Silicon carbide waste as a source of mixture materials for cement mortar

This paper presents an investigation of the feasibility of recycling silicon carbide waste (SCW) as a source of mixture materials in the production of cement mortar. Mortars with SCW were prepared by replacing different amounts of cement with SCW, and the properties of the resulting mortars, such as the fluidity, strength and shrinkage, were studied in this work. Thermogravimetry-differential scanning calorimetry and scanning electron microscopy were employed to understand the reasons for the property changes of the mortars. The results indicate that SCW decreases the initial and 1-h fluidity of fresh mortar but improves the loss of fluidity. The mortar with SCWexhibits a lower strength at 3 d and 7 d but a higher strength at 28 d and 56 d compared to the control. The shrinkage rate of cement mortar with SCW shows an obvious decrease as the replacement ratio increases. In addition, the content of calcium hydroxide in hardened paste also shows that SCW has some impact on the hydration of the cement-SCW system. The microstructures of the hardened paste also show evidence for a later strength change of mortar containing SCW. This work provides a strategic reference for possibly applying SCW as a mixture material in the production of cement mortar.

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Cement industry: sustainability, challenges and perspectives

Cement-based materials, such as concrete and mortars, are used in extremely large amounts. For instance, in 2009 concrete production was superior to 10 billion tons. Cement plays an important role in terms of economic and social relevance since it is fundamental to build and improve infrastructure. On the other hand, this industry is also a heavy polluter. Cement production releases 5–6% of all carbon dioxide generated by human activities, accounting for about 4% of global warming. It can release huge amounts of persistent organic pollutants, such as dioxins and heavy metals and particles. Energy consumption is also considerable. Cement production use approximately 0.6% of all energy produced in the United States. On the other hand, the chemistry underlying cement production and its applications can be very helpful to overcome these environmental issues. In terms of manufacture, there are many alternative materials that can be used to minimize carbon dioxide production and reduce energy consumption, such as calcium sulfoaluminates and β-Ca₂SiO₄—rich cements. Using residues from other industrial sectors can also improve the sustainability of cement industry. Under adequate conditions, waste materials such as tyres, oils, municipal solid waste and solvents can be used as supplementary fuel in cement plants. Concrete can be used for encapsulation of waste materials such as tyres, plastics and glasses. In this review, we discuss some aspects of the cement industry associated with environmental science. Other issues such as economic aspects, the chemistry of cement manufacture and its properties are also presented. Special attention is given to the role that cement chemistry can play in terms of sustainability. The most relevant aspects are outlined, such as the use of alternative materials, new possibilities and also the recycling of materials. It is also argued that an important aspect is the role of research and development necessary to improve cement sustainability.     

Environmental protection by utilization of the slag from magnesium production in building materials

This paper presents the results of research on the utilization of slag produced as the waste material of metallic magnesium production. This material is a fine powder with a high magnesium content. The characterization of slag was performed by XRD, DTA and TG analysis. Chemical composition and mechanical properties of slag were also determined. By using a mixture this slag and limestone aggregate, it is possible to obtain dry mortar which, mixed with water, gives a material fully satisfying for plastering mortar. By adding inorganic pigments (Fe₂O₃, Ca₂O3, etc.) decorative mortars are obtained, and when they are spread over the foundation made of brick or concrete, they retain their colour on the entire coating and surface of the mortar.     

Removal of contaminants in leachate from landfill by waste steel scrap and converter slag

