Polishing Powder Research Articles

Investigation into the purification and regeneration of rare earth polishing powder waste via continuous solid-phase conversion

The concentration of rare earth elements (lanthanum, cerium, and praseodymium) within rare earth polishing powder waste (REPPW) typically exceeds 50 %, with the majority of impurities comprised of silicon and aluminum-related compounds. Transforming REPPW into recycled rare earth polishing powders that adhere to polishing standards in an eco-friendly and economically viable way presents a significant challenge in the industry. Traditional acid or alkaline processes predominantly recover rare earth elements as oxides, which are underutilized due to their high costs. Considering the varying forms of impurities and rare earth compounds found in REPPW, this research introduces a novel physicochemical decontamination and continuous chemical transformation process aimed at producing regenerated rare earth polishing powders. Under optimal conditions, the physicochemical two-step decontamination process achieved a rare earth recovery rate surpassing 92 %, while silicon and aluminum removal rates reached 86.12 %. During the continuous chemical transformation of REPPW, the rare earth phases in an alkaline setting followed the sequence REOF (CeO2) → RE(OH)3 → RECO3OH→RECO3F→CeLa2O3F3(CeO2), which not only facilitated phase reorganization but also enhanced the particle surface structure. Notably, these chemical transformations did not disrupt the rare earth distribution; instead, they indirectly boosted product purity and uniformly dispersed within the regenerated polishing powder particles, thereby improving polishing efficiency. Consequently, the adoption of this innovative regeneration process for polishing powders holds substantial importance for the sustainable utilization of rare earth resources.

(La0.8Sr0.2)0.95Mn0.5Fe0.5O3Perovskite as anEfficient Bi‐Functional Electrocatalyst for Oxygen‐Involved Reaction and Zn‐Air Batteries

AbstractThe perovskite‐type oxide (La0.8Sr0.2)0.95Mn0.5Fe0.5O3, synthesized using lanthanum resources recovered from polishing powder waste and manganese resources obtained from zinc anode mud, was obtained via a facile polymer‐assisted combustion method, and further applied in zinc‐air batteries.The crystal phase and microstructure features of the thus‐obtained nanoparticles were characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), and nitrogen adsorption‐desorption measurements. The results showed that the (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 particles, with nanoscale size, possess a high specific surface area and a suitable Mn3+/Mn4+ molar ratio, which will benefit both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). As expected, the thus‐fabricated (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 electrode exhibits a high current density of 71.2 and 85.2 mA cm−2 at −0.2 V and 0.6 V vs. Hg/HgO, respectively, which is superior to that of the commercial Pt/C catalyst (58 and 31 mA cm−2, respectively).Subsequently, this compound oxide can be an air electrode in a rechargeable zinc‐air battery. The assembled battery, using (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 as the cathode, exhibits a discharge voltage of 1.05~1.16 V and a charge voltage of 2.03~2.13 V under 15 mA cm−2 for 150 h.The excellent electrochemical results presented in this study highlight the potential of (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 as a highly efficient and commercially viable bifunctional electrocatalyst for applications in rechargeable zinc‐air batteries.

Efficient Self-cleaning and antibacterial ceramics with active sites fully exposed obtained from rare earth waste

The utilization of rare earth polishing powder waste (RPW) to prepare antibacterial ceramics can effectively avoid problems of pollution in the recycling process and waste of rare earth resources. Herein, a novel RPW-based antibacterial ceramics was developed, which possesses the core-shell structure with ceramics as the cores and the CeO2/BiOCl as the superficial coating. The antibacterial ceramics display notable antibacterial activity, and the inactivation rates of 3.3 log under visible light irradiation in 30 min and 2.4 log under darkness in 1 h were achieved, and the zone of inhibition values was found to be 16.6 mm for E.coil. The hardness of antibacterial ceramics was measured to be 897 (±38) HV, higher than commercial porcelain's hardness (600 HV). The antibacterial mechanism was verified by the Ce ion release, reactive species, and fluorescence-based live/dead cells. This study presents a novel antibacterial ceramic structure and green economic reuse method of rare earth waste.

