Desorption Solution Research Articles

Investigation of the adsorption/desorption mechanism of perfluoroalkyl substances on HLB-WAX extraction phases for microextraction

The C–F alkyl structural backbone of per- and polyfluoroalkyl substances makes this class of molecules resistant to heat and degradation, leading to their high persistence and mobility in the environment and bioaccumulation in the tissues of living organisms. In this study, 15 PFAS with an alkyl chain length from C4 to C14, currently monitored by the U.S. Environmental Protection Agency (EPA), were preconcentrated by solid-phase microextraction (SPME) and analyzed by liquid chromatography-tandem mass spectrometry. The adsorption and desorption mechanisms of PFAS onto ion-exchange extraction phases was evaluated to understand the extraction process of PFAS from various environmental matrices under different conditions. This was achieved using two SPME geometries, namely fibers and thin films. The use of thin films resulted in a twofold improvement in extraction efficiency compared to fibers, especially for the short-chain PFAS. Methanol:water (80:20, v/v) was chosen as the optimized desorption solution, with ammonium formate added to minimize carryover. Extraction time profiles for both SPME geometries showed faster equilibration with thin films (30 min) compared to fibers (90–120 min). The linear dynamic range obtained with this method using fibers and thin films ranged from 10 to 5000 ng L−1 and 2.5–5000 ng L−1, respectively, with acceptable accuracy (70–130%) and precision (<15%). LOD ranged within 2.5–10 ng L−1 for fibers and 0.01–0.25 ng L−1 for thin films. Investigating the factors affecting PFAS recovery in complex samples enabled the quantitative assessment of PFAS contamination in various environmental water samples such as seawater, melted snow and biospecimens like human plasma. A 96-SPME holder was used for validation, which is compatible with sampling in 96-well plates and ensures high throughput in the analysis of real samples. The total concentration of PFAS detected in seawater and snow was 51.3 ng L−1 and 16.4 ng L−1, respectively.

Application of oxidized multi-walled carbon nanotubes and zeolite nanoparticles for simultaneous preconcentration of codeine and tramadol in saliva prior to HPLC determination

In this work, a dispersive micro-solid phase extraction technique along with high-performance liquid chromatography-UV detection was developed for simultaneous preconcentraion and determination of trace levels of codeine and tramadol in human saliva. This method is based on the adsorption of codeine and tramadol on a mixture of oxidized multi-walled carbon nanotubes and zeolite Y nanoparticles with 1:1 ratio as an efficient nanosorbent. Various analytical parameters influencing the adsorption step including the amount of adsorbent, the pH of the sample solution, the temperature, the stirring rate, the contact time of the sample solution, and the adsorption capacity were investigated. Based on the results, 10 mg adsorbent, sample solutions with pH = 7.6, temperature of 25 °C, stirring rate 750 rpm and contact time 15 min, in the adsorption step shows the best results for both drugs. Then the effective parameters on the analyte desorption stage such as the type of desorption solution, pH of the desorption solution, desorption time and desorption volume were investigated. Studies have shown that water/methanol (50:50 v/v) as desorption solution, pH = 2.0, desorption time of 5 min and desorption volume of 2 ml gives the best results.Chromatographic separation was performed on a RP-Shim-pack CLC-ODS-C18 column (250 mm × 4.6 mm, 5 µm) with isocratic mode. The mobile phase contained of acetonitrile:phosphate buffer (18:82, v/v) at pH = 4.5 and the flow rate was 1 ml.min−1. The wavelength of UV detector was adjusted at 210 nm and 198 nm for codeine and tramadol, respectively.Under optimum conditions, the extraction efficiencies of 98.5% and 99.2% were achieved for codeine and tramadol respectively. Enrichment factor of 13, detection limit of 0.3 μg L−1, relative standard deviation of 4.07 for codeine; and an enrichment factor of 15, a detection limit of 0.15 μg L−1, and standard deviation of 2.06 for tramadol were calculated. The linear range of the procedure for each drug was 1.0 to 1000 μg L−1. This method was successfully applied for the analysis of codeine and tramadol in saliva samples.

