Investigation of the physical and chemical parameters affecting biodegradation of diesel and synthetic diesel fuel contaminating Alaskan soils

In cold regions, biodegradation of fuel spills can take a prolonged period of time. Conventional fuels and crude oil contain contaminants such as aromatics and PAH which can pose risks to humans and the environment. The goal of the present study was therefore to investigate the biological degradation of an alternative synthetic fuel, Syntroleum, which is less toxic and, as shown in this study, more easily biodegradable than conventional diesel fuel. Use of alternative fuels such as Syntroleum would be especially beneficial in sensitive regions where spills of conventional fuel are highly undesirable. Gravel and sand from Interior Alaska were spiked with diesel and synthetic diesel fuel (arctic-grade Syntroleum). After adding an inoculum, samples were incubated in the laboratory at different temperatures (6 °C and 20 °C), contamination levels (2000 mg and 4000 mg of fuel/kg dry soil), nutrient dosages (300 mg N/kg soil and 0 mg N/kg soil) and moisture contents (2%, 4%, 8% and 12% gravimetric water content). The objective of this research was to investigate the effect of physical and chemical environmental conditions on the biodegradability of contaminants and to determine optimal conditions for biodegradation by indigenous microorganisms. The respiration rate (CO₂ production) was measured as an indicator of microbial activity and mineralization of contaminants, and complemented by analysis for hydrocarbons at the end of the experiment by gas chromatography/mass spectrometry. Both fuel types were biodegraded, with up to 75% mineralization after 17 weeks. The faster degradation rate was achieved in Syntroleum-contaminated soils with a degradation-rate constant of 0.0064–0.0106 d^− 1 at 20 °C. At 6 °C, diesel fuel showed minimal degradation during several short-term studies (4–6 weeks), less than 5% total mineralization of the hydrocarbons in the fuel. The average degradation-rate constant for Syntroleum at 6 °C was 0.0016 d^− 1 during a 4-week study, while the degradation-rate constants became much higher (0.0045–0.005 d^− 1) for the long-term experiments (12–17 weeks), resulting in significant mineralization of total carbon present. The different moisture contents in the sandy soil showed no significant impact on respiration. The addition of fertilizer was essential to achieve good degradation rates. After the end of the 17-week experiment, the recovered contaminant was approximately 50% less in the case of Syntroleum when nutrients were added to the soil as compared with nutrient-deficient conditions. Respiration rates were higher in sand than in gravel, which may be due to differences in soil porosity and the available surface area for more even hydrocarbon distribution. Degradation rates varied significantly over time. A first-order model, which used different rate constants for three growth phases, was able to model cumulative carbon dioxide production quite well over a period of four months. In the carbon mass balance, the sum of the diesel range organics recovered from the soil plus the produced carbon dioxide accounted for approximately 30–85%. The remaining amount of carbon either was incorporated into biomass, degraded incompletely, or evaporated.     

Producing clean diesel fuel by co-hydrogenation of vegetable oil with gas oil

The goal of our investigation was the production of partially bio-derived fuels in the gas oil boiling point range. Our aim was the production of diesel fuel blending components by co-hydrogenation of mixtures of high-sulphur gas oil (about 1.0%) and vegetable oil raw materials with different vegetable oil contents (0, 5, 15, 25 and 100%). The experiments were carried out on a NiMo/Al₂O₃ catalyst with a targeted composition (T = 300–380°C, P = 60–80 bar, LHSV = 1.0/h and H₂/HC = 600 Nm³/m³). We obtained that both the vegetable oil conversion reactions and the gas oil quality improvement reactions took place. Under the favourable operational conditions (360–380°C, P = 80 bar, LHSV = 1.0/h and H₂/HC = 600 Nm³/m³ and up to 15% vegetable oil content of the feed), the main properties of the high-yield (>90%) products except for the Cold Filter Plugging Point (CFPP) value satisfied the requirements of the standard of diesel fuels (EN 590:2009). The amount of vegetable oil higher than 15% reduced the desulphurization efficiency, because of the intake of large quantities of oxygen with the triglyceride molecules of the vegetable oil. The products—depending on the vegetable oil content of the feedstocks—have an increased n- and i-paraffin content, so their combustion properties are very favourable, and the emission of particles is lower.     