Kilogram-Scale Recovery of La/Ce and Regeneration of Rare-Earth Polishing Powder Products from Ceria-Based Polishing Powder Waste

Kilogram-Scale Recovery of La/Ce and Regeneration of Rare-Earth Polishing Powder Products from Ceria-Based Polishing Powder Waste

Combining thermodynamic modeling and experiments to characterize the effect of ceramic polishing powder in cement-based materials

Ceramic polishing powder (CPP), a by-product of ceramic tile production, has the potential to prepare building materials. While the hydration and thermodynamic properties of CPP remain largely unexplored, thereby limiting its widespread application. This study utilized R3 tests to demonstrate that CPP exhibits pozzolanic activity comparable to that of fly ash. Then it analyzed the effects of substituting 10–20 % of cement with CPP on the hydration products, microstructure, and mechanical properties of composite materials, utilizing a synergistic approach that combines thermodynamic simulations with experimental investigations. The findings showed that adding CPP does not generate new crystalline products but enhances the formation of C-S-H through the pozzolanic reaction, which consumes calcium hydroxide. However, adding over 25 % CPP significantly lowered the pH of the pore solution, altering hydration products and causing volume contraction. In addition, CPP improved the microstructure at later ages, particularly by increasing micropores, leading to enhanced mechanical properties at 28 and 90 days. For instance, at a w/b ratio of 0.5, the 90 days compressive strengths of composite mortars CPP10, CPP15, and CPP20 were recorded at 67.0 MPa, 63.3 MPa, and 65.1 MPa, respectively. These values represented increases of 17.3 %, 10.9 %, and 14.0 % over the control group (57.1 MPa). Conversely, this also resulted in increased autogenous shrinkage due to higher capillary pressure. Notably, the 6 days shrinkage of CPP15 and CPP20 was about 50 % higher compared to that of the pure cement mortar. These findings highlight the necessity of balancing CPP content for optimal performance.

Selective extraction of lithium and REEs from waste rare earth polishing powder: A two-stage leaching technique

Rare earth polishing powder waste (REPPW) is a Li-containing rare earth solid waste generated from glass-ceramic polishing processes. The key to its value-added recycling is selective extraction of Li and rare earth elements (REEs), however, only REEs recovery were addressed in conventional recycling processes. Aiming at this research gap, this work proposes a two-stage leaching technique consisting of Na2CO3 roasting, low concentration H2SO4 leaching (Li), and HCl reduction leaching (REEs). In the first stage, the leaching ratio of Li reached 99.0 %, while those of Ce and La were only 0.02 % and 2.5 %, respectively. It is found that inactive LiAlSi2O6 phase in the REPPW was transferred to leachable Li2SiO3 during Na2CO3 roasting with a leaching Ea of 85.32 kJ·mol−1, while La formed insoluble NaLa(SO4)2, whose precipitation route can be regulated by the leaching temperature. In the second stage, HCl-ascorbic acid (Vc) leaching system was adopted for REEs extraction from the first stage leaching residue, leading to an overall REEs recovery of 90.8 %. This work proposed a promising selective recycling route for Li and REEs in REPPW and would help for developing value-added REPPW recycling processes.

Modified rare earth waste composite material for simultaneous denitrification and recovery of phosphate in water

Nitrogen and phosphorus discharged into water bodies with sewage are the main causes of water eutrophication.Currently,the adsorption method is a cost-effective and efficient denitrification and phosphorus removal technology. In this study, waste polishing powder, manganese dioxide and sepiolite are used as raw materials, and a novel adsorbent of Sep-pp-MnO2 is prepared through co-precipitation and redox methods for simultaneous removal of ammonia nitrogen and recovery of phosphate in water.The physicochemical properties of the adsorbent are characterised, and the adsorption performances and denitrification and phosphorus removal mechanisms are determined. Results showed that,at a temperature of 25°C and pH of 8, the maximum removal of ammonia nitrogen reaches 11.47 mg/g, while the adsorption capacity for phosphates is 14.93 mg/g. Adsorption mechanisms indicated that the removal mechanism of phosphate is ligand exchange, while the removal mechanism of ammonia nitrogen involves electrostatic attraction and oxidation to nitrogen. Recycling experiments showed that after five desorption cycles, the material could achieve a removal of 4.7 mg/g for ammonia nitrogen, an adsorption capacity of 8.25 mg/g for phosphate and a phosphate recovery rate of 55 % after desorption with 0.1 M NaOH solution. Municipal wastewater validation experiments demonstrated that when the dosage of Sep-pp-MnO2 was 4 g/L,Treated water met the Class B requirements of the comprehensive emission standard for pollutants from urban sewage treatment plants in China (GB18918–2002). This study explores a new method for efficient simultaneous nitrogen and phosphorus removal in water and provides a feasible idea for alleviating the shortage of phosphate rock resources.

