Decomposition Ratio Research Articles

Strongly enhanced piezoelectric-catalysis of ZnSnO3/graphite hybrid materials for dye wastewater decomposition

In this study, the strongly-enhanced piezoelectric catalytic performance for dye decomposition was exhibited by sol-gel-synthesized ZnSnO3 with the addition of a certain proportion of graphite. With increasing graphite content from 0 to 5%, decomposition ratio of RhB dyes first increases and then decreases, reaching maximum value of ∼100% for the ZnSnO3 with 3% graphite addition. Reaction rate constant reached a maximum of ∼0.098 min−1 at 3% graphite content, while that of the pristine ZnSnO3 is only ∼0.02 min−1. Graphite particles can transfer piezoelectrically-negative charges, which helps to reduce the recombination of charges, thereby improving piezoelectric catalytic performance. Strong piezoelectric catalytic activity makes novel ZnSnO3/graphite hybrid materials potential for dye decomposition from wastewater.

Natural piezoelectric tourmaline mineral for piezocatalytic decomposition of organic dyes under vibration

AbstractPiezoelectric materials can convert mechanical energy into electrical energy, and further piezocatalysis can be designed based on the product between piezoelectric effect and electrochemical redox effect, which is hopeful for the actual dye decomposition. Tourmaline is a natural mineral with spontaneous polarization, which is an ideal piezocatalytic material and is rarely reported in dye decomposition. In this work, after 100 mg tourmaline powder is vibrated for 120 min, the piezocatalytic dye decomposition ratios of rhodamine B (RhB), methylene blue, and methyl orange are ∼95%, ∼46%, and ∼23%, respectively. The corresponding first‐order reaction kinetic values for these three dyes are 0.02681, 0.00639, and 0.00246 min−1, respectively. By adjusting the pH value of the initial RhB solution to 5, the decomposition ratio can reach ∼99% after only 60 min of vibration. In the process of dye decomposition, it is determined that the main active substances are hydroxyl radicals and superoxide radicals via electron spin–resonance spectra test. The spontaneous polarization performance of tourmaline can effectively adsorb dye molecules to promote the catalytic reaction. Natural tourmaline minerals are abundant, low cost, and environmentally friendly making them suitable for large‐scale piezocatalysis of mineral materials.

Efficient recycling of carbon fiber from carbon fiber reinforced composite and reuse as high performance electromagnetic shielding materials with superior mechanical strength

Carbon fiber reinforced boron phenolic resin composite (CF/BPR) is widely used. However, it is hard to decompose its waste for highly cross-linked networks. Herein, a solvothermal decomposition route was proposed to decompose CF/BPR and recycle carbon fibers. Decomposition ratio of resin (Dr) reached 99.78%. Possible decomposition mechanism was proposed based on characterizations of decomposition products. Composite was decomposed for synergistic effects of physical swelling, mechanical impact and chemical decomposition. Surface morphology and microstructure characterization of recycled carbon fibers (RCFs) confirmed that resin was highly removed while no significant harm was caused to RCFs. It was found that RCFs reinforced boron phenolic resin composite (RCFs/BPR) had superior punch type shear strength due to improved wettability and interfaces. Moreover, RCFs/BPR exhibited superior electromagnetic shielding performance in X-band frequency for improved conductive network. This work presents a facile and efficient pathway for decomposing composite waste and reuse as high performance electromagnetic shielding materials.

Ultrasound-assisted photocatalytic degradation of RhB by Bi-doped AgNbO3 under internal electric field control

Donor doping is a promising method to regulate ferroelectric properties and grain size. Herein, Ag1–3xBixNbO3 (x = 0, 0.01, 0.02, 0.03, and 0.04) powders were prepared by a conventional solid-state sintering method. The grain size gradually decreases with increasing x. The piezo-photocatalytic decomposition ratio of Rhodamine B (RhB) is 96.3% within 60 min for Ag0.91Bi0.03NbO3-air, and the rate constant k value reaches 0.057 min−1, which is comparable to that of precious metal-loaded catalysts. It is worth mentioning that Ag0.91Bi0.03NbO3-air exhibits great piezo-photocatalytic activity among these samples, because the rational introduction of Bi into AgNbO3-air can control the grain size, ferroelectric property, and remanent polarization. This study provides insight into donor doping and grain size engineering strategies in the hope of providing additional insights into the environmental field.