Low temperature soil petroleum hydrocarbon degradation at various oxygen levels

A laboratory incubation study was conducted on a petroleum-contaminated soil from Macquarie Island in sub-Antarctic Australia to develop a target O₂ level for bioventing. The soil was amended with NH₄NO₃ (175 mg N kg^− 1 soil) and ¹⁴C-hexadecane (250 mg kg^− 1 soil) and placed in sealed respirometry chambers. The headspaces in the chambers were adjusted to 0, 1, 2.6, 5.2, 10.5, and 20.9% O₂. Each chamber was connected to an NaOH CO₂ trap and to an O₂ feed line (except the 0% O₂ chambers were connected to an N₂ feed line). Chambers were supplied with O₂ in response to pressure drop resulting from CO₂ trapping. Soils were incubated at 6 °C for 12 weeks. O₂ consumption and petroleum degradation were maximized in chambers with 10.4% O₂. There was a slight decline in both O₂ consumption and petroleum degradation at 20.9% O₂. As O₂ concentrations declined below 10.4% O₂ both O₂ consumption and petroleum degradation declined markedly. ¹⁴C collected in the CO₂ traps did not follow this pattern, but was greater in the 1% O₂ chambers than in 2.6 or 5.2% O₂ chambers. Nitrogen remaining at the conclusion of the study indicated that nitrate was completely consumed in the 0, 1, 2.6, and 5.2% O₂ chambers. nC₁₇:pristane and nC₁₈:phytane ratios in the soil at the conclusion of the incubation were significantly lower in the 10.4% O₂ chambers than in those with 20.9% O₂, and more petroleum hydrocarbons were consumed in the 10.4% chambers. Preferential degradation of pristane and phytane in the presence of limited O₂ may be the result of denitrification, evidenced by lower residual nitrate levels in the 10.4 than the 20.9% O₂ environment. Ten percent O₂ is suggested as a target for O₂ enhanced bioremediation.     

Multivariate analysis of a biologically activated carbon (BAC) system and its efficiency for removing PAHs and aliphatic hydrocarbons from wastewater polluted with petroleum products

The efficiency of a biologically activated carbon system for treating wastewater polluted with petroleum products was examined and the effects of process parameters on its efficacy were evaluated. In each experiment 17 alkylated and 19 non-alkylated polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPHs, C₁₀–C₄₀) were extracted using semipermeable membrane devices from wastewater before and after treatment. The acquired data during experiments were analyzed using principal component analysis (PCA). The treatment system robustly removed dissolved PAHs across the studied ranges of the process parameters, providing overall removal efficiencies of 96.9–99.7% for the sum of 36 PAHs. However, the major contributor to their removal was sorption rather than biodegradation, and despite the general efficiency of the process there was up to a 9-fold range in the sums of quantified PAHs in the effluents between experiments. Combinations of long process contact time (24 h) with high temperature (24 °C) and moderate oxygen concentration (6–7 mg O₂ L⁻¹) resulted in good removal of bioavailable PAHs. The removal of TPHs was more dependent on biological activities during the wastewater treatment, and consequently more dependent on the process parameters. In addition, small but significant proportions of PAHs were volatilized and released during the wastewater treatment.     

Heterogeneous Fenton-like discoloration of methyl orange using Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/MWCNTs as catalyst: kinetics and Fenton-like mechanism

The kinetics and Fenton-like mechanism are two challenging tasks for heterogeneous Fenton-like catalytic oxidation of organic pollutants. In this study, three kinetic models were used for the kinetic studies of Fe₃O₄/MWCNTs-H₂O₂ Fenton-like reaction for MO degradation. The results indicated that this reaction followed the first-order kinetic model. The relationship of reaction rate constant and temperature followed the Arrhenius equation. The activation energy and frequency factor of this system were calculated as 8.2 kJ·mol^-1 and 2.72 s^-1, respectively. The quantifications of Fe ions dissolution and ?OH radicals generation confirmed that the homogeneous and heterogeneous catalyses were involved in Fe₃O₄/MWCNTs-H₂O₂ Fenton-like reaction. The reaction rate constant was closely related with Fe ions dissolution and ?OH radicals generation. Fe₃O₄/MWCNTs nanocomposites had typical ferromagnetic property and could be easily separated from solution by an external magnet after being used. Furthermore, Fe₃O₄/MWCNTs nanocomposites exhibited good stability and recyclability. Finally, the Fenton-like mechanisms on homogeneous and heterogeneous catalyses were described.     

Coupling extraction–flotation with surfactant and electrochemical degradation for the treatment of PAH contaminated hazardous wastes

The performance of a two-stage process combining extraction of polycyclic aromatic hydrocarbons (PAHs) with an amphoteric surfactant (CAS) followed by electro-oxidation of PAH-foam concentrate was studied for the decontamination of aluminum industry wastes (AIW) and polluted soils. The PAH suspensions extracted from AIW and soils were treated in a 2 L-parallelepipedic electrolytic cell containing Ti/RuO₂ anodes and stainless steel cathodes. Current densities varying from 4.6 to 18.5 mA cm⁻² have been tested with and without addition of a supporting electrolyte (6.25 to 50 kg Na₂SO₄ t⁻¹ of dry waste). The best performance for PAH degradation was obtained while the electrolytic cell was operated during 90 min at a current density of 9.2 mA cm⁻², with a total solids concentration of 2.0%, and in presence 12.5 kg Na₂SO₄ t⁻¹. The application of the process on AIW (initial PAH content: 3424 mg kg⁻¹) allowed extracting 42% of PAH, whereas 50% of PAH was electrochemically degraded in the resulting foam suspensions. By comparison, 44% to 60% of PAH was extracted from polluted soils (initial PAH content: 1758 to 4160 mg kg⁻¹) and 21% to 55% of PAH was oxidized in the foam suspensions. The electrochemical treatment cost (including only electrolyte and energy consumption) recorded in the best experimental conditions varied from 99 to 188 USD $ t⁻¹ of soils or AIW treated.     

Fenton-like oxidation of Rhodamine B in the presence of two types of iron (II,III) oxide

The catalytic efficiency of iron (II, III) oxide to promote Fenton-like reaction was examined by employing Rhodamine B (RhB) as a model compound at neutral pH. Two types of iron (II, III) oxides were used as heterogeneous catalysts and characterized by XRD, Mössbauer spectroscopy, BET surface area, particle size and chemical analyses. The adsorption to the catalyst changed significantly with the pH value and the sorption isotherm was fitted using the Langmuir model for both solids. Both sorption and FTIR results indicated that surface complexation reaction may take place in the system. The variation of oxidation efficiency against H₂O₂ dosage and amount of exposed surface area per unit volume was evaluated and correlated with the adsorption behavior in the absence of oxidant. The occurrence of optimum amount of H₂O₂ or of exposed surface area for the effective degradation of RhB could be explained by the scavenging effect of hydroxyl radical by H₂O₂ or by iron oxide surface. Sorption and decolourization rate of RhB as well as H₂O₂ decomposition rate were found to be dependent on the surface characteristics of iron oxide. The kinetic oxidation experiments showed that structural Fe^II content strongly affects the reactivity towards H₂O₂ decomposition and therefore RhB decolourization. The site density and sorption ability of RhB on surface may also influence the oxidation performance in iron oxide/H₂O₂ system. The iron (II, III) oxide catalysts exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle. The sorption on the surface of iron oxide with catalytic oxidation using hydrogen peroxide would be an effective oxidation process for the contaminants.     

