Ash Pellets Research Articles

Structural properties and temperature effect of sintered fly ash pellets concrete

In order to create a sustainable environment, it is essential to use industrial waste as a building construction material. For a growing nation like India, Fly Ash (FA) as a waste produced abundantly from the thermal power plants is always a significant problem. Sintered fly ash pellets produced form fly ash can be utilized as coarse aggregate in concrete, which will be considered beneficial towards sustainability of the natural resources. This current research attempts to examine the temperature effects on the structural behaviour of the concrete made from sintered fly pellets as a replacement of coarse aggregate. As sintered fly ash pellets make the concrete lighter in comparison to natural coarse aggregate concrete, the structural properties such as load deflection behaviour of beam and mechanical properties need to be investigated. In addition to structural properties, it is also essential to explore durability aspect of the same. Experimental investigation revealed that formation of shear crack is generated earlier in FA sintered pellet concrete beam in comparison to natural coarse aggregate concrete beam. However, FA pellet concrete performs better in compressive strength, split tensile strength, whereas flexural strength shows inferior strengths. Durability test that involved exposure to higher temperatures (90 °C, 180 °C & 250 °C) provides good compressive strength in case of fly ash pallet concrete. But one outstanding achievement is that the rate of gaining of strength increases from 7 days to 28 days is faster than control mix. The experimental observation recommended that FA sintered pellet concrete should be utilized in case of lighter weight concrete wherever required rather than in major structural element construction.

Catalytic Upgrading of Plastic Waste of Electric and Electronic Equipment (WEEE) Pyrolysis Vapors over Si–Al Ash Pellets in a Two-Stage Reactor

This study investigated thermal cracking and catalytic upgrading of waste from electric and electronic equipment (WEEE) plastics on a semi-batch reactor coupled to a heated catalyst fixed bed (2-stage vapor cracking). The catalyst used is a Si–Al ash obtained from commercial activated carbon pellets treated with concentrated NaOH solution and calcination. The purpose of the study was to characterize the waste stream through its thermogravimetry analysis and pyrolysis products, study the effect of temperature (350–500 °C) and catalyst quantity (0.0–7.5 %.wt) on yields of reaction products, physical chemical properties, and chemical composition of bio-oil in order to understand and evaluate production of fuels and chemical feedstock by recycling of WEEE plastic through catalytic upgrading. Time-fractioned samples were taken in determined reaction times (15, 30, 45, and 60 min) to study the evolution of cracking reactions during experiment runs through changes to chemical composition (GC/MS). A comparison with other previous work is also presented to show similarities between different feedstocks using the same thermal unit. The results indicate composition of brominated acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), and high impact polystyrene (HIPS) for the WEEE plastic. The temperature of 350 °C produced better results when considering acid value but presented lower bio-oil yields (38%) and high gas yields (42%). Catalytic upgrading experiments revealed the increased presence of polycyclic aromatic hydrocarbons (PAH) with an increase in viscosity of bio-oil, increase in char yield (from 11% to 24%), and decrease in gas yields (15% to 5%). Chemical composition showed presence of aromatic hydrocarbons such as styrene, methyl-styrene, and diphenyl-propane and nitrogenated compounds such as benzene-butane-nitrile, phenolic compounds, PAHs, and brominated compounds. WEEE plastic pyrolysis is a challenging subject due to contaminant presence and varying composition, and chemical composition evaluation according to reaction time provides interesting insights into the evolution of semi-batch pyrolysis/catalytic upgrading experiments. Standardization and reproducibility of the tool should be conducted to continue the evaluation of pyrolysis and catalytic upgrading of a wide range of feedstocks.

