Precipitation Of Calcium Hydroxide Research Articles

Sustainable treatment of boron from oilfield produced water for optimum recovery using zirconium chloride oxo-precipitation

This study focuses on the recovery of boron from oilfield-produced water employing the chemical oxo-precipitation method. Zirconium chloride was used to recover boron as a sustainable approach. The study aimed to optimize the parameters to achieve the highest possible boron recovery. It also sought to investigate the impact of operating parameters, including pH, time, oxidizing agent, and dosage of the precipitant, on boron recovery. The optimal operating conditions were optimized through response surface methodology (RSM). A comparative study was conducted with barium chloride (chemical oxo-precipitation) and calcium hydroxide (conventional precipitation). The results indicated that the highest boron recovery was achieved at 97% by utilizing chemical oxo-precipitation with zirconium chloride. Meanwhile, barium chloride and calcium hydroxide recovered boron at 89% and 88%, respectively. The precipitates were characterized by Fourier transform infrared (FTIR), x-ray fluorescence (XRF), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX). The XRF and EDX characterization analysis confirmed the highest boron recovery at 97% with zirconium chloride. SEM showed that zirconium chloride precipitated visible amorphous insoluble solids. The chemical-oxo-precipitation procedure outperforms barium chloride and calcium hydroxide precipitation. The zirconium chloride oxo-precipitation method was proved to be a greener solution for boron recovery.

Low-Temperature Water Electrolysis Under a Sustained pH-Gradient for the Electrochemically-Induced Decarbonation of Limestone into Hydrated Lime

Conventional low-temperature water electrolysis processes operate either at high or low pH to enhance conductivity, minimizing electrical resistance. Neutral water electrolysis in a buffer solution is considered non-competitive due to higher energy consumption. Nevertheless, interest in water electrolysis using a salt-based electrolyte has grown due to its ability to generate a pH gradient inside the cell. Electrolysis using a neutral salt-based electrolyte has higher operating costs due to its higher standard equilibrium potential (due to the pH gradient) and lower conductivity. Although this approach incurs higher operating costs, it presents a unique advantage: the production of additional valuable elements thanks to the pH gradient generated.In 2019, Ellis & al. [1] highlighted the possibility to use this pH gradient to electrify the production of hydrated lime (calcium hydroxide). Lime has applications in different areas such as the removal of impurities during steel production and aqueous or gaseous effluent treatments. It can also be used as a precursor of cement. Cement production is accounting for 8% of global CO2 emissions. The acidity generated by water oxidation at the anode dissolves the calcium carbonate inserted. Carbon dioxide from the dissolution is recovered with the oxygen generated. The calcium cations migrate through the cationic membrane towards the cathodic compartment to react with the hydroxide ions generated by water reduction at the cathode. Calcium hydroxide is finally collected after precipitation. Figure 1 compares the conventional process with the electrochemical way and describes more precisely the steps involved in Figure 1. More recently, another way of exploiting this gradient has been proposed by Ni & al. [2] for the recycling of spent Li-ion batteries. With the growing interest in process electrification, other applications may emerge.In this paper, this hybrid electrochemical system for the simultaneous production of hydrogen, oxygen and calcium hydroxide has been intensively studied. Water electrolysis has been performed in a two-compartment cell at different applied currents. Calcium concentration and pH measurement enabled the study of the sub-step efficiencies and equilibria in anodic and cathodic chambers. Perfect faradic efficiencies were obtained with perchlorate salt electrolytes and platinum-free electrodes. The establishment of the pH gradient has been proven and correlated with the transport number of protons through the cationic membrane. Finally, the kinetics of calcium ion migration and calcium hydroxide precipitation have been investigated as well. Continuous addition of calcium carbonate as opposed to a single excess addition was shown to be able to tune the working pH in the anodic compartment and thereby reducing the risk of precipitation on the membrane. Our experimental results lead to the formulation of practical recommendations for achieving optimal reaction stoichiometry in each stage. These findings pave the way for scaling up a promising new sustainable process for lime and cement production.[1] L. D. Ellis, A. F. Badel and M. L. Chiang, "Toward electrochemical synthesis of cement," PNAS, vol. 117, no. 23, pp. 12584-12591, 2019.[2] N. Jihong, Z. Jiayin, B. Jinhong and G. Xiaofei, "Recycling the cathode materials of spent Li-ion batteries in a H-Shaped neutral water electrolysis cell," Separation and Putification Technology , vol. 278, p. 119485, 2022. Figure 1 - Conventional and electrochemical production route of Ca(OH)2 and a simplified scheme of the hybrid electrolyzer used in this work, with the reactions involved. Figure 1

Highly efficient recovery of phosphate and fluoride from phosphogypsum leachate: Selective precipitation and adsorption

Phosphogypsum, a typical by-product in the phosphorus chemical industry, could generate a large amount of leachate containing phosphate and fluoride in the process of rainfall and long-term stacking, which not only causes serious environmental pollution, but also leads to a waste of resources. In this study, a united treatment of calcium hydroxide precipitation and lanthanum zeolite (La-ZFA) adsorption was proposed to achieve the recovery of phosphate and fluoride from phosphogypsum leachate. In phosphogypsum, most phosphorus could be leached except P in the residual occurrence form, while for fluoride, only water-soluble F could be effectively leached. The optimum leaching amounts of phosphate and fluoride were 22.59 and 4.64 mg/g, respectively, at liquid-solid ratio of 400:1, leaching time of 120 min, pH of 6.0, particle size of >200 mesh (<0.075 mm), and leaching temperature of 25°C. Using Ca(OH)2 as the precipitant, the phosphate could be precipitated selectively from phosphogypsum leachate by controlling pH and time, and the concentrations of it decreased significantly to 0.29 mg/L at pH 10.0, with a removal efficiency of 99.48%. XRD, SEM and Visual MINTEQ software analysis proved that the main component of the precipitate was hydroxyapatite (Ca5(PO4)3(OH)). After P precipitation, a series of sorbents for fluoride were investigated, and La-ZFA sorbent was chosen and utilized to recover the fluoride from the leachate through a cyclic fixed-bed column. The efficiency of La-ZFA was basically not affected by the high concentration sulfate, and it can selectively adsorb fluoride from phosphogypsum leachate, leading to a final fluoride concentration of 0.29 mg/L in the effluent. The characterization demonstrated that fluoride might be adsorbed onto the La-ZFA via ligand exchange with hydroxy groups. The proposed method in this study is expected to sequentially recover phosphate and fluorine from the leachate of phosphogypsum, and it has great guiding significance for resource utilization and management of phosphogypsum.

Enhanced biogas yield in anaerobic digestion of citric acid wastewater by pre-treatment: The effect of calcium hydroxide precipitation and electrocoagulation process

During the production and use of citric acid (CA), which is frequently used in food, chemistry, metallurgy and other related industries, wastewater with high organic load and acidity is generated. Discharge of these wastewaters into the receiving environment without adequate purification causes serious pollution problems. However, treating such wastewater with hybrid processes allows both the formation of valuable by-products and an increase in the degree of purification. In this study, the biogas production potential of citric acid wastewater (CAWW), which was pre-treated by chemical precipitation and electrocoagulation (EC) processes, was investigated. Pre-treatment experiments were designed using Box-Behnken Design (BBD) and chemical oxygen demand (COD) concentrations after hydrated lime (Ca(OH)2) precipitation and EC processes were determined as 4960 mg/L and 5120 mg/L, respectively. The pre-treated CAWW were finally used for the secondary treatment by anaerobic digestion (AD) process. After AD process COD degradation determined as 67% and 98% for Ca(OH)2 precipitation and EC process, respectively. In addition, the biogas production of the pre-treated CAWW increased approximately 2 and 7 times for the Ca(OH)2 precipitation and EC processes, respectively, compared to the untreated. The methane (CH4) content of the produced biogas increased by 18% and 50% for Ca(OH)2 precipitation and EC processes, respectively. According to 48-hour acute toxic test result, daphnia mortality decreased from 50% concentration of CAWW after AD, even 10% concentration is non-toxic to daphnia. In conclusion, the complementarity of Ca(OH)2 precipitation and EC processes with AD promoted both the removal of organics from wastewater and the production of valuable by-products.