Melting characteristics during the vitrification of MSWI fly ash with a pilot-scale diesel oil furnace

Treatment of municipal solid waste incineration (MSWI) fly ash is becoming an important issue in China. A pilot-scale experiment was carried out to treat MSWI fly ash by using a diesel oil furnace (DOF) for more than 6 months. The effects of melting temperature on volume reduction, weight loss, compositional changes, and toxicity of leach water for molten slag have been investigated and reported. Results indicated that the volume reduction fraction of raw fly ash (RFA) and washed-fly ash (WFA) was 75–80% and the weight loss fraction was 23.8–30% at 1260–1350 °C. During the vitrification, CaO, A1₂O₃, and SiO₂ percentages in fly ash increased as the temperature increased, especially for SiO₂, which was caused by both the decomposition of carbonates or sulfates and the volatilization of metal chlorides because the main components in secondary fly ash collected from fabric filter bags were NaCl and KCl. The leaching concentrations of heavy metals in molten slag were lower than the standard values of TCLP. The releasing levels of dioxin and other pollutants (such as SO₂, HCl, CO, NO_x, etc.) in flue gas were all lower than the Chinese standard.     

Theoretical Study of Benzene Interaction on Kaolinite

Clay minerals represent a growing research area in the development of new materials. Clay and clay-based materials have been widely investigated in efforts to design adsorbents. Furthermore, adsorption has been applied in order to remove organics and as an important strategy to remediate soils and groundwater contaminated with petroleum hydrocarbons. Among clays, kaolinite, Al₂Si₂O₅(OH)₄, is a layered aluminosilicate of 1:1 clay minerals family. Therefore, we have performed semi-empirical AM1 and ab initio RHF/3-21G* calculations in order to investigate the benzene interaction on kaolinite surface. The cluster model method was employed. Benzene structure was fully optimized. Molecular orbitals and electrostatic potential was also analyzed. The ab initio and semi-empirical results shows the benzene molecule largely tilted in relation to the hydroxyl layer. The π orbital of benzene has changed slightly indicating the interaction through the hydroxyl and benzene π orbital.     

Properties of hydraulic paste of basic oxygen furnace slag

Basic Oxygen Furnace (BOF) slags are by-products of the conversion of pig iron to steel. They mainly contain C₂S, C₂F, Fe_1−xO, CaO, Ca(OH)₂ and CaCO₃. According to their chemical composition they are a valuable mineral resource as additions in certain hydraulic binders. This paper presents a hydration study of the BOF slag pastes preserved at different temperatures and in different environments. Pastes are characterized by X-ray diffraction and scanning electron microscopy. The compressive strengths of hydrated pastes are given at 7, 28, 90 and 190 days. Results show that – BOF slags containing 40% of C₂S – have attractive mechanical properties. Hydration tests under water showed a pastes swelling due to the hydration of CaO contained in BOF slags. A lime extinction procedure was proposed as alternative to standard PR NF EN 13282-2. This approach is more effective for these materials: the volume expansion of pastes cured in water is avoided and the compressive strengths are thus significantly improved.     

Carrier-Free H2O2 Self-Supplier for Amplified Synergistic Tumor Therapy

Chemodynamic therapy (CDT) utilizes Fenton or Fenton-like reactions to convert hydrogen peroxide (H₂O₂) into cytotoxic hydroxyl radicals (•OH) and draws extensive interest in tumor therapy. Nevertheless, high concentrations of glutathione (GSH) and insufficient endogenous H₂O₂ often cause unsatisfactory therapeutic efficacy. Herein, a GSH-depleting and H₂O₂ self-providing carrier-free nanomedicine that can efficiently load indocyanine green (ICG), β-lapachone (LAP), and copper ion (Cu²⁺) (ICG-Cu²⁺-LAP, LICN) to mediate synergetic photothermal and chemotherapy in enhanced chemodynamic therapy is designed. The results show that  LICNs successfully enter tumors owing to the enhanced permeability and retention effect. Through the reductive intracellular environment, Cu²⁺ in LICN can react with intracellular GSH, alleviate the antioxidant capacity of tumor tissues, and trigger the release of drugs. When LICN is subjected to near-infrared (NIR) irradiation, enhanced photothermal effect and upregulated expression of NAD(P)H quinone oxidoreductase-1 (NQO1) are observed. Meanwhile, the released LAP not only supports chemotherapy but also catalyzes NQO1 and produces sufficient endogenous H₂O₂, thereby increasing the efficiency of Cu⁺-based Fenton-like reaction. Notably, GSH depletion and H₂O₂ self-sufficiency generate sufficient •OH and kill tumor cells with high specificity. Overall, the study provides an innovative strategy to self-regulate GSH and H₂O₂ levels for effective anticancer therapy.     