Influence of presaturated coconut fibre ash pellets in concrete

Influence of presaturated coconut fibre ash pellets in concrete

Growth of complex volcanic ash aggregates in the Tierra Blanca Joven eruption of Ilopango Caldera, El Salvador

Aggregation processes control both the residence time and dispersal of volcanic ash during eruptions yet remain incompletely understood. The products of aggregation vary from simple ash clusters to large, complexly layered accretionary lapilli. Here we detail the micro-stratigraphy of a single population of accretionary lapilli that grew during the ∼431 CE Tierra Blanca Joven eruption from Ilopango Caldera, El Salvador. The accretionary lapilli were sampled 10 km from the caldera source within a sequence of ash-rich pyroclastic density current deposits and intercalated fall material, known as unit D, which is traceable >40 km from Ilopango. Scanning electron microscopy and image analysis reveal common facies that form distinct layers within the accretionary lapilli. Each facies is distinguished by quantitative and qualitative variations in particle size distribution, porosity, and particle fabric. We infer that these textures resulted from aggregation conditions that differed in terms of liquid water availability, particle concentration and grain size distributions. In our proposed model, a characteristic sequence of facies accreted from core to rim in the accretionary lapilli during passage through ash clouds generated by vent-derived plumes and pyroclastic density currents. The accretionary lapilli are mostly composed of smaller aggregates (ash clusters, ash pellets) and grew predominantly by accretion of already-formed aggregates, rather than by grain-by-grain accretion of individual particles. This finding is consistent with observations of rapid aggregate growth in volcanic plumes, suggesting a common evolutionary pathway for accretionary lapilli formation across diverse eruptions.

The influence of mineral addition on the Optimised Advanced Ash Fusion Test (OAAFT) and its thermochemical modelling and prediction

Specific minerals in ash are triggers for ash fusion during combustion. This study analyses, for the first time, the link between individual minerals and the ash fusion of pseudo ash pellets using the Optimised Advanced Ash Fusion Test (OAAFT) and FactSage modelling. The study analysed 20 pseudo ash pellets whose composition spanned a wide range of fuels used in the power generation industry. Varying quantities of the 4 main minerals were used to create the pseudo pellets; CaO (0–40%), Fe2O3 (0–40%), MgO (0–25%), and Silica-Alumina ratio (0.5:1–4:1). The OAAFT produced characteristic ash fusion curves for the pseudo pellets and individual minerals. The study also gained insight into the link between mineral transformations and ash fusion by comparing these profiles to the slag formation predictions in the FactSage modelling. Excellent alignment was obtained between the OAAFT curves and FactSage data. The OAFFT curves can be described as individual fingerprints of the ash fusion behaviour of the sample, which can be broken down into individual components. This data cannot be obtained from the conventional ash fusion test. By combining OAAFT and FactSage data, power generators can replicate slagging and fouling issues and identify the major components which are causing issues. The addition of mineral additives can be tested to analyse how slagging and fouling issues can be tackled for specific fuels. This will be of increasing importance as fuel blending and new complex fuels such as refuse derived fuels enter the market.

Thermodynamic Equilibrium Kinetics of Sewage Sludge Ash Pellets for the Removal of Methylene Blue (MB) from Aqueous Solutions

The utilization of Sewage Sludge Ash Pellets (SSAP) as an efficient sorbent material for dye removal is highlighted in this work. On MB removal, the effects of several factors such as contact time, agitation speed, solution pH, adsorbent dosage, and beginning concentration were investigated. When the MB concentration was 25 mg/L, the SSAP concentration was 30 g/L, and the speed was 250 rpm, the maximum removal efficiency was 98 %. The equilibrium time was found to be 60 minutes, and the maximum dye removal occurred at pH 10 for SSAP adsorbents. The Langmuir and Freundlich isotherm models were used to analyze the adsorption data. Adsorption isotherm studies revealed that the Langmuir model fits this case better. In most cases, the R2 correlation coefficient value exceeds 0.95. According to the findings of this study, SSAP can be used as an effective adsorbent for the removal of MB from aqueous solutions.

Control of Endogenous Phosphorus Release at the Sediment–Water Interface by Lanthanum-Modified Fly Ash