Chemical Regeneration of Activated Carbon After Adsorption of Ni(II) Ions

The chemical regeneration of activated carbon (AC) has recently received greater attention because it allows high-cost granular AC and AC fibers to be reused with less effort and energy. The chemical regeneration of activated carbon after Ni(II) ions adsorption was investigated in this study. Various desorbing solutions were used to recover adsorbed Ni(II) ions to AC. The concentration of the most effective desorbing solution was optimized. The adsorption efficiency of the regenerated AC using merely an acidic desorbing solution was reduced. Therefore, additional treatment after desorption using an acidic desorbing solution was carried out using sodium hydroxide solution. The optimum concentration of sodium hydroxide was determined. Using 3% HCl and H2SO4 as desorbing solutions, more than 80% of Ni(II) ions could be desorbed from AC. However, the readsorption efficiency of Ni(II) ions by AC was reduced to less than 50% after the first regeneration. By treating the regenerated AC from the acidic desorbing solution with 1 % NaOH, the efficiencies in the Ni(II) ions adsorption and desorption were fully recovered to almost 100%.

Development of the thin film solid phase microextraction (TF-SPME) method for metabolomics profiling of steroidal hormones from urine samples using LC-QTOF/MS.

In the present study, the development and optimization of a thin film solid phase microextraction method (TF-SPME) was conducted for metabolomics profiling of eight steroid compounds (androsterone, dihydrotestosterone, dihydroepiandrosterone, estradiol, hydroxyprogesterone, pregnenolone, progesterone and testosterone) from urine samples. For optimization of extraction method, two extraction sorbents (PAN-C18 and PS-DVB) were used as they are known to be effective for isolation of low-polarity analytes. The stages of sample extraction and analyte desorption were considered as the most crucial steps in the process. Regarding the selection of the most suitable desorption solution, six different mixtures were analyzed. As a result, the mixture of ACN: MeOH (1:1, v/v) was chosen in terms of the highest analytes' abundances that were achieved using the chosen solvent. Besides other factors were examined such as the volume of desorption solvent and the time of both extraction and desorption processes. The analytical determination was carried out using the ultra-high performance liquid chromatography coupled with high resolution tandem mass spectrometry detection in electrospray ionization and positive polarity in a scan mode (UHPLC-ESI-QTOF/MS). The developed and optimized TF-SPME method was validated in terms of such parameters as extraction efficiency, recovery as well as matrix effect. As a result, the extraction efficiency and recovery were in a range from 79.3% to 99.2% and from 88.8% to 111.8%, respectively. Matrix effect, calculated as coefficient of variation was less than 15% and was in a range from 1.4% to 11.1%. The values of both validation parameters (recovery and matrix effect) were acceptable in terms of EMA criteria. The proposed TF-SPME method was used successfully for isolation of steroids hormones from pooled urine samples before and after enzymatic hydrolysis of analytes.

Potential of waste mangosteen shell in the removal of cadmium ions: Effects of pH, contact time, and temperature

In this study, waste biomass adsorbents produced from mangosteen shells (MGS) were prepared (denoted as MGS500 and MGS1000). The physical and chemical characteristics, such as scanning electron microscopy, thermogravimetric-differential thermal analysis, specific surface area, pore volumes, surface functional groups, and point of zero charge of the prepared MGS samples were determined, and the adsorption capacity of cadmium ions from aqueous media was assessed. The effects of pH, adsorption time, temperature, and coexistence on adsorption were carefully assessed using an inductively coupled plasma optical emission spectrometer under several experimental conditions. The adsorption capacity decreased in the order, MGS < MGS500 < MGS1000. The optimal pH for cadmium ion removal was 5.0. The amount of cadmium ions adsorbed gradually increased with time, and adsorption equilibrium was achieved within 24 h after adsorption. Additionally, the amount of adsorbed cadmium ions increased with increasing adsorption temperature. To elucidate the adsorption mechanism in detail, the elemental distribution and X-ray photoelectron spectra of the prepared adsorbents were analyzed. Finally, desorption solutions such as HNO3, H2O, and NaOH were used to desorb the absorbed cadmium ions from MGS1000. Under our experimental conditions, the desorption percentage of cadmium ions was approximately 98.8% using HNO3. In conclusion, MGS1000 exhibited a good adsorption capacity of 12.0 mg/g for adsorbing cadmium ions from aqueous media and desorption capacity with HNO3 at 1000 mmol/L.

