Free CaO Research Articles

The Improve of Accelerated Carbonation on Engineering Properties of Basic Oxygen Furnace Slag

Basic oxygen furnace (BOF) slag is characterized by high hardness, low abrasion, and high roughness. It is suitable as graded aggregate for engineering applications. However, the conversion process generated a great amount of unreacted free CaO, resulting in expansion and thus making the slag inconvenient for use in engineering applications. Accelerated carbonation of BOF slag is equivalent to natural weathering. Moreover, it can effectively shorten the weathering time. This study found that accelerated carbonation not only reduce expansion behaviors but also strengthen physical and mechanical properties. According to test results, the abrasion resistant, soundness, California bearing ratio, shear strength, and compressive strength have increased after carbonation.

English

There is an increased interest in the reuse of ash waste from biomass combustion, being a sustainable source of energy. This paper investigates the partial replacement of cement and sand in building materials with fly ash waste generated from combustion of woody biomass waste. The results show that the ash widens the particle size distribution of cement and has minerals complementary to portland cement, thus justifying its application as cement replacement, but with a relatively high amount of free CaO and MgO that may exert significant expansion. With ash addition, the rate of hydration, strength, and workability decreased. The optimum dosage showed 15 % of ash, replacing 5 % of cement and 3.33 % of sand, which can still produce a structural grade cementitious material with acceptable workability and mechanical properties. The ash exhibits hydraulic and pozzolanic activity that initially increases and subsequently decreases the amount of Ca(OH) 2 in the hydrated material.

Acidification and sulfide formation control during reductive dechlorination of 1,2-dichloroethane in groundwater: Effectiveness and mechanistic study

To enhance the reductive dechlorination of 1,2-dichloroethane (DCA) in groundwater, substrate injection may be required. However, substrate biodegradation causes groundwater acidification and sulfide production, which inhibits the bacteria responsible for DCA dechlorination and results in an odor problem. In the microcosm study, the effectiveness of the addition of ferrous sulfate (FS), desulfurization slag (DS), and nanoscale zero-valent iron (nZVI) on acidification and sulfide control was studied during reductive dechlorination of DCA, and the emulsified substrate (ES) was used as the substrate. Up to 94% of the sulfide was removed with FS and DS addition (0.25 wt%) (initial DCA concentration = 13.5 mg/L). FS and DS amendments resulted in the formation of a metal sulfide, which reduced the hydrogen sulfide concentration as well as the subsequent odor problem. Approximately 96% of the DCA was degraded under reductive dechlorination with nZVI or DS addition using ES as the substrate. In microcosms with nZVI or DS addition, the sulfide concentration was reduced to less than 15 μg/L. Acidification can be controlled via hydroxide ions production after nZVI oxidation and reaction of free CaO (released from DS) with water, which enhanced DCA dechlorination. The quantitative polymerase chain reaction results confirmed that the microcosms with nZVI added had the highest Dehalococcoides population (up to 2.5 × 108 gene copies/g soil) due to effective acidification control. The α-elimination mechanism was the main abiotic process, and reductive dechlorination dominated by Dehalococcides was the biotic mechanism that resulted in DCA removal. More than 22 bacterial species were detected, and dechlorinating bacteria existed in soils under alkaline and acidic conditions.

Densification and properties of ZrO2 nanoparticles added magnesia–doloma refractories

In this work the effect of nano- and microZrO2 addition on the densification and hydration resistance of MgO–CaO refractories was investigated. 0, 2, 4, 6 and 8wt% ZrO2 was added to MgO–CaO refractories that contain 35wt% CaO. The crystalline phases and microstructure characteristics of specimens sintered at 1650°C for 5h in an electric furnace were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The physical properties are reported in terms of bulk density, apparent porosity and hydration resistance. Results show that with addition of ZrO2 the bulk density and hydration resistance of the samples increased while apparent porosity decreased. Also the hydration resistance of the samples was appreciably improved by the addition of ZrO2 due to its effect on decreasing the amount of free CaO in the refractories, promotion of densification as well as modification of the microstructure. Also it revealed that the nanoZrO2 addition was more effective than microZrO2 due to its higher activity.

