Utilization of flotation wastes of copper slag as raw material in cement production

Copper slag wastes, even if treated via processes such as flotation for metal recovery, still contain heavy metals with hazardous properties posing environmental risks for disposal. This study reports the potential use of flotation waste of a copper slag (FWCS) as iron source in the production of Portland cement clinker. The FWCS appears a suitable raw material as iron source containing >59% Fe(2)O(3) mainly in the form of fayalite (Fe(2)SiO(4)) and magnetite (Fe(3)O(4)). The clinker products obtained using the FWCS from the industrial scale trial operations over a 4-month period were characterised for the conformity of its chemical composition and the physico-mechanical performance of the resultant cement products was evaluated. The data collected for the clinker products produced using an iron ore, which is currently used as the cement raw material were also included for comparison. The results have shown that the chemical compositions of all the clinker products including those of FWCS are typical of a Portland cement clinker. The mechanical performance of the standard mortars prepared from the FWCS clinkers were found to be similar to those from the iron ore clinkers with the desired specifications for the industrial cements e.g. CEM I type cements. Furthermore, the leachability tests (TCLP and SPLP) have revealed that the mortar samples obtained from the FWCS clinkers present no environmental problems while the FWCS could act as the potential source of heavy metal contamination. These findings suggest that flotation wastes of copper slag (FWCS) can be readily utilised as cement raw material due to its availability in large quantities at low cost with the further significant benefits for waste management/environmental practices of the FWCS and the reduced production and processing costs for cement raw materials.     

Red mud addition in the raw meal for the production of Portland cement clinker

The aim of the present research work was to investigate the possibility of adding red mud, an alkaline leaching waste, which is obtained from bauxite during the Bayer process for alumina production, in the raw meal for the production of Portland cement clinker. For that reason, two samples of raw meals were prepared: one with ordinary raw materials, as a reference sample ((PC)Ref), and another with 3.5% red mud ((PC)R/M). The effect on the reactivity of the raw mix was evaluated on the basis of the unreacted lime content in samples sintered at 1350, 1400 and 1450 degrees C. Subsequently, the clinkers were produced by sintering the two raw meals at 1450 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the red mud did not affect the mineralogical characteristics of the so produced Portland cement clinker. Furthermore, both clinkers were tested by determining the grindability, setting time, compressive strength and expansibility. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of the red mud did not negatively affect the quality of the produced cement.     

Utilization of municipal solid waste incineration ash in Portland cement clinker

Municipal solid waste incineration (MSWI) ash is used in part as raw materials for cement clinker production by taking advantage of the high contents of SiO₂, Al₂O₃, and CaO. It is necessary for environmental reasons to establish a material utilization system for the incineration waste ash residue instead of disposing these ashes into landfill. The aim of this paper is to study the feasibility of replacing clinker raw materials by waste ash residue for cement clinker production. MSWI bottom ash and MSWI fly ash are the main types of ashes being evaluated. The ashes were mixed into raw mixture with different portions of ash residue to produce cement clinker in a laboratory furnace at approximately 1400°C. X-ray diffraction and X-ray florescence techniques were used to analyze the phase chemistry and chemical composition of clinkers in order to compare these ash-based clinkers with commercial Portland cement clinker.     

Potential use of pyrite cinders as raw material in cement production: Results of industrial scale trial operations

Pyrite cinders, which are the waste products of sulphuric acid manufacturing plants, contain hazardous heavy metals with potential environmental risks for disposal. In this study, the potential use of pyrite cinders (PyCs) as iron source in the production of Portland cement clinker was demonstrated at the industrial scale. The chemical and mineralogical analyses of the PyC sample used in this study have revealed that it is essentially a suitable raw material for use as iron source since it contains >87% Fe₂O₃ mainly in the form of hematite (Fe₂O₃) and magnetite (Fe₃O₄). The samples of the clinkers produced from PyC in the industrial scale trial operation of 6 months were tested for the conformity of their chemical composition and the physico-mechanical performance of the resultant cement products. The data were compared with the clinker products of the iron ore, which is used as the raw material for the production Portland cement clinker in the plant. The chemical compositions of all the clinker products of PyC appeared to conform to those of the iron ore clinker, and hence, a Portland cement clinker. The mechanical performance of the mortars prepared from the PyC clinker was found to be consistent with those of the industrial cements e.g. CEM I type cements. It can be inferred from the leachability tests (TCLP and SPLP) that PyC could be a potential source of heavy metal pollution while the mortar samples obtained from the PyC clinkers present no environmental problems. These findings suggest that the waste pyrite cinders can be readily used as iron source for the production of Portland cement. The availability of PyC in large quantities at low cost provides further significant benefits for the management/environmental practices of these wastes and for the reduction of mining and processing costs of cement raw materials.     

