Fly Ash Suspensions Research Articles

Observations on the rheological response of alkali activated fly ash suspensions: the role of activator type and concentration

This paper reports the influence of activator type and concentration on the rheological properties of alkali-activated fly ash suspensions. A thorough investigation of the rheological influences (yield stress and plastic viscosity) of several activator parameters, including: (i) the cation type and concentration of alkali hydroxide and (ii) the alkali-to-binder ratio (n) and silica modulus (Ms), and (iii) the volume of the activation solution, on the suspension rheology is presented. The results indicate a strong dependence on the cation and its concentration in the activation solution. The viscosity of the activation solution and the volumetric solution-to-powder ratio are shown to most strongly influence the plastic viscosity of the suspension. The suspension yield stress is predominantly influenced by the changes in fly ash particle surface charge and the ionic species in the activator. A shift from non-Newtonian to Newtonian flow behavior is noted in the case of silicate-based suspensions for Ms ≤ 1.5. This behavior, which is not observed at higher MS values, or when the fly ash is dispersed in hydroxide solutions or pure water, is hypothesized to be caused by colloidal siliceous species present in this system, or surface charge effects on the fly ash particles. Comparisons of the rheological response of alkali-activated suspensions to that of portland cement-water suspensions are also reported.

An improved estimation of shear rate using rotating coaxial-cylinder Fann viscometer: A rheological study of bentonite and fly ash suspensions

Bentonite is commonly used as a drilling fluid additive for viscosity control during drilling of oil wells. Rheological behavior of bentonite suspensions is very complex and it is very difficult to predict accurate shear rates from viscometer readings. This paper deals with the accurate estimation of shear rates of bentonite suspensions using rotating coaxial-cylinder Fann viscometer readings. Rotor rotations and bob deflections are the two important Fann viscometer readings which are used to predict shear rates with the help of generalized viscometer difference equation. Rheological behavior of bentonite suspensions are also compared with classified fly ash suspensions with varying particle size and solid loading. The proposed shear rate equation is quite general and can be applied to any fluid.

Electrodialytic removal of Cd from biomass combustion fly ash suspensions

Due to relatively high concentrations of Cd, biomass combustion fly ashes often fail to meet Danish legislative requirements for recycling as fertilizer. In this study, the potential of using electrodialytic remediation for removal of Cd from four different biomass combustion fly ashes was investigated with the aim of enabling reuse of the ashes. The ashes originated from combustion of straw (two ashes), wood chips, and co-firing of wood pellets and fuel oil, respectively. A series of laboratory scale electrodialytic remediation experiments were conducted with each ash. The initial Cd concentration in the ashes varied between 8.8mg Cd/kg (co-firing ash) and 64mg Cd/kg (pre-washed straw ash), and pH varied from 3.7 (co-firing ash) to 13.3 (wood ash). In spite of such large variations between the ashes, the electrodialytic method showed to be sufficiently robust to treat the ashes so the final Cd concentration was below 2.0mg Cd/kg DM in at least one experiment done with each ash. This was obtained within 2 weeks of remediation and at liquid to solid (L/S) ratios of L/S 16 for the pre-washed straw ash and L/S 8 for the straw, co-firing and wood ash.

Evaluation of the Possibilities of Sequestration of Carbon Dioxide in Aqueous Suspensions of Selected Fly Ash