Direct oxidation route from metal to ceramic: Study on cobalt oxide

The study deals with the direct-oxidation kinetics of micronic-cobalt metal particles and its simulation for the complete transition from metal to ceramic. The simulation was also experimentally verified. All the three possible interfaces, Co/CoO, CoO/Co₃O₄ and Co₃O₄/O₂ (air), have been taken into consideration for the simulation. The complete oxidation kinetics has been investigated from the thermogravimetric studies under isothermal conditions in the temperatures 973–1173 K. A quantitative interpretation based on the diffusion of Co or oxygen ions through the grown oxide layer has been proposed. The activation energy for the oxidation kinetics calculated from the Arrhenius law was 161 ± 20 kJ mol⁻¹.     

Phase transformation and low temperature sintering of manganese oxide and scandia co-doped zirconia

The powders of 89 mol% ZrO₂-11 mol% Sc₂O₃ (11ScSZ) doped with various Mn₂O₃ contents were prepared by a co-precipitation method combined with a SCFD (supercritical fluid drying) route. Inhibition of the cubic-rhombohedral phase transformation in both oxidation and reduction atmospheres is achieved for 11ScSZ by the addition of 2.0 mol% Mn₂O₃. The Mn₂O₃ addition can lower the sintering temperature of 11ScSZ ceramics, and the 11ScSZ-2Mn₂O₃ compact can be sintered to nearly full density at 850 °C. 11ScSZ-2Mn₂O₃ ceramic with the cubic structure sintered at 900 °C possesses the conductivity of ∼ 0.10 S cm^− 1 at 800 °C, which is very promising for intermediate temperature solid oxide fuel cell (SOFC) applications.     

Bacterial biosurfactant in enhancing solubility and metabolism of petroleum hydrocarbons

Biosurfactant can make hydrocarbon complexes more mobile with the potential use in oil recovery, pumping of crude oil and in bioremediation of crude oil contaminant. In the investigation, bacterial isolates capable of utilizing poly-cyclic aromatic hydrocarbons like phenanthrene, pyrene and fluorene were used. A gradual decrease of the supplemented hydrocarbons in the culture medium was observed with corresponding increase in bacterial biomass and protein. The medium having the combined application of fluorine and phenanthrene caused better biosurfactant production (0.45 g l⁻¹) and (0.38 g l⁻¹) by Pseudomonas aeruginosa strains MTCC7815 and MTCC7814. The biosurfactant from MTCC7815 (41.0 μg ml⁻¹) and MTCC7812 (26 μg ml⁻¹) exhibited higher solubilization of pyrene; whereas, MTCC8165 caused higher solubilization of phenanthrene; and that of MTCC7812 (24.45 μg ml⁻¹) and MTCC8163 (24.49 μg ml⁻¹) caused more solubilzation of fluorene. Higher solubilization of pyrene and fluorene by the biosurfactant of MTCC7815 and MTCC7812, respectively enhanced their metabolism causing sustained growth. Biosurfactants were found to be lipopeptide and protein–starch–lipid complex in nature and they could reduce the surface tension of pure water (72 mN m⁻¹) to 35 mN m⁻¹. The critical micelle concentration (CMC) was also lower than the chemical surfactant sodium dodecyl sulphate (SDS). They differed in quantity and structure. The predominant rhamnolipids present in biosurfactants were Rha–C₈–C₁₀ and Rha–C₁₀–C₈.     