Effect of the Mineralogical Phases in Steelmaking Slag Fertilizer on the Dissolution Behavior of Nutritious Elements and Rice Growth

Steelmaking slag contains various mineralogical phases, including water soluble phases such as free CaO and the solid solution consisting of 2CaO·SiO2 and 3CaO·P2O5. However, the contribution of each of these phases to the rice growth through the supplement of nutritious element in the rice soil is not clear. In this research, we modified a commercial fertilizer made of steelmaking slag to produce one without the free CaO phase and another without either the free CaO or the solid solution of 2CaO·SiO2 and 3CaO·P2O5. Experiments were conducted using these modified fertilizers, aiming to understand the dissolution behavior of the nutritious elements in aqueous solution with and without rice soil, and their effect on rice growth. As seen in the dissolution test in aqueous solution, an initial increase in Ca was suppressed by removing free CaO, and the dissolution of both Ca and Si decreased to half upon the removal of the solid solution compared with the original fertilizer. A column test that simulates the rice soil field showed that an initial increase in pH was suppressed, and the dissolution of Si and Fe increased by removing free CaO. Rice growth test showed that the Si content in both the soil solution and the rice uptake increased by removing free CaO but decreased when the solid solution was removed.

Roles of Mineralogical Phases in Aqueous Carbonation of Steelmaking Slag

Mineralogical phases of steelmaking slags have significant influences on the carbonation of the slags. In this paper, the effects of temperature and reaction time on the conversion of calcium-related phases and the carbonation degree of a slag sample were studied. The experimental conditions were a liquid-to-solid ratio of 20 mL/g, a carbon dioxide flow rate of 1 L/min and a slag particle size of 38–75 μm. The results show that the optimum carbonation temperature and reaction time are 60 °C and 90 min, respectively, and calcite phase content is about 26.78% while the conversion rates of Ca3Al2O6, CaSiO3, Ca2SiO4 and free CaO are about 40%, 42.46%, 51% and 100%, respectively, and the carbon dioxide sequestration efficiency is about 170 g/kg slag.

Strategi Perencanaan Jumlah Material Tambahan dalam Memproduksi Semen dengan Pendekatan Taguchi untuk Meminimalkan Biaya Produksi (Study Kasus PT Semen Padang)

Cement is a construction material with a specific quality that must be meet standard requirements and customer requirements. Through a good and continuous quality control, it will produce cement with consistent quality as its Quality Planning. Cement quality is calculated after adding water by measuring its setting time, compressive strength developing, heat of hydration, expantion/shrinkage, and its durability to environment effect. In cement application, primary parameter to determine cement quality is its compressive strength. Some factors that affect compressive strength of cement are reactivity and amount of Tricalcium Silicate (C3S) of Clinker, Clinker freelime (free CaO), amount of SO3 in Cement, amount of additional materials (insoluble residue/IR and loss on ignition/LOI), and sieve on 45 µm residue of cement. This research is intended to find how insoluble residue/IR, loss on ignition/LOI, and amount of SO3 will affect compressive strength of cement. Various percentages of IR, LOI, and SO3 in cement will result different compressive strength. Taguchi Method is applied to determine material proportion. With Orthogonal Array calculation for 3 factors and 4 levels, it will result 16 calculation running times (L16 4**3). In laboratory scale, cement for this research has been being manufactured and then its compressive strength for 3 days, 7 days, and 28 days will be measured. Determination of optimal proportion will be calculated by statistic method for higher compressive strength and lower manufacturing cost. Keywords: compressive strenght, cement, taguchi method, proportionAbstrak Semen merupakan bahan konstruksi yang memerlukan kualitas yang sesuai dengan permintaan konsumen dan memenuhi persyaratan standar. Melalui pengendalian kualitas yang baik dan dilakukan secara terus menerus akan diperoleh kualitas semen yang stabil dan sesuai dengan perencanaan kualitas (Quality Planning). Kualitas semen diukur, berdasarkan performansinya saat penambahan air, yaitu bagaimana proses pengikatan semen, perkembangan kuat tekan, panas hidrasi, pemuaian/penyusutan volume dan ketahanan semen terhadap pengaruh lingkungan (durability). Dalam praktek pemakaian semen di lapangan, parameter utama untuk menentukan kualitas semen adalah parameter kuat tekan. Beberapa faktor yang mempengaruhi kuat tekan semen adalah reaktivitas dan jumlah trikalsium silikat (C3S) klinker, freelime klinker (CaO bebas), jumlah SO3 dalam semen, jumlah material tambahan (BTL dan LOI) dan kehalusan semen dalam sieve on 45 µm. Pada paper ini akan meneliti faktor yang mempengaruhi kuat tekan semen yaitu parameter BTL, LOI dan SO3. Variasi prosentase parameter BTL, LOI dan SO3 dalam semen akan mempengaruhi pencapaian kuat tekan. Penentuan proporsi material yang akan diteliti menggunakan metode Taguchi. Dengan perhitungan Orthogonal Array untuk 3 faktor dan 4 tingkatan level diperoleh jumlah penelitian yang dilakukan adalah 16 kali (L16 4**3). Pada saat ini sedang dilakukan pembuatan semen skala Laboratorium dan dilanjutkan dengan pengujian kuat tekan semen pada umur 3 hari, 7 hari dan 28 hari. Penentuan proporsi optimal dihitung secara metoda statistika untuk kuat tekan tinggi dan biaya produksi yang rendah.Kata kunci: kuat tekan, semen, metoda taguchi, proporsi