Multi-promoters modified CaO-based sorbent derived from mixed waste slag for long-term CO2 cyclic capture

Calcium looping, a carbon dioxide (CO2) capture technique, may provide an effective route to eliminate climate change brought by the steadily rising anthropogenic CO2 emissions. However, the key challenge for calcium looping is the sintering-induced decay over the numerous cycles for CaO-based sorbents. Herein, multi-promoters modified CaO-based sorbents, derived from the mixed waste slag of marble waste powder (MWP) and rare earth polishing powder wet slag (REPP), are prepared by a simultaneous hydrating and calcining process. The cyclic CO2 capture is explored by a thermogravimetric analyzer, and the promotion mechanism is investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, CO2 temperature-programmed desorption, and reaction kinetics fitting. Results indicate that the multicomponent promoters from the REPP, including CeO2, Ca12Al14O33, and LaPO4, enhance the carbonation cyclic activity of CaO from MWP. The best-performing MWP-REPP sorbent with 15 wt% REPP shows less than a 10 % drop decay and the CO2 carbonation conversion remains at 75 % (0.46 g CO2/g sorbent) after 50 repeated cycles. The excellent cyclic capture performance is attributed to the synergistic interaction between the promoters and CaO, where the CeO2 promoter owns abundant oxygen vacancies, and the Ca12Al14O33 and LaPO4 promoters provide the blocked effect, thus facilitating the CO2 sorption and inhibiting the CaO from sintering. This work presents useful guidance for improving the cyclic sorption stability of CO2 from waste slags.

Rapid and efficient synthesis of energy-saving cool pigments and environmental restoration materials using rare earth secondary resources

This paper proposes a method for the short-process recovery and reuse of rare earth secondary resources. Low-value rare earth polishing powder waste (WP), trichromatic phosphor waste (WT), NdFeB permanent magnetic waste (WN), and SmCo permanent magnetic waste (WS) were used as the raw materials. Based on the concept of combinatorial chemistry, energy-efficient cool pigments and environmental remediation materials were synthesized by a solid-phase method. The results showed that the synthesized materials had fluorite-type and garnet-type structures. In terms of cool pigments, doping with different rare earth permanent magnets can enrich the color (including yellow, green, brown, gray, and blue) and cause fluctuations in the near-infrared (NIR) reflectance (59.05–99.54 %) and NIR solar reflectance (55.32–95.64 %). Yellow fluorite-type pigments (WP: WT = 1:1) have the highest NIR reflectance (R = 99.54 %), while brown fluorite-type pigments (WP: WN = 1:0.1) and blue garnet-type pigments (WP:WS = 1:0.1) have relatively high NIR reflectance, 88.18 % and 59.30 %, respectively. The synthesized pigments possessed better chemical stabilities and thermal insulation performance. In terms of environmental remediation materials, the adsorption capacities of fluorite-type materials for F− and PO43− can reach 84.03 mg/g and 85.3 mg/g, respectively. In summary, materials synthesized from rare earth waste exhibit excellent potential for use in energy-efficient wastewater treatment and promote the sustainable utilization of secondary rare earth resources.

A novel air-polishing powder from natural eggshell.

This study compares the ability of extrinsic stain removal and surface roughness changes on tooth surfaces after using two different types of dental air polishing powder: Sodium bicarbonate and novel eggshell powder. For the study of extrinsic stain removal, twenty bovine teeth were soaked in coffee for extrinsic stain formation. Group 1 and Group 2 were polished with sodium bicarbonate powder and novel eggshell powder, respectively. The acquired stains of teeth were recorded as baseline, and color changes after cleaning with two different powders were also measured by colorimeter. Sixteen samples from eight human posterior teeth were used for the surface roughness test. Surface roughness values (Sa) of two groups (sodium bicarbonate and novel eggshell powder) were measured by a contact-type profilometer before and after polishing with two types of powders. The data showed that the average ΔE* value of the sodium bicarbonate group was higher than that of the novel eggshell powder group (P < 0.05). The average ΔSa value of the sodium bicarbonate group was higher than that of the novel eggshell powder group (P < 0.05). Sodium bicarbonate powder showed higher stain removal ability and surface roughness changes than the novel eggshell powder.

