Ammonium Acetate Concentration Research Articles

Comparative analysis of multi-effect evaporators in an ammonium acetate concentration process for L-methionine production

The process of treating an acetic acid aqueous solution generated during L-methionine production with ammonia and recovering a highly concentrated ammonium acetate aqueous solution using a multi-effect evaporator process was studied. The electrolyte non-random two-liquid model was applied to calculate the activity in the electrolyte solution, and the Hayden-O’Connell model was used to consider the dimerization reaction of acetic acid in the vapor phase. The dissociation equilibrium constant of acetic acid was modeled based on experimental values, and all other thermodynamic property models and parameters were used as implemented in the Aspen Plus software. Economic evaluation was carried out with various sensitivity tests, considering the loss of acetic acid and ammonia, as well as the steam cost. Evaporator operation was found to be more economical when the molar ratio of acetic acid to ammonia was equal, feed concentration was high, feed flow rate was low, and evaporator temperature was low. These results were confirmed in actual plant operations, with significant correlations between the feed flow rate and evaporator temperature. Our findings have significant implications for the development of sustainable and economical L-methionine production methods that enable the recycling of ammonium acetate.

Optimizing solid phase extraction and HPLC-MS/MS parameters for reliable quantification of COVID-19 pharmaceuticals in Mexico City’s wastewater: A design of experiments approach

Through the COVID-19 health crisis, a plethora of new medications, along with some discontinued pharmaceuticals, were directly tested on population to assess their efficacy in symptom management. Consequently, residues from these treatments were systematically disposed into sewage systems, presenting a novel contamination challenge in urban centers. To effectively address this issue by environmental authorities, the presence of these pollutants in wastewater must be accurately quantified. Herein, we conducted a meticulous study to validate an analytical method based on solid-phase extraction (SPE) and high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) to detect six pharmaceuticals (metformin, famotidine, indomethacin, dexamethasone, azithromycin, and ivermectin) in wastewater. Using a Plackett-Burman design (PBD), the eight parameters significantly impacting on the HPLC-MS/MS technique were established based on the analytical signal of the six analytes. Subsequently, in conjunction with a Box-Behnken design (BBD), optimal analysis conditions were determined as follows: injection volume: 10 µL, column temperature: 20 °C, capillary voltage: 4100 V, drying gas temperature and flow rate of 350 °C and 7 L min−1 respectively, nebulizer pressure: 15 psi, concentration of formic acid and ammonium acetate in the mobile phase of 0.1 % and 10 mmol/L, respectively. SPE was optimized through a univariable experimental design. OASIS HLB cartridges exhibited the highest extraction efficiency compared to highly polar and non-polar adsorbents. The optimal sample loading conditions were set as 250.0 mL of water sample at pH = 9.0. The washing conditions were 5.0 mL of a 95:5 water:methanol solution, while elution conditions were optimal using 6.0 mL of a 98:2 methanol:formic acid solution. After evaporating the eluate to dryness and reconstituting in 1.0 mL of a 98:2 methanol:formic acid solution, a concentration factor of 250 was achieved. The analytical method was validated using for matrices, namely, raw and treated wastewater, wastewater percolated through soil and groundwater. Acceptable levels of precision and accuracy were achieved for all analytes in the tested matrices. Using the validated method, the six pharmaceuticals were quantified in environmental samples, revealing high levels of metformin, dexamethasone, and azithromycin in Mexico City’s sewage. Highly polar compounds displayed mobility through environment as they were present in effluent samples, percolated wastewater, and groundwater.