Utilization of steel slag for Portland cement clinker production

The aim of the present research work is to investigate the possibility of adding steel slag, a by-product of the conversion of iron to steel process, in the raw meal for the production of Portland cement clinker. Two samples of raw meals were prepared, one with ordinary raw materials, as a reference sample ((PC)(Ref)), and another with 10.5% steel slag ((PC)(S/S)). Both raw meals were sintered at 1450 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the steel slag did not affect the mineralogical characteristics of the so produced Portland cement clinker. Furthermore, both clinkers were tested by determining the grindability, setting times, compressive strengths and soundness. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of the steel slag did not negatively affect the quality of the produced cement.     

Incorporation of coal combustion residuals into calcium sulfoaluminate-belite cement clinkers

In recent years, calcium sulfoaluminate-belite (CSAB) cement has been promoted as a sustainable alternative to Portland cement due to lower energy used and less CO₂ emitted during production, while providing comparable performance. However, a potential problem facing the widespread adoption and production of CSAB cement is the cost and availability of raw materials and it is therefore desirable to find alternative raw materials to keep costs competitive. In this study, two CSAB cement clinkers with a similar target phase composition were synthesized from combinations of natural and waste materials (coal combustion residuals). The two CSAB cement clinkers were compared against a CSAB clinker made from reagent-grade chemicals, enabling examination of the effects of impurities on performance. Cements made from the clinkers were examined for hydration rate, hydration product formation, dimensional stability, and compressive strength.     

Belite cements obtained from ceramic wastes and the mineral pair CaF2/CaSO4

The cement industry is seeking alternative approaches to reduce the high energy and environmental costs of Portland cement manufacture. One such alternative is belite cement. In the present study clinkers with high (36–60%) belite contents were obtained at 1350 °C from raw mixes consisting of ceramic waste and the fluxing/mineralised pair CaF₂/CaSO₄. The factors found to affect the mineralogical composition and the clinker phase polymorphs obtained were the lime saturation factor (LSF), the presence of ceramic waste and the addition of CaF₂ and CaSO₄.The reactivity of these belite clinkers with water was analysed with isothermal conduction calorimetry. A statistical study was then conducted on the findings to determine the effect of each variable when the response signals were peak heat flow rate and the time needed to reach that peak. The statistical analysis identified the optimal experimental conditions to be a LSF of 90%, a CaSO₄ content of 2.60%, and the absence of both ceramic waste and CaF₂.     

Preparation of calcium sulphoaluminate cement using fertiliser plant wastes

Phosphochalks from fertiliser plants contain significant amount of calcium sulphate along with P(2)O(5) and fluorine. The presence of these impurities makes them unsuitable for most applications and, hence its availability in millions of tons. We demonstrate that it is possible to prepare calcium sulphoaluminate-aluminoferrite based special cements having strength values comparable to ordinary Portland cement (OPC) using these waste chalks. Such cements are insensitive to the presence of impurities in the raw mixture, clinker at low temperatures (1,230 degrees C) and the clinkers produced are soft and friable. An empirical technique has been developed to predict the phase composition of the clinkers given the chemical composition of the starting raw mixture. The proposed low temperature clinkering route appears to be a promising method for converting waste phosphochalks into construction grade cements.     

Dredged sediments used as novel supply of raw material to produce Portland cement clinker

The maintenance of waterways generates large amounts of dredged sediments that are an environmental issue. This paper focuses on the use of fluvial sediment to replace a portion of the raw materials of Portland cement clinker, which would otherwise come from natural resources. The mineralogy of the synthetic cement was characterised using X-ray diffraction and scanning electron microscopy and its reactivity was followed by isothermal calorimetry. Comparisons were made to a commercial ordinary Portland cement (CEM I 52.5). Compressive strength measurements were conducted on cement pastes at 1, 2, 4, 7, 14, 28 and 56 days to study strength development. The results showed that Portland cement clinker can be successfully synthesised by using up to 39% sediment. The compressive strengths developed by the cement made from sediment were equivalent to those obtained with the reference at early ages and 20% higher at long term.     

Utilization of oil shale in the production of Portland clinker

Oil shale can potentially be utilized in manufacturing the Portland cement. In addition to the utilization of the spent oil shale after combustion, it can also reduce the required temperature for the clinkering reactions during the production of Portland clinker. A study on the Jordanian oil shale was performed to maximize the use of oil shale ash in the manufacturing of Portland cement. It was found that Jordanian oil shale can be used up 15% with the typical raw materials to produce Portland clinker without altering its principle properties. The corresponding temperature required to generate the required liquid for the clinkering reactions as well as the essential ingredients for clinker was found to be around 1300 °C. The optimized blend ratio obtained was equal to of 16% oil shale ash, 18% kaolinite, and 66% calcite. The operating temperatures for this optimized blend ratio were found to be between 1300 and 1350 °C. The resulting Portland clinker from this ratio will need further testing in accordance with international standards for Portland cement to examine properties like strength, setting time, etc.     

