The efficient, selective, and economical sorbents for the removal of Sr radionuclides are largely needed for the decontamination of effluents with high salinity. In this study, the removal of Sr was ...investigated using the zeolite produced from the Bayer process liquids. Based on the XRD, SEM/EDS analysis, the product was pure and highly crystalline zeolite 4A (Z4A). Removal of Sr was fast (5 min for 100% removal at 8.80 mg/L), with high maximum sorption capacity (252.5 mg/L), and independent on the initial pH in the range 3.5-9.0. Specific sorption of Sr by protonated groups on the Z4A surface was operating in addition to ion-exchange with Na ions. The selectivity of Z4A decreased in the order Sr > Ca > K > Mg > Na. 84% of Sr was separated from seawater within 5 min, at the Z4A dose of 5 g/L, while efficiency increased to 99% using the dose of 20 g/L. Desorption of radioisotope
Sr from seawater/Z4A solid residue was very low in deionized water (0.1-0.2%) and groundwater (0.7%) during 60 days of leaching. Z4A is a cost-effective, selective, and high-capacity medium for Sr removal, which provides high stability of retained radionuclides.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Strontium (Sr) and sodium (Na) are the most used modifiers in the aluminum casting industry. Both lose their concentration (fade) during holding in the melting furnace. Three types of chemical ...reactions in the melt may cause modifier fading: vaporizing, oxidizing, or reacting with some other elements from the melt. Due to Na and Sr’s very low vapor pressure, their vaporization from the aluminum melt was excluded as a reason for the modifiers’ fading. Oxidation looks like the major chemical reaction that causes the fading of Na and Sr from an aluminum melt. The present paper aimed to quantify the fading of Na and Sr in an Al–Si–Cu–Mg alloy. The loss of modifiers (Na and Sr) during melt holding in a furnace can be analytically quantified using equations taken from the literature. The calculated surface reaction rate constant (ks) can estimate the modifier’s loss during melt holding in industrial and laboratory furnaces.
The influence of process parameters in the three-stage purification of aluminate solution from the Bayer process and aluminum hydroxide was considered in this paper. One of the ways of purification ...is treating the aluminate solution in order to reduce the concentrations in the starting raw material (solution) and then treating the aluminum hydroxide at a certain temperature and time in order to obtain an alumina precursor of adequate quality. The purification process itself is divided into three phases. The first phase involves the treatment of sodium aluminate with lime in order to primarily remove Ca2+ and (SiO3)2− impurities. Phase II aims to remove impurities of Zn2+, Fe2+, and Cu2+ by treatment with controlled precipitation using specially prepared crystallization centers. In Phase III, Na+ is removed by the process of hydrothermal washing of Al2O3 ∙ 3H2O. In this work, parameters such as temperature (T), reaction time (t), and concentration of lime (c) were studied in order to remove the mentioned impurities and obtain the purest possible product that would be an adequate precursor for special types of alumina.
Cobalt’s pivotal role in global development, especially in lithium-ion batteries, entails driving increased demand and strengthening global trading networks. The production of different waste ...solutions in metallurgical operations requires the development of an environmentally friendly research strategy. The ultrasonic spray pyrolysis and hydrogen reduction method were chosen to produce nanosized magnetic powders from waste solution based on iron and cobalt obtained during the purification process of used polycrystalline diamond blanks. With specific objectives focused on investigating the impact of reaction temperature and residence time on the morphology, chemical composition, and crystal structure of synthesized nanosized cobalt powders, our research involved 15 experimental runs using two reactors with varying residence times (7.19 s and 23 s) and distinct precursors (A, B, and C). Aerosol droplets were reduced at 600 to 900 °C with a flow rate of 3 L/min of argon and hydrogen (1:2). Characterization via scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction revealed that higher temperatures influenced the spherical particle morphology. Altering cobalt concentration in the solution impacted the particle size, with higher concentrations yielding larger particles. A short residence time (7.9 s) at 900 °C proved optimal for cobalt submicron synthesis, producing spherical particles ranging from 191.1 nm to 1222 nm. This research addresses the environmental significance of recovering magnetic particles from waste solutions, contributing to sustainable nanomaterial applications.