Numerical modeling of microstructure development and chloride diffusion coefficient of cement paste with ellipsoidal particles

In view of the important role of cement profile in hydration process, pore structure characteristic, porosity and chloride ingression of cement paste, this paper aims to propose a numerical method for predicting the chloride diffusion coefficient of cement paste by considering the particle shape. By introducing periodic boundary conditions and contact function, the three-dimensional fresh cement paste with ellipsoidal particles is firstly constructed. By taking into account the interferences induced by overlapping of hydration layers between adjacent hydrated cement particles and calcium hydroxide precipitation, the vector hydration model is proposed. Each hydrated cement particles is composed of inner and outer hydration layers, unhydrated cement particle and partial calcium hydroxide embedded in the hydration layer. After the validity of hydration model is verified by the experimental data of hydration degree and the content of hydration products, the effects of aspect ratio on hydration degree, pore size distribution and porosity are evaluated. Secondly, based on first-passage theory, the Brownian motion algorithm applicable to voxel model is proposed. In order to improve the simulation efficiency, the first-passage radius and Brownian number are determined. The accurancy of this approach is fully verified by comparing with sufficient experimental data. Finally, resorting to this numerical algorithm, the effects of the aspect ratio and the diffusion coefficients of inner and outer hydration layer on chloride diffusion coefficient are analyzed.

Flexible droplet transportation and coalescence via controllable thermal fields

Flexible droplet transportation and coalescence are significant for lots of applications such as material synthesis and analytical detection. Herein, we present an effective method for controllable droplet transportation and coalescence via thermal fields. The device used for droplet manipulation is composed of a glass substrate with indium tin oxide-made microheaers and a microchannel with two transport branches and a central chamber, and it's manipulated by sequentially powering the microheaters located at the bottom of microchannel. The fluid will be unevenly heated when the microheater is actuated, leading to the formation of thermal buoyancy convection and the decrease of interfacial tension of fluids. Subsequently, the microdroplets can be transported from the inlets of microchannel to the target position by the buoyancy flow-induced Stokes drag. And the droplet migration velocity can be flexibly adjusted by changing the voltage applied on the microheater. After being transported to the center of central chamber, the coalescence behaviors of microdroplets can be triggered if the microheater located at the bottom of central chamber is continuously actuated. The droplet coalescence is the combined effect of decreased fluid interfacial tension, the shortened droplet distance by buoyancy flow and the increased instability of droplet under the elevated temperature. The droplet coalescence efficiency is also related to the voltage of microheater, by increasing the voltage from 3.5 V to 7 V, the needed time for droplet coalescence dramatically decrease from 220s to 1.4 s. Finally, by the droplet coalescence-triggered calcium hydroxide precipitation reaction, we demonstrate the applicability of the droplet manipulation method on specific sample detection. Therefore, this approach used for droplet transportation and coalescence can be attractive for many droplet-based applications such as analytical detection.

Zinc oxide in alkali-activated slag (AAS): retardation mechanism, reaction kinetics and immobilization

The relatively fast setting of alkali-activated slag (AAS) greatly restricts its wide application. ZnO can serve as the retardant for AAS. However, the role of ZnO in AAS is not well understood. This paper investigates the retardation mechanism of ZnO in the AAS system and the effects of ZnO on the reaction and performance of AAS. Results showed that a ZnO dosage of 2 wt% prolonged the setting of AAS paste by 72 min and inhibited the growth of C-(A)-S-H gels within the first 6 h of the reaction. The retardation of ZnO in AAS could be attributed to the ‘nucleation inhibition’, in which Zn2+ inhibits the generation of calcium hydroxide precipitation owing to the preferential incorporation of Ca in the calcium zincate (CZ) phase, thus reducing the nucleation sites and slowing down C-(A)-S-H gels growth, until all Zn ions are transformed into CZ phase or bonded in the AAS framework. ZnO slightly reduced the compressive strength and reaction extent of AAS, and was immobilized in AAS through various physicochemical approaches. This study provides a new look into the interaction between ZnO and AAS systems.

Effect of Unavoidable Ion (Ca2+) in Pulp on the Dispersion Behavior of Fine Smithsonite.

