Alkaline Materials Research Articles

Effect of cullet on firing temperature and dielectric properties of porcelain insulator

Porcelain insulators prepared from locally available ceramic materials, such as Hosaena clay, quartz, partially replaced feldspar by cullet (rich in alkaline materials). The physical and electrical properties, such as water absorption, apparent porosity, bulk density, linear shrinkage, and dielectric strength as a function of firing temperature, were evaluated. The XRD and AAS measurement results show Hosaenna clay mainly belongs to kaolinite minerals with a sufficient SiO2 (45.60wt. %), Al2O3 (35.52wt. %), and it possesses reasonable plasticity nature. The SEM and Electrical properties measurement shows the porcelain insulators fired at 1150 °C & 1200 °C showed homogenized primary and secondary mullite with optimum glassy phase and good dielectric strength for practical applications. The primary & secondary mullite and glassy phases were grown early at a firing temperature of 1150 and 1200 °C, due to the partial replacement of feldspar by cullet. The porcelain insulator prepared from the composition of 45%clay, 35%feldspar, 10%quartz and 10%cullet and fired at 1200 °C showed dielectric strength 8.9kv/mm, water absorption (0.459%), apparent porosity (1.530%), bulk density (4.29 g/cm3), and linear shrinkage (4.18%). Therefore, incorporating economic alkaline materials such as cullet to improve the alkalinity of the locally available clay materials, Hosaenna clay, Arero feldspar, and Arero quartz reduces the firing temperature with excellent dielectric strength.

Use of aircraft in ocean alkalinity enhancement

Ocean Alkalinity Enhancement (OAE) is a proposed Negative Emissions Technology (NET) to remove atmospheric CO2 through the dispersion of alkaline materials (e.g.: calcium hydroxide, slaked lime, SL) into seawater, simultaneously counteracting ocean acidification. This study considers aircraft discharge of SL and its consequent dry deposition, extending to the marine environment a technique used in freshwater. A feasibility analysis assesses potential, costs, benefits, and disadvantages, considering scenarios with different assumptions on aircraft size, discharge height and duration, and wind conditions.Due to the small size of SL particles (median diameter 9 μm), the dispersion from aircraft is highly enhanced by wind drift; the smallest SL particles may drift thousands of kilometres, especially if discharged from elevated altitudes. This could pose problems related to powders particles settling on remote lands.Although calcium hydroxide maximum concentration into water (from 0.01 to 82 mg L−1) is for almost all the scenarios lower than the most stringent threshold for the ecosystem impacts on a 96-h exposure, the ecologically sensitive sea surface microlayer (SML) should be considered in detail.The high CO2 emissions of the Landing to Take-Off Cycle (LTO) of the aircraft and their limited payload lead to a significant CO2 penalty, ranging in analysed scenarios between 28% and 77% of the CO2 removal potential; very fast discharge could reduce the penalty to 11% - 32%. Preliminary cost analysis shows that the cost of the SL discharge through aircraft is high, between € 30 and € 1846 per ton of CO2 removed (neglecting the lime cost), substantially higher than the cost for discharge by surface vessels resulting from previous studies, which restricts the practical use of this strategy.