Mineralogical composition of EAF slag and stabilised AOD slag aggregates and dimensional stability of slag aggregate concretes

An interesting valorisation way of EAF slag and stabilised AOD slag is their use as aggregates in concrete. Mineralogical studies of these steel slags are therefore necessary. In this study, observations of slag aggregates under UV light are associated with usual mineralogical analyses (XRD, SEM and EDS) to ensure more representative results of the mineralogical variability within slag aggregates. Relationships between aggregate mineral composition and UV fluorescence colours are proposed. Mineralogical studies also show that the stainless steel slag contains low amounts of expansive mineral phases (free CaO, free MgO) that could affect concrete volume stability. To verify this finding, swelling measurements of high strength concretes made of EAF slag and stabilised AOD slag aggregates are carried out. The linear expansion of stainless steel slag concretes is slightly higher than that measured for concretes with silico-calcareous aggregates.

Optimal fluorite/gypsum mineralizer ratio in Portland cement clinkering

This paper presents an analysis of the joint effect of fluorite and gypsum as mineralizers in the manufacture of Portland cement. A laboratory- scale Box-Behnken statistical design was used to quantify the effects of the explanatory variables fluorite content (0.00, 0.25, 0.50, and 0.75%), fluorite/gypsum ratio (2/15, 1/3 and 8/15), and clinkering temperature (1250, 1300, and 1350 °C) on the response variable free CaO content in the clinker produced. The clinker was characterized by the ethylene method, XRD, DSC and optical microscopy. Free CaO decreases of 81% and 56% were found in the mineralized clinker, compared to the same clinker without mineralizers, at 1300 °C and 1250 °C, respectively. Petrographic analysis showed that at lower temperatures, the amount of alite in the mineralized clinker was higher than the amount of alite in the clinker without mineralizers. The best condition was found for the fluorite/gypsum ratio of 2/15.

