Search

Abstract: The effect of Zn2+ on both the kinetic and equilibrium aspects of arsenic adsorption to magnetite nanoparticles was investigated at pH 4.5–8.0. At pH 8.0, adsorption of both arsenate and arsenite to magnetite nanoparticles was significantly enhanced by the presence of small amount of Zn2+ in the solution. With less than 3 mg/L of Zn2+ added to the arsenic solution prior to the addition of magnetite nanoparticles, the percentage of arsenic removal by magnetite nanoparticles increased from 66% to over 99% for arsenate, and from 80% to 95% for arsenite from an initial concentration of ∼100 μg/L As at pH 8.0. Adsorption rate also increased significantly in the presence of Zn2+. The adsorption-enhancement effect of Zn2+ was not observed at pH 4.5–6.0, nor with ZnO nanoparticles, nor with surface-coated Zn–magnetite nanoparticles. The enhanced arsenic adsorption in the presence of Zn2+ cannot be due to reduced negative charge of the magnetite nanoparticles surface by zinc adsorption. Other cations, such as Ca2+ and Ag+, failed to enhance arsenic adsorption. Several potential mechanisms that could have caused the enhanced adsorption of arsenic have been tested and ruled out. Formation of a ternary surface complex by zinc, arsenic and magnetite nanoparticles is a possible mechanism controlling the observed zinc effect. Zinc-facilitated adsorption provides further advantage for magnetite nanoparticle-enhanced arsenic removal over conventional treatment approaches. Synopsis: Arsenic adsorption to magnetite nanoparticles at neutral or slightly basic pH can be significantly enhanced with trace amount of Zn2+ due to the formation of a ternary complex. [ABSTRACT FROM AUTHOR]

• Metal-phosphonate colloidal inhibitor (MPCI) is a promising squeeze chemical. • Citrate-assisted one-pot synthesis route was introduced to prepared MPCI. • Low-solubility MPCI with 40 nm prepared in a facile and economical manner. • 100% MPCI breakthrough realized within 2.5 pore volumes in sand column. • MPCI normalized squeeze lifetime is as high as 1100 m3 kg−1 in sand medium. Mineral scale deposition is a serious flow assurance concern threatening the safety and integrity of oilfield operations. Subsurface and wellbore scale control is commonly managed by scale squeeze treatment. Compared to the conventional chemical inhibitor pill applied in a scale squeeze treatment, colloidal scale inhibitor materials are capable of enhancing inhibitor transportability in formation medium and extending squeeze lifetime. A number of functional scale inhibitor colloidal materials have been synthesized in the previous studies including the crystalline low solubility materials. However, these reported synthesis routes are complicated to follow, involving extensive experimental setup. In this study, a one-pot synthesis route has been presented to prepare metal-phosphonate colloidal inhibitor (MPCI) material in a facile and economical manner. This method is based upon a citrate-assisted approach where a low solubility MPCI material with 40 nm particle size can be produced. Laboratory transport experiment suggests that calcium-based MPCI can be transportable through sand medium at representative oilfield conditions with 100% breakthrough realized within 2.5 pore volumes in sand-packed column. Laboratory squeeze simulation tests indicate that this material is able to return inhibitor with a stable return concentration for an extended squeeze lifetime. The calculated normalized squeeze lifetime of calcium-based MPCI is as high as 1100 m3 kg−1 in sand medium. Magnesium and Zirconium based MPCI can increase the stabilized inhibitor return concentration up to 3 mg L−1. This study expands our understanding of the colloidal inhibitor materials and promotes the potential field application of such materials for oilfield scale squeeze treatment. [ABSTRACT FROM AUTHOR]

Understanding scale deposition kinetics and the mechanism of inhibition is important for scale prediction and remedial strategies in the energy industry. A novel experimental apparatus was designed to understand calcite scale deposition kinetics under relevant industrial conditions and to determine scaling inhibition effects of four phosphonate and two polymer inhibitors. A 1-D transport-reaction model was also developed to conceptually simulate the behavior of the inhibitor within the reaction column following basic laws of advection and adsorption. Inhibition experiments showed that for all phosphonate inhibitors tested and PPCA, the minimum effective inhibitor concentration needed to induce an inhibition effect within a maximum 1 h time frame was also sufficient to achieve 100% inhibition within the column. The exception, CMI, only achieved 80% inhibition. The 1-D transport-reaction model was then used to simulate the experimental data, assuming Langmuirian adsorption of the inhibitor within the column. Preliminary simulations suggest a maximum adsorption of 1–8 mg/m2 for phosphonate inhibitors, indicating that a multilayer adsorption mechanism operates under our experimental conditions. • A novel flow through apparatus mimicking calcite scale formation as it occurs in oil production pipelines was developed. • A 1D advection-reaction model was developed to interpret deposition kinetics and inhibition in flow through experiments. • Under high salinity and temperature conditions, calcite scale deposition was found to be diffusion controlled. • Langmuirian adsorption is the likely mechanism by which inhibitors attach to scale surfaces and prevent further growth. • Preliminary simulations suggest that a multilayer adsorption mechanism operates under our experimental conditions. [ABSTRACT FROM AUTHOR]

