HNO3 Solution Research Articles

Recovery of precious metals from mobile phone waste: Studies on leaching and adsorption by functionalized activated carbon

In today's world, the utilization of electronic devices, particularly mobile phones, has seen a remarkable surge and they are a valuable source of recovery of precious metals. The current study reports on the physical and chemical processing of mobile phone waste into leachate, followed by recovery of precious metals, using ionic liquid functionalized activated carbon (ACF). The recovery process was explored both in batch and column study. The presence of base metals in the final leachate was minimized by employing multi-stage chemical leaching, leading to a more efficient purification process. Moreover, adjustment of HCl concentration in the leachate leads to decreased in other metals interference during adsorption. Following the batch adsorption results, a favorable interaction between IL and metal complexes leads to a quantitative adsorption of the precious metals. In addition, ACF also gave an excellent performance in the column adsorption process with the high bed depth and low flow rate of the leachate as the influential parameter. An increase in the bed depth and a decrease in leachate flow rate proportionally increases the values of kTh (rate constant), qe (adsorption capacity), and KYN (rate constant) and positively increases the 50% breakthrough time (τ). Moreover, the final purification of the adsorbed metals was performed selectively through sequential desorption, employing Na2S2O3, NH4SCN, and HNO3 solutions. Finally, the adsorption capability of ACF shown a negligible change after five repetitive adsorption-desorption cycles. Thus, the current study presents a method to process mobile phone waste and selectively recover the precious metals from the leachate.

All-in-one treatment: Capture and immobilization of 137Cs by ultra-stable inorganic solid acid materials HMMoO6·nH2O (M = Ta, Nb)

Capture and immobilization of 137Cs is urgent for radioactive contamination remediation and spent fuel treatment. Herein, an effective all-in-one treatment method to simultaneously adsorb and immobilize Cs+ without high-temperature treatment is proposed. According to the strategy of incorporating high-valency metal ions into molybdates to increase the material stability and affinity towards radionuclides, layered HMMoO6·nH2O (M = Ta (1), Nb (2)) are prepared. Both materials exhibit excellent acid resistance (even 15 mol/L HNO3). They maintain remarkable adsorption capacity for Cs+ in 1 mol/L HNO3 solutions and can selectively capture Cs+ under excessive competitive ions. Furthermore, they show successful cleanup for actual 137Cs-liquid-wastes generated during industrial production. In particular, adsorbed Cs+ can be firmly immobilized in interlayer spaces of materials due to the highly stable anionic framework. The removal mechanism is attributed to ion exchange between Cs+ and interlayer H+ by multiple characterizations. Study of the structure-function relationship shows that the occurrence of Cs+ ion exchange is closely related to plate-like layered structure. This work develops an efficient all-in-one treatment method for capturing and immobilizing radiocesium by ultra-stable inorganic solid acid materials with low energy consumption and high safety for radionuclide remediation.

Efficient removal of U(VI) from aqueous solution using poly(amidoxime-hydroxamic acid) functionalized graphene oxide.

The efficient development of selective materials for uranium recovery from wastewater and seawater is crucial for the utilization of uranium resources and environmental protection. The potential of graphene oxide (GO) as an effective adsorbent for the removal of environmental contaminants has been extensively investigated. Further modification of the functional groups on the basal surface of GO can significantly enhance its adsorption performance. In this study, a novel poly(amidoxime-hydroxamic acid) functionalized graphene oxide (pAHA-GO) was synthesized via free radical polymerization followed by an oximation reaction, aiming to enhance its adsorption efficiency for U(VI). A variety of characterization techniques, including SEM, Raman spectroscopy, FT-IR, and XPS, were employed to demonstrate the successful decoration of amidoxime and hydroxamic acid functional groups onto GO. Meanwhile, the adsorption of U(VI) on pAHA-GO was studied as a function of contact time, adsorbent dosage, pH, ionic strength, initial U(VI) concentration, and interfering ions by batch-type experiments. The results indicated that the pAHA-GO exhibited excellent reuse capability, high stability, and anti-interference ability. Specially, the U(VI) adsorption reactions were consistent with pseudo-second-order and Langmuir isothermal adsorption models. The maximum U(VI) adsorption capacity was evaluated to be 178.7mg/g at pH 3.6, displaying a higher U(VI) removal efficiency compared with other GO-based adsorbents in similar conditions. Regeneration of pAHA-GO did not significantly influence the adsorption towards U(VI) for up to four sequential cycles. In addition, pAHA-GO demonstrated good adsorption capacity stability when it was immersed in HNO3 solution at different concentrations (0.1-1.0mol/L) for 72h. pAHA-GO was also found to have anti-interference ability for U(VI) adsorption in seawater with high salt content at near-neutral pH condition. In simulated seawater, the adsorption efficiency was above 94% for U(VI) across various initial concentrations. The comprehensive characterization results demonstrated the involvement of oxygen- and nitrogen-containing functional groups in pAHA-GO in the adsorption process of U(VI). Overall, these findings demonstrate the feasibility of the pAHA-GO composite used for the capture of U(VI) from aqueous solutions.

