Effects of recycled glass substitution on the physical and mechanical properties of clay bricks

In this study, wasted glasses from structural glass walls up to 45 wt.% were added into clay mixtures in brick manufacturing process. Physical and mechanical properties of clay bricks were investigated as functions of the wasted glass content and the firing temperature. The results indicated that with proper amount of wasted glasses and firing temperature, clay bricks with suitable physical and mechanical properties could be obtained. The compressive strength as high as 26–41 MPa and water absorption as low as 2–3% were achieved for bricks containing 15–30 wt.% of glass content and fired at 1100 °C. When the glass waste content was 45 wt.%, apparent porosity and water absorption was rapidly increased.     

Effects of using arsenic–iron sludge wastes in brick making

The arsenic–iron sludge generated in most of the treatment systems around the world is discharged into the nearest watercourse, which leads to accumulative rise of arsenic and iron concentrations in water. In this study, attempts were made to use the arsenic–iron sludge in making bricks and to analyze the corresponding effects on brick properties. The water treatment plant sludge is extremely close to brick clay in chemical composition. So, the sludge could be a potential substitute for brick clay. This study involved the addition of sludge with ratios 3%, 6%, 9% and 12% of the total weight of sludge–clay mixture. The physical and chemical properties of the produced bricks were then determined and evaluated and compared to control brick made entirely from clay. Results of different tests indicated that the sludge proportion and firing temperature were the two key factors in determining the quality of bricks. The compressive strength of 3%, 6%, 9% and 12% sludge containing brick samples were found to be 14.1 MPa, 15.1 MPa, 9.4 MPa and 7.1 MPa, respectively. These results indicate that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion. Leaching characteristics of burnt bricks were determined with the variation of pH at a constant temperature. The optimum amount of sludge that could be mixed with clay to produce good bonding of clay–sludge bricks was found to be 6% (safely maximum) by weight.     

Utilization of textile effluent wastewater treatment plant sludge as brick material

In the present work, the feasibility of using sludge generated in wastewater treatment plants of textile industry as a partial replacement for clay in the conventional brick manufacturing process is examined. Physico-chemical properties of the sludge and clay were studied. The characteristics of bricks with replacement of sludge (0–50 %) with an increment of 3 % were determined. All the brick samples satisfied the requirements of Indian Standards norms in terms of weight loss on ignition. The bricks with sludge up to 15 % satisfied the prescribed norms for compressive strength and water absorption. Results also showed that the brick weight loss on ignition was mainly attributed to the organic matter content in the sludge being burnt off during the firing process. The characteristics of bricks such as efflorescence, density and weight loss on ignition for bricks with replacement of clayey soil with textile sludge up to 15 % also satisfied the requirements of the Indian Standard. Thus, textile sludge up to 15 % can be effectively added to make brick material.     

Utilisation of IGCC slag and clay steriles in soft mud bricks (by pressing) for use in building bricks manufacturing

The subject of this study is the application to the construction of soft mud bricks (also known as pressed bricks), both green and heat-treated bodies, built from raw materials from Santa Cruz de Mudela, Ciudad Real, and IGCC slag from the power central of Puertollano (Ciudad Real, Spain). For this purpose, industrial level tests have been performed: the production of these kind of bricks from mixes of waste from ores of construction clays and to significant fraction of different ratios and clay granulometries mixed with IGCC slag. The results of this experimentation suggests that not only can IGCC slag be applied to a ceramic process, but also its use gives several advantages, as water and energy savings, as well as improvements on the final properties of products.     

