Glass-ceramics from vitrified sewage sludge pyrolysis residues and recycled glasses

Effect of Sewage Sludge Addition on Microstructure and Mechanical Properties of Kaolin-Sewage Sludge Ceramic Bricks

The dramatic increase in sewage sludge production requires researchers to develop and explore more commercially viable ways for alleviating current environmental and socioeconomic challenges connected with its routine management. It has been established that sewage sludge can be processed to fabricate various valuable products or as fuels for electricity generation. In this research, kaolin (calcined from coal gangue) and sewage sludge were successfully used to prepare porous ceramic bricks without any additives. The effect of sewage sludge on the microstructure, phase composition, and mechanical properties of kaolin-sewage sludge ceramic bricks was investigated. The results show that the kaolin-sewage sludge ceramic bricks are mainly composed of mullite (3Al2O3·2SiO2), sillimanite (Al2SiO5), aluminum phosphate (AlPO4), hematite (Fe2O3) as well as a small amount of quartz (SiO2). The ceramic bricks present a typical porous structure, and the number and size of micropores increases noticeably with the increase of sewage sludge content. The sintering shrinkage rate and porosity of ceramic bricks increased significantly with the increase of sewage sludge content, which is mainly attributed to the increase of liquid phase proportion and high temperature volatilization. Sewage sludge can significantly improve the mechanical properties of kaolin-sewage sludge ceramic bricks. When the sewage sludge content is 30 wt.%, the ceramic bricks present the maximum compressive strength and flexural strength and high porosity (32.74%). The maximum sintering shrinkage rate and porosity are 12.17% and 40.51%, respectively.

Microwave-assisted catalytic pyrolysis of waste printed circuit boards, and migration and distribution of bromine

Microwave-assisted pyrolysis (MAP) of waste printed circuit boards (WPCB) was performed to investigate the characteristics of pyrolysis product and Br fixation. Pyrolysis conversion increased with increasing temperature, reaching 93.3 % at 650 °C. However, increasing heating time did not exhibit remarkable influence on pyrolysis conversion. At 350 °C, phenols were main compounds in the oil accounting for 91.15 %. As the temperature increased to 650 °C, polycyclic aromatic hydrocarbons and monocyclic aromatic hydrocarbons (except phenols) increased to 20.55 % and 19.03 %, respectively. Meanwhile, the total content of CO₂, CO, CH₄ and H₂ in the non-condensable gases increased significantly. Addition of ZSM-5 and kaolin promoted the recombination reaction of pyrolysis products, increased the relative percentage of monocyclic aromatic hydrocarbons (except phenols) and C₁₁-C₂₀ compounds in the oil, and reduced non-condensable gases. The oxygen bomb-ion chromatography was used to evaluate the Br content of pyrolysis residues. Higher pyrolysis temperature enhanced transfer of Br to pyrolysis gas. K₂CO₃, Na₂CO₃ and NaOH reacted with hydrogen bromide to generate KBr and NaBr, which significantly improved the Br fixation efficiency of pyrolysis residues (i.e. from 29.11%-99.80%, 96.39 % and 86.69 %, respectively) and reduced Br content in pyrolysis gas.

Physicochemical and elemental analyses of sandstone quarrying wastes to assess their impact on soil properties

The use of sandstone as a building material has increased around the world and sandstone quarrying and its wastes pose a potential threat to human health and the environment. More than 50% of the excavated stone is wasted in the form of scrap stone and waste slurry during sandstone quarrying and processing. Sandstone wastes can adversely change native soil properties and should be reused as construction material. The present study aimed to characterise wastes generated during sandstone quarrying and processing, assess their impact on the soil environment and explore their reuse potential. The results of this study show that fine slurry waste has physicochemical properties between sand and sandy loam while the properties of the slurry solids and scrap stone are similar to those of sandstone. Fine stone waste on intrusion into soil reduced the hydraulic conductivity and porosity of soil potentially reducing its productivity. The liquid stone slurry contained metals like Mn, Ni and As at concentrations higher than drinking water standards. These metals may contaminate water sources and affect human health. Therefore, the use of stone wastes as aggregate for road and building construction would be beneficial and would reduce their adverse impacts on the environment.