Pengaruh Penambahan Serat Kawat Bendrat Terhadap Kuat Lentur Beton Geopolimer

Currently, innovation continues to be developed to replace cement with other materials so that the use of cement as a building material can be reduced. Utilization of coal waste (fly ash) is an alternative to subtitude cement. From previous studies, fly ash mixed with alkaline materials in the form of NaOH and Na2SiO3 in a ratio of 1:5 can produce geopolymer concrete. This geopolymer concrete research was continued by adding bendrat wire fibers into the geopolymer concrete mixture. The method used in testing the aggregate, testing the compressive strength of normal concrete K225, testing the flexural strength of normal concrete and geopolymer concrete refers to SNI. Another additional material that is mixed is bendrat wire fiber. The research was carried out in the form of making flexible beams of 10 cm x 10 cm x 50 cm with fiber variations of 0%, 0.5%, and 1,0% at the age of 14 and 28 days. The results of the flexural strength test of the BN beam at the age of 28 days can withstand loads than BG. The average flexural strength obtained with variations of BN, BN+SB 0.5% and BN+SB 1.0% respectively were 2.796 MPa, 3.113 MPa, and 3.879 MPa. The results of testing the average flexural strength of geopolymer concrete beams at 28 days, obtained variations of BG, BG+SB 0.5%, and BG+SB 1.0% respectively were 0 MPa, 0.055 MPa and 0.104 MPa. In addition, geopolymer concrete cannot be used as a beam and the addition of bendrat wire fiber to geopolymer concrete cannot withstand the tensile load on the concrete.

Efficiency and bacterial diversity of an improved anaerobic baffled reactor for the remediation of wastewater fromalkaline-surfactant-polymer (ASP) flooding technology.

Alkaline-surfactant-polymer (ASP) flooding technology is used to maximize crude oil recovery. However, the extensive use of alkaline materials makes it difficult to treat the water used. Here, an improved multi-zone anaerobic baffled reactor (ABR) using FeSO4 as electron acceptor was employed to treat the wastewater from ASP flooding technology, and the effects on major pollutants (hydrolyzed polyacrylamide, petroleum substances, surfactants suspended solids) and associated parameters (chemical oxygen demand, viscosity) were evaluated. Gas chromatography-mass spectrometry (GC-MS) was used to follow the degradation and evolution of organic compounds while high-throughput DNA sequencing was used to determine the bacterial diversity in the ABR. The results obtained after 90 d of operation showed decreases in all parameters measured and the highest mean removal rates were obtained for petroleum substances (98.8%) and suspended solids (77.0%). Amounts of petroleum substances in the ABR effluent could meet the requirements of a national standard for oilfield reinjection water. GC-MS analysis showed that a wide range of chemicals (e.g. aromatic hydrocarbons, esters, alcohols, ketones) could be sequentially removed from the influent by each zone of ABR. The high-throughput DNA sequencing showed that the bacteria Micropruina, Saccharibacteria and Synergistaceae were involved in the degradation of pollutants in the anaerobic and anoxic reaction zones, while Rhodobacteraceae and Aliihoeflea were the main functional microorganisms in the aerobic reaction zones. The results demonstrated that the improved ABR reactor had the potential for the treatment of wastewater from ASP flooding technology.

A consideration on the one-part mixing method of alkali-activated material: problems of sodium silicate solubility and quick setting

This research investigates the properties of alkali-activated materials (AAMs) using sodium metasilicate, with the ratio of SiO2:Na2O equals 1. This study was conducted to achieve the following three aims. Firstly, to understand the solubility mechanism of granular sodium metasilicate pentahydrate (Na2SiO3.5H2O) when used in a one-part mixing method. Secondly, to investigate the properties of AAMs when a sodium metasilicate aqueous solution is used as an alkaline material and as a source of silica. Lastly, to study the retardation effect of sucrose on AAMs. This research used aluminum silicate precursors, such as low-calcium fly ash, slag, and micros silica, alkali activators, such as NaOH pellets and Na2SiO3.5H2O, and standardized sand. The alkaline activators were first dissolved in water using a water bath shaker to achieve the alkaline solution. Sucrose, which is about 2% of the weight of the solid precursors, was added to modify the reaction process between the precursors and the alkaline materials. Four types of samples were prepared: M1, M2, M3, and M4, with the fly ash, slag, and silica fume ratios of 80:20:0, 70:30:0, 75:20:5, and 100:0:0, respectively. The research conducted solubility test of the alkaline materials, flowability, 7-, 28-, 56-day compressive and flexural tests, drying shrinkage test of mortar samples, and the setting tests of pastes with and without sucrose. The results show that the dissolution time of the NaOH was much shorter, whereas Na2SiO3.5H2O needed a solvent with a temperature of around 40 °C to be fully dissolved. This problem of solubility decreases the quality of AAMs formed using the one-part mixing method. Among the mortar samples, the M4 had the highest flow rate, while M3 had the lowest flow rate. M2 had the highest compressive and flexural strength of 43.4 MPa and 6.1 MPa, respectively. The setting time test shows that sucrose retards the reaction process in AAM.

