Acid Washing Treatment Research Articles

Study on the Acidic Modification of Mesoporous HZSM-5 Zeolite and Its Catalytic Cracking Performance

Mesoporous HZSM-5 zeolites with nanocrystal stacking morphology were directly synthesized via hydrothermal methods without mesoporous templates. The synthesized mesoporous HZSM-5 was subjected to hydrothermal–citric acid washing treatment. The structural and acidic properties of the samples before and after modification were characterized using various techniques. The catalytic performance for butene conversion to propylene was investigated under atmospheric pressure, 500 °C, and a butene weight hourly space velocity (WHSV) of 10 h−1 in a continuous-flow micro-fixed bed reactor. The results show that propylene selectivity increased significantly from 24.7% before modification to 44%, and propylene yield increased from 22% to 38%. After 2 h of hydrothermal–citric acid washing modification, the catalyst maintained a butene conversion rate of 76% and a selectivity of 47% at 525 °C and a WHSV of 10 h−1 after 130 h of continuous reaction, with a propylene yield of 37%. The results indicate that moderate hydrothermal–citric acid washing modification leads to the removal of aluminum from the zeolite framework, reducing the amount and strength of acid but increasing the mesopore quantity. This helps control the reaction pathways and diffusion of intermediate products, suppresses some side reactions, and improves the selectivity and yield of the desired product, propylene, while significantly enhancing catalytic stability.

ZIF-Co3O4@ZIF-Derived Urchin-Like Hierarchically Porous Carbon as Efficient Bifunctional Oxygen Electrocatalysts.

Co3O4 nanoparticles were sandwiched into interlayers between ZIF-8 and ZIF-67 to form ZIF-Co3O4@ZIF precursors. Pyrolysis of ZIF-Co3O4@ZIF yielded an urchin-like hierarchically porous carbon (Co@CNT/NC), the thorns of which were carbon nanotubes embedded Co nanoparticles. With large specific surface area and hierarchically porous structure, as-prepared Co@CNT/NC exhibited excellent bifunctional oxygen electrocatalytic performances. It has good ORR performance with E1/2 of 0.85 V, which exceeds the Pt/C half-wave potential (E1/2=0.83 V). In addition, Co@CNT/NC has an OER performance close to that of RuO2. To further demonstrate the effect of Co modifying on the properties, the samples were subjected to acid washing treatment. Co-based nanoparticles were proved to After acid washing, there was obvious loss of Co particles in Co@CNT/NC, resulting in poor oxygen electrocatalysis. So, the pyrolysis products of ZIF-8-Co3O4@ZIF-67 retained large specific surface area and porous structure can be retained, and on the other hand, the carbon tube structure and original polyhedron framework. Besides, existence of Co nanoparticle@carbon nanotube provided more active sites and improved the ORR and OER performances.

Promotion of Cu/Ce supported red mud for NO removal from low and medium temperature flue gas

Red mud is a solid waste in aluminum industry and has been proven to be an efficient alternative to NOx selective catalytic reduction (SCR) catalysts. Acid washing treatment to red mud can improve its alkalinity and surface properties, and increase the conversion rate of NOx. In this paper, Cu, Ce, and Cu/Ce was supported on acid washed red mud and NOx catalytic conversion performance on metal modified red mud catalysts was studied. The research results indicate that Cu+ and Cu2+ in the Cu supported catalyst effectively promote NO conversion rate of red mud in low-temperature (200–300 °C) flue gas, reaching a maximum of 90.7%; Ce3+ and Ce4+ in Ce supported catalysts effectively promote the NO conversion rate of red mud in flue gas at 200–400 °C, reaching a maximum of 94.0%; Cu/Ce supporting exhibits better NO conversion rate than single metal supported catalysts at low-temperatures, the optimal Cu:Ce ratio for supporting is 1:1; and also exhibits better NO conversion rate than Cu supported catalysts at high-temperature (300–400 °C), reaching a maximum of 95.5%. The reason may be that under the synergistic effect of Cu/Ce, ACRM-Cu1Ce1 has stronger low-temperature redox ability, higher weak acidic peaks, higher average oxidation state of Fe ions, and higher Cu+ content.

