Raw Material For Cement Production Research Articles

Efficiency of Chemical and Biological Leaching of Copper Slag for the Recovery of Metals and Valorisation of the Leach Residue as Raw Material in Cement Production

Copper slags produced in vast quantities in smelting operations could be considered as secondary material sources instead of stockpiling them in landfills. This study investigates the recovery of valuable metals from copper slag and the valorisation of the leach residue as construction material in line with the principles of a circular economy. By taking into account that the environmental characterization of the as-received copper slag did not allow its disposal in landfills without prior treatment, chemical and biological leaching were tested for the recovery of metals. Pre-treatment with acids, namely HNO3 and H2SO4, resulted in the extraction of several target metals and the production of an almost inert waste. Despite the clearly better oxidative conditions prevailing in the bioleaching reactors, chemical leaching resulted in the higher dissolution of Cu (71% vs. 51%), Co (70% vs. 36%), and Zn (65% vs. 44%). The acid consumption was much lower during the bioleaching experiments compared to the chemical leaching. The bioleach residue was suitable for its use as supplementary cementitious material, showing a better performance than the reference sample without causing any detrimental effects to the calcium aluminate cement (CAC) quality. The complete valorisation of copper slags is expected to improve the economics of the process, by avoiding landfill costs and producing saleable products with high added value.

Approach to the management of gold ore tailings via its application in cement production

A large number of gold ore tailings pose a serious threat to the ecological environment. At the same time, with the increase of cement demand, the siliceous raw material used for cement production is in short supply and its price is rising. In this study, the gold ore tailings were used a siliceous raw material for cement production. The results proved that the clinker phases of the cements produced with different addition of gold ore tailings are 3CaO·SiO2, 2CaO·SiO2, 3CaO·Al2O3, and 4CaO·Al2O3·Fe2O3, and their hydration products are portlandite, calcium silicate hydrate, and ettringite, both of which are same as that of the cement produced without gold ore tailings. The optimum addition of gold ore tailings is 5 wt% and the calcination temperature for the cement production is 1450 °C. Furthermore, this study proved that the application of gold ore tailings in cement production can cut down the cost of siliceous raw material for cement enterprises in practice, which is also conducive to the management of gold ore tailings.

A Proposition of an In situ Production of a Blended Cement.

Many byproducts and waste materials with pozzolanic properties can substitute natural raw materials in cement production. Some of these waste materials like fly ash and blast furnace slag are commonly harnessed by cement industry. Others are of seldom use due to limitations of the very centralized cement production systems currently in use. In the authors opinion, it is necessary to change this system to enable efficient utilization of various waste materials that are available locally (e.g., white and red ceramics). In this study, a new partially centralized system of cement production is proposed. The adoption of a new system would significantly reduce the volume of long-distance transportation and enable utilization of numerous locally available waste materials that are currently dismissed. The last stage of production of the ready-to-use cement would take place in situ. The cement would be produced on demand and be immediately used for concrete production on-site. The research program was conducted considering the importance of the quality of cements obtained in the new way, substituting up to 12% of its mass by white ceramics. The research program was proof of concept of the proposed cement production system. It was shown that the quality of “in situ cement” does not differ from standard cements.

A comparative study of geometric and geostatistical methods for qualitative reserve estimation of limestone deposit