Blast furnace slag for SO2 capture: Optimization and prediction using RSM and ANN

The main reaction parameters examined were the amount of blast furnace slag, the hydration duration, ammonium acetate concentration, and temperature. The Response surface methodology was employed to quantify their impact on the sorbent's surface area. Using a central composite design, the surface area of the resulting sorbent corresponding to Brunauer-Emmett-Teller (BET) was investigated. The sorbents produced range in surface area from 49.89 to 155.33 m2/g. Additionally, the effectiveness and response prediction capacities of the Response Surface Methodology (RSM) and Artificial Neural Network (ANN) modeling methodologies were investigated. The models were assessed using various statistical metrics, including (MSE) mean squared error, (ARE) average relative errors, the (SSE) sum of squared errors, (HYBRID) Hybrid fractional error function, (SAE) Sum of the absolute errors, (R2)coefficient of determination, and Root means square. According to statistical evidence, the ANN approach surpassed the RSM-CCD model approach. The surface area of the sorbent was shown to be significantly influenced by interactions between variables in addition to all the individual variables examined. The sorbent was made from a material with substantial structural porosity based on SEM. The functional groups were identified using FTIR. The XRF determined the elemental composition of BFS-based sorbents.

Optimization and validation of a bioanalytical HPLC-UV technique for simultaneous determination of underivatized phenylalanine and tyrosine in the blood for phenylketonuria diagnosis and monitoring.

This study aimed to develop a fast, accurate, and precise high-performance liquid chromatography with UV detection method for simultaneous analysis of underivatized phenylalanine (Phe) and tyrosine (Tyr) in biological samples. Separation of the analytes was accomplished using a Discovery HS F5-3 column, which offered better retention and peak symmetry for the tested analytes. Chromatographic conditions were optimized using central composite experimental design, and three factors were investigated: the concentration of ammonium acetate (A), the acetonitrile proportion in the mobile phase (B) and the column oven temperature (C). The approach was verified using β-expectation tolerance intervals for total error measurement that did not exceed 15%. Optimal settings were A = 50mm, B = 24% and C = 28°C. The method applicability was determined using human plasma from 75 volunteers. The limits of detection and quantification of the technique were satisfactory at 9 and 29 μm for Phe and 4 and 13 μm for Tyr. The mean analytical bias in spiking levels was acceptable, ranging from -1.649 to +1.659% for both substances, with RSD <5% in all instances. The suggested approach was successfully used to analyze Phe and Tyr in human blood samples and calculate the Phe/Tyr ratio.

Application of a Quality by Design Approach to Develop a Simple, Fast, and Sensitive UPLC-MS/MS Method for Quantification of Safinamide, an Antiparkinson’s Drug, in Plasma

Safinamide is an orally active, selective monoamine oxidase-B inhibitor with dopaminergic and non-dopaminergic properties approved by the European Medicine Agency and US Food and Drug Administration for the treatment of mid- to late-stage fluctuating Parkinson’s disease (PD) used in combination with other PD medications such as levodopa. In this study, an analytical quality by design (AQbD) approach was applied to optimize an LC-MS/MS bioanalytical method to determine safinamide in human plasma. A full 33 factorial design was used to optimize safinamide separation conditions, with a method first screened and optimized using chromatographic responses, including peak area and retention time. The results showed that temperature had a significant indirect effect on retention time and peak area (p &lt; 0.05), while ammonium acetate concentration had an insignificant indirect impact on peak area or retention time. However, the temperature was significantly agonistic to the effect of buffer concentration (p &lt; 0.05). The resultant optimized chromatography conditions utilized 9.0 mM ammonium acetate buffer and acetonitrile (22.0:78.0) as mobile phases at a column temperature of 23.2 °C. The assay was linear from 0.1–1000 ng/mL, met acceptance criteria for inter- and intra-assay precision and accuracies across three quality controls, and was successfully applied to in vitro microsomal metabolic stability. The UPLC/MS/MS method was found to be adequately sensitive and suitable for routine safinamide pharmacokinetic studies.

Singularly narrow size distributions of 200 nm polystyrene latex spheres determined by high resolution mobility analysis

