Sorption Of Elements Research Articles

Enhancement of sorption capacity to Sr and Cs of a cement composite by addition of brick powder

Concrete is a suitable material for secondary casings in multi-barrier systems used in radioactive waste repositories, because it is durable and radiation- and thermal resistant and it has good mechanical properties. The casings should also limit possible leaching of radionuclides in case of failure of inner barriers. An efficient way to tackle this problem is the addition of a sorption material in the concrete mixture. Here mechanical and thermal properties of concrete containing different amounts of brick powder are studied in relation to the concrete mixture porosity. It is found out that, as expected, the bulk density and compressive and bending strengths decreased with an increasing amount of the brick powder. In addition, the sorption of cesium and strontium chlorides into the mixtures was analyzed under laboratory conditions, and their sorption isotherms and distribution coefficients were calculated. The results indicate that brick has higher sorption capacity for Sr than for Cs. Relatively low distribution coefficients indicate, however, that the studied brick is not a very suitable additive material for sorption of Sr and Cs elements.

Rare earth elements (REY) sorption on soils of contrasting mineralogy and texture

Rare earth elements (REY) are the lanthanide elements (Z = 57–71), which have an ever-growing occurrence in present-day industries, agriculture, and modern life. Consequently, environmental concentrations are expected to increase accordingly as a result of intensified utilization. Soils are an important sink for REY, yet little research has been conducted concerning activity, inputs, and lability in soil systems. This study evaluated the REY (lanthanides + yttrium) sorption and partition coefficients (Kd) in two broadly representative natural soils (A horizon), with contrasting mineralogy and organic character, formed under distinct environmental conditions: an Oxisol from Brazil and a Mollisol from the USA. Batch reactions of soils suspended in a background electrolyte solution of 5 μmoles kg−1 of Ca(NO3)2 at 1:100 solid to solution were reacted with 80 μmoles kg−1 REY added individually and in multi-REY competitive systems to evaluated adsorption after 3 h and 72 h over a wide pH range (from ca. 2 to 8). Results showed sorption was similar for all REY within each soil type when examined at the natural measured soil pH; Mollisol pH 6.85, Oxisol pH 4.35. However, REY sorption (by Kd) was nearly two-fold greater in the Mollisol compared to the Oxisol for the single REY experiments. Multi-REY competitive sorption reactions showed a decrease in Kd for both soils at 3 and 72 h, and to a greater extent for the Mollisol, indicating soil type had a strong effect on the sorption affinity of each REY. It was also observed that REY sorption increased from low to high pH (pH 2–8) in the Oxisol, and increased with pH from 2 up to the point zero charge (PZC) in the Mollisol, then stabilized. The varying REY Kd values from these two distinct and abundant soils, with and without REY competition, and over a range of pH are explained in terms of soil mineralogy (i.e., 2:1 clays in the Mollisol; oxides in the Oxisol) and organic matter content. Our findings show that soil characteristic controls sorption, precipitation, and cation exchange capacity, which are the key mechanisms for predicting REY fate and transport in the environment.

Trace elements sorption by bentonite in the presence of bacteria

Sorption of lead and copper by calcium bentonite, living and destroyed cells of gram-positive bacteria Bacillus subtilis, as well as in systems including the clay mineral and one of the biotic components in the concentration range of the elements from 25 to 250 μM was studied. The effect of acidity on the biosorption of trace elements was shown. The maximum biosorption of lead and copper was observed at pH 6 and reached 0.72 and 0.52 mM/g of dry matter, respectively. At pH 6 the maximum biosorption by the destroyed cells was also observed — 0.81 mM/g of lead and 0.71 mM/g of copper. Accumulation of trace elements by living and destroyed cells significantly exceeded their sorption by calcium bentonite. In the ternary systems, including bentonite and bacterial cells or bentonite and cell debris, there was an increase in the sorption of lead and copper compared to bentonite alone. At the same time, the sorption of trace elements by a mixture of bentonite and cell fragments was lower than the additively calculated sorption by the individual components for both lead and copper at all concentrations studied. A similar pattern was observed for the system of living cells and bentonite for copper and living cells and bentonite for lead at low metal concentrations.