The Ba x Sr 1-x SO 4 solid solution is ubiquitously present in both geological and industrial processes, where they mostly form under non-equilibrium conditions. Compared with those formed under equilibrium conditions, the Ba x Sr 1-x SO 4 solid solution formed at non-equilibrium condition has significantly higher Sr incorporation at the same aqueous phase compositions. The solid composition of Ba x Sr 1-x SO 4 formed at non-equilibrium condition is critical for the study of chemical palaeoceanography as well as the solid solution nucleation and growth kinetics. However, few studies have been conducted to investigate the composition of the Ba x Sr 1-x SO 4 solid solution when it precipitates at non-equilibrium conditions. In this study, the distribution coefficient of Ba2+ and Sr2+ between the Ba x Sr 1-x SO 4 solid solution and the aqueous phases (K D,Sr-Barite) at non-equilibrium conditions was studied with barite saturation index (SI barite) from 0.9 to 1.5, [Sr2+]/[Ba2+] molality ratio from 0.33 to 30, temperature (T) from 50 to 90 °C and ionic strength (IS) from 0.01 M to 3 M as NaCl, with celestite being undersaturated. The composition of the Ba x Sr 1-x SO 4 solid solution formed at non-equilibrium conditions can then be calculated from the K D,Sr-Barite values. The results show that the K D,Sr-Barite value decreases with the increase of aqueous Sr2+ concentration at fixed SI barite and T conditions. The IS effect on the K D,Sr-Barite value is small. Based on the experimental results, a new empirical model is developed to accurately predict the measured compositions of Ba x Sr 1-x SO 4 solid solution at non-equilibrium conditions under a wide T and IS conditions as follows (the plot of the predicted log 10 K D ,Sr-Barite versus the measured log 10 K D ,Sr-Barite with R 2 = 0.9995) : K D , S r - B a r i t e = - 1.21 - 1.84 SI barite + 1928.1 SI barite × T + a Sr 2 + , a q a Ba 2 + , a q - 1 Several theoretical models have also been compared against the experimental data. The birth and spread crystal growth model (B + S model) could accurately predict the solid composition of Ba x Sr 1-x SO 4 at higher barite SI and/or higher T conditions (barite SI = 1.5 at 70 °C and barite SI = 1.2–1.5 at 90 °C with [Sr2+]/[Ba2+] = 0.33–10). However, the B + S model predictions show larger deviations at lower SI and/or lower T conditions (barite SI = 0.9 and 1.2 at 50 °C and barite SI = 0.9 at 70 °C with [Sr2+]/[Ba2+] = 0.33–10 in this study). For other theoretical models, such as the CNT model and the BCF model, the predicted solid compositions of Ba x Sr 1-x SO 4 are significantly higher than the measured results. This quantitative study of the Ba x Sr 1-x SO 4 solid solution compositions could help reconstruct oceanic physical conditions and chemistry. It also establishes a solid foundation to further investigate the kinetics of the Ba x Sr 1-x SO 4 solid solution formation during non-equilibrium geological and industrial processes. [ABSTRACT FROM AUTHOR]