A (Bi2O2)2+ layer as a significant carrier generator and transmission channel in CaBi2Nb2O9 platelets for enhanced piezo-photo-catalytic performance

The low photocatalytic conversion efficiency, poor light absorption and high charge recombination rate of traditional semiconductor photocatalysts continues to be a significant research challenge. In this paper, by combining detailed experimental and modeling techniques, we report on the unique potential of CaBi2Nb2O9 (CBN) platelets that can couple both piezo- and photo- multi-field effects to overcome these issues and realize high-efficiency hydrogen production and dye degradation. The surface adsorption of OH− and dye molecules is improved as a result of the built-in electric field, thereby demonstrating an enhanced piezo- and photo-catalytic H2 production activity, with a high rate of 96.83 μmol g−1 h−1. The piezo-photocatalytic decomposition ratio for 100 mL RhB dye of 10 mg/L can reach up to 98.7 % in 32 min using only 0.05 mg of CBN platelets (k = 0.131 min−1). It is shown that the careful introduction of regularly arranged layers of (Bi2O2)2+ into the CBN platelet structure provides a high transport of photoelectrons via a pathway of (Bi2O2)2+ → (CaNb2O7)2− → CBN surface. The electron density distribution of Bi atoms is also found to be enriched on the facets of (020) and (200) crystal planes in the CBN platelets, which is beneficial to the oxidation reduction reaction. Furthermore, the large deformation of CBN platelet during the application of ultrasound leads to an increase of the piezo-induced built-in electric field to improve charge separation and migration. This work therefore provides a new perspective in the design and manufacture of advanced materials with enhanced piezo- and photo-catalytic performance by exploiting multi-field coupling effects.

Recyclable Carbon Cloth-Supported ZnO@Ag3PO4 Core-Shell Structure for Photocatalytic Degradation of Organic Dye.

The extensive use of organic dyes in industry has caused serious environmental problems, and photocatalysis is a potential solution to water pollution by organic dyes. The practical application of powdery photocatalysts is usually limited by the rapid recombination of charge carriers and difficulty in recycling. In this study, recyclable carbon cloth-supported ZnO@Ag3PO4 composite with a core-shell structure was successfully prepared by solvothermal treatment and subsequent impregnation-deposition. The as-prepared carbon cloth-supported ZnO@Ag3PO4 composite showed an improved photocatalytic activity and stability for the degradation of rhodamine B (RhB), a model organic dye, under visible light irradiation. The decomposition ratio of RhB reached 87.1% after exposure to visible light for 100 min, corresponding to a reaction rate constant that was 4.8 and 15.9 times that of carbon cloth-supported Ag3PO4 or ZnO alone. The enhanced performance of the composite can be attributed to the effectively inhibited recombination of photoinduced electron-hole pairs by the S-scheme heterojunction. The carbon fibers further promoted the transfer of charges. Moreover, the carbon cloth-supported ZnO@Ag3PO4 can be easily separated from the solution and repeatedly used, demonstrating a fair recyclability and potential in practical applications.

