic vapour recompression

In the context of the development of the SIX© Ion exchange process, the Dutch water company (PWN) decided to investigate options for treatment of the brine arising from the regeneration of the resin. Main goals for the brine treatment are volume reduction and product recovery (water + NaCl). In this regard a biological denitrification (DNF) aiming at total nitrate removal followed by a nanofiltration (NF) aiming at ion separation (monovalent/bivalent) focused on NaCl re-use were implemented on a pilot scale recovering 80% of the total SIX brine (implying 80%recovery of NaCl). Further NF concentrate minimization and Sodium Chloride reclamation would allow a reduction of the disposal fees and chemical uses and therefore largely increase the overall process sustainability. During operation on a pilot scale with a capacity of 250l/h, the Dynamic Vapour Recompression (DVR) technology has proved itself to be capable to reduce the raw regenerate another 6 to 10 times reaching meanwhile the solubility limits of NaCl and other salts making their recovery on a solid stream possible. The condensate that resides after DVR treatment is low contaminated and is therefore suitable for re-injection upstream the SIX pre-treatment process. Laboratory scale evaporation tests showed that salts would precipitate according to the following order: BaSO4 >BaCO3 > MgSO4 > MgCO3 >CaCO3 > CaSO4 > Na2CO3 > Na2SO4 and NaCl. A sequenced thickening by DVR treatment leads to selective precipitation of BaSO4, BaCO3, MgCO3, CaCO3 and CaSO4 at concentration factor around 8 but beyond a CF of 10 it leads to a more or less simultaneous precipitation of NaCl, Na2CO3 and Na2SO4 without fouling/clogging problems of the DVR. A reuse of a heterogeneous (co)precipitate solid fraction is difficult; however this problem could be countered by further investigation on a temperature controlled precipitation of Na2CO3 and Na2SO4. Cooling down the DVR brine saturated in dissolved sodium chloride, sulphate and bicarbonate to a temperature of 5 °C increases solubility differences between sodium chloride and its two contaminants, making their separation possible.

Carboxylate-terminated double-hydrophilic block copolymer as an effective and environmental inhibitor in cooling water systems

In an attempt to control Ca3(PO4)2, CaCO3, and CaSO4 deposits in industrial recycling water systems, an acrylic acid (AA)-allyloxy poly(ethylene glycol) polyglycerol carboxylate (APEG-PG-COOH) copolymer was synthesized as a nonphosphorus inhibitor. The synthesized polymer was characterized by 1H NMR. The performance of PAA/APEG-PG-COOH on inhibition of Ca3(PO4)2, CaCO3 and CaSO4 precipitation was studied through static scale inhibition tests. It was shown that PAA/APEG-PG-COOH exhibited excellent ability to control inorganic minerals, with approximately 100% CaSO4 inhibition and 99.89% Ca3(PO4)2 inhibition at levels of 3 and 6mg/L PAA/APEG-PG-COOH, respectively. PAA/APEG-PG-COOH also displayed ability to prevent the formation of CaCO3 scales. The effects on formation of Ca3(PO4)2, CaCO3 and CaSO4 were investigated with combination of Scanning electronic microscopy (SEM), Transmission electron microscopy (TEM), and X-ray powder diffraction (XRD) analysis, respectively.

Washing of metal contaminated soil with EDTA and process water recycling

We demonstrate here, in a laboratory scale experiment, the feasibility of using the base/acid pair Ca(OH)2/H2SO4 to impose a pH gradient for EDTA recycling and, coupled with an electrochemical advanced oxidation process using a graphite anode, of recycling process water as part of a novel remediation technology for multi-metal contaminated soils. In the first batch, 60mmolEDTAkg−1 of soil removed 72, 27, and 71% of Pb, Zn, and Cd, respectively, from soil contaminated with 5329±685, 3401±193, and 35±6mgkg−1 of Pb, Zn, and Cd, respectively. In the subsequent four batches, we demonstrated that up to 88% of EDTA was recycled from each batch, with the potential to extract up to 98, 94, and 109% of Pb, Zn, and Cd, respectively, that the fresh EDTA extracted. Accumulation of salts in the process water through multiple remediation batches/recycles was prevented by CaSO4 precipitation. Recycled process water toxicity testing indicated no significant effect on plant seed germination but some inhibition of root elongation.

Solubility and Solubility Product Determination of a Sparingly Soluble Salt: A First-Level Laboratory Experiment

A simple experiment was devised to let students determine the solubility and solubility product, Ksp, of calcium sulfate dihydrate in a first-level laboratory. The students experimentally work on an intriguing equilibrium law: the constancy of the product of the ion concentrations of a sparingly soluble salt. The determination of solubility is proposed either in an equimolar precipitation of CaSO4·2H2O, from which the Ksp is obtained, or working with an excess of one of the two reagents.