A high-resolution differential mobility analyzer (DMA) is used for the first time to study the mobility distribution of Polystyrene Latex (PSL) particles. We investigate in particular some unique, nominally 200 nm and 100 nm PSL particles, known by other methods to be unusually monodisperse. The suspensions are electrosprayed after adding ammonium acetate to a concentration of 10 mmol/L. Mobility analysis is carried out after charge reduction with a second electrospray of the opposite polarity. The 200 nm particles typically produce two narrow peaks, with relative intensities that depend on electrospray parameters. Under the most favorable spraying conditions achieved, the more mobile peak becomes dominant, is narrowest, and has a repeatable mobility; we attribute it provisionally to the unpolluted suspended particles. The less mobile peaks are substantially more variable but never entirely removed. We initially attributed them to attachment of involatile solutes in the suspension to the atomized PSL particles; however, this hypothesis is put in doubt by later observations. The measured relative width of the mobility distribution for the most mobile peak is FWHMZ = (1.65 ± 0.08) %. This translates into a width for the diameter distribution FWHMd = (1.09 ± 0.05) % or standard deviation σd = (0.46 ± 0.02) %, by far the most monodisperse polymeric submicron particle suspension so far reported. Concentrations of ammonium acetate of 100 mmol/L and 40 mmol/L were also tested in order to reduce residue attachment by forming smaller initial electrosprayed drops. These higher salinities, however, led to capillary clogging, apparently because the narrow electrospraying jet precludes the passage of the PSL particles. The 100 nm particles gave a wider variation in mean diameter and size distribution depending on electrospraying parameters, perhaps because of the suspension's considerably larger content of involatile solutes. Unlike the 200 nm particles, no spraying condition was found under which a precisely repeatable size distribution could be achieved for the 100 nm particles. However, the data do point to an estimated upper bound on the size distribution width of FWHMd ≈ 3 % (σd ≈ 1.3 %), which is uniquely narrow for particles of this size.

Evaluation of Hold-Up Volume Determination Methods and Markers in Hydrophilic Interaction Liquid Chromatography.

Common methods for hold-up time and volume determination in Reversed-Phase Liquid Chromatography (RPLC) have been tested for Hydrophilic Interaction Liquid Chromatography (HILIC). A zwitterionic ZIC-HILIC column has been used for the testing. The pycnometric determination method, based on differences in column weight when filled with water or organic solvent, provides the overall volume of solvent inside the column. This includes the volume of eluent semi-sorbed on the packing of the column, which acts as the main stationary phase. The homologous series approach, based on the retention behavior of homologues in relation to their molecular volume, allows the determination of accurate hold-up volumes. However, the application of this method is time-consuming. In some cases, large neutral markers with poor dipolarity/polarizability and hydrogen bonding interactions can be used as hold-up volume markers. This is the case of dodecylbenzene and nonadecane-2-one in clearly HILIC behaving chromatographic systems, the use of decanophenone as a marker can be even extended to the boundary between HILIC and RPLC. The elution volume of the marker remains nearly unaffected by the concentration of ammonium acetate in the mobile phase up to 20 mM. The injection of pure solvents to produce minor base-line disturbance as hold-up markers is strongly discouraged, since solvent peaks are complex to interpret and depend on the ionic strength of the eluent.

Trace Analysis Method Based on UPLC-MS/MS for the Determination of (C2-C18) Per-and Polyfluoroalkyl Substances and Its Application to Tap Water and Bottled Water.

As the usage of long-chain perfluoroalkyl and polyfluoroalkyl substances (PFASs) may be gradually restricted, short-chain and even ultra-short-chain PFASs have been widely produced and used, which has put forward new requirements for the simultaneous analysis of the above substances. Using solid phase extraction two-fraction elution and ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS), an experimental method was established for the simultaneous analysis of ultrashort-chain, short-chain, and long-chain PFASs and the precursor perfluorohexanesulfonamide (FHxSA) in low-concentration water, such as tap water and bottled water. By optimizing the volume of methanol in the first-fraction elution, the concentration of ammonia in the second-fraction elution, and the concentration of ammonium acetate in the mobile phase, the high recovery and low detection limit (0.01-3 ng/L) were obtained. In addition, this method was used to measure nine tap water samples and six bottled water samples for validation, and the results showed that the concentration of PFASs in bottled water was lower than that in tap water. This study first reported the trifluoroacetic acid concentration in bottled water (6.61 ± 9.60 ng/L), which was lower than that in tap water (1712 ± 174 ng/L). The main substances in tap water and bottled water are both ultrashort-chain PFASs (C2-C3), accounting for more than 50%. There are few reports on the simultaneous analysis of ultrashort-chain, short-chain, and long-chain PFASs (C2-C18) and the precursor FHxSA in low-concentration water samples, and the new method can be further developed for different environmental media.