A Study on Strengthening of Concrete Structures

Concrete is the most commonly used building material due to its high strength, moldability, weather-resistant, and fire resistance, among other benefits. In recent years, there has been a growth in the usage of Micro Silica fume. Through the Ore sand Bridge building, records show that Micro Silica was used in the concrete. These fabrics are not only environmentally sustainable, but they also have technological advantages on both new and hardened mortar products. Both goods are agricultural by-products, but their usage decreases the amount of primary raw materials removed from the earth. Latent hydraulic content is micro silica fume and fly ash. It has intrinsic cementation effects, which must be activated. Combining the powder with Portland cement is a popular way to achieve these results. Pozzolana is the name given to pulverized fly ash. These materials may not have intrinsic cementation properties, but a cementation substance is created when mixed with a high alkaline material.

A Study on Strengthening of Concrete Structures

Concrete is the most commonly used building material due to its high strength, moldability, weather-resistant, and fire resistance, among other benefits. In recent years, there has been a growth in the usage of Micro Silica fume. Through the Ore sand Bridge building, records show that Micro Silica was used in the concrete. These fabrics are not only environmentally sustainable, but they also have technological advantages on both new and hardened mortar products. Both goods are agricultural by-products, but their usage decreases the amount of primary raw materials removed from the earth. Latent hydraulic content is micro silica fume and fly ash. It has intrinsic cementation effects, which must be activated. Combining the powder with Portland cement is a popular way to achieve these results. Pozzolana is the name given to pulverized fly ash. These materials may not have intrinsic cementation properties, but a cementation substance is created when mixed with a high alkaline material.

Deterioration of PVC floor covering due alkaline moisture

Concrete as alkaline (pH ∼12,5) and moist material can cause deterioration of polyvinyl chloride (PVC) floor coverings and adhesives through alkaline hydrolysis. Attempts to prevent alkaline hydrolysis have mainly been made by installing PVC floor coverings above ‘dry-enough’ concrete or by using self-levelling low-alkali (pH ∼11…11,5) screeds between concrete and floor coverings. In this study, screed, adhesive and PVC floor covering combinations have been varied by using different floor covering conditions in laboratory test series. VOC emissions have been analysed from flooring material samples (Bulk-VOC). The test samples have been measured for two to three years after installing floor covering. According to the results, a 5 mm layer of low-alkali screed (pH less than 11,5) will effectively protect PVC flooring against alkaline hydrolysis. It could also be concluded that the pH level immediately under floor covering has a better correlation with VOC emission than the RH of concrete in the moment of installing the floor covering.

Application of Rietveld refining method for the production of geopolymeric binders

The activated alkaline materials constitute a group of eco-efficient binders. For materials with a low calcium content, excess free sodium in the alkaline activation process results in efflorescences that weaken the matrix. The excess of free sodium occurs due to failures in the quantification of the reactive fraction consumed by the alkaline activation reactions. The present work compares the conventional dosage methods with the method used by the Rietveld refinement, based on the application of the external standard (EP). To determine the amorphous phase content in the materials, chemical (XRF) and mineralogical (XRD) analyzes were performed on metakaolin and silica fume. The formulations were then dosed using both methods, the molar ratios of Na2O/Al2O3 and SiO2/Al2O3 varying between 0.8 and 1.4. and 3.3–3.6, respectively. The activated alkaline matrix dosed by the EP method exhibited mechanical resistance approximately twice as high as that dosed by the conventional method. The formulation EP-3.6–1.0 showed greater mechanical strength, in addition to high resistance to dissolution in hydrochloric acid (52% of the material remained indissoluble). The optimal SiO2/Al2O3 and Na2O/Al2O3 molar ratios were equal to 3.6 and 1.0, respectively, approaching works that used precursors with a high degree of amorphism.