Variable thermal transport in black, blue, and violet phosphorene from extensive atomistic simulations with a neuroevolution potential

Phosphorus has diverse chemical bonds, and even in its two-dimensional form, there are three stable allotropes: black phosphorene (Black-P), blue phosphorene (Blue-P), and violet phosphorene (Violet-P). Due to the complexity of these structures, no efficient and accurate classical interatomic potential has been developed for them. In this paper, we develop an efficient machine-learned neuroevolution potential model for these allotropes and apply it to study thermal transport in them via extensive molecular dynamics (MD) simulations. Based on the homogeneous nonequilibrium MD method, the thermal conductivities are predicted to be 12.5±0.2 (Black-P in armchair direction), 78.4±0.4 (Black-P in zigzag direction), 128±3 (Blue-P), and 2.36±0.05 (Violet-P) Wm−1K−1. The underlying reasons for the significantly different thermal conductivity values in these allotropes are unraveled through spectral decomposition, phonon eigenmodes, and phonon participation ratio. Under external tensile strain, the thermal conductivity in black-P and violet-P are finite, while that in blue-P appears unbounded due to the linearization of the flexural phonon dispersion that increases the phonon mean free paths in the zero-frequency limit.

Lead-Free Bi0.5Na0.5TiO3 Ferroelectric Nanomaterials for Pyro-Catalytic Dye Pollutant Removal under Cold-Hot Alternation.

In this work, explicitly pyro-catalytic performance is observed in sol-gel-synthesized ferroelectric Bi0.5Na0.5TiO3 lead-free nanomaterials, and its application for dye wastewater purification is also actualized under temperature fluctuations varying from 23 °C to 63 °C. The decomposition ratios of the pyro-catalytic Bi0.5Na0.5TiO3 nanomaterials on Rhodamine B, methyl blue and methyl orange can reach 96.75%, 98.35% and 19.97%, respectively. In the pyro-catalytic process, the probed active species such as hydroxyl radicals, superoxide radicals and holes play an extremely important role in decomposing dye molecules. The ferroelectric Bi0.5Na0.5TiO3 lead-free nanomaterials will have an excellent prospect for dye wastewater purification due to its explicit pyro-catalysis.

Dechlorination of Polyvinyl Chloride via Solvothermal Treatment with Glycerol

Solvothermal treatment using glycerol effectively removes chlorine from polyvinyl chloride (PVC). Additive-free PVC was dechlorinated by treatment with glycerol in an autoclave at 200–240 °C. Liquid glycerol was coexistent with a red powder after the reaction at 200 °C. At reaction temperatures of 220 and 240 °C, the liquid glycerol disappeared, and carbonization proceeded to form a black powder. In this reaction, the glycerol was directly converted into glycidol. Epichlorohydrin was also produced from the glycerol via 1,3-dichloro-2-propanol as an intermediate. The PVC was converted into the polyethylene oxide structure, following the generation of the polyene structure by zip-elimination. Finally, the converted PVC was resinified by an epoxidation reaction with the glycidol and epichlorohydrin. Thus, glycerol acted as a useful reaction medium for this reaction system. The analysis of the decomposition ratio and dechlorination yield showed that the PVC was converted into solid products in high yields via chlorine release, and 30% of the glycerol was solidified by resinification at 240 °C. The effects of the additives on dechlorination were investigated using commercially available PVC sheets. Elemental analysis showed that the calorific value of the solid product dechlorinated at 240 °C was found to be higher than that of standard bituminous coal.

Valorization of ball-milled waste red mud into heterogeneous catalyst as effective peroxymonosulfate activator for tetracycline hydrochloride degradation

