Subsequent Sorption Research Articles

Investigation of pullulan polysaccharide as a sphalerite depressant for chalcopyrite separation: Flotation behavior and interfacial adsorption mechanism

The remarkable differences in the metallurgical processes of copper and zinc require their host minerals to be separated as far as possible during beneficiation. For chalcopyrite and sphalerite, the primary host minerals of copper and zinc, their green and efficient separation in the beneficiation stage remains a great challenge. This work is the first to employ environmentally friendly pullulan polysaccharide (PP) as a sphalerite depressant to assist in the concentration of chalcopyrite. Flotation experiments have revealed that PP possesses a selective depression action on sphalerite without having a large influence on the recovery of chalcopyrite. Characterization analysis has revealed that PP can be adsorbed onto chalcopyrite and sphalerite surfaces, but with a different response to subsequent sorption collectors. PP adsorbs to the Zn atoms on sphalerite surfaces via its O atoms in the C−O−H group and thus prevents the adsorption of sodium butyl xanthate (BX). The Fe sites on the chalcopyrite surface can adsorb PP, but this process does not affect the BX adsorption as the Cu sites remain exposed. Hence, PP can enhance the hydrophilicity of sphalerite without interfering with the hydrophobicity of chalcopyrite, resulting in a desirable separation effect. Overall, this work offers a promising scheme for the concentration of chalcopyrite from sphalerite during beneficiation, thereby contributing to the efficient exploitation of copper and zinc resources.

Carbon materials for effective purification of aqueous solutions from tributyl phosphate.

This study investigates various sorbents for the effective sorption of dissolved organic substances, using tributyl phosphate (TBP) as a model compound. TBP is one of the most commonly used extractants in the nuclear industry. Four different carbon materials with high specific surface areas (2000-3000 m2 g-1) were selected for evaluation. The sorption of TBP from nitric acid solutions was examined over a wide range of concentrations. The samples with the largest specific surface areas showed the highest sorption capacity for organic matter. To enable repeated use, a purification scheme was developed to restore the sorbents' original properties. The samples were subjected to various treatments, analyzed using X-ray photoelectron spectroscopy, and used in subsequent sorption experiments.

Smart dual responsive alginate grafted copolymeric hydrogel for sorption of recalcitrant methylene green from water

ABSTRACT The sorptive removal of recalcitrant dyes from aquatic media holds paramount significance in the contemporary research. The pressing problem has been addressed by facile fabrication and subsequent sorption studies on sodium alginate grafted poly (N-isopropyl acrylamide-co-acrylic acid) [Na-Alg-g-p(NIPAm-co-AAc)] hydrogel for sorption of methylene green (MG). The sorbent achieved equilibrium in 30 minutes, whereas highest sorption capacity was noted at optimum pH 5. At 25°C, the sorbed quantity of the adsorbate enhanced with the rise in initial concentration. The data of isothermal studies fitted well into the Langmuir isotherm as suggested by relatively higher R2 of ≈ 0.98. The sorption obeyed pseudo-second-order kinetics as evidenced by exceptionally higher R2 (0.999) and substantial agreement in experimentally obtained and theoretically calculated second-order rate constant. The validity of Langmuir isotherm and pseudo-second-order kinetic models imply the occurrence of chemisorption between anionic [Na-Alg-g-p(NIPAm-co-AAc)] sorbent and cationic MG. Moreover, the material exhibits dual (pH and temperature) responsive nature because the amount sorbed undergoes variation with change in temperature and pH. The results signify potential candidature of the fabricated sorbent for the reclamation of dye contaminated water and related applications.

Thermal Stability and Resistance to Biodegradation of Humic Acid Adsorbed on Clay Minerals

