Fly Ash Pretreatment Research Articles

Accelerated carbonation pretreatment of municipal solid waste incineration fly ash and its conversion to geopolymer with coal fly ash

Recycling municipal solid waste incineration fly ash (FA) to prepared geopolymer has received wide attentions due to its excellent physical–chemical properties. However, the rich chloride salts and heavy metals in FA limit its FA additive amount during geopolymerization. To address large-scale FA conversion to geopolymer, this work conducted the carbonation pretreatment of FA with H2CO3, (NH4)2CO3 and Na2CO3 (made as H-FA, N-FA and Na-FA, respectively) and further converted it into geopolymers with coal fly ash (CFA). The effect of carbonated FA (50–70 wt.%) on the compressive strength characteristics, efflorescence properties and leaching properties of geopolymer was investigated. The results showed that three types of carbonate solutions changed the mineral phases of FA and consequently affected the properties of geopolymers. The main mineral phases of H-FA and Na-FA were calcite, while calcite and vaterite were the coexisting main mineral phases of N-FA. The prepared geopolymers with Na-FA exhibited the best performance (denser microstructure, better compressive strength, etc.), owing to the formation of more C-S-H and calcite. In particular, the compressive strength of geopolymer with 60 wt.% Na-FA reached the maximum value of 149.89 MPa at curing time for 28 d. Furthermore, the highest leaching concentration of Na in the geopolymers was only 4.52 mg/L, which was at a low level. The leaching concentrations of Pb, Cd, Cr, Cu, Ni and Zn in the geopolymers were far lower than the thresholds of GB 18598–2019. The results confirmed that carbonation pretreatment was a promising approach to improve the recycling of hazardous FA, and converting it to geopolymers with CFA, and FA-based geopolymers had the potential to be applied as building materials.

Study on the reduction of chlorine and heavy metals in municipal solid waste incineration fly ash by organic acid and microwave treatment and the variation of environmental risk of heavy metals

Municipal solid waste incineration (MSWI) fly ash usually needs to undergo dechlorination or heavy metal stabilization pretreatment for further treatment, recycling or disposal. In this paper, the removal effect of chlorine in fly ash by water washing, lactic acid, citric acid and microwave treatment was studied, and XANES was used to analyze chlorine chemical form in fly ash. In addition, the heavy metals in fly ash were also checked. The results indicated that double washing and triple washing could remove 88.0 % and 95.5 % of chlorine from fly ash respectively. The “double water washing + microwave/organic acid” could remove about 96.6 % of chlorine, and 42.9 % and 47.2 % of insoluble chloride respectively. The microwave treatment could maximize the stabilization of heavy metals with a BI value of 39.1 %, 0.11 %, 1.65 %, 15.4 % and 3.98 % for Cd, Cr, Cu, Pb and Zn. The elution of heavy metals by citric acid was obvious. “Double water washing + citric acid” removed 87.0 % of Cd, 17.2 % of Cr, 11.9 % of Cu, 39.6 % of Pb and 43.6 % of Zn, but the environmental risk of Cu and Cr increased about 2–3 % after the treatment. The results of this study provide guidance for the pretreatment of fly ash before resource utilization.

Studies on the modification of fly ash structure with alkaline pre-treatment as a green composite flame retardant filler

A green composite made up of renewable and recyclable materials has become one of the advanced material’s attractive topics. The smooth fly ash surface used in the green composite for flame retardancy enhancement are hard to bind with hydrophobic polymer. Thus, the surface modification of this filler is needed to increase its surface roughness and pore size to be more compatible with its polymer matrix. In this research study, the alkaline pre-treatment of fly ash has been performed by using sodium hydroxide solution (NaOH) with various concentrations (5 w/w%, 10 w/w%, 15 w/w%, 20 w/w%). For pore size and morphological of the filler’s evaluation, few analyses such as Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Barret-Joyner-Halenda (BJH) and Brunauer-Emmett-Teller (BET) pore size and volume analysis were conducted. Treated fly ash with 20 w/w% sodium hydroxide concentration gives the better morphological structure in terms of pore diameter, volume, area and high composition of aluminium, silicon with lower calcium and sulphur contents compared to others. Hence, the potential of the physiochemical properties of the green composite produced by using this modified filler will be improved as the adhesiveness of the filler with its matrix increased.

Environmental impact assessment of alkali-activated mortar with waste precursors and activators

Synthetic activators used in alkali-activated binder are the primary contributors to its adverse environmental effects. Therefore, this study aims to perform a life cycle assessment of alkali-activated mortar (AAM) prepared from industrial waste as precursors and activators. The impact analysis is performed through ReCiPe methodology for six different AAM mixes. Environmental impacts of replacing conventional precursors (fly ash and slag) with waste ceramic powder (WCP) and red mud (RM) and conventional activators (sodium silicate (SS) and sodium hydroxide (SH)) with RM, desulfurization dust, and silica fume are assessed. The efficiency of ReCiPe is compared with recommendations from the International Reference Life Cycle Data System. Sensitivity analysis for SH produced using three different techniques and simplified cost analysis for the mortar mixes is conducted. SS is observed to contribute 50–59% of climate change for mixes with conventional activator combination. WCP as a precursor warrants higher dosage of SS and SH, thereby increasing the environmental impact. Replacing SS with silica fume has the least negative effects on ecosystem quality and human health. AAM prepared with conventional activators shows lower resource depletion due to a lower dosage of activators and the absence of pretreatment of fly ash. ReCiPe can be used to evaluate all the impact categories except freshwater ecotoxicity and human toxicity, for which USEtox is suggested. Sensitivity analysis shows that the membrane cell process of SH production is eco-efficient. Savings of up to 14% are observed by replacing both precursors and activators with industrial residues.

Mechanical Transformation of Fly Ash toward Its Utilization in Cemented Paste Backfill

Fly ash (FA) showed low reactivity when being used to prepare the binder for cemented paste backfill (CPB). In the present work, wet‐grinding treatment was used to increase the pozzolanic reactivity of FA and promote its sustainable utilization. The results showed that wet‐grinding could be a suitable and efficient technology for FA pretreatment. Wet‐grinding strongly modified the structure of FA by decreasing the crystalline phase content and the binding energy of Si 2p and Al 2p, contributing to the increase in pozzolanic reactivity of FA. The performance of CPB samples prepared by wet‐ground FA was then optimized. This was reflected by the acceleration in the sample setting and increase in the strength development. The compressive strength of the CPB samples prepared by wet‐ground FA for 120 min was increased by around 40% after curing for 28 d compared with the control samples.

Low-Temperature Pretreatment of Organic Feedstocks with Selected Mineral Wastes Sustains Anaerobic Digestion Stability through Trace Metal Release.

A low-cost approach for enhancing mesophilic (37 °C) anaerobic digestion (AD) of organic waste using a low-temperature (37 °C) pretreatment with different mineral wastes (MW) was investigated. A higher and stable methane production rate, in comparison to MW-free controls, was achieved for 80 days at organic loading rates of 1-2 g VS/L·d, using a feed substrate pretreated with incinerator bottom ash (IBA). The boiler ash and cement-based waste pretreatments also produced high methane production rates but with some process instability. In contrast, an incinerator fly ash pretreatment showed a progressive decrease in methane production rates and poor process stability, leading to reactor failure after 40 days. To avoid process instability and/or reactor failure, two metrics had to be met: (a) a methanogenesis to fermentation ratio higher than 0.6 and (b) a cell-specific methanogenic activity to cell-specific fermentation activity ratio of >1000. The prevalence of Methanofastidiosum together with a mixed community of acetoclastic (Methanosