High Reagent Consumption Research Articles

Flow Injection Amperometric System Coupled with a Well-Plate for Fast Screening of Total Antioxidant Capacity

ABSTRACTA flow injection (FI) system with an amperometric detection in combination with a 96-well-plate has been developed for high throughput screening of total antioxidant capacity. It is based on the reaction between dichromate and antioxidants Chromium reducing antioxidant capacity (CHROMAC) assay. Antioxidant reduces dichromate leading to a decrease of dichromate concentration, in which reacts further with triiodide reagent. The slow reaction between antioxidant and dichromate takes place in parallel in a 96-well microplate, with the reaction time sufficiently long to reach steady state conditions. Microliter volumes of the remaining dichromate solution were manually injected into the FI amperometric system. Reaction with iodide in acidic medium produces triiodide which undergoes electrochemical reduction on a glassy carbon working electrode at 200 mV versus a Ag/AgCl reference electrode. The decrease of electrical current was directly proportional to the antioxidant capacity. The optimum conditions have been achieved as follow: 160 mg L−1 of potassium dichromate, pH of dichromate solution of 2.82, 0.005 mol L−1 of potassium iodide, 0.20 mol L−1 of hydrochloric acid, and 3.0 mL min−1 total flow rate. The developed method was applied for the determination of total antioxidant capacity of tea and herbal infusions and fruit juice samples. The results obtained indicated that the developed method had good correlation with the batch CHROMAC spectrophotometric method and 1,1-diphenyl-2-picrylhydrazyl scavenging assay. The proposed method provides fast and high throughput analysis, convenient operation, and low consumption of chemical reagents and samples.

Electrochemical recovery of minor concentrations of gold from cyanide-free cupric chloride leaching solutions

Abstract Despite of being the most common hydrometallurgical process for extraction of gold from ores and concentrates, cyanide leaching is blamed for its hazardous impact on environment and human health. These concerns have given a rise for alternative cyanide-free technologies, such as cupric chloride leaching. However, the state-of-art processes for gold recovery from chloride solutions are facing issues of high reagent consumption and poor selectivity. This article describes an innovative method for recovery of minor concentrations of gold from hydrometallurgical solutions by repetitive Electrochemical Deposition-Redox Replacement (EDRR) cycles. In contrast to conventional carbon-in-leach/resin-in-leach technologies or solvent extraction, the proposed electrochemical method does not require addition of any chemicals in the process and remarkably selective gold recovery can be achieved from concentrated cupric solution by tailoring the process parameters. A number of electrochemical experiments was performed in order to identify the process variables affecting the Au recovery. Results indicate that so called cut-off potential and deposition time were the EDRR parameters having the strongest impact on gold recovery at fixed concentration of Cu and Au ions. The Au content in the metal deposit after 250 EDRR cycles exceeded 75% and the Au:Cu ratio has increased by a factor of 1000, from 1:340 in the solution up to 3.3:1 in the final product. X-ray photoelectron spectroscopy analysis of the cathode surface confirmed full replacement of sacrificial copper with gold. Obtained results prove that the EDRR method can be efficiently used for the recovery of trace amounts of gold from cupric chloride solutions used for cyanide-free gold leaching.

Femtosecond Laser Direct Write Integration of Multi-Protein Patterns and 3D Microstructures into 3D Glass Microfluidic Devices