The efficient dispersion of particles is a prerequisite for the efficient flotation of fine smithsonite. However, unavoidable ions (Ca2+) in the pulp have become a challenge for the efficient separation of fine smithsonite, due to the high content of pulp and small radius of hydrated ions. Therefore, the dispersion behavior and mechanism of Ca2+ action on smithsonite are important for improving the efficiency of smithsonite flotation. In this study, the effects of Ca2+ on the dispersion behavior of fine smithsonite were studied using a turbidity test. The results showed that the dispersion behavior of smithsonite was good in the absence of Ca2+ at a range of pH = 4-12. However, the measured turbidity values of smithsonite decreased with the addition of calcium ions. In particular, the dispersion behavior of smithsonite became worse at pH &gt; 10. Zeta potential test results showed that the smithsonite's surface potential shifted positively, and the absolute value of potential decreased in the presence of Ca2+. The results of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis showed that calcium ions were adsorbed on the smithsonite surface, which may have caused ion exchange or the generation of calcium hydroxide precipitation leading to particle coalescence behavior. The calculations of solution chemistry and DLVO theory indicated that calcium ions adsorbed on the surface of smithsonite to form Ca(OH)+ or precipitation, which reduced the potential energy of interparticle interactions and led to the disruption of dispersion behavior of smithsonite.

Effect of types of curing environments on the self-healing capacity of mortars incorporating crystalline admixture

The presence of microcracks can lead to a reduction in the durability of concrete structures. In recent years, crystalline admixture has been used to repair microcracks in concrete. In this study, the effect of different amounts of crystalline admixture on the performance of mortar was firstly determined. In order to reveal the purpose of this study, a mortar with 4% crystalline admixture has been healed under three types curing environments (standard curing, water immersion, and saturated calcium hydroxide solution). The self-healing effect of the specimens was characterized macroscopically by water absorption tests and visualized crack images after repair. The type of crack filler was determined by microscopic analysis experiments XRD and SEM-EDX. The experimental results show that, firstly, the self-healing effect of mortar with crystalline admixture is limited by standard curing environments. Secondly, water immersion environment plays a weak role in promoting crack healing of mortars without crystalline admixture, and the addition of crystalline admixture leads to self-healing of the mortar due to a large amount of production of hydrated calcium silicate. Finally, the saturated calcium hydroxide solution has a beneficial effect on the self-healing of cracks in mortars without crystalline admixture due to the precipitation of calcium hydroxide from the healing solution. After the addition of crystalline admixture to the mortar, calcium ions and water promote the generation of calcium silicate hydrate, and the precipitation of calcium hydroxide acts together to fill the crack, resulting in the crack being completely healed.

Hydration kinetics and microstructure development of normal and NaAlO2‐activated Al‐doped β‐C2S pastes

AbstractSodium aluminate (NaAlO2) can be used to accelerate hydration of Portland cements. Here, we compare the use of NaAlO2 solutions with deionized water on the hydration of Al‐doped β‐C2S. The microstructure development of hydration product C‐S‐H obtained from hydrated Al‐doped β‐C2S was investigated. NaAlO2 significantly improved the hydration kinetics of Al‐doped β‐C2S due to the enhancement in the precipitation of calcium hydroxide and stimulation of C‐(A)‐S‐H nucleation and increased the early‐age mechanical strength of Al‐doped β‐C2S pastes. NaAlO2 promoted the incorporation of Al in the C‐(A)‐S‐H structure and accelerated the formation of C‐(A)‐S‐H phases containing tetra‐, penta‐ and hexa‐coordinated Al in its composition. The alkali cations modified the electrostatic equilibrium of the C‐(A)‐S‐H, thus promoting the development of the nano‐mechanical properties.

Influences of PCE superplasticizers with varied architectures on the formation and morphology of calcium hydroxide crystals

The impact of polycarboxylate (PCE) superplasticizers on calcium hydroxide (CH) precipitation and morphology were studied aiming at further understanding retardation effect of PCEs on cement hydration. Three comb-like PCEs with varied architecture and two linear copolymers (PAS) charged by carboxylic and sulfonic groups were synthesized. CH precipitate was prepared by simultaneous feeding NaOH and CaCl2 solutions in bulk solution containing various polymers. Analytical techniques of solution conductivity, ICP−OES, TG, XRD and SEM were used. Results show that the required [Ca] for massive CH precipitation is greatly increased by the presence of the polymers, suggesting inhibited nucleation and growth of CH crystals. The large incorporation of the polymers remarkably reduces the crystal size and consequently increases the specific surface area of the obtained CH. The polymers with higher density of carboxylic groups present stronger impacts on CH precipitation while such effect of the solely sulfonic group charged PAS is negligible.