Application of different alkaline materials as polluted soil amendments: A comparative assessment of their impact on trace element mobility and microbial functions

Treatment with chemical amendments is among the best techniques to remediate soils highly polluted with trace elements. The use of waste-derived products has several advantages in this regard, mainly in terms of reducing process costs and conserving natural resources. In this study, the performance of the synthetic zeolite NaP1 derived from coal combustion fly ash (SZ) and the by-product generated from the processing of aluminum salt slags (BP) was evaluated with this aim in comparison to calcite (CC). For this purpose, mine soils polluted with Zn, Cd, and Pb were amended under controlled laboratory conditions with different doses (0%, 1%, 2%, 5%, and 10%) of SZ, BP, or CC, and their impact on trace element mobility and microbial functions was evaluated. Specifically, the mobile and mobilizable trace element pools, basal soil respiration, and different enzyme activities were analyzed. Both SZ and BP performed better than CC in the immobilization of trace elements, reaching, respectively, mobility decreases up to 89–94% and 66–87% when applied at a dose of 10%. These amendments reduced the mobile trace element pool by precipitating them as acid-soluble precipitates and/or retaining them in the reducible fraction of soils. The alkaline nature of these materials and the concomitant increase in soil pH caused by their application mainly accounted for this behavior. Additionally, soil microbial functionality improved after amendment, especially in the case of SZ, as shown by dehydrogenase and alkaline phosphatase activities, which significantly increased (p < 0.05) up to 536% and 48%, respectively. Therefore, applying SZ or BP as soil amendments can significantly decrease the mobile trace element contents of heavily polluted soils without negatively affecting soil quality, thus facilitating plant growth to revegetate and reclaim degraded spaces.

Assessing the carbon capture capacity of South Wales’ legacy iron and steel slag

The industrial revolution was responsible for releasing over 1.5 trillion tonnes of carbon dioxide into the atmosphere resulting in a global temperature increase of ∼1 °C. It also produced billions of tonnes of alkaline materials that have the potential to react with some of that CO2, and this carbon capture potential may be used to help prevent climate change. Here we assess the carbon capture potential of legacy iron (Fe) and steel wastes in South Wales, the United Kingdom, and show that between 0 and 77% of total carbonation potential has been reached in the samples (equating to maximum potential between 40 and 608 kg CO2 /t of slag has been removed from the atmosphere by direct carbonation) across 10 historic works (out of 48 that operated in the region), even after > 140 years. The current work suggests that there is a capture potential of up to 17 Mt CO2 by direct carbonation which represents a potential carbon sink for future emissions. Iron and steel slag contains Ca silicate minerals, often dominated by melilite group phases (gehlenite, Ca2Al2SiO7 and akermanite, Ca2MgSi2O7), but also includes minor phases like olivine (fayalite, (Fe,Mn)2SiO4 and fosterite, Mg2SiO4). The presence of mineral carbonate phases such as calcite, magnesite, ankerite, and kutnohorite in the material demonstrates carbonation reaction has occurred after slag formation. Given that there is still carbonation potential to be realised, and that materials produced in the future from the iron and steel industry could play an important role in meeting our climate targets, then new management strategies are needed to maximise the use of this resource.

