Removal Of Impurities Research Articles

Surface modification of PVDF membranes with quaternized chitosan for selective separation of negatively charged polysaccharides – exemplified with heparin

Several animal polysaccharides, e.g. heparin, are industrially produced for clinical applications. Isolation of these molecules involves multi-step purification process including polycationic adsorbents adsorption and the removal of macromolecular impurities, e.g. protein, causing time-consuming and environmental pollution. In this study, a novel quaternized chitosan@PVDF/SiO2 (QCCS@PS) membrane was fabricated for selective separation of heparin while simultaneously rejecting protein through an efficient one-step separation. A series of characterization results confirmed that the membranes were successfully fabricated. The QCCS@PS membrane exhibited an adsorption capacity to heparin at various pH. The adsorption curve fitting results showed that the adsorption process was more consistent with the PFO kinetic model. Zeta potential and X-ray photo-electron spectroscopy results indicated heparin could be attracted to the surface of the QCCS@PS membrane via electrostatic interaction by -N(CH3)3+ groups of the membrane. A comparable separation performance of heparin and protein was obtained for the prepared membranes. The results indicated the selectivity factor of heparin to BSA could be improved from 2.49 to 11.08 by using the QCCS@PS membrane due to electrostatic attraction to heparin and electrostatic repulsion to BSA. Furthermore, the membrane could be practically applied in selective separation and purification heparin from crude heparin. Thus, this positively charged membrane technology could be applied for the green, efficient and selective separation of heparin, as well as other negatively charged polysaccharides.

Synthesis of high-value CaCO3 via indirect CO2 fixation utilized blast furnace slag

Ultrasonic and bubbling carbonation method achieved precipitation of CaCO3 was described as a particularly advantageous method for synthesizing low-dispersity vaterite CaCO3. Herein, high-purity vaterite CaCO3 microspheres with regular morphology was synthesized from blast furnace slag (BFS) through mineral phase leaching, precipitation impurity removal, and CO2 solidification in ultrasonic reaction field. The results demonstrated that the method employed for distributing bubbling CO2 under an ultrasonic field aided both CO2 fixation and indeed the formation of homogenized vaterite. And vaterite synthesis is further aided by factors such as low initial calcium ion concentration, low reaction temperature, high CO2 concentration, and short aging time. Furthermore, a sphere-dumbbell-sphere mechanism has been proposed as a possible growth mechanism for the spheroidal structures. Finally, large-scale production of high value-added vaterite CaCO3 would eventually be attained at carbonation temperature of 20 ℃, Ca2+ concentration of 0.1 mol·L−1, CO2 proportion in the gas mixture of 70 %.

Tungsten separation behavior on preparation of high-purity cerium by combined vacuum gravity sedimentation–directional solidification

In light of the difficult removal of harmful impurity tungsten (W) in Ce metal, in this paper a combined vacuum gravity sedimentation‒directional solidification method was innovatively designed and the W separation behavior was investigated. By reducing the electron beam power instantly and gradually at reduction rates of 1, 3 and 5 kW/min, it is found that W is enriched at the bottom of ingots as the melt solidifies. The enrichment effect is much better than that of single purification method and the enrichment degree increases as the beam reduction rate decreases, attributed to the k0(W) ＞ 1 and ρ(W) ＞ ρ(Ce). Overall, the minimum content of W impurity can decrease from 630 to 0.1 ppm at the top of the ingot, and the purity of Ce increases from 99.932 wt% to 99.995 wt% by this combined method. Additionally, this paper provides a new method for the removal of high density and low evaporation coefficient impurities in low vapor pressure rare earth metals.

Gas flow–directed growth of aligned carbon nanotubes from nonmetallic seeds

Kite growth is a process that utilizes laminar gas flow in chemical vapor deposition to grow long, well-aligned carbon nanotubes (CNTs) for electronic application. This process uses metal nanoparticles (NPs) as catalytic seeds for CNT growth. However, these NPs remain as impurities in the grown CNT. In this study, nanodiamonds (NDs) with negligible catalytic activity were utilized as nonmetallic seeds instead of metal catalysts because they are stable at high temperatures and facilitate the growth of low-defect CNTs without residual metal impurities. Results demonstrate the successful growth of over 100-μm-long CNTs by carefully controlling the growth conditions. Importantly, we developed an analysis method that utilizes secondary electron (SE) yield to distinguish whether or not CNTs grown from metal impurities. The absence of metallic NPs at the CNT tips was revealed by the SE yield mapping, whereas the presence of some kind of NPs at the same locations was confirmed by atomic force microscopy (AFM). These results suggest that most of the aligned CNTs were grown from nonmetallic seeds, most likely ND-derived NPs, via the tip-growth mode. Structural characterizations revealed the high crystallinity of CNTs, with relatively small diameters. This study presents the first successful use of nonmetallic seeds for kite growth and provides a convincing alternative for starting materials to prepare long, aligned CNTs without metal impurities. The findings of this study pave the way for more convenient fabrication of aligned CNT-based devices, potentially simplifying the production process by avoiding the need for the removal of metal impurities.