Inhibition of Ca3(PO4)2, CaCO3, and CaSO4 Precipitation for Industrial Recycling Water

In an attempt to control Ca3(PO4)2, CaCO3, and CaSO4 deposits in industrial recycling water systems, an acrylic acid (AA)–allylpolyethoxy carboxylate (APEC) copolymer was examined as a nonphosphorus inhibitor. The synthesized AA–APEC copolymer was characterized by FT-IR. The performance of AA–APEC on inhibition of Ca3(PO4)2, CaCO3, and CaSO4 precipitation was compared with that of current commercial inhibitors. It was shown that AA–APEC exhibited excellent ability to control inorganic minerals, with approximately 82.88% CaSO4 inhibition and 99.89% Ca3(PO4)2 inhibition at levels of 3 and 6 mg/L AA–APEC, respectively. AA–APEC also displayed ability to prevent the formation of CaCO3 scales. Transmission electron microscopy (TEM) images indicated that the outstanding performance of AA–APEC on Ca3(PO4)2 inhibition resulted from a decrease in size of Ca3(PO4)2 solid particles thereby dispersing these particles throughout a fluid, while CaCO3 inhibition was attributed to the formation of ribbon-shaped structures...

Effect of bacteria and salinity on calcium sulfate precipitation

Membrane and thermal desalination are plagued by composite fouling because of inorganic, biological and organic constituents. Interactive effects in composite fouling, though of paramount practical importance, are mostly ignored. This paper presents interactive effects of biological matter, Pseudomonas Fluorescence (PF), on precipitation of calcium sulfate, a sparingly soluble salt and an inorganic foulant. Experiments were conducted in isothermal (25°C) batch tests. The effect of PF and its concentration on CaSO4 precipitation and deposit structure at varying salinities were determined. The Pitzer model, suitable for high salinities, is used in calculation of instantaneous CaSO4's ion activity products. The Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) show that salinity and concentration levels alter the crystal structure but not the crystal phase (gypsum). Under the influence of PF, crystallization of CaSO4 did not occur and sulfur levels significantly increased; it can be surmised that microbial activity of PF reduced the sulfate ions to elemental sulfur and altered precipitation of CaSO4. This does not suggest that biological fouling or presence of bacteria generally inhibits precipitation fouling of calcium sulfate; it underlines that the generally ignored interactive effects are of significant importance and should be considered as corner stone in advancement of fouling research.

Holocene sabkha and coastal systems of Qatar: models for the interpretation of ancient Arabian plate carbonate evaporite reservoirs and coastal management

Abstract Facies tracts, sediment types, stacking patterns, and diagenetic histories of Holocene sabkhas of Qatar provide compelling analogues for the interpretation of ancient, carbonate-evaporite sequences of the Arabian Plate. The use of modern analogues to aid in the interpretation of geological and engineering data is well established in the petroleum industry. Comparison of sabkhas from different physiographic regions of Qatar that formed during the latest Holocene cycle of sea level rises reveals new insights into the characterization of ancient rocks. These observations provide the basis for a revision of the definition of facies tracts described in the geological literature as sabkhas. This study reports on a country-wide study of the sedimentation history of coastal areas, based on extensive field mapping, geotechnical studies, age dating and geochemistry. Data is integrated in ArcGIS, a relational database. The results are equally valuable in conservation, environmental and geotechnical studies and archaeological research and teaching. Coastal areas of Qatar are marked by extremely low relief, with the result that high-frequency oscillations in sea level create offsets in facies tracts. Age dating reveals that inland sabkhas are relicts of a high stand in sea level approximately 4000-6000 years ago. These areas are presently subaerially exposed and eroding. Extensive pedogenic modification of marine sediments (burrowing, infiltration, micrite precipitation) creates characteristic textures. Groundwater modification includes extensive precipitation of CaSO4, halite,lime micrite, and dolomite. The variability observed in Qatar sabkhas alters the way in which a common modern analogue is applied to the interpretation of subsurface data. These observations warrant revision of the definition of a sabkha. We propose that sabkhas are normal, coastal sediments, modified by near-surface groundwater saturated in CaSO4. A sabkha is a diagenetic overprint, not a depositional system. This proposed model helps aid in recognition of ancient sabkhas.

Inhibition of Calcium Sulfate and Strontium Sulfate Scale in Waterflood

Summary One of the most common methods of preventing downhole and topside mineral-scale formation in oil fields is through the use of chemical-scale inhibitors. Several aspects of the brine composition may affect the performance of the various scale inhibitors used in oilfield applications. This study was conducted to investigate the permeability reduction caused by deposition of calcium sulfate (CaSO4) and strontium sulfate (SrSO4) in Malaysian sandstone and Berea cores from mixing injected Malaysian seawaters (SW) (Angsi and Barton) and formation water (FW) that contain a high concentration of calcium and strontium ions at various temperatures (50 to 95°C) and differential pressures (75 to 200 psig). Scale-inhibition efficiency was determined in both the bulk jar and the core tests by using scale inhibitors methylene phosphonic acid (DETPMP), polyphosphino carboxylic acid (PPCA), and phosphorus-based scale inhibitor (PBSI) at various temperatures (50 to 95°C) and concentrations. The results showed a large extent of permeability damage caused by calcium and strontium sulfates that deposited on the rock pore surface. At higher temperatures, the rate of CaSO4 and SrSO4 precipitation increases because the solubilities of CaSO4 and SrSO4 scales decrease with increasing temperature. At 90°C temperature, PBSI was the best inhibitor because it reduced more scale deposition compared to the DETPMP and PPCA inhibitors.