This study may be the first investigation to be performed into the potential benefits of recycling industrial waste in controlling contaminants in leachate. Batch reactors were used to evaluate the efficacy of waste steel scrap and converter slag to treat mixed contaminants using mimic leachate solution. The waste steel scrap was prepared through pre-treatment by an acid-washed step, which retained both zero-valent iron site and iron oxide site. Extensive trichloroethene (TCE) removal (95%) occurred by acid-washed steel scrap within 48 h. In addition, dehalogenation (Cl⁻ production) was observed to be above 7.5% of the added TCE on a molar basis for 48 h. The waste steel scrap also removed tetrachloroethylene (PCE) through the dehalogenation process although to a lesser extent than TCE. Heavy metals (Cr, Mn, Cu, Zn, As, Cd, and Pb) were extensively removed by both acid-washed steel scrap and converter slag through the adsorption process. Among salt ions (NH₄⁺, NO₃⁻, and PO₄³⁻), PO₄³⁻ was removed by both waste steel scrap (100% within 8 h) and converter slag (100% within 20 min), whereas NO₃^- and NH₄⁺ were removed by waste steel scrap (100% within 7 days) and converter slag (up to 50% within 4 days) respectively. This work suggests that permeable reactive barriers (PRBs) with waste steel scrap and converter slag might be an effective approach to intercepting mixed contaminants in leachate from landfill.     

EDS analysis of Portland ash cement degradation in an aggressive environment

The behaviour of Portland cement with and without 30% fly ash addition in aggressive solutions was studied. This paper considers the sulphate corrosion of the hardened cement paste. The cement paste test samples were prepared, cured in water for 21 day and then exposed to the influence of aggressive environment (10% (NH₄SO₄ solution). The measurements of several properties were carried out and the results were analyzed.

The image of the surface composition and morphology of the cement paste test samples was made by scanning electron microscopy (SEM). Concentration gradient of sulphate ions in cement paste depth was obtained by energy‐dispersive analysis (EDS).     

Corrosion rules for ordinary concrete exposed to sulfur dioxide-containing environments

Sulfur dioxide (SO₂) significantly influences the durability of concrete. Concrete corrosion in SO₂-containing environments is a serious concern. In this study, an accelerated test was devised to examine the change rules of concrete corrosion in SO₂-containing environments. Experiments were conducted to explore changes in mass, strength, and sulfatized depth with different water–cement ratios and a series of SO₂ concentrations. Data indicated that the water–cement ratio and SO₂ levels all impact the durability of concrete.     

Determination of F2-isoprostanes in cultured human lung epithelial cells after exposure to metal oxide and silica nanoparticles by high-performance liquid chromatography/tandem mass spectrometry

The environmental impact of nanotechnology has caused a great concern. Many in vitro studies showed that many types of nanoparticles were cytotoxic. However, whether these nanoparticles caused cell membrane damage was not well studied. F₂-isoprostanes are specific products of arachidonic acid peroxidation by nonenzymatic reactive oxygen species and are considered as reliable biomarkers of oxidative stress and lipid peroxidation. In this article, we investigated the cytotoxicity of different nanoparticles and the degree of cellular membrane damage by using F₂-isoprostanes as biomarkers after exposure to nanoparticles. The human lung epithelial cell line A549 was exposed to four silica and metal oxide nanoparticles: SiO₂ (15 nm), CeO₂ (20 nm), Fe₂O₃ (30 nm), and ZnO (70 nm). The levels of F₂-isoprostanes were determined by using high-performance liquid chromatography/mass spectrometry. The F₂-isoprostanes’ peak was identified by retention time and molecular ion m/z at 353. Oasis HLB cartridge was used to extract F₂-isoprostanes from cell medium. The results showed that SiO₂, CeO₂, and ZnO nanoparticles increased F₂-isoprostanes levels significantly in A549 cells. Fe₂O₃ nanoparticle also increased F₂-isoprostanes level, but was not significant. This implied that SiO₂, CeO₂, ZnO, and Fe₂O₃ nanoparticles can cause cell membrane damage due to the lipid peroxidation. To the best of our knowledge, this is the first report on the investigation of effects of cellular exposure to metal oxide and silica nanoparticles on the cellular F₂-isoprostanes levels.     

