Na3PO4 Solution Research Articles

Waste Zinc–Carbon Battery Recycling: Focus on Total Material Recovery

Currently, less attention is paid to zinc–carbon batteries, although they are still widely used and are among the major types of batteries collected and recycled. The recycling technologies currently in use do not allow the complete recovery of resources, are not self-sufficient and require additional financing. Therefore, this paper aims to study the possibility of complete recycling of waste zinc–carbon batteries and to suggest the practical use of the final products generated in the recycling process. The possibility of complex processing of spent zinc–carbon batteries using mechanical separation and processing of the battery’s components (steel case, zinc electrode, graphite electrode, polypropylene and paper insulators) is justified. The separation of spent electrolytes from other components of batteries with hydrochloric acid was studied. It was shown that the extraction of Zn2+ and NH4+ cations takes place following the addition of an equivalent amount of Na3PO4 solution and water-insoluble NH4ZnPO4 salt sedimentation. Waste agglomerate (mixture of MnO2, MnO(OH), and graphite) was regenerated to its initial composition (MnO2, graphite) at a temperature of 300–325 °C; manganese (III) hydroxide was oxidized to manganese (IV) dioxide. Thermal destruction of polypropylene and paper insulators with additional introduction of polyethylene into the primary mixture produced pyrolysis liquid, pyrocarbon and pyrolysis gas as products. The practical use of the products obtained and compliance with the environmental requirements of the suggested method of waste batteries recycling were shown.

Micro-Arc Oxidation Phenomenon for Producing Coatings of AZ31B Mg Alloy Using Na3PO4 with Varying KOH Concentrations and Voltages: A Study

Complex salt solution systems are commonly used as electrolytes for microarc oxidation (MAO). To investigate the MAO phenomenon in simple electrolytes and evaluate the efficacy of MAO coatings, an Na3PO4 monosalt solution was used as the MAO electrolyte. In this study, the effects of the voltage and Na3PO4 concentration on the spark discharge phenomenon, thickness, roughness, and corrosion resistance of the coatings were investigated. The results showed that MAO coatings were effectively synthesised at high concentrations and voltages. Furthermore, the addition of KOH to the Na3PO4 monosalt solution resulted in discernible spark discharge and improved the corrosion resistance of the coatings. Thus, an MAO coating can be efficiently prepared using Na3PO4 solution as the electrolyte. In addition, the addition of KOH to the Na3PO4 monosalt solution reduced the voltage required for coating formation and enhanced the corrosion resistance of the coating.

The high-strength and toughness Janus bionic periosteum matching bone development and growth in children

Pediatric periosteum requires suitable strength to stabilize bone injury and match the rapid growth of children's bone, as well as strong osteogenic and angiogenic capacity to promote bone repair. Here, a Janus membrane was constructed based on the natural gradient network of bacterial nano-cellulose (BNC), the molecular chain assembly of fish collagen (Col I) was achieved through the formation of amide bond from the amino group on the collagen and carboxyl group on the BNC surface after selective oxidization by using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical). In situ synthesis of nano-hydroxyapatite (nHA) was conducted in the looser network of BNC by adjusting pH after addition in sequence of Ca(NO3)2·4H2O and Na3PO4 solution. The Janus membrane possessed Young's modulus and tensile capacity within the ligament range (0.113 GPa and 29.63 MPa, respectively), which allow material-bone fixation and integration. In vitro biomolecular experiments showed that the Janus periosteum promoted the proliferation of bone marrow mesenchymal stem cells and the expression of angiogenic and osteogenic factors. The promotions in angiogenesis and osteogenesis were further verified in vivo. Overall, the Janus biomimetic periosteum met the requirements of growth and development in children, indicating its regenerative potential for the treatment of periosteum-associated diseases in children.