An integrated process of calcium hydroxide precipitation and air stripping for pretreatment of flue gas desulfurization wastewater towards zero liquid discharge

Flue gas desulfurization wastewater (FGDWW) is produced during flue gas desulfurization process in coal-fired power plants. It has a complex composition and high pollutant concentration and is harmful to the environment. The Chinese government has regulated the zero liquid discharge (ZLD) of FGDWW. To achieve this, an integrated process of calcium hydroxide precipitation and air stripping for the pretreatment of FGDWW was developed in this study. Ca2+ and OH− were added in the calcium hydroxide precipitation step and reacted with SO42−, F− and Mg2+ in the real FGDWW to form precipitates for removal. The SO42− concentration was lower than the detection limit at pH 4, and the F− and Mg2+ concentrations were reduced to 4 and 46 mg/L at pH 11, respectively. The NH4+ concentration decreased to 7.86 mg/L after air stripping for 120 min at pH 11. The excess Ca2+ was removed by further stripping, and the pH value decreased to about 8.0. The F− and NH4+ removal rates were significantly higher in the real than the simulated FGDWW. After the pretreatment, the concentrations of SO42−, F−, Mg2+, NH4+, Ca2+, total dissolved solids (TDS), and chemical oxygen demand (CODCr) in the real FGDWW decreased to 0.00, 1.5, 20.35, 8.26, 8.61, 8260 and 86 mg/L, and the corresponding removal rates were 100.00%, 97.50%, 99.59%, 96.43%, 98.97%, 78.48% and 94.29%, respectively. The molar concentration ratio of Cl− and Na+ changed from 3.14:1 in the raw FGDWW to 1.02:1 in the pretreated FGDWW by adding Na2CO3 in the air stripping step to reduce membrane fouling in the reverse osmosis (RO) process. The treated FGDWW could be recycled, and the by-products (gypsum, (NH4)2SO4, CaCO3 and NaCl) could be utilized. This technology achieved ZLD of FGDWW, representing a clean pathway and promoting the sustainable development of the power industry. The added chemicals did not remain in the pretreated FGDWW, adhering to with the principle of cleaner production. The pretreatment technology exhibited not only high removal efficiency for the main pollutants, but also low operational cost and convenient automatic control.

PEG-assisted controlled precipitation of calcium hydroxide and calcium carbonate nanostructures for cement reinforcement

Herein, we have developed simple, one-stage and cheap precipitation methods for synthesizing Ca(OH)2 and CaCO3 nanoparticles with average sizes of (75 ± 8)0.95 and (70 ± 10)0.95 nm, respectively. Both methods are based on CaCl2 precursor and cheap polyethylene glycol (PEG) surfactant. The influence of the precipitation conditions on the size and morphology of crystallites was studied, and the required conditions for the formation of anisotropic crystals of Ca(OH)2 and CaCO3 were identified. Preliminary studies showed that all concentrations of isotropic CaCO3 nanoparticles increased the flexural and compressive strength of 2-day cement by more than 50% and more than 30%, respectively. The best overall result was achieved with 0.06% of CaCO3 nanoparticles, which increased the compressive and flexural strength of 28-day cement by ≈ 9% and ≈12%, respectively. The compressive strength of all the samples with Ca(OH)2 nanoparticles at 2 days and 28 days increased by more than 20% and more than 5%, while the flexural strength of all 2-day cements increased by more than 25%.

Fractionation of pulp and precipitated CaCO3\u2013pulp composites: effects on sheet properties of selective CaCO3 precipitation onto fiber size fractions

CaCO3-pulp composite was prepared via precipitation of calcium hydroxide in the presence of pulp. In order to investigate the precipitation selectivity and mechanism, the substrate pulps and the obtained composites were fractionated (R30, R100, R200, R400 and a sedimented fraction that passed the 400 mesh wire) using a Bauer-McNett unit. The main fractionation criterion was therefore fiber length. The pulp used was CTMP (chemithermomechanical pulp), yielding a precipitated calcium carbonate-chemithermomechanical pulp (PCC-CTMP) composite with a targeted PCC-to-CTMP ratio of 1:1. The PCC consisted primarily of nano-sized primary particles which formed aggregates and clusters on the fibers. When the fiber morphology, zeta potential and surface charge density of the fractions were determined, a correlation was found between the surface charge density of the CTMP and the ash content of the corresponding PCC-CTMP fractions. This supports the hypothesis that the precipitation on the CTMP fiber is driven by the charge interparticle interaction. The use of refined CTMP furnishes and fractionation of the PCC-CTMP furnishes demonstrates that PCC is preferably fixed on fines and fibrils since it appears at a higher content in the fines fractions. Fiber activation via fiber split, removal of primary wall and surface defibrillation enhanced the affinity of the PCC for the fibrils. The laboratory handsheets prepared from the material demonstrated the importance of controlling the substrate fiber properties for the mineral-fiber composite, e.g. via refining, as differences between the refining levels and fractions were found to lead to differences in both optical properties and bonding.Graphic abstract