Red mud (RM), a kind of iron-rich industrial waste produced in the alumina production process, can be utilized as a potential iron-based material for the removal of refractory organic pollutants from wastewater in advanced oxidation processes (AOPs). In this work, high-iron RM (rich in iron) was activated in a ball mill and applied as an effective activator of peroxymonosulfate (PMS) for tetracycline hydrochloride (TC-HCl) degradation. Compared with that of unmilled RM (69.7%), the TC-HCl decomposition ratios of ball-milled RM (BM-RM) (72.2%–92.0%) were all improved in the presence of PMS. Systematic characterization suggested that ball milling could optimize the physicochemical properties of RM, such as increased surface area, increased oxygen vacancies, enhanced electrical conductivity, and increased exposure of Fe(II) sites, all of which could effectively improve RM for PMS activation to degrade TC-HCl. The quenching experiments and electron paramagnetic resonance technique revealed that 1O2 and SO4·- contributed dominantly to the TC-HCl degradation. Ultra performance liquid chromatography mass spectrometry analysis combined with density functional theory calculation revealed that the degradation pathways of TC-HCl were driven by hydroxylation, N-demethylation and dehydration in BM-RM/PMS system. Based on quantitative structure-activity relationship prediction using the Toxicity Estimation Software Tool software, the toxicity of almost all intermediates was significantly reduced. An obvious inhibition effect on TC-HCl was occurred in the presence of Cl−, whereas the presences of NO3− and SO42− had little effect. However, HCO3− improved TC-HCl removal efficiency. BM-RM had a wide working pH range (pH = 3–11) and showed good stability and reusability in use. Overall, this work not only offers a simple and promising approach to improve the catalytic activity of RM, but also opens new insights into the ball-milled RM as an effective PMS activator for wastewater treatment.

Natural day–night temperature variations driving pyrocatalytic wastewater treatment and CO2 reduction based on room-temperature rhombohedral–tetragonal phase transition of lead-free ferroelectric BZT-0.5BCT fibers

Environmental remediation approaches in terms of wastewater treatment and CO2 reduction using environmental energy are highly desirable for an industrialized society. Herein, the pyrocatalytic performance of electrospun lead-free ferroelectric Ba(Ti0.8Zr0.2)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT, x = 0.2, 0.3, 0.4, 0.5, 0.6) micro-nano fibers is investigated, and BZT-0.5BCT is identified as an efficient pyrocatalyst for water pollutants decomposition driven by rhombohedral–tetragonal (R-T) phase transition. Phase changes can induce high pyroelectric coefficients. In response to 0–60 °C thermal cycles, the decomposition ratio of Rhodamine B (RhB) by BZT-0.5BCT fibers after nine thermal cycles is approximately 70%. Moreover, under outdoor day-night temperature fluctuations, about 76% of RhB and 95% of methylene blue (MB) can be degraded after 10 and 7 days respectively because BZT-0.5BCT has an R-T phase change point of around 30 °C. For Cr(VI) (potassium dichromate) and tetracycline (TE), the fibers also show good pyrocatalytic degradation ability. Due to destruction of bacterial cell membranes by superoxide groups, high levels of antimicrobial activity could also be achieved against Escherichia coli (99.99%) and Staphylococcus aureus (92.83%). Furthermore, the pyrocatalytic reduction of CO2 to acetaldehyde by BZT-0.5BCT can reach approximately 382.47 μmol g−1 after 20 thermal cycles of 0–60 °C. Therefore, such outstanding catalytic performance of pyroelectric BZT-0.5BCT fibers enables pyroelectric catalysis as a potential approach for both all-round wastewater treatment and CO2 reduction.

Fluidization thermal decomposition of sodium fluosilicate

To break through the thermodynamic limitation that sodium fluosilicate only can be completely decomposed at high temperature, the technology of pre-decomposition under SiF4 atmosphere and deep decomposition under air condition at lower temperature was developed. The hydrolysis reaction of sodium fluosilicate can be effectively restrained when drying under vacuum or low temperature. Thermal decomposition results of sodium fluosilicate indicate that temperature has a very significant effect on its decomposition. The decomposition ratio can reach 79.4% at 600 °C for 1 h, and 99.6% at 700 °C for 1 h under air condition, respectively. Gas velocity and the type of inert gas have no significant effect on its decomposition. Fine particles affect its decomposition performance due to agglomeration, while coarse particles have good thermal decomposition performance without significant differences. The decomposition reaction process in fluidized bed satisfies the classical Avrami Erofe'EV model, with the reaction order of 1.5 and the activation energy of 61.35 kJ·mol−1.