This article studies sorption regularities and evaluates thermal stability and resistance to microbial degradation of humic acid during three sorption cycles on bentonite clay, kaolinite, and muscovite using TGA/DSC, XRD, hydrophobic chromatography, light and electron microscopy, etc. The experiment revealed that kaolinite sorbed more humic acids (HAs) in terms of unit surface area (1.03 × 10−3 C, g/m2) compared to bentonite (0.35 × 10−3 C, g/m 10−3 g/m2). Sorption at pH 4.5 showed HA fractionation in amphiphilicity and chemical composition. HA was sorbed on the surface of all sorbents, mainly via hydrophobic components. No intercalation of HA into the interlayer spaces of montmorillonite was observed during sorption. Sorption via hydrophilic interactions was mostly performed on muscovite and bentonite rather than on kaolinite. Sorption of HA resulted in changes in its chemical composition and decreased C/N compared to free HA, which demonstrated selective sorption of nitrogen-containing compounds more typical of muscovite. All minerals adsorbed only a relatively thermolabile HA fraction, while its thermal stability increased compared to that before the experiment. The thermal stability and ratio of the Exo2/Exo1 peak areas on the DSC curves of sorbed HA increased with each subsequent sorption cycle. We revealed the following relationship between thermal stability and resistance to microbial oxidation of the sorbed HA: The higher the thermal stability, the less available the sorbed HA becomes for utilization by microorganisms.

Performance evaluation of PVA/PEO/LiCl composite as coated heat exchangers desiccants

Composite desiccants have led to a growing interest because of their eco-friendliness, sustainability, and excellent dehumidification properties. In this paper, we present a method for constructing a dehumidification composite of PVA/PEO/LiCl that is eco-friendly and recyclable. The results show that PVA/PEO/LiCl has better dehumidification performance than SG, SG/LiCl, PVA/PEO, and PVA/PEO/CaCl2 as coated heat exchangers desiccants. The addition of LiCl caused the internal hydrophilic polymeric hygroscopic carriers to work in concert with the membrane porosity. This resulted in a considerable increase in the membrane's hygroscopic rate and capacity, as well as improved mechanical qualities. As the concentration of LiCl was increased, the surface sealing of the PVA/PEO polymer improved dramatically, and the shape of the polymer-formed film changed from loose to firmly packed. The structural shift toward densification boosted the strength of the co-blended dehumidified films. With a PVA/PEO/LiCl ratio of 1:1:2.5 and the coating thickness of 10–15 µm, the greatest dehumidification effectiveness is achieved. During five subsequent sorption and desorption procedures, the sorption of PVA/PEO/LiCl remained between 70 and 75%, demonstrating its outstanding reusability and cycling stability.

High-temperature sulfur capture by a Mn-Mo sorbent: An investigation of regeneration conditions and SO2 formation and prevention

The regeneration performance of a solid sorbent (alumina-supported 15Mn8Mo) for sulfur capture at high temperature has been studied. The regeneration of the sulfided sorbent was performed by oxidizing at different temperatures (400 – 800 °C) and O2concentrations (0.21 – 21 %). Temperature had a larger impact on the regeneration thanO2concentration. An unwanted side reaction during sulfur capture is SO2formation. Two pathways to SO2formation were identified, either via sulfate formation and decomposition or via oxidation of H2S. A new regeneration method which avoids SO2formation and achieves low residual H2S level in the gas phase involves adding an extra H2pre-reduction step between the regular O2-regeneration and the subsequent sorption step, i.e., a O2– H2regeneration. The stability of the sorbent was verified by 10 repeated sorption/regeneration cycles, with the sorbent regenerated either via the oxidative method or the new O2– H2regeneration method.

Monitoring microplastic-contaminant sorption processes in real-time using membrane introduction mass spectrometry.

Microplastics are environmentally ubiquitous and their role in the fate and distribution of trace contaminants is of emerging concern. We report the first use of membrane introduction mass spectrometry to directly monitor the rate and extent of microplastic-contaminant sorption. Target contaminant (naphthalene, anthracene, pyrene, and nonylphenol) sorption behaviours were examined at nanomolar concentrations with four plastic types: low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS). Under the conditions employed here, short-term sorption kinetics were assessed using on-line mass spectrometry for up to one hour. Subsequent sorption was followed by periodically measuring contaminant concentrations for up to three weeks. Short-term sorption followed first order kinetics with rate constants that scaled with hydrophobicity for the homologous series of polycyclic aromatic hydrocarbons (PAHs). Sorption rate constants on LDPE for equimolar solutions of naphthalene, anthracene, and pyrene were 0.5, 2.0, and 2.2 h-1, respectively, while nonylphenol did not sorb to pristine plastics over this time period. Similar trends among contaminants were observed for other pristine plastics with 4- to 10-fold faster sorption rates associated with LDPE when compared to PS and PP. Sorption was largely complete after three weeks, with the percent analyte sorbed ranging from 40-100% across various microplastic-contaminant combinations. Photo-oxidative ageing of LDPE had little effect on PAH sorption. However, a marked increase in nonylphenol sorption was consistent with increased hydrogen-bonding interactions. This work provides kinetic insights into surface interactions and describes a powerful experimental platform to directly observe contaminant sorption behaviours in complex samples under a variety of environmentally relevant conditions.