This study optimizes the modification and granulation of fly ash to make it more stable at the sediment–water interface. Through laboratory simulations, the modified fly ash pellets were optimally granulated to cover the sediment–water interface, and its control effect and mechanism were evaluated. The results showed that the phosphorus adsorption effect of lanthanum-modified fly ash was 34% and 40% higher compared with those of acid-modified and alkali-modified fly ash, respectively, with the phosphorus adsorption effect reaching 85%. The best dosing ratio was about 0.3 g/L. Adsorption was affected by pH and was more effective under weak alkalinity, close to the Langmuir adsorption model, which was consistent with the unimolecular layer adsorption characteristics and the presence of chemisorption and physical adsorption. The saturation adsorption amount of phosphate by lanthanum-modified fly ash was 8.89 mg/g. The optimized granulation conditions for lanthanum-modified fly ash pellets were a fly ash/montmorillonite ratio of 7:3, a roasting temperature of 900 °C, a roasting time of 4 h, and a particle size of 3 mm. After 20 days, the orthophosphate removal rate was more than 60% higher than that of the control group, with a total phosphorus removal rate of 43%. After covering for 60 days, active phosphorus in the surface layer of the sediment was gradually transformed into a stable phosphorus form, with calcium phosphorus accounting for 70% of the total inorganic phosphorus. The ability of the sediment to release phosphorus to the overlying water body was also significantly weakened. Meanwhile, the total phosphorus removal rate in the overlying water at the sediment–water interface reached more than 40%, and orthophosphate removal reached more than 60%, indicating an obvious phosphorus control effect. Transmission electron microscopy analysis showed that lanthanum was present at locations enriched with elemental phosphorus and was adsorbed onto the material surface. Therefore, lanthanum-modified fly ash pellets are a promising in situ phosphorus control agent with good endogenous phosphorus pollution control abilities in eutrophic water bodies.

Scale-up of immobilized amine sorbent pellets for landfill gas upgrading, using benchtop and pilot equipment

Upgrading CO2/CH4 enriched biogas effluents, especially from landfills, is a viable route towards simultaneously generating renewable methane for energy production and purified carbon dioxide for industries like oil and gas, whose main use is enhanced oil recovery. Pelletized basic immobilized amine sorbents (BIAS) previously utilized for post-combustion CO2 capture are prime candidates for CO2 removal from landfill gas (inherent CH4 enrichment) because of the pellets' high CO2 selectivity and tunability for optimized performance at different temperatures and gas compositions. This work examines the process parameters and material properties that are key in the production scale-up of our previously developed polychloroprene latex-polyethylenimine (PEI, MW = 25,000) binder/silica-fly ash pellet supports. Thicker pastes with aqueous binder solution/powder ratios between 2.9/1 and 3.24/1 exhibited average storage moduli of G' ≥ 9.5 × 106 ± 1.2 × 105 Pa and were easily prepared then transformed into separable cylindrical ropes via a lab-scale mixer-extruder machine. The dried supports displayed good crush strength and a > 98% efficient amine impregnation. Pellets containing 32 wt% PEI800/N-N-diglycidyl-4-glycidyloxyaniline crosslinker (1/0.13 wt. ratio) showed a high 1.95 mmol CO2/g capture from simulated landfill gas (60% CO2/39% CH4/1% O2) at 75 °C that dropped <30% after 24 h at 105 °C under the same gas environment. Scalability of the material was demonstrated by producing a 3.3 kg batch of pellet supports with pilot-scale mixer and extruder equipment. Similar strength and CO2 capture performance for the PEI-functionalized commercial pellets as those for the lab-scale pellets strongly indicate the viability of these materials for pilot-scale landfill gas CO2 capture/upgrading.

Impact resistance of concrete produced with plain and reinforced cold-bonded fly ash aggregates

In this paper, the impact resistance of concrete produced with cold-bonded fly ash aggregates (FAAs) in partial or full replacement, by volume, of crushed limestone coarse aggregates was investigated. Fly ash aggregates were produced as plain (PFAA), with 0.1% crumb rubber (CRRFAA) and with 0.1% polypropylene fibers (PPFRFAA), by weight, as reinforcement. Nine concretes are produced at w/c of 0.40 by replacing crushed stone coarse aggregate at 4–8 mm, 8–16 mm and 4–16 mm size fractions with fly ash aggregate together with the control concrete having a target compressive strength of 50 MPa. While use of different types of FAAs resulted in slight to substantial decrease of compressive and splitting tensile strengths and impact resistance of concretes, higher values are obtained in concretes with FAAs replacing 8–16 mm size group of crushed stone coarse aggregate. Polypropylene fiber and crumb rubber addition into the fly ash pellets increased the ability of the aggregates to absorb energy and thus the impact resistance of concrete. The polypropylene fibers protruding from the surface of FAAs might have caused better adherence of the FAAs to the cement paste to result in higher impact resistance.