Acid mine drainage (AMD) remediation by red mud (RM) can benefit process sustainability and waste valorization. Though the AMD properties upon using RM have been broadly investigated, the key ...features and the environmental stability of spent RM are poorly defined. The current study aimed to compare the AMD neutralization and metal removal potential of the fresh (FRM) and aged (ARM) Bayer red mud and evaluate the textural, mineralogical, chemical, radiological properties of solid residues, and the stability of toxic elements. The FRM had larger particles and exhibited higher pH, iron oxide content, and radioactivity than ARM, which could be driven by ARM leaching and settling inside the tailings pond. FRM displayed marginally higher neutralization and metal removal capacity than ARM. Reaction with AMD led to partial dissolution of cancrinite minerals without significant changes in the particle size distribution. The leachability of investigated toxic elements (As, Ba, Cd, Cr, Cu, Ni, Pb, Se, Zn) from neutralization residues complied with the limits set for inert waste by the EN 12457–2 test. Owing to the RM neutralization, the leachability of Al, As, Cr, and V decreased with respect to pristine samples. While Zn and Mn sorbed from AMD were stable following SPLP and EN 12457–2 tests, the sequential extraction revealed increased environmental availability, posing a potential risk during disposal or application if accompanied by a decline in pH. The slight increase in radioactivity upon RM neutralization indicates that changes in radionuclide inventory should be monitored when using RM in neutralization.
Fluorapatite nanopowders with different amounts of fluoride ions were
prepared using the surfactant-assisted microwave method under isothermal
conditions. Microwave irradiation was applied for the ...rapid formation of
crystals. A micellar solution of polyoxyethylene (23) lauryl ether was used
as a regulator of nucleation and crystal growth. Characterization studies
from X-ray diffraction, field-emission scaning electron microscopy and
Fourier-transform infrared spectra showed that crystals have an apatite
structure and particles of all samples are nano size, with an average length
of 50 nm and about 15-25 nm in diameter. Antimicrobial studies have
demonstrated that synthesized fluorapatite nanopowders exhibit activity
against tested pathogens: Escherichia coli, Staphylococcus aureus and
Candida albicans. Activity increased with the amount of fluoride
ions. The synthesized fluorapatite nanomaterials are promising as
materials in environmental protection and medicine for orthopedics and
dental restorations.
Due to their remarkable magnetic properties, such as a high maximum energy product, high remanence, and high coercivity, NdFeB magnets are used in a variety of technological applications. Because of ...their very limited recycling, high numbers of spent NdFeB magnets are widely available in the market. In addition to China’s monopoly on the supply of most rare earth elements, there is a need for the recovery of these critical metals, as their high import price poses an economic and environmental challenge for manufacturers. This paper proposes a pyrometallurgical recycling method for end-of-life NdFeB magnets by oxidizing them in air as first required step. The main goal of this method is to oxidize rare earth elements from NdFeB magnets in order to prepare them for the carbothermic reduction. The experimental conditions, such as the oxidation temperature and time, were studied in order to establish the phase transformation during oxidation using the Factsage Database and experimental conditions. Our thermogravimetric analysis TGA analysis revealed an increased sample mass by 35% between room temperature and 1100 °C, which is very close to the total calculated theoretical value of oxygen (36.8% for all elements, and only 3.6% for rare earth elements REE), confirming the complete oxidation of the material. The obtained quantitative analysis of the oxidation product, in (%), demonstrated values of 53.41 Fe2O3, 10.37 Fe3O4; 16.45 NdFeO3; 0.45 Nd2O3, 1.28 Dy2O3, 1.07 Pr2O3, and 5.22 α-Fe.
In a semi-ideal gas, entropy changes cannot be determined through the medium
specific heat capacity in a manner as determined by the change of internal
energy and enthalpy, i.e. the amount of heat ...exchanged. Taking this into
account, the authors conducted two models through which it is possible to
determine the change in the specific entropy of a semi-ideal gas for
arbitrary temperature interval using the spread sheet method, using the mean
values of the appropriate functions. The idea is to replace integration,
which occurs here in evitably, with mean values of the previous functions.