Перспективы использования полимерсодержащих материалов и сорбентов для мембранной ультрафильтрации, сорбции и концентрирования нуклеиновых кислот из водных сред. Обзор

Unlike antibiotics and heavy metals, nucleic acids exist in the aquatic environment as a part of prokaryotic and eukaryotic microorganisms (bacteria, fungi, etc.) rather than in a free form. In this regard, the most important primary stage of sample preparation of an object for the quantitative analysis of DNA and RNA in natural and wastewaters includes membrane ultrafiltration of an aqueous sample, followed by its sorption preconcentration on a solid phase carrier. The efficiency of ultrafiltration and subsequent sorption of nucleic acids from natural and wastewaters largely depends on the material of filters, membranes, and sorbents. Polymeric materials are widely used due to their special properties: the affinity of polymers for biological objects, the ability to create pores of any required size, good mechanical properties and resistance to the extraction of microorganisms captured. The paper reviews the 15-year-old scientific literature on filtering, membrane and sorption polymeric materials used to extract nucleic acids from aqueous media and preserve them. Polymeric sorbents for collecting and concentrating DNA and RNA from the liquid phase, as well as storing nucleic acids, are covered. It has been found that ultrafiltration is used at a relatively low concentration of the analyzed object, followed by extraction of the substance using commercially available kits, including cartridges. Sorption (solid-phase concentration) is used to extract nucleic acids at their relatively high concentration in the analyte. The main polymeric materials used include cellulose and its derivatives (nitrocellulose, cellulose acetate, mixed cellulose nitrate–acetate, diethylaminoethylcellulose, polyethyleneiminocellulose), agarose, dextran, polyestersulfone, polycarbonate, fluoroplasts, polyacrylates and polymethacrylates, polyaramids, polyamides, polyvinyl alcohol, polyaniline, polycaprolactone, polyacrylamide and polymethacrylamide, polystyrene. Chitosan, modified polycaprolactone, and magnetic particles coated with polydopamine, polyethyleneimine, polyvinylpyrrolidone, polystyrene, or polyamidoamine dendrimer are considered as promising polymers for further research in this field.

Influence of the material of weighing bottles on loss-on-drying reproducibility

One of the factors influencing the uncertainty of residual moisture measurements in biological medicinal products is the accumulation of electrostatic charge on the surfaces of weighing bottles and laboratory balances, which results in poor weighing reproducibility. The authors believe that the simplest and most economical solution to this problem is to use weighing bottles made of a conductive material, e.g. metal. The aim of the work was to evaluate the influence of the material of weighing bottles on the reproducibility of loss-on-drying (LOD) methods. Materials and methods: Model samples for the study were prepared from a sucrose-gelatin medium by lyophilisation and subsequent moisture sorption to achieve a certain residual moisture content. The authors assessed the samples’ mass uniformity using Shewhart’s X-charts, and analysed their residual moisture content using a loss-on-drying procedure with glass and metal weighing bottles. Statistical processing of the results was carried out by calculating the main statistical indicators: Student’s t-test and Fisher’s F-test. Results: Four batches of model samples were prepared and standardised in terms of average mass using Shewhart’s charts. The effect of weighing bottle materials was most pronounced at low residual moisture contents (less than 0.5%), with the relative standard deviation (RSD) values for the results obtained with glass and metal weighing bottles reaching 76% and 35%, respectively. For the samples with a higher residual moisture content (2–5%), the minimum RSDs with glass and metal weighing bottles were 15% and 6%, respectively. Conclusions: The study allowed for evaluating the influence of the material of weighing bottles on the results of LOD measurements and demonstrated a higher reproducibility with metal weighing bottles. This confirms the possibility of using metal weighing bottles in quality assessment of biological medicinal products for human use with LOD methods.