Boron nitride nanotubes synthesis from ammonia borane by an inductively coupled plasma

Boron nitride nanotubes (BNNTs) have been studied extensively due to their unique properties. Hydrogen-assisted induction thermal plasma with hBN powder has been reported in the past to produce high-yield small-diameter BNNTs. However, removal of unprocessed hBN and other BN-based impurities has been a challenge. This study presents a new approach for BNNT synthesis using ammonia borane (AB) as the raw material while maintaining the high yield and similar nanotube diameter and number of walls. Our findings demonstrate that the use of AB results in enhanced synthesis of BNNTs with reduced B and BN impurities formation. The presence of H in the proximity of B following AB decomposition facilitated more efficient formation of BH-based precursors that also lowered the partial pressure of B and restricted its condensation and coagulation into large B particles, ultimately leading to an increased density of B seeds required for BNNTs nucleation. Both the increased formation of BNNT precursors and B seeds contributed to more efficient BNNTs formation. XRD analysis revealed that AB-BNNTs contained no hBN, less tBN, and more BNNTs compared to hBN-BNNTs. Additionally, TGA and OES measurements confirmed formation of less B and production of more BH species, respectively. Our results suggest that AB as a feedstock for BNNT synthesis in induction thermal plasma offers a promising alternative to hBN powder.

Simplified solvent extraction process for high-purity Ni/Co mixed solution for lithium–ion batteries

ABSTRACT The demands for Ni-based raw materials increase as Ni–Co–Mn ternary cathode materials become the main axis of the battery industry. Conventional hydrometallurgical process to produce raw materials from Ni ore for battery application is as follows: (i) leaching of metal ions by acid, (ii) solvent extraction process to extract target metals, and (iii) crystallization process to produce final single-metal compound as powder products. The conventional solvent extraction process is a three-circuit process comprising impurity removal, Co extraction, and Ni extraction circuits. Unlike conventional process, in this work, we suggest a simplified two-circuit process to simultaneously extract Ni and Co to produce Ni/Co mixed solution for cathode material precursor production. Accordingly, the efficiency of site utilization can be maximized by reducing the investment cost for the manufacturing process and downsizing mixer-settler facilities. Further, eco-friendly effects such as reducing the consumption of titrants and cutting down the process costs and wastewater discharge can be realized.

Removal of Impurities from EAFD Ammonium Carbonate Leachate and Upgrading the Purity of Prepared ZnO.

The paper describes cementation as a suitable method applied in the refining of EAFD leachates in order to obtain required purity of ZnO for specific industrial application. For study of cementation conditions, the leachate from alkaline leaching with (NH4)2CO3 was used. The leachates contained a high amount of zinc (8000-12,000 µg/mL) and a low content of impurities such as iron, lead, copper, chromium and manganese in the range of 1-21 µg/mL. Cementation conditions were predicted by thermodynamic study, theoretically confirming the viability of the proposed experiments at the considered pH = 8-9. Cementation experiments were carried out using powdered zinc and aluminium (5 g/L) as cementation agents in the first phase separately. To increase the cementation efficiency, their combination was used (2.5:2.5 g/L or 5:5 g/L) at temperatures of 20, 40, 60 and 80 °C for 30 min. The optimum cementation conditions were established as: Zn:Al = 5:5 g/L, 60 °C. Under the given conditions, 100% of Fe, Cu, Pb and Mn were removed from the leachate. The ZnO with the maximum purity of 96.67% was obtained by crystallization of cemented leachate at 105 °C, followed by calcination at 900 °C for 4 h. ZnO with such a purity is suitable for use in the electrical or rubber industries.