Evaluation of B2O3 as replacement for CaF2 in CaO–Al2O3 based mould flux

In order to develop low fluoride or fluoride free CaO–Al2O3 based mould flux for casting high aluminium steel, an investigation was carried out to study the effect of substituting CaF2 with B2O3 on heat transfer and crystallisation behaviour of CaO–Al2O3 based mould flux by employing a heat transfer simulator of mould flux and a single hot thermocouple technique. The results showed that addition of CaF2 promoted heat transfer of CaO–Al2O3 based mould flux, which was opposite to the effect of CaF2 on heat transfer in conventional CaO–SiO2 based mould flux. Addition of CaF2 inhibited crystallisation of CaO–Al2O3 based mould flux by lowering the start crystallisation temperature and prolonging the incubation time of crystallisation. B2O3 showed similar effects to CaF2 on heat transfer and crystallisation of CaO–Al2O3 based mould flux, but its ability to promote heat transfer and suppress crystallisation was stronger than CaF2. Ca3B2O6 (melting temperature 1480°C) was found as the primary crystalline phase in fluoride free CaO–Al2O3 based mould flux compared with the primary crystalline phase Ca2Al3O6F (melting temperature 1507°C) in fluoride bearing (20% CaF2) CaO–Al2O3 based mould flux.

The utilisation of fly ash in CO2 mineral carbonation

Abstract The fixation of CO2 in the form of inorganic carbonates, also known as mineral carbonation, is an interesting option for the removal of carbon dioxide from various gas streams. The captured CO2 is reacted with metal-oxide bearing materials, usually naturally occurring minerals. The alkaline industrial waste, such as fly ash can also be considered as a source of calcium or magnesium. In the present study the solubility of fly ash from conventional pulverised hard coal fired boilers, with and without desulphurisation products, and fly ash from lignite fluidised bed combustion, generated by Polish power stations was analysed. The principal objective was to assess the potential of fly ash used as a reactant in the process of mineral carbonation. Experiments were done in a 1 dm3 reactor equipped with a heating jacket and a stirrer. The rate of dissolution in water and in acid solutions was measured at various temperatures (20 - 80ºC), waste-to-solvent ratios (1:100 - 1:4) and stirrer speeds (300 - 1100 min-1). Results clearly show that fluidised lignite fly ash has the highest potential for carbonation due to its high content of free CaO and fast kinetics of dissolution, and can be employed in mineral carbonation of CO2.

Inhibition of Cr(III) oxidation during thermal treatment of simulated tannery sludge: The role of phosphate

The presence of Ca compounds may be an important factor contributing to oxidation of Cr(III) to Cr(VI) during the incineration of tannery sludge. In this study, Cr(III) oxidation was inhibited by preventing Ca participating in Cr(III) oxidation reactions via incorporating it in phosphate minerals. Cr(III) oxidation was remarkably suppressed through immobilizing Ca in phosphate minerals. Around 16% of Cr(III) would be oxidized in samples without phosphate heated at 900°C for 1h, which could be reduced substantially to 0.25% with the addition of phosphate at n(P)/n(Ca)=2. Moreover, phosphate not only captured free CaO, inhibiting Cr(III) oxidation, but seized Ca from CaCrO4, resulting in formed Cr(VI) being reduced. Inhibition of Cr(III) oxidation performed resistant to elevating temperature over 1000°C and prolonged retention time, due to the irreversible incorporation of Ca into phosphate mineral species. Moreover, incorporating Ca into phosphate minerals thoroughly eliminated the potential of Ca to trigger Cr(III) oxidation. Additionally, the P-hosting phases produced (e.g., Ca(PO3)3 and Cr(PO3)3) were also able to capture free CaO and inhibit Cr(III) oxidation, so Cr(III) oxidation continued to be inhibited during flue gas cooling and fly ash reheated process. A case study, in which tannery sludge was heated, confirmed that adding phosphate effectively inhibited Cr(III) oxidation. Adding phosphate could therefore be an effective way of inhibiting Cr(III) oxidation when solid waste containing Cr(III) is heated.