Petrogenetic characteristics of molten slag from the pyrolysis/melting treatment of MSW

MSW slag materials derived from four pyrolysis melting plants in Japan were studied from the viewpoint of petrology in order to discriminate the glass and mineral phases and to propose a petrogenetic model for the formation process of molten slag. Slag material is composed of two major components: melt and refractory products. The melt products that formed during the melting process comprise silicate glass, and a suite of minerals as major constituents. The silicate glass is essentially composed of low and high silica glass members (typically 30% and 50% of SiO(2), respectively), from which minerals such as spinels, melilite, pseudowollastonite, and metallic inclusions have been precipitated. The refractory products consist mainly of pieces of metals, minerals and lithic fragments that survived through the melting process. Investigations demonstrated that the low silica melts (higher Ca and Al contents) were produced at upper levels of high temperature combustion chamber HTCC, at narrower temperature ranges (1250-1350 degrees C), while the high silica melts formed at broader temperature ranges (1250-1450 degrees C), at the lower levels of HTCC. The recent temperature ranges were estimated by using CaOAl(2)O(3)SiO(2) (CAS) ternary liquidus diagram that are reasonably consistent with those reported for a typical combustor. It was also understood that the samples with a higher CaO/SiO(2) ratio (>0.74-0.75) have undergone improved melting, incipient crystallization of minerals, and extensive homogenization. The combined mineralogical and geochemical examinations provided evidence to accept the concept of stepwise generation of different melt phases within the HTCC. The petrogenesis of the melt products may therefore be described as a two-phase melt system with immiscible characteristics that have been successively generated during the melting process of MSW.     

模拟氯化钠盐渣的高温处理

采用高温处理法对模拟氯化钠盐渣（简称盐渣）进行处理,研究了加热过程中气体有机物产生量随加热时间的变化规律以及加热温度对气体有机物产生量的影响,并分析了盐渣的高温处理效果。实验结果表明：含苯盐渣、含异丁醇盐渣、含氯苯盐渣、含二甲苯盐渣和混合盐渣在高于盐渣中所含有机物沸点30 ℃的条件下加热120 min,盐渣中的有机物去除率均大于99.99%;混合盐渣的加热温度越高,气体有机物的产生速率越快,相同时间内有机物的去除率也越大;盐渣中有机物的气化分离可分为3个阶段,初始阶段有机物气化速率较小,中间阶段气体有机物产生量迅速增加,最后阶段大部分有机物从盐渣中气化分离;盐渣中的有机物在高温气化时,会发生一定的化学反应,有微量的新物质生成。     

The hydration characteristics and utilization of slag obtained by the vitrification of MSWI fly ash

This study investigated the effects of slag composition on the hydration characteristics of slag blended cement (SBC) pastes. Synthetic slag samples were prepared by melting CaO-modified and Al(2)O(3)-modified municipal solid waste incinerator (MSWI) fly ash. MSWI fly ash was mixed with 5% CaO and 5% Al(2)O(3) (by weight), respectively, resulting in two fly ash mixtures. These mixtures were then melted at 1400 degrees C for 30 min to produce two types of slag with different contents, designated at C-slag and A-slag. Both the C-slag and A-slag samples exhibited a pozzolanic activity index higher than the unmodified slag sample. The results show that the synthetic slags all met the Taiwan EPA's current regulatory thresholds. These synthetic slags were then blended with ordinary Portland cement (OPC) at various weight ratios ranging from 10 to 40%. The 28-day strength of the C1 paste was higher than that developed by the OPC paste, suggesting that the C-slag contributed to the earlier strength of the SBC pastes. At curing times beyond 28 days, the strength of the A1 paste samples approached that of the OPC paste samples. It can be seen from this that increasing the amount of calcium and aluminum oxide increases the early strength of SBC. The C-slag blended cement paste samples showed an increase in the number of fine pores with the curing time, showing that the C-slag enhanced the pozzolanic reactions, filling the pores. Also, the incorporation of a 10% addition of C-slag also tended to enhance the degree of hydration of the SBC pastes during the early ages (3-28 days). However, at later ages, no significant difference in degree of hydration between the OPC pastes and the SBC pastes was observed with the 10% C-slag addition. However, the incorporation of A-slag did decreased the degree of hydration. A slag blend ratio of 40% significantly decreased the hydration degree.     