Adsorption and Desorption Behavior and Mechanism of Ruthenium in Nitrite-Nitric Acid System.

Ruthenium is required to separate from high-level liquid waste (HLLW) because Ru is a valuable resource and is negatively influential on the vitrification process of HLLW. However, the separation of Ru is very challenging due to its complicated complexation properties. In this study, the adsorption and desorption characteristics of ruthenium on a synthesized SiPyR-N3 (weak-base anion exchange resin with pyridine functional groups) composite were investigated in nitric acid and nitrite-nitric acid systems, respectively, and the adsorption mechanism was explored. The experimental results showed that SiPyR-N3 has a significantly better adsorption effect on Ru in the nitrite-nitric acid system than in the nitric acid system, with an increase in the adsorption capacity of approximately three times. The maximum adsorption capacity of Ru is 45.6 mg/g in the nitrite-nitric acid system. The SiPyR-N3 possesses good adsorption selectivity (SFRu/other metal ions is around 100) in 0.1 M NO2--0.1 M HNO3 solution. The adsorption processes of Ru in the two different systems are fitted with the pseudo-second-order kinetic model and Langmuir model for uptake kinetics and adsorption isotherms, respectively. The results obtained from the FT-IR, XPS, and UV absorption spectrometry indicate that NO2- was involved in the adsorption process either as a complexing species with the metal ions or as free NO2- from the solution. A 0.1 M HNO3 + 1 M thiourea mixed solution shows effective desorption performance, and the desorption efficiency can reach 92% at 328 K.

Effect of alkali metal nitrates on palladium dissolution in nitric acid solutions

Hydrometallurgical unit operations are typically used to recover palladium (Pd) from its ores and secondary resources with high selectivity owing to their low energy consumption, cost effectiveness, and volume flexibility. Herein, diluted HNO3 solutions with added nitrate salts were used to dissolve Pd powders. Moreover, solutions of nitrates with same valency cations (such as HNO3, LiNO3, NaNO3, KNO3, CsNO3, and NH4NO3) and same period cations (such as NaNO3, Mg(NO3)2, and Al(NO3)3) were used to reveal the involved beneficial effects of the nitrates on the Pd dissolution in an environment friendly way with low acidity of the solutions. Among all added alkali metal nitrates, LiNO3 resulted in the highest Pd dissolution efficiency, which was attributed to the higher dissociation constant of LiNO3, resulting in a higher concentration of free nitrate and hence a higher oxidation potential of the overall system. The dissolution process was systematically investigated to determine the optimal temperature (353 K), LiNO3 and HNO3 concentrations (6 and 1 mol L−1, respectively), stirring speed (500 rpm), and reaction time (5 h). These optimal conditions yielded a dissolution efficiency of 99.6%. Notably, as the reaction proceeded, the Pd powder surfaces corroded to form numerous holes, indicating that internal diffusion control also affected Pd dissolution.

4D-Printed Elution-Peak-Guided Dual-Responsive Monolithic Packing for the Solid-Phase Extraction of Metal Ions.