Native Mass Spectrometry for Peptide-Metal Interaction in Picoliter Cell Lysate.

Native mass spectrometry, which takes a high concentration of ammonium acetate (NH4OAc) for ionization, coupled with tedious and solvent-consuming purification, which separates proteins from complicated environments, has shown great potential for proteins and their complexes. A high level of nonvolatile salts in the endogenous intracellular environment results in serious ion suppression and has been one of the bottlenecks for native mass spectrometry, especially for protein complexes. Herein, an integrated protocol utilizing the inner surface of a micropipette for rapid purification, desorption, and ionization of peptide-metal interaction at subfemtomole level in cell lysate was demonstrated for native mass spectrometry. The methods showed robust and reproducibility in protein measurement within 1 min from various buffers. The E. coli cells expressing with various proteins were lysed and used to test our method. The specific interaction between the peptide-metal complex in cell lysates could be reserved and distinguished by mass spectrometry.

Preparation of high-purity lead carbonate and lead oxide from spent lead paste

Compared with pyrometallurgical recycling, hydrometallurgical recycling of spent lead paste has obvious advantages such as energy saving and emission reduction, however, hydrometallurgical recycling of spent lead paste is also characterized by high levels of impurities (e.g.,Fe, Ba and Cu) in the recovered products. In this study, a green process for the conversion of spent lead paste into high-purity lead carbonate is presented. The process consists of four steps: sulfation, desulfurization leaching, distillation and carbonization to obtain high-purity lead carbonate. The details are as follows: (1) Spent lead paste (mainly composed of lead sulfate, lead dioxide, lead oxide and lead monomers) was converted into sulfated lead paste using sulfuric acid, hydrogen peroxide and sodium chloride. (2) The sulfated lead paste was reacted with ammonium acetate to leach the lead while desulfurizing; the leaching rate was reached 99.94% under the conditions of 30 wt% ammonium acetate concentration, 40 °C reaction temperature and 7.5 min reaction time. (3) Glycerol was added to the mother liquor and distilled to obtain a glycerol solution containing lead acetate. (4) Using ammonium carbonate (aq) as a carbonizing agent, reacting for 20 min under the condition that the molar ratio of CO32−/Pb is 1.10 can make more than 99.9% of lead precipitate to obtain high-purity lead carbonate products. (5) The lead carbonate product decomposed into orthorhombic α-PbO at 350 °C. (6) Recovered lead oxide product has better electrochemical performance than commercial lead oxide. This process prepares high-purity lead carbonate and lead oxide products with reduced energy consumption and recycles the spent lead paste. This study provides a feasible technology for green recycling of spent lead paste.

Studies on the Effects of Process Conditions on Separation of B1, B2 and B3 Vitamin Mixture Using HILIC and RPLC Chromatography

In this work, a series of experiments on the retention of B1 (riboflavin), B2 (thiamine) and B3 (nicotinic acid) vitamins in the HILIC and RPLC conditions have been performed involving the effects of organic modifier type and content, pH of the eluent and buffering salt (ammonium acetate) concentration in the mobile phase as well as temperature of the system. For the needs of this study, three columns of different features have been chosen: Acclaim™ Mixed–Mode HILIC–1 (Dionex, Sunnyvale, CA, USA), Eurospher II 100–5 HILIC (Knauer, Berlin, Germany) and the RPLC column Nucleodur® C18 Gravity-SB (Macherey-Nagel, Duren, Germany). The influence of acetonitrile and methanol content in the eluent and process temperature have been tested and, based on that, the most promising systems have been selected regarding the possible separation of the vitamin mixture. Both the pH and buffering salt concentrations in the eluent have been adjusted in order to indicate the most effective system, which turned out to be the one involving the Nucleodur column and the eluent with 90% methanol, at pH 6 and Cbuff = 20 mmol/dm3, which enables separation of the mixture within a time as short as 2.5 min at a 1.0 mL/s flowrate in isocratic conditions.