Although sulfide scales of FeS, PbS, and ZnS do not occur as frequently as carbonate and sulfate scales, it is difficult to remove them once they are formed and deposited. Effective prevention and remediation of sulfide scales have not been fully developed. For sulfide scales, the conventional threshold inhibition approach is not as effective as for carbonate and sulfate scales, presumably, due to strong ion pairs formation of FeS0 and fast precipitation kinetics of FeS s. Polyacrylamide (PAM), polyvinyl pyrrolidone (PVP), and carboxymethyl cellulose (CMC) were examined as dispersants for sulfide scales to prevent and mitigate sulfide scale deposition through controlling the particle sizes of FeS, PbS and ZnS. PAM, PVP, and CMC dispersed FeS particles more effectively at pH 6.7 than 5.0 and temperature 70 °C than 90 °C. PAM and CMC successfully dispersed FeS particles even in extremely high ionic strength (I) of 4.6 M, while, PVP, slightly less effective, up to I = 2.6 M. At pH 5.0 and 90 °C, CMC was able to disperse FeS particles up to I = 1.3 M and PVP up to I = 0.6 M. In contrast, PAM could not disperse FeS particles at all. When FeS particles were dispersed in the presence of polymeric dispersants, FeS particle sizes remained in nanometer ranges, from 100 to 600 nm. Our results demonstrated that CMC was the best dispersant for FeS particles among the three polymers we tested. For CMC, the larger molecular weight and the lower degree of substitution of carboxylic groups on cellulose, the more effective dispersant CMC became. PbS and ZnS were also well dispersed in the presence of CMC. Almost all fraction of PbS particles was smaller than 200 nm, while about 60% of ZnS particles were smaller than 200 nm. Results demonstrated that the promising treatment selection of CMC as a universal dispersant for sulfide scales. • The growth and deposition of FeS, PbS and ZnS were effectively prevented with carboxymethyl cellulose (CMC). • Dispersed sulfide scales remained in nanometer size ranges. • CMC could be applied as a universal dispersant for sulfide scale control in oilfield operation conditions. • Dispersant for sulfide scales should form strong complex with sulfide minerals and provide structural rigidity. [ABSTRACT FROM AUTHOR]

Abstract Ferric hydroxide precipitation and flocculation is the most commonly used method for the removal of arsenic in water treatment. However, citrate often interrupts the precipitation of ferric hydroxides and thus affects arsenic removal. To date, the mechanisms controlling the effects of citrate on arsenic removal with ferric hydroxide flocculation and precipitation at very low citrate-to-Fe molar ratios are not well understood. Herein, we report a new mechanism by which citrate inhibits arsenic removal using ferric hydroxide. At a substoichiometric citrate-to-Fe molar ratio of 0.28, citrate forms a high-molecular-weight Fe−citrate (Fe 4 Cit) species. The optimized structure of the Fe 4 Cit species was obtained by the density functional theory calculation. To the best of our knowledge, this study is the first to report the formation and to identify the structure of dominant Fe–citrate species at a very low citrate-to-Fe molar ratio. Graphical abstract Image 1 Highlights • Citrate at substoichiometric concentrations inhibits ferric hydroxide precipitation. • This effect results in hindered arsenic removal at low citrate-to-Fe molar ratios. • Inhibition effect by citrate is due to the formation of Fe–citrate species. • Structure of Fe–citrate species is identified as [Fe 4 O 13 H 3 Cit·2H 2 O]+. [ABSTRACT FROM AUTHOR]

Abstract Surfactants are important environmental chemicals due to their extensive domestic and industrial applications, such as subsurface organic pollution remediation and enhanced oil recovery. However, the interaction of surfactants with subsurface material particularly the desorption behavior of surfactants is less understood. Surfactant desorption is essential to control the fate and transport of surfactants as well as organic pollutants. In this study, the sorption and desorption of linear sodium dodecylbenzene sulfonate (SDBS) and sodium hexadecyl diphenyl oxide disulfonate (DPDS) with two types of soil sediment samples are compared. Sorption of surfactants can be modeled by hydrophobic sorption. Less DPDS sorption is observed at a higher aqueous concentration, which is attributed to the competition between surfactant micelles and sediment organic matter for DPDS sorption. A significant fraction of the sorbed surfactants resists desorption, and this is not a result of surfactant precipitation or desorption kinetics. Surfactant desorption behavior is similar to the irreversible desorption of hydrocarbons from soil with only half of the resistant phase surfactant being readily extracted by heated solvent extraction. The sorption/desorption data are interpreted with a molecular topology and irreversible sorption model. The knowledge of this study can be useful in understanding the environmental fate and transport of these common anionic surfactants. The methodology developed in this study can be expanded to study the sorptive nature of a wider range of surfactants in the environment. Graphical abstract Image 1 Highlights • Both SDBS and DPDS surfactants show a sorption maximum near the CMC. • DPDS micelles compete with sediment organic matter for DPDS sorption. • Desorption of SDBS and DPDS deviate significantly from the sorption process. • Surfactant desorption is similar to hydrocarbon irreversible desorption from soil. • A higher surfactant aqueous concentration reduces surfactant loss due to sorption. [ABSTRACT FROM AUTHOR]