Four-dimensional printing (4DP) technologies are revolutionizing the fabrication of stimuli-responsive devices. To advance the analytical performance of conventional solid-phase extraction (SPE) devices using 4DP technology, in this study, we employed N-isopropylacrylamide (NIPAM)-incorporated photocurable resins and digital light processing three-dimensional printing to fabricate an SPE column with a [H+]/temperature dual-responsive monolithic packing stacked as interlacing cuboids to extract Mn, Co, Ni, Cu, Zn, Cd, and Pb ions. When these metal ions were eluted using 0.5% HNO3 solution as the eluent at a temperature below the lower critical solution temperature of polyNIPAM, the monolithic packing swelled owing to its hydrophilic/hydrophobic transition and electrostatic repulsion among the protonated units of polyNIPAM. These effects resulted in smaller interstitial volumes among these interlacing cuboids and improvements in the elution peak profiles of the metal ions, which, in turn, demonstrated the reduced method detection limits (MDLs; range, 0.2-7.2 ng L-1) during analysis using inductively coupled plasma mass spectrometry. We studied the effects of optimizing the elution peak profiles of the metal ions on the analytical performance of this method and validated its reliability and applicability by analyzing the metal ions in reference materials (CASS-4, SLRS-5, 1643f, and Seronorm Trace Elements Urine L-2) and performing spike analyses of seawater, groundwater, river water, and human urine samples. Our results suggest that this 4D-printed elution-peak-guided dual-responsive monolithic packing enables lower MDLs when packed in an SPE column to facilitate the analyses of the metal ions in complex real samples.

Preliminary Study of the Effect of pH on Ce, Nd, La, Pr Recovery from REOH Concentrate

The separation of uranium, thorium, and rare earth elements (REE) from monazite sand was carried out using the PLUTHO pilot plant facility. The REEs were produced in the form of hydroxide concentrates (REOH). Further separation process must be carried out to obtain high-purity elements for application in advanced industries such as polisher material for hard materials, infrared protective glass, and Ni-metal hydride batteries. The Major Element of REEs are Cerium (Ce), Lanthanum (La), Neodynium (Nd), and Praseodymium (Pr). Those elements can be separated by various methods such as fractional precipitation, extraction, ion exchange, and others. This research was carried out using the Fractional Precipitation method. Rare earth elements have chemical properties that permit ready dissolution and easy precipitation. The fractional precipitating reagent commonly used is NH4OH because it will not contaminate the precipitate due to the volatility of NH3. The parameter used in this preliminary study was pH from 4 to 9. The separation process was started with the dissolution of the REOH concentrate in a solution of HNO3 to obtain RE nitrate. After the dissolution process, oxidation and precipitation were carried out by the addition of KMnO4 as an oxidizing agent and Na2CO3 as a precipitating agent at pH 4 to obtain high recovery efficiency of cerium. The precipitation was pH varies continued by pH adjustment using NH4OH starting from pH 4 to pH 9 to separate La, Nd, and Pr. The analysis of Ce, La, Nd, and Pr concentration was carried out using ICP-OES. The optimum pH recovery for Ce, Nd, and Pr was found at pH 4 with a concentration of 19986.4 ppm, 3532.34 ppm, and 3796.81 ppm, respectively, while at pH 8.5 for La with a concentration of 5846.59 ppm.

How to overcome the difficulty in assaying Ni in biodiesel samples? Extraction induced by microemulsion breaking and square wave adsorptive stripping voltammetry could be the answer

Herein, a simple, green, and relatively inexpensive approach to determine nickel (Ni) in biodiesel samples by square wave adsorptive cathodic stripping voltammetry (SWAdCSV) is presented. A method based on the accumulation of Ni as Ni(II)-dimethylglyoxime (Ni(II)(HDMG)2) on the glassy carbon electrode was carried out in a solution containing the aqueous phase extract (APhEx) obtained from an extraction induced by microemulsion breaking (EIMB), which was achieved by adding a few microliters of ultrapure water to a microemulsion composed of biodiesel, n-propanol and a diluted HNO3 solution. The LOD and LOQ were 0.2 μg L−1 and 0.8 μg L−1, respectively, and the accuracy was evaluated by recovery assays of spiked samples and by analyzing a standard reference material. Results obtained from a comparative method (HR-CS GF AAS) were also used for this evaluation. The method was applied to biodiesel samples produced from different feedstocks. To the best of the authors knowledge, it is the first time that: 1) Ni in biodiesel is determined by a voltammetric method; 2) EIMB is applied to extract Ni from this matrix and 3) this type of sample preparation method is used with adsorptive stripping voltammetry.