Sorption properties of carbamoylmethylphosphonated-based polymer combining both sorption and thermosensitive properties: New valuable hydrosoluble materials for rare earth elements sorption

The sorption properties of gadolinium (Gd) by an original carbamoylmethylphosphonate (cmp)-based acrylamide polymer combining both chelating and thermosensitive properties namely poly(diethyl-6-(acrylamido)hexylcarbamoyl-methylphosphonate) (P(CPAAm6C)) are presented for the first time. For pH = 1 and at 20 °C, the maximum sorption capacity reached 0.6 mmol·g−1 for the highest Gd concentrations. Different parameters influencing the sorption of Gd were studied as pH, ionic strenght and temperature. The temperature was shown to influence both the sorption and the stability of the complex cmp-Gd formed by coordination mode with CO and PO functions. The selectivity of the cmp group for Gd was demonstrated in Gd/Ni mixture and shows its thermosensitive polymer is very promising for the development of selective sorption processes.

Biosorption of Rare-Earth Elements and Yttrium by Heterotrophic Bacteria in an Aqueous Environment

This paper reports the results of the experimental determination of the coefficient of sorption of rare-earth elements and yttrium (REY) under conditions of acidic pH using several strains of heterotrophic bacteria (Microbacterium sp., Curtobacterium sp., Bacillus subtilis, Pseudomonas putida, and Bacillus pumilis) that are widespread in natural and technogenic waters of the Far East (Russia). Insignificant fractionation between heavy and light rare-earth elements, negative cerium and dysprosium anomalies, and a positive europium anomaly were revealed. The selectivity of REY biosorption by gram-positive and gram-negative bacteria, as well as inertia of the biosorption process under more acidic conditions of the medium, were shown.

Granulated Bog Iron Ores as Sorbents in Passive (Bio)Remediation Systems for Arsenic Removal.

The main element of PbRS (passive (bio)remediation systems) are sorbents, which act as natural filters retaining heavy metals and carriers of microorganisms involved in water treatment. Thus, the effectiveness of PbRS is determined by the quality of the (ad)sorbents, which should be stable under various environmental conditions, have a wide range of applications and be non-toxic to (micro)organisms used in these systems. Our previous studies showed that bog iron ores (BIOs) meet these requirements. However, further investigation of the physical and chemical parameters of BIOs under environmental conditions is required before their large-scale application in PbRS. The aim of this study was (i) to investigate the ability of granulated BIOs (gBIOs) to remove arsenic from various types of contaminated waters, and (ii) to estimate the application potential of gBIOs in technologies dedicated to water treatment. These studies were conducted on synthetic solutions of arsenic and environmental samples of arsenic contaminated water using a set of adsorption columns filled with gBIOs. The experiments performed in a static system revealed that gBIOs are appropriate arsenic and zinc adsorbent. Dynamic adsorption studies confirmed these results and showed, that the actual sorption efficiency of gBIOs depends on the adsorbate concentration and is directly proportional to them. Desorption analysis showed that As-loaded gBIOs are characterized by high chemical stability and they may be reused for the (ad)sorption of other elements, i.e., zinc. It was also shown that gBIOs may be used for remediation of both highly oxygenated waters and groundwater or settling ponds, where the oxygen level is low, as both forms of inorganic arsenic (arsenate and arsenite) were effectively removed. Arsenic concentration after treatment was <100 μg/L, which is below the limit for industrial water.