ACID WASH INFLUENCES ON PHYSICOCHEMICAL CHARACTERISTICS OF BAMBOO LEAVES ASH

Silica production from sandstone requires tremendous fossil resources that threaten our environment. Hence, greener resources from biomass should be utilized. One of them is from bamboo leaves which contain rich silica in ash. Even so, acid wash should be applied to achieve higher silica purity. This work aims to investigate the acid wash influences on the physicochemical characteristics of bamboo leaves ash (BLA). The treatment used 1 mol/L HCl under 1-h, 2-h, and no acid wash as a control. The BLA crystallography indicates a fully amorphous phase of silica. Interestingly, 1-h acid wash precisely reduces the silica purity from 95.35% to 94.74%, but it then increases to 96.06% under 2-h acid wash. It is also notified that the longer acid wash duration could alleviate leaves’ mechanical strength. After calcination, consequently, a smaller average particle size of BLA was nominated under 2-h acid wash (6.32 mm). It was then followed by 1-h acid wash (21.32 mm) and no acid wash (149.44 mm). The 2-h acid wash is concluded able to intensify silica purity as well as reduce the particle size of BLA. Finally, acid wash treatment becomes important to facilitate further BLA extraction in order to achieve high purity of silica.

The Fate of Heavy Metals and Risk Assessment of Heavy Metal in Pyrolysis Coupling with Acid Washing Treatment for Sewage Sludge.

Pyrolysis is an emerging and effective means for sludge disposal. Biochar derived from sludge has broad application prospects, however, is limited by heavy metals. In this study, the fate of heavy metals (HMs) in pyrolysis coupling with acid washing treatment for sewage sludge was comprehensively investigated for the first time. Most of the HMs redistributed in the pyrolyzed residues (biochar) after pyrolysis, and the enrichment order of the HMs was: Zn > Cu > Ni > Cr. Compared with various washing agents, phosphoric acid presented a superior washing effect on most heavy metals (Cu, Zn, and Cr) in biochars derived at low pyrolysis temperature and Ni in biochars derived at high pyrolysis temperature. The optimal washing conditions for heavy metals (including Cu, Zn, Cr, and Ni) removal by H3PO4 were obtained by batch washing experiments and the response surface methodology (RSM). The total maximum HM removal efficiency was 95.05% under the optimal washing specifications by H3PO4 (acid concentration of 2.47 mol/L, L/S of 9.85 mL/g, and a washing temperature of 71.18 °C). Kinetic results indicated that the washing process of heavy metals in sludge and biochars was controlled by a mixture of diffusion and surface chemical reactions. After phosphoric acid washing, the leaching concentrations of HMs in the solid residue were further reduced compared with that of biochar, which were below the USEPA limit value (5 mg/L). The solid residue after pyrolysis coupling with acid washing resulted in a low environmental risk for resource utilization (the values of the potential ecological risk index were lower than 20). This work provides an environmentally friendly alternative of pyrolysis coupling with acid washing treatment for sewage sludge from the viewpoint of the utilization of solid waste.

Effects of chlorine and peroxyacetic acid wash treatments on growth kinetics of Salmonella in fresh-cut lettuce

Fresh-cut produces are often consumed uncooked, thus proper sanitation is essential for preventing cross contamination. The reduction and subsequent growth of Salmonella enterica sv Thompson were studied in pre-cut iceberg lettuce washed with simulated wash water (SWW), sodium hypochlorite (SH, free chlorine 25 mg/L), and peroxyacetic acid (PAA, 80 mg/L) and stored for 9 days under modified atmosphere at 9, 13, and 18 °C. Differences in reduction between SH and PAA were non-existent. Overall, visual quality, dehydration, leaf edge and superficial browning and aroma during storage at 9 °C were similar among treatments, but negative effects increased with temperature. These results demonstrated that PAA can be used as an effective alternative to chlorine for the disinfection of Salmonella spp. in fresh-cut lettuce. The growth of Salmonella enterica sv Thompson was successfully described with the Baranyi and Roberts growth model in the studied storage temperature range, and after treatment with SWW, chlorine, and PAA. Subsequently, predictive secondary models were used to describe the relationship between growth rates and temperature based on the models’ family described by Bělehrádek. Interestingly, the exposure to disinfectants biased growth kinetics of Salmonella during storage. Below 12 °C, growth rates in lettuce treated with disinfectant (0.010–0.011 log CFU/h at 9 °C) were lower than those in lettuce washed with water (0.016 log CFU/h at 9 °C); whereas at higher temperatures, the effect was the opposite. Thus, in this case, the growth rate values registered at 18 °C for lettuce treated with disinfectant were 0.048–0.054 log CFU/h compared to a value of 0.038 log CFU/h for lettuce treated with only water. The data and models developed in this study will be crucial to describing the wash-related dynamics of Salmonella in a risk assessment framework applied to fresh-cut produce, providing more complete and accurate risk estimates.

Treatment of recycled rubber crumb to reduce content of hazardous elements

One of the major trends in material science consists of the reuse of various waste and by-products in order to reduce the environmental load associated with extensive landfilling and other waste disposal scenarios. Specifically, disposal of end-of-life tires and related reuse of this durable material represents a major issue for modern society. In this regard, various attempts can be recognized in the available literature. However, the production of tires is related to the use of various hazardous compounds such as heavy metals and polycyclic aromatic hydrocarbons in particular. These pollutants have an adverse effect not only on the natural environment but also on human health. On this account, the present paper deals with the treatment of rubber crumb as a possible way how to mitigate the environmental and health risk. Methods including the acid washing and hot-air scrubbing are employed with different duration to access the efficiency of the procedure. Presented results based on acid washing and hot-air treatment show a significant reduction below 10 mg/kg in polycyclic aromatic hydrocarbons content compared to untreated material (57 mg/kg). Consequent utilization of treated rubber crumb in the concrete as the aggregate replacement is not accompanied with increased reduction of mechanical properties compared to conventional rubber crumb. Namely, the reduction in strength was linear up to 30 wt% replacement of natural aggregate and further increase in the replacement ratio did not result in substantial deterioration in strength. Based on the obtained results, the described treatment procedure should be more broadly employed to avoid undesired consequences on human health as well as natural environment.

Effect of Thermal and Non-Thermal Processing on Nutritional, Functional, Safety Characteristics and Sensory Quality of White Cabbage Powder.

This study was aimed to improve nutritional, functional and consumer safety aspects of cabbage powder (CP). White cabbage (Brassica oleracea var. capitata f. alba) was dehydrated to CP following microwave heating, blanching, alkali or acid washing treatments. The results for nutrients and mineral composition of raw and processed CP elucidated raw CP to exhibit significantly (p < 0.05) higher amounts of protein (12.2%), dietary fiber (25.2%), Na (52 mg/100 g), Ca (355 mg/100 g), K (286 mg/100 g), Fe (14 mg/100 g) and Zn (32 mg/100 g). Among different processing techniques, microwave treatment resulted in a higher rate of reduction for alkaloids, oxalates, tannins and phytates contents, i.e., 77%, 85%, 85%, and 86%, respectively. Likewise, microwave treatment was found more effective in reducing residual levels of neonicotinoids, pyrethroids, organophosphates including imidacloprid, cypermethrin, bifenthrin, chlorpyrifos and deltamethrin in cabbage in the range of 0.98−0.12 ppm, 1.22−0.23 ppm, 1.03−0.15 ppm, 1.97−0.43 ppm, and 2.12−0.36 ppm, respectively. CP supplementation at the rate of 5% in unleavened flatbreads was observed to maintain textural and sensory attributes of the product. The results suggest microwave heating as a cost-effective technique to reduce toxicants load in cabbage powder. Further, ~5% supplementation of CP in wheat flour may also improve nutritional and functional properties of the baked goods.

Effects of Storage Temperature, Packaging Material and Wash Treatment on Quality and Shelf Life of Tartary Buckwheat Microgreens.

Tartary buckwheat microgreens (TBM) are popular worldwide products but display an extremely short shelf life. Thus, the effects of storage temperature, packaging material, and wash treatment on the quality and shelf life were analyzed. Headspace composition, weight loss, electrolyte leakage, microbial population and sensory quality were investigated during storage. Results showed that shelf life and quality of TBM decreased with the increment of storage temperature when stored at 5-25 °C. During 5 °C storage, LDPE bags were the best packaging materials for preserving the quality of LDPE, PE and HDPE bags. On the basis of 5 °C and LDPE packages, ClO2 + citric acid wash treatment could further inhibit quality deterioration and extend the shelf life. The results demonstrated bioactive constituents and antioxidant capacity were significantly affected by storage time. The study provides insights into developing optimal packaging and storage conditions for TBM.

Improvement of water splitting activity of silver-excess AgTaO3 photocatalysts via nitric acid washing treatment

Silver tantalate (AgTaO3 with a bandgap of 3.4 eV) particles loaded with Rh–Cr oxide cocatalyst are used as photocatalysts for water splitting reactions with a high apparent quantum efficiency (AQE). AgTaO3 prepared via solid-state reaction at high temperatures may possess metallic Ag particles on the surface, resulting in Ag+ defects in the bulk of the material. These defects result in low activity owing to the increase in the recombination of photogenerated electrons and holes. Therefore, adding Ag in excess to suppress the formation of Ag+ defects would improve the photocatalytic activity of AgTaO3. In contrast, the excess Ag forms numerous metallic Ag particles on the AgTaO3 surface, which decrease the photocatalytic activity owing to the electron migration to the Ag particles. This study investigated the effectiveness of washing treatments using concentrated HNO3 to remove the metallic Ag particles formed on the Ag-excess AgTaO3 surface. After loading the Rh0.5CrOx cocatalyst, the water splitting activity of AgTaO3 photocatalysts prepared with varying amounts of excess Ag and washed with different concentrations of HNO3 was examined. The water splitting activity of 5 mol% Ag-excess AgTaO3 improved significantly when treated with 13 M HNO3 for 1 h. While the AQE of overall water splitting was 20 % for the Rh0.5CrOx/AgTaO3 prepared in a stoichiometric ratio, the Rh0.5CrOx/AgTaO3 with excess Ag showed higher activity (AQE = 39 % at 254 nm) after washing with concentrated HNO3.

Melting and Generation of Micro-Protrusions on Cathode Surface During Spark Conditioning Process in Vacuum

Spark conditioning is an effective method to increase the dielectric strength in vacuum by melting and removing micro-protrusions on the cathode surface. We aim to optimize the conditioning effect in vacuum for the application of vacuum circuit breakers (VCBs) to higher voltage levels. To obtain high breakdown (BD) voltage, the control of BD charge in the conditioning process is required. When a BD occurs, we have suggested that micro-protrusions can be generated on the cathode surface by particles from the anode. For the suitable control of BD charge, the meltability of generated micro-protrusions and their size are important. In this article, we focus on the generation of micro-protrusions on the cathode surface in conditioning process. First, we conduct spark conditioning by repetitive impulse voltages of rod–plane electrodes made of OFHC Cu in a vacuum chamber with different BD charges. Later, we observe the surface of rod cathode with a digital microscope in order to count the number of visible protrusions and measure their radii. By considering the meltability of micro-protrusions, we quantitatively reveal the existence of residual protrusions that cannot be completely melted by BD. Next, we estimate the maximum size of generated micro-protrusions by BD charge. In consideration of the collision of ions into the anode accelerated by the anode sheath voltage, we estimate the meltable amount of anode material by the BD charge. We confirm that the radii of experimentally measured protrusions are close to the estimated ones. Moreover, we consider the difference in dielectric strength due to the difference in the initial surface condition of the electrodes. We clarify that the dielectric strength is improved by applying acid wash and heat treatment to the electrodes before conditioning, which can be optimized by the BD charge and the initial surface condition of the electrode.

Influence of the synthesis parameters on the proton exchange membrane fuel cells performance of Fe–N–C aerogel catalysts

Fe–N–C aerogel catalysts were prepared by sol–gel polycondensation of resorcinol, melamine and formaldehyde precursors in the presence of FeCl 3 salt, followed by supercritical drying and thermal treatments. The effect of the mass ratio of precursors on the microstructure, iron speciation and oxygen reduction reaction (ORR) performance of the Fe–N–C aerogels was investigated by N 2 sorption, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, X-ray absorption spectroscopy, CO chemisorption and rotating disk electrode in acidic medium. The best ORR performance (activity and mass transport) was obtained by an optimum balance between pore structure and active Fe-N x species. Through acid washing, the durability of the catalyst was further improved by eliminating unstable and inactive species, particularly iron nanoparticles and iron carbide. From the CO chemisorption and turnover-frequency value, the surface sites were comparable with the highest values reported in literature. Finally, Fe–N–C aerogel catalyst was implemented a in membrane–electrode assembly with an active area of 25 cm 2 and tested in single cell, emphasizing the importance of the ink formulation on the performance. • Optimum balance between pore texture and active FeNx species for best ORR performance. • Better mass-transport properties due to higher mesopore volume in the Fe–N–C catalyst. • XAS and 57 Fe Mössbauer spectroscopies identified FeN x and Fe-inorganic species. • Acid washing treatment eliminates the unstable and inactive Fe-inorganic species. • Need to adapt the ink formulation to the catalyst texture for high performance MEAs.

The role of the surface acidic/basic centers and redox sites on TiO2 in the photocatalytic CO2 reduction

The development of sustainable processes for CO2 reduction to fuels and chemicals is one of the most important challenges to provide clean energy solutions. The use of sunlight as renewable energy source is an interesting alternative to power the electron transfer required for artificial photosynthesis. Even if redox sites are mainly responsible for this process, other reactive acidic/basic centers also contribute to the overall reaction pathway. However, a full understanding of the CO2 photoreduction mechanism is still a scientific challenge. In fact, the lack of agreement on standardized comparison criteria leads to a wide distribution of reported productions, even using the same catalyst, which hinders a reliable interpretation. An additional difficulty is ascertaining the origin of carbon-containing products and effect of surface carbon residues, as well as the reaction intermediates and products under real dynamic conditions. To determine the elusive reaction mechanism, we report an interconnected strategy combining in-situ spectroscopies, theoretical studies and catalytic experiments. These studies show that CO2 photoreduction productions are influenced by the presence of carbon deposits (i.e. organic molecules, carbonates and bicarbonates) over the TiO2 surface. Most importantly, the acid/base character of the surface and the reaction medium play a key role in the selectivity and deactivation pathways. This TiO2 deactivation is mainly initiated by the formation of carbonates and peroxo- species, while activity can be partially recovered by a mild acid washing treatment. We anticipate that these findings and methodology enlighten the main shadows still covering the CO2 reduction mechanism, and, most importantly, provide essential clues for the design of emergent materials and reactions for photo(electro)catalytic energy conversion.