Selective Removal of Transient Metal Ions from Acid Mine Drainage and the Possibility of Metallic Copper Recovery with Electrolysis

ABSTRACT The low pH and high salinity of acid mine drainage (AMD) fundamentally complicates the sorption processes. We explored the selective removal of Cu, Ni and Co ions present in AMD from the excess of ferrous ions of using a chelating resins Lewatit® MonoPlus TP 220 and Lewatit® TP 208. Also, the recovery of metal copper from desorption solution using electrolysis was investigated. The results showed that the most effective sorption of metal ions was achieved with chelating sorbent Lewatit® TP 220. The dynamic capacity of the sorbent under the given conditions (pH= 2.5 ± 0.03, presence of Fe(II/III), Zn(II), Mn(II)) decreased in the following order: Cu(II) (43.3 ± 1.4 g/L) > Ni(II) (22.1 ± 2.1 g/L) > Co(II) (3.6 ± 0.4 g/L). Chelating resin Lewatit® TP 208 under the same conditions showed lower efficiency: Cu(II) (30.6 ± 1.3 g/L) > Ni(II) (9.1 ± 0.17 g/L) > Co(II) (1.3 ± 0.08 g/L). The weak base anion exchanger Purolite® A 832 was successfully used to take up Cu(II) from ammonia solution and easily regenerated with sulfuric acid. The sorption capacity for Cu(II) was calculated to be 19.2 ± 0.5 g/L. Electrolysis experiments were performed with a fluidized bed electrolysis reactor where metallic copper was regenerated from desorption solutions and purified sulfuric acid solutions were obtained.

Spectro-kinetic investigations on the release mechanism of lysozyme from layer-by-layer reservoirs

The investigations of protein adsorption and release on interfaces aid in the elucidation of the protein-surface interaction mechanism, which has several applications in the biomedical area. The spectro-kinetic and morphological analysis of the release of lysozyme (Lyz) from chitosan/polystyrene sulphonate (CHI/PSS) multilayer immobilized at pHs 10.6, 8.8 and 5.0 shows that the extent of release strongly depends on the pH of Lyz loading and the ionic strength of the desorbing solution. When compared to pH 8.8, the release for pH 10.6 achieves equilibrium more rapidly. At loading pH 10.6, the release is surface-mediated, at pH 8.8, it is both surface- and bulk-mediated, while at pH 5.0 it is bulk mediated with minimal release. Lyz released for loading pH 10.6 retains its native secondary structure. Kinetic fitting suggests that high loading pH 8.8–10.6 and high release ionic strength (0.5–1.0 M NaCl) lead to burst release of Lyz from CHI/PSS multilayer. Surface morphology changes of multilayer interface upon Lyz loading and release are highlighted by SEM topography and AFM height distribution analysis. The present work indicates that CHI/PSS multilayer system can function as a reservoir for burst as well as controlled release of lysozyme by selecting the loading pH and ionic strength.

Performance influence of polyacrylic acid dispersant on nuclear grade anion exchange resin

Secondary circuit water chemistry control is vital for the safe operation of nuclear power plants. Polyacrylic acid (PAA) is used in the secondary circuit water system to reduce the fouling of the steam generator (SG) because of its good dispersion effect. However, PAA as a macromolecular organic matter possibly causes organic fouling for anion exchange resin of the water purification system and affects its performance. Some research reported that the performance of resin changes after PAA application. But it is not clear whether this change is related to PAA. In this research, the anion resins were performed for five cycles, and each cycle included batch PAA adsorption, dynamic PAA desorption and resin rinse. Results showed that NaOH solution could realize the desorption of PAA on anion resin, but desorption solution and rinse water consumption slightly increased with the cycle number. Meanwhile, residual PAA linearly increased with the cycle number, but the rate was relatively slow. Furthermore, the performance influence of PAA on anion resin was investigated. The exchange capacity and kinetic performance for anion resin slightly decreased after PAA cycle. The effluent conductivity of anion resin bed increased after PAA cycle, but it could not cause the adverse influence of sodium leakage. The contrast experiment of H2SO4 cycle showed that resin aging was the primary reason for the change of resin performance, rather than residual PAA. Within the fewer cycles, PAA and anion resin had better compatibility.