An advanced ash fusion study on the melting behaviour of coal, oil shale and blends under gasification conditions using picture analysis and graphing method

• Ash fusion behaviour was investigated via an image-based characterisation method. • Oil shale ash is an effective refractory additive to delay ash fusion of coal. • Low melting aluminosilicates reduces sintering temperature of ash samples. • Sinter strength of ash pellet increases with dilatometric shrinkage. • Oil shale improves ash chemistry without adversely affecting reaction quality. This study investigates the potential of solid fuel blending as an effective approach to manipulate ash melting behaviour to alleviate ash-related problems during gasification, thus improving design, operability and safety. The ash fusion characteristics of Qinghai bituminous coal together with Fushun, Xinghua and Laoheishan oil shales (and their respective blends) were quantified using a novel picture analysis and graphing method, which incorporates conventional ash fusion study, dilatometry and sintering strength test, in a CO/CO 2 atmosphere. This image-based characterisation method was used to monitor and quantify the complete melting behaviour of ash samples from room temperature to 1520 °C. The impacts of blending on compositional changes during heating were determined experimentally via X-ray diffraction and validated computationally using FactSage. Results showed that the melting point of Qinghai coal ash to be the lowest at 1116 °C, but would increase up to 1208 °C, 1161 °C and 1160 °C with the addition of 30%–50% of Laoheishan, Fushun, and Xinghua oil shales, respectively. The formation of high-melting anorthite and mullite structures inhibits the formation of low-melting hercynite. However, the sintering point of Qinghai coal ash was seen to decrease from 1005 °C to 855 °C, 834 °C, and 819 °C in the same blends due to the formation of low-melting aluminosilicate. Results also showed that blending directly influences the sintering strength during the various stages of melting. The key finding from this study is that it is possible to mitigate against the severe ash slagging and fouling issue arising from high calcium and iron coals by co-gasification with a high silica-alumina oil shale. Moreover, blending coals with oil shales can also modify the ash melting behaviour of fuels to create the optimal ash chemistry that meets the design specification of the gasifier, without adversely affecting thermal performance.

Structural behavior of self-curing concrete with partial replacement of coarse aggregates with fly ash pellets

As we are in the world to conserve water for our daily needs, the present technologies have to be optimized in a feasible way, especially to one of the process curing in construction field. Thus, indeed there is an immediate need to do research on water used for curing process on concrete. Curing is one of the significant process for the concrete to have sufficient moisture content particularly at early stages of concreting in order to enhance the property of the concrete. It also plays a major role in concrete by developing pore structure and microstructure thus enhances its performance and durability. By considering these importance’s about curing and also to minimize the water for curing of concrete, a study has been conducted on concrete with the help of Polyethylene Glycol-400 (PEG-400) a water soluble self-curing agent to reduce the usage of water for curing. The present study also emphasis the use of fly ash pellets (FAP) prepared from the waste fly ash as coarse aggregate partially. The trail mix of concrete is proportioned replacing coarse aggregate by 10%, 15%, 20%, 25% and 30% with FAP and the compressive strength of the concrete were determined and found the optimum percentage replacement of coarse aggregate with FAP is at 25% resulting maximum compressive strength. The mechanical properties of concrete using water-soluble Polyethylene Glycol (PEG 400) have been found and also identified the optimum dosage to achieve maximum mechanical properties of the concrete. The increase in water retention capacity in the concrete and reducing the water evaporation in curing process can be done by using self-curing agent and it will absorb the water from the atmosphere thus saves water in the curing process compare to conventional concrete. The concrete mechanical properties containing self-curing agent are studied at various percentage such as 0.5, 0.7, 0.75, 0.8 and 1.0 added by weight of cement and compared with those of conventionally cured concrete. From the investigation it has been concluded that optimum dosage of PEG-400 for maximum mechanical property of M25 grade of concrete containing 25% of fly ash pellets as coarse aggregate is at the percentage of 0.75 by weight of cement.