One-step in situ growth of a simple and efficient pore-sealing coating on micro-arc oxidized AZ31B magnesium alloy

Micro-arc oxidation (MAO) is an environmentally friendly and effective way to generate a dense and homogeneous coating with high corrosion resistance on magnesium alloys. However, the inherent porous structure of MAO coating can lead to the invasion of corrosive media to the substrate and thus reduce its corrosion resistance. Herein, we reported a novel one-step in situ growth of a pore-sealing coating on MAO-coated AZ31B alloy by hydrothermal treatment in Na3PO4 solution. The surface morphology, chemical composition and growth process of the pore-sealing coating were thoroughly studied by FESEM, XRD, FTIR and XPS. The micro-pores and micro-cracks of the MAO coating can be fully covered by the pore-sealing coating with spherical structure, which is mainly composed of Mg(OH)2 and Mg3(PO4)2. The corrosion resistance of the coatings prepared at different hydrothermal time was evaluated by electrochemical test and immersion test. Compared with the bare AZ31B substrate, the current density of the composite coating with hydrothermal treated for 18 h decreased by three orders of magnitude from 8.40 × 10−5 A/cm2 to 1.59 × 10−8 A/cm2, indicating a remarkable enhancement of the corrosion resistance. The MAO/Mg(OH)2/Mg3(PO4)2 composite coating shows high adhesive strength with the substrate, especially the outermost Mg3(PO4)2 layer with the inner Mg(OH)2 layer. In addition, the in situ growth and corrosion protection mechanisms of the pore-sealing composite coating are also proposed.

An efficient strategy for photocatalytic hydrogen peroxide production over oxygen-enriched graphitic carbon nitride with sodium phosphate

Photocatalytic hydrogen peroxide (H2O2) production is a promising strategy to replace the traditional production processes; however, the inefficient H2O2 productivity limits its application. In this study, oxygen-rich g-C3N4 with abundant nitrogen vacancies (OCN) was synthesized for photocatalytic H2O2 production. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy indicated that oxygen-containing functional groups (–COOH and C–O–C) were obtained. Electron paramagnetic resonance confirmed the successful introduction of nitrogen vacancies. OCN exhibited efficient photocatalytic H2O2 production performance of 1965 µmol L−1 h−1 in air under visible-light irradiation. The high H2O2 production was attributed to the enhanced adsorption of oxygen, enlarged specific surface area, and promoted carrier separation. An increased H2O2 production rate (5781 µmol L−1 h−1) was achieved in a Na3PO4 solution. The improved performance was attributed to the changed reactive oxygen species. Specifically, the adsorbed PO43− on the surface of the OCN promoted the transfer of holes to the catalyst surface. •O2− obtained by O2 reduction reacted with adjacent holes to generate 1O2, which could efficiently generate H2O2 with isopropanol. Additionally, PO43−, as a stabilizer, inhibited the decomposition of H2O2.

A sustainable process for selective recovery of lithium as lithium phosphate from spent LiFePO4 batteries

This work demonstrates a novel, systematic and sustainable route for the treatment of cathode powder of spent LiFePO4 batteries. First time, lithium was selectively leached using formic acid as lixiviant with H2O2 as an oxidant. Effect of different parameters i.e., formic acid and H2O2 concentration, pulp density, temperature and time have been studied. The optimised leaching conditions were used for the selective leaching of Li and Li was precipitated as Li3PO4 in two steps, i.e., firstly, in situ precipitation at pH = 12.5, 60 °C and then at pH = 12.5, 90 °C using saturated Na3PO4 solution from the pregnant leach solution. The products were recovered with high purity (>99.5%) and X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) techniques were used for characterization. The overall study confirmed the suitability of the developed scheme for industrial application to provide economic and environmental benefits. Green chemistry metrics and the revenue generated from the developed process were calculated which revealed that the process is indeed green, sustainable, and economic.

Characterization of Microstructure and Composition of Plasma Electrolytic Oxide Film Formed on AZ31 Mg Alloy

Magnesium alloy has been widely investigated as a biodegradable implant material owing to its unique properties to degrade spontaneously in human body fluid without causing toxicity. However, the degradation rate needs to be controlled. An effective way to lower down the degradation rate of Mg alloy is by coating with plasma electrolytic oxidation (PEO) technique. In this research, the microstructure and mechanical hardness of the PEO film formed on AZ31 were investigated. The film was prepared under a constant current of 400 A/m2 in the Na3PO4 solution at 30°C. The voltage-time curve showed an immediate increase of current during the first 25 s before reaching a steady-state voltage of 150 V. The spark discharge revealed as white micro discharges. The film formed for 3 min exhibited a high surface roughness with a large variety of thickness in the range of 1-20 µm. The film contained pores and cracks. The big pores with diameter size 10-20 µm were formed as a result of gas entrapment, while the small pores with a radius of 1-3 µm were associated with the discharge tunnel during the PEO process. The X-ray diffraction pattern indicated that the film composed of crystalline Mg3(PO4)2.