Rare earth dissolution from polishing powder waste in H2O2-H2SO4 system: Condition optimization and leaching mechanism

Recycling high-grade rare earth polishing powder waste (REPPW) is crucial for protecting the environment and sustainable utilization of rare earth resources. Leaching REPPW in the eco-friendly H2O2-H2SO4 suffers from the lack of understanding of the leaching mechanism. Here, the leaching mechanism was investigated under the optimal leaching conditions, i.e., T = 353 K, L/S ratio = 40 mL/g, H2SO4 concentration = 4 mol/L and initial H2O2 concentration = 0.8 mol/L, by which leaching efficiency of Ce and La reached 99.3% and 99.1%, respectively. Furthermore, pseudo steady state kinetic analysis suggested a five-step leaching mechanism involving CeO2 hydroxylation, H2O2-CeO2 coordination, ≡CeIII−H2O2 deprotonation, ≡CeIV−HO2− reduction and ≡CeIII−HO2∗ protonation, which was verified by the agreement between experimental data and the proposed reaction model. This work proposes a leaching mechanism of REPPW and would help develop an effective and sustainable recycling process for rare earth secondary resources.

Efficient processing rare earth polishing powder solid waste by thiourea-H2SO4 system: Process optimization and thiourea decomposition effect

Utilization of waste rare earth polishing powder (REPPW) is significant for protecting the environment and enhancing strategical rare earth resource recycling. However, efficient extraction of rare earth oxides (REOs) from REPPW in an environmental-friendly and low-cost manner remains a great challenge in this area. In this study, a reductive H2SO4 leaching process using the low toxicity thiourea as the reducing agent is proposed to extract rare earth elements (REEs) from the REPPW. Under the optimal conditions of thiourea concentration of 0.078 mol·L−1, H2SO4 concentration of 1.50 mol·L−1, temperature of 353 K, and liquid-to-solid ratio of 15 mL·g−1, the leaching ratios of Ce and La reached 93.8% and 93.2%, respectively. Moreover, the thiourea behavior during the REPPW leaching process was studied. The results indicates that the thiourea not only acted as reductant but also tended to decompose in a CS(NH2)2→(SCN2H3)2→S route. The decomposed thiourea amounted to 18.07% of its original dosage, which formed precipitation during aging of the leachate. However, it influenced neither Ce/La concentration in the leachate nor purity of the product. The recycled REOs with purities higher than 93% were prepared from the leachate by oxalate precipitation-oxidation roasting, showing no relation with the aging time.

Separation of La/Ce in rare earth polishing powder waste via Two-Stage hydrochloric acid leaching and corresponding leaching mechanism

Rare earth polishing powder waste (REPPW) usually contains lanthanum (La) and cerium (Ce) with content over 50 %, thus its recovery is important for the cyclic utilization of rare earth. In the traditional acid leaching process, La and Ce are simultaneously leached and required further separation. Based on their leaching behavior difference, a two-stage hydrochloric acid leaching process was proposed in this study to recover and primarily separate La and Ce in REPPW. With the optimal operation conditions, La enriched solution with a relative purity of 91.11 % and Ce enriched solution with a relative purity of 92.85 % were obtained and their recovery ratio were 59.47 and 85.15 %, respectively. After precipitation and calcination, products of La2O3 with purity of 83.67 % and CeO2 with purity of 93.38 % were obtained. Besides, individual leaching kinetics of La and Ce in low-acid leaching were studied using various shrinking core models. Based on the analysis of phase components and micromorphology evolution of REPPW during the leaching process, the leaching mechanism of REPPW was determined. Combined the leaching regularity with the fitting results, the leaching process of La was controlled by interfacial transfer and product layer diffusion, and the Ce was by product layer diffusion. The apparent activation energies of the LaOF and CeO2 leaching reactions were 89.97 kJ/mol and 79.03 kJ/mol, respectively.

Wear resistance of sensors based on surface plasmon resonance phenomenon

Surface plasmon resonance is used for detecting and measuring various analytes characteristics by sensitive elements in sensor devices. At this, the problem of wear of the sensitive elements, contacting with gaseous and liquid environments whose characteristics are measured, arises during operation of sensor devices based on the surface plasmon resonance phenomenon. Wear of a surface gold nanolayer may be caused by various factors such as maintenance (cleaning before measurements), chemical reactions and abrasiveness of the environment. This problem becomes particularly significant when suspensions are measured. Solid particles in the suspensions have abrasive properties, which leads to modifications of the surface, reduction of the thickness and damage of the sensitive gold layer. As a result, more frequent replacements of sensitive elements are required significantly increasing the measurements cost. In this paper, influence of water suspensions of an optical polishing powder “Polarite” on the wear and the associated changes of the characteristics of a sensitive element is investigated. The need to find solutions of the problem of improving its wear resistance is highlighted.