Ocena możliwooeci sekwestracji ditlenku węgla w wodnych zawiesinach wybranych popiołów lotnych Energetyka zawodowa jest największym emitentem antropogenicznego ditlenku węgla. Podstawowymi paliwami w Polsce są paliwa stałe - węgiel kamienny oraz węgiel brunatny, w procesach spalania których powstają znaczne ilooeci odpadów, głównie popiołów lotnych. Popioły z węgla brunatnego, ze względu na skład chemiczny i fazowy, a tym samym właoeciwooeci, mają dotychczas ograniczone zastosowanie gospodarcze. Jedną z możliwooeci ich wykorzystania jest mineralna sekwestracja ditlenku węgla, ze względu na relatywnie dużą zawartość aktywnych CaO i MgO, które mogą reagować z ditlenkiem węgla w zawiesinach wodnych. W artykule przedstawiono teoretyczną pojemność związania oraz wyniki badań pochłaniania CO2 przez zawiesiny popiołowo-wodne sporz ądzone z popiołów lotnych ze spalania węgla brunatnego z El. Pątnów i El. Turów. Obliczona dla badanych popiołów maksymalna teoretyczna pojemność związania ditlenku węgla wyniosła odpowiednio: 14% dla popio łów z El. Pątnów oraz 14,4% dla popiołów z El. Turów. Badania wykazały, że najwięcej CO2 - 8,15 g/100 g popiołu - zostało pochłonięte przez zawiesiny sporządzone z popiołu fluidalnego z El. Turów o stosunku masowym popiołu do wody wynoszącym 0,8:1. W przypadku popiołu z El. Pątnów pochłanianie było mniejsze i wyniosło maksymalnie 8,7 g CO2/100 g popiołu. Największy przyrost pochłaniania CO2 obserwowano w pierwszych 30 minutach prowadzenia procesu karbonatyzacji w zawiesinach popiołu lotnego z El. Pątnów i pierwszych 15 minutach w zawiesinach popiołu lotnego z El. Turów. Po tym czasie pochłanianie wzrastało już powoli. Stwierdzono wzrost temperatury w komorach instalacji, potwierdzający zachodzenie procesu karbonatyzacji oraz jej endotermiczny charakter. Najwyższą temperaturę - 44,8°C zarejestrowano w zawiesinie popiołów z El. Turów o stosunku popiołu do wody - 0,8:1, w której stwierdzono również największe pochłanianie CO2. Przedstawione wyniki badań potwierdzają przydatność tych popiołów do sekwestracji ditlenku węgla.

Removal mechanism of phosphate from aqueous solution by fly ash

This work studied the effectiveness of fly ash in removing phosphate from aqueous solution and its related removal mechanism. The adsorption and precipitation of phosphate by fly ash were investigated separately in order to evaluate their role in the removal of phosphate. Results showed that the removal of phosphate by fly ash was rapid. The removal percentage of phosphate in the first 5 min reached 68–96% of the maximum removal of phosphate by fly ash. The removal processes of phosphate by fly ash included a fast and large removal representing precipitation, then a slower and longer removal due to adsorption. The adsorption of phosphate on fly ash could be described well by Freundlich isotherm equation. The pH and Ca 2+ concentration of fly ash suspension were decreased with the addition of phosphate, which suggests that calcium phosphate precipitation is a major mechanism of the phosphate removal. Comparison of the relative contribution of the adsorption and precipitation to the total removal of phosphate by fly ash showed that the adsorption accounted for 30–34% of the total removal of phosphate, depending on the content of CaO in fly ash. XRD patterns of the fly ash before and after phosphate adsorption revealed that phosphate salt (CaHPO 4·2H 2O) was formed in the adsorption process. Therefore, the removal of phosphate by fly ash can be attributed to the formation of phosphate precipitation as a brushite and the adsorption on hydroxylated oxides. The results suggested that the use of fly ash could be a promising solution to the removal of phosphate in the wastewater treatment and pollution control.

Utilization of Carbon Dioxide in Fly Ash and Water Mixtures

Greenhouse gases emission, mainly carbon dioxide, is one of the most important problems of the recent years. That is why many actions have been taken up, not only to reduce emission of greenhouse gases but to store them and utilize as well. The reduction of the carbon dioxide emission is extremely difficult in the case of its largest source—power industry. This industry also produces other type of waste—fly ashes. The authors’ idea is to utilize carbon dioxide by its fixation in fly ash suspension and deposit in underground mines.

Rheology of non-Newtonian suspensions of fly ash: effect of concentration, yield stress and hydrodynamic interactions

Two different water-washed municipal solid waste (MSW) incinerator fly ashes were investigated. The rheological behaviour of these fly ashes in aqueous suspensions was studied using a parallel plate rheometer. Shear-thinning behaviour was observed in one sample whereas thixotropic behaviour was found in the other. Viscosity depends on both the volume fraction of solids in the suspension and on the yield stress. The data could be well correlated to a model we proposed which takes into account the volume fraction of solid and the shear rate. The comparison with various models of the literature is discussed. The hydrodynamic theory of particle movement in non-Newtonian fluids is discussed, focusing on inertia and viscous effects. Two modified Reynolds numbers involving respectively the shear rate and the yield stress, and with the shear rate and the volume fraction of solids, are proposed and discussed. The flow regime in the investigated experimental conditions is laminar and governed by hydrodynamic interactions. The results also show that inertia cannot be neglected.