INFLUENCE OF PRESATURATED SUGARCANE BAGASSE ASH PELLETS IN CONCRETE

This paper summarizes the experimental investigation on mechanical behavior of concrete in which Sugarcane bagasse ash (SCBA) pellets is used as a partial replacement of fine aggregate. As river sand is a scanty material now a day, there is an urgent need to look into alternate material. Now a day’s artificial aggregate are popular as a substitution of fine aggregate to make better concrete. Sugarcane bagasse ash (SCBA) aggregate pellets derived from waste sugarcane bagasse which is available plentifully. The concrete made by partially replacing M-sand with presaturated SCBA aggregate for self curing purpose is investigated. At that, maximum of 20% (by volume) was replaced. Workability and mechanical properties are analyzed. Test results indicate the concrete mix with 15% replacement by volume of SCBA aggregate exhibited better results in case of self curing condition, when compared to other mixes.

Artificial Neural Network to Predict the Compressive Strength of Semilightweight Concrete Containing Ultrafine GGBS

Abstract Design strength is usually determined after a 28-day curing period as per codal provisions. The prediction of compressive strength before curing reduces waiting time and expedites regular construction activity. The aim of this study is to develop a neural network model to predict the 28-day compressive strength of semilightweight concrete (sLWC) containing ultrafine ground granulated blast-furnace slag (UFGGBS). In this investigation, a novel lightweight coarse aggregate that is made up of wood ash was used to prepare sLWC. Six input parameters, such as cement, UFGGBS as cement replacement, lightweight wood ash pellets as coarse aggregate, fine aggregate, water content, and superplasticizer, were used to train the model. The 28-day compressive strength was taken as an output parameter. A total of 384 data was collected from 24 sLWC mixes, each containing 16 specimens, and trained in an artificial neural network (ANN) using a feedforward-backpropagation model. Trained data were validated with a set of tested data. The correlation coefficient R2 values for trained and tested data were 0.932 and 0.917, respectively, with least errors. The study concluded that ANN was a reliable and fast tool for predicting the compressive strength of sLWC. It also efficiently reduced cost and time.

Utilization of coal fly and bottom ash pellet for phosphorus adsorption: Sustainable management and evaluation

Recycling of coal combustion solids can have several environmental benefits. The objective of this study was to evaluate a sustainable approach to recycle coal fly ash and bottom ash as pelletized-adsorbents for dissolved phosphorus (P). Sodium Dodecyl Sulfate (SDS), a foaming agent, was added to enhance the phosphorus adsorption capacity of fly ash pellets (FAP) and bottom ash pellets (BAP) during the pellet fabrication. Ten types of fly ash pellets and bottom ash pellets with varying Sodium Dodecyl Sulfate proportions (FAP-0/BAP-0: 0% SDS; FAP-1/BAP-1: 2% SDS; FAP-2/BAP-2: 4% SDS; FAP-3/BAP-3: 6% SDS; FAP-4/BAP-4: 8% SDS by weight) were manufactured with a high temperature (700℃) modification process. The results indicated that the bottom ash pellet was more suitable adsorbent than fly ash pellet due to the better phosphorus adsorption capacity and lower heavy metal leaching. After the addition of Sodium Dodecyl Sulfate, the volumetric porosity of fly ash pellets and bottom ash pellets increased by 45.5%–163.6%, 52.9%–76.5%, respectively. However, higher Sodium Dodecyl Sulfate fraction did not result in better pellet phosphorus removal, since FAP-2 and BAP-3 resulted in the highest phosphorus removal among the pellets tested in this study. The results from X-ray diffraction demonstrated that Calcium and Silica were the major phases in the pellets. This study provides a feasible approach to reuse fly ash and bottom ash as effective pelletized-adsorbents for water quality improvement. These pellets can be applied in edge-of-field and in-stream treatment to control P loss from the agricultural area.

Physicochemical Analysis of Two Aged Diesel Particulate Filters Placed at Close Coupled and Under Floor Positions of the Vehicles

This work investigated the aged diesel particulate filter substrate analysis procedure and ash physicochemical analysis method with various instruments such as CT, XPS, SEM and XRD. The procedure for analyzing two DPFs aged with the same lubricant oil but located in different locations was followed to determine the ash formation mechanism. We analyzed DPFs in their non-destructive state with X-ray computed tomography to determine the form how the ash was deposited, and after decanning the DPF, we verified ash formation with micro X-CT. A scanning electron microscope was used to determine the morphology of the ash and DPF substrates, and the distributions of the components were analyzed using energy dispersive spectroscopy. The ash pellets were used for X-ray photoelectron spectroscopy analysis to determine the percentages of different components, and the crystal structure of the ash powder was determined using a X-ray diffractometer. The result of this study is that the deposition patterns and composition of the ash components differ depending on where the DPF is mounted due to differences in temperature and pressure experienced during aging. Calcium is accounted for the largest percentage of the materials that formed the ash.