Treatment of DEHP-rich PVC waste in subcritical urine wastewater: Efficient dechlorination, denitrification, plasticizer decomposition, and preparation of high-purity phthalic acid crystals

It is difficult to dispose diethylhexyl phthalate-rich polyvinyl chloride (DEHP-rich PVC) waste due to the high level of chlorine and plasticizer. On the other hand, the denitrification of urine wastewater with high nitrogen content also faces great challenges. In this study, a synergistic treatment strategy was developed for the DEHP-rich PVC waste and urine wastewater by a subcritical water process. Subcritical urine wastewater (SUW) was used as a reaction medium in the synergistic treatment. PVC dechlorination, DEHP decomposition, and denitrification of urine wastewater were synchronously achieved in the one pot SUW. Under the optimal conditions (300 °C, 15 min, 1:5 g/mL), the PVC dechlorination ratio, urine wastewater denitrification ratio and DEHP decomposition ratio could reach 98.4%, 64.9%, and 99.2%, respectively. The decomposition of DEHP mainly included hydrolysis, nucleophilic substitution, and acylation. DEHP could be converted into phthalic acid crystal at 220 °C with a yield of 66.25% due to the efficient hydrolysis action of SUW. All the removed Cl was transferred from PVC matrix to aqueous phase. Hydroxyl nucleophilic substitution is the principal dechlorination path of PVC. The reactions between N-containing species and DEHP in SUW resulted in the high-efficiency denitrification of urine wastewater, and the N element was fixed in solid residue or transferred to oil phase as amides compounds. It is believed that the proposed SUW process is a promising technology for the synergistic treatment of DEHP-rich PVC waste and urine wastewater.

Fabrication of cerium titanate cellulose fiber nanocomposite materials for the removal of methyl orange and methylene blue from polluted water by photocatalytic degradation

In this study, cellulose fibers (Cf), extracted from sunflower seed husk, and different molar ratios of cerium titanate (Ce-Ti) NPs were prepared from sunflower seed husk extract by a green biosynthesis approach. Cf and Ce-Ti NPs were reacted via cross-linking reaction to synthesize a novel nanocomposite photocatalyst of Ce-Ti/Cf. Using Fourier-transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM-EDX) spectroscopy, all manufactured materials were characterized. The results obtained from FTIR and EDX analyses indicated that Cf and its nanocomposites (0.1 Ce-Ti/Cf, 0.3 Ce-Ti/Cf, and 0.5 Ce-Ti/Cf) were successfully prepared by harnessing biomass extract from sunflower seed husk. Furthermore, XRD revealed that the degree of crystallinity of the nanocomposites was enhanced by increasing the molar ratios of the Ce-Ti NPs. The photocatalytic activity of as-fabricated 0.1 Ce-Ti/Cf, 0.3 Ce-Ti/Cf, and 0.5 Ce-Ti/Cf nanocomposite samples was investigated on methylene blue (MB) and methyl orange (MO) dyes as model organic compounds found in wastewaters. The effects of dose, contact time, and pH on the photocatalytic activity of the synthesized nanocomposites, the photodegradation kinetic parameters of MB, and MO degradation with/without the addition of H2O2 were also studied. The results revealed that high photodegradation efficiency could be obtained as the ratio of TiO2 in the Ce-Ti nanocomposite formula increases. Moreover, after sunlight irradiation, the adsorption capacity and the dye decomposition ratio significantly increase during the early contact time and reach equilibrium at about 240 and 120 min for 0.5 Ce-Ti/Cf nanocomposite photocatalyst in the absence and presence of hydrogen peroxide, respectively. In light of the obtained results and the practical wastewater treatment study conducted, the prepared photocatalyst from Ce-Ti/Cf nanocomposites could be a promising material for treating dye wastewater especially collected from Egypt.

