Alkaline Washing Research Articles

Impacts of alkaline washing pretreatment on municipal solid waste incineration fly ash (MSWI FA) and resulting geopolymers

The safe disposal and utilization of municipal solid waste incineration fly ash (MSWI FA) has emerged as a crucial challenge, primarily due to elevated levels of heavy metals and chlorides. In this study, the influence of key factors in different pretreatment methods on the physicochemical properties of MSWI FA was analyzed, and the effects and mechanism of different pretreatment methods on the resulting geopolymers were studied. Under the conditions of a liquid-solid ratio (L/S) of 7 mL/g, a rotational speed of 500 r/min, and a stirring time of 20 min, the alkali washing with 1 mol/L NaOH solution exhibited better effect than water washing. The total content of chlorides and the content of soluble chloride in AFA (MSWI FA with alkali washing) were 1.53 % and 0.85 %, respectively. Alkali washing had a greater influence on the migration of heavy metals from MSWI FA to filtrate than water washing. Meanwhile, alkaline washing exhibited better effect in calcium retention and sulfur removal. The pretreatment process enhanced the gel formation in geopolymers, subsequently exerting a significant influence on the compressive strength and leaching concentration of heavy metals. Thermogravimetric analysis showed the bound water content in AG (8.46 %) was the greatest in all simples, indicating that exerted the most pronounced impact on the gel formation during geopolymerization. And, the lower ratio of Si-O-Na to Si-O-T in AG (0.20) indicated a longer geopolymeric chains, which explained the higher compressive strength of geopolymers during the initial curing period. This article provides a new pretreatment method to promote the resource utilization of MSWI FA.

A method for high value-added utilization of BOF slag: Towards slag recycling and phosphorus recovery

Basic oxygen furnace (BOF) slag is a bulk solid waste generated in steelmaking process, containing large amounts of valuable components. However, its utilization ratio is not high in China, resulting in serious environmental pollution and resource waste. To realize the high value-added utilization of BOF slag, selective leaching was adopted to separate the P-bearing dicalcium silicate from slag. The leaching ratios of Si and P were much higher than those of Fe and Mn. The oxidized BOF slag exhibited a superior leaching of P. 85.6 % of P and 68.0 % of Si was separated from BOF slag while the leaching ratio of Fe was negligible in the HCl solution at pH 3. Almost all the dicalcium silicate was removed by leaching whereas the dicalcium ferrite remained. The tailing containing 46.1 % Fe2O3 and 32.9 % CaO can be reused as a steelmaking feedstock. The leachate was treated to extract phosphates by chemical precipitation. Approximately 98 % of phosphate ions was precipitated in the leachate when the pH increased to 8. Some silica gel was removed from the precipitate via alkaline wash and a phosphate containing 28.4 % P2O5 was recovered, which could be used as a phosphorus fertilizer. This study provided a method for BOF slag recycling in steelmaking process and phosphorus recovery.

Transformation of Fly Ash-Based Oxide Particles into a Functional Silica-Alumina Aerogel and Its Potential Application as an Anti-icing Surface.

Lightweight, surface hydrophobic, highly insulating, and long-lasting aerogels are required for energy conservation and ice-repellent applications. Here, we present the conversion of fly ash to a silica-alumina aerogel (SAA) by utilizing its high silica content. The extracted silica component replaces expensive precursors typically used in conventional aerogel production. Ice adhesion performance was compared to that of polypropylene (PP), an insulating commodity polymer. First, we removed some salt impurities and heavy metals via water and alkaline washing protocols. Then, we produced SAA via the ambient pressure drying method by using trimethylchlorosilane (TMCS) as an adhesion promoter. The newly produced SAA has a surface area of 810 m2 g-1 and shows hydrophobic properties with a contact angle of 140 ± 5°. The thermal conductivity of SAA is 0.0238 W m-1 K-1 with C P = 1.1922 MJ m-3 K-1. The ice adhesion strength of the PP substrate was calculated as 188.30 ± 51.24 kPa, while the ice adhesion strength of the SAA was measured as 1.21 ± 0.40 kPa, which was about 150 times lower than that of PP. This indicated that SAA had icephobic properties since ice adhesion strength was less than 10 kPa. This study demonstrates that fly ash-based SAA can be utilized as an economical material with a large surface area and exceptional thermal insulation capacity and is free of harmful compounds (heavy metals), making it potentially suitable as an anti-ice thermal insulation material.