Mining projects especially relating to limestone deposits require an accurate knowledge of tonnage and grade, for both short and long-term planning. This is often difficult to establish as detailed exploration operations, which are required to get the accurate description of the deposit, are costly and time consuming. Geologists and mining engineers usually make use of geometric and geostatistical methods, for estimating the tonnage and grade of ore reserves. However, explicit assessments into the differences between these methods have not been reported in literature. To bridge this research gap, a comparative study is carried out to compare the qualitative reserve of Oyo-Iwa limestone deposit located in Nigeria, using geometric and geostatistical methods. The geometric method computes the reserve of the limestone deposit as 74,536,820 ​t (mean calcite, CaO grade ​= ​52.15) and 99,674,793 ​t (mean calcite, CaO grade ​= ​52.32), for the Northern and Southern zones of the deposit, respectively. On the other hand, the geostatistical method calculates the reserve as 81,626,729.65 ​t (mean calcite, CaO grade ​= ​53.36) and 100,098,697.46 ​t (mean calcite, CaO grade ​= ​52.96), for the two zones, respectively. The small relative difference in tonnage estimation between the two methods (i.e., 9.51% and 0.43%), proves that the geometric method is effective for tonnage estimation. In contrast, the relative difference in grade estimation between the two methods (i.e., 2.32% and 1.26%) is not negligible, and could be crucial in maintaining the profitability of the project. The geostatistical method is, therefore, more suitable, reliable and preferable for grade estimation, since it involves the use of spatial modelling and cross-validated interpolation. In addition, the geostatistical method is used to produce quality maps and three-dimensional (3-D) perspective view of the limestone deposit. The quality maps and 3-D view of the limestone deposit reveal the variability of the limestone grade within the deposit, and it is useful for operational management of the limestone raw materials. The qualitative mapping of the limestone deposit is key to effective production scheduling and accurate projection of raw materials for cement production.

Oil-based mud cutting as an additional raw material in clinker production

Oil-Based Mud (OBM) cutting is a hazardous by-product generated during oil-well drilling. Its chemical composition suggests that it might be suitable as a raw material in cement manufacturing. It is rich in calcium oxide, silica, and aluminium oxide, which are the major oxides in raw materials for cement manufacturing. In this research, OBM cutting is used as a constituent of the raw meal for cement clinker production. Raw meal mixtures were prepared by mixing different ratios of raw materials increasing OBM content. The impact of the addition of OBM cutting on the resulting clinker has been investigated. The results demonstrate that OBM cutting could be recycled in the manufacturing of Portland cement clinker. Clinker prepared using OBM cutting had very similar properties to that prepared from limestone. This result could represent an opportunity for solving an environmental problem.The addition of OBM cutting lowers the calcination temperature, and increases the rate of carbonate dissociation. However, it also leads to a higher free lime in clinker, which is a result of the presence of trace elements, such as barium. Overall, its use as a raw material in cement production could provide a cost-effective, environment-friendly route for the management of OBM cutting.

Characterization of Poultry Litter Ash in View of Its Valorization

The overall aim of this research was to evaluate the valorization potential of the poultry litter ash produced in the biomass power plant of BMC Moerdijk (the Netherlands), since the ash contains phosphorus (P) and potassium (K), which are both essential nutrients. As a first step, the ash was characterized by means of chemical analysis. Ash collected in the superheater section of the boiler had the highest P concentration (10.6%). Furthermore, the P concentration in the ash decreased as it was collected further downstream in the boiler and flue gas cleaning part of the installation. K showed an opposite concentration trend, that is, its concentration was the lowest in the superheater ash (9.4%) and increased to 15.5% in the electrostatic precipitator ash. Based on the results of the chemical analysis, different valorization options could be considered. Although poultry litter ash has the same heavy metal/P ratio as poultry litter and is free of pathogens and toxic organic substances, its recycling as a P/K fertilizer is hindered by legal constraints. Furthermore, the use of the ash in/as animal feed is not straightforward because of its origin (animal feces) and waste status. Besides P and K, other ash elements such as calcium, silicon, magnesium, iron and aluminum can also be valorized, for example by using the ash as building material or in cement production. However, in these applications the high P and K concentration of the ash can be a technical obstacle rather than a benefit. In this regard, it can be interesting to separate the fertilizer elements, that is, P and K, from the rest of the ash by means of for example a wet chemical extraction after which the remaining solid residue better meets the composition requirements for building material or raw material for cement production.

Agricultural Solid Waste as Source of Supplementary Cementitious Materials in Developing Countries.