In situ biomimetic formation of nano‐hydroxyapatite crystals on chitosan microspheres

Chitosan (CS) is a biocompatible, noncytotoxic biomaterial used before as base material for composites. On the other hand, nano‐hydroxyapatite (nHA) is one of the main components of human bones, highly used for biomedical applications. In this work, CS microspheres were produced under a W/O emulsion system. CS microspheres with calcium ions were then exposed to Na3PO4 solution. In situ biomimetic nHA crystals were formed on CS microspheres to generate 15.14 ± 3.15‐μm composite microspheres. The microspheres were subsequently seeded with MG63 osteoblasts to observe their cell responses. All microspheres were characterized via scanning electron microscopy (SEM), phase‐contrast photomicroscopy, and X‐ray diffraction (XRD) analysis. The results showed flake‐like shape and islet‐like growth of nHA depositions presented on the surface of the CS microspheres. In vitro tests indicated that the CS/nHA microparticles were not only biocompatible but also enhanced cell adhesion and elongation due to the in situ biomimetic synthesis method.

Remarkable improvement in corrosion resistance of anodized AZ31 alloy by sealing with beeswax-colophony resin

The nature of an anodic oxide film formed on Mg alloys is porous and cleaved. Sealing of the pores is necessary to enhance the corrosion resistance of the alloys. This work reports the effect of beeswax-colophony sealant on the corrosion resistance of anodic oxide layer formed on AZ31 magnesium (Mg) alloy. Anodization was conducted in 0.5 M Na3PO4 solution at 30°C at a constant voltage 5 V with variation time 10, 20, and 30 min. The resulting anodic film exhibited thicknesses of 6.3, 14.8, and 16.7 µm for 10, 20, and 30 min anodization time, respectively. The film was presumably composed of Mg(OH)2 and Mg3(PO4)2 as predicted by EDX analysis. Sealing was done by dipping the specimen in a mixture of beeswax-colophony with ratio 7:1. The corrosion test was performed by weight loss method in 0.9% NaCl solution at 37°C for 14 days. The unsealed and sealed specimens exhibited a similar increase in weight loss with increasing exposure time. However, the sealed specimens showed remarkably lower material loss below 3.8 mg/cm2 relative to the unsealed specimens with weight loss up to 11.5 mg/cm2. The corrosion rate of the sealed specimens was five times lower than the unsealed ones.

Fabrication of carbonate apatite honeycomb and its tissue response.

Carbonate apatite (CO3 Ap) block can be used as a bone substitute because it can be remodeled to new natural bone in a manner conforming with the bone remodeling process. Among the many porous structures available, honeycomb (HC) structure is advantageous for rapid replacement of CO3 Ap to bone. In this study, the feasibility to fabricate a CO3 Ap HC was studied, along with its initial tissue response in rabbit femur bone defect. First, a mixture of Ca(OH)2 and a wax-based binder was extruded from a HC mold. Then the fabricated HC was heated for binder removal and carbonation at 450°C in a mixed O2 -CO2 atmosphere, forming a CaCO3 HC. When the CaCO3 HC was immersed in 1 mol/L Na3 PO4 solution at 80°C for 7 days, its composition changed from CaCO3 to CO3 Ap, maintaining the structure of the original CaCO3 HC. Compressive strengths of the CaCO3 and CO3 Ap HCs were 65.2 ± 7.4 MPa and 88.7 ± 4.7 MPa, respectively. When the rabbit femur bone defect was reconstructed with the CO3 Ap HC, new bone penetrated the CO3 Ap HC completely. Osteoclasts and osteoblasts were found on the surface of the newly formed bone and osteocytes were also found in the newly formed bone, indicating ongoing bone remodeling. Furthermore, blood vessels were formed inside the pores of CO3 Ap HC. Therefore, CO3 Ap HC has good potential as an ideal bone substitute. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1014-1020, 2019.