Bond strength of epoxy-based composites at the interface with surface deposited metal layer: A comparative study with different dimensional fillers

With the complexity of the working environment, pure epoxy resin can no longer meet the requirements, and the weak interfacial bonding between metal layer and epoxy-based composites limits its development. In this work, we propose a novel molecular grafting modification technique by using the active functional groups of polymers, which can apply to epoxy-based composites with various fillers to improve the adhesive strength of the interface between the metal film and matrix. 3D surface profile and surface wettability were used to characterize the effect of fillers on the surface of epoxy composites. Scanning electron microscope (SEM) and Raman spectroscopy were utilized to judge the interface failure modes of the composites. Peeling test and surface-enhanced Raman scattering (SERS) were conducted to examine how fillers affected adhesion. The results showed that silane grafting substantially improved the bonding between the epoxy-based composite matrix and the metal layer without the need for alkaline washing and palladium (Pd) activation steps on the substrate. The average adhesive strength can reach a maximum of 17.76 N/cm. The study also revealed the effect of filler size on the interfacial adhesive strength. The interfacial adhesive strength was increased by two dimensional lamellar materials, decreased by one-dimensional tubular materials, and remained unaffected by zero-dimensional spherical materials. This study may have positive implications for improving interfacial bonding between metal and polymer composite surfaces.

Preparation of active zinc oxide from zinc-containing dust and synergistic recovery process of valuable elements

Zinc-containing dust generated from the iron and steel industry is enriched with a large amount of heavy metal substances and rare elements, which is a hazardous waste and a secondary resource. In this study, a new process for the preparation of active zinc oxide and synergistic recovery of valuable elements using zinc-containing dust was proposed. Firstly, a fire process was used to make the valuable components such as Zn, Cd, K, Na, Pb, Bi, In and Sn secondary enriched in the zinc-rich dust. Then the leaching and recovery of K (99.74 %) and Na (98.12 %) were realized by alkaline washing method taking advantage of the solubility difference. Thermodynamic analysis showed that controlling the pH of the leaching system could realize the selective separation of the valuable components. The experimental results showed that the leaching rates of Zn and Cd reached 86.95 % and 92.28 %, respectively, under the optimal experimental conditions, while Pb, Sn, Bi and In were enriched in the neutral leaching slag. Cd sponge (70.3 %) was obtained after the neutral leach solution was treated by Zn powder replacement process. The purified zinc sulfate solution was used to prepare active zinc oxide (97.04 %) by direct precipitation at a molar ratio of CO32–/Zn2+ of 1.15 and a temperature of 50 °C. The average particle size of the product was 21.95 nm, which was in accordance with the industry standard. Neutral leaching slag realized Bi (91.5 %), Sn (71.01 %) and In (94.0 %) in high acid leaching process, and Pb was enriched in slag in the form of PbSO4. The high acid leach solution is hydrolyzed, extracted and replaced to obtain BiOCl, crude tin and crude indium. This process realizes the comprehensive recovery and high-value utilization of various valuable elements in zinc-containing dust sludge, and has significant environmental, economic and social benefits.

Effect of the Inorganic Modification Mode on the Mechanical Properties of Rubber Recycled Concrete.

The reasonable and effective application of waste tires and discarded concrete in concrete is an important branch of green concrete development. This paper investigates the effects of the inorganic modification mode on the basic mechanical properties of rubber recycled concrete based on indoor tests. Inorganic modification, such as water washing, acid washing, and alkaline washing modification, was mainly used to treat and modify rubber particles. The factors affecting the compressive strength, the splitting tensile strength, the flexural strength, the axial compressive strength, and the modulus of elasticity of modified rubber recycled concrete were analyzed. The study results show that the incorporation of recycled aggregates and rubber reduced the mechanical properties of concrete, with the compressive and splitting tensile strengths showing the greatest reductions of 27.36% and 27.24%, respectively. Three modification methods significantly improved the mechanical properties of rubber recycled concrete. The alkali washing modification method was the most effective, maximally improving the mechanical properties of rubber recycled concrete by 7.53-15.51%. The effects of the three modifications on the mechanical properties of concrete were ranked as follows: alkali washing > acid washing > water washing. This study provides a data basis for the practical application of rubber recycled concrete in engineering and a test basis for the development of green concrete.