Sulfonated polyacrylate copolymer (also known as vinyl sulfonated co-polymer; VS-Co) have been widely used in mineral scale control. However, the speciation chemistry of such polymers in solution is not fully understood. In this paper, the acid-base and calcium complex solution chemistry of a VS-Co has been determined from 0.01 to 2 m ionic strength and from 25 to 90 °C by combining electrostatic theory with potentiometric titrations. To process the titration data, VS-Co is treated as a hypothetical, averaged monoacid, HA, with the same concentration of the active carboxylic functional groups of VS-Co. The acid and calcium dissociation reactions of this acid are simply considered as 1:1 type hypothetical reactions, namely HA↔H + + A − and Ca(A⋯A)↔Ca 2+ + (A⋯A) 2− , with (A⋯A) 2− as an arbitrary combinations of two dissociated A − units. The microconstants of the acid dissociation reaction are fitted with a linear electrostatic model with p K a = p K a , intr + b e l e c θ A − , where p K a , intr is an intrinsic constant referring to the condition of zero dissociation, θ A − is the deprotonated fraction of carboxylic functional groups and b elec is an electrostatic factor based on polyelectrolyte theory. Similarly, the microconstants of the Ca 2+ dissociation reaction are fitted with p K CaA 2 = p K CaA 2 , intr + 2 b elec θ A − with doubled electrostatic effect since the complexation of Ca 2+ with the polymer is considered to neutralize two negative charges. To quantitatively describe the speciation of VS-Co at various conditions, the p K a , intr , p K CaA 2 , intr , and b elec values are fitted empirically as a function of temperature ( T , K), and ionic strength ( I , m): p K a , intr = 5.068 − 128.398 T − 0.924 × I 1 / 2 + 0.311 × I p K CaA 2 , intr = 5.754 − 888.644 T − 5.749 × I 1 / 2 + 2.221 × I b e l e c = 3.234 − 1.321 × I 1 / 2 + 0.399 × I . Fitted results suggests no significant effect of temperature on the electrostatic factor b elec , which is consistent with electrostatic theory. Results from this study can be used to predict the equilibria of VS-Co in a solution, at various temperature, ionic strength, pH, and metal concentrations. [ABSTRACT FROM AUTHOR]

• This model elucidates possible mechanisms of gypsum crystallization and inhibition. • The induction time of gypsum crystallization and inhibition is accurately predicted. • This model can help significantly improve the membrane treatment efficiency. • The new model has practical implications in various industries. Water desalination using membrane technology is one of the main technologies to resolve water pollution and scarcity issues. In the membrane treatment process, mineral scale deposition and fouling is a severe challenge that can lead to filtration efficiency decrease, permeate quality compromise, and even membrane damage. Multiple methods have been developed to resolve this problem, such as scale inhibitor addition, product recovery ratio adjustment, periodic membrane surface flushing. The performance of these methods largely depends on the ability to accurately predict the kinetics of mineral scale deposition and fouling with or without inhibitors. Gypsum is one of the most common and troublesome inorganic mineral scales in membrane systems, however, no mechanistic model is available to accurately predict the induction time of gypsum crystallization and inhibition. In this study, a new gypsum crystallization and inhibition model based on the classical nucleation theory and a Langmuir type adsorption isotherm has been developed. Through this model, it is believed that gypsum nucleation may gradually transit from homogeneous to heterogeneous nucleation when the gypsum saturation index (SI) decreases. Such transition is represented by a gradual decrease of surface tension at smaller SI values. This model assumes that the adsorption of inhibitors onto the gypsum nucleus can increase the nucleus superficial surface tension and prolong the induction time. Using the new model, this study accurately predicted the gypsum crystallization induction times with or without nine commonly used scale inhibitors over wide ranges of temperature (25–90 °C), SI (0.04–0.96), and background NaCl concentration (0–6 mol/L). The fitted affinity constants between scale inhibitors and gypsum show a good correlation with those between the same inhibitors and barite, indicating a similar inhibition mechanism via adsorption. Furthermore, by incorporating this model with the two-phase mineral deposition model our group developed previously, this study accurately predicts the gypsum deposition time on the membrane material surfaces reported in the literature. We believe that the model developed in this study can not only accurately predict the gypsum crystallization induction time with or without scale inhibitors, elucidate the gypsum crystallization and inhibition mechanisms, but also optimize the mineral scale control in the membrane filtration system. [Display omitted]. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cadmium selenide nanoparticles (NPs) are colloidally stable in 1M NaCl brine solution. [•] A nonionic ethoxylated alcohol surfactant (Neodol) provides this salt stability. [•] NPs are colloidally stable up to 70°C, near the surfactant cloud point temperature. [•] NPs can travel through crushed calcite and sandstone and through a sandstone core. [•] NP adsorption during porous media flow can occur due to surfactant clouding. [ABSTRACT FROM AUTHOR]