High-temperature structural change of CrOx-LaOx-Al2O3 catalyst for lean-burn exhaust treatment

Solid-state reaction in the system of CrOx-Al₂O₃ and CrOx-LaOx-Al₂O₃ and their sintering at 500–1100°C were examined by X-ray diffraction, electron spin resonance (ESR) and surface area measurement for the development of heat-stable catalytic ceramic in lean-burn exhaust treatment. CrOx-LaOx-Al₂O₃ catalyst, even heated at 1000°C in air, showed the removal conversion of 100% for C₃H₆, 95% for CO and 7% for NO at 500°C for high velocity automotive lean-burn exhaust with A/F = 18 and S.V. = 10⁵h^–1. La-modification of catalyst was effective to high surface area stabilization and the improvement of complete oxidation activity of CO and hydrocarbons.     

A pilot study of three-stage biological–chemical treatment of landfill leachate applying continuous ferric sludge reuse in Fenton-like process

This pilot study describes a three-stage continuous process for treating landfill leachate containing significant concentrations of recalcitrant organic substances. The proposed technological scheme consisted of an activated sludge pre-treatment combined with a Fenton-like process enhanced by continuous sludge reuse and followed by an activated sludge post-oxidation. Biological pre-treatment removed >99, 86, >99, 83 and 86 % of BOD₇, COD, NH₄ ⁺–N, phenols and the sum of lignin and tannins, respectively. Operational conditions in the ferric sludge-catalysed Fenton-like process stage were carefully adjusted in order to maintain the efficacy and practicability of combined treatment scheme. Although the application of ferric sludge as a catalyst in the Fenton-like oxidation reduced COD removal efficiency by 32 % as compared to the conventional Fenton process, lower process efficiency was compensated by reducing the water exchange ratio to 50 % without increasing the consumption of reagents. Moreover, an intermittent addition (added to every second treatment cycle) of fresh ferrous iron catalyst at a H₂O₂/Fe²⁺ w/w ratio of 20/1 increased the BOD₇/COD ratio from 0.04 to 0.32 and resulted in 60 % COD removal. A cyclic addition (added to every treatment cycle) of the same amount of catalyst increased the BOD₇/COD ratio from 0.09 to 0.32, and a 10 % higher COD removal efficiency as compared to intermittent catalyst addition was achieved. Finally, biological post-treatment of the leachate resulted in more than 95 % removal of each measured parameter. Overall, the combined technological scheme with continuous ferric sludge reuse in the Fenton-like stage proved promising alternative for landfill leachate treatment.     

From iron(III) precursor to magnetite and vice versa

The syntheses of nanosize magnetite particles by wet-chemical oxidation of Fe²⁺ have been extensively investigated. In the present investigation the nanosize magnetite particles were synthesised without using the Fe(II) precursor. This was achieved by γ-irradiation of water-in-oil microemulsion containing only the Fe(III) precursor. The corresponding phase transformations were monitored. Microemulsions (pH  12.5) were γ-irradiated at a relatively high dose rate of 22 kGy/h. Upon 1 h of γ-irradiation the XRD pattern of the precipitate showed goethite and unidentified low-intensity peaks. Upon 6 h of γ-irradiation, reductive conditions were achieved and substoichiometric magnetite (Fe_2.71O₄) particles with insignificant amount of goethite particles found in the precipitate. Hydrated electrons , organic radicals and hydrogen gas as radiolytic products were responsible for the reductive dissolution of iron oxide in the microemulsion and the reduction Fe³⁺ → Fe²⁺. Upon 18 h of γ-irradiation the precipitate exhibited dual behaviour, it was a more oxidised product than the precipitate obtained after 6 h of γ-irradiation, but it contained magnetite particles in a more reduced form (Fe_2.93O₄). It was presumed that the reduction and oxidation processes existed as concurrent competitive processes in the microemulsion. After 18 h of γ-irradiation the pH of the medium shifted from the alkaline to the acidic range. The high dose rate of 22 kGy/h was directly responsible for this shift to the acidic range. At a slightly acidic pH a further reduction of Fe³⁺ → Fe²⁺ resulted in the formation of more stoichiometric magnetite particles, whereas the oxidation conditions in the acidic medium permitted the oxidation Fe²⁺ → Fe³⁺. The Fe³⁺ was much less soluble in the acidic medium and it hydrolysed and recrystallised as goethite. The γ-irradiation of the microemulsion for 25 h at a lower dose rate of 16 kGy/h produced pure substoichiometric nanosize magnetite particles of about 25 nm in size and with the stoichiometry of Fe_2.83O₄.     