One-step purification of solid phase micro-extraction based on MIL-101(Cr) for the determination of vanillin, methyl vanillin and ethyl vanillin in edible vegetable oil samples

A method for the determination of vanillin, methyl vanillin and ethyl vanillin in edible vegetable oil by one-step purification combined with high performance liquid chromatography tandem mass spectrometry was established. A solid-phase micro-extraction one-step purification and impurity removal device was constructed based on the needle filter filled with MIL-101(Cr) material, and the purification process was quickly completed in the filter head with the help of syringe driving force. Under the optimized conditions of several factors affecting the extraction efficiency, the linear range was 0–500 ng/mL and the correlation coefficient (r) was greater than 0.9994. Under the six spiked concentrations, the recovery of edible vegetable oil was between 88.6% and 98.5%, and the RSDs were between 2.41% and 5.78%. The recoveries of inter-day and intra-day tests were 90.9%–93.0% and 90.6%–100.5%, respectively. The precision of inter-day and intra-day analysis were 6.09%–7.05% and 2.75%–4.49%, respectively. This method was used to detect 100 batches of commercial vegetable oil, only vanillin was detected, the detection rate was 52.0%, and the detection concentration was 107–872 μg/kg. The positive samples were confirmed by HPLC-QTOF/MS. The results showed that this method had the advantages of simple operation and high detection throughput, and was suitable for rapid analysis of vanillin, methyl vanillin and ethyl vanillin in different types of edible vegetable oil samples.

Genomic DNA causes membrane fouling during sterile filtration of cell lysates

During biopharmaceutical production, efficient removal of impurities via filtration is essential. It is desirable to achieve high filter capacities along with a high degree of clearance. However, the complexity of bacterial cell lysates makes it difficult to properly estimate the filtration behavior. Here we investigated how host cell-derived impurities impacted the performance of commercially available sterile filters, with a focus on characterizing the dsDNA-induced decrease of filter capacity. Pressure flow curves at a constant flow, combined with particle analytics (e.g., nanoparticle-tracking analysis), indirectly revealed that dsDNA had a major influence on rapid membrane fouling. The observed phenomenon was more pronounced when using filters with small pore sizes (<0.2 µm). Filter capacity could be substantially increased by reducing the size of the present dsDNA fragments, or by decreasing the potential for dsDNA-driven electrostatic interactions with positively charged molecules. In general, our present findings highlight the importance of monitoring dsDNA even during the primary recovery of proteins in cell lysates.

Purification and enrichment of rare earth in ion-adsorbed rare earth ores using fatty acid based separation processes

Among many impurity elements in ion-adsorption rare earth (RE) ores, aluminum (Al) with similar structure to rare earth elements (REEs) is difficult to be removed. In this paper, four fatty acid based ionic liquids (ILs) were designed and synthesized for the purpose of removing Al impurity. Due to the better extraction and separation capacity, [methyltrioctylammonium][neodecanoate] ([N1888][NDA]) was screened and further studied. The extraction and separation conditions of Al with [N1888][NDA] were optimized, and the separation factor of Al/REEs reached 304.43. At the same time, the stripping and recycling experiment of [N1888][NDA] were carried out. [N1888][NDA] had high separation efficiency for Al and RE, which was of guiding significance for the removal of impurity. Based on the above investigations, a process combining fractional extraction and extraction-precipitation was developed to remove most of the impurity ions in the MgSO4 leaching solution. The process converted the low concentration RE sulfate solution ([RE3+] = 0.18 g·L−1) into high concentration RE chloride product ([RE3+] = 158.3 g·L−1, REO = 193.7 g·L−1). Moreover, the process effectively removed the Al, Mg and Ca in the leaching solution and the purity of RE product reached 99.2 wt%.

Strategies for UF/DF-Based Impurity Removal in the Post-conjugation Purification of Antibody–Drug Conjugates

Strategies for UF/DF-Based Impurity Removal in the Post-conjugation Purification of Antibody–Drug Conjugates

Leaching kinetic mechanism of iron from the diamond wire saw silicon powder by HCl

The diamond wire saw silicon powder (DWSSP) is considered to be a harmful to the environment because of finer particles, the large specific surface area and flammability. Removal of Fe impurity is very essential for recovering Si from DWSSP due to the large amount of Fe introduced during the silicon powder generation process. In the study, the thermodynamics of Fe leaching with HCl was analyzed and determined iron was theoretically present as ions in solution. Furthermore, the effects of different concentrations, temperatures and liquid–solid ratios on Fe leaching from HCl were investigated. The leaching rate of Fe reached 98.37% at the optimal parameters (HCl concentration of 12 wt%, leaching temperature of 333 K, liquid–solid ratio of 15 ml/g) with 100 min. The leaching kinetics of Fe in HCl was analyzed by shrinking core model and homogeneous model, respectively. The study indicated the process of leaching Fe from DWSSP conforms to the secondary reaction model of homogeneous model which coincided with the porous structure of DWSSP due to agglomeration. The apparent activation energy required (49.398 kJ/mol) in the first stage is lower than that (57.817 kJ/mol) in the second stage because of the porous structure. In conclusion, this paper provided a suitable way to purify the diamond wire saw silicon powder. This work provides an important guide for the industrial recovery and preparation of high purity silicon from DWSSP by the most environment-friendly and low-cost approach.