Microfluidic devices and biochips offer miniaturized laboratories for the separation, reaction, and analysis of biochemical materials with high sensitivity and low reagent consumption. The integration of functional or biomimetic elements further functionalizes microfluidic devices for more complex biological studies. The recently proposed ship-in-a-bottle integration based on laser direct writing allows the construction of microcomponents made of photosensitive polymer inside closed microfluidic structures. Here, we expand this technology to integrate proteinaceous two-dimensional (2D) and three-dimensional (3D) microstructures with the aid of photo-induced cross-linking into glass microchannels. The concept is demonstrated with bovine serum albumin and enhanced green fluorescent protein, each mixed with photoinitiator (Sodium 4-[2-(4-Morpholino) benzoyl-2-dimethylamino] butylbenzenesulfonate). Unlike the polymer integration, fabrication over the entire channel cross-section is challenging. Two proteins are integrated into the same channel to demonstrate multi-protein patterning. Using 50% w/w glycerol solvent instead of 100% water achieves almost the same fabrication resolution for in-channel fabrication as on-surface fabrication due to the improved refractive index matching, enabling the fabrication of 3D microstructures. A glycerol-water solvent also reduces the risk of drying samples. We believe this technology can integrate diverse proteins to contribute to the versatility of microfluidics.

Rapid Screening of Graphitic Carbon Nitrides for Photocatalytic Cofactor Regeneration Using a Drop Reactor

Artificial photosynthesis is the imitation of natural photosynthesis, which promises an efficient way to use solar energy to synthesize organic matters, in which the key step is the coenzyme regeneration (NADH/NADPH). To achieve an efficient regeneration rate, various photocatalysts have been developed, such as g-C3N4 and mesoporous carbon nitride (mpg-C3N4). Generally, efficiency determination of different photocatalysts requires laborious experiments, high consumption of reagents, and a considerable amount of time. Here, based on the one-step artificial photosystem I method, we processed the analytical experiment in a very simple PDMS well (20 μL, a drop) to achieve a rapid screening of photocatalysts. For comparison, we used two types of graphitic carbon nitrides, few-layer g-C3N4 and mpg-C3N4. Compared with the slurry systems, firstly, the regeneration rate of mpg-C3N4 drop-reactor system is 4.3 times and 7.1 times those of the few-layer g-C3N4-slurry system and mpg-C3N4-slurry system, respectively. Secondly, this one-drop method reduces the typical verification time from 90 min to 5 min and lowers the liquid volume from 20 mL to 20 μL. Thirdly, this operation is a pump-free and soft lithography technique-free process. The miniaturization of the photocatalytic reaction in the PDMS well improves the regeneration rates, saves samples, and achieves high-throughput screening of multiple photocatalysts.

Characterization of an induced pressure pumping force for microfluidics

The electro-osmotic pumping and pressure-driven manipulation of fluids are considered as the most common strategies in microfluidic devices. However, both of them exhibit major disadvantages such as hard integration and high reagent consumption, and they are destructive methods for detection and photo bleaching. In this paper, an electric field-effect flow control approach, combining the electro-osmotic pumping force and the pressure-driven pumping force, was developed to generate the induced pressure-driven flow in a T-shaped microfluidic chip. Electro-osmotic flow between the T-intersection and two reservoirs was demonstrated, and it provided a stable, continuous, and electric field-free flow in the section of the microchannel without the electrodes. The velocity of the induced pressure-driven flow was linearly proportional to the applied voltages. Both numerical and experimental investigations were conducted to prove the concept, and the experimental results showed good agreement with the numerical simulations. In comparison to other induced pressure pumping methods, this approach can induce a high and controllable pressure drop in the electric field-free segment, subsequently causing an induced pressure-driven flow for transporting particles or biological cells. In addition, the generation of bubbles and the blocking of the microchannel are avoided.

Platinum recycling going green via induced surface potential alteration enabling fast and efficient dissolution.

The recycling of precious metals, for example, platinum, is an essential aspect of sustainability for the modern industry and energy sectors. However, due to its resistance to corrosion, platinum-leaching techniques rely on high reagent consumption and hazardous processes, for example, boiling aqua regia; a mixture of concentrated nitric and hydrochloric acid. Here we demonstrate that complete dissolution of metallic platinum can be achieved by induced surface potential alteration, an ‘electrode-less' process utilizing alternatively oxidative and reductive gases. This concept for platinum recycling exploits the so-called transient dissolution mechanism, triggered by a repetitive change in platinum surface oxidation state, without using any external electric current or electrodes. The effective performance in non-toxic low-concentrated acid and at room temperature is a strong benefit of this approach, potentially rendering recycling of industrial catalysts, including but not limited to platinum-based systems, more sustainable.