Nano-Structure Designing Promotion Osseointegration of Hydroxyapatite Coated Ti-6Al-4V Alloy Implants in Diabetic Model.

Mammalian diabetes mellitus which contains altered microenvironment always impairs diverse cellular processes such as osteogenesis, angiogenesis and tissue regeneration via different mechanisms. For researches in materials science, modifying the ability of osteogenesis and angiogenesis in dental implants shows its significant importance. Nano-structure designing is considered as a facile strategy to improve the surface bioactivity of the implants. In this study, the nanorod-structured hydroxyapatite (HA) coatings on Ti-6Al-4V implants were facilely designed by the combination of plasma-spraying and hydrothermal treatment via varying reaction media. Intriguingly, hydrothermal treatment eliminated the glassy phase and impurity phases of HA coatings, and nanorod-structured surface was successfully constructed under hydrothermal treatment in Na₃PO₄ solution. Additionally, the HA coatings with nanorod-structured surface effectively promoted the adhesion and proliferation and further enhanced osteogenic differentiation of DM-rBMSCs in vitro. Moreover, the osseointegration of Ti-6Al-4V implants with nanorod-structured HA coating was also enhanced in diabetes mellitus rabbit model in vivo. Therefore, the nano-structured surface modification of HA coating on Ti-6Al-4V implants could target pathological bone loss via strengthening osteogenesis and angiogenesis and further potentially used as a therapeutic coating to promote diabetic osteointegration.

Towards a better understanding of the aggregation mechanisms of iron (hydr)oxide nanoparticles interacting with extracellular polymeric substances: Role of pH and electrolyte solution

Extracellular polymeric substances (EPS) are ubiquitous in the soil and water environment and interact strongly with mineral surfaces. However, these interactions and their impacts on the behavior and fate of minerals remain poorly understood. Here, for a better understanding of the colloidal stability of minerals in the environment, we investigated the aggregation of goethite (α-FeOOH) nanoparticles (NPs) in the presence of EPS from Bacillus subtilis under different environmental conditions (pH, ionic strength and ionic valence). Results showed that the aggregation processes of goethite NPs are determined by the solution chemistry, and the colloidal stability of goethite NPs is strongly influenced by the addition of EPS. In the absence of ionic strength, the addition of EPS promotes the aggregation of goethite NPs only when the pH (pH = 6) is less than the point of zero charge for the goethite nanoparticles (pHpzc ≈ 8). In the presence of ionic strength, the aggregation rate of goethite NPs increases with increasing concentration of NaCl, NaNO3 and Na2SO4 solutions, and after the addition of EPS solution, the critical coagulation concentrations (CCC) of goethite NPs are increased from 43.0, 56.7 and 0.39 mM to 168.0, 304.9 and 126.2 mM in the three electrolyte solutions, indicating that the addition of EPS inhibits the aggregation of goethite NPs. While in Na3PO4 solution, when the concentration of Na3PO4 solution ranged from 0 to 1 mM, the aggregation rate of goethite NPs increases first, followed by a decrease, and with the concentration of Na3PO4 solution exceeding 1 mM, the aggregation rate of goethite NPs increases again, due to the charge screening by sodium counter ions. This study provides a fundamental understanding of the behavior of goethite NPs in natural soil and water environments.

The properties of hydroxyapatite ceramic coatings produced by plasma electrolytic oxidation

Calcium phosphate coatings produced on the surface of Ti6Al4V by plasma electrolytic oxidation (PEO) using different concentrations of hydroxyapatite (HA) in a 0.12M Na3PO4 (NAP) electrolyte solution was investigated. It was found that the amount of calcium phosphate particles infiltrated into the coating layer as well as the thickness and the surface roughness of the coating increased with increasing HA concentration. The porosity of the ceramic coatings indicated an inverse relationship with the concentration of HA particles dispersed in the NAP solution. The result also demonstrates that higher scratch adhesive strength was achieved using 1.5g/L HA solution, producing a critical load of 2099mN, while 0g/L HA only produced a critical load of 1247mN. The adhesion becomes independent of thickness when the concentration of HA exceeds 1.5g/L. The failure of the coating was characterized by large periodic hemispherical chipping, while intermittent delamination was noticed with the coating embedded with HA particles. This study demonstrate the viability of using PEO to produce a thin layer of HA ceramic coating on Ti6Al4V suitable for biomedical applications.