Benefits of chemically treated steel fibers on enhancing the interfacial bond strength from ultra-high-performance concrete

This study investigated the effects of various chemical treatments on the pullout behavior of steel fibers in ultra-high-performance concrete (UHPC). Various methods used in previous studies were adopted and reproduced using macro straight steel fibers. The methods included acetone and acid washing, zinc phosphating, nanosilica coating, and ethylenediaminetetraacetic acid (EDTA) electrolyte solution treatment. The surface conditions and roughness of each treated fiber were analyzed using scanning electron microscopy and atomic force microscopy. The fiber pullout test results indicated that the surface roughness increased between 1.5 and 24.9 times, and that a roughened fiber surface leads to an improvement in the average bond strength. Acetone washing was the most effective in improving the pullout resistance of the fiber due to its cleansing effect. Acid washing resulted in a slip-hardening behavior, which improved the pullout energy significantly. The zinc phosphating treatment exhibited the lowest average bond strength increase rate. Nanosilica coating was found to considerably improve adhesion; however, it caused fractures as inclined. EDTA electrolyte solution treatment significantly improved the average bond strength in proportion to the surface roughness. By considering the energy absorption capacity, the optimum treatment time of EDTA electrolyte solution was proposed to be less than 6 h.

The importance of inherent inorganics and the surface area of wood char for its gasification reactivity and catalytic activity towards toluene conversion

Gasification char is an effective catalyst for tar reforming because of the abundance of surface active sites, which are available for heterogeneous conversion of hydrocarbons and interactions with the reforming agents. This paper focuses on the importance of certain char properties for the gasification and catalytic reforming. Specifically, the gasification reactivity of spruce char is examined, along with its performance as a catalyst for toluene conversion. The material used for this work was produced via gasification of spruce wood chips in the pilot TwoStage Viking plant (Technical University of Denmark, Risø). To obtain a set of samples with varied surface area characteristics and inorganic content, three pre-treatments were applied to samples of this char: acid washing, steam activation, and high-temperature treatment. The gasification and catalytic experiments performed with the untreated and modified materials revealed that the reactivity of the char during gasification in CO2 depends mostly on the metal content in the sample, whereas the conversion of toluene was insensitive to the char inorganic content, but strongly correlated with the surface area available for heterogeneous reactions with toluene.

Synthesis of a Three-Dimensional Interconnected Oxygen-, Boron-, Nitrogen-, and Phosphorus Tetratomic-Doped Porous Carbon Network as Electrode Material for the Construction of a Superior Flexible Supercapacitor.

To construct a high-performance next-generation carbon-based flexible supercapacitor, high porosity, large mass density, and high flexibility are three significant challenging goals. However, one side always affects another. Herein, high-density tetratomic-doped porous composite carbon derived from sustainable biomaterials is achieved via two-step processes of carbonization and acid-washing treatment. The assembled carbon-based electrodes are highly doped with various heteroatoms (B, O, N, and P) for 33.59 atom %, resulting in abundant porosity, high densities, high pseudocapacitive contribution for 84.5%, and superior volumetric capacitive performance. The fabricated flexible electrode exhibits high flexibility, high mass loading (316 mg cm-3), and remarkable tensile strength (44.6 MPa). Generally, the volumetric performance is key and a significant parameter to appraise the electrochemical characteristics of flexible supercapacitors within a limited space. The aqueous symmetric supercapacitor demonstrates a high volumetric energy density and an excellent power density of 2.08 mWh cm-3 and 498.4 mW cm-3, respectively, along with 99.6% capacitance retention after 20 000 cycles, making it competitive to even some pseudocapacitors.

Porcine Reproductive and Respiratory Syndrome Virus Interferes with Swine Influenza A Virus Infection of Epithelial Cells

Respiratory infections are still a major concern in pigs. Amongst the involved viruses, the porcine reproductive and respiratory syndrome virus (PRRSV) and the swine influenza type A virus (swIAV) have a major impact. These viruses frequently encounter and dual infections are reported. We analyzed here the molecular interactions between viruses and porcine tracheal epithelial cells as well as lung tissue. PRRSV-1 species do not infect porcine respiratory epithelial cells. However, PRRSV-1, when inoculated simultaneously or shortly before swIAV, was able to inhibit swIAV H1N2 infection, modulate the interferon response and alter signaling protein phosphorylations (ERK, AKT, AMPK, and JAK2), in our conditions. SwIAV inhibition was also observed, although at a lower level, by inactivated PRRSV-1, whereas acid wash treatment inactivating non-penetrated viruses suppressed the interference effect. PRRSV-1 and swIAV may interact at several stages, before their attachment to the cells, when they attach to their receptors, and later on. In conclusion, we showed for the first time that PRRSV can alter the relation between swIAV and its main target cells, opening the doors to further studies on the interplay between viruses. Consequences of these peculiar interactions on viral infections and vaccinations using modified live vaccines require further investigations.