Microfluidic Studies of Polymer Adsorption in Flow

Adsorption of polymer molecules under flow conditions governs a broad range of desired or undesired phenomena and has a broad range of applications. Microfluidic platforms integrated with analytical instrumentation offer the capability to study polymer adsorption in flow in a time‐ and labour‐efficient manner. Precise control of the microchannel dimensions and flow parameters enables accurate control of shear forces imposed on polymer solutions and on the molecules deposited on the surface, along with high sensitivity, enhanced reliability, and low reagent consumption. This review highlights recent advances in theoretical and experimental microfluidic studies of polymer immobilization under flow conditions in three area, namely, biosensing, biofouling, and studies of thrombosis and hemostasis. image

Multi-reverse flow injection analysis integrated with multi-optical sensor for simultaneous determination of Mn(II), Fe(II), Cu(II) and Fe(III) in natural waters

Multi-reverse flow injection analysis (Mr-FIA) integrated with multi-optical sensor was developed and optimized for the simultaneous determination of multi ions; Mn(II), Fe(II), Cu(II) and Fe(III) in water samples. The sample/standard solutions were propelled making use of a four channels peristaltic pump whereas 4 colorimetric reagents specific for the metal ions were separately injected in sample streams using multi-syringe pump. The color zones that formed in the individual mixing coils were then streamed into multi-channels spectrometer, which comprised of four flows through cell and four pairs of light emitting diode and photodiode, whereby signals were measured concurrently. The linearity range (along with detection limit, µgL−1) was 0.050–3.0(16), 0.30–2.0 (11), 0.050–1.0(12) and 0.10–1.0(50)mgL−1, for Mn(II), Fe(II), Cu(II) and Fe(III), respectively. In the interim, the correlation coefficients were 0.9924–0.9942. The percentages relative standard deviation was less than 3. The proposed system was applied successfully to determine targeted metal ions simultaneously in natural water with high sample throughput and low reagent consumption, thus it satisfies the criteria of Green Analytical Chemistry (GAC) and its goals.

Cost-effective flow injection amperometric system with metal nanoparticle loaded carbon nanotube modified screen printed carbon electrode for sensitive determination of hydrogen peroxide

Various metal nanoparticles (NPs) decorated on carbon nanotube (CNT) was modified on the home-made screen printed carbon electrode (SPCE) in order to enhances sensitivity of hydrogen peroxide (H2O2) determination. The simple casting method was used for the electrode modification. The monometallic and bimetallic NPs modified electrodes were investigated for their electrochemical properties for H2O2 reduction. The Pd-CNT/SPCE is appropriated to measure the H2O2 reduction at a potential of −0.3V, then this modified electrode was incorporated with a home-made flow through cell and applied in a simple flow injection amperometry (FI-Amp). Some parameters influencing the resulted modified electrode and the FI-Amp system were studied. The proposed detection system was able to detect H2O2 in the range of 0.1–1.0mM, with detection limit of 20µM. Relative standard deviation for 100 replicated injections of 0.6mM H2O2 was 2.3%. The reproducibility of 6 electrodes preparing in 3 different lots was 8.2%. It was demonstrated for determination of H2O2 in disinfectant, hair colorant and milk samples. Recoveries in the range of 90–109% were observed. The developed system provided high stability, good repeatability, high sample throughput and low reagent consumption.

A nanocoaxial-based electrochemical sensor for the detection of cholera toxin.