New operation method of a membrane capacitive deionization system with a dual-solution mode for improving the desorption rate

A new operation method of a membrane capacitive deionization (MCDI) system with a dual-solution mode was proposed. In this method, the concentration of the solution supplied to the cell was different during the adsorption and desorption processes. After adsorption was performed for the adsorption solution (AS) of 10 mM NaCl, desorption was performed while changing the concentration of the desorption solution (DS) to 10–70 mM. As the DS concentration increased, the discharge rate (desorption rate) linearly increased. The average discharge rates at DSs of 10 and 70 mM are 0.187 and 0.278C/g·s, respectively, which increases by approximately 1.5 times. As the DS concentration increases, the time constant (product of the electrical resistance and capacitance) of the cell decreases, resulting in an increase in the desorption rate. At the end of the desorption process, some DS remained inside the cell, reducing the charge efficiency of the subsequent adsorption process. By changing the flushing time, it was possible to control the charge efficiency and the water recovery.

A simple and green solid phase extraction method for oligonucleotides using adsorbent with amino and carboxylic moieties

The study aimed to use a material with amino and carboxylic moieties to extract unmodified and phosphorothioate oligonucleotides. The charge of amine and carboxyl groups at the surface has changed with the change in pH of the adsorption (pH 4.5) and desorption solution (pH 9.5). Thus, both the binding and elution of the oligonucleotides were based on electrostatic interactions, and the procedure required only 10 mM ammonium acetate, with the change of pH depending on the extraction step. The developed procedure was successfully applied to extract oligonucleotides from aqueous solutions and serum samples. The method is simple and fast, providing good reproducibility (SD between 1 and 4%) and relatively high oligonucleotide recovery (81–98% for standards, 60–71% for diluted serum samples, and 80–92 for LLE serum extracts). Moreover, only environmentally friendly solvents were used.

In-pipette-tip natural-feather-supported liquid microextraction for conveniently extracting hydrophobic compounds in aqueous samples: A proof-of-concept study

In this study, a novel in-pipette-tip natural-feather-supported liquid microextraction (NF-SLME) method was developed for conveniently extracting hydrophobic compounds in aqueous samples. Natural feathers were used as the support medium of an oily extraction solvent and an in-pipette-tip extraction device was simply constructed with the cost less than 0.1 CNY. The whole extraction process could be conveniently conducted with a pipettor. As a proof of concept, the in-pipette-tip NF-SLME method was applied to extract antidepressants in urines. The best extraction recoveries were obtained when the extraction solvent was 15 μL of n-octanol, the pH of the sampling solution was 10.0, the desorption solution was 200 μL of acetonitrile, and the numbers of cycles of drawing solution in/out for extraction and elution were 5 and 2, respectively. Coupled with high-performance liquid chromatography–ultraviolet, a quantification method was validated in ranges of 0.05–10 μg/mL with satisfactory linearities (R2 ≥ 0.988). The limits of quantification were calculated to range from 0.032 to 0.048 μg/mL, which is adequate for antidepressant analysis in urine. The potential of the in-pipette-tip NF-SLME method was further illustrated by the successful extraction of triazole pesticides and androgenic steroids with good recoveries.