Towards a compact coating formed on Al6061 alloy in phosphate based electrolyte via two-step PEO process and K2ZrF6 additives

In this work oxide coatings were prepared on Al6061 aluminum alloy using one and two-step plasma electrolytic oxidation (PEO) process. Under various conditions K2ZrF6 was added to the phosphate based electrolyte solution which was used to prepare one and two-step PEO coatings. Microstructure and phase composition of the final coatings were examined using SEM and XRD. The investigation revealed that that the solo use of K2ZrF6 caused the formation of highly rich ZrO2 and pseudo craters based coatings, however with damaged inner layer structure. By using a combined solution of K2ZrF6 and Na3PO4 (film formation agent), the coating growth and structural density were highly improved. Further enhancement in the coating properties such as high corrosion resistance ~7.63×105Ω·cm2 and hardness were obtained by applying two step processes in the combined K2ZrF6 - Na3PO4 solution.

Chemical passivation as a method of improving the electrochemical corrosion resistance of Co-Cr-based dental alloy.

The purpose of the study was to evaluate corrosion resistance of Wirobond C® alloy after chemical passivation treatment. The alloy surface undergone chemical passivation treatment in four different media. Corrosion studies were carried out by means of electrochemical methods in saline solution. Corrosion effects were determined using SEM. The greatest increase in the alloy polarization resistance was observed for passive layer produced in Na2SO4 solution with graphite. The same layer caused the highest increase in corrosion current. Generally speaking, the alloy passivation in Na2SO4 solution with graphite caused a substantial improvement of the corrosion resistance. The sample after passivation in Na2SO4 solution without graphite, contrary to others, lost its protective properties along with successive anodic polarization cycles. The alloy passivation in Na3PO4 solution with graphite was the only one that caused a decrease in the alloy corrosion properties. The SEM studies of all samples after chemical passivation revealed no pit corrosion - in contrast to the sample without any modification. Every successive polarization cycle in anodic direction of pure Wirobond C® alloy enhances corrosion resistance shifting corrosion potential in the positive direction and decreasing corrosion current value. The chemical passivation in solutions with low pH values decreases susceptibility to electrochemical corrosion of Co-Cr dental alloy. The best protection against corrosion was obtained after chemical passivation of Wirobond C® in Na2SO4 solution with graphite. Passivation with Na2SO4 in solution of high pH does not cause an increase in corrosion resistance of WIROBOND C. Passivation process increases alloy resistance to pit corrosion.

Characteristic Features of Plasma Electrolytic Treated Layers in Na3PO4 Solution

Plasma electrolytic oxidation (PEO) treatment of Ti6Al4V (Ti) using various concentrations of Na3PO4 (NAP) has been carried out. Based on the PEO process, characteristics of the treated layers, such as structure, chemical composition, phases, roughness, hardness and porosity level were investigated. Irregular micro-channel spots were found on all treated surfaces. Larger pores were more evident on the PEO treated with NAP-7.5g/L, and are considered to be related to the high intensity of micro-arc discharges on Ti surface. XRD analyses revealed that the surfaces of treated layers are composed of Ti, TiO6 and anatase. The Profilometry test depicted that the surface roughness of PEO treated layers is significantly higher than bare Ti. The thickness and hardness of PEO-treated layers increased with increasing NAP concentration and found to be highest with sample processed with NAP-10g/L. Among all the NAP concentration used, 5g/L showed the least level of porosity. Reflection on the results portends that the PEO treated with 10g/L concentrations could serve a potential candidate for clinical purposes.