Changes in mineralogical and leaching properties of converter steel slag resulting from accelerated carbonation at low CO2 pressure

Steel slag can be applied as substitute for natural aggregates in construction applications. The material imposes a high pH (typically 12.5) and low redox potential (Eh), which may lead to environmental problems in specific application scenarios. The aim of this study is to investigate the potential of accelerated steel slag carbonation, at relatively low pCO₂ pressure (0.2 bar), to improve the environmental pH and the leaching properties of steel slag, with specific focus on the leaching of vanadium. Carbonation experiments are performed in laboratory columns with steel slag under water-saturated and -unsaturated conditions and temperatures between 5 and 90 °C. Two types of steel slag are tested; free lime containing (K3) slag and K1 slag with a very low free lime content. The fresh and carbonated slag samples are investigated using a combination of leaching experiments, geochemical modelling of leaching mechanisms and microscopic/mineralogical analysis, in order to identify the major processes that control the slag pH and resulting V leaching. The major changes in the amount of sequestered CO₂ and the resulting pH reduction occurred within 24 h, the free lime containing slag (K3-slag) being more prone to carbonation than the slag with lower free lime content (K1-slag). While carbonation at these conditions was found to occur predominantly at the surface of the slag grains, the formation of cracks was observed in carbonated K3 slag, suggesting that free lime in the interior of slag grains had also reacted. The pH of the K3 slag (originally pH ± 12.5) was reduced by about 1.5 units, while the K1 slag showed a smaller decrease in pH from about 11.7 to 11.1. However, the pH reduction after carbonation of the K3 slag was observed to lead to an increased V-leaching. Vanadium leaching from the K1 slag resulted in levels above the limit values of the Dutch Soil Quality Decree, for both the untreated and carbonated slag. V-leaching from the carbonated K3 slag remained below these limit values at the relatively high pH that remained after carbonation. The V-bearing di-Ca silicate (C2S) phase has been identified as the major source of the V-leaching. It is shown that the dissolution of this mineral is limited in fresh steel slag, but strongly enhanced by carbonation, which causes the observed enhanced release of V from the K3 slag. The obtained insights in the mineral transformation reactions and their effect on pH and V-leaching provide guidance for further improvement of an accelerated carbonation technology.     

Reduction of tar using cheap catalysts during sewage sludge gasification

Solid-fuel conversion or gasification study of sewage sludge and energy recovery has become increasingly important because energy recovery and climate change are emerging issues. Various types of catalysts, such as dolomite, steel slag and calcium oxide, were tested for tar reduction during the sewage sludge gasification process. For the experiments on sewage sludge gasification reactions and tar reduction using the catalysts, a fixed bed of laboratory-scale experimental apparatus was set up. The reactor was made of quartz glass using an electric muffle furnace. The sewage sludge samples used had moisture contents less than 6%. The experimental conditions were as follows: sample weight was 20 g and reaction time was 10 min, gasification reaction temperature was from 600 to 800°C, and the equivalence ratio was 0.2. The quantity of catalysts was 2–6 g, and temperatures of catalyst layers were 500–700°C. As the reaction temperature increased up to 800°C, the yields of gaseous products and liquid products increased, whereas char and tar products decreased, showing effects on gas product compositions. These results were considered to be due to the increase of the water-gas reaction and Boudouard reaction. In the case of experiments with catalysts, dolomite (4 g), steel slag (6 g) and calcium oxide (6 g) were used. When the temperature of catalysts increased, the weight of the tar produced decreased with different cracking performances by different catalysts. Reforming reactions were considered to occur on the surface of dolomite, steel slag and calcium oxide, causing cracking of the hydrocarbon structure, which eventually showed reduced tar generation.     

干式还原法处理铬渣的机理及应用

采用干式还原法处理铬渣。在多级还原焙烧炉中于高温条件下,将过量的煤粉和铬渣混合后与O₂反应,经冷却、擦磨、磁分离后可得到铁精砂和处理后铬渣。介绍了干式还原法处理铬渣的机理和工艺参数。以3种铬渣试样进行应用试验,经多级还原焙烧—磁分离后,铬渣中的Cr（Ⅵ）质量浓度为0.05~0.18 mg/L,低于HJ/T301—2007标准中的要求（0.50 mg/L）,可作为建材原料加以利用。磁分离得到的铁精砂产品中铁的质量分数大于50%,铁回收率大于70%。目前设计的多级还原焙烧炉单炉处理铬渣能力为150 kt/a,标煤消耗为35 kg/t,处理成本约为60元/t。     