Porous silica synthesis out of coal fly ash with no residue generation and complete silicon separation

● Both amorphous and crystalline silicon are completely separated from coal fly ash. ● Porous silica is synthesized out of coal fly ash. ● No residues is produced during the whole synthesis process. ● The one-step method to synthesize silica don’t need long-time reaction and aging. Ordered mesoporous silica materials exhibit enormous potential in industrial production. Since coal fly ash (CFA) is abundant in Si, it has become a green and promising way to utilize CFA by synthesizing porous silica materials. However, the stable crystalline structure of CFA limits the extraction of Si, and the residue is generated during the process of extracting Si. In this work, we proposed a no-residue method to synthesize ordered mesoporous silica out of CFA. Sodium carbonate (Na₂CO₃) was used to reconstruct the crystals of the CFA, and the calcined mixture then directly reacted with the precipitators. This method combined the process of Si extraction and porous material synthesis. In this method, no residue was generated and the silicon in both amorphous and crystalline phases of CFA was fully utilized. By this method, the extraction efficiency of Si was increased from 31.75% to nearly 100%. The as-synthesized mesoporous silica had a highly-ordered pore structure with a space group of la-3d, a surface area of 663.87 m²/g, a pore volume of 0.41 cm³/g, and an average pore diameter of 2.73 nm. The mechanism of crystalline transformation and material structure formation were systematically studied. This method provides a new idea to dispose of CFA and synthesize porous silica materials.     

The Reuse of Urban and Industrial Waste in Tai-Lin-Pu Reclamation Project,Taiwan

Abstract

This study introduces the principles of KMG's (Kaoshiung Municipal Government) dealing with the non-poisonous urban and industrial waste through reclamation of shore land in reinforcing a sense of coastal protection and land development in Tai-Lin-Pu coastal area, southern Taiwan.

Through a series of experimental studies, we found that substitutes of coarse aggregate with a broad spectrum of integrating slag powder, fly ash, and cementitious material can be obtained with a benefit up to 80% saving of cement. the integrated aggregates from the non-poisonous industrial wastes were subsequently made into armour units and used in the field tests at Tai-Lin-Pu coastal area, where the shorelines are seriously eroded. After being subjected to several severe typhoon advents, the results showed that the waste-made units used as the protection breakwater, together with construction wastes and excavated soil as the filling material, prove to be an effective practice in utilizing recycled urban waste to reclaim erosive shore lands. Moreover, this study also demonstrates that through detailed analysis of the waste characteristics, scrap material could be turned into valuable construction aggregates, and highlights the value of non-poisonous urban and industrial waste as a alternative resource for the shore protection engineering.     

Verbleib von spurenschadstoffen bei der methylesterherstellung aus altspeisefett im technikumsmaßstab

Aims and Scope

In Germany, 120,000 tons per year of waste edible fats are collected from the catering and the food industry Until recently, these fats have widely been used as a nutritional additive for poultry and other animals fodder. Due to the BSE crisis and some affairs based on dioxins in feeding stuff, waste fats are now barely used as fodder. Currently, these fats substitute fresh vegetable oils in the chemical industry and are used as raw material for the production of biodiesel. Therefore, alternative fields of application are required. In this context, the Deutsche Bundesstiftung Umwelt (DBU) is sponsoring a joint research project which deals with the production and testing of cooling lubricants based on monoesters made from waste edible fats.

Methods

In a first step, characteristics and quality of wasteedible fats of different origins were chemically analysed and monitored. The investigations covered the following fat specific parameters: total contamination, sulphate ash, water content, peroxide number, iodine value, kinematical viscosity, neutralisation number (free fatty acids) and fatty acid spectra. In the next step, a process development/optimisation was carried out for the production of methylesters based on the raw material waste fat, leading to the construction of a pilot plant. To investigate the fate of trace pollutants during the production process of waste-fat methylester, samples were systematically contaminated with polycyclic aromatic hydrocarbons, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and the elements Al, Cd, Cr, Cu, Ni, P, Pb, Sn, and Zn. These contaminated fat samples were transesterified in laboratory scale. The primary and by-products were analysed subsequently.

Results

Valuable hints on the design of the technical process of fatty adid methylester production based on waste edible fats were gained by regarding the fat specific parameters. For example, filtration and dewatering of the waste fats proved necessary. The saturated fatty acids, most wanted for the production of cooling lubricants due to their high oxidation stability, were present in the range of 11,3% to 31,6%. Due to the low content of free fatty acids, a base catalysed process occurred more suitable for the transesterification of the waste edible fats. Trace analytical investigations concerning inorganic and organic pollutants proved a low basic contamination of the waste edible fats. Experiments with systematic contamination of the fats indicated an accumulation of the heavy metals in the glycerol phase during the transesterification process, whereas the organic pollutants were detected in the methylester fraction by amounts of 80% to 95%.