Monitoring soil lead and zinc contents via combination of spectroscopy with extreme learning machine and other data mining methods

In order to limit pollution risk and develop proper remediation strategies, soil quality has to be controlled by rapid and sustainable monitoring measures. Visible and near-infrared reflectance spectroscopy (VisNIR) is an attractive surrogate to time-consuming and costly classical soil assessment protocols. It highly depends on selecting appropriate data mining methods for regression analysis. In this study, performance of a state of the art learning algorithm called extreme learning machine (ELM), was evaluated through comparing with the other calibration methods proposed in the literature for predicting lead (Pb) and Zinc (Zn) concentrations. Solid samples collected from a mine waste dump (n=120) were scanned using a Fieldspec3 portable spectroradiometer with a measurement range of (350–2500nm) in a laboratory. Transformation of the reflectance spectra to absorbance was followed by three pre-processing scenarios including Savitzky-Golay smoothing (SG), first derivative (FD) and second derivative (SD). Partial Least Square Regression (PLSR), Support Vector Machine (SVM) and neural networks with two learning algorithms models (back propagation and extreme learning machine), were calibrated on spectral features selected by genetic algorithm, and then applied to predict soil metal concentrations. The best prediction accuracy was obtained by FD-ELM method with R2p, RMSEp, concordance correlation coefficient and RPD values of 0.93, 63.01, 0.98 and 5.92 for Pb and 0.87, 167.90, 0.91 and 5.62 for Zn, respectively. Study of the prediction mechanism proved that element sorption by spectrally active Fe-oxide and clay contents of the soil was the major mechanism by which the spectrally featureless Pb and Zn ions can be predicted. The spatial patterns of predicted toxic elements showed that FD-ELM had the most similarity with those maps obtained by interpolating measured values. Over all, it is concluded that reflectance spectroscopy combined with the ELM algorithm is a rapid, inexpensive and accurate tool for indirect evaluation of Pb and Zn and mapping their spatial distribution in dumpsite soils of Sarcheshmeh copper mine.

Rare earth elements sorption to iron oxyhydroxide: Model development and application to groundwater

Iron oxyhydroxides are among the most important colloids that control rare earth elements (REE) concentrations and transport in natural hydrosystems. In this study, REE surface complexation to iron oxyhydroxides (Fe(OH)3(a)) was described by using the Donnan diffuse layer model and a two-site (i.e. ≡FesOH and ≡FewOH) model. The specific surface area and pH of zero charge were fixed as 100000 m2/mol and 8.0, respectively. The surface site density for weak and strong binding sites were fixed at 0.1 moL/mol Fe (≡FewOH) and 0.001 moL/mol Fe (≡FesOH) respectively. The two site types were used with pKa1int = 7.29 and pKa2int = 8.93. Using linear free energy relationship, the estimated equilibrium surface complexation constants (log K) increased from light REE (LREE) to heavy REE (HREE). Results of REE modeling calculation using the determined log K revealed a good fit of experimental data, showing an order of sorption on iron oxyhydroxides: HREE > MREE > LREE and preferential sorption of HREE at a lower pH. However, sorption edges only showed a slight change with ionic strength (0.1–0.7 moL/L) for the whole REE series. The generalized model was subsequently used to evaluate the impact of iron oxyhydroxides on REE speciation in groundwater. Application of the model to “model groundwater” showed that iron oxyhydroxide complexes of REE were significant in near neutral and weakly alkaline pH. This study contributes to putting forward a comprehensive database which would be useful for the application of surface complexation model to describe REE sorption by amorphous ferric hydroxides in nature.

Key role of the sorption process in alteration of metal and metalloid quantification by fouling development on DGT passive samplers

The DGT technique (diffusive gradients in thin films) is widely used for passive sampling of labile trace metals and metalloids in natural waters. Although development of fouling on the protective membranes is frequently observed, its effect on DGT sampling has been barely investigated. This study evaluates the influence of fouling on sampling of trace cationic metals Cd(II), Cu(II), Ni(II) and Pb(II) and oxyanions As(V), Cr(VI), Sb(V) and Se(VI). Fouling was developed in situ on polycarbonate membranes in four diverse natural freshwater environments and sampling alteration was assessed in controlled laboratory experiments. Accumulation of oxyanions and Ni was unaltered in the presence of fouling whereas significant alteration occurred in sampling of Cd, Cu and Pb (at pH ∼5.4). Characterization of the fouled membranes highlighted the intervention of sorption phenomenon as sampling alteration was systematically observed alongside element sorption onto fouled membrane. A preliminary flowchart for identifying potentially biased quantifications linked to fouling development during in situ DGT deployment in natural waters is proposed.