Reusability of sewage sludge in clay bricks

Bricks produced from sewage sludge in different compositions were investigated. Results of the tests indicated that the sludge proportion is a key factor in determining the brick quality. Increasing the sludge content results in a decrease in brick shrinkage, bulk density, and compressive strength. Brick weight loss on ignition was mainly due to the contribution of the contained organic matter from the sludge being burnt off during the firing process, as well as inorganic substances found in both clay and sludge. The physical, mechanical, and chemical properties of the bricks that were supplemented with various proportions of dried sludge from 10 to 40wt% and generally complied with the General Specification for Brick as per the Malaysian Standard MS 7.6:1972, which dictates the requirements for clay bricks used in walling in general. A standard leaching test method also showed that the leaching of metals from the bricks is very low.     

Stabilization/solidification of ashes in clays used in the manufacturing of ceramic bricks.

This paper presents the results of the lixiviation of metals from different mixtures of fly and bottom ashes that have been stabilized and solidified in clays used in the manufacture of bricks. The ashes used for this study were obtained from a Hoffmann-type brick furnace adapted for the incineration of municipal solid waste during the manufacturing of ceramic bricks. The ashes were stabilized in clay in different proportions of clay:ash mix (99:1, 95:5, 90:10, 80:20 and 60:40). Such mixes were used to manufacture bricks that were calcined at a temperature ranging from 50 to 1100 degrees C. The clay, ashes and manufactured bricks were characterized using X-ray diffraction, fluorescent X-ray, thermogravimetry, differential thermal analysis, atomic absorption spectroscopy and scanning electronic microscopy. In addition, toxicity characteristic leaching procedure lixiviation tests were performed according to the EPA 1311 method for the determination of heavy metals. The results showed an affinity between clay and ash, and also that the bricks manufactured with these mixtures present low lixiviation levels. The tests also showed the highest decrease in the concentration of arsenic, nickel, chromium, zinc and silver for 99:1 mixtures. The 95:5 mixture was found to be the most favourable for the stabilization (greater concentration decrease) of lead and cadmium. Selenium was the metal with the lowest concentration change whereas arsenic, nickel, chromium, zinc and cadmium showed the greatest concentration change in all mixtures, with the exception of cadmium in the mixture 99:1.     

Reprocessing of metallurgical slag into materials for the building industry

Several methods of reprocessing metallurgical (blast furnace) slag into materials for the building industry, based on melting aggregates with submerged combustion, were developed and tested. The first method involves melting hot slag with some additives directly in a slag ladle with a submerged gas-air burner, with the objective of producing stabilized slag or glass-ceramic. The second method involves direct draining of melted slag from a ladle into the slag receiver, with subsequent control of the slag draining into the converter where special charging materials are added to the melt, with the objective of producing glass-ceramic. A third method involves melting cold slag with some additives inside a melting converter with submerged gas-air burners, with the objective of producing glass-ceramic fillers for use in road construction. Specific to the melting process is the use of a gas-air mixture with direct combustion inside the melt. This feature provides melt bubbling to help achieve maximum heat transfer from combustion products to the melt, improve mixing (and therefore homogeneity of the melt), and increases the rate of chemical reactions. The experimental data for different aspects of the proposed methods are presented. The reprocessed blast-furnace slag in the form of granules can be used as fillers for concretes, asphalts, and as additives in the production of cement, bricks and other building materials. As well, reprocessed blast-furnace slag can be poured into forms for the production of glass-ceramic tiles.     

Physicochemical properties of slags produced at various amounts of iron addition in lead smelting

In the process of lead production from lead-bearing materials generated in copper metallurgy, a large amount of hazardous waste in the form of slag is produced. To assess the effect of the slag on the environment, its physicochemical properties were determined. In this study, the following methods were used: wavelength dispersive X-ray fluorescence (WD XRF), X-ray diffraction (XRD), and Bunte-Baum-Reerink method to determine softening and melting points, as well as viscosity examination and leaching tests. The measurements were performed on the slag produced with two different amounts of iron addition to the lead smelting process. The resulting slags, an oxide rich phase slag and a sulfide rich phase slag have different compositions and physicochemical properties. It was found that the increase in iron addition causes an increase in the softening melting point of the oxide rich phase slag by about 100 °C, and a twofold increase in the viscosity of both slag phases. The increase in iron addition also results in the decrease in As leachability and increase in Zn, Fe, and Cu leachability from the slags. Slag produced with increased iron addition has a greater impact on the environment.