Phosphorus recovery and reuse in water bodies with simple ball-milled Ca-loaded biochar

The demand to control eutrophication in water bodies and the risk of phosphorus scarcity have prompted the search for treatment technologies for phosphorus recovery. In this study, ball-milled Ca-loaded biochar (BMCa@BC) composites were prepared with CaO and corn stover biochar as raw materials by a new ball-milling method to recover phosphorus from water bodies. Experimental results demonstrated that BMCa@BC could efficiently adsorb phosphorus in water bodies with an excellent sorption capacity of 329 mg P/g. Hydrogen bonding, electrostatic attraction, complexation, and surface precipitation were involved in adsorption process. In addition, phosphorus recovered by BMCa@BC had high bioavailability (86.7 % of TP) and low loss (3.3 % of TP) and was a potential slow-release fertilizer. P-laden BMCa@BC significantly enhanced seed germination and growth in planting experiments, proving that it could be used as a substitute for P-based fertilizer. After five cycles of regeneration, BMCa@BC still showed good adsorption recovery and the P-enriched desorption solution could be recovered as Ca-P products with the fertilizer value. Overall, BMCa@BC has good cost-effectiveness and practical applicability in phosphorus recovery. This provides a new way to recover and reuse phosphorus effectively.

The Application of the Activated Carbon from Cordia africana Leaves for Adsorption of Chromium (III) from an Aqueous Solution

The objective of this study is to investigate the adsorption performance of activated carbon derived from the leaves of Cordia africana for the removal of Cr (III) from an aqueous solution. The plant sample was collected, washed, dried, grounded, and sieved at 125 μm mesh size. Adsorbent activation was done using H3PO4 at concentrations of 25–85% and pyrolysis temperature of 400–500°C. The activated carbon was characterized by proximate, SEM, BET, and FTIR analyses. A batch adsorption study was conducted to determine the effect of contact time, adsorbent dose, initial chromium concentration, and mixing speed on Cr (III) removal. The regeneration of the activated carbon was investigated by using 1 M of HNO3 as a desorbing solution for seven cycles. At optimum acid concentration and pyrolysis temperature, a surface area of 700 m2/g was recorded. The moisture content, volatile matter, ash composition, fixed carbon, and bulk density of the activated carbon were found to be 5.3%, 24.2%, 6.2%, 64.3%, and 0.75 g/mL, respectively. The SEM and FTIR analyses indicated that the surface morphology was full of cracks and different peaks were associated with plenty of functional groups, respectively. The maximum Cr (III) removal was attained at a contact time of 180 min (89%), adsorbent dose of 1.5 g (54%), initial concentration of 0.6 g/L (47%), and mixing speed of 300 rpm (64%). The equilibrium data were better described by Freundlich isotherm at R2 value of 0.88, which implies that the adsorption process is conducted on a heterogeneous surface. The pseudo-first-order kinetics model with R2 value of 0.99 best fits with the equilibrium data, which implies that physisorption controls the adsorption kinetics. Generally, it can be concluded that this locally prepared adsorbent is promising for the removal of chromium from industrial wastewater, but further factorial approach assessment has to be checked.

Lignin Microspheres Modified with Magnetite Nanoparticles as a Selenate Highly Porous Adsorbent.

Highly porous lignin-based microspheres, modified by magnetite nanoparticles, were used for the first time for the removal of selenate anions, Se(VI), from spiked and real water samples. The influence of experimental conditions: selenate concentration, adsorbent dosage and contact time on the adsorption capacity was investigated in a batch experimental mode. The FTIR, XRD, SEM techniques were used to analyze the structural and morphological properties of the native and exhausted adsorbent. The maximum adsorption capacity was found to be 69.9 mg/g for Se(VI) anions at pH 6.46 from the simulated water samples. The modified natural polymer was efficient in Se(VI) removal from the real (potable) water samples, originated from six cities in the Republic of Serbia, with an overage efficacy of 20%. The regeneration capacity of 61% in one cycle of desorption (0.5 M NaOH as desorption solution) of bio-based adsorbent was gained in this investigation. The examined material demonstrated a significant affinity for Se(VI) oxyanion, but a low potential for multi-cycle material application; consequently, the loaded sorbent could be proposed to be used as a Se fertilizer.