Enhanced degradation of tetracycline over FeS-based Fenton-like process: Autocatalytic decomposition of H2O2 and reduction of Fe(III)

This study constructed a FeS-based Fenton-like process to explore the degradation of TTC in the presence of copper ions. The acidic condition of pH 3 was more favorable to the H2O2 decomposition and TTC degradation, and it was slightly enhanced by Cu(II). The production of •OH from H2O2 was revealed through radical scavenging and benzoic acid probe experiments, and the ratio of H2O2 decomposition to •OH production was about 1–1.5, which is comparatively consistent with the theoretical ratio. FeS-based Fenton process was proved to be a homogenous system, the slow release of Fe(II) source and the autocatalytic cycle of Fe(III) to Fe(II) resulting from the reductive species of TTC and dissolved S(-II) improved the production of •OH and the degradation of TTC, which was proved by comparing TTC degradation, TOC removal, H2O2 decomposition and Fe(II) concentration with different iron sources (FeS, Fe(II) and Fe(III)) and external addition of dissolved S(-II). The possible degradation pathways of TTC were subsequently inferred according to the detected products by LC-MS. Understanding these autocatalytic processes is essential to reveal the transformation of redox-active substances in environments and may have potential significance in applying FeS-based Fenton-like process for the treatment of wastewater containing reductive organic matters.

Environment-friendly recycling of CFRP composites via gentle solvent system at atmospheric pressure

The recovery of high-value carbon fibers from carbon fiber-reinforced polymer (CFRP) composites is essential for ensuring a sustainable future. In this work, a simple and eco-friendly approach was presented for the chemical recycling of anhydride-cured epoxy-based CFRP composites with a mixed solution of monoethanolamine (MEA) and potassium hydroxide (KOH). In this solvent catalyst system, the resin matrix was decomposed by cleaving the ester bonds. Thus, a high CFRP composite decomposition ratio of 99% was achieved at ∼160 °C within 60 min under ambient pressure. The recovered carbon fibers (CFs) had a clean surface and retained more than 95% of their original stiffness and strength. Moreover, one of the highlights of this process was that the excess MEA solvent and degraded epoxy resin (DER) were recovered from the degraded organic products (DOP) by simple distillation. The DER was reused in combination with the original epoxy resin system to prepare new resin material with good mechanical properties, forming a closed-loop chemical recycling route. The advantages of this method include facile reaction conditions, near-complete recovery of CFs and solvent, and the absence of harmful solid waste, demonstrating that this recycling process has a high degree of environmental friendliness.

Mechanistic insight into cost-effective dedicated oxidation of alkanes by inactivating soil organic matter with FeOOH formed in situ

Modified Fenton technique has been widely used to remediate soils contaminated with crude oil but significantly limited to soil organic matter (SOM) consuming oxidants. In this study, soils with developed SOM inactivation by FeOOH formed in situ were created and spiked with crude oil (total petroleum hydrocarbons (TPH): 19453 mg/kg), then treated by modified Fenton reagents. The reaction activity of hydroxyl radicals (•OH) relative to TPH (K) notably increased to 0.65 when the degree of developed inactivation of the SOM (β) was 100% (DIS-100), which was 1.45, 2.03 and 2.83-fold than that of DIS-50, DIS-15 and control (CK), respectively. Meanwhile, the higher the K, the more •OH transferred, which realized the efficient oriented oxidation of TPH. Moreover, improving the transfer of •OH from SOM to TPH was more important than increasing •OH production in soil remediation. With the β increasing to 100%, the ratio of invalid H2O2 decomposition to produce O2 decreased to 22%, equal to 25% reduction compared to CK. Therefore, when β was 100%, the utilization efficiency of H2O2 was improved to 1.48 mg/mmol, which was approximately 1.39, 3.35 and 5.43-fold higher than the efficiency got by DIS-50, DIS-15 and CK, respectively, achieving the cost-effective dedicated oxidation of TPH. In addition, the FeOOH cross-linked with SOM via Fe–O–C and Fe–N bonds to develop inactivation of SOM. In general, this study highlighted a new insight into the effect of developed inactivation of SOM on soil remediation.