Sewage sludge incineration ash for coimmobilization of lead, zinc and copper: Mechanisms of metal incorporation and competition

Heavy metals such as lead, zinc, and copper always coexist in industrial wastes and tend to be released if the wastes are not treated properly. With abundant contents of aluminum, iron and silicon, sewage sludge incineration ash can provide a ceramic matrix for potential heavy metal stabilization. By using ceramic sintering, this study explored the coimmobilization mechanisms of lead, zinc and copper, with detailed explications on phase transformation, metal distribution and the effect of metal content. PbAl₂Si₂O₈ was identified as the major phase for lead immobilization in series with low heavy metal content, while most of the lead was incorporated into Pb₉(PO₄)₆ in high metal series. The Zn_xCu_1-xFe_yAl_2-yO₄ spinel solid solution was the predominant product phase for copper and zinc stabilization in both reaction series, but zinc was more competitively incorporated into the spinel structure. Moreover, the pattern of heavy metal distribution in the sintered products was largely affected by the metal type and elemental composition of the reaction system. Although different leaching behaviors were observed for the three heavy metals, their leachability was found to reach very low value after the thermal treatment processes. This study proposed a "waste-to-resource" strategy to largely alleviate the environmental burden of solid wastes and heavy metal pollution by using sewage sludge incineration ash as raw materials for low-temperature glass-ceramics, with a simultaneous effect on metal immobilization.

Energy efficient production of glass-ceramics using photovoltaic (P/V) glass and lignite fly ash

This study investigates an innovative approach for the valorization of specific wastes generated from the energy sector and the production of glass-ceramics. The wastes used were photovoltaic (P/V) glass, produced from the renewable energy sector, and lignite fly ash, produced from the conventional energy sector. The process first involved the production of glass after melting specific mixtures of wastes, namely (i) 70% P/V glass and 30% lignite fly ash, and (ii) 80% P/V glass and 20% lignite fly ash, at 1200 °C for 1 h as revealed by the use of a heating microscope. The results indicated that the P/V glass, as a sodium-potassium-rich inorganic waste, reduces energy requirements of the melting process. The produced glass was then used for the production of glass-ceramics. Dense and homogeneous glass-ceramics, exhibiting high chemical stability and no toxicity, were produced after controlled thermal treatment of glass at 800 °C. The mechanical (compressive strength, Vickers hardness) and physical (open porosity, bulk density and water absorption) properties of the produced glass-ceramics were evaluated. X-ray diffraction (XRD) and Energy Dispersive X-ray fluorescence (ED-XRF) were used for the characterization of the raw materials and the produced glass-ceramics. Scanning electron microscopy (SEM) provided further insights on the microstructure of the final products. The properties of the produced glass-ceramics, namely water absorption and compressive strength, render them suitable for applications in the construction industry. The waste valorization approach followed in this study is in line with the principles of circular economy.

Amino-functionalized sewage sludge-derived biochar as sustainable efficient adsorbent for Cu(II) removal

Sludge biochar as promising low-cost adsorbent has increasingly gained interests, but its poor surface functionality severely undermines its adsorption capacity and selectivity. Here a facile amino functionalization strategy was first proposed to enhance the surface functionality of sewage sludge derived biochar (SSDB) via the combination of sol-gel process for mesoporous silica coating and silylation for highly selective removal of Cu(II). The prepared amino-functionalized SSDB showed excellent adsorption capacity of 74.51 mg/g at room temperature, increasing by nearly 118% with regard to the unfunctionalized SSDB, and prominent selectivity (minute separation factor SF_{Co, Ni, Zn/Cu}) toward Cu(II) uptake. Characterizations demonstrated amine groups on the SSDB, the surface density of which reached 1.34 mg/m². The adsorption kinetics of Cu(II) on amino-functionalized SSDB was well described by a pseudo-second order kinetic model while the adsorption isotherm data was well fitted by Sips model. The pH range in which the adsorption preferentially occurred was 3-5. The occurrence of amine group protonation undermined adsorption performance at a pH < 3. These effects of amino-functionalized SSDB toward Cu(II) uptake were a result of the grafted amine groups specifically complexing with Cu(II) in the tetrahedron. Hence, prominent adsorption performance and low-cost feedstock make amino-functionalized SSDB a sustainable adsorbent for Cu(II) removal in water resulting in a cleaner utilization of sewage sludge.