Sensitive, real-time detection of biomarkers is of critical importance for rapid and accurate diagnosis of disease for point of care (POC) technologies. Current methods do not allow for POC applications due to several limitations, including sophisticated instrumentation, high reagent consumption, limited multiplexing capability, and cost. Here, we report a nanocoaxial-based electrochemical sensor for the detection of bacterial toxins using an electrochemical enzyme-linked immunosorbent assay (ELISA) and differential pulse voltammetry (DPV) or square wave voltametry (SWV). The device architecture is composed of vertically-oriented, nanoscale coaxial electrodes in array format (~10(6) coaxes per square millimeter). The coax cores and outer shields serve as integrated working and counter electrodes, respectively, exhibiting a nanoscale separation gap corresponding to ~100 nm. Proof-of-concept was demonstrated for the detection of cholera toxin (CT). The linear dynamic range of detection was 10 ng/ml-1 µg/ml, and the limit of detection (LOD) was found to be 2 ng/ml. This level of sensitivity is comparable to the standard optical ELISA used widely in clinical applications, which exhibited a linear dynamic range of 10 ng/ml-1 µg/ml and a LOD of 1 ng/ml. In addition to matching the detection profile of the standard ELISA, the nanocoaxial array provides a simple electrochemical readout and a miniaturized platform with multiplexing capabilities for the simultaneous detection of multiple biomarkers, giving the nanocoax a desirable advantage over the standard method towards POC applications.

A Review of Thiocyanate Hydrometallurgy for the Recovery of Gold

Over the past century, numbers of hydrometallurgical processing technologies have been conducted for gold leaching in mining and second resource, such as cyanidation, being with high toxicity and low reaction rate, and non-cyanide---thiosulphate leaching and thiourea leaching, etc, having relatively high reagent consumption. Recently, ammonium thiocyanate was selected as leaching reagent in the laboratory study. Just as some papers shown, thiocyanate can be complexed tightly with Au+ or Au3+ to form water-soluble complexes according to the dynamic and thermodynamic system of thiocyanate gold and regenerated or obtained as a by-product in technological processes. And the extraction process is affected by many factors, such as thiocyanate concentration, oxidant concentration, liquid-solid ratio, temperature, and reaction time, especially pH and the category of oxidants, which can be chosen properly to make the method extensively applied in industrialization. Recent studies have shown that the gold leaching with thiocyanate under alkaline conditions is also viable using oxygen as oxidant. Then this article compares and analyzes the use of different oxidants in acid or alkali environment reaching a 96% leaching efficiency and the techniques of gold recycle from thiocyanate gold solutions. However, as the restriction for post-processing cost of thiocyanate and the strict requirement for the equipment in the acidic conditions or high pressure conditions, additional research should be directed towards making incorporation with other extraction methods perfectly. Two development tendencies are presented in this paper: (1) as additive; (2) as the lixiviant under alkaline or neutral conditions.

Ammoniacal thiosulfate leaching of pressure oxidized sulfide gold concentrate with low reagent consumption

Ammoniacal thiosulfate leaching of pressure oxidized sulfide gold concentrate received from a gold mine is studied. The main chemical composition of the concentrate was Au 32g/t, Ag 12g/t, Fe 59%, S 21% and As 19%. The experimental variables studied were ammonia concentration, thiosulfate concentration, copper concentration, and temperature. The highest gold extraction (89%) was achieved with the following leaching solutions: 0.2molS2O3/L, 0.2molNH3/L, and 0.1gCu/L; and with the following conditions: solids, 30m-%; pressure, 1atm; continuous aeration (0.2L/min); temperature, 30°C; and leaching time, 6h. Measured thiosulfate and copper concentrations after 6h of leaching were 0.19M and 0.08g/L, respectively. The results from the leaching experiments showed that the pressure oxidized gold concentrate was effectively leached in an ammoniacal thiosulfate leaching solution with minimal reagent consumption. The study shows that the widely reported problem of high reagent consumption can be circumvented in leaching of pressure oxidized sulfide gold concentrate by the use of low reagent concentrations. The results indicate good premises for gold recovery by ion-exchange resins, since minimal thiosulfate consumption also ensures low polythionate concentration, which is an important issue in gold recovery with ion-exchange resins. The minimal reagent consumption also indicates that there are good possibilities to circulate the leaching solution for re-use in the leaching stage after gold recovery and solid–liquid separation.