Kinetics of sphalerite dissolution for potential zinc recovery via oxidative leaching

ABSTRACT In this study, the leaching of zinc from sphalerite in nitric acid (HNO3)/hydrogen peroxide (H2O2) binary solution was examined via kinetic study. The result showed that the amount of zinc leached increased as the temperature and leachant concentration increased, from 53.8 to 91% for H2O2 concentrations of 2 and 10 M; 53 to 93.2% for temperature of 30 and 90°C, respectively, and decreased as the solid/liquid ratio and particle diameter increased from 92.3 to 55.9% for S/L ratios of 20 and 50 g/L; 93.4 to 51.1% for particle diameters of <75 µm and <425 µm, respectively. The solid film diffusion model provided the finest description of the experimental data while chemical reaction was established as the rate-limiting step, with activation energy of 26.52 kJ/mol. Hence, a binary solution of HNO3 and H2O2 was established as a viable route towards recovering zinc from sphalerite.

Study of sample preparation, by acid digestion assisted by microwave radiation in a closed system, to determine inorganic contaminants in street cocaine samples by ICP OES and ICP MS

Knowledge of the inorganic composition of cocaine makes it possible to correlate the drug with its refinement and dilutions1, it is important to highlight that when aiming to study the adulteration/production of street cocaine it is interesting to carry out the total solubilization of the sample2. Thus, acid digestion using microwave radiation in a closed system is a widely used technique due to the speed and efficiency of digestion3. Thus, acid solubilization procedures and acid digestion assisted by radiation via microwaves of the sample were studied, varying the mass of the sample (0.050g, 0.100g, 0.200g and 0.500g) and concentration of the HNO3 solution (5%, 10% , 30%, 40% and 50% v/v). In order to verify whether the different sample preparation procedures and whether the final acidity interferes with the quantification of the analytes studied. ICP OES analysis was carried out on a high purity sample prepared by direct solubilization and digestion. The result of the intensities test for the elements Co, Cu, Mo, Pb and Zn, with final acidity of HNO3 2% or 4% v/v, demonstrated that samples prepared by direct solubilization or digested by microwaves, with final acidity of HNO3 2% v/v, presented very close intensity values for the elements analyzed, indicating that the types of sample preparation studied (solubilization or digestion) did not present significant interferences in the analysis by ICP OES.

Ultrathin Layered Structure and Oxygen Vacancies Mediated Efficient Charge Separation toward High Photocatalytic Activity in BiOIO3 Nanosheets.

Previous bismuth-based photocatalysts usually employ a strong acid solution (e.g., HNO3 solution) to obtain an ultrathin structure toward high photocatalytic activity. In this work, the ultrathin layered BiOIO3 nanosheets are successfully synthesized using just the glucose hydrothermal solution. The high-concentration glucose solution shows the obvious acidity after the hydrothermal process, which leads to the quick decrease in thickness of BiOIO3 nanosheets from ∼45.58 to ∼5.74 nm. The ultrathin structure can greatly improve charge carriers' separation and transfer efficiency. The generation of reductive iodide ions brings about oxygen vacancies in the ultrathin nanosheets, then the defect energy level is formed, causing the decreased band gap and improving the visible light absorption. Compared to thick BiOIO3 nanosheet with little oxygen vacancies, much higher carrier separation efficiency and visible light absorption are achieved in the ultrathin nanosheets with oxygen vacancies, resulting in an excellent photocatalytic performance (0.1980 min-1 for RhB degradation), which is much higher than most other bismuth-based photocatalysts. The superoxide radicals (•O2-) and holes (h+) are the major active species responsible for high photocatalytic activity. This work affords an environmentally friendly strategy to synthesize ultrathin photocatalysts with superior photocatalytic properties.