Interaction of Sludge Particles and Wear Particles of Polishing Powder in the Process of Polishing of Polymeric Optical Materials

Interaction of Sludge Particles and Wear Particles of Polishing Powder in the Process of Polishing of Polymeric Optical Materials

Test research on the effect of waste ceramic polishing powder on the compressive strength and chloride penetration resistance of seawater concrete

Waste ceramic polishing powder (CPP) is a by-product created during the grinding and polishing process of the ceramic industry, which adversely affects the environment. In this research, it was used as auxiliary material to partially replace cement during the casting of the test specimens. The effect of cement substitution by 0%, 5%, 10%, 20%, 30%, 40% and 50% of the CPP with seawater and freshwater mixing on the compressive strength and resistance to chloride penetration of the concrete is compared. Moreover, the microstructure development and hydration products of both pastes are determined by different methods. Experimental results show that the compressive strength and resistance to chloride penetration of concrete samples, with the CPP and seawater mixing, is superior to that of the freshwater specimen, with the CPP mixing at the same curing time and the same CPP content. The compressive strength of both types of concrete tends to decrease with increasing content of CPP replacing cement. The compressive strength of concrete meets design requirements when the rate of cement replacement is up to 30% of CPP content when mixed with seawater, but the compressive strength of concrete meets design requirements when the rate of substitution cement reaches a maximum of 10 wt% CPP content mixed with freshwater. In contrast, the resistance to chloride penetration of both types of concrete mixed with CPP is better than that of the specimen without CPP and with the increase of cement replacement rate with CPP, the chloride resistance of concrete shows a rising trend. Under the same CPP substitution and the same curing time, the resistance of chloride penetration of concrete with freshwater mixing is lower than that of concrete mixed with seawater. In addition, the main hydration products in freshwater and seawater pastes with that CPP mixing were CH, ettringite and CSH. In particular, the component of the CPP promoted the formation of Friedel’s salt in concrete mixed with seawater. Seawater increased CH content at an early age (7 days) and decreased later (28 days). At a later age, most of the chlorides in seawater with that CPP component were immobilized by hydrocalumite, which microstructure became denser and compacted structure of concrete.

A method of real-time monitoring beam output stability of intense pulsed ion beam

Intense pulsed ion beam (IPIB) technology has made remarkable progress in surface modification, mixing, polishing, film deposition, and nano powder synthesis in recent years. However, the surface properties of materials under IPIB irradiation are highly sensitive to beam intensity variations. Deviations from acceptable parameter range can change the surface characteristics and increase prevalence of defects. Consequently, the real-time online monitoring of beam stability during irradiation experiments and promptly identifying of pulses exhibiting significant parameter jitter are of significance in accurately analyzing results and optimizing surface modification. This study presents a fast-response pulse X-ray diagnostic system by employing EJ-200 plastic scintillator, 9266FLB photomultiplier tube, and Tektronic TDS 2024 four-channel oscilloscope. Single particle test demonstrates that the system achieves a time resolution of 6 ns, meeting the requirements for temporal response to detecting pulse X-ray signals with a half-width of ~80 ns. By adjusting the insulation magnetic field strength of the ion diode, the IPIB output level is regulated. The diagnostic system successfully captures X-rays emitted by the external magnetic insulated ion diode operating at different output levels. Simultaneously, the ion beam energy density is measured by using an infrared camera. To mitigate diagnostic errors stemming from target ablation, the maximum energy density is controlled to be below 1.32 J/cm&lt;sup&gt;2&lt;/sup&gt;. Analysis results establish a positive correlation between X-ray intensity and ion beam energy density. This relationship arises from the influence of the insulating magnetic field adjustment on the diode's operating voltage, which subsequently affects the bremsstrahlung radiant intensity and ion beam emission intensity. This correlation offers the potential for the real-time monitoring of IPIB beam output stability by utilizing X-ray signals. To further corroborate the synchronized changes in pulse X-ray intensity and ion beam intensity, Faraday cup is employed as an alternative to infrared imaging method for measuring ion current density. Results demonstrate that the amplitude of the X-ray signal changes synchronously with fluctuations of ion current density. It is worth noting that when the output intensity of ion beam deviates significantly (more than 10% of the preset value), the diagnostic system will respond quickly. These findings validate the efficacy of the proposed non-interceptive diagnostic method of real-time monitoring the intense pulsed ion beam output stability.