Batch-type study of Cs, Co, and Tc binding with hydrated cement under hyperalkaline conditions

In the presented study the binding of Cs, Co, and Tc with hardened cement paste (HCP) under hyperalkaline conditions, with respect to sorption reversibility, has been investigated using batch-type experiments. The Cs, Co, and Tc sorption kinetics were determined and the distribution coefficients K d , representing the experimental systems, were obtained. The reversibility of the element sorption has been discussed in accordance with the published data. It was shown that the sorption kinetics was rapid and the equilibrium was attained within 1–5 days. The K d values clearly demonstrated the sorption dependence on both the chemical composition of the HCP and the element speciation.

Redistribution of elements between wastes and organic-bearing material in the dispersion train of gold-bearing sulfide tailings: Part I. Geochemistry and mineralogy.

Migration and redistribution of elements during prolonged interaction of cyanide wastes with the underlying natural organic-bearing material have been studied in two ~40cm deep cores that sample primary ores and their weathering profile (wastes I and II, respectively) in the dispersion train of gold-bearing sulfide tailings in Siberia. Analytical results of SR-XRF, whole-rock XRF, AAS, CHNS, and SEM measurements of core samples show high K, Sr, Ti, and Fe enrichments and correlation of P2O5 and Mn with LOI and Corg. Organic material interlayered or mixed with the wastes accumulates Cu, Zn, Se, Cd, Ag, Au, and Hg. The peat that contacts wastes II bears up to 3wt.% Zn, 1000g/t Se, 100g/t Cd, and 8000g/t Hg. New phases of Zn and Hg sulfides and Hg selenides occur as abundant sheaths over bacterial cells suggesting microbial mediation in sorption of elements. Organic-bearing material in the cores contains 10-30g/t Au in 2-5cm thick intervals, both within and outside the intervals rich in sulfides and selenides. Most of gold is invisible but reaches 345g/t and forms 50nm to 1.5μm Au0 particles in a thin 2-3cm interval of organic remnants mixed with wastes I. Vertical and lateral infiltration of AMD waters in peat and oxidative dissolution of wastes within the dispersion train of the Ursk tailings lead to redistribution of elements and their accumulation by combined physical (material's permeability, direction AMD), chemical (complexing, sorption by organic matter and Fe(III) hydroxides) and biochemical (metabolism of sulfate-reducing bacteria) processes. The accumulated elements form secondary sulfates, and Hg and Zn selenides. The results provide insights into accumulation of elements in the early history of coal and black shale deposits and have implications for remediation of polluted areas and for secondary enrichment technologies.

Zn(II), Mn(II) and Sr(II) Behavior in a Natural Carbonate Reservoir System. Part I: Impact of Salinity, Initial pH and Initial Zn(II) Concentration in Atmospheric Conditions

The sorption of inorganic elements on carbonate minerals is well known in strictly controlled conditions which limit the impact of other phenomena such as dissolution and/or precipitation. In this study, we evidence the behavior of Zn(II) (initially in solution) and two trace elements, Mn(II) and Sr(II) (released by carbonate dissolution) in the context of a leakage from a CO2 storage site. The initial pH chosen are either equal to the pH of the water-CO2 equilibrium (~ 2.98) or equal to the pH of the water-CO2 -calcite system (~ 4.8) in CO2 storage conditions. From this initial influx of liquid, saturated or not with respect to calcite, the batch experiments evolve freely to their equilibrium, as it would occur in a natural context after a perturbation.The batch experiments are carried out on two natural carbonates (from Lavoux and St-Emilion) with PCO2 = 10−3.5 bar, with different initial conditions ([Zn(II)]i from 10−4 to 10−6 M, either with pure water or 100 g/L NaCl brine). The equilibrium regarding calcite dissolution is confirmed in all experiments, while the zinc sorption evidenced does not always correspond to the two-step mechanism described in the literature. A preferential sorption of about 10% of the concentration is evidenced for Mn(II) in aqueous experiments, while Sr(II) is more sorbed in saline conditions. This study also shows that this preferential sorption, depending on the salinity, is independent of the natural carbonate considered. Then, the simulations carried out with PHREEQC show that experiments and simulations match well concerning the equilibrium of dissolution and the sole zinc sorption, with log KZn(II) ~ 2 in pure water and close to 4 in high salinity conditions. When the simulations were possible, the log K values for Mn(II) and Sr(II) were much different from those in the literature obtained by sorption in controlled conditions. It is shown that a new conceptual model regarding multiple Trace Elements (TE) sorption is required, to enable us to better understand the fate of contaminants in natural systems.