Pu distribution among mixed waste components at the Hanford legacy site, USA and implications to long-term migration

Beginning in 1943, process wastes containing approximately 1.85 × 1015 Bq (200 kg) of plutonium (Pu) were released into unlined cribs, trenches, and field tiles at the Hanford Site, Washington, USA. The 216-Z-9 (Z-9) unlined trench received over 4 × 106 L of mixed Pu processing waste from the Plutonium Finishing Plant (PFP) consisting of high ionic strength (∼ 5 M nitrate, ∼ 0.6 M aluminum), acidic (pH ∼ 2.5) solutions, which also contained the organic solvents: tributyl phosphate (TBP), dibutyl butylphosphonate (DBBP), carbon tetrachloride (CCl4), and lard oil. A small fraction of Pu migrated deep into the subsurface vadose zone to depths of 37 m, but the mechanisms controlling Pu migration beneath the trench are unknown. In this study, we determined Pu partitioning behavior in a series of binary and ternary batch experiments containing aqueous, organic, and solid phases representative of the waste constituents and natural sediments of the Z-9 trench in order to develop a conceptual model for the transport of Pu in the subsurface. Our results show that Pu at equilibrium with low pH, high nitrate waste and in the presence of a TBP/organic phase can migrate as a Pu-TBP-nitrate complex in the organic phase as long as the low pH and high nitrate concentrations are maintained. Reducing the nitrate concentrations or increasing the pH will lead to Pu partitioning into the aqueous phase from the organic phase with subsequent sorption to native Hanford sediments. The results of this work suggest that Pu migration in the subsurface is likely driven by weak sorption of aqueous Pu under low pH conditions as well as the formation of Pu-TBP-nitrate complexes in the organic phase. Long-term Pu migration will be limited by the transient nature of the low pH conditions and the dispersion of the nitrate plume.

Partitioning and mobility of arsenic (As) and lead (Pb) in an ancient Pb–Zn mine in central Mexico: Role of amorphous ferric arsenate

This study delves into the interactions between Pb and As and poorly-crystalline minerals, particularly amorphous ferric arsenate (AFA), in an ancient mine characterized by highly-dispersed pollutants due to strongly acidic conditions (pH 2.2 to 2.6) originated from mine drainage (AMD). On-site observations accompanied by laboratory-based mineral formation and transformation experiments were undertaken to examine the reactions of mobile Pb and As from abandoned mine residues on the mineralogy of the impacted sediments, as well as to examine associated controls on their mobility. Natural attenuation of Pb and As mobility predominantly occurred via formation of lead arsenate (PbHAsO4), Pb–As-rich Fe(III) minerals, and AFA, resulting in solid-phase concentrations ranging from ∼1088 to ∼1545 and from ∼278 to ∼734 mg kg−1 for Pb and As, respectively. Subsequent sorption experiments with synthetic AFA revealed the retention of Pb by the formation of anglesite (PbSO4) due to an appreciable sulfur content (up to 4 wt%) in AFA chemical composition, whereas As was effectively retained by a non-exchangeable surface adsorption mechanism. The results of this study show the occurrence of metastable phases like AFA in AMD environments as well as its role in controlling Pb and As mobility under strongly acidic conditions.

Removal of tartrazine, ponceau 4R and patent blue V hazardous food dyes from aqueous solutions with ZnAl-LDH/PVA nanocomposite

Zinc-aluminum-based layered double hydroxide-polyvinyl alcohol (ZnAl-LDH/PVA) nanocomposite has been synthesized by one-pot co-formation method. An intercalation approach was realized using (ZnAl LDH/PVA) nanocomposite as adsorbent and photocatalyst for adsorption and solar photodegradation of hazardous food dyes—tartrazine, ponceau 4R and patent blue V. The characterization of synthesized nanocomposite was carried out by XDR, SEM, FTIR and UV-Vis. The adsorption of dyes onto the synthesized adsorbent was carried out under different initial dye concentrations, pH, adsorbent weight and three different temperatures. The optimal pH for tartrazine, ponceau 4R and patent blue V was determined as 2.0, 7.0 and 2.0, respectively. The optimal temperature at optimal pH was 303 K after 40 min. Pseudo-first-order kinetic model, Langmuir and Temkin isotherm models were represented well for the definition of the adsorption mechanism of tartrazine. The adsorption of ponceau 4R and patent blue V on the ZnAl-LDH/PVA nanocomposite follows the Freundlich isotherm. The value of the slope of 1/n for ponceau 4R and patent blue V is more close to the unit (1/n = 0.668 and 0.768, respectively), which indicates the possibility of the adsorption process according to the Freundlich model. Because the adsorbent shows a photocatalytic property, after high effective sorption, the cyclic reusability of the sorbent was ensured by keeping the sample in its dye solution at 308 K in bright sunlight for 5 hours. The completely decolorized sorbent has shown high efficiency in subsequent sorption experiments.