The models are derived based on the functional dependence of the actual
specific heat capacity on the temperature. The theorem used is that of the
mean value of a function as well as the mathematical properties of the
definite integral. The mean value of a fractional function is determined via
its integrand while the logarithmic functions were performed by applying a
suitable transformation of the differential calculus. The relations derived
relation, using the computer program, have enabled the design of appropriate
thermodynamic tables through which it is possible to determine the change in
entropy of arbitrary state changes in an efficient and rational manner,
without the use of calculus or finished forms. In this way, the change in the
entropy of a semi-ideal gas is determined for an arbitrary temperature
interval using the method which is analogous to that applied in determining
the change of internal energy and enthalpy or the amount of heat exchanged,
which was the goal of the work. Verification of the proposed method for both
the above functions was performed for a a few characteristic semi-ideal gases
where change c(T) is significant, for the three adopted temperature
intervals, for the characteristic change of state. This was compared to the
results of the classical integral and the proposed method through the
prepared tables. In certain or special cases, it is possible to apply the
presented method also in determining the change in entropy of the real gas.
Apart from that, the paper shows that the change in entropy for the observed
characteristic case can be represented or graphically determined using the
planimetric method of diagrams with suitably selected coordinates.
nema
The objective of the present study was to determine the impact of cadmium (Cd) concentration in the soil on its uptake by tobacco plants, and to compare the ability of diverse extraction procedures ...for determining Cd bioavailability and predicting soil-to-plant transfer and Cd plant concentrations. The pseudo-total digestion procedure, modified Tessier sequential extraction and six standard single-extraction tests for estimation of metal mobility and bioavailability were used for the leaching of Cd from a native soil, as well as samples artificially contaminated over a wide range of Cd concentrations. The results of various leaching tests were compared between each other, as well as with the amounts of Cd taken up by tobacco plants in pot experiments. In the native soil sample, most of the Cd was found in fractions not readily available under natural conditions, but with increasing pollution level, Cd amounts in readily available forms increased. With increasing concentrations of Cd in the soil, the quantity of pollutant taken up in tobacco also increased, while the transfer factor (TF) decreased. Linear and non-linear empirical models were developed for predicting the uptake of Cd by tobacco plants based on the results of selected leaching tests. The non-linear equations for ISO 14870 (diethylenetriaminepentaacetic acid extraction - DTPA), ISO/TS 21268-2 (CaCl
2
leaching procedure), US EPA 1311 (toxicity characteristic leaching procedure - TCLP) single step extractions, and the sum of the first two fractions of the sequential extraction, exhibited the best correlation with the experimentally determined concentrations of Cd in plants over the entire range of pollutant concentrations. This approach can improve and facilitate the assessment of human exposure to Cd by tobacco smoking, but may also have wider applicability in predicting soil-to-plant transfer.
Full text
Available for:
BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
This paper presents the results of determining the pseudo-total concentration of five heavy metals in the soil on which the destruction of ammunition, mines, and explosive devices is carried out by ...the method of open detonation. In the analyzed area, the concentrations of cadmium, lead, nickel, copper, and zinc were determined, while from the physical properties of the soil were determined the granulometric composition and the pH. The aim of the study is to determine the origin and total load on heavy metals and, based on that, to assess the dangers and impact of the site in terms of the soil pollution by heavy metals. In accordance with the regulations of Bosnia and Herzegovina, the results of the soil testing showed a significant load of copper (up to seven times) and cadmium (up to six times), and exceeding the allowed values for nickel and zinc in some places. Lead was the only metal whose concentration was within the maximum allowed and according to that the soil was classified as unpolluted. A sample of soil from the edge of the pit is the only sample in which all heavy metals, except Ni, were within the maximum allowable concentration. In regard to the concentration of the examined metals, the soil of the pit is classified as medium polluted from the aspect of copper, cadmium, and nickel and highly contaminated with zinc. The concentrations of copper and zinc in the examination area correspond to contaminated soil that represents ecological risk, which requires soil remediation.
PDF