The Use of Chloro-Complexation to Enhance Cadmium Uptake by Zea mays and Brassica juncea: Testing a “Free Ion Activity Model” and Implications For Phytoremediation

Maize and Indian mustard plants were studied to: 1) investigate the effect of Cl− complexation on Cd uptake from soil historically amended with sewage sludge (Cd 58 mg kg−1) and, 2) model the uptake of Cd by these plants with a Free Ion Activity Model (FIAM). Plants were treated with NaCl (50 to 300 mM in the soil pore water) along with controls using Na2SO4. Cadmium enhanced solubility in soil by Cl− generally reflected increases in Cd uptake by both plants. The free ion Cd2+ activity in soil solution, as modeled by WHAM-VI, remained almost unchanged despite the wide range of NaCl concentrations. Therefore, Na+ exchange for Cd2+ could not fully explain the differences in Cd content between the Cl− treatments because of the high buffering Cd2+ capacity in soil. Activities of Cd-chloro complexes showed the best correlations with the Cd concentrations in the plants compared to the activity of Cd2+. The FIAM showed a reasonable good fit for the plants when assuming competition by Cd2+ and CdCl+ for root sorption sites. Indirect evidence suggests that CaSO4 precipitation may have limited the formation of CdSO4 complexes and reduced Cd soil solubility. The implications of these results for phytoremediation are discussed.

A NEW MODEL FOR PERMEABILITY REDUCTION RATE DUE TO CALCIUM SULFATE PRECIPITATION IN SANDSTONE CORES

In this work, a reliable dimensionless correlation is proposed for prediction of permeability reduction rate in porous media, which is verified by experimental data obtained in this work in glass bead and sand pack as well as the core data from the literature. Although this correlation is based on the data which were obtained in our work in glass bead and sand-packed media at low pressure, it shows considerable flexibility to match with the extracted data for sandstone cores at high pressure, various flow rates, different temperatures and concentrations of calcium, and sulfate ions in brine solutions. In addition, a novel relationship for predicting the rate of precipitation of CaSO4 in porous media along with a modification for kinetic reaction rate is developed which is a function of initial permeability, initial porosity of porous media, volume flow rate, saturation index of injected solution, temperature, and cross-sectional area of porous media.

Low-Sulfate Seawater Injection into Oil Reservoir to Avoid Scaling Problem

This study presents the results of laboratory experiments carried out to investigate the formation of calcium, strontium and barium sulfates from mixing Angsi seawater or low sulfate seawater with the following sulfate contents (75, 50, 25, 5 and 1%) and formation water contain high concentration of calcium, strontium and barium ions at various temperatures (40-90°C) and atmospheric pressure. The knowledge of solubility of common oil field scale formation and how their solubilities are affected by changes in salinity and temperatures is also studied. Results show a large of precipitation occurred in all jars containing seawater while the amount of precipitation decreased when the low sulfate seawater was used. At higher temperatures the mass of precipitation of CaSO4 and SrSO4 scales increases and the mass of precipitation of BaSO4 scale decreases since the solubilities of CaSO4 and SrSO4 scales decreases and the solubility of BaSO4 increases with increasing temperature. It can be concluded that even at sulfate content of 1% there may still be a scaling problem.

Electrodialysis with brine solutions oversaturated with calcium sulfate

Electrodialysis (ED) was applied to concentrate brine solutions of various concentrations — similar to effluentsfrom the desalination of brackish and industrial water — to about 20%. The consequent reduction in effluent volumes would facilitate a reduction in disposal costs. The energy requirement for concentrating solutions from 70 to 300 mN (0.4–1.8%) to 3.9 N (20%) was in the range 1.5–7.1 kWh/m 3, in contrast to approximately 25 kWh/m 3 by thermal evaporation. With the aim of preventing precipitation of CaSO4 on the membranes, laboratory-scale ED experiments were carried out on solutions of different compositions to determine the conditions that would lead to the precipitation of excess gypsum on gypsum seeds in a separate precipitator. The results were then applied in a pilot-scale ED unit in which the brine that circulated through the ED brine cells passed through a separate CaSO, precipitator containing gypsum seeds.

Calcium Sulfate Precipitation in the Presence of Nondominant Calcium Carbonate: Thermodynamics and Kinetics

This study addresses the fouling of heat exchangers by coprecipitating inorganic salts. It investigates the effects of nondominant CaCO3 on thermodynamics and kinetics of CaSO4 precipitation as well as on scale structure. Even though precipitating salts coexist in industrial water systems, because of the complexity of the fouling process, research has primarily been concentrated on a single salt precipitation. In addition, all thermodynamic predictive models and softwares only consider the effect of coexisting salts through the ionic strength by Debye−Huckel or modified forms of that. The results of this investigation indicate that the presence of a coprecipitating salt with a common ion affects the solubility constants of the salts, and therefore application of the solubility data obtained under a single salt precipitation is questionable for coprecipitating salts with common ions. Also, the kinetics of precipitation is affected by the presence of a common ion, and the traditional method of kinetic analy...