     

Incorporation of sewage sludge in clay brick and its characterization.

This study reports the use of sewage sludge generated from sewage treatment plant (STP) as raw material in a clay brick-making process. The physico-chemical and mineralogical characterization of the sewage sludge and clay were carried out in order to identify the major technological constraints and to define the sludge pretreatment requirements if necessary. Moreover, the effects on processing conditions and/or on changes of typical final characteristics are also evaluated. Bricks were produced with sewage sludge additions ranging from 10 to 40% by dry weight. The texture and finishing of the surface of sludge-amended clay bricks were rather poor. As for the physical and chemical properties, bricks with a sludge content of up to 40 wt.% were capable of meeting the relevant technical standards. However, bricks with more than 30 wt.% sludge addition are not recommended for use since they are brittle and easily broken even when handled gently. A tendency for a general degradation of brick properties with sludge additions was observed due to its refractory nature. Therefore, sludge bricks of this nature are only suitable for use as common bricks, which are normally not exposed to view, because of poor surface finishing.     

Properties of alkali-activated systems with stone powder sludge

This article investigates the effects of stone powder sludge on the microstructure and strength development of alkali-activated fly ash and blast furnace slag mixes. Stone powder sludge produced from a crushed aggregate factory was used to replace fly ash and granulated blast furnace slag at replacement ratios of 0%, 10%, 20%, and 30% by mass. The unit weight and compressive strength of the samples were measured, and scanning electron microscopy/energy dispersive spectroscopy and X-ray diffraction (XRD) analyses were performed. The test results indicated that the compressive strength of alkali-activated blast furnace slag mixes using stone powder sludge was higher than that of the alkali-activated blast furnace slag control mix, but the compressive strength of alkali-activated fly ash mixes decreased with increasing replacement ratio of stone powder sludge. Microscopy results indicated that for alkaliactivated blast furnace slag samples, broken surfaces were more evident than for the alkali-activated fly ash samples. For all XRD diagrams, broad and diffuse peaks were observed around 2θ = 35° (d = 2.96–3.03 Å), implying amorphous or short-ordering structure phases.     

Volatilization behavior of lead from molten slag under conditions simulating municipal solid waste melting

To reutilize molten slag derived from an ash melting process, the lead volatilization mechanism under reducing conditions was investigated. Reducing conditions were established by introducing a CO-CO₂-N₂ gas mixture to the reactor or by adding graphite to the molten slag prior to the experiments. As samples, two types of simulated molten slag composed of CaO-SiO₂-Al₂O₃ mixed with PbO were used and the lead volatilization behavior was studied at 1773 K. It was found that the lead volatilization rate increased on increasing the amount of reducing agent for both graphite and the CO-CO₂ gas mixture. For the CO-CO₂ reducing gas mixture, this increase was mainly attributed to PbO conversion to Pb. For the addition of graphite, the increase in lead volatilization ratio was considered to partially result from PbO conversion to Pb and partially from a reaction of graphite with SiO₂ yielding volatile SiO. The volatile SiO gas was then emitted from the furnace, which brought about a reduction in the SiO₂ content of the slag. As a result, the slag viscosity decreased, which led to an enhancement of the lead volatilization ratio.     