Elemental, morphological and thermal analysis of mixed microalgae species from drain water

Abstract In this study, Stigonematales sp. microalgae were collected from drain water and characterized for its' morphological edifice, elemental composition, thermal condition and energy generation capacity by using scanning electron microscopy, energy dispersive X-ray, thermogravimetric analyzer and bomb calorimeter, respectively. Scanning electron micrographs revealed the top view of microalgae and ash pellet with carbon coated specimens at low voltage (5.0 kV) through the secondary electron image detector. Elemental analysis revealed all the major and minor constituents of this microalgae species and its' ash in terms of dry weight (%) and atomic weight (%). Thermogravimetric analysis was conducted at heating rate, 10 °C/min and this experimental results determined moisture content, volatile matter, ash content and fixed carbon of the sample with 4.5%, 35%, 39.5% and 21%, respectively. Microalgae powder blended with bituminous coal by 75%, 50% and 25% measured calorific value 14.07 MJ/kg, 19.88 MJ/kg and 26.42 MJ/kg, respectively. Microalgae (75%) -coal (25%) blend showed excellent amount of energy content, 24.59 MJ/kg. Microalgae blended with coal unveiled an outstanding outcome with elevation of the volatile matter and drop of the ash content. Optimization of microalgae-coal blend in large-scale application can initiate bright future in renewable energy exploration.

Role of fixed carbon and metal oxides in char during the catalytic conversion of tar from RDF gasification

The catalytic activity of char (fixed carbon + metal oxides) recovered from a commercial waste gasification plant and char-derived ash (metal oxides only) from the oxidation of the char (i.e. the controlled oxidation of the amorphous carbon in the char) was investigated for the cracking and steam reforming of tar. The latter was obtained following the soxhet extraction of sludge collected during a cleaning process (water scrubbing) on primary syngas. The tar was evaporated along with water in an evaporator maintained at 650 °C and entrained by a nitrogen flow. Tar in the gas phase was sent to a reformer where cracking + reforming tests were carried-out at 900 °C and 1 bar using char and char-derived ash pellets as catalysts. These catalysts were characterized using TGA, AE, XRD, SEM, EDX, XRF, ICP-MS, BET and Matersizer. Char-derived ash and char both hold similar metals and mineral structures. Following a 2 h conditioning at 900 °C, the fixed carbon in the char exhibited a larger surface area and pore volume while the char-derived ash revealed larger particle from the merging of vicinal minerals. No metal evaporation was observed after 24 h at 900 °C. During cracking and reforming, the initial 2–6 rings tar mixture extracted from the gasification residues sludge, loaded in the stream of nitrogen + steam at 65 g/Nm3, was reduced to 173.3 and 90.2 mg/Nm3, when using char-derived ash and char respectively. Pure syngas (CO + H2) was produced as the only permanent gases while carbon deposition was noticed in the solid beds. Even though the extent and type of tar were essentially similar when char and char-derived ash were used, the kinetics to reach steady state were slower for the char-derived ash. Steam content did not seem to impact on the tar conversion. However WG and WGS reactions most probably occurred, which might contribute to modulate the H2/CO molar ratio in the produced gas according to its targeted downstream utilization.

Preparation and characterization compatible pellets for immobilization of colloidal sulphur nanoparticles

Mercury pollution in atmosphere is dominated by mercury vapour release from coal burning and gold-amalgam separation in gold mining. The initial steps in formulating a compatible mercury absorbent for mercury stabilization was fabrication of pellet supported colloidal sulphur. Sulphur is used to stabilize mercury vapour by formation of metacinnabar that has much lower toxicity. The sulphur reactivity toward mercury vapour can be enhanced by using colloidal sulphur nanoparticles immobilized on compatible pellets. Clay pellets would have heat resistance but in fact, they were less stable in aqueous solution although their stability increased with inclusion of rice husk ash and sawdust or pineapple leaf fibre in the composite. Pellets made of rice husk ash and polyvinyl acetate were stable in water at least for 24 hours. Sulphur from thiosulfate precursor that immobilized onto surface of pellet using chitosan as the stabilizer and the binding agent gave lower sulphur content compared to sulphur from other precursors (sulphur powder and sulphur-CS2). Sulphur from thiosulfate precursor was in form of colloid, has nanosize, and disperse particles on the surface of rice husk ash pellets. Sulphur immobilization methods affect on sulphur particles exposure on the pellet surface.