Selective removal of ReO4−/TcO4− by an imidazolyl-based polymer from 3 M HNO3 solution

The effective removal of 99TcO4− in the radioactive waste is very important and ReO4− was often used as the substitute of TcO4− for research. In this paper, an imidazolyl-based polymer TIB-TBPB was successfully synthesized and exhibited excellent adsorption performance for ReO4−. The results showed that the framework of TIB-TBPB is benzene-rich structure, which enhances its hydrophobicity and allows it to exhibit excellent thermal stability and acid-base stability. It could maintain the excellent recyclability even in 3 M HNO3. TIB-TBPB possessed the high capacity of 882 mg g−1 and the superb removal depth for ReO4− and TcO4− with Kd of 2.34 × 106 mL g−1 and 1.35 × 106 mL g−1, respectively. Furthermore, TIB-TBPB has the advantages of excellent selectivity, recyclability and could remove 65.7 % and 86.4 % of ReO4− from 3 M HNO3 and the Hanford LAW simulated nuclear waste, respectively. DFT calculation explained the selectivity of TIB-TBPB for ReO4− over NO3− and verified the experimental results. In a word, the excellent performance suggested TIB-TBPB would be a promising material for TcO4− /ReO4− removal.

Interpreting crystallographic and microcrystalline structural effect for demineralization of low-grade thermal coal in multi-stage chemical leaching: A cleaner combustion approach

Chemical leaching is one of the most efficient methods for improving low-grade coal due to its ability to remove both inorganic and organic minerals economically. This study examined the qualitative demineralisation using the XRD and FTIR analyses. Moreover, microcrystalline analysis was investigated by analysing the Micro-Raman spectra, and ash composition was analysed using XRF Spectroscopy analysis for coal samples. Furthermore, a correlation was established between a Raman parameter (AD/AG) and a crystallite parameter (Lc). The demineralisation mechanism was postulated in light of the findings to explain how significant impurities (SiO2 and Al2O3) with iron-bearing elements (Fe2O3 and FeS2) were curtailed during multi-stage leaching. The maximum deashing and demineralisation were obtained by treatment with 40% (w/v), i.e. 10 M NaOH, followed by HCl with HNO3 solution in a 3:1 ratio, with an average particle size of 180 μm. 79% ash reduction and 48% enhancement in GCV were achieved compared to raw coal.

Disruption of a three-component solution as a novel strategy for Cu and Ni extraction from vegetable oils for their determination by GF AAS

In this work, we propose a novel approach for extracting Cu and Ni from vegetable oils (which can be expanded to other metals). The method is based on the transference of the analytes to an aqueous acid phase due to the disruption of a three-component solution. The extraction was carried out in two steps. In the first step, a three-component solution was prepared comprising the sample, 1-octanol, and HNO3 solution. Next, the homogeneous system was disrupted by adding 1.0 mL of deionized water, and two phases were formed. The aqueous extract deposited in the bottom of the flask was collected with a micropipette, and Cu and Ni were determined by graphite furnace atomic absorption spectrometry (GF AAS). The developed method presented limits of quantification (LOQ) of 0.25 and 0.17 ng g−1 for Cu and Ni, respectively, and was successfully applied in the analysis of eleven oil samples from different origins.

Microwave-sustained inductively coupled atmospheric-pressure plasma (MICAP) for the elemental analysis of complex matrix samples

Microwave induced plasma optical emission spectrometry (MIP-OES) has gained widespread attention in the last few years for trace elemental analysis. Among the new generation of MIPs it is worth to mention the microwave-sustained inductively coupled atmospheric-pressure plasma (MICAP) for which previous works have shown similar detection capabilities to those afforded by ICP-OES. Nevertheless, this instrument has not been applied yet to complex matrix sample analysis. Therefore, the goal of this work is to evaluate MICAP-OES performance (e.g., analytical figures of merit, matrix effects, etc.) for elemental analysis of samples of different nature (e.g., environmental, food and polymers). To this end, both spectral and non-spectral interferences were investigated for 19 elements (Ag, Al, As, B, Ca, Cd, Co, Cr, Cu, Fe, Ga, In, Mg, Mn, Ni, Pb, Sr, Tl, Zn) in the presence of inorganic acid, organic and saline solutions and compared to a 5 % w w−1 HNO3 solution. Unlike previous MIPs, experimental data showed that the optimum nebulizer gas flow rate for a given emission wavelength was mostly independent of matrix characteristics. Regarding matrix effects, this device was highly robust operating both inorganic acid and organic matrices. Interestingly, when operating saline matrices, changes on emission signal by easily ionizable elements were less significant than those early reported by alternative MIP cavities. Moreover, due to MICAP spectrometer design employed allows real-time simultaneous analysis, Rh, Pd, Sc and Y were suitable internal standards to minimize non-spectral interferences. Finally, MICAP-OES can be successfully applied to the elemental analysis of different complex matrix samples (i.e., CRM-DW1 Drinking water; BCR-146 Sewage sludge industrial; BCR-185 Bovine liver; BCR-278R Mussel tissue; NIST-1549 Non-fat milk powder; ERM-EC681k Polyethylene (high level) and BCR-483 Sewage sludge amended soil).