Preliminary Flowsheet Development for Mixed Rare Earth Elements Production from Apatite Leaching Aqueous Solution Using Biosorption and Precipitation

A flowsheet was developed to extract mixed Rare Earth Elements (REEs) from an aqueous solution generated by nitric acid leaching of apatite concentrate. In this study, Platanus orientalis (P. orientalis) leaf powder was employed in the biosorption process to purify the pregnant leach solution. The sorption and desorption processes were investigated and optimized. The results demonstrated the successful extraction of REEs from the pregnant leach solution using the biosorbent. Hydrochloric acid effectively desorbed REEs from the loaded P. orientalis leaf powder. Thermodynamic studies indicated that REEs’ sorption on P. orientalis leaf powder was an endothermic and spontaneous process. Precipitation and calcination steps yielded mixed rare earth oxides (REOs) with an assay of approximately 87%. The final product, mixed REOs, can be further refined through releaching and a secondary impurity removal stage prior to entering the individual REE separation process. Alternatively, it can be fed directly into the solvent extraction process or alternative technologies to obtain individual heavy and light REEs.

Toward sustainability for upcycling SoG-Si scrap by an immersion rotational segregation purification process

Recycling solar grade silicon (SoG-Si) scrap is critical for the sustainability of solar energy and fulfilling to close material loops in circular economics. A major challenge is to control trace impurities efficiently in short time for upgrading scrap to a level of SoG-Si. Here, a new immersion rotational separation purification (IRSP) process is developed to enhance trace impurities removal and the crystal growth from remelted metal by driving the rotating shear flow to improve the efficiency of solute and heat transfer. In a departure from conventional practice that forces extremely low solidification rate limited by the diffusion layer depth at approximately equilibrium solidification interface, here IRSP achieves the deep removal of impurities and the increase of solidification rate by the non-equilibrium rotating solidification interface. In the non-equilibrium solidification process caused by mold rotation, the rotating shear flow not only reduces the diffusion layer depth to improve impurity removal efficiency, but also increases the temperature gradient of the melt at the solidification front that is conducive to the increase of crystal growth rate. The new method is applicable to molten Si and the production of SoG-Si (99.9998%) has been demonstrated, which is able to improve the quality of recycled SoG-Si requiring a low energy input. It is expected that this process helps close high purity Si material loops, reduce resource consumption and the carbon footprint of the photovoltaic industry.

Automated Sampling System for Monitoring 85Kr in Air

Radioactive krypton-85 (85Kr) gas, a chemically inert and non-proliferation indicator, is derived from fission products. Its detection relies on the Budesamt für Strahlenschutz–Institute of Atmospheric Radioactivity (BfS-IAR) method, which necessitated impurity removal using soda lime, silica gel, and liquid nitrogen for cryogenic adsorption. This manual process requires frequent replacements, posing challenges for its automation. To address this, we developed a prototype krypton sampling system as an interim research product for the fully automated remote monitoring of covert nuclear activity. The system incorporates a hollow fiber membrane for impurity removal, a computer-controlled multi-position valve for sampling, and an electric cooler for adsorption. The impurity removal modules demonstrated high efficiencies, removing H2O and CO2 at 99.8% and 97.8% rates, respectively. Further, the custom-made sampling system can process 16 samples in a single run without analyst intervention. We conducted experiments to verify the automatic krypton sampling capability. The activity concentration of 85Kr in ambient air was measured using the BfS-IAR processing and detection system. The system exhibited a recovery rate of ~7.8% for krypton in 1000 L air, demonstrating good continuous remote monitoring capability. This study promotes the development of an automated analysis system for the detection of 85Kr in ambient air.