Insights into effects of ageing processes on Cd-adsorbed biochar stability and subsequent sorption performance

The conversion of agricultural biomass wastes into biochar has enormous potential to improve soil quality. Particularly, biochar particles introduced into the natural environment readily bind environmental pollutants. The interaction of biochar and adsorbed pollutants will, however, be impacted by long term ageing. The mechanism of biochar adsorption performance that could be affected by such early-adsorbed pollutant is not understood. Herein, we study the effects of different ageing processes on Cd-adsorbed biochar stability by K2CrO7–H2SO4 oxidation method for carbon loss evaluation, and sorption capacity towards diethyl phthalate (DEP). We adopted artificially accelerated ageing methods to simulate various processes: HNO3/H2SO4, H2O2 oxidative, leaching, high temperature, freeze-thaw cycles, and dry-wet cycles. The results showed that all the Cd-adsorbed aged biochars had more C–C/C–H functional groups and exhibited higher carbon stability than pristine aged biochars. Specially, the carbon loss (20.2–25.2%) of Cd-adsorbed biochar showed almost two times lower than pristine biochar (34.5–35.4%) after high temperature and leaching ageing due to enhancing Cd-π bonding, which could resist strong K2Cr2O7/H2SO4 oxidation. Such interaction synergistically promoted the sequestration of adsorbed Cd on biochars. The subsequent sorption performance for DEP on Cd-adsorbed biochars was slightly higher than pristine biochar after H2O2 oxidative and leaching ageing. Whereas, the dominate mechanism of DEP removal on Cd-adsorbed biochars changed to hydrophobic partitioning after high temperature, freeze-thaw cycles and dry-wet cycles ageing, leading to a decreased DEP sorption capacity. Hence, the biochar application must be comprehensively considered the susceptibilities due to reciprocal effects of early adsorbed pollutant and natural ageing environment, which helps us both assess and take measures to minimize potential risks in the environment. The present study suggests the continuous irrigation and tropical or temperature climate regions would be suitable for long-term biochar application in soil remediation and carbon sequestration.

Sorption and desorption of organic matter in soils as affected by phosphate

The contribution of different adsorption processes to soil organic matter (SOM) stabilization and the consequences of the intensification of land use on the adsorption of SOM are not yet fully understood. Therefore, this study aimed to explore the adsorption of dissolved organic carbon (DOC) in soils as well as desorption of organic carbon (OC) caused by phosphate addition. We conducted desorption and sorption experiments with DOC, phosphate (Na2HPO4), and chloride (KCl) in topsoil and subsoil samples from a Ferralsol, an Andosol, and a Podzol. Furthermore, we quantified the size of DOC by size-exclusion chromatography.We found that phosphate addition caused a strong increase in the DOC concentration in all soils. The DOC concentration was elevated by up to a factor of 4.5 compared to a control (water only) within five minutes after phosphate addition and kept increasing further with time, particularly in the Ferralsol. After 10 days, the DOC concentrations in the P addition treatment were between 5.5 and 18.0 times higher than in the control treatment. In contrast, chloride addition did not lead to increased DOC concentrations compared to the control (water only). Phosphate addition led mostly to desorption of organic matter of medium molecular size (10–100 and 100–1000 kDa) in the Ferralsol and the Andosol and of large molecular size (>1000 kDa) in the Podzol. In contrast, potassium chloride addition shifted the size distribution of DOC in the soil solution towards small compounds (<10 kDa), likely because KCl addition affected the aggregation of DOC compounds, in contrast to Na2HPO4 addition. Furthermore, phosphate addition also decreased subsequent sorption of DOC in the Ferralsol and the Andosol by a factor of up to 2.9 and 2.1, respectively.Our results have far-reaching implications because they show that phosphate addition can lead to desorption, and thus to destabilization of SOM, particularly in Ferralsols, and can also prevent further sorption of organic matter in soils. Our study provides a mechanistic explanation of why phosphate addition can decrease soil organic carbon sequestration and stabilization. This mechanism should be considered in the analysis of land-use and tillage effects on SOM sequestration in the future. Furthermore, our study indicates that also medium and large molecular size organic matter is stabilized through adsorption in soils.