Outlook

In a next step, the further processing of the methylesters to monoesters with alcohols of the chain length C2 to C8 will be presented. Associated results of chemical-analytical investigations on the process and the application of the cooling lubricants will also be given.     

Leaching characteristics of heavy metals during cement stabilization of fly ash from municipal solid waste incinerators

The leaching characteristics of heavy metals in products of cement stabilization of fly ash from a municipal solid waste incinerator were investigated in this paper. The stabilization of heavy metals such as Cd, Pb, Cu, and Zn in fly ash from such incinerators was examined through the national standard method in China based on the following factors: additive quantity of cement and Na₂S, curing time, and pH of leaching liquor. The results showed that as more additives were used, less heavy metals were leached except for Pb, which is sensitive to pH of the leachate, and the worse effect was observed for Cd. The mass ratio of cement to fly ash = 10% is the most appropriate parameter according to the national standard method. When the hydration of cement was basically finished, stabilization of heavy metals did not vary after curing for 1 d. The mixtures of cement and fly ash had excellent adaptability to environmental pH. The pH of leachate was maintained at 7 when pH of leaching liquor varied from 3 to 11.     

Effect of silica additive on the thermal stability of catalysts for NOx abatement

The aim of the plesent investigation was to study the effect of SiO₂ addition on the thermal deactivation of V₂O₅/WO₃/TiO₂ catalysts used for NOx pollution abatement. The results suggest that the degradation of the catalytic properties is strongly correlated to the structural ageing which is, in turn, mainly related to the anatase–rutile phase transformation and to the WO₃ phase segregation. The addition of SiO₂ strongly influences the temperature at which these phenomena occur. In fact, it was found that the introduction of this oxide stabilizes the material, retarding the collapse of surface area, and increases the temperature of the anatase to rutile phase transition.     

Characterization of chlorine and heavy metals for the potential recycling of bottom ash from municipal solid waste incinerators as cement additives

Bottom ash is an inevitable by-product from municipal solid waste (MSW) incineration plants. Recycling it as additives for cement production is a promising disposal method. However, the heavy metals and chlorine are the main limiting factors because of the potential environmental risks and corrosion of cement kilns. Therefore, investigating heavy metal and chlorine characteristics of bottom ash is the significant prerequisite of its reuse in cement industries. In this study, a correlative analysis was conducted to evaluate the effect of the MSW components and collection mode on the heavy metal and chlorine characteristics in bottom ash. The chemical speciation of insoluble chlorine was also investigated by synchrotron X-ray diffraction analysis. The results showed that industrial waste was the main source of heavy metals, especially Cr and Pb, in bottom ash. The higher contents of plastics and kitchen waste lead to the higher chlorine level (0.6 wt.%–0.7 wt.%) of the bottom ash. The insoluble chlorine in the MSW incineration bottom ash existed primarily as AlOCl, which was produced under the high temperature (1250°C) in incinerators.

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Utilization of the waste phosphogypsum for the Portland cement clinker production

This paper presents the results of investigation on the utilization of the phosphogypsum for the Portland cement clinker production. Characterization of the phosphogypsum and raw materials for rotary kilns was performed. Phosphogypsum, in quantities of 1%, 2%, 3% and 5%, was added to raw meal from regular production of rotary kiln and then the homogenization of raw meals and their chemical characterization was done. High temperature DTA and thermo‐microscopic investigations have been performed also. Raw meals without and with the addition of phosphogypsum have been laboratory sintered. Chemical composition of Portland cement clinkers has been defined and potential clinker phase composition has been calculated according to Bogue's formula from the chemical composition. Results are very encouraging regarding the energy consumption and Portland cement clinker quality. Phosphogypsum could be successfully applied as mineralizer in cement production, because with its addition, better composition of Portland cement clinker at the same sintering conditions could be obtained.     