Concrete production utilizes cement as its major ingredient. Cement production is an important consumer of natural resources and energy. Furthermore, the cement industry is a significant CO2 producer. To reduce the environmental impact of concrete production, supplementary cementitious materials such as fly ash, blast furnace slag, and silica fume are commonly used as (partial) cement replacement materials. However, these materials are industrial by-products and their availability is expected to decrease in the future due to, e.g., closing of coal power plants. In addition, these materials are not available everywhere, for example, in developing countries. In these countries, industrial and agricultural wastes with pozzolanic behavior offer opportunities for use in concrete production. This paper summarizes the engineering properties of concrete produced using widespread agricultural wastes such as palm oil fuel ash, rice husk ash, sugarcane bagasse ash, and bamboo leaf ash. Research on cement replacement containing agricultural wastes has shown that there is great potential for their utilization as partial replacement for cement and aggregates in concrete production. When properly designed, concretes containing these wastes have similar or slightly better mechanical and durability properties compared to ordinary Portland cement (OPC) concrete. Thus, successful use of these wastes in concrete offers novel sustainable materials and contributes to greener construction as it reduces the amount of waste, while also minimizing the use of virgin raw materials for cement production. This paper will help the concrete industry choose relevant waste products and their optimum content for concrete production. Furthermore, this study identifies research gaps which may help researchers in further studying concrete based on agricultural waste materials.

Study on the Performance of Green Cement with Large Amount of Steel Slag Addition

In this paper, the experimental study of steel slag cement is carried out. The waste steel slag is used as one of the raw materials for cement production. According to the chemical composition and physical properties, the optimum admixture ratio of steel slag for cement production is 20%. Active SiO2 as additive can improve the strength, shrinkage, stability and concrete performance of steel slag cement. The utilization of waste steel slag is beneficial to environmental protection and achieving the goal of turning waste into treasure.

Effect of Source-Classified Collection of Municipal Solid Waste on Heavy Metals and Pozzolanic Properties of Incineration Residues

The adoption of source-classified collection of municipal solid waste (MSW) systems has improved waste management and resource conservation in developing countries, including China. Here, we evaluated the effects of a new MSW source-classified collection system on the distribution and leaching of heavy metals in incineration residues as well as on the pozzolanic properties of residues used as additives in cement production. Cu, Cr, and Mn were found primarily in bottom ash, while the volatile metals Zn, Pb, and Cd became enriched primarily in fly ash during combustion. However, effective presorting of MSW prior to incineration reduced the heavy metal content of the MSW source material and increased the combustion efficiency and heat values of MSW. The system of source-classified collection of MSW resulted in decreased concentrations of heavy metals in bottom ash, as well as decreased leachate toxicity, which improved the viability of bottom ash for use as a non-hazardous raw material in cement production. The consistently high temperatures sustained during incineration of source-classified MSW increased the concentrations and leachate toxicity of Cd, Pb, Cu, Zn, and Cr in fly ash. Pozzolanic activity testing revealed that bottom ash may be used as a pozzolanic material in cement production, but that fly ash is not suitable. In contrast to bottom ash from the incineration of mixed MSW, bottom ash from the incineration of source-classified MSW fully satisfies China’s “Pozzolanic materials used for cement production” standards due to its low loss on ignition, high grindability, and the desired rupture strength, compressive strength, and stability that it adds to mortar mixtures.

Effect of the Milling Agents on Pozzolanic Activity of Glass

Currently the replacement of primary raw materials in cement production is relevant topic. One of the potentially usable materials can be recycled glass. But its disadvantage is tendency to agglomeration. This experiment describes the effects of the milling agents on the milling process of the glass powder. At first step seven different milling agents were compared among others and next the dependence between pozzolanic activity and specific surface are were monitored for two of them. The utilization of milling agents increased glass specific surface area significantly. Nevertheless, pozzolanic activity of the glass can be reduced when using milling agents because they may also act to a certain extent repellently to the reaction solution.