Comparision of traditional and laboratory methods of sulphur processing

BackgroundSince ancient times, the essential element sulphur has played an important role in different medical fields. It is one of the main materials used in herbo-mineral pharmaceutics in Ayurveda. However, for Ayurvedic pharmaceutical preparations, the purity of sulphur is crucial in avoiding any harmful reactions and to enhance the medicinal quality. Therefore, it is subjected to a process called ‘gandhaka shodhana’ using cow's milk, ghee or occasionally plant extracts. The plant, Eclipta alba (L.) Hassak, containing many bioactive compounds, is one of the extracts known to be used in the ‘shodhana’ process of sulphur. However, in comparison to the laboratory purification method of sulphur neither the effect of this ‘shodhana’ process in removing impurities from sulphur nor its effect on the structure and morphology of sulphur has been evaluated. ObjectivesThis study identifies physical, morphological, and structural changes that occur in sulphur when it is subjected to the ‘shodhana’ process compared to the changes that occur in sulphur obtained after simple laboratory purification. MethodologyBoth samples were characterized using Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction, Differential Scanning Calorimetry, Thermogravimetric Analysis, Fourier Transform Infrared spectroscopy, and Raman spectroscopy. Observed physical changes such as colour, allotropic form, odour, hardness, transparency, and lustre of the samples were also determined using recommended techniques. ResultsAlthough the laboratory purification method separates the sulphur from physical and chemical impurities, Ayurveda ‘shodhana’ process with E. alba converts the sulphur into a more pharmaceutically suitable form by making it more nebulous and introducing higher brittleness, FT-IR data shows removal of chemical impurities from sulphur during ‘shodhana’ process in contrast to laboratory purified sample.

Influence of xenon difluoride on the optical properties of fluorozirconate and fluorohafnate glasses

To study the effect of xenon difluoride as a fluorinating agent on optical properties of glasses in ZBLAN (ZrF4–BaF2–LaF3–AlF3–NaF) and HBLAN (HfF4–BaF2–LaF3–AlF3–NaF) systems, their optical transmission in the range from UV to IR was investigated. The treatment of the initial fluorides with XeF2 was shown to lead to a broadening of the transmission region of the obtained glasses both in the UV and IR ranges. Moreover, the treatment of the batch with xenon difluoride leads to the removal of oxygen-containing impurities that absorb in the region of 2.8 μm.

The Removal of Impurities from Domestic Graphite Concentrate by H2SO4 Solution and NaOH Solution Leaching

The Removal of Impurities from Domestic Graphite Concentrate by H2SO4 Solution and NaOH Solution Leaching

In English

It has been found that ultrasonic treatment of diamond nanopowders contributes to surface cleaning due to the removal of non-diamond carbon and impurities from the surface boundary of nanodiamond grains (from 0.4 and 0.32 % for ASUD-99 and 0.67 and 0.55 % for ASUD 75, respectively). It does not affect the total sorption volume and the values of the specific surface of the studied samples do not change, but it changes the composition of groups on the surface of diamond nanoparticles, which affect its hydrophilicity. In the samples of АSUD-75 after ultrasonic treatment, a redistribution of the ratio of the intensities of valence vibrations of С=О bonds in the lactone (anhydride) group (1742 cm–1) and the quinone (carboxyl) group (1683 cm–1) is observed, which indicates the decay of the lactone ring and its transformation into carbonyl and carboxyl groups. All samples of АSUD-99 have a hydroxyl group O-H (3400 cm−1), which does not change significantly under the influence of ultrasound. This explains the noticeable change in agglomeration for ASUD-75 in contrast to ASUD 99.

Enhancing the separation of Fe/Al/Ca impurities from metallurgical silicon to purify by slagging-directional solidification

Metallurgical silicon (MG-Si) with low content of Fe, Al and Ca impurities is very important for the production of organosilicon. A novel approach of slagging-directional solidification was investigated to remove Fe, Al and Ca impurities. Firstly, the study analyzed the effect of cooling methods and solidification rates on removal of Fe, Al and Ca impurities during directional solidification without the slagging agent. Then, the crystal morphology and impurity micromorphology of silicon ingots obtained with optimal conditions were analyzed and found the shape of the impurity was related to the crystal morphology of the ingot, precipitating at grain boundaries. On this basis, the removal of Fe, Al and Ca impurities by the slagging-directional solidification was studied. The result showed Al and Ca impurities in silicon were few and a small amount of Fe impurity was in the form of Fe–Si. The mechanism of the slagging-directional solidification was analyzed and revealed that it not only effectively removed Al and Ca impurities from MG-Si, but also decreased the effective segregation coefficient of Fe and enhanced the separation of Fe impurity. The method of slagging-directional solidification provides a new idea for the separation of Fe, Al and Ca from MG-Si.