Thermochemical conversion of municipal solid waste into energy and hydrogen: a review

The rising global population is inducing a fast increase in the amount of municipal waste and, in turn, issues of rising cost and environmental pollution. Therefore, alternative treatments such as waste-to-energy should be developed in the context of the circular economy. Here, we review the conversion of municipal solid waste into energy using thermochemical methods such as gasification, combustion, pyrolysis and torrefaction. Energy yield depends on operating conditions and feedstock composition. For instance, torrefaction of municipal waste at 200 °C generates a heating value of 33.01 MJ/kg, while the co-pyrolysis of cereals and peanut waste yields a heating value of 31.44 MJ/kg at 540 °C. Gasification at 800 °C shows higher carbon conversion for plastics, of 94.48%, than for waste wood and grass pellets, of 70–75%. Integrating two or more thermochemical treatments is actually gaining high momentum due to higher energy yield. We also review reforming catalysts to enhance dihydrogen production, such as nickel on support materials such as CaTiO₃, SrTiO₃, BaTiO₃, Al₂O₃, TiO₃, MgO, ZrO₂. Techno-economic analysis, sensitivity analysis and life cycle assessment are discussed.

     

Cardioprotective effect of Lagenaria siceraria (Mol) ameliorates isoproterenol-induced cardiac toxicity in rats by stabilizing cardiac mitochondrial and lysosomal enzymes

A study was conducted to determine the effect of the chironomid larval tube on heavy metal toxicity. Silica gel was provided as a substrate with which the chironomid larvae could construct larval tubes. A series of 96 h LC₅₀ bioassays were conducted with and without the presence of the silica gel substrate, to allow comparison between the two test conditions. From the study it was observed that a 10–15% variation in LC₅₀ value occurred. The 96 h LC₅₀ for copper at the temperatures 35, 28, 20, 15, and 10°C was observed to be 7.5, 9.5, 7.5, 4.5, 3.6, and 2.8 mg L^?1, respectively. The same test when conducted in the presence of silica gel produced LC₅₀ values of 26.50, 33.50, 15.82, 12.77, and 9.94 mg L^?1 for the same temperatures. This would demonstrate that the larval tube did, to some extent, protect the larvae from the effects of the heavy metal.     

Research on transesterification parameters for producing plant sterols with supercritical methanol

The supercritical fluid method, regarded as a type of individual production process in the course of preparing plant sterols, has become a promising technology, which possesses advantages of high conversion rate without any pretreatment and need of a catalyst. This study examined the reaction process of the deodorizer distillate (DOD), which mainly included the direct transesterification of DOD to convert into free sterols. The effects of the ratio of methanol to DOD, reaction temperature and time on transesterification were studied. Furthermore, the interactions between different factors were also assessed using the response surface methodology. The optimal conditions obtained were as follows: reaction temperature 553 K, reaction time 80 min, and CH₃OH: DOD = 25:1 (mass ratio). Under these conditions, 36.42% sterol concentration was obtained, which is significantly higher in comparison with the initial sterols’ concentration in raw material (22.45%).     

Source apportionment of ambient PM10 in urban areas of Wuxi, China

A total of 168 PM₁₀ samples were collected during the year of 2005 at eight sites in the city of Wuxi in China. Fifteen chemical elements, three water-soluble ions, total carbon and organic carbon were analyzed. Six source categories were identified and their contributions to ambient PM₁₀ in Wuxi were estimated using a nested chemical mass balance method that reduces the effects of colinearity on the chemical mass balance model. In addition, the concentrations of secondary aerosols, such as secondary organic carbon, sulfate and nitrate, were quantified. The spatially averaged PM₁₀ was high in the spring and winter (123 ??g·m^?3 and low in the summer-fall (90 ??g·m^?3). According to the result of source apportionment, resuspended dust was the largest contributor to ambient PM₁₀, accounting for more than 50% of the PM₁₀ mass. Coal combustion (14.6%) and vehicle exhaust (9.4%) were also significant source categories of ambient PM₁₀. Construction and cement dust, sulfates, secondary organic carbon, and nitrates made contributions ranging between 4.1% and 4.9%. Other source categories such as steel manufacturing dust and soil dust made low contributions to ambient PM₁₀.     