Synergy of Hydrothermal and Organic Acid Washing Treatments in Chinese Fir Wood Vinegar Preparation.

Pretreatment is an effective method to change the pyrolysis behavior and improve the product properties of biomass. In this study, the effects of hydrothermal treatment (HTT) and hydrothermal treatment combined with organic acid washing (HTT-A) on Chinese fir waste (CF) pyrolysis and preparation of wood vinegar (WV) were investigated. The results indicated that HTT promoted the decomposition of hemicellulose and disrupted the chemical structure, while HTT-A partly removed the lignin as well as hemicellulose. HTT-A showed a more effective removal efficiency of alkali/alkaline earth metals (AAEMs) than HTT. Both HTT and HTT-A delayed the initial decomposition temperature but promoted the pyrolysis process. The yields of WVs increased after HTT and HTT-A, while the moisture contents reduced, obviously. HTT increased the relative contents of phenols from 47.04 to 59.85% but reduced the relative contents of acids from 24.31 to 18.38%, whereas HHT-A reduced the relative contents of phenols but increased those of aldehydes. In addition, HTT and HTT-A showed the different effects on chemical compositions of WVs, especially for phenolic and acid compounds. This study indicated that HTT and HTT-A were the efficient methods to produce WVs with target chemical components, which would be conducive to the efficient application of WVs.

Surface Modification of Cured Inorganic Foams with Cationic Cellulose Nanocrystals and Their Use as Reactive Filter Media for Anionic Dye Removal.

In this work, a surface cationized inorganic–organic hybrid foam was produced from porous geopolymer (GP) and cellulose nanocrystals (CNCs). GPs were synthesized from alkali-activated metakaolin using H2O2 as a blowing agent and hexadecyltrimethylammonium bromide (CTAB) as a surfactant. These highly porous GPs were combined at pH 7.5 with cationic CNCs that had been synthesized from dissolving pulp through periodate oxidation followed by cationization in a deep eutectic solvent. The GP-CNC hybrid foams were employed as reactive filters in the removal of the anionic dye, methyl orange (MO; 5–10 mg/L, pH 7). The effects of a mild acid wash and thermal treatments on the structure, properties, and adsorption capacity of the GPs with CNCs and MO were investigated. The CNCs aligned as films and filaments on the surfaces of the neutralized GPs and the addition of CNCs improved MO removal by up to 84% compared with the reference sample. In addition, CTAB was found to disrupt the attachment of CNCs on the pores and improve adsorption of MO in the GPs with and without CNCs.

PURIFICATION OF PHOSPHOGYPSUM FOR USE AS CEMENT RETARDER BY SULPHURIC ACID TREATMENT

Phosphogypsum is a by-product of the wet phosphoric acid production. In this study, chemical compositions of phosphogypsum waste (PG) in Hai Phong diammonium phosphate plant (DAP1) and Lao Cai diammonium phosphate plant (DAP2) in Vietnam were surveyed for the purpose of gypsum recovery by P2O5, F removal to meet TCVN11833 for use treated gypsum as cement retarder. Studies of impurities P2O5, F, TOC removal by sulfuric acid 10 % at 28 0C was presented. The results found that the combination of a low concentration of sulfuric acid treatment, washing, lime neutralizing, and thermal treatment was successful in Phoshogypsum treatment for use as cement retarder. The cement test proved that treated PG could partially replace natural gypsum as a retarder.Keywords: phosphogypsum treatment, phosphorus pentoxide removal, calcium sulfate transition phase, cement retarder.