Properties and Performance of a Pulverized Fly Ash Grout

A laboratory investigation was conducted in order to develop a new grout based on fly ash produced in Greece. Ptolemaida fly ash was selected because of its hydraulic properties and was pulverized (Blaine specific surface over 8,300 cm²/gr, \iD\D15\N=1.3 μm, \iD\D50\N=6 μm, and \iD\D85\N=20 μm) in order to improve its groutability and its hydraulic activity. Pulverized fly ash (PFA) suspensions with selected additives have properties comparable to those of ordinary and microfine cement suspensions. Clean sands were injected using two specially constructed devices. Hydraulic conductivity, unconfined compression, and UU and CU-PP triaxial compression tests were conducted on grouted sand specimens. Coarse sands can be grouted effectively with PFA suspensions. Conventional groutability ratios were found to overestimate the groutability of these suspensions. Grouting with PFA suspensions reduces sand hydraulic conductivity by up to seven orders of magnitude and yields unconfined compression strength values up to 3,000 kPa. The Mohr-Coulomb failure criterion represents the behavior of grouted sand with cohesion values ranging from 280 to 450 kPa and angle of internal friction slightly higher than that of the sands.

Development of a pulverized fly ash suspension grout

A Greek lignite fly ash was selected because of its hydraulic properties and was pulverized to produce a specific surface of 8300 cm2/g, and a gradation with D15, D50, and D85 equal to 1.3 μm, 6 μm and 20 μm, respectively. The pulverized fly ash suspension properties were optimized by adding a suitable superplasticizer and a suitable accelerator at optimum dosages. The experimental evaluation of suspension properties included sedimentation tests, viscosity'measurements, rheological properties, setting times and development of strength with time. Groutability and effectiveness were evaluated by injecting selected suspensions into clean sands. Pulverization improves remarkably the behavior of fly ash suspensions. Suspensions with water to solids ratios of 1.5:1 and 2:1 by weight and containing additives, behave as Bingham fluids, have apparent viscosity lower than 70 cP, bleed capacity lower than 5%, initial setting time lower than 24 h, and can be injected into relatively coarse sands. These characteristics are comparable to those obtained for ordinary and microfine cement suspensions, showing that pulverized fly ash suspensions can be used for permeation grouting.

Cytokines involved in the systemic inflammatory response induced by exposure to particulate matter air pollutants (PM(10)).

Elevated levels of ambient particulate matter (PM(10)) have been associated with increased cardiopulmonary morbidity and mortality. We previously showed that the deposition of particles in the lung induces a systemic inflammatory response that includes stimulation of the bone marrow. This marrow response is related to mediators released by alveolar macrophages (AM) and in this study we measured cytokines produced by human AM exposed to ambient particles of different composition and size. Identified cytokines were also measured in the circulation of healthy young subjects exposed to air pollutants during the 1997 Southeast Asian forest fires. Human AM were incubated with particle suspensions of residual oil fly ash (ROFA), ambient urban particles (EHC 93), inert carbon particles, and latex particles of different sizes (0.1, 1, and 10 microm) and concentrations for 24 h. Tumor necrosis factor-alpha (TNF-alpha) increases in a dose-dependent manner when AM were exposed to EHC 93 particles (p < 0.02). The TNF response of AM exposed to different sizes of latex particles was similar. The latex (158 +/- 31%), inert carbon (179 +/- 32%), and ROFA (216 +/- 34%) particles all show a similar maximum TNF response (percent change from baseline) whereas EHC 93 (1,020 +/- 212%, p < 0.05) showed a greater maximum response that was similar to lipopolysaccharide (LPS) 1 microg/ml (812 +/- 320%). Macrophages incubated with an optimal dose of EHC 93 particles (0.1 mg/ml) also produce a broad spectrum of other proinflammatory cytokines, particularly interleukin (IL)-6 (p < 0.01), IL-1 beta (p < 0.05), macrophage inflammatory protein-1 alpha (MIP-1 alpha) (p < 0.05), and granulocyte macrophage colony-stimulating factor (GM-CSF) (p < 0.01) with no difference in concentrations of the anti-inflammatory cytokine IL-10 (p = NS). Circulating levels of IL-1 beta, IL-6, and GM-CSF were elevated in subjects exposed to high levels of PM(10) during an episode of acute air pollution. These results show that a range of different particles stimulate AM to produce proinflammatory cytokines and these cytokines are also present in the blood of subjects during an episode of acute atmospheric air pollution. We postulate that these cytokines induced a systemic response that has an important role in the pathogenesis of the cardiopulmonary adverse health effects associated with atmospheric pollution.