CO2 capture using fly ash from coal fired power plant and applications of CO2-captured fly ash as a mineral admixture for concrete

The utilization of fly ash as a solid sorbent material for CO2 capture via surface adsorption and carbonation reaction was evaluated as an economically feasible CO2 reduction technique. The results show that fly ash from a coal fired power plant can capture CO2 up to 304.7 μmol/g fly ash, consisting of 2.9 and 301.8 μmol/g fly ash via adsorption and carbonation, respectively. The CO2 adsorption conditions (temperature, pressure, and moisture) can affect CO2 capture performance of fly ash. The carbonation of CO2 with free CaO in fly ashes was evaluated and the results indicated that the reaction consumed most of free CaO in fly ash. The fly ashes after CO2 capture were further used for application as a mineral admixture for concrete. Properties such as water requirement, compressive strength, autoclave expansion, and carbonation depth of mortar and paste specimens using fly ash before and after CO2 capture were tested and compared with material standards. The results show that the expansion of mortar specimens using fly ash after CO2 capture was greatly reduced due to the reduction of free CaO content in the fly ash compared to the expansion of specimens using fresh fly ash. There were no significant differences in the water requirement and compressive strength of specimens using fly ash, before and after CO2 capture process. The results from this study can lead to an alternative CO2 capture technique with doubtless utilization of fly ash after CO2 capture as a mineral admixture for concrete.

Characteristic Properties of the Fly Ash from Coal Combustion

Environmental impacts and sustainable development are two words, which are mentioned every day. The responsibility of our generation is growing up. People consider about the new ways of using materials. Some of them were waste in the recent past. In present time people think about the possibilities how the waste could be reduced, recycled, reused or recovered. In this paper are presented the chemical and physical properties of different coal ash. In the research were tested the XRD analyse, the quantity of Free CaO, the granulometry, volume stability, loose bulk density and shake down loose bulk density.

A Comparative Study of Physicochemical and Mineralogical Properties of LD Slag from Some Selected Steel Plants in India

The scope of this study is to compile several analytical techniques in order to carry out physico-chemical and mineralogical properties of Linz-Donawitz (LD) slag. The physical properties such as bulk density, specific gravity, particle size distribution, porosity, permeability and water holding capacity etc., have been determined. The pH and electrical conductivity of the samples were very high, indicating high percentage of lime and ionic form of various salts. The specific gravity and bulk density were found high due to fine particles. Particle size distribution results showed that the LD slag samples were well graded. The EDS X-ray showed that major elemental compositions of LD slag samples were O and Ca by weight. The XRD analysis showed that the pattern of LD slag samples were very complex, with several overlapping peaks and the presence of free MgO and CaO. From the FE-SEM analysis it was observed that LD slag particles had sub angular to angular shapes and very rough surface texture with distinct crystal structures. Fourier transform infrared spectroscopy (FTIR) analysis revealed that portlandite (Ca(OH)2) and periclase (MgO) are the dominant phases in LD slag. The XRF analysis showed that the major components of the LD slags are CaO, FeO and SiO 2 .

Coal fly ash alkalis content characterization by means of a full factorial design

Concrete structures durability is affected by the alkali ions amount in the pore solution when potentially reactive aggregates are employed. Then, a long-term durability indicator of concrete could be the coal fly ash alkali content. Such alkali ions are provided by the Portland cement, but also by the coal fly ash when is used as a main cement constituent. In this work, fly ashes from the combustion of a South African coal were investigated. The scope of this paper is to deep in the knowledge of coal fly ash alkalis content and, in particular, how it is affected by free CaO and reactive silica content and fineness. Evaluation of variables was done by using a 23 full factorial design. The maximum Na2Oequ of 1.68% was obtained at 1% free CaO, 40% reactive silica and 30% residue on 45µm (fineness). Reactive silicon is the main parameter influencing Na2Oequivalent amount in coal fly ash.

Dissolution Behavior of Nutrient Elements from Fertilizer Made of Steelmaking Slag, in an Irrigated Paddy Field Environment