The recycling effect of BOF slag in the portland cement properties

The basic oxygen furnace (BOF) slag use as raw material for cement production carries economic, environmental and technical benefits to the cement industry, reducing energy costs, material consumption and waste storage areas. This study evaluates the partial replacement of blast furnace slag by BOF slag in the production of slag portland cement. Specimens were shaped with addition equivalent to 0; 1.8; 3.6 and 5.4%, in basic oxygen furnace slag weight, to the slag portland cement. The specimens were characterized by the setting time, axial compressive strength at ages 3, 7, 28 and 91days, hot and cold expansibility. The cement with added basic oxygen furnace slag obtained gain in the initial and final strengths for all replacement levels. For the most replacement content (5.4%), the gain in compressive strength obtained amounts to 35% after 3days and 29% after 28days of hydration. The addition of basic oxygen furnace slag in slag portland cement composition had little influence on setting time.

Hydration characteristics of recycling reduction slag and waste sludge by co‐sintered treatment produced as eco‐cement

Waste materials have traditionally been discarded in landfills and often dumped directly into ecosystems without adequate treatment. However, possible reuse and recycling alternatives should be investigated and implemented. Recent environmentally friendly approaches have been aimed at achieving sustainable development by conserving natural resources and minimizing the discarding of materials. The objective of the present study was to investigate the hydration characteristics of reduction slag, limestone sludge, stone sludge, and iron‐oxide sludge for fabricating four types of eco‐cement clinkers. The compound raw materials were burned for 2 h at 1400°C to form eco‐cement clinkers. The results showed that the major components of ordinary Portland cement (OPC), namely C3S, C2S, C3A, and C4AF, were present in the eco‐cement clinkers. The compressive strength development of EcoA pastes (containing 78% limestone sludge, 19.51% stone sludge, and 2.49% iron‐oxide sludge) was similar to that of the commercial OPC products. The compressive strength of the EcoD pastes (containing 71% limestone sludge, 19.51% stone sludge, 2.49% iron‐oxide sludge, and 7% reduction slag) decreased as the amount of α‐C2S increased. Mercury intrusion porosimetry indicated that the pore volume of the pastes gradually decreased with an increase in the curing time. Furthermore, the results of physical‐mechanical tests showed that reduction slag, limestone sludge, stone sludge, and iron‐oxide sludge can be used as raw materials in cement production at no cost to the producer, thereby reducing the production costs. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1466–1473, 2017

Evaluation of dioxins and dioxin-like compounds from a cement plant using carbide slag from chlor-alkali industry as the major raw material

Carbide slag produced from chlor-alkali industry contains high amounts of calcium compounds and can potentially be used as raw material for cement production; however, it contains large amounts of chlorine so it is essential to evaluate the emissions of chlorinated organic pollutants, including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polychlorinated naphthalenes (PCNs). A field study of the emission profiles of these pollutants in a cement plant using such slag was performed. The average concentrations of PCDD/Fs, PCBs, and PCNs in stack gases collected at the kiln back end were 6.31, 1.07, and 31.89pg TEQ m−3, respectively. PCDFs dominated over PCDDs in particulate samples. Di- to pentachlorinated biphenyls were dominant homologs in the particulate samples. MonoCBs were the dominant homolog in stack gases from the kiln back end, and homolog concentrations decreased with increasing chlorine numbers. Mono- and diCNs accounted for 48–98% of PCNs. The estimated toxic equivalents of stack gas emissions of PCNs, classified as new persistent organic pollutants under Stockholm Convention, were unexpectedly higher than those of PCDD/Fs and PCBs. A mass balance indicated that all of the toxic equivalents were reduced by this cement kiln system. The highest 2,3,7,8-PCDD/F output is with clinker.