Intensifying separation of Pb and Sn from waste Pb-Sn alloy by ultrasound-assisted acid leaching: Selective dissolution and sonochemistry mechanism

Clean and efficient extraction and separation of precious metals from discarded Pb-Sn alloy is critical to the sustainable utilization of solid waste resources. Dense oxide layer and compact alloy texture in the waste Pb-Sn alloy pose challenges to the effective leaching process. Ultrasonic waves are demonstrated to improve separation efficiency via the favorable physical and chemical effects in solution system. In this study, ultrasound-assisted leaching technology is attempted to rapidly and selectively extract Pb from the waste Pb-Sn alloy, and gives emphasis on ultrasonic electrochemical behaviors. The Eh-pH diagrams of Sn-H2O and Pb-H2O systems were firstly analyzed to lay the selective dissolution foundation. It’s indicated that oxidizing HNO3 lixiviant is suitable to realize the selective separation of Pb. Both Sn and Pb can be dissolved to ionic Sn2+ and Pb2+ in the HNO3 solution. However, Sn2+ rapidly oxidizes to Sn4+ and Sn4+ further hydrolyzes to insoluble SnO2, which will agglomerate on unreacted materials to limit internal metal leaching in conventional leaching process. Due to the vibratory stripping of oxide layer by physical effect of ultrasound, the conventional acid leaching time for Pb extraction can be halved with the ultrasound assistance. About 99.12 % Pb and only 0.1 % Sn are dissolved in ultrasound-assisted leaching under the following optimal parameters: 0.5 mol/L HNO3, leaching temperature of 80 °C, time of 30 min, liquid-to-solid ratio of 20 mL/g, and ultrasound intensity of 0.52 W/cm2. Leaching kinetics of Pb, phase transition, microstructure evolution, Pb-Sn galvanic corrosion and dissolution polarization curve were studied to determine the ultrasonic enhanced dissolution mechanism. Notably, Pb and Sn form a microcorrosion galvanic cell in which Sn acts as a cathode and is protected while the Pb undergoes intensifying corrosion as the anode giving rise to the higher Pb dissolution efficiency. Eventually, it’s suggested that Pb can be rapidly extracted and separated from the waste Pb-Sn alloy during the ultrasound-assisted HNO3 leaching process via the ultrasound physical and chemical effects, especially the sonochemistry aspect of intensified spot corrosion and galvanic corrosion. The proposed ultrasonic electrochemical corrosion in this work were applicable to the extraction of valuable metals from various waste alloys through leaching method.

Solid-phase extraction (SPE) of Ni(II), Cd(II) and Pb(II) ions using pyromellitic dianhydride functionalized silica gel prior to flame atomic absorption spectrometric determination

In this work, a novel pyromellitic dianhydride modified silica gel (PMDA-SG) was firstly fabricated for column solid-phase extraction (SPE) of Ni(II), Cd(II), and Pb(II) ions at trace levels from aqueous solutions, aiming to determine their trace level using flame atomic absorption spectrometer. PMDA-SG was confirmed by FT-IR and C,H,N elemental analysis. Optimization of the SPE column for Ni(II), Cd(II) and Pb(II) ions using the PMDA-SG loaded column involved a comprehensive investigation of the key factors. The optimum conditions were found as follows: a sample solution pH of 7.0, a sample flow rate of 5 mL/min, a maximum solution volume of 500 mL, and an eluent consisting of 5 mL of 1.0 mol L−1 HNO3 solution. To validate the developed SPE method, a certified reference material of Ontario Lake water (NWTMDA-54.4) was employed, and a good fit was observed in the obtained data. The SPE method demonstrated good precision in the determination of Ni(II), Cd(II) and Pb(II) at 20 ng mL−1 (n = 5), yielding relative standard deviation values lower than 5%. Trace levels of Ni(II), Cd(II) and Pb(II) in environmental water samples form laboratory tap, Sapanca Lake, Çark Stream and Sakarya River were successfully quantified by FAAS after preconcentration using PMDA-SG filled column.