Enhanced conductivity measurement techniques for evaluation of fly ash pozzolanic activity

Evaluation of pozzolanic activity of low-lime fly ashes was carried out by means monitoring of conductivity of fly ash suspensions in calcium hydroxide solution. Contribution of soluble salts from fly ashes to conductivity may be taken into account for evaluating pozzolanic properties of fly ashes. The pozzolanic activity was calculated as the percentage of loss in conductivity, %LC, prior the corresponding salinity correction, at several reaction times (100, 1000 and 10 000 s) and at different reaction temperatures (40°C, 60°C and 80°C). Considerations about the influence of hydrated lime/fly ash ratio in conductivity measurements have been described, and 0.04:1 ratio was proposed for yielding best results. Finally, no suitability of the proposed methodology for high-lime fly ashes was demonstrated.

Effect of superplasticizers on the rheological properties of fly ash suspensions containing activators of the pozzolanic reaction

Rheological studies have been carried out on the effect of a superplasticizer from the sulphonated melamine formaldehyde (SMF) group upon the properties of fly ash suspensions containing a small quantity of mineral admixtures such as cement, lime and gypsum. The superplasticizers' efficiency has appeared to depend greatly on the admixture used. The highest liquefaction degree was found in fly ash suspensions containing both cement and gypsum together and the next it was, when only cement was added. These suspensions exhibit features of a newtonian fluid of low plastic viscosity, when the water to solid ratio (w/s) is 0.3 and a superplasticizer has been used. However, fly ash suspensions with lime, under analogous conditions, produce a considerable increase of the rheological parameters. This may be explained by the effect of the very high specific surface area of hydrated lime upon the consistency of fly ash suspensions.

98/02468 The possibilities of the absorption of nitric oxides by dense fly ash suspensions. Part I : Sulkowski, W. et al. Chemical Inz. Ekol., 1997, 4, (3), 419–426. (In Polish)

98/02468 The possibilities of the absorption of nitric oxides by dense fly ash suspensions. Part I : Sulkowski, W. et al. Chemical Inz. Ekol., 1997, 4, (3), 419–426. (In Polish)

Development of a Laboratory-Scale Leaching Plant for Metal Extraction from Fly Ash by Thiobacillus Strains

Semicontinuous biohydrometallurgical processing of fly ash from municipal waste incineration was performed in a laboratory-scale leaching plant (LSLP) by using a mixed culture of Thiobacillus thiooxidans and Thiobacillus ferrooxidans. The LSLP consisted of three serially connected reaction vessels, reservoirs for a fly ash suspension and a bacterial stock culture, and a vacuum filter unit. The LSLP was operated with an ash concentration of 50 g liter, and the mean residence time was 6 days (2 days in each reaction vessel). The leaching efficiencies (expressed as percentages of the amounts applied) obtained for the economically most interesting metal, Zn, were up to 81%, and the leaching efficiencies for Al were up to 52%. Highly toxic Cd was completely solubilized (100%), and the leaching efficiencies for Cu, Ni, and Cr were 89, 64, and 12%, respectively. The role of T. ferrooxidans in metal mobilization was examined in a series of shake flask experiments. The release of copper present in the fly ash as chalcocite (Cu(2)S) or cuprite (Cu(2)O) was dependent on the metabolic activity of T. ferrooxidans, whereas other metals, such as Al, Cd, Cr, Ni, and Zn, were solubilized by biotically formed sulfuric acid. Chemical leaching with 5 N H(2)SO(4) resulted in significantly increased solubilization only for Zn. The LSLP developed in this study is a promising first step toward a pilot plant with a high capacity to detoxify fly ash for reuse for construction purposes and economical recovery of valuable metals.