Reduction of clinkerization temperature by using phosphogypsum

Valorization of phosphogypsum as mineralizer in the burning of Portland cement clinker was studied in our laboratory. X-ray fluorescence, optical microscope technique and powder X-ray diffraction were then used to characterize the synthesized clinker and its raw mixture in terms of chemical composition and clinker mineralogical composition. The effects of phosphogypsum on structural and morphological properties of clinker minerals and on the presence of alite were followed by scanning electron microscopy combined with microprobe analysis. The addition of phosphogypsum to the cement raw mixture shows that the burning temperature decreases and therefore improves the production process of clinker. The addition of 10% phosphogypsum permits a complete clinkerization at low burning temperature (1200 degrees C), instead of 1470 degrees C, which increases the cement factory efficiency by 25% and extends the service life of furnace fire brick. Structural and morphological analysis of clinker produced under the new conditions show that phosphogypsum preserve perfectly the crystalline structure of silicate phases, which leads to the improvement of physical and mechanical properties of cement.     

Examination of the jarosite-alunite precipitate addition in the raw meal for the production of sulfoaluminate cement clinker

The aim of the present research work was to investigate the possibility of adding a jarosite-alunite chemical precipitate, a waste product of a new hydrometallurgical process developed to treat economically low-grade nickel oxides ores, in the raw meal for the production of sulfoaluminate cement clinker. For that reason, two samples of raw meals were prepared, one contained 20% gypsum, as a reference sample ((SAC)Ref) and another with 11.31% jarosite-alunite precipitate ((SAC)J/A). Both raw meals were sintered at 1300 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the jarosite-alunite precipitate did not affect the mineralogical characteristics of the so produced sulfoaluminate cement clinker and there was confirmed the formation of the sulfoaluminate phase (C4A3S), the most typical phase of this cement type. Furthermore, both clinkers were tested by determining the grindability, setting time, compressive strength and expansibility. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of jarosite-alunite precipitate did not negatively affect the quality of the produced cement.     

The effect of clinker and limestone quality on the gas permeability,water absorption and pore structure of limestone cement concrete

In this paper the effect of clinker and limestone quality on the air permeability, water absorption and pore structure of limestone cement concrete is investigated. Portland limestone cements of different fineness and limestone content have been produced by intergrinding clinker, gypsum and limestone. Two clinkers with different chemical composition, mineralogical composition and strength development as well as three limestones, differing by their calcite, dolomite, quartz and clay contents, have been used. It is shown that the clinker quality significantly affects the gas permeability and sorptivity of the limestone cement concrete. Limestone cements with high C₃A and alkalis content seem to be more appropriate for improving the permeability properties of concrete. In addition, the effect of the limestone quality on the concrete permeability is not well established. The pore size distribution and more specifically the mean pore size affects the gas permeability and the sorptivity of the concrete. Finally it is concluded that, depending on the clinker quality and the cement fineness, limestone cement concrete, with an optimum limestone content, can give lower gas permeability and water absorption rate as compared with pure cement concrete.     

Relation between cement composition and compressive strength of pure pastes

In Europe, cement paste compressive strength models are frequently described by a power law similar to that of Féret. The French LCPC has also adopted this mathematical approach in its recent concrete mixture proportioning model. However the coefficient k and exponent b of the adopted power law were calibrated with only one Portland cement clinker, starting from pure pastes with various concentrations. These parameters do not take into account the chemical properties of the clinker. The purpose of this work was to check if the clinker chemical nature had an influence on the mechanical performances of the pastes (at 28 days). Complementary tests with eight cements coming from six different cement plants were then carried out. The mathematical treatment of the results made it possible to connect coefficient k to the silica content of the clinkers and more particularly to their C₃S rates. It is linked to the strength of hydrated cement paste. Thus, the suggested approach significantly improves the accuracy of paste strength calculation. These results can be used to calculate concrete strength.     

Environmental management of bottom ash from municipal solid waste incineration based on a life cycle assessment approach

Conventional bottom ash (BA) management consists of a solidification process using inorganic binder reagents, such as cement. However, despite the heavy metal content, the use of BA as a natural aggregate has become increasingly more common. In particular, bottom ash is used as a raw material for clinker, cement mortar or frit production, as a drainage layer in landfills or as a sub-base material in road construction. In this study, the life cycle assessment approach was used to evaluate and compare ash solidification with ash recycling in Portland cement production as a clinker and gypsum substitute. The findings showed that the substitution of ash for clinker resulted in the lowest natural resources (NR) consumption and the lowest environmental burdens (EB). The decrease in the clinker substitution percentage generated a higher NR consumption and an increased EB. In ash recycling, the distance between the incinerator and the cement facility is an important parameter in the decision-making process. Specifically, ash solidification presented less favourable results than ash recycling (with a clinker substitution of 25 %), despite the increasing distance between the incinerator and the cement facility. However, when the clinker substitution decreased to 2.5 % or when ash was substituted for gypsum, the distance played an important role in the water impact.     