Recyclable separation and recovery of carbon fibers from CFRP composites: Optimization and mechanism

• Carbon fibers are recovered from CFRP via chemical swelling and electrochemical oxidation. • Solvent DMSO is recyclable in this separation and recovery method. • Recovered carbon fibers exhibit good surface morphology and mechanical properties. Chemical swelling and electrochemical oxidation are combined to realize the separation and recovery of carbon fibers from carbon fiber-reinforced plastic (CFRP) in dimethyl sulfoxide (DMSO) at normal temperature and pressure. The results showed that the depolymerization rate of epoxy resin in CFRP increased with increasing ammonium acetate concentration and current density, and the influence of the current density was more significant than that of the concentration. Microscopic analysis showed that the recycled carbon fibers had few residual resin on their surfaces and mild electrochemical oxidation etching, and recycled carbon fiber monofilament achieved a tensile strength and an interfacial shear strength that were 93.55% and 118.76% those of the original fibers.

Multiple Regulation Effects of Ammonium Acetate on ZnO Growth Process in Chemical Bath Deposition.

Chemical bath deposition method has been used to synthesize a variety of ZnO morphology structures. However, the specificity and interaction of acetate and ammonium ions with ZnO crystal during the growth process remain elusive. This study contributes to understand the roles of ammonium acetate on the growth mechanism of ZnO in Zn(NO3 )2 -HMTA system. The growth process indicates that the nucleation experienced Zn2+ -layered basic zinc salts (LBZs)-ZnO process, while the self-assembled unit changed from urchin-shaped, rod-shaped to a fully coupled twin-shaped structure with increasing ammonium acetate concentration. Ammonium acetate dominates the growth process by combing the ligand-ligand interaction of acetate ions binding to the same Zn-rich (0001) polar surface and ammonium ions regulating hexamethylenetetramine (HMTA) hydrolysis. Relatively regular hexagonal wurtzite structure and a dissolve-renucleation-regrowth process which retains the twin-shaped template and renucleates at the same position are observed at ∼10 mM ammonium acetate. Photoelectrochemistry (PEC) measurements show that the uniform hexagonal ZnO rods (Y-10, the sample named as Y-x (x represents x mM ammonium acetate, herein, x is 10 mM)) have a maximum photocurrent density of 1.54 mA cm-2 at 1.23 V (vs. RHE), much higher than that of the dumbbell-shaped ZnO rods (Y-50, 0.20 mA cm-2 ) at the same voltage. These results provide a further explanation of morphology regulation mechanisms on ZnO synthesis processes and pave the road for more practical applications.

Inhibition of argininosuccinate synthase (ASS) affected ammonia excretion in yellow catfish Pelteobagrus fulvidraco during acute ammonia poisoning

Ammonia is toxic to most fish. Different fish have different treatment methods for ammonia toxicity, mainly including urea cycle and glutamine synthesis pathway, depending on their physiological status. A two-stage study was carried out to test the inhibition of argininosuccinate synthase (ASS) effects on ammonia detoxification in hyperammonemia yellow catfish. At the stage 1, fish were injected lethal half concentration (LC50) of ammonium acetate and sampled at 0, 1, 3, 6, 12 and 24 h post-injection. The result found that plasma ammonia content of fish was injected with ammonium acetate reached its highest level at hour 1, which was used as the optimal sampling time in stage 2. At the stage 2, the four experimental groups were carried out: NaCl group was injected intraperitoneally with 0.9% sodium chloride as control; NH3 group was injected with LC50 ammonium acetate; NH3+BPP group was injected with mixture of ammonium acetate and bradykinin-potentiating peptide (BPP); BPP group was injected with BPP. The results showed that inhibition of ASS can lead to accumulation of ammonia in plasma and kidney, and glutamine in liver and kidney; and decreases ASS, argininosuccinate lyase, arginase activates, and ornithine, glutamate, alanine, proline, tyrosine, methionine contents, and increases ornithine transcarbamylase, glutaminase activates, and citrulline, aspartate, arginine, glutamine, histidine, isoleucine, phenylalanine, lysine contents; and result in upregulation of ASS, ASL, CPS 1, OTC, GS and GLS genes expression. This result indicates that the inhibition of ASS in yellow catfish with ammonia poisoning will lead to the urea cycle disorder; yellow catfish can enhance the detoxification capacity of ammonia by improving glutamine synthesis when the urea cycle is inhibited; argininase played an important role in ammonia detoxification of yellow catfish.