Large-scale preparation of powder composites xNiO/(1-x)Al2O3 in reactions of solution combustion synthesis

The conditions for the production of composites by Solution Combustion Synthesis (SCS) from reaction solutions of aluminum and nickel nitrates of various concentrations with glycine have been studied. The concentration of reaction solutions increases the product yield and the productivity of SCS process. The effect of the presence of Al³⁺ cations in reaction solutions on the combustion reaction intensity reduction has been established. The SCS precursors contained metallic nickel, nickel oxide and amorphous alumina. The phase composition of the samples changed in the process of annealing: nickel oxidation, crystallization of γ-Al₂O₃ (600 °C) and formation of NiAl₂O₄ spinel (600–800 °C) were observed. The maximal specific surface area value recorded after annealing at 800 °C was 59–63 m²/g. In samples obtained with a lower fuel content, γ-Al₂O₃ or a mixture of γ-Al₂O₃ and NiAl₂O₄ crystallize on the surface of composite particles. The concentration of NiO on the surface of composites obtained from precursors synthesized from concentrated solutions at φ = 1.4 is close to the nominal composition.     

Characterization and activation of Basic Oxygen Furnace slag

BOF slags are by-products of steel conversion. They are a valuable mineral resource for the construction but have chemical properties that directly control their stability or any hydraulic activity. This paper provides a complete characterization and quantification of BOF slag phases in order to better understand their potential hydraulic activity. The acceleration of the hydration by chemical admixtures is also presented. The BOF slag variability is investigated on several samples with different origins and ages.BOF slag with different origins mainly contain 38-52% C₂S, 20-30% C₂F, 1-7% Ca(OH)₂, 11-13% Fe_1−xO, 2-8% CaO. Calcium silicate is present in β-C₂S form which is the active polymorph present in clinker. BOF slags have poor hydraulic activity at early ages which can be enhanced by calcium chloride addition.     

Shrinkage and strength of alkaline activated ground steel slag/ultrafine palm oil fuel ash pastes and mortars

This study evaluated the contributions of steel slag and activators ratio to the shrinkage of the alkali-activated ground steel slag (G)/ultrafine palm oil fuel ash (U) or AAGU pastes and mortars. The base materials were combined such that G/U+G varied from 0 to 0.8 (pastes) and 0–0.6 (mortars) with the use of 10M-NaOH_aq and Na₂SiO_3aq (Ms = SiO₂/Na₂O of 3.3) as activators whose ratios (Na₂SiO_3aq/10M NaOH_aq) were varied as 1.0/1.0 and 2.5/1.0. The findings revealed that steel slag reduced the AAGU shrinkage through pore-refinement, elimination of microcracks, and improvement in the microstructural density and strength. The changing of Na₂SiO₃/10NaOH ratio in the synthesis of AAGU products from 2.5 to 1.0 slightly reduced the shrinkage through the modification of amorphousity and nature of the products (C-A-S-H/C-S-H). The maximum 90-day slag-free AAGU paste and mortar shrinkages were 60.80 × 10³ με and 11.82 × 10³ με but reduced to 25.88 × 10³ and 2.71 × 10³ με, respectively as G/(U+G) = 0.4 in AAGU_0.4.