Assemblies of two multimeric enzymes using mesoporous silica microspheres toward cascade reaction fields

A highly efficient, rapid cascade reaction system with coupled enzyme reactions is developed using mesoporous silica microspheres having a large pore diameter of 24.5 nm as an immobilization scaffold for two multimeric enzymes. The simultaneous adsorption of glucose oxidase and catalase on the pores of the mesoporous silica microspheres cause aggregation of the two enzymes, resulting in extremely low adsorbed amounts of the enzymes. The present study overcomes this limitation by immobilizing the two enzymes sequentially on the mesoporous silica pores, which significantly increases the decomposition ratio of hydrogen peroxide (an intermediate product). The localization and assembly of the two enzymes encapsulated in the mesopores were confirmed by labeling with fluorescent dyes for direct visualization and by detection of the fluorescence resonance energy transfer between the two enzymes, respectively, under a confocal laser scanning microscope field. The activity in the cascade reaction by the dual enzyme–mesoporous silica composite was significantly improved via the dense arrangement of the two enzymes on the surface of the mesoporous silica microspheres.

A Literature Review of Modelling and Experimental Studies of Water Treatment by Adsorption Processes on Nanomaterials.

A significant growth in the future demand for water resources is expected. Hence researchers have focused on finding new technologies to develop water filtration systems by using experimental and simulation methods. These developments were mainly on membrane-based separation technology, and photocatalytic degradation of organic pollutants which play an important role in wastewater treatment by means of adsorption technology. In this work, we provide valuable critical review of the latest experimental and simulation methods on wastewater treatment by adsorption on nanomaterials for the removal of pollutants. First, we review the wastewater treatment processes that were carried out using membranes and nanoparticles. These processes are highlighted and discussed in detail according to the rate of pollutant expulsion, the adsorption capacity, and the effect of adsorption on nanoscale surfaces. Then we review the role of the adsorption process in the photocatalytic degradation of pollutants in wastewater. We summarise the comparison based on decomposition ratios and degradation efficiency of pollutants. Therefore, the present article gives an evidence-based review of the rapid development of experimental and theoretical studies on wastewater treatment by adsorption processes. Lastly, the future direction of adsorption methods on water filtration processes is indicated.

Tungsten extraction from scheelite hydrochloric acid decomposition residue by hydrogen peroxide

• W was leached from crude tungstic acid or residue by an efficient and clean method. • H 2 O 2 dissolved W from crude tungstic acid or residue selectively. • The W leaching ratio exceeded 96% for crude tungstic acid and 99% for the residue. • Pure tungstic acid was obtained from peroxotungstic acid solution. • More than 99.6% of W was precipitated from peroxotungstic acid solution. To reduce the amount of ammonia wastewater produced during traditional tungsten metallurgy, a novel method has been developed. Hydrogen peroxide was first used to selectively dissolve tungsten from crude tungstic acid and scheelite hydrochloric acid decomposition residue. Then, the peroxotungstic acid solution obtained was heated to prepare pure tungstic acid through thermal decomposition . The results showed that when the temperature was 40–45 °C, the molar ratio of hydrogen peroxide to tungstic acid was 2:1, and the reaction time was 60 min, more than 96 % of the crude tungstic acid was dissolved. Tungsten was easily leached from the hydrochloric acid decomposition residue under the conditions of a hydrogen peroxide concentration of 1.95 mol/L, 60 min, and 30 °C. The tungsten leaching ratio was 99.4 %. Using a decomposition temperature higher than 95 °C, seed addition amount more than 2.5 g/L, an acid concentration of 1 mol/L, and a reaction time of 120 min, the final W concentration in the mother liquor was 0.5 g/L and the decomposition ratio of peroxotungstic acid was more than 99.6 % with the product being WO 3 ·H 2 O. This research showed that hydrogen peroxide could dissolve tungstic acid and scheelite hydrochloric acid decomposition residue, and that the peroxotungstic acid obtained was readily decomposed into tungstic acid, which made it possible to leach scheelite cleanly and efficiently.