Pseudocapacitive and battery-type organic polymer electrodes for a 1.9 V hybrid supercapacitor with a record concentration of ammonium acetate

Aqueous all-organic battery-supercapacitor hybrid (BSH) devices are emerging as promising alternative energy storage systems to conventional metal-ion batteries/supercapacitors in terms of their easy processability, high tunability, cost-effectiveness, and recyclability. In this study, we demonstrate an all-organic BSH device using a record concentration of ammonium acetate (30 m NH4Ac) as a cheap and green electrolyte. This novel water-in-salt system possesses an electrochemical stability window up to 2.1 V. In addition, organic polymers comprising of perylenetetracarboxy diimide core and the mixed aromatic amine groups are employed as negative and positive electrodes, respectively. The polymers show low water solubility, good crystallinity, and nano-morphology, which make them decent candidates for the all-organic aqueous BSH device. More importantly, electrochemical kinetic analysis of polymer electrodes reveals that the negative and positive electrodes display pseudocapacitive and battery-type behaviors, respectively. For the first time, an all-organic BSH device with 30 m NH4Ac is fabricated, which delivers a specific capacity of 42 mA h g−1 at 200 mA g−1 and capacity retention of ca. 63% after 5000 cycles. It further shows the maximum energy density of 16.5 Wh kg−1 and power density of 719 Wh kg−1, depicting great potential in energy storage applications.

Application of Magnetic Nanoparticles Coated with Crosslinked Zwitterionic Poly(ionic liquid)s for the Extraction of Oligonucleotides.

Magnetic nanoparticles coated with zwitterionic poly(ionic liquid)s were applied for dispersive solid-phase extraction of oligonucleotides. The materials were synthesized by miniemulsion copolymerization of ionic liquids and divinylbenzene on magnetic nanoparticles. The functional monomers contain a positively charged imidazolium ring and one of the anionic groups: derivatives of acetate, malonate, or butyl sulfonate ions. Adsorption of unmodified DNA oligonucleotide on obtained materials was possible in ion-exchange (IE) and hydrophilic interactions (HI) mode. The adsorption in IE was possible at low pH and was almost complete. The adsorption in HI mode required the usage of appropriate addition of organic solvent but did not provide full adsorption. Studies on the desorption of the analytes included determining the impact of ammonium acetate concentration and pH and organic solvents addition on the recovery. The material containing acetic fragments as an anionic group was selected for the final procedure with the use of 10 mM ammonium acetate (pH = 9.5)/methanol (50/50, v/v) as an elution solution. The magnetic dispersive solid-phase extraction procedure was tested for the oligonucleotides with various modifications and lengths. Moreover, it was applied to extract DNA oligonucleotide and its synthetic metabolites from enriched human plasma without any pre-purification, with recoveries greater than 80%.

Determination of Antidepressants in Human Plasma by Modified Cloud-Point Extraction Coupled with Mass Spectrometry.

Cloud-point extraction (CPE) is rarely combined with liquid chromatography coupled to mass spectrometry (LC–MS) in drug determination due to the matrix effect (ME). However, we have recently shown that ME is not a limiting factor in CPE. Low extraction efficiency may be improved by salt addition, but none of the salts used in CPE are suitable for LC–MS. It is the first time that the influences of a volatile salt—ammonium acetate (AA)—on the CPE extraction efficiency and ME have been studied. Our modification of CPE included also the use of ethanol instead of acetonitrile to reduce the sample viscosity and make the method more environmentally friendly. We developed and validated CPE–LC–MS for the simultaneous determination of 21 antidepressants in plasma that can be useful for clinical and forensic toxicology. The selected parameters included Triton X-114 concentration (1.5 and 6%, w/v), concentration of AA (0, 10, 20 and 30%, w/v), and pH (3.5, 6.8 and 10.2). The addition of 10% of AA increased recovery twice. For 20 and 30% (w/v) of AA, three phases were formed that prolonged the extraction process. The developed CPE method (6% Triton X-114, 10% AA, pH 10.2) was successfully validated through LC–MS/MS simultaneous determination of 21 antidepressants in human plasma. The linearity was in the range of 10–750 ng/mL (r2 > 0.990).