Magnetized vermiculite loaded with waste polishing powder to recover phosphorus in waste water

In view of the phosphorus pollution in water bodies and the shortage of phosphate rock resources, the preparation of cheap, accessible and easy-to-recycle adsorbents for the recovery of phosphorus in sewage has attracted much attention. In this study, waste rare earth polishing powder (WP) was doped with magnetized vermiculite (Mev) at a mass ratio of 1:1 through acid leaching and advection precipitation method to prepare the magnetic Mev-WP composite material for adsorbing and recovering phosphorus in the water. The results show that Mev-WP is easy to be separated from water by an external magnetic field and the main reason why Mev-WP specificity can adsorb phosphorus is that the rare earth elements of La and Ce in the polishing powder are loaded on the flake magnetized vermiculite in the form of La (OH)3 and Ce(OH)3. The phosphorus adsorption process of Mev-WP is an endothermic mono-layer chemical adsorption that includes boundary layer diffusion and internal diffusion, of which the boundary layer diffusion is the rate-limiting step, which can complete rapid adsorption within 30 min. Except for HCO3− ions, other coexisting anions in the water have no significant effect on adsorption, but the adsorption capacity is greatly affected by pH. At pH 11 to 3, the material is a stable and environmentally-friendly adsorbent, and with the decrease of pH, the adsorption capacity increases significantly. When the pH is 3, at 25 °C, the adsorption capacity can reach up to 63.79 mg/g. The phosphorus adsorption mechanism of Mev-WP is electrostatic attraction and ligand exchange between -OH on La-OH and Ce-OH and phosphate groups in the water to generate La-O-P and Ce-O-P coordination complexes to remove phosphorus. After 5 times desorption and recycling, the phosphorus recovery rate of the material reaches 65 %, and the deep phosphorus removal verification in urban sewage is effective. Studies have shown that Mev-WP is a promising specific phosphorus recovery agent.

Coordination-enhanced extraction of rare earth metals from waste polishing powder and facile preparation of a mesoporous Ce-La oxide

Efficient and environmental-friendly recycling of rare earth polishing powder waste (REPPW) is imperative not only to ecological well-being but also to sustainability of critical rare earth resources. However, the low leaching efficiency of rare earth elements in mild acidic conditions and complicated synthesis procedure of high-end products hindered industrial recycling of REPPW. Herein, an ascorbic acid-H2SO4 system with mild conditions, i.e., ascorbic acid concentration = 0.042 mol/dm3, H2SO4 concentration = 1 mol/dm3, liquid to solid ratio = 20 cm3/g and temperature = 353 K, is proposed for leaching REPPW, in which the leaching ratios of Ce and La reached 96.79 % and 93.81 %, respectively. The coordination stability constants of Ce3+-ascorbic acid, i.e., β1 = 106.88 and β2 = 1013.03, were determined by pH-potentiometry, which revealed that the enhanced Ce3+ dissolution in this mild leaching system was attributed to Ce3+-ascorbic acid coordination. Subsequently, a high-purity, mesoporous Ce-La oxide cube was synthesized from the leaching solution by a facile chemical precipitation method at atmospheric pressure and temperature. The product had a composition of 78.07 wt% CeO2 and 21.93 wt% La2O3, and its average pore diameter was 7.30 nm. Its reducibility was 1.52 times higher than the theoretical value, suggesting a high potential for catalyzing redox reactions. This work proposes an efficient and value-added process for recycling REPPW, which helps to enlighten the sustainable utilization of secondary rare earth resources.

Effect of 3.7 at% F doping on the atomic structure and reducibility of CeO2(111) surface: A first principles calculation

Density functional theory calculations was conducted to clarify effect of fluorination on the reducibility of CeO2 polishing powder. The atomic structure and O vacancy formation energy of F-doped CeO2(111) surface were systematically calculated, and electronic structure was also analyzed to understand the calculation results. It showed that the CeO1.963(111) surface needs absorb 7.853 eV to be reduced further, so it is difficult to generate the second O vacancy (V2). After fluorination, the first O vacancy (V1) in CeO1.926F0.037(111) surface caused adjacent atoms to move significantly, and O vacancy formation energy decreased to 2.913 eV, which promoted the formation of V2. Moreover, electronic structure calculation also showed that the interaction between O2p and Ce4f5d orbits was enhanced in reduced CeO1.963(111) surface, which hindered the formation of V2. The F2p orbit in CeO1.926F0.037(111) surface moved towards the low energy level, V1 made the reduced surface stable and promoted the formation of V2.