A simple, fast and inexpensive approach to quantify low concentrations of iron in biodiesel by voltammetry after extraction induced by microemulsion breaking.

An alternative approach to assay iron (Fe) in biodiesel by differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) is presented herein. The sample treatment involved a simple, rapid, but effective extraction of Fe from biodiesel into an aqueous phase after microemulsion (ME) breaking. Then, Fe was determined as the complex Fe(III)-PAN (1-(2-pyridylazo)-2-naphthol) on a glassy carbon electrode (GCE) in the presence of bismuth (Bi(III)). The extraction induced by microemulsion breaking (EIMB) was achieved by adding 0.80 mL of ultrapure water into a water-in-oil ME containing 7.00 mL biodiesel, 2.70 mL n-propanol and 0.30 mL of 0.25 mol L-1 HNO3 solution. No deliberate addition of surfactant was necessary to form and maintain the ME. The EIMB resulted in a 1.30 mL lower aqueous phase extract (APhEx) and an upper oily phase. DP voltammograms were recorded with a portable potentiostat, showing the potentiality of carrying out the determination out of a central laboratory. Another feature was the non-necessity of deaerating the solution to eliminate the dissolved O2. The limits of detection (LOD) and quantification (LOQ) were 1.7 μg L-1 (140 mg kg-1) and 5.5 μg L-1 (455 mg kg-1), respectively. The accuracy of the method was evaluated by recovery assays of spiked samples, by analyzing a standard reference material and by comparisons with high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS).

Determination of yttrium in phosphorus powder from fluorescent lamps by microwave-induced optical emission spectrometry (MIP OES) after ultrasound-assisted extraction.

In this work, we propose a novel method for yttrium determination by microwave-induced optical emission spectrometry (MIP OES). It is based on the ultrasound-assisted extraction of yttrium with a diluted HNO3 solution and was applied to yttrium determination in phosphorus powder from fluorescent lamps. The method was optimized employing a multivariate strategy, based on a Box-Behnken design, taking into account three experimental factors: mass of the sample (25 to 75 mg), sonication time (15 to 165 min) and HNO3 concentration in the extractant solution (2.0 to 6.0 mol L-1). According to the data obtained in the optimization process, only the sonication time and the HNO3 concentration had an influence on the extraction of yttrium from the samples. The data also indicated that yttrium must be strongly linked to the matrix, since its quantitative extraction was only possible when using the maximum values of the two factors. Therefore, under optimized conditions, we could quantitatively extract yttrium from 75 mg of sample using a 6 mol per L HNO3 solution and a sonication time of 165 min. The limits of detection and quantification for the method were 0.4 and 1.2 μg g-1, respectively, and the intermediary precision (three days) was 14%. The concentration of Y in the analyzed samples varied from 5.37 ± 1.82 to 298 ± 31 μg g-1, and recoveries of 91.0 ± 34.6 and 106 ± 23% were obtained in comparison to total digestion. The results obtained by the proposed method were not statistically different (at the 95% confidence level) from those obtained after the total digestion of the samples when applying the Student's t-test.

Development of eco-friendly pretreatment processes for high-purity silicon recovery from end-of-life photovoltaic modules.

This study examines the efficacy of photovoltaic (PV) recycling processes and technologies for the recovery of high-purity silicon powder from waste solar modules. In order to facilitate the simplification of complex processes, such as the conventional nitric acid dissolution, solvent and ultrasonic irradiation, and solvent dissolution, a variety of mechanical separation processes have been established. These processes are designed to enhance the efficiency and effectiveness of the aforementioned processes. And a novel method for separating EVA from recycled Si powder was devised, which studied the WGS process using aqueous solutions of H2O, HNO3, and NaCl with different specific gravities. The WGS process using NaCl solution demonstrated superior performance, removing over 94% of the EVA, requiring less energy input and producing 73% less CO2 emissions compared to the thermal process. These technologies facilitate the transition towards a circular economy and bolster the implementation of carbon-neutral initiatives.