Retarder effect on hydrating oil well cements investigated using in situ neutron/X-ray pair distribution function analysis

Understanding the role of retarder on the chemical nature and molecular architecture of hydrating cement paste is essential for engineering oil well cements with additives. Here, synchrotron X-ray and total neutron scattering with pair distribution function (PDF) analysis were performed in combination with calorimetry and nuclear magnetic resonance (NMR) to examine the retarder effect in hydrating tri-calcium silicate (C3S) and Class G oil well cement paste. Primarily, the retarder, Diethylenetriamine pentamethylene phosphonic acid (DTPMP) influenced the hydration by affecting the Ca-O and Ca-Si pair correlation providing evidence of calcium playing a predominant role in the retardation process. Secondary effects related to Calcium-Silicate-Hydrate (C-S-H) nuclei poisoning influencing the suppression of calcium hydroxide precipitation were observed. These findings provide insights into the retardation mechanism of hydrating cement paste influenced by calcium depletion when subjected to phosphonate retarders.

Improved methane production and sulfate removal by anaerobic co-digestion corn stalk and levulinic acid wastewater pretreated by calcium hydroxide.

Levulinic acid wastewater containing high concentration of sulfate was generated while producing levulinic acid by straw depolymerization with dilute sulfuric acid. In this study, levulinic acid wastewater was pretreated by calcium hydroxide precipitation, then co-digestion of pretreated levulinic acid wastewater and corn stalk was conducted for the further removal of sulfate from levulinic acid wastewater and production of bioenergy. Effects of sulfate loading and substrate level on methane production and sulfate removal from co-digestion were investigated. The results showed that the highest methane production potential of 249.93 mL/g volatile solid (VS) was achieved when the sulfate loading is 0.31 g/L and the substrate level is 32.3 g/L, which was significantly higher than 182.53 mL/g VS achieved for mono-digestion of corn stalk. The sulfate removal of 86.82-98.10% was obtained when sulfate loading is >0.31 g/L, and the concentration of sulfate in the biogas slurry was <0.09 g/L after 28 days of anaerobic co-digestion regardless initial sulfate loading. The results of microbial community analysis demonstrated that the relative abundance of methanogenic bacteria (such as Methanoculleus and Methanosarcina) had increased significantly at sulfate loading of 0.31 g/L, and the relative abundance of sulfate-reducing bacteria (Desulfotomaculum) increased from 0.01% to 2.11% when the sulfate loading rose from 0.10 g/L to 1.47 g/L under the substrate level of 32.3 g/L. This means that co-digestion of corn stalk and levulinic acid wastewater after calcium hydroxide pretreatment (CHP) was beneficial for methane production and sulfate removal.

Design and Application of High-Temperature Raw-Seawater-Based Fracturing Fluids

Summary Typically, water-based fracturing treatments consume a large volume of fresh water. Providing consistent freshwater sources is difficult and sometimes not feasible, especially in remote areas and offshore operations. Therefore, several seawater-based fracturing fluids have been developed in an effort to preserve freshwater resources. However, none of these fluids minimizes fracture-face skin and proppant-conductivity impairment, which can be critical for unconventional well treatments. Several experiments and design iterations were conducted to tailor raw-seawater-based fracturing fluids. These fluids were designed to have rheological properties that can transport proppant under dynamic and static conditions. The optimized seawater-based fracturing-fluid formulas were developed such that no scale forms when additives are mixed in or when the fracturing-fluid filtrate is mixed with different formation brines. The tests were conducted using a high-pressure/high-temperature (HP/HT) rheometer, coreflood, and by aging cells at 250 to 300°F. The developed seawater-based fracturing fluids were optimized with an apparent viscosity greater than 100 cp at a shear rate of 100 seconds–1 and a temperature of 300°F for more than 1 hour. The use of polymeric- and phosphonate-based scale inhibitors (SIs) prevented the formation of severe calcium sulfate (CaSO4) scale in mixtures of seawater and formation brines at 300°F. Controlling the pH of fracturing fluids prevented magnesium and calcium hydroxide precipitation that occurs at a pH value of greater than 9.5. Most importantly, SIs had a negative effect on the viscosity of seawater fracturing fluid during testing because of their negative interaction with metallic crosslinkers. The developed seawater-based fracturing fluids were applied for the first time in an unconventional and a conventional carbonate well and showed very promising results; details of field treatments are discussed in this paper.