Phosphate-induced aggregation kinetics of hematite and goethite nanoparticles

The purpose of the present study is to examine the effect of phosphate on the aggregation kinetics of hematite and goethite nanoparticles. The dynamic light scattering method was used to study the aggregation kinetics of hematite and goethite nanoparticles. Specific adsorption of phosphates could promote aggregation through charge neutralization at low P concentrations, stabilize the nanoparticle suspensions at medium P concentrations, and induce aggregation through charge screening by accompanying cations at high P concentrations. Two critical coagulation concentration (CCC) values were obtained in each system. In NaH2PO4, the goethite CCC at low phosphate concentrations was smaller than hematite and vice versa at high phosphate concentrations. Stronger phosphate adsorption by goethite rapidly changed the zeta potential from positive to negative at low phosphate concentrations, and the zeta potential became more negative at high phosphate concentrations. The clusters of hematite nanoparticles induced by phosphate adsorption had an open and looser structure. Solution pH and the phosphate adsorption mechanisms in NaH2PO4, KH2PO4, and Na3PO4 solutions affected zeta potential values and controlled the stability of hematite suspensions during aggregation. High pH and preference for non-protonated inner-sphere complexes in Na3PO4 solution decreased the zeta potential of positively charged hematite and promoted aggregation. Activation energies followed the order NaH2PO4 > KH2PO4 > Na3PO4 at low P concentrations. K+ was more effective than Na+ in promoting hematite aggregation due to the non-classical polarization of cations. Phosphate can enhance or inhibit the aggregation of hematite and goethite nanoparticles in suspensions by changing surface charge due to specific adsorption onto the particles. The phosphate-induced aggregation of the nanoparticles mainly depended on the initial concentration of phosphate.

Selective adsorption of hemoglobin with polyoxometalate-derived hybrid by solidification of super-lacunary phosphotungstate polyoxoanions

A novel polyoxometalate (POM)-based hybrid P8W48-APTS is prepared by the solidification of super-lacunary P8W48O18440- polyoxoanions with APTS in an acidic medium. The oxygen (O−) atoms in P8W48O18440- are bound to silicon atoms in APTS by the formation of Si-O linkage through dehydration condensation. The solidification is confirmed by characterizations with XRD, FT-IR, TGA, SEM and EDXS. Selective isolation of proteins of interest, hemoglobin (Hb) in this case, from complex sample matrices is achieved by using P8W48-APTS hybrid as adsorbent under controlled conditions. 5.0mg of P8W48-APTS hybrid results in an adsorption efficiency of 93% for 100mgL−1 hemoglobin in 1.0mL sample solution at pH 7. The adsorption behavior of Hb onto P8W48-APTS hybrid fits Langmuir adsorption model, corresponding to an adsorption capacity of 355.0mgg−1. The retained Hb could be readily recovered with either a SDS solution (0.1molL−1) or a Na3PO4 (0.1molL−1) solution as stripping reagent, providing recoveries of 94.6% or 83.9%, respectively. The biological activity of Hb remains 96.7% after an adsorption/desorption process (with elution by SDS), which illustrates virtually no change on the conformation of hemoglobin. The P8W48-APTS hybrid has been applied for the selective adsorption of Hb from human whole blood, and the results are demonstrated by SDS-PAGE assay.

Silk fibroin hydroxyapatite composite thermal stabilisation of carbonic anhydrase