Boron-doped titania for separation and purification of lactoferrin in dairy products

Lactoferrin (LF), a natural iron regulating glycoprotein, exists in animal milk and plays multiple beneficial roles. Bovine LF is obtained by separation and purification from cow's milk, and has been added as a food additive to functional foods and infant formula now. Therefore, accurate analysis of LF in these foods is very important, but there are challenges such as poor selective extraction and separation efficiency. In this work, considering the cis-diol in LF, boron-doped titania (B-doped TiO2) material was prepared for selectively enrich LF from dairy products. In order to increase the saturation capacity of extracted LF, the amount of boron for doping was optimized, and maximum binding capacity of 63.9 mg g−1 was achieved when the atomic ratio of B to Ti was 1.65 with improved affinity in terms of KD value. In addition, the primary parameters affecting extraction efficiency such as extraction time, extraction pH, desorption time, and desorption solution were also optimized. The method of dispersive solid phase extraction based on B-doped TiO2 combined with ultra-high performance liquid chromatography-ultraviolet detection (UHPLC-UV) was developed and validated. The material greatly reduced the cost of sample pretreatment and the method also was applied to detect the LF in different dairy products such as liquid milk, fermented milk, and infant formula. This method could be used for routine analysis, separation and purification of LF.

Wheat brans as waste biomass based on a potential bio–adsorbent for removing platinum(IV) ions from aqueous phase

This study reviews the preparation of adsorbents, specifically wheat bran, from waste biomass for the adsorption/recovery of Pt(IV) ions from aqueous phase. Herein, the physicochemical characteristics of virgin wheat bran (WB) and WB calcined at 500 °C and 1000 °C (WB500 and WB1000, respectively) were evaluated. Elemental distribution and binding energy analyses confirmed the presence of Pt on the WB sample surfaces after adsorption. The amount of Pt(IV) ions adsorbed was as follows: WB500 (1.1 mg/g) < WB (4.1 mg/g) < WB1000 (27.4 mg/g). The adsorbed Pt(IV) ions were then successfully desorbed from the WB samples using desorption solutions. Notably, WB1000 exhibited adsorption capacities of 6.0, 5.4, and 23.3 mg/g for adsorbing Pt from Pt-containing drugs such as CDDP, CBDCA, and L-OHP, respectively, from aqueous phase. Thus, WB calcined at 1000 °C shows promising properties as an adsorbent for Pt(IV) ion removal/recovery.

Synthesis of zinc oxide derived from wastewater of glove manufacturing via adsorption-desorption-precipitation path

The demand for ZnO significantly increased over the past decades. Extraction and refinement of zinc ores results in the release of hazardous wastes to the environment. In particular, the tremendous demand for disposable nitrile gloves during the Covid-19 pandemic has spiked superior demand for ZnO used as a crosslinking agent in the manufacturing process and leads to the generation of zinc containing wastewater traditionally removed via chemical precipitation. This paper focuses on the application of adsorption for zinc removal which opens an opportunity to recycle zinc to synthesize secondary zinc oxide. This study evaluated the feasibility of zinc oxide synthesis via the adsorption-desorption-chemical precipitation pathway. Palm shell activated carbon (PSAC), a low-cost adsorbent, was used for the removal of zinc from the synthetic and industrial wastewaters. Subsequently, zinc desorption was carried out using 0.3 M HCl. Then ZnO was synthesized from the desorption solutions via chemical precipitation using potassium hydroxide. Average zinc conversion rate of 98 % was achieved in this study. The synthesized ZnO exhibited high surface area of 97.4 m2/g after calcination (400 °C, 3 hr), high purity and crystallinity. The results confirmed the feasibility of zinc ions recovery for recycling to produce secondary good quality zinc oxide.

Magnetic Separation of Oxoacid of Boron from Salt-Lake Brine by Synergistically Enhanced Boron Adsorbents of Glucose-Functionalized SiO2 and Graphene.