An analysis of the properties of Portland limestone cements and concrete

In this paper the main factors affecting the properties of Portland limestone cements are discussed while the hydration behavior of limestone cements is examined. In addition, the intergrinding process, concerning the production of the limestone cements, is studied. Finally the properties and the behavior of limestone cement concrete as well as the corrosion behavior of limestone cement mortar are investigated. It is concluded that the fineness of clinker and limestone is strongly connected with the limestone content and the fineness of the cement. The limestone cements indicate satisfactory strength and generally demand less water than the relative pure cements. The limestone addition improves the clinker reactivity and the exploitation of its hydraulic potential. The Portland limestone cements indicate competitive concrete properties and improve the corrosion performance of the concrete.     

The influence of phosphorous pentoxide on the phase composition and formation of Portland clinker

The influence of phosphorous pentoxide (P₂O₅) on the phase composition and formation of Portland clinker was studied in laboratory conditions. Phosphorous pentoxide in the form of calcium phosphate was added to common cement-making raw meal in graded quantities up to 5 wt.%. The raw meal properties were studied by thermal analysis. The development of clinker formation by burning for periods ranging from 20 s to 30 min in a special semi-automatic oven with a manipulator was followed using light optical microscopy. The phase composition of clinkers burnt to equilibrium was quantified by the optical point counting method. The entry of P₂O₅ into clinker minerals was determined by electron microprobe analyses. The laboratory tests show that at 0.7 wt.% of P₂O₅ in the clinker the alite (Ca₃SiO₅) content decreases and belite (Ca₂SiO₄) content increases. At a P₂O₅ content of 4.5 wt.% alite formation was totally blocked and the resulting clinker contained free lime in equilibrium with belite.     

Clinkers and cements obtained from raw mix containing ceramic waste as a raw material. Characterization,hydration and leaching studies

A clinker and a cement obtained from a raw mix containing ceramic waste as an alternative raw material were characterized in the present study. Their hydration, physical–chemical properties and leaching behaviour in different acid media were also explored. The findings showed that both the clinker and the cement met all the requirements set out in European standards EN 197-1 [1], although they had higher ZnO, ZrO₂, and B₂O₃ contents than an industrially produced reference product.According to the hydration studies, initial hydration was somewhat retarded in the new cement, which exhibited longer initial and final setting times and lower 2-day mechanical strength. The SEM/BSE/EDS microstructural study showed, however, that morphologically and compositionally, the hydration products formed were comparable to unadditioned Portland cement paste products. While low concentrations of Zn and B were observed to leach in acid media, the biotoxicity trials conducted confirmed that these concentrations were not toxic. Zr was retained in the cement pastes.     

X射线K值法在水泥物相中的应用

美国F.H.Chung提出的K值法近几年来在建材是到了推广和应用。基于K值法，我们采用计算机软件来计算峰的面积，从而 准确性，用化学纯原料制成水泥熟料中的四个主要矿物即C3S，C2S，C3A和C4AF；然后再用K值法对水泥熟料中的四个主要矿物进行定量分析研究，同时研究不同定量峰、参比物对结果的影响。实验研究结果表明，利用X射线K值法可以测定水泥熟料中的物相含量。     

Synthesis and hydration of calcium sulfoaluminate-belite cements with varied phase compositions

The production of portland cement is energy intensive and contributes significantly to greenhouse gas emissions. One method of reducing the environmental impact of concrete production is the use of an alternative binder, such as calcium sulfoaluminate-belite (CSAB) cement. The relatively low lime requirement of CSAB cement compared to portland cement reduces energy consumption and carbon dioxide emissions from cement production. Moreover, CSAB cement can be produced at temperatures approximately 200 °C lower than portland cement, further reducing energy and carbon dioxide. Major drawbacks to the implementation of CSAB cements are the lack of standard phase composition and published data on composition-processing-performance relationships. In this study, three CSAB cement clinkers with different phase compositions were synthesized from reagent-grade chemicals. The synthetic clinkers were analyzed for phase composition using X-ray diffraction and phase distribution using scanning electron microscopy. The synthetic clinkers were then tested for hydration rate using isothermal conduction calorimetry to investigate the effects of phase composition and gypsum addition on early-age hydration behavior. A proportioning method for predicting phase composition was refined and an equation for calculating the minimum gypsum content for CSAB cement clinker was developed.