To produce fertilizer made of steelmaking slag, the combination of mineralogical phases is necessary to be appropriate not only for refining at high temperature, but also for supplementing nutrient elements in paddy fields. In this research, first, the variations in the chemical composition and mineralogical structure of various brands of fertilizer made of steelmaking slag were investigated. The basicity (CaO/SiO2), free-CaO content, total Fe content, and Fe2+/Fe3+ ratio of fertilizer were found to vary widely depending on the brand. In addition, regarding the mineralogical phases, solid solution consisting of 2CaO·SiO2 and 3CaO·P2O5, MgO–FeO, CaO–Fe2O3, free CaO, metallic Fe, and the other phase which included liquid phases at refining temperature were observed. The mass fraction of each phase also varied depending on the brand. Second, the dissolution behavior of each mineralogical phase in the fertilizers into water that simulated the early stage of flooding condition was studied. Regarding the dissolution of Ca, free CaO dissolved in a short time, and the solid solution of 2CaO·SiO2 and 3CaO·P2O5 dissolved slowly. Fe barely dissolved from any mineralogical phase except the other phase which consisted of CaO–SiO2–FeO. A clear relationship was observed between the dissolution of Fe and the mass fraction of other phase as well as the ratio of Fe2+ to Fe3+ in Fe oxides in fertilizer made of steelmaking slag.

Evaluation of the Chemical and Mechanical Properties of Hardening High-Calcium Fly Ash Blended Concrete.

High-calcium fly ash (FH) is the combustion residue from electric power plants burning lignite or sub-bituminous coal. As a mineral admixture, FH can be used to produce high-strength concrete and high-performance concrete. The development of chemical and mechanical properties is a crucial factor for appropriately using FH in the concrete industry. To achieve sustainable development in the concrete industry, this paper presents a theoretical model to systematically evaluate the property developments of FH blended concrete. The proposed model analyzes the cement hydration, the reaction of free CaO in FH, and the reaction of phases in FH other than free CaO. The mutual interactions among cement hydration, the reaction of free CaO in FH, and the reaction of other phases in FH are also considered through the calcium hydroxide contents and the capillary water contents. Using the hydration degree of cement, the reaction degree of free CaO in FH, and the reaction degree of other phases in FH, the proposed model evaluates the calcium hydroxide contents, the reaction degree of FH, chemically bound water, porosity, and the compressive strength of hardening concrete with different water to binder ratios and FH replacement ratios. The evaluated results are compared to experimental results, and good consistencies are found.

Effect of sludge addition to coal on Na, K and S volatilisation in ashing process and ash fusibility

The effect of the addition of three types of sludge (L, O and F) on both the Na, K and S volatilisation and the slagging behaviour of a bituminous coal (H) was studied. Na, K and S volatilise in the coal, the sludges and their blends partially, and there exist linear relationships between their contents in ashes and the ratio sludge ash/blend ashes for each coal–sludge blend ash series. However, in blends with F (treated with FeCl3 and lime), S relationship is not linear due mainly to the following effects: a) sulphur retention by CaO to form CaSO4, and b) decrease of free CaO due to the formation of ferrites, silicates and phosphates. To determine the slagging tendency, the ash fusion temperatures (AFTs) were related with ash chemical and mineral composition by using the slagging factor, the base/acid ratio, the Fe2O3/CaO ratio, the P2O5 content, and the ternary equilibrium phase diagram SiO2–Al2O3–CaO. Sludge addition to coal produces a decrease in AFTs that depends on the percentage of sludge added, the sludge phosphorus content and additives (FeCl3 and/or lime), the fact that ash composition is near to those of the eutectics, and the formation of Si and P amorphous compounds.

Properties of regenerated MgO–CaO refractory bricks: Impurity of silicon dioxide

Regenerated MgO–CaO refractory brick samples with 0, 1·5, 3·0 wt-% SiO2 addition were prepared by using spent MgO–CaO bricks and fused magnesia as raw materials. Their phases, microstructures and flexural strength at room and 1573 K were investigated, respectively, and the maximum content of SiO2 impurity in regenerated samples had been subsequently achieved. The results showed that main phases of regenerated samples were all MgO, free CaO (f-CaO), Ca3SiO5 (C3S) and Ca2FeAlO5. Because some Al3+, Fe3+ had dissolved in the crystal lattice of C3S, it resulted in the decreasing of content of f-CaO and low melting point phase of C4AF along with the increasing of SiO2 addition, moreover, the flexural strength of regenerated samples at room temperature reduced while flexural strength at 1573 K enhanced. The maximum content of SiO2 impurity was about 4·11 wt-% in regenerated samples considering their properties for cement kiln.