Epithelial injury induced by exposure to residual oil fly-ash particles: role of reactive oxygen species?

Exposure of animals to airborne particulates is associated with pulmonary injury and inflammation. In the studies described here, primary cultures of rat tracheal epithelial (RTE) cells were exposed to suspensions of residual oil fly ash (ROFA). ROFA exposure resulted in progressive cytotoxicity whereby the amount of lactate dehydrogenase (LDH) released was significantly greater at 24 h than at 6 h after exposure. In a dose-dependent manner, exposure to 5, 10, or 20 microg/cm2 of ROFA for 24 h resulted in cytotoxicity and detachment of cells from the collagen matrix, along with altered permeability of the RTE cell layer. ROFA exposure caused cellular glutathione levels to decrease, producing a condition of oxidative stress in the RTE cells. Treatment of RTE cells with buthionine sulfoxamine, an inhibitor of gamma-glutamyl cysteine synthetase, was found to augment ROFA-induced cytotoxicity. Treatment with dimethylthiourea (DMTU) inhibited ROFA-induced LDH release and permeability changes in a dose-dependent manner. Treatment with the nitric oxide synthase inhibitor NG-monomethyl-D-arginine (D-NMA) for 24 h was without effect. In rats intratracheally instilled with ROFA (500 microg/rat), intraperitoneal administration of DMTU (500 mg/kg) significantly ameliorated the degree of pulmonary neutrophilic inflammation present at 24 h. Overall, these in vitro findings suggest that ROFA-induced RTE cell injury may be mediated by hydroxyl-radical-like reactive oxygen species (i.e., species scavenged by DMTU) that are generated via non-nitric oxide pathways. The delay in induction of maximal RTE cell injury may reflect the time necessary to produce an oxidative burden by depleting antioxidant defenses such as cellular glutathione.

Lung retention and bioavailability of arsenic after single intratracheal administration of sodium arsenite, sodium arsenate, fly ash and copper smelter dust in the hamster

Arsenic is present in airborne particulate material released by coal-fired power plants and non-ferrous metal smelters. We have assessed whether the physico-chemical properties of arsenic in such particles play a role in its lung retention and uptake by the body. Female hamsters were given a single intratracheal instillation of fly ash or copper smelter dust suspensions (at doses of 50 or 100 μg As kg(-1)) or identical amounts of soluble tri- and pentavalent arsenic, in the presence or absence of an inert dust material (tungsten carbide). The concentration of the element was measured in a 24 hour urine sample collected on the 1st, 2nd and 6th day after treatment and arsenic remaining in lung tissue was determined at the end of the same time periods. Both lung retention and urinary As excretion indicate a prolonged contact of the lung tissue with particulate As in contrast to soluble As salts. In addition to the effect of solubility described here, more research is needed to determine the effect of particle size and lung loading on retention, as well as the potential differences in the lung inflammatory response using arsenic-rich particulates from various sources.

Autoxidation of sulphur dioxide in aqueous flyash suspensions

Abstract The fact that the thermal power and other plants continuously belch SO2 and flyash concurrently made us to look into the chemistry of autoxidation of aqueous sulphur dioxide in aqueous suspensions of four different flyash samples obtained from three different thermal power and a fertilizer plants. The particle sizes and metal contents of each flyash sample were determined. Detailed kinetics investiaation showed the major catalysis to be due to leached trace metal ions, and in agreement with the general rate law. where, a = ≤ 0.5; b = 1.5–2; c = 0.4–1.5 The atmospheric calculations indicated the conversion rates of around 0.34 to 1. “59% due to wetted flyash aerosols.