Biogeochemical coefficients as indicators of nutrient element sorption in jerivá (Syagrus romanzoffiana (Chamisso) Glassman), a palm tree species from Brazil

The absorption coefficients usually applied to biogeochemical prospection may provide information on the substrate (soil) in natural and contaminated ecosystems, since the chemical composition of the plants tends to reflect the availability of the elements. The biogeochemical coefficients could be a parameter to assess the bioaccumulation potential of a flora species, interactions involving the soil–plant system, and presence or absence of contaminants, such as metals. This study applies the biological absorption coefficient, the temporal absorption coefficient, and the acropetal coefficient as parameters to evaluate the differential absorption in the selected representative species. The Syagrus romanzoffiana (Chamisso) Glassman chosen as a representative species in this study is a palm tree species commonly known in Brazil as “palmeira jeriva” (jeriva palm tree). The representative species is widely used in landscaping and vegetation restoration in urban areas. It shows major regional dispersion and is endemic in South America. The results indicate that jeriva palm tree could be a useful indicator of soil contamination in tropical areas.

Manganese and iron oxide-coated redox bars as a tool to in situ study the element sorption in wet soils

When studying redox conditions in soils with manganese (Mn) and iron (Fe) oxide-coated redox bars, we observed the formation of Fe oxides along the Mn oxide coating and assumed sorption of other elements from soil solution to oxide surface. The objective of this study was to investigate the formation of Fe oxides along Mn redox bars and to analyze element sorption from soil solution to either Mn or Fe oxide along redox bar coatings. We protruded Mn redox bars into solutions with defined Fe2+ concentrations and removed the bars at distinct time intervals. The Mn oxide coating and potential Fe oxides were extracted using dithionite-citrate-bicarbonate (DCB). To investigate in situ element sorption behavior, we used previously field-installed redox bars, protruding these Mn redox bars into acidified hydroxylamine hydrochloride (AAH) to selectively extract Mn oxide and afterwards into DCB to dissolve the remaining Fe oxide coating. This two-step extraction procedure enabled the differentiation of elements bonded to either Mn or Fe oxide. Additionally, we analyzed the redox bar coatings at a very small scale ( Pb > Zn, Fe oxide preferentially sorbed oxyanions with As > P > Mo > V, respectively. “Field”-Fe oxides precipitating along the Mn redox bars sorbed elevated levels of As and P compared with the action of synthesized “lab”-Fe oxides along Fe redox bars, a finding which we attribute to short-range-ordered Fe phases with elevated sorption capacity. Besides providing information regarding the monitoring of soil redox status, the developed sequential two-step extraction procedure enables the differentiation of the selective sorption of elements in the soil solution to the coating of Mn and Fe redox bars. The collection of Fe oxides formed naturally along the Mn redox bar coatings further enables the investigation of temporally and spatially diverse Fe oxide-forming processes.