The adsorption separation and extraction of low-concentration boron from salt-lake brine have great significance. Magnetic separation avoids the problem of adsorbent granulation and improves the usage efficiency. The silicon-based adsorbents have attracted interest due to their superior acid and alkali resistance, in which polyhydroxy graphene enhances the adsorption of boron ions. Herein different boron adsorbents, derived by magnetic separation, were developed and characterized by SEM, TEM, XPS, VSM, FT-IR, and XRD analysis. The adsorption-desorption performance of boron adsorbents with different compositions was evaluated. The isotherms and kinetics parameters of the boron extraction were evaluated based on adsorption-desorption tests. The graphene-based magnetic adsorbent (Go-Fe3O4@SiO2@mSiO2-Glu) registered a high boron adsorption capacity of 23.90 mg/g at pH = 9 in the boron solution and 24.84 mg/g for East Taigener salt-lake brine. The Na+, Mg2+, Ca2+, and Cl− ions have little interference with the boron adsorption. The adsorbents exhibit magnetic separation performance and good cycle life. The results showed that acid-alkali desorption solution has little effect on the adsorbents, and the composite of graphene enhances the adsorption of boron ions. The adsorbents developed in this study are promising to recover boron from low-concentration boron-containing salt-lake brines.

Recovery of Chromium(VI) Ions Using a Nickel–Aluminum–Zirconium Complex Hydroxide Based on Adsorption and Desorption Treatment

In this study, we evaluate the desorption or recovery capacity of chromium(VI) ions using desorption solutions containing sodium hydroxide (NaOH) or sodium sulfate (Na2SO4). A complex hydroxide of nickel-aluminum-zirconium (NAZ) was prepared as the adsorbent for the removal of chromium(VI) ions. The results from repeated adsorption/desorption experiments on chromium(VI) ions using NAZ complex hydroxide were evaluated. The desorption percentage of chromium(VI) ions increased with the increase in the concentration of NaOH or Na2SO4 in the desorption solution. The determined optimal concentration of NaOH or Na2SO4 in the desorption solution was 10 mmol/L under the used experimental conditions. After three adsorption-desorption cycles, the recovery percentages of chromium(VI) ions using NaOH and Na2SO4 were 60% (total amounts adsorbed and desorbed were 102 and 61 mg/g, respectively) and 75% (total amounts adsorbed and desorbed were 96 and 72 mg/g, respectively), respectively. Additionally, we confirmed the existence of chromium on the surface of the NAZ complex hydroxide. After three adsorption/desorption cycles, the crystal structure of the NAZ complex hydroxide was maintained. These results indicated the potential of the NAZ complex hydroxide using a desorption solution containing NaOH or Na2SO4 for the recovery of chromium(VI) ions.

Internal coordination of vanadium industrial waste—Preparation of hydroxyapatite and fluorine wastewater purification

In the vanadium industry, raffinate poses potential environmental risks due to the presence of corrosive fluoride and toxic heavy metals, and waste neutralizing slag (NS) was largely stockpiled given the low economic value, resulting in extensive land occupation and secondary pollution risks. Hydroxyapatite (HAP) was synthesized uniformly from the NS using the hydrothermal method, with no surfactants or additives used except for the three inexpensive reactants required. It was discovered that the pH of the raw material, the temperature, and the length of the hydrothermal reaction all had a significant effect on the adsorption characteristics of the produced HAP. When the conditions for synthesizing HAP were set with a pH of 11.5, a hydrothermal reaction temperature of 120 °C, and a reaction time of 1.5 h, the HAP had the optimum impact on raffinate treatment. The products' characterization by XRD, FTIR, SEM-EDS, and BET corroborated the successful synthesis of homogeneous HAP under the process conditions. The waste stream from the hydrothermal synthesis of HAP was recovered and crystallized to obtain a sodium sulfate by-product which was determined for purity. Adsorbed at room temperature for 1 h, the HAP synthesized by NS has a maximum percentage adsorption of 99.66 % and a saturation adsorption capacity of 43.64 mg/L for F ions in the raffinate. Additionally, the HAP removed over 95 % of the trace heavy metal ions Cr, As, and Cd from the raffinate. The saturated HAP was treated using a hydrothermal regeneration process, and the regenerated HAP retained a fluoride percentage adsorption still reaching 99.28 %. The thermodynamic and leaching experiments reveal that the desorption solution for the regeneration of HAP has the performance to increase the efficiency of vanadium recovery. This technique recycles waste NS to produce high-value HAP, which purification treatment of the raffinate with a high fluorine and contaminants content, solves the problem of treating two types waste of vanadium industry waste (NS and raffinate), and allows for the recycling of valuable element fluorine in vanadium industrial effluent.