Research on Biological Materials with Uranium Biosorption by Microalgae: A Review

With the development of nuclear science, uranium-contained wastewater was heavily generated. If not properly handled, it is bound to bring environmental and human health hazards. Conventional uranium-contained wastewater treatment technologies are limited in certain aspects, such as high reagent and energy consumption, secondary pollution and so on. The microalgae-based biosorption technique for treating uranium-contained wastewater is an economical, simple, effective and feasible approach. This paper summarized the basic mechanism of the technology, and discussed the effects of different pH, algal cell biomass concentration, initial uranium ion concentration and the growth state of algal cells on the biological treatment process of uranium-contained wastewater. Finally, the study explored the future prospects of the technology.

Novel method of stabilizing water pretreatment for reverse osmosis desalination

The preparation of functionalized filter media (FFM), its ability to release active antiscalant substances and its application for water treatment in water heating processes and as a pretreatment in reverse osmosis (RO) desalination were investigated in this study. FFM is a novel method of stabilizing water pretreatment designed to be free of the disadvantages of conventional methods of water scaling potential reduction which require expensive equipment, produce significant amounts of waste, have high reagent consumption or are strongly dependent on water composition. FFM was derived from anion exchange resin modified with phosphonate and polymer scale inhibitors. In order to choose the most suitable anion exchange resin for preparation of FFM, different types of resins were tested for sorption of phosphonate compounds. The effect of the anionic composition of water and the effect of the polymer inhibitor on the rate of phosphonate release were investigated. Finally, FFM was tested as a scaling reduction water treatment for a water heating process with heating coils and as a pretreatment before reaching the RO unit. In both cases the results obtained show great promise for the functionalized material in antiscaling water pretreatment.

The Application of MnO2 in the Removal of Manganese from Acid Mine Water

In recent years, much attention has been devoted in developing inexpensive or alternative systems for treating acid mine drainage (AMD). Manganese is a common component of AMD, and it is traditionally removed by precipitation. However, in order to meet the standard limits for discharging, usually <1 mg L−1, it is necessary to raise the pH above 10 which implies in high consumption of reagents and a final pH that does not meet the required value for discharging. This study investigated the removal of manganese from an acid mine effluent and laboratory solutions by using an industrial residue consisted of manganese dioxide (MnO2). The pH of the acid effluent is around 2.7, and the manganese concentration is approximately 140 mg L−1. Batch experiments assessed the influence of pH and the efficiency of manganese dioxide (MnO2) in the Mn+2 removal. In the presence of MnO2, the metal concentration meets the discharging limit at pH range of 6.8 to 7.2. Experiments carried out with columns packed with MnO2 assessed the influence of the flow rate on the process. Best results were obtained for columns fed with mine water neutralized with limestone at pH 7.0 and a residence time of 3.3 h. The maximum manganese loading capacity for MnO2 was around 14 mg g−1. RAMAN spectroscopy showed that the MnO2 is essentially constituted of pyrolusite. In addition, the solid hausmannite (Mn3O4) was observed on the surface of the MnO2 residue after its contact with the Mn+2 solution.

Enhanced Leachability of a Lean Weathered Crust Elution-Deposited Rare-Earth Ore: Effects of Sesbania Gum Filter-Aid Reagent

The enhanced leachability of rare-earth ore from the lean weathered crust elution-deposited rare-earth ores with ammonium sulfate solution as lixiviant and sesbania gum as a filter-aid reagent was elucidated and optimized with chromatographic plate theory. The effects of the flow rate, the concentration of lixiviant, the sesbania gum filter-aid reagent, and the lixiviant consumption on the leaching process were examined with column elution. The results show that the sesbania gum has a positive effect on the leaching process; the relationship between the height equivalent to a theoretical plate (HETP) and the leaching flow rate can be described by the van Deemter equation. There is an optimum flow rate in the leaching process. The optimum concentration of the sesbania gum in lixiviant was discovered. Moreover, sesbania gum added in lixiviant also reduces lixiviant consumption and promotes the optimum leaching flow rate. It provides a new approach to leaching the lean weathered crust elution-deposited rare-earth ores with high efficiency and low reagent consumption. The approach also can reduce the NH4 (+)-N pollution. (C) The Minerals, Metals & Materials Society and ASM International 2013