Event Abstract Back to Event Silk fibroin hydroxyapatite composite thermal stabilisation of carbonic anhydrase Zishuai Zhang1, Joao J. Lopes1, Benedetto Marelli2, Forenzo F. Omenetto2, David D. Kaplan2, Jake E. Barralet1 and Geraldine Merle1 1 McGill University, Dentistry, Canada 2 Tufts University, Engineering, United States Enzyme immobilization has been widely developed as a method to maximise operational and thermal stability and minimise the cost by reuse[1]. Several approaches have been employed for enzyme immobilization, like adsorption, covalent binding, affinity immobilization and entrapment et al. However, the immobilized enzyme always has less catalytic activity due to the loss of active sites[2], which hampered its practical application. Carbonic anhydrase (CA), a zinc metalloenzyme which captures and transforms CO2 to protons and bicarbonate ions, was used as model enzyme[3]. Here we developed a novel technique to immobilise enzyme without altering its active conformation, preventing desorption and allowing its reuse1. Enzyme was adsorbed and entrapped during the self-assembly of hydroxyapatite via ultrasonic bonding and silk fibroin was deposited to prevent enzyme from desorption. This macromolecule was further assembled into organized crystalline domains of beta sheets and less organized more flexible domains[4] to create mechanically strong barrier very resistant to changes in temperature and moisture[5]. Briefly, HA nanoparticles were prepared by precipitation of a mixture of calcium nitrate tetrahydrate with ammonium phosphate dibasic. After HA nanoparticles were mixed with Na3PO4 solution and CA and subjected to an ultrasonic treatment[6]. In parallel, B.mori silkworm cocoons were boiled in Na2CO3 solution to remove sericin, then fibers were extracted and dried[7]. The fibers were dissolved into LiBr solution, and after 2 days at room temperature, fibroin solution was centrifuged. Silk fibroin layers were deposed on the surface of the enzymatic microparticles by alternating incubations cycles in 5wt% silk solution and ethanol solutions. Beside the determination of the physico-chemical properties of the microparticle such as specific surface area and morphology, enzymatic activity and stability measurements were performed. By applying ultrasound the initial HA nanoparticles formed mechanically robust HA microparticles (Figure 1A) that were separated from the unbounded nanoparticles by washing and sieving. As observed by SEM, the HA microparticles had a linear dimension of ~75-125μm (Figure 1A) and a nanoporosity of less than 100nm (Figure 1B). After consecutive heat treatments of one hour at temperatures increasing from 50°C to 140°C (Figure 2), the free enzyme degraded at 50°C with no catalytic activity measureable whereas the enzyme simply adsorbed on HA exhibited a gradual loss of activity with 30% of remaining activity at 90°C. However the thermal stability was much greater when the silk was incorporated with 80% of its initial activity retained up to 110°C. To better characterize this thermal stability, we also recorded the enzymatic activity in an amine solvent, MDEA at 80˚C. The enzymatic activity remained unchanged up to 3 days, decreased to 45% and then remained stable for 3 weeks. In summary, silk fibroin hydroxyapatite nano-composite showed a remarkable operational, storage and thermal stability, with enzymatic activity almost unchanged after a one hour’s treatment at 110°C and the assembly retained 45% of its initial activity after 3 weeks of continuous heating at 80°C in an amine solution. This thermal stability was excellent compared with described CA immobilization systems and indicates that silk fibroin may limit thermally induced enzyme conformation changes and prevent desorption.

Separation and recovery of metal values from leach liquor of waste lithium nickel cobalt manganese oxide based cathodes

In this study, a hydro-metallurgical process has been proposed to separate and recover valuable metals from citric acid leach solution of waste lithium nickel cobalt manganese oxide based cathodes. Nickel, cobalt, manganese and lithium were effectively separated and recycled by a combined method of selective precipitation and solvent extraction. First, about 98% of nickel was selectively precipitated by dimethylglyoxime reagent under conditions of equilibrium pH of 6 and molar ratio of Ni2+ to dimethylglyoxime of 0.5, with little loss of other metals. Then about 97% of cobalt was precipitated by ammonium oxalate and recovered as CoC2O4·2H2O under conditions of equilibrium pH of 6, reaction temperature of 55°C and molar ratio of C2O42+ to Co2+ of 1.2. The recovery of manganese was conducted by solvent extraction method using D2EHPA with 70–75% saponification rate. About 97% of manganese was extracted under optimal experimental conditions and recovered as MnSO4 after stripped with sulfuric acid solution. The McCabe–Thiele isotherm indicated that three extraction stages were needed for complete extraction of manganese at specific extraction condition. Finally, about 89% of lithium was precipitated and recovered as Li3PO4 by 0.5molL−1 Na3PO4 solution. This combined hydro-metallurgical recovery process is a relatively simple and environment-friendly route, which all metal values in the leach liquor can be effectively separated and recovered and both dimethylglyoxime and D2EHPA can be recycled and re-used.