The reuse of waste glass for enhancement of heavy metals immobilization during the introduction of galvanized sludge in brick manufacturing

The mixing of galvanized sludge in fired clay brick manufacturing has been regarded as an alternative approach for the consumption of galvanized sludge. Decreasing the surface area and porosity of fired brick definitely lowers the risk of heavy metal release. In this study, a novel method is proposed to reduce the surface area and porosity of bricks and promote heavy metal immobilization by adding waste glass. The introduction of waste glass enhanced the physical and mechanical performances of fired clay bricks and resulted in an increase in bulk density and compressive strength and a decrease in water absorption. Microstructure analysis showed that the texture of the bricks turned from porous to smooth and homogeneous due to the introduction of waste glass. Porosity analysis showed that surface area and pore volume of fired brick were substantially reduced. When the added waste glass amount exceeded 15 wt%, the heavy metal concentrations that leached from bricks containing 10 wt% galvanized sludge fired at 950 °C met the regulatory requirement. These results demonstrate that waste glass can be reused to enhance the stabilization/solidification of heavy metals, during the mixing of hazardous waste in bricks and ceramics manufacturing process.

Experimental study of fry-drying and melting system for industrial wastewater sludge

In South Korea, ocean dumping of organic sludges has been prohibited by the London Convention and by Korean regulations. Therefore, the Government of South Korea has sought an alternative process for the disposal of organic sludges. Recently, the combined fry-drying and melting system has been recognized as an efficient way to utilize the energy content of organic industrial sludge. Three kinds of fry-dried industrial sludges (obtained from industrial sites DG, DJ and GM), which had average heating value of 20,470kJ/kg and less than 5% water content, were tested. Unlike sewage sludge, industrial sludge contains high concentrations of heavy metals and thus cannot be directly utilized as refuse-derived fuel. The dried sludges were melted in a furnace and then rapidly cooled to form vitrified slags; the vitrification of SiO2 securely encapsulates hazardous heavy metals within the crystalline structure of the slag. To evaluate the hazard of vitrified slag, the heavy metal elution concentration was analyzed. Following vitrification, Hg, Cd, Cr(+6), HCN and Pb concentrations were not detectable, whereas Cu concentration decreased from 26.78mg/L to 0.42mg/L in DJ sludge, from 27.10mg/L to 0.13mg/L in DG and from 49.47mg/L to 0.047mg/L in GM sludge.

Recycling of inorganic waste in monolithic and cellular glass-based materials for structural and functional applications

The stabilization of inorganic waste of various nature and origin, in glasses, has been a key strategy for environmental protection for the last decades. When properly formulated, glasses may retain many inorganic contaminants permanently, but it must be acknowledged that some criticism remains, mainly concerning costs and energy use. As a consequence, the sustainability of vitrification largely relies on the conversion of waste glasses into new, usable and marketable glass-based materials, in the form of monolithic and cellular glass-ceramics. The effective conversion in turn depends on the simultaneous control of both starting materials and manufacturing processes. While silica-rich waste favours the obtainment of glass, iron-rich wastes affect the functionalities, influencing the porosity in cellular glass-based materials as well as catalytic, magnetic, optical and electrical properties. Engineered formulations may lead to important reductions of processing times and temperatures, in the transformation of waste-derived glasses into glass-ceramics, or even bring interesting shortcuts. Direct sintering of wastes, combined with recycled glasses, as an example, has been proven as a valid low-cost alternative for glass-ceramic manufacturing, for wastes with limited hazardousness. The present paper is aimed at providing an up-to-date overview of the correlation between formulations, manufacturing technologies and properties of most recent waste-derived, glass-based materials. © 2016 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Thermal plasma treatment of stormwater sediments: comparison between DC non-transferred and partially transferred arc plasma