The coupling effect of calcium concentration and pH on early hydration of cement

Pore solution provides the physical and chemical environment for cement hydration, in which calcium, silicon, and hydroxyl ions released by dissolution of cement clinker are transferred into the hydration products such as calcium silicate hydrates (C-S-H) and calcium hydroxide (CH). Therefore, both calcium ions and pH not only have significant influence on the dissolution of cement clinker but also on the precipitation of CH and C-S-H. However, how they influence the kinetics of cement hydration, especially at the very early stage, remains unclear. With the attempt to explore this influence potassium oxalate and oxalic acid were used to regulate the calcium concentration and pH within pore solution independently. Cement pastes with different formulations were investigated by the combination of calorimetric measurements and pore solution analysis.The results suggest that simultaneous removal of calcium and hydroxyl ions can significantly increase the length of induction period and reduce the height of the silicate reaction peak in the calorimetric curves, whereas the removal of hydroxyl or calcium ions alone cannot. The calculation of saturation index of alite, CH, and C-S-H indicates that undersaturation degree of alite during induction period is well related to the length of induction period and simultaneous removal of calcium and hydroxyl ions is likely to cause lower undersaturation degree of alite, longer induction period, and postponed time of silicate peak. The increase of pH could result in a higher sulfate concentration and subsequently a higher aluminate peak, and a shorter time interval between silicate and aluminate peak.

Potential Use of Incineration Fly Ash as a Sustainable Low Cost Material for Heavy Metals Removal from Acid Mine Drainage

The objective of this study is to investigate the potential use of MSW incineration fly ash as an economic material for the removal of heavy metals (Pb, Mn, Fe, and Cu) from AMD. Batch adsorption experiment was conducted to examine the effects of pH, adsorbent dosage and contact time on metal ions removal in synthetic AMD using MSW incineration fly ash. Precipitation of calcium hydroxide and sodium hydroxide was used for comparison with MSW incineration fly ash by adjusting the pH (5 ~ 11) by coagulation method with 20 min reaction time. Comparing the application of Ca(OH)2 and Na(OH), fly ash proves more efficient which may be due to its porosity and chemical composition. The results from adsorption studies showed that maximum adsorption rate was achieved at 0.4g dose when various fly ash dosages were added to the solution with 60 min optimum time and removal efficiency of heavy metals was over 96%. The effectiveness of fly ash can be related to its high calcium (CaO 55%) content. Efficiency of heavy metals removal was directly linked to the amount of fly ash in the reaction mixture and to the final pH attained. pH plays a significant role in heavy metal uptake. The main removal mechanism was adsorption at the surface of the fly ash together with the precipitation and co- precipitation from the solution with chemicals. Therefore the use of MSW incineration fly ash for treatment of AMD would represent a new market opportunity for this waste product. It can also be useful for neutralizing AMD and possibly reduce its adverse effects to the environment with efficient removal of metal ions from AMD.

Microstructure of interface between fibre and matrix in 10-year aged GRC modified by calcium sulfoaluminate cement

Time-dependent property changes in glass fibre reinforced cement (GRC) mainly result from a combination of the alkalinity of the matrix and densification of the matrix (e.g. due to calcium hydroxide precipitation) within and around the glass fibre strands. The microstructure of the interface between matrix and fibres in GRC has a significant impact on its durability. This paper describes a study of two GRC formulations (with OPC, and OPC plus calcium sulfoaluminate based matrices) aged for 10years at 25°C. Thin-section petrography (TSP) and SEM are used to compare the microstructure of both polished surfaces and fractured surfaces. The aged OPC/GRC demonstrates significantly brittle behaviour with substantial densification of C–S–H/CH intermixture occurring around glass fibres. In contrary, the aged composite made with the OPC plus calcium sulfoaluminate shows greatly retained toughness, accompanied by considerably flexible interfacial and interfilamentary areas around the glass fibres.