Valorisation of recycled concrete sands in cement raw meal for cement production

The demolition of old structures in concrete generates materials which can be recycled in the form of aggregates for new concrete, thus preserving natural resources. These recycled concrete aggregates are composed of natural elements bounded with hardened hydrated cement paste. The fine fraction (sands and fillers) is however more difficult to reuse than aggregates because it contains a high proportion of cement paste which absorbs a lot of water. The recycling of these products in the cement process is an interesting alternative way. In this paper, the possibility to use recycled concrete and fine material from de-dusting process of crushing platform for demolition concrete as alternative raw material for cement production was investigated. After a full chemical characterization of the recycled concrete sands and fines (XRF, XRD, DTA-TGA…), several cement raw-mixes were prepared by substituting partially or fully clay or marl. The generated clinkers have been characterized by different analytical techniques (TGA/DTA, XRF, XRD, SEM…). If the chemical composition of the raw is well balanced, the substitution of one of the cement raw meal components by recycled concrete sands does not affect the clinker. However, the free lime content may vary, including the initial quartz content of the recycled concrete sands used.

The Improvement of the Pozzolanic Properties of Recycled Glass during the Production of Blended Portland Cements

The replacement of primary raw materials in cement production is a relevant topic today. One potentially usable raw material is recycled glass. The disadvantage of glass is its tendency towards aggregation. Due to this phenomenon fine glass incement composites work only physically and mechanically as filler rather than as an active pozzolan. The possibilities of improving the pozzolanic properties of recycled glass by means of new milling techniques were examined in this paper. Next to the pozzolanic activity of recycled glass, the advancement of the hydration process of the binder and the effect on the physical and mechanical properties were also monitored. A combination of a ball mill and a nontraditional high-speed pin mill DESI 11 was selected for sample preparation. Portland clinker and recycled glass mixed at a ratio of 80: 20wt. % were used for the preparation of the blended cement. The pozzolanic activity of the pure recycled glass was evaluated using a modified Chapelle test. The hydration process of glass grains in the cement composite was observed using an SEM with an EDX probe. The effect of the grinding technology on the cement rheology and on the compressive and flexural strength was also assessed. The results of the experiment show that the improvement of the pozzolanic properties of recycled glass by using it as the basis of blended cement is possible. The synergistic effect of the co-grinding of the components was observed. The glass particles were better distributed in the composite and could react with Portland cement hydration products. It positively influenced the values of the material's physical and mechanical parameters.

Ocena sposobnosti drobljenja recikliranega stekla pri proizvodnji mešanih cementov

The replacement of primary raw materials in cement production is a current topic. Potentially usable raw materials include recycled glass. The disadvantage of glass is its tendency to aggregate. The conventional method for the production of blended cement is separate grinding and then homogenizing the components. However, in this case aggregated fine glass in the cement composites acts only physically and mechanically as a filler rather than as an active pozzolan. An interesting option to prevent the formation of aggregates formed from glass is co-grinding. This procedure is not very common in practice. Various ingredients of blended cements have widely different grindabilities, and it is therefore better to grind them separately. The aim is to compare the co-grinding and separate grinding of a combination of Portland clinker and recycled glass. The grindability was tested on clinker, glass, and blended cements prepared by co-grinding and by separate grinding. The results of the experiment show that by co-grinding the components of blended cement with the addition of 20 % of recycled glass as a pozzolan, a synergy effect caused by the various mechanical properties of the components occurs. The aggregation of grains is less significant than during separate grinding and it leads to a better grinding effect. This knowledge can by utilized in the design and processing of new blended cements. Also, co-milling the glass-cement system can eliminate the stage of homogenization, and, therefore save energy.

Setting Control of Completely Recyclable Concrete with Slag and Aluminate Cements

A completely recyclable concrete (CRC) is designed to have a chemical composition equivalent to the one of general raw materials for cement production. By doing so, this CRC can be used at the end of its service life in cement manufacturing without the need for ingredient adjustments. In one of the designed CRC compositions, blast-furnace slag cement (BFSC) was combined with calcium aluminate cement (CAC), which resulted in fast setting. In an attempt to control this fast setting, different retarders and/or the combination of lime and calcium sulfate were added to the system. The workability (slump and flow), setting time (ultrasonic transmission measurements and Vicat), strength development (compressive strength tests), and hydration behavior (isothermal calorimetry) were studied. It was found that the combined addition of lime and calcium sulfate results in a workable mixture that becomes even more workable if a retarder is also added to the system.