Combined disc pelletisation and thermal treatment of MSWI fly ash

An environmentally friendly and cost efficient way for the management of municipal solid waste incineration (MSWI) fly ash represents its thermal co-treatment together with combustible waste. However, the safe introduction and storage of MSWI fly ash in the waste bunker is challenging and associated with severe problems (e.g. dust emissions, generation of undefined lumps and heat in case of moistened MSWI fly ash). Therefore, the aim of this study is to investigate the suitability of pelletisation as a pretreatment of MSWI fly ash. In particular, MSWI fly ash was characterised after sampling, pelletisation and thermal treatment and the transfer of constituents to secondary fly ash and flue gas was investigated. For this purpose, MSWI fly ash pellets with a water content of about 0.15 kg/kg and a diameter of about 8 mm have been produced by disc pelletiser and treated in an electrically heated pilot-scale rotary kiln at different temperatures, ranging from 450 °C to 1050 °C. The total contents of selected elements in the MSWI fly ash before and after thermal treatment and in the generated secondary fly ash have been analysed in order to understand the fate of each element. Furthermore, leachable contents of selected elements and total content of persistent organic pollutants of the thermally treated MSWI fly ash were determined. Due to the low total content of Hg (0.7 mg/kg) and the low leachate content of Pb (<0.36 mg/kg), even at the lowest treatment temperature of 450 °C, thermally treated MSWI fly ash pellets can be classified as non-hazardous waste. However, temperatures of at least 650 °C are necessary to decrease the toxic equivalency of PCDD/F and DL-PCB. The removal of toxic heavy metals like Cd and Pb is significantly improved at temperatures of 850 °C, 950 °C or even 1050 °C. The observed metal removal led to relatively high contents of e.g. Cu (up to 11,000 mg/kg), Pb (up to 91,000 mg/kg) and Zn (up to 21,000 mg/kg) in the secondary fly ash. This metal enriched secondary fly ash might represent a potential raw material for metal recovery (e.g. via acidic leaching). Due to the high content of total dissolved solids observed in the leachate of thermally treated MSWI fly ash pellets, a wet extraction procedure is suggested to enable its safe disposal at non-hazardous waste landfills.

Evaluation of fly ash pellets for phosphorus removal in a laboratory scale denitrifying bioreactor

Nitrate and orthophosphate from agricultural activities contribute significantly to nutrient loading in surface water bodies around the world. This study evaluated the efficacy of woodchips and fly ash pellets in tandem to remove nitrate and orthophosphate from simulated agricultural runoff in flow-through tests. The fly ash pellets had previously been developed specifically for orthophosphate removal for this type of application, and the sorption bench testing showed a good promise for flow-through testing. The lab-scale horizontal-flow bioreactor used in this study consisted of an upstream column filled with woodchips followed by a downstream column filled with fly ash pellets (3 and 1 m lengths, respectively; both 0.15 m diameter). Using influent concentrations of 12 mg/L nitrate and 5 mg/L orthophosphate, the woodchip bioreactor section was able to remove 49–85% of the nitrate concentration at three hydraulic retention times ranging from 0.67 to 4.0 h. The nitrate removal rate for woodchips ranged from 40 to 49 g N/m3/d. Higher hydraulic retention times (i.e., smaller flow rates) corresponded with greater nitrate load reduction. The fly ash pellets showed relatively stable removal efficiency of 68–75% across all retention times. Total orthophosphate adsorption by the pellets was 0.059–0.114 mg P/g which was far less than the saturated capacity (1.69 mg/g; based on previous work). The fly ash pellets also removed some nitrate and the woodchips also removed some orthophosphate, but these reductions were not significant. Overall, woodchip denitrification followed by fly ash pellet P-sorption can be an effective treatment technology for nitrate and phosphate removal in subsurface drainage.