Characterisation of major component leaching and buffering capacity of RDF incineration and gasification bottom ash in relation to reuse or disposal scenarios

Thermal treatment of refuse derived fuel (RDF) in waste-to-energy (WtE) plants is considered a promising solution to reduce waste volumes for disposal, while improving material and energy recovery from waste. Incineration is commonly applied for the energetic valorisation of RDF, although RDF gasification has also gained acceptance in recent years. In this study we focused on the environmental properties of bottom ash (BA) from an RDF incineration (RDF-I, operating temperature 850-1000 °C) and a RDF gasification plant (RDF-G, operating temperature 1200-1400 °C), by evaluating the total composition, mineralogy, buffering capacity, leaching behaviour (both at the material’s own pH and as a function of pH) of both types of slag. In addition, buffering capacity results and pH-dependence leaching concentrations of major components obtained for both types of BA were analysed by geochemical modelling. Experimental results showed that the total content of major components for the two types of BA was fairly similar and possibly related to the characteristics of the RDF feedstock. However, significant differences in the contents of trace metals and salts were observed for the two BA samples as a result of the different operating conditions (i.e. temperature) adopted by the two RDF thermal treatment plants. Mineralogy analysis showed in fact that the RDF-I slag consisted of an assemblage of several crystalline phases while the RDF-G slag was mainly made up by amorphous glassy phases. The leached concentrations of major components (e.g. Ca, Si) at the natural pH of each type of slag did not reflect their total contents as a result of the partial solubility of the minerals in which these components were chemically bound. In addition, comparison of total contents with leached concentrations of minor elements (e.g. Pb, Cu) showed no obvious relationship for the two types of BA. According to the compliance leaching test results, the RDF-G BA would meet the limits of the Italian legislation for reuse and the European acceptance criteria for inert waste landfilling. RDF-I BA instead would meet the European acceptance criteria for non hazardous waste landfilling. A new geochemical modelling approach was followed in order to predict the leaching behaviour of major components and the pH buffering capacity of the two types of slags on the basis of independent mineralogical information obtained by XRD analysis and the bulk composition of the slag. It was found that the combined use of data regarding the mineralogical characterization and the buffering capacity of the slag material can provide an independent estimate of both the identity and the amount of minerals that contribute to the leaching process. This new modelling approach suggests that only a limited amount of the mineral phases that control the pH, buffering capacity and major component leaching from the solid samples is available for leaching, at least on the time scale of the applied standard leaching tests. As such, the presented approach can contribute to gain insights for the identification of the types and amounts of minerals that control the leaching properties and pH buffering capacity of solid residues such as RDF incineration and gasification bottom ash.     

Effect of exposure test conditions on leaching behavior of inorganic contaminants from recycled materials for roadbeds

Throughout the utilization of recycled materials, weathering factors such as humidity, gas composition and temperature have the potential to change the material properties and enhance the release of inorganic contaminants. In this research, the effects of weathering factors on recycled gravel materials for roadbeds were evaluated by applying three kinds of accelerating exposure tests: freezing–melting cycle test, carbonation test, and dry–humid cycle test. The effects of exposure tests were determined by X-ray diffraction (XRD) analysis and serial batch leaching test, making it possible to identify the change in release mechanisms. Sixteen elements, mainly metals, were investigated. Tested samples were molten slag from municipal solid waste, molten slag from automobile shredded residue, and crushed natural stone.After the exposure tests, the increase of cumulative release in the leaching test was generally less than 2.0 times that of the samples without the exposure test. Among the three test conditions, freezing–melting showed a slightly higher effect of enhancing the release of constituents. XRD analysis showed no change in chemical species. From these results, it was determined that the stony samples were stable enough so that their properties were not significantly changed by the exposure tests.     

炼钢精炼渣气固碳酸化反应吸附CO2

采用炼钢精炼渣,通过气固碳酸化反应吸附CO₂,考察了不同吸附温度下精炼渣对纯CO₂和模拟高炉煤气中CO₂的吸附能力。实验结果表明：吸附温度对精炼渣吸附CO₂反应有显著的影响,升高温度可以提高精炼渣对CO₂的吸附能力;在400 ℃时,精炼渣吸附纯CO₂和模拟高炉煤气中CO₂的量分别为4.7 mg/g和9.8 mg/g;吸附温度升高到500 ℃和550 ℃时,精炼渣对纯CO₂的吸附能力强于高炉煤气中CO₂;在550 ℃时,精炼渣吸附纯CO₂和模拟高炉煤气中CO₂的量达到最高,分别为14.7 mg/g和12.9 mg/g。