Triton X-100 improves the reactivity and selectivity of sulfidized nanoscale zerovalent iron toward tetrabromobisphenol A: Implications for groundwater and soil remediation

Sulfidized nanoscale zerovalent iron (SNZVI) with improved reactivity and selectivity has shown great potential for environmental remediation. However, it is unclear if SNZVI could be applied for the remediation of soil washing solution, and how a soil-washing surfactant affects the reactivity and selectivity of SNZVI. Here, we assess the impact of Triton X-100 (TX-100) on the reactivity and selectivity of a sulfidized commercial NZVI toward tetrabromobisphenol A (TBBPA). While sulfidation of NZVI improved its reactivity and electron efficiency toward TBBPA, TX-100 could further improve these promoting effects, which was 8–21 and 4–7 times higher than those without TX-100, respectively, depending on TX-100 concentration. Because TX-100 could induce the solubilization of TBBPA, sorb onto the SNZVI surface, and favor the subsequent sorption and degradation of TBBPA. SNZVI performance for successive treatments of TBBPA contaminated water was also greatly improved by TX-100. Moreover, washing the TBBPA-contaminated soil with TX-100 could efficiently extract the TBBPA, and almost all of the TBBPA in the soil washing solution could be efficiently degraded by SNZVI. These results suggest that TX-100 is a good additive to SNZVI for improving its performance, and SNZVI coupled with TX-100 can be a promising technology for the remediation of TBBPA-contaminated soil.

Development of a combined processing technology for low-sulfide gold-bearing ores

This paper presents the results of laboratory dressability studies for low-sulfide gold-bearing ores using combined processing and subsequent oxidation leaching of the resulting combined concentrate. According to the current raw materials processing circuit used at the Sekisovskoye deposit, gravity concentration experiments were first carried out using the following laboratory equipment: a Knelson KSMD 3 centrifugal concentrator, an SKO-05 concentration table, and a two-chamber diaphragm jigging machine (i.e., OML by TsNIGRI). A significant portion (0.5 to 1.0 g/t) of the gold remains in the gravity concentration tailings. Subsequent flotation experiments for the tailings suggest that additional gold recovery is possible. The gold content in the final flotation tailings was in the range of 0.15–0.25 g/t. The final gold recovery in the combined process was therefore 93.7–96.5 %. The subsequent sorption cyanidation of the concentrate according to the current processing circuit allows depositing an average of 75.0–80.0 % Au on the coal. At the same time, the residual gold content in the sorption leaching tailings is significant and amounts to 3.6–7.5 g/t. The preliminary oxidation experiments for the concentrate slurry indicate the possibility of a more complete gold recovery with subsequent leaching, including sorption leaching. The residual gold content in the cakes was measured at 0.7–1.5 g/t, which ultimately yielded 95–96 % recovery at the leaching stage. The research was completed with the financial support of the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan under grant No. АР05130143.

Hydrous manganese dioxide modified poly(sodium acrylate) hydrogel composite as a novel adsorbent for enhanced removal of tetracycline and lead from water

In this study, hydrous manganese dioxide (HMO) modified poly(sodium acrylate) (PSA) hydrogel was produced for the first time to remove tetracycline(TC) and lead(Pb(II)) from water. The as-prepared composite was characterized using various techniques, such as SEM-EDS, FTIR, XRD, BET, and XPS, to elucidate the successful loading of HMO and analyze subsequent sorption mechanisms. Different influencing parameters such as adsorbent dose, initial concentration of adsorbates, reaction time, solution pH, and temperature were also investigated. The adsorption kinetic studies of both TC and Pb(II) removal indicated that equilibrium was achieved within 12 h, with respective removal rates of 91.9 and 99.5%, and the corresponding adsorption data were fitted to the second-order kinetics model. According to the adsorption isotherm studies, the sorption data of TC best fitted to the Langmuir isotherm model while the adsorption data of Pb(II) were explained by the Freundlich isotherm model. The maximum adsorption capacities of both TC and Pb(II) were found to be 475.8 and 288.7 mg/g, respectively, demonstrating excellent performances of the adsorbent. The uptake capacity of PSA-HMO was significantly influenced by the level of solution pH, in which optimum adsorption amount was realized at pH 4.0 in the TC and Pb(II) systems, respectively. Thermodynamic studies showed the process of TC and Pb(II) adsorptions were endothermic and spontaneous. Overall this study elucidated that PSA-HMO composite can be a promising candidate for antibiotics and heavy metal removal in water treatment applications.