Hydrodechlorination of trifluoro-trichloroethane to chlorotrifluoroethylene: Revealing the deactivation mechanism and regeneration strategy of Pd-Cu/AC catalyst

Chlorotrifluoroethylene (CTFE) is a vital fluorinated olefinic monomer produced through the catalytic hydrodechlorination of trichlorotrifluoroethane (CFC-113), an eco-friendly process. However, hydrodechlorination catalysts for olefin production often suffer from poor stability. The Pd/AC catalyst and Pd-Cu/AC catalyst prepared by co-impregnation method exhibited poor stability, Pd-Cu/AC catalyst with CFC-113 conversion dropping to around 37% after 50 h of hydrodechlorination reaction. BET, TEM, XPS and XRD of fresh and deactivated Pd /AC catalysts indicate that the deactivation of Pd /AC catalysts is due to high-temperature agglomeration of Pd. Comparative analysis of fresh and deactivated Pd-Cu/AC catalysts using BET, TEM, and TG techniques revealed decreased dispersion of active sites, reduced surface area, catalyst aggregation deactivation, and a significant decrease in Cu content. Furthermore, the results of NH3-TPD revealed that the acid sites of the catalyst increased significantly. XRD spectra indicated the formation of new species, basic copper chloride (Cu2(OH)3Cl), during the reaction. As the reaction progressed, these new species agglomerated, leading to a gradual loss of catalyst activity. Moreover, the deactivated catalyst was successfully reactivated using a simple alkaline washing method.

Alkaline electrolyzed water AS a potential green degreaser for meat processing stainless steel surface

AbstractThe meat industry faces significant challenges regarding removing fat, oil, and grease (FOG) residues from meat processing stainless steel surfaces, compounded by limited resources and inadequate cleaning knowledge. As an innovative solution to these difficulties, alkaline electrolyzed water (AlEW), a sustainable green degreaser, is proposed to replace the traditional alkaline wash. AlEW is produced through two–chamber (membrane) electrolysis at the cathode. AlEW with a strong reducing potential (−800 to −900 mV), high pH (10.0–11.5), and high dissolved oxygen are used to remove FOG residues from meat processing stainless steel surfaces. Our comprehensive analysis highlights the advantages of AlEW as a sustainable alternative to conventional degreasers for the meat industry, including ease of use, no storage requirements, and reduced costs for wastewater treatment. Our findings underscore AlEW's potential to improve the meat industry's quality, safety, and environmental sustainability. This review contributes to ongoing discussions about sustainable food industry solutions, aligning with the 2030 Agenda for Sustainable Development goals. In conclusion, AlEW is a promising alternative to conventional degreasers, advancing sustainability in the meat industry.Practical ApplicationsThis research introduces an innovative solution to a significant challenge in the meat processing industry—effective removal of fat, oil, and grease residues from equipment surfaces. Traditional methods involving costly and environmentally harmful chemicals have drawbacks. Our study proposes the use of alkaline electrolyzed water (AlEW) as a green degreaser. AlEW, generated by passing electric current through saltwater, exhibits high alkalinity that dissolves residues efficiently. This eco‐friendly approach not only ensures thorough cleaning but also reduces costs and addresses environmental concerns. By offering a sustainable and cost‐effective alternative, AlEW has the potential to revolutionize cleaning practices in the meat industry, enhancing food safety, operational efficiency, and sustainability. This advancement holds promise for wider adoption, benefiting both producers and consumers alike.

Application of Magnetic Nanocomposites in Water Treatment: Core–Shell Fe3O4 Material for Efficient Adsorption of Cr(VI)