Analysis of incinerator waste emissions containing toxic elements by sorption–continuum source electrothermal atomic absorption spectrometry

Possibilities of the determination of toxic elements, As, Cd, Co, Cr, Cu, Ni, Pb, Se, Sn, and Te, in emissions from a waste incineration plant are studied by high-resolution electrothermal atomic absorption spectrometry of with a continuum spectral source. A procedure is developed for the preparation of samples of solid domestic waste by the sorption of toxic elements on an S,N-containing sorbent. The analytical conditions of work on an atomic absorption spectrometer with a continuum spectral source are chosen. An improvement of performance characteristics in comparison to the known procedures is shown. A procedure of the determination of the chosen toxic elements in emissions from an incineration plant by electrothermal atomic absorption spectrometry with improved performance characteristics is developed and passed through metrological certification.

Sorption of rare-earth elements from phosphogypsum sulfuric acid leaching solutions

Sorption technology for extracting rare-earth elements (REEs) from sulfuric acid solutions of phosphogypsum percolation leaching has been developed. Sorption conditions that enable to reach maximum REE content in the sorbent at minimum content of thorium and calcium have been found.

Surface complexation modeling of neptunium(V) sorption to lepidocrocite (γ-FeOOH)

Abstract Lepidocrocite (γ-FeOOH), an important iron-bearing mineral found to exist with a relatively high abundance in the soils of the Chinese nuclear test sites, has rarely been studied for its sorption of transuranic elements from the nuclear wastes. This work develops a quantitative surface complexation model describing the sorption and speciation of Np(V) on synthetic lepidocrocite (γ-FeOOH). Batch sorption experiments on γ-FeOOH were performed under a range of conditions (25 ℃, 0.1 M NaClO4, pH = 4 – 11, 5 μM Np(V), and atmospheric conditions). The Diffuse Layer Model (DLM) was applied to describe the surface-complexation reaction. The data were best-fitted with a single surface-complexation reaction, (≡XOH + NpO2 + = XONpO2 0 + H+) that occurred at the lepidocrocite/water interface to form an inner-sphere Np(V) complex with lepidocrocite. The results are complemented by the Np L III-edge EXAFS data that show that Np(V) was absorbed on γ-FeOOH as monomeric neptunyl ions, with no observations of multinuclear surface complexes or surface precipitates. A prominent peak at ∼3 Å in the EXAFS Fourier Transform spectra can be attributed to a Np-Fe scattering path, consistent with the formation of an inner sphere Np(V)-lepidocrocite surface complex. Formation of aqueous NpO2(CO3) x 1–2x complexes prevents Np(V) sorption at higher pH values but it is unclear if ternary lepidocrocite-Np-carbonate complexes may also form. These data indicate that there are subtle differences in Np(V) interactions with hematite, goethite, and lepidocrocite which is likely a manifestation of the differences in surface reactivity of the three minerals.

Biochar application to hardrock mine tailings: Soil quality, microbial activity, and toxic element sorption

Waste rock piles from historic mining activities remain unvegetated as a result of metal toxicity and high acidity. Biochar has been proposed as a low-cost remediation strategy to increase soil pH and reduce leaching of toxic elements, and improve plant establishment. In this laboratory column study, biochar made from beetle-killed pine wood was assessed for utility as a soil amendment by mixing soil material from two mine sites collected near Silverton, Colorado, USA with four application rates of biochar (0%, 10%, 20%, 30% vol:vol). Columns were leached seven times over 65days and leachate pH and concentration of toxic elements and base cations were measured at each leaching. Nutrient availability and soil physical and biological parameters were determined following the incubation period. We investigated the hypotheses that biochar incorporation into acidic mine materials will (1) reduce toxic element concentrations in leaching solution, (2) improve soil parameters (i.e. increase nutrient and water holding capacity and pH, and decrease compaction), and (3) increase microbial populations and activity. Biochar directly increased soil pH (from 3.33 to 3.63 and from 4.07 to 4.77 in the two materials) and organic matter content, and decreased bulk density and extractable salt content in both mine materials, and increased nitrate availability in one material. No changes in microbial population or activity were detected in either mine material upon biochar application. In leachate solution, biochar increased base cations from both materials and reduced the concentrations of Al, Cd, Cu, Pb, and Zn in leachate solution from one material. However, in the material with greater toxic element content, biochar did not reduce concentrations of any measured dissolved toxic elements in leachate and resulted in a potentially detrimental release of Cd and Zn into solution at concentrations above that of the pure mine material. The length of time of effectiveness and specific sorption by biochar is variable by element and the toxic element concentration and acidity of the initial mine material.