Switchgrass as oil and water-spill sorbent: Effect of particle size, torrefaction, and regeneration methods

Switchgrass, both raw and torrefied, was tested for its ability to sorb water or oil. The cyclic performance was also examined, utilizing centrifugal extraction as the regeneration method. Both oil and water sorption capacity increase with the decreasing size of raw switchgrass particles. Results indicate that 3 mm raw switchgrass can sorb water at a capacity of about 6 times its mass and can sorb oil at a capacity of about 3 times its mass, which makes it a suitable biodegradable sorbent. Torrefaction at 220 °C for 30 min reduces water sorption capacity by an average of 55% but does not have a statistically significant impact on oil sorption. Sorption of liquid is negatively correlated to particle size. Centrifugation is able to partially desorb either liquid from the sorbent, and subsequent sorption cycles do not display lower sorption capacity than the first cycle when calculated on a dry mass basis.

Highly enhanced oxidation of arsenite at the surface of birnessite in the presence of pyrophosphate and the underlying reaction mechanisms

Manganese(IV) oxides, and more especially birnessite, rank among the most efficient metal oxides for As(III) oxidation and subsequent sorption, and thus for arsenic immobilization. Efficiency is limited however by the precipitation of low valence Mn (hydr)oxides at the birnessite surface that leads to its passivation. The present work investigates experimentally the influence of chelating agents on this oxidative process. Specifically, the influence of sodium pyrophosphate (PP), an efficient Mn(III) chelating agent, on As(III) oxidation by birnessite was investigated using batch experiments and different arsenic concentrations at circum-neutral pH. In the absence of PP, Mn(II/III) species are continuously generated during As(III) oxidation and adsorbed to the mineral surface. Field emission-scanning electron microscopy, synchrotron-based X-ray diffraction and Fourier transform infrared spectroscopy indicate that manganite is formed, passivating birnessite surface and thus hampering the oxidative process. In the presence of PP, generated Mn(II/III) species form soluble complexes, thus inhibiting surface passivation and promoting As(III) conversion to As(V) with PP. Enhancement of As(III) oxidation by Mn oxides strongly depends on the affinity of the chelating agent for Mn(III) and from the induced stability of Mn(III) complexes. Compared to PP, the positive influence of oxalate, for example, on the oxidative process is more limited. The present study thus provides new insights into the possible optimization of arsenic removal from water using Mn oxides, and on the possible environmental control of arsenic contamination by these ubiquitous nontoxic mineral species.

In Situ Adsorption of Mixed Anionic/Cationic Collectors in a Spodumene–Feldspar Flotation System: Implications for Collector Design

Herein, we investigated the effects of mixed collectors with varying alkyl chain lengths and ligand types on the hydrophobicity of the spodumene-feldspar flotation system. Various collector-mineral interactions were compared using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy with two-dimensional correlation spectroscopy (2D-COS), in situ microcalorimetry, and X-ray photoelectron spectroscopy (XPS). The highest flotation separation performance can be achieved at a molar ratio of 6:1 and pH 8-9. The in situ microcalorimetry results revealed that the difference in the adsorption reaction heat of the mixed collector is larger than that of the single anionic collector. Moreover, the inconformity between the magnitude of adsorption reaction heat and the results observed for flotation recovery indicates that the heat of the reaction presumably involves the adsorption configurations of the collectors and the amounts adsorbed. In in situ ATR-FTIR with 2D-COS, it can be observed that octanohydroxamic acid/dodecylamine (OHA/DDA) is adsorbed much more intensely onto feldspar than onto spodumene due to the availability of more space on feldspar for the subsequent sorption of DDA after the prior bidentate chemisorption of OHA under alkaline conditions, whereas the sodium oleate (NaOL)/DDA adsorption sequence at pH 4-5 was the reverse of that at pH 8-9. Lastly, XPS was employed to provide further supplemental evidence for the bonding between these two minerals and single anionic/mixed collectors at the optimal pH of 8-9. In this study, the powerful in situ detection technologies can establish a new platform for exploring the underlying mechanism of new reagents at the solid-liquid interface. Moreover, the in-depth understanding related to the adsorption behavior of the mixed collector is beneficial for facilitating the selection and design of efficient and environmentally friendly flotation collectors with improved selectivity.