Since ferric tetroxide (Fe3O4) has strong magnetic properties, coating amorphous silica (SiO2) with Fe3O4 nanoparticles can protect the magnetic Fe3O4 particles and form a new magnetic adsorbent with a core–shell structure and small pore size, the strong magnetic properties of which can efficiently solve the problem of the difficult separation and recovery of heavy metals from wastewater affecting present-day adsorption techniques. In this paper, SiO2-coated nanoscale Fe3O4 particles were prepared using a modified sol–gel method for the adsorption and removal of Cr(VI) at lower pollution concentrations. The adsorbent was characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and a magnetic vibration sample magnetometer (VSM), and its adsorption performance was systematically investigated in terms of initial concentration, pH, and temperature. The experiments showed that the adsorption effect was optimal when the initial solution Cr(VI) was 40 mg/L. The adsorption capacity increased with a decrease in the initial solution’s pH and decreased with an increase in temperature. Furthermore, the adsorption capacity of Cr(VI) at low concentrations was much higher than that of other conventional adsorbents, the calculated unit adsorption capacity reached 13.609 mg·g−1, and the removal rate reached 64.8%. In addition, the strong magnetic nanocomposite (MS) had excellent recoverability, could achieve desorption via alkaline washing, and retained about 75% of the initial adsorption capacity after six cycles.

Synthesis of CuAl-LDHs by Co-Precipitation and Mechanochemical Methods and Selective Hydrogenation Catalysts Based on Them

The paper presents the results of the synthesis and study of CuAl layered double hydroxides (LDHs) as well as their application as catalysts for the selective hydrogenation of crotonaldehyde. Phase-homogeneous LDHs were obtained by co-precipitation and mechanochemical methods, and critical parameters ensuring the formation of the target product were identified. In the case of coprecipitation, the formation of LDH is most affected by the pH of the reaction medium and the CO32−/Al3+ ratio. The optimal CO32−/Al3+ ratio is ca. 0.5–0.8 and pH 9.5–10.0. When mechanochemical synthesis is used, at 500 m·s−2 and 60 min, it is possible to obtain a single-phase CuAl LDH, whereas at higher energies, LDH is destroyed. The mechanochemical method makes it possible not only to reduce the synthesis time and the amount of alkaline wash water but also to obtain more dispersed copper particles with a higher hydrogenating activity. The conversion of 2-butenal (T = 80 °C, P = 0.5 MPa, 180 min, ethanol) for this sample was 99.9%, in contrast to 50.5% for the catalyst obtained by co-precipitation. It is important that, regardless of the conversion, both catalysts showed high selectivity (S = 90–95%) for the double bond hydrogenation.

Removal Effectiveness for Washing Ce(IV), U(VI), and Zr(IV) Ions from Contaminated Purex Solvent by Hydrazine Carbonate

The contaminated solvent from the Purex process is washed with alkaline detergents such as sodium carbonate, which generates a large amount of secondary wastes. Therefore, hydrazine carbonate as a salt-free reagent deserves to be studied in depth. In this study, the Ce(IV), U(VI), and Zr(IV) metal ions in organic phases containing dibutyl phosphate (HDBP) of 30% tributyl phosphate (TBP)–dodecane were washed with hydrazine carbonate. The effects of the oscillation time (1 to 15 min); temperature (25°C to 85°C); cumulative number of washes (one to four times); mass fraction of hydrazine carbonate (0.1% to 20%); volume ratio of the aqueous phase to the organic phase (0.2 to 5); HDBP concentration (0 to 0.4 M); HNO3 concentration (0.05 to 8 M); and concentration of Ce(IV), U(VI), and Zr(IV) metal ions on the removal percentages of Ce(IV), U(VI), and Zr(IV) metal ions in polluted solvents were studied. The results showed that when the organic phase containing 0.02 M HDBP was washed three times with 5% hydrazine carbonate at 25°C, the removal percentages of the Ce(IV), U(VI), and Zr(IV) ions were 96%, 98%, and 94%, respectively. Meanwhile, the retention concentrations of the three in the organic phase were 35, 28, and 78 mg/L, respectively. The increase of the mass fraction of hydrazine carbonate enhances the removal of the metal ions from the organic phase into the aqueous phase. High acid is not conducive to alkaline washing of metal ions. The increase of HDBP concentration not only promotes extraction but also increases the retention capacity of the organic phase and has the most significant effect on Zr(IV). U(VI) promotes the preferential washing of Zr(IV) while Ce(IV) increases the metal retention concentration of Zr(IV) in the organic phase.

Screening the Impact of Surfactants and Reaction Conditions on the De-Inkability of Different Printing Ink Systems for Plastic Packaging.