A comprehensive study on the characterization and comparison of oil‐containing sludge and alkali‐containing sludge

In this study, a systematic study on the characterization of two kinds of steelmaking sludges, oil‐containing sludge (Sludge‐I) and alkali‐containing sludge (Sludge‐II), were carried out by using X‐ray fluorescence spectrometry (XRF), leaching toxicity test, X‐ray diffraction (XRD), scanning electron microscopy (SEM), TG‐DSC, and proximate analysis, and their potential of being recycled as alternative fuel and raw materials in cement production was also discussed. Results showed that Al2O3, Fe2O3, SiO2, and CaO were the major compositions in calcinated Sludge‐I and Sludge‐II after being calcinated at 850°C. The calorific values of Sludge‐I and Sludge‐II were 8513 J g−1 and 3299 J g−1 and the combustible contents were 62.22% and 34.03%, respectively. The content of alkalis in Sludge‐I was lower than that in Sludge‐II and both of these values were within the scope of requirement for cement. Considering the similar compositions as cement raw materials, high calorific values and combustible contents, both of the two sludges had potential of being recycled as alternative fuel and raw materials in cement production. But the higher heat and lower alkali content in Sludge‐I made its potential better. The research would be helpful to understand the composition and thermal behavior of the sludges and to further develop more ideal utilization methods. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 957–961, 2016

Analysis of MSWI Bottom Ash Reused as Alternative Material for Cement Production

The bottom ash sample was obtained from one of three stably running municipal solid waste incineration plants in Beijing. The major components of bottom ash, i.e. CaO, SiO2, Al2O3, Fe2O3, were similar to that of ordinary Portoland cement, suggesting that bottom ash had the potential for reuse as cement material. In this paper, the smaple was sieved into 8 fractions according to the particle size distirbution. The content of CaO and chloride in the bottom ash almost decreased with the increase of particle size of bottom ash, contrary to the SiO2 content variation in the bottom ash. The Al2O3 and Fe2O3 content were relatively stable in the bottom ash with different particle size. The chloride, which could cause serious corrosion in the cement kiln, in 8 portion of bottom ash were all higher than its allowable limit in raw material for cement production and clinker quality, the dosage of bottom ash used as alternative material for cement production must be stringently controled, and some proper treatment must be used to reduce the corrion caused by chloride. The heavy metals concentration in the bottom ash were relatively high, but met standard requirements for heavy metals concentration in raw meterial. The content of alkaline oxide (K2O, Na2O) and sulphur, also affected cement production, in bottom ash with differernt particle size were all relative high. The bottom ash had the potential to be recycled as alternative material for cement production, but proper treatment measures, such as by-pass system, must be taken to satisfy the cement production, clinker quality and environmental safety.

RECYCLABILITY OF FLY ASH CONCRETE PAVEMENT MADE WITH LIMESTONE AGGREGATE

The present study aims to develop a recyclable concrete pavement incorporating fly ash. All aggregates used in the concrete were crushed limestone sand and gravel, so the concrete pavement can be recycled into raw materials for cement production. To use fly ash as much as possible and to obtain adequate strength development, the present study focuses on pavement concrete made with cement-replacement ratio of 40% by mass. The foci of the study were to confirm the recyclability for cement production and to evaluate the applicability of the recyclable pavement concrete. Portland cement was made with the fly ash concrete to examine fundamental properties of the cement. Physical and chemical properties of the recycled cement were tested and compared to the properties of ordinary Portland cement defined in Japanese standards. The fundamental tests confirmed that the physical and chemical properties of the recycled cement meet the requirements of Portland cement. It is concluded that the recyclable fly ash concrete pavement having high early strength is a preferred material in terms of sustainability.