Vertical and spatial distribution of biogenic silica in the sediment of the gulf of Riga,Baltic Sea

The vertical and spatial concentration trends of biogenic silica (BSi) were investigated in a variety of sediment types from the Gulf of Riga. These trends were compared with the concentration of organic carbon to examine how variations in the mass sedimentation and the dissolution rate of BSi versus bacterially mediated oxidation of organic matter affect the distribution of BSi in different environments. The effects of important physical and biogeochemical factors on the distribution of BSi have also been examined.

The concentration of BSi in the surface sediment at accumulation bottoms ranges between 0.8–1.5 mmol/g with an average concentration of 1.1 mmol/g. This is about two times the concentration that has been reported in similar sediments in the open Baltic proper. Much lower concentrations were measured in erosion and transitional areas; on average around 0.2 and 0.6 mmol/g, respectively.

A comparison between recent sedimentation rate measurements (²¹⁰Pb) and concentrations of BSi within different accumulation bottoms suggests an approximate inverse relationship with each other. The importance of variation in the sedimentation rate on the surface BSi concentration is supported by the fact that higher C_org/BSi ratios are found in periphery accumulation zones close to transition areas (larger supply of carbon rich allochthonous material that dilutes settled amounts of BSi) than at accumulation bottoms in the central part of the Gulf. The C_org/BSi ratio in the sediment is always lower than in living siliceous algae which shows that the microbial degradation of organic carbon is always greater than the inorganic dissolution of BSi, irrespective of the assemblage of silica and non‐silica species.

The general vertical concentration pattern at accumulation sites showed a decreased concentration with increased depth down to 2–6 cm below seafloor where the concentration gradually equalizes. The concentration in the equalizing zone is on average about 20% lower than in the uppermost centimeter. This implies that the main part of the BSi entering the accumulation bottoms is permanently buried and that a great amount of silica already has been released during halmyrolysis. The spatial and vertical BSi trends at sites in transitional and erosional areas reflects prevailing sedimentation conditions with a low concentration in sections with a dominance of sand and gravel (no deposition of fine material) and a higher concentration in the sections containing stiff glacial clay (former accumulation area).

The average annual burial amount of BSi in the Gulf has been estimated to be around 50 000 tons of which most is buried in accumulation bottoms outside the central muddy part of the Gulf. The buried amount is about 60% of the annual river load of silica.     

Acid mine drainage from inactive eastern coal operations

The most widely used technique for abatement of acid drainage from inactive surface mines and refuse disposal areas is revegetation of a soil cover applied to the waste material. Nonetheless, acid production often persists and in some cases, limits establishment of vegetation. This paper reports on several field studies intended to determine the location of pyrite oxidation zones and migration pathways of oxidation products at inactive spoil and refuse sites.Oxygen required for pyrite oxidation is believed to he provided in the gaseous state from the atmosphere. Therefore, the oxygen concentration in unsaturated mine waste should provide an estimate of the weathering tendency in the local environment. We are currently monitoring gas composition in refuse and spoil at six sites. Barren refuse appeared to be oxygenated (>2% 0₂) in a shallow zone extending less than 1 metre below the surface during most of the year. Preliminary data from coal spoil showed that oxygen can be available throughout the unsaturated thickness, even at a revegetated site. Gas composition varied vertically and laterally at a single site and also appeared to show seasonal dependence.Hydrologic factors are also important in acid production and transport. Discharge monitoring alone does not adequately describe the mass transport of acid products through the spoil. For example, at one reclaimed mine the mean sulfate content in six monitoring wells ranged from 24% to 240% of the mean concentration at the discharge point. Sources of recharge and relative flow rates determine the contribution of a particular zone to overall discharge quality.These basic studies of acid production and transport indicate some shortcomings of standard reclamation practices at certain sites. This information will he used to develop alternative abatement technology designed to mitigate acid production at the source.