One of the major applications (40% in Europe) of plastic is packaging, which is often printed to display required information and to deliver an attractive aesthetic for marketing purposes. However, printing ink can cause contamination in the mechanical recycling process. To mitigate this issue, the use of surfactants in an alkaline washing process, known as de-inking, has been employed to remove printing ink and improve the quality of recyclates. Despite the existence of this technology, there are currently no data linking the de-inking efficiency with typical printing ink compositions. Additionally, it is necessary to investigate the de-inking process under the process parameters of existing recycling plants, including temperature, NaOH concentration, and retention time. This study aims to evaluate the performance of commonly used printing inks with different compositions under various washing scenarios for plastic recycling in conjunction with different de-inking detergents containing surfactants or mixtures of surfactants. The results indicate that the pigments applied to the ink have no significant effect on the de-inking process, except for carbon black (PBk 7). Nitrocellulose (NC) binder systems exhibit high de-inkability (over 95%) under the condition of 55 °C and 1 wt.% NaOH. However, crosslinked binder systems can impede the de-inking effect, whether used as a binder system or as an overprint varnish (OPV). The de-inking process requires heating to 55 °C with 1 wt.% NaOH to achieve a substantial effect. Based on the findings in this work, breaking the Van der Waals forces, hydrogen bonds, and covalent bonds between the printing ink and plastic film is an essential step to achieve the de-inking effect. Further research is needed to understand the interaction between surfactants and printing inks, enabling the development of de-inkable printing inks and high-performance surfactants that allow for de-inking with less energy consumption. The surfactant and NaOH have a synergistic effect in cleaning the printing ink. NaOH provides a negative surface charge for the adsorption of the cationic head of the surfactant and can hydrolyze the covalent bonds at higher concentrations (>2 wt.%).

Microbubble-Assisted Cleaning-in-Place Process for Ultrafiltration System and Its Environmental Performance

Membrane filtration is a key technology in dairy processing for the separation of dairy liquids to clarify, concentrate, and fractionate a variety of dairy products. Ultrafiltration (UF) is widely applied for whey separation, protein concentration and standardization, and lactose-free milk production, though its performance can be hindered by membrane fouling. As an automated cleaning process commonly used in the food and beverage industries, cleaning in place (CIP) uses large amounts of water, chemicals, and energy, resulting in significant environmental impacts. This study introduced micron-scale air-filled bubbles (microbubbles; MBs) with mean diameters smaller than 5 μm into cleaning liquids to clean a pilot-scale UF system. During the UF of model milk for concentration, cake formation was identified as the dominant membrane fouling mechanism. The MB-assisted CIP process was conducted at two bubble number densities (2021 and 10,569 bubbles per mL of cleaning liquid) and two flow rates (130 and 190 L/min). For all the cleaning conditions tested, MB addition largely increased the membrane flux recovery by 31-72%; however, the effects of bubble density and flow rate were insignificant. Alkaline wash was found to be the main step in removing proteinaceous foulant from the UF membrane, though MBs did not show a significant effect on the removal due to the operational uncertainty of the pilot-scale system. The environmental benefits of MB incorporation were quantified by a comparative life cycle assessment and the results indicated that MB-assisted CIP had up to 37% lower environmental impact than control CIP. This is the first study incorporating MBs into a full CIP cycle at the pilot scale and proving their effectiveness in enhancing membrane cleaning. This novel CIP process can help reduce water and energy use in dairy processing and improve the environmental sustainability of the dairy industry.

Physicochemical and pozzolanic properties of municipal solid waste incineration fly ash with different pretreatments.

Swelling caused by gas generated from municipal solid waste incineration fly ash (MSWIFA) when it is mixed with alkali limits its uses. Besides, the leaching of anion salts and heavy metals contained in MSWIFA poses a high risk to environment. This study presents the feasibility of a one-step alkaline washing, one-step thermal quenching and two-step combination of alkaline washing and thermal quenching pretreatment methods in altering the key properties of MSWIFA for promoting its reusability. It was found that apart from H2(gas), NH3(gas) was also generated during the alkaline washing of the MSWIFA. Besides, pretreatments led to the reduction in particle size, the increase in pore volume and specific surface area of the MSWIFA, as well as the removal of chloride and sulfate anions. All the pretreatment methods were effective in reducing leaching of heavy metals to below levels of nonhazardous waste except Cd and Pb with alkaline washing. Furthermore, both the chemical Frattini test and the mechanical activity index test showed improvement in pozzolanic activities of the MSWIFA after the pretreatments. Overall, the combined pretreatment method was most effective in eliminating gas emission, and reducing leaching of metal ions and anions from the ash, while enhancing the pozzolanic activity of the ash.