Biomass Mediated Conversion of Acidic Phosphogypsum into Alkaline Material through Thermal Treatments

Biomass Mediated Conversion of Acidic Phosphogypsum into Alkaline Material through Thermal Treatments

KOH-Based Modified Solvay Process for Removing Na Ions from High Salinity Reject Brine at High Temperatures

The traditional Solvay process and other modifications that are based on different types of alkaline material and waste promise to be effective in the reduction of reject brine salinity and the capture of CO2. These processes, however, require low temperatures (10–20 °C) to increase the solubility of CO2 and enhance the precipitation of metallic salts, while reject brine is usually discharged from desalination plants at relatively high temperatures (40–55 °C). A modified Solvay process based on potassium hydroxide (KOH) has emerged as a promising technique for simultaneously capturing carbon dioxide (CO2) and reducing ions from reject brine in a combined reaction. In this study, the ability of the KOH-based Solvay process to reduce brine salinity at relatively high temperatures was investigated. The impact of different operating conditions, including pressure, KOH concentration, temperature, and CO2 gas flowrate, on CO2 uptake and ion removal was investigated and optimized. The optimization was performed using the response surface methodology based on a central composite design. A CO2 uptake of 0.50 g CO2/g KOH and maximum removal rates of sodium (Na+), chloride (Cl−), calcium (Ca2+), and magnesium (Mg2+) of 45.6%, 29.8%, 100%, and 91.2%, respectively, were obtained at a gauge pressure, gas flowrate, and KOH concentration of 2 bar, 776 mL/min, and 30 g/L, respectively, and at high temperature of 50 °C. These results confirm the effectiveness of the process in salinity reduction at a relatively high temperature that is near the actual reject brine temperature without prior cooling. The structural and chemical characteristics of the produced solids were investigated, confirming the presence of valuable products such as sodium bicarbonate (NaHCO3), potassium bicarbonate (KHCO3) and potassium chloride (KCl).

Effect of Cullet on Firing Temperature and Dielectric Properties of Porcelain Insulator

In this study, porcelain insulators produced from locally available ceramic materials, Hosaena clay, Arero feldspar, and Arero quartz and cullet as alkaline materials. The chemical compositions of clay are determined using an atomic absorption spectrometer (AAS). The thermal response, mineralogy, morphology, and plasticity nature of the clay sample measured using TGA/DTA, XRD, SEM, and Atterberg test, respectively. Four test batches were prepared with progressive addition of cullet and sintered in the temperature range of 1100 ─1250°C at 50°C intervals. The physical and electrical properties of fired samples such as water absorption, apparent porosity, bulk density, and linear shrinkage; and dielectric strength as a function of firing temperature evaluated. The XRD and AAS results revealed that Hosaenna clay mainly belongs to kaolinite mineral with a sufficient SiO2 (45.60wt. %) and Al2O3 (35.52wt. %), and it possesses reasonable plasticity nature. The porcelain insulators fired at 1150°C & 1200°C showed homogenized primary and secondary mullets with optimum glassy phase and good dielectric strength for practical applications. The primary & secondary mullets and glassy phases were grown early at a firing temperature of 1150 and 1200°C, due to the partial replacement of feldspar by cullet. The porcelain insulators prepared from the composition of 45%clay, 35%feldspar, 10%quartz and 10%cullet and fired at 1200°C showed dielectric strength 8.9kv/mm, water absorption (0.459%), apparent porosity (1.530%), bulk density (4.29g/cm 3 ), and linear shrinkage (4.18%). Therefore, the addition of economic alkaline materials such as cullet in the locally available clay materials, Hosaenna clay, Arero feldspar, and Arero quartz reduces the firing temperature and with excellent dielectric strength.

Effect of Acetic Acid on Compressive Strength and Geometric Texture of the Surface of C20/25 Class Concrete

Concrete is a highly alkaline material; therefore, the presence of organic acids (acetic, butyric, lactic) from agricultural sewage constitutes a threat to the concrete and the environment. The investigations were aimed at simulating the influence of highly concentrated organic acids on concrete elements of livestock buildings. Cubic samples 100 × 100 × 100 mm of the ordinary concrete were immersed in 10% acetic acid for 270 days. Then, the compressive strength and mass decrement of the samples were determined as well as using SEM images and a 3D-profilograph to profile the surface roughness and depth of changes evoked in the structure of the samples by penetrating acid. The results were compared with those for a control sample (not subjected to the effects of aggressive agents) as well as for samples placed in a neutral and alkaline environment. The compressive strength of the samples stored in the acidic environment was 22.23% lower than that of the control sample, whereas the compressive strength of those samples stored in an alkaline environment were 44.27% higher. Conclusions from these investigations can be of innovative importance in the preparation of environmental impact reports, which are necessary for obtaining permission for the construction and use of livestock buildings, and afterward in the reduction of the impact of these buildings on the environment and surface and underground water resources.