Extraction of lead from electrolytic manganese anode mud by microwave coupled ultrasound technology

In this work, extraction of lead from Electrolytic Manganese Anode Mud (EMAM) by microwave coupled ultrasound was studied. The results showed that microwave roasting promoted the conversion of MnO2 to Mn2O3 and Mn3O4, which greatly facilitated the subsequent leaching process of lead and the introduction of ultrasound effectively enhanced the leaching process. The leaching rate for lead from EMAM was arrived to 86.98% under the optimum conditions with the ammonium acetate concentration of 2 mol/L at 343 K and the stirring speed of 300 rpm for 60 min. With the introduction of specific power ultrasound, the leaching of lead was increased by about 10%. The microwave roasting combined with ultrasonic enhanced leaching can effectively for the reuse and reduction of EMAM which provides ideas for further investigation of lead pollution control and resource utilization in EMAM.

Enhanced dissolution rate of magnesium hydroxide via magnesia/ammonium acetate hydration system: statistical optimization and possible mechanism

AbstractBACKGROUNDThe dissolubility of magnesium hydroxide is often the main factor limiting its application effect in the environmental field, and the dissolution rate of magnesium hydroxide during its synthesis is also worthy of attention. In this paper, response surface methodology was used to synthesize magnesium hydroxide with different dissolution rates through a magnesium oxide/ammonium acetate hydration system, and the possible formation mechanism as well as dissolution performance is discussed.RESULTSCompared with the hydration temperature and time, the concentration of ammonium acetate has a more significant effect on the dissolution rate of hydrated magnesium hydroxide. A maximum dissolution rate of 43.8 ± 0.3 mmol min−1 mol−1 magnesium hydroxide could be obtained when the working factors were ammonium acetate concentration 15 g L–1, hydration temperature 75.5 °C and time 112 min.CONCLUSIONThe correlation study between structural characterization and the dissolution test shows that the complexation and replacement of acetate, in situ generation and release of ammonia appear to have some critical effects on magnesium hydroxide crystallization behaviour and induce the formation of thin, curved and defective structures. Crystals with such structures have been reported to have a higher dissolution activity. The results of this study provide an indication for screening hydration synthetic agents of high‐dissolution‐rate magnesium hydroxide. © 2020 Society of Chemical Industry (SCI)

Asymmetrical flow field-flow fractionation to probe the dynamic association equilibria of β-D-galactosidase

Protein dynamics play a significant role in many aspects of enzyme activity. Monitoring of structural changes and aggregation of biotechnological enzymes under native conditions is important to safeguard their properties and function. In this work, the potential of asymmetrical flow field-flow fractionation (AF4) to study the dynamic association equilibria of the enzyme β-D-galactosidase (β-D-Gal) was evaluated. Three commercial products of β-D-Gal were investigated using carrier liquids containing sodium chloride or ammonium acetate, and the effect of adding magnesium (II) chloride to the carrier liquid was assessed. Preservation of protein structural integrity during AF4 analysis was essential and the influence of several parameters, such as the focusing step (including use of frit-inlet), cross flow, and injected amount, was studied. Size-exclusion chromatography (SEC) and dynamic light scattering (DLS) were used to corroborate the in-solution enzyme oligomerization observed with AF4. In contrast to SEC, AF4 provided sufficiently mild separation conditions to monitor protein conformations without disturbing the dynamic association equilibria. AF4 analysis showed that ammonium acetate concentrations above 40 mM led to further association of the dimers (“tetramerization”) of β-D-Gal. Magnesium ions, which are needed to activate β-D-Gal, appeared to induce dimer association, raising justifiable questions about the role of divalent metal ions in protein oligomerization and on whether tetramers or dimers are the most active form of β-D-Gal.