Remediation of Micro-Pollution in an Alkaline Washing Solution of Fly Ash Using Simulated Exhaust Gas: Parameters and Mechanism

Currently, there is an urgent need to remediate heavy metals (HMs) and high alkalinity in the washing solution of fly ash (FA). This study investigated the remediation with simulated exhaust gases of two CO2 partial pressure and revealed the removal efficiency of target pollutants, mainly including Pb ions. The results verify that under the preferred conditions of 25 °C and 15 mL/min flow rate, bubbling two kinds of simulated flue gases could efficiently remove 97.9–99.2% of Pb ions. Moreover, the initial 40 min removal of Pb ions fits in a way with a pseudo-first-order equation. Based on the thermodynamic parameters, we infer that the removal of Pb ions was a spontaneous, exothermic, and entropy-decreasing process. Furthermore, residual HMs and terminal pH after remediation of the FA washing solution basically met the regulatory threshold values of the integrated wastewater discharge standard in China (GB 8978−1996). Additionally, the particles obtained from the washing solution of FA were identified as CaCO3, which was mainly composed of vaterite and calcite crystalline. This study provides a fundamental guide for remediating multiple pollutants in the washing solution of FA and simultaneously sequestrating carbon emissions from power plants and industries.

Cyclic growth and tillering of layered polycrystalline zinc hydroxide sulfate and the resulting dendritic fractals

Two-dimensional dendritic fractals of layered zinc hydroxide sulfate (LZHS) were allowed to grow on a porous ZnO substrate-coated glass slide in an aqueous ZnSO4 solution through the dissolution-redeposition process. The generated LZHS seeds with polycrystalline structure gradually evolved into two-dimensional dendritic fractals with a diameter of 50∼100 μm through a plant-like growth mode involving tillering and the formation of layered tiller buds at branch ends. Such tiller mechanism is proposed to explain the evolution of LZHS fractals based on results obtained by the scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and energy dispersive X-ray detection. The synthesized polycrystalline LZHS fractals can be topologically converted into hierarchical nanostructured zinc oxide by thermal pyrolysis combined with an alkaline wash process. After the modification by octyltrimethoxysilane, the topological zinc oxide surfaces, corresponding to the immersion time of 2, 4 and 6 h, showed superhydrophobic property with a water contact angle of 153.4°, 157.6°, and 164.7°, respectively. The enhanced hydrophobicity of zinc oxide films compared with the porous ZnO substrate surface is mainly attributed to the topological fractal morphologies and hierarchical nanostructures.

Ecological dyeing of acrylic yarn with colorant derived from natural lac dye

In recent years, the application of natural dyes in textile coloration has attracted significant study interest. In this current study, the bio-based dyeing of synthetic textile fiber, specifically acrylic yarn, with natural lac dye was investigated. The yarn was dyed using a meta-mordanting technique. The dyeing parameters, including temperature, time, pH of the dye bath, dye concentration, mordant type, and mordant concentration, were examined. Two eco-mordants, aluminium sulfate and ferrous sulfate, are compared against an eco-restricted copper sulfate in terms of color strength and fastness. The results demonstrated that the meta-mordanting technique can be used to dye acrylic fiber using natural lac dye. The optimum dyeing results were achieved using an acidic pH (2-3) and a temperature of 100℃ for 40 min of dyeing time. The color strength of the dyed samples was enhanced by the application of mordants. Color uniformity was achieved by controlling the temperature gradient in the Tg region. In terms of color change, the wash fastness properties of the dyed samples were found to be poor to moderate due to the dye's susceptibility to alkaline washing. In terms of color fastness to rubbing and light, ferrous sulfate and copper sulfate produced superior results.