Use of sedimentation ponds for removal of metals from ash transport waters

AbstractThis study investigated the feasibility of using existing ash sedimentation ponds at coal‐fired power plants as treatment reactors to reduce concentrations of metals in bottom ash and fly ash transport waters by precipitation and/or adsorption onto iron oxyhydroxide. Intrapond treatment offers economic advantages over construction of a plant for treatment of ash pond effluent. Bench‐scale experiments were conducted with bottom ash and fly ash suspensions to investigate pH control and removals of aluminum, manganese, and arsenic under different chemical conditions, including addition of ferric chloride to promote adsoption on iron oxyhydroxide. The effects of pH and iron addition on ash‐water partitioning of the metals of interest were studied via batch experiments. In addition, the ability to control pH and promote removal of manganese in an intrapond treatment process was investigated using semi‐continuous, bench‐scale, pond‐simulation reactors. Results of the reactor experiments indicated that the pH could be maintained in range of 8 to 8.5 by dosing the influent with the proper amount of base as determined by batch titration, and that by doing so the influent manganese concentration of 2ppm could be consistently lowered to less than 0.2 ppm. The effects of accumulation of settled ash were examined in the reactor studies and with the use of a coupled hydraulic/sedimentation model for ash ponds. Overall, results of this study suggest that concentrations of most metals of interest in ash pond water can be kept low with control of pH, in situ precipitation of iron oxyhydroxide, and effective sedimentation of particles. Further examination of the intrapond treatment approach is warranted.

Long-Term Carcinogenicity Study in Syrian Golden Hamster of Particulate Emissions from Coal- and Oil-Fired Power Plants

Male Syrian golden hamsters were given 15 weekly intratracheal instillations with suspensions of coal fly ash or oil fly ash. Controls were instilled with saline containing gelatine (0.5 g/100 mL) or to check particle effects with suspensions of hematite (Fe2O3). The common weekly dose was 4.5 mg/hamster. In addition, one subgroup of hamsters was treated with oil fly ash at a weekly dose of 3.0 mg/hamster and another with coal fly ash at a weekly dose of 6.0 mg/hamster. Other groups of hamsters were treated with suspensions of benzo[a]pyrene (BaP) or with suspensions on coal fly ash, oil fly ash, or Fe2O3 coated with BaP. The mass median aerodynamic diameters of the coal and oil fly ashes were 4.4 microns and 28 microns, respectively. Hamsters treated with oil fly ash showed a higher frequency of bronchiolar-alveolar hyperplasia than hamsters in the other treatment groups. Squamous dysplasia and squamous metaplasia were most frequent in animals treated with suspensions of BaP or BaP-coated particles. The earliest appearance of a tumor, the highest incidence of tumors, and the highest incidence of malignant tumors were observed in hamsters treated with oil fly ash coated with BaP. Squamous cell carcinoma and adenosquamous carcinoma were the most frequent malignant tumors. No malignant tumors and only few benign tumors were observed in hamsters instilled with suspensions of fly ash not coated with BaP. The present study gives no indication that coal fly ash could create more serious health problems than oil fly ash.

Long-term carcinogenicity study in Syrian golden hamster of particulate emissions from coal- and oil-fired power plants.

Male Syrian golden hamsters were given 15 weekly intratracheal instillations with suspensions of coal fly ash or oil fly ash. Controls were instilled with saline containing gelatine (0.5 g/100 mL) or to check particle effects with suspensions of hematite (Fe2O3). The common weekly dose was 4.5 mg/hamster. In addition, one subgroup of hamsters was treated with oil fly ash at a weekly dose of 3.0 mg/hamster and another with coal fly ash at a weekly dose of 6.0 mg/hamster. Other groups of hamsters were treated with suspensions of benzo[a]pyrene (BaP) or with suspensions on coal fly ash, oil fly ash, or Fe2O3 coated with BaP. The mass median aerodynamic diameters of the coal and oil fly ashes were 4.4 microns and 28 microns, respectively. Hamsters treated with oil fly ash showed a higher frequency of bronchiolar-alveolar hyperplasia than hamsters in the other treatment groups. Squamous dysplasia and squamous metaplasia were most frequent in animals treated with suspensions of BaP or BaP-coated particles. The earliest appearance of a tumor, the highest incidence of tumors, and the highest incidence of malignant tumors were observed in hamsters treated with oil fly ash coated with BaP. Squamous cell carcinoma and adenosquamous carcinoma were the most frequent malignant tumors. No malignant tumors and only few benign tumors were observed in hamsters instilled with suspensions of fly ash not coated with BaP. The present study gives no indication that coal fly ash could create more serious health problems than oil fly ash.