The disposal of enormous amount of stormwater sediments becomes an emerging worldwide problem. Stormwater sediments are contaminated by heavy metals, phosphorus, trace organic and hydrocarbons, and cannot be disposed without treatment. Thermal plasma decontamination technology offers a high decomposition rate in a wide range of toxic organic compound and immobilization of heavy metal. In this study, we compared the treatment results between two different modes of thermal plasma: (1) a non-transferred direct current (DC) mode and (2) a partial DC-transferred mode. The reductions of total organic carbon (TOC) were, respectively, 25% and 80% for non-transferred and partially transferred plasma, respectively. Most of the toxic organic compounds were converted majorly to CxHy. In the gaseous emission, the accumulated CxHy, CO, NO and H2S were significantly higher in partially transferred mode than in non-transferred mode. The solid analysis demonstrated that the concentrations of Ca and Fe were enriched by 500% and 40%, respectively. New chemical compositions such as KAlSi3O8, Fe3O4, NaCl and CaSO4 were formed after treatment in partially DC-transferred mode. The power inputs were 1 and 10 kW, respectively, for non-transferred DC mode and a partially DC-transferred mode. With a lower energy input, non-transferred plasma treatment can be used for decontamination of sediments with low TOC and metal concentration. Meanwhile, partially transferred thermal plasma with higher energy input is suitable for treating sediments with high TOC percentage and volatile metal concentration. The organic compounds are converted into valuable gaseous products which can be recycled as an energy source.

Vitrification as an alternative to landfilling of tannery sewage sludge

Due to high content of heavy metals such as chromium, tannery sewage sludge is a material which is difficult to be biologically treated as it is in the case of organic waste. Consequently, a common practice in managing tannery sewage sludge is landfilling. This poses a potential threat to both soil and water environments and it additionally generates costs of construction of landfills that meet specific environment protection requirements. Vitrification of this kind of sewage sludge with the addition of mineral wastes can represent an alternative to landfilling. The aim of this study was to investigate the possibility of obtaining an environmentally safe product by means of vitrification of tannery sewage sludge from a flotation wastewater treatment process and chemical precipitation in order to address the upcoming issue of dealing with sewage sludge from the tannery industry which will be prohibited to be landfilled in Poland after 2016. The focus was set on determining mixtures of tannery sewage sludge with additives which would result in the lowest possible heavy metal leaching levels and highest hardness rating of the products obtained from their vitrification. The plasma vitrification process was carried out for mixtures with various amounts of additives depending on the type of sewage sludge used. Only the materials of waste character were used as additives. One finding of the study was an optimum content of mineral additives in vitrified mixture of 30% v/v waste molding sands with 20% v/v carbonate flotation waste from the zinc and lead industry for the formulations with flotation sewage sludge, and 45% v/v and 5% v/v, respectively, for precipitation sewage sludge. These combinations allowed for obtaining products with negligible heavy metal leaching levels and hardness similar to commercial glass, which suggests they could be potentially used as construction aggregate substitutes. Incineration of sewage sludge before the vitrification process lead to increased hardness of the vitrificates and reduced leaching of some heavy metals.

Magnetic Glass Ceramics by Sintering of Borosilicate Glass and Inorganic Waste

Ceramics and glass ceramics based on industrial waste have been widely recognized as competitive products for building applications; however, there is a great potential for such materials with novel functionalities. In this paper, we discuss the development of magnetic sintered glass ceramics based on two iron-rich slags, coming from non-ferrous metallurgy and recycled borosilicate glass. The substantial viscous flow of the glass led to dense products for rapid treatments at relatively low temperatures (900–1000 °C), whereas glass/slag interactions resulted in the formation of magnetite crystals, providing ferrimagnetism. Such behavior could be exploited for applying the obtained glass ceramics as induction heating plates, according to preliminary tests (showing the rapid heating of selected samples, even above 200 °C). The chemical durability and safety of the obtained glass ceramics were assessed by both leaching tests and cytotoxicity tests.

Recycling of porcelain tile polishing residue in portland cement: hydration efficiency

Ceramic tiles are widely used by the construction industry, and the manufacturing process of ceramic tiles generates as a major residue mud derived from the polishing step. This residue is too impure to be reused in the ceramic process and is usually discarded as waste in landfills. But the analysis of the particle size and concentration of silica of this residue shows a potential use in the manufacture of building materials based on portland cement. Tests were conducted on cement pastes and mortars using the addition of 10% and 20% (mass) of the residue. The results of compressive strength in mortars made up to 56 days showed a significant increase in compressive strength greater than 50%. The result of thermogravimetry shows that portlandite is consumed by the cement formed by the silica present in the residue in order to form calcium silicate hydrate and featuring a pozzolanic reaction. This effect improves the performance of cement, contributes to research and application of supplementary cementitious materials, and optimizes the use of portland cement, reducing the environmental impacts of carbon dioxide emissions from its production.