Coral-like TiO2/organosilane hybrid particles with rapid adsorption of methyl orange

TiO2/Bis[3-(trimethoxysilyl)propyl]amine (BTMSPA) hybrid particles with a coral morphology were prepared using a facile method and used for the removal of methyl orange (MO) dye from wastewater. The structure of the TiO2/BTMSPA particles and the adsorption mechanism for MO were analyzed. Meanwhile, the adsorption isotherms and kinetics of MO on the particles were also studied. During the preparation of the TiO2/BTMSPA hybrid adsorbent, some of the BTMSPA linked the TiO2 particles to form a skeleton, while the remaining BTMSPA grew in situ on the TiO2 surface into nanopapillae, forming a micro/nano-porous coral-like structure. The secondary amine group in BTMSPA acted as an adsorbent via a single molecular layer chemisorption mechanism. In a neutral environment, the decolorization rate of MO was 83.3% after 1 min, eventually reaching 91.2 %. The maximum adsorption capacity was determined to be 90.3 and 369.3 mg/g under neutral and acidic conditions, respectively. Furthermore, the hybrid particles also showed excellent performance for the removal of other anionic dyes and such as methyl blue and amaranth red, with a 100 % decolorization rate. The adsorbent had good universality and excellent regeneration performance after an alkaline washing step.

Preparation of molded biomass carbon from coffee grounds and its CH4/N2 separation performance

Coffee grounds are promising precursors for excellent porous carbon adsorbents. During the preparation of the porous carbons, sodium silicate was used as a binder and pore-forming agent, and extrusion molding technology was used to prepare them in a columnar form. After carbonization, steam activation and silica removal by alkaline washing, high-strength columnar porous carbon adsorbents (CGCs) were obtained. Their CH4/N2 separation performance was studied by multicomponent breakthrough experiments. The Brunauer-Emmett-Teller (BET) surface area of CGC-1.5 (where 1.5 is the mass ratio of a 9 wt% sodium silicate aqueous solution to the coffee grounds) is 527 m2·g-1. Both the N2 and CO2 adsorption isotherms show that the CGCs are rich in micropores and mesopores, with the micropores size mainly centered at about 0.48 nm. FT-IR results show that CGC-1.5 has abundant oxygen-containing functional groups. At 298 K and 0.1 MPa, its equilibrium adsorption capacity for CH4 is 0.87 mmol·g-1, and the separation selectivity for a CH4/N2 mixture (3/7, vol/vol) is 10.3, which is better than most biomass-based porous carbon adsorbents and crystalline materials. Dynamic breakthrough tests show that CGC-1.5 has an excellent CH4/N2 separation performance at both high and atmospheric pressures. The dynamic selectivities at 298 K, 0.11 and 0.5 MPa are 10.4 and 17.9, respectively. The adsorption capacity is unchanged after 10 adsorption-desorption cycles. The mechanical strength of CGC-1.5 is as high as 123 N·cm-1, which meets the criteria of industrial applications.

Phosphonate removal from membrane concentrate by electro-coagulation

In this study, the efficiency of electrocoagulation (EC) with iron electrodes was applied to remove two phosphonates, 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) and nitrilotris(methylene) triphosphonic acid (NTMP) from concentrates. This work provides a detailed description of the experimental procedure and results on phosphonate removal and recovery from different electrolytes, including synthetic and real reverse osmosis (RO) membrane concentrates. This research showed high selectivity of EC, removing 100% and 80% of the NTMP and the HEDP respectively, confirming no competition with sulfates, nitrates, or silica. When experimenting with other electrolytes, calcium showed to be critical in enhancing the flocculation process, while calcium carbonate precipitation contributed to capturing the phosphonates from the concentrate. The produced iron oxide (sludge) was confirmed as goethite and akaganéite, and finally transformed into hematite, indicating the oxidation from Fe2+ to Fe3+ during the EC process. After the iron precipitate collection, an alkaline wash of the sludge was enough to recover 100% of the initial phosphorus from the NTMP phosphonate. However, further research is needed to optimize the recovery procedure and to improve the results with the HEDP. 70 and 140 A·m−2 current densities were optimal to bring HEDP and NTMP concentrations down to 32 μM (1 mg·L−1) in only 30 and 10 min respectively. In these conditions, the operational costs, 1.10 and 0.03 €·m−3 of treated concentrate, were estimated for HEDP and NTMP respectively. Even when EC has been widely studied for phosphate removal, this technique has been barely applied to treat concentrates containing phosphonate-based antiscalants. EC opens new possibilities for phosphonates and phosphorus to be removed and recovered respectively from membrane and other concentrates.