Process optimization on leaching of a lean weathered crust elution-deposited rare earth ores

The process on leaching of rare earth from the lean weathered crust elution-deposited rare earth ores with ammonium sulfate solution was elucidated and optimized with the chromatographic plate theory. The effects of the flowrate, the packed ore height, the concentration of leach reagents and leach reagent consumption on leaching performance were examined with column elution. It was found that the relationship between the height equivalent to a theoretical plate (HETP) and leaching flowrate can be described by the van Deemter equation. There is an optimum flowrate in the leaching process. It provides a scientific approach to leaching the lean weathered crust elution-deposited rare earth ores with high efficiency and low reagent consumption, and is applied to optimize the leach process and extraction conditions, to improve the rare earth received rate and to reduce the NH4+–N pollution.

High-Precision, Room Temperature Screening Assay for Inhibitors of Microsomal Prostaglandin E Synthase-1

Microsomal prostaglandin E synthase-1 (mPGES-1) is the major enzyme catalyzing the isomerization of prostaglandin (PG) H2 to PGE2. Here we report the development of a robust and practical automated assay in a 384-well format for room temperature screening of mPGES-1 inhibitors with high precision and low reagent consumption. The assay should enable precise structure-activity relationship development. It uses acetonitrile as solvent for PGH2, FeCl2/citrate as stop reagent, and a short reaction time. Combined with high-precision liquid transfer and extensive mixing after addition of reactants, these properties let the assay reach Z′ > 0.7 and high reproducibility of inhibitor IC50 values. Thorough investigation of the quality of mixing in all liquid transfer steps proved crucial for reaching high-precision performance.Abbreviations: mPGES-1 (microsomal prostaglandin E synthase-1); FRET (fluorescence resonance energy transfer); HTRF (homogeneous time-resolved fluorescence); PGH2 (prostaglandin H2); PGE2 (prostaglandin E2); SAR (structure-activity relationship); COX-2 (cyclooxygenase-2); GSH (glutathione); ALP (automated labware positioner)

Upgrading difficult-to-float coal using microemulsion

Oxidized coals are difficult to float. Therefore, in this paper, a special flotation procedure was investigated for upgrading this type of coal. The procedure is called direct contact flotation. It relies on mixing dry coal either with pure (anhydrous) flotation reagent(s) or microemulsion. By applying the new direct contact flotation procedure, a coal yield reaching > 95% using anhydrous flotation reagents was achieved, but with relatively high consumption of reagents (up to 30 g/kg). This high reagent consumption may be attributed to the fines included in the flotation feed (100% less than 0.5 mm, with 40% less than 75 µm). On the other hand, the clean coal yield was found to be approximately 88% when mixing dry oxidized coal with microemulsion droplets from dodecane and dodecyl tetra (ethylene glycol) ether (C12E4) in water at a total reagent dosage of 10 g/kg. The direct contact of coal either with unhydrous reagents or microemulsion also provided a high flotation selectivity.

Digital Polymerase Chain Reaction in an Array of Femtoliter Polydimethylsiloxane Microreactors

We developed a simple, compact microfluidic device to perform high dynamic-range digital polymerase chain reaction (dPCR) in an array of isolated 36-femtoliter microreactors. The density of the microreactors exceeded 20000/mm(2). This device, made from polydimethylsiloxane (PDMS), allows the samples to be loaded into all microreactors simultaneously. The microreactors are completely sealed through the deformation of a PDMS membrane. The small volume of the microreactors ensures a compact device with high reaction efficiency and low reagent and sample consumption. Future potential applications of this platform include multicolor dPCR and massively parallel dPCR for next generation sequencing library preparation.