Effects of overliming on the nutritional status of grapevines with special reference to micronutrient content

Aluminium plays a central role in soil acidity, which is one of the main constraints on grape production in humid, northern temperate viticultural regions. To decrease the acidity of vineyard soil, it is usually amended with alkaline materials that provide conjugate bases to weak acids (liming). However, one practical consideration is the danger of overliming, which has potential implications in terms of yield reduction and decreased bioavailability of several mineral nutrients. The main aim of this study was to evaluate the effects of overliming using dolomitic lime on grapevines growing on acid soil. The effects on the topsoil fertility parameters (0–30 cm), petiole and berry nutrient levels, berry weight and must quality properties were studied in a vineyard planted with Vitis vinifera L. cv. Mencía for three years (2014–2016). Data analysis performed using a mixed model that took into account both random effects (year of sampling) and fixed effects (liming treatments) showed that overliming decreased the manganese content in both leaf and berry tissues. Until now, nothing was known about the effects of overliming on both vine nutritional status and harvest quality properties, thus this study fills an important knowledge gap.

Long-term effects of biochar on trace metals accumulation in rice grain: A 7-year field experiment

Biochar (BC) is an emerging amendment for minimizing the phytoavailability of trace metals in soil-crop system, but its relevant durability and mechanism are unclear. A 7-year field study was conducted in double rice paddy land of mid-subtropical China. Wheat straw BC was once applied at rates of 24 and 48 Mg ha−1 (LBC and HBC, respectively). Results showed that the increase in soil total organic C (TOC, 41.1–54.6%), pH (0.41–0.86 units) and cation exchange capacity (13.7–23.3%) for the HBC was kept for 14, 11 and 4 seasons (p < 0.05), respectively. Meanwhile, the reduction in soil CaCl2-extractable Cd, Pb, Zn and Mn (29.5–61.6%, 38.2–81.0%, 36.5–70.7%, 19.1–56.7%, respectively, p < 0.05) was maintained for 9–11 seasons. And, the reduction in grain Cd, Pb, Zn and Mn (23.0–59.5%, 15.2–49.8%, 17.5–22.9%, 13.4–34.2%, respectively, p < 0.05) was maintained for 4–6 seasons. Similar but weaker effects were observed for the LBC. And, their durable periods (except for TOC) for the LBC were about 1/3–1/2 of those for the HBC. Phytoavailability of Cd, Pb, Zn and Mn in soil-rice system was negatively correlated with soil pH and TOC (p < 0.05). Therefore, the immobilization durability of the BC on trace metals in soil-rice system are mainly attributed to the primary fixation of stable microstructure and functional groups, and mediated by the associated changes in soil pH. Alkaline materials should be taken as supplemental agents to strengthen the immobilization durability of the BC on trace metals in soil-rice system.