Gypsum addition to soils contaminated by red mud: implications for aluminium, arsenic, molybdenum and vanadium solubility

Red mud is highly alkaline (pH 13), saline and can contain elevated concentrations of several potentially toxic elements (e.g. Al, As, Mo and V). Release of up to 1 million m(3) of bauxite residue (red mud) suspension from the Ajka repository, western Hungary, caused large-scale contamination of downstream rivers and floodplains. There is now concern about the potential leaching of toxic metal(loid)s from the red mud as some have enhanced solubility at high pH. This study investigated the impact of red mud addition to three different Hungarian soils with respect to trace element solubility and soil geochemistry. The effectiveness of gypsum amendment for the rehabilitation of red mud-contaminated soils was also examined. Red mud addition to soils caused a pH increase, proportional to red mud addition, of up to 4 pH units (e.g. pH 7→11). Increasing red mud addition also led to significant increases in salinity, dissolved organic carbon and aqueous trace element concentrations. However, the response was highly soil specific and one of the soils tested buffered pH to around pH 8.5 even with the highest red mud loading tested (33% w/w); experiments using this soil also had much lower aqueous Al, As and V concentrations. Gypsum addition to soil/red mud mixtures, even at relatively low concentrations (1% w/w), was sufficient to buffer experimental pH to 7.5-8.5. This effect was attributed to the reaction of Ca(2+) supplied by the gypsum with OH(-) and carbonate from the red mud to precipitate calcite. The lowered pH enhanced trace element sorption and largely inhibited the release of Al, As and V. Mo concentrations, however, were largely unaffected by gypsum induced pH buffering due to the greater solubility of Mo (as molybdate) at circumneutral pH. Gypsum addition also leads to significantly higher porewater salinities, and column experiments demonstrated that this increase in total dissolved solids persisted even after 25 pore volume replacements. Gypsum addition could therefore provide a cheaper alternative to recovery (dig and dump) for the treatment of red mud-affected soils. The observed inhibition of trace metal release within red mud-affected soils was relatively insensitive to either the percentage of red mud or gypsum present, making the treatment easy to apply. However, there is risk that over-application of gypsum could lead to detrimental long-term increases in soil salinity.

Dibromo and diiodo derivatives of [4.4]dibenzo-24-crown-8 as novel efficient sorbents of elements from mineral acid solutions

The sorption behavior of novel functionalized endoreceptors, halogen (Br, I) derivatives of [4.4]dibenzo-24-crown-8, with respect to sorption of 34 elements from 1–5 M HNO3 solurions and 29 elements from 1–5 M HCl solutions were studied. The receptors poorly extract elements from nitric acid solutions but are strong sorbents of some elements from concentrated hydrochloric acid solutions. The highest distribution ratios of elements (D, cm3/g) for sorption from 5 M HCl were observed for 4′,4″,5″[4.4]dibromodibenzo-24-crown-8: Au (D = 880) > Ga (469) > Sb (70) > Fe (55) > Sn (14.3) > Mo (10.3) > Re (2.9) > Cd (1.4) > Ge (0.61) > In (0.33) ≈ Zn (0.32) ≈ Ni (0.31) > Zr (0.29) ≈ Cr (0.28) > Sr, Tl (0.25) > Be (0.24) > Mn (0.22) ≈ La (0.21) ≈ Ba (0.20) > Ca, K, Mg, Si (< 0.1). A new way for increasing the sorption properties of dibenzocrown ethers by introducing bromine substituents into the polyether benzene rings was established. The sorption of elements from concentrated hydrochloric acid solutions follows an anion exchange mechanism by analogy with extraction of these elements.