Potential of Maritime Transport for Ocean Liming and Atmospheric CO2 Removal

Proposals to increase ocean alkalinity may make an important contribution to meeting climate change net emission targets, while also helping to ameliorate the effects of ocean acidification. However, the practical feasibility of spreading large amounts of alkaline materials in the seawater is poorly understood. In this study, the potential of discharging calcium hydroxide (slaked lime, SL) using existing maritime transport is evaluated, at the global scale and for the Mediterranean Sea. The potential discharge of SL from existing vessels depends on many factors, mainly their number and load capacity, the distance traveled along the route, the frequency of reloading, and the discharge rate. The latter may be constrained by the localized pH increase in the wake of the ship, which could be detrimental for marine ecosystems. Based on maritime traffic data from the International Maritime Organization for bulk carriers and container ships, and assuming low discharge rates and 15% of the deadweight capacity dedicated for SL transport, the maximum SL potential discharge from all active vessels worldwide is estimated to be between 1.7 and 4.0 Gt/year. For the Mediterranean Sea, based on detailed maritime traffic data, a potential discharge of about 186 Mt/year is estimated. The discharge using a fleet of 1,000 new dedicated ships has also been discussed, with a potential distribution of 1.3 Gt/year. Using average literature values of CO2 removal per unit of SL added to the sea, the global potential of CO2 removal from SL discharge by existing or new ships is estimated at several Gt/year, depending on the discharge rate. Since the potential impacts of SL discharge on the marine environment in the ships' wake limits the rate at which SL can be applied, an overview of methodologies for the assessment of SL concentration in the wake of the ships is presented. A first assessment performed with a three-dimensional non-reactive and a one-dimensional reactive fluid dynamic model simulating the shrinking of particle radii, shows that low discharge rates of a SL slurry lead to pH variations of about 1 unit for a duration of just a few minutes.

A novel acidic phosphoric-based geopolymer binder for lead solidification/stabilization

Many contaminated sites are acidic and the existing binders are mainly alkaline materials. Alkaline binders are used to treat contaminated sites in acidic environments and the solidification/stabilization (S/S) effect is affected by acid corrosion. Therefore, good application prospects exist in developing a binder suitable for the treatment of acidic contaminated sites. In this paper, a new acidic phosphoric-based geopolymer (named APG binder) was synthesized with fly ash as a raw material and aluminum dihydrogen phosphate as the reactant, and the APG binder was used for Pb2+ S/S for the first time. The pH of the APG binder with Pb2+ ranged from 2.56 to 4.09 during 7–28 days of curing, and its compressive strength with Pb2+ exceeded 10 MPa at 28 days. Moreover, Pb2+ had a significant impact on the APG binder compressive strength, and when the Pb2+ content was 0.6%, the APG binder yielded a maximum compressive strength of 6.5, 9.1 and 14.28 MPa at 7, 14, and 28 days, respectively. Furthermore, the compressive strength correlated well with pH and electrical conductivity. The proposed APG binder had a better S/S effect on Pb2+ than that of cement and alkali-activated geopolymers in acidic environments. The stabilization mechanism of the APG binder for Pb2+ included chemical precipitation, physical adsorption and encapsulation.

Recycling of Carbon Fiber-reinforced Epoxy Resin-based Composites Using a Benzyl Alcohol/Alkaline System

High-efficiency recycling of carbon fiber-reinforced epoxy resin-based composites is difficult because of their three-dimensional network structure. In this article, a benzyl alcohol/alkaline system was used to recycle carbon fiber-reinforced epoxy resin-based composites cured by an anhydride. The degradation rate, mechanical properties and degradation mechanism of the recycled carbon fiber were determined by gas chromatography-mass spectrometry, Fourier transform infrared spectroscopy, liquid chromatography-mass spectrometry, scanning electron microscope and X-ray photoelectron spectroscopy. The experimental results indicated that there were two steps in benzyl alcohol/K3PO4 degradation system. The first was transesterification by benzyloxy selective attack to give small-molecule esters. Then the esters were saponified by the alkaline materials. After degradation, the stratification of resin and benzyl alcohol occurred, which was conducive to their separation. The optimal degradation time was 40 min under the weight ratio of alkaline material to benzyl alcohol of 1:10, atmospheric pressure, and temperature of 195 °C and the decomposition efficiency exceeded 90 %. A clean carbon fiber surface was obtained with an oxygen content comparable to that of the original carbon fiber. The tensile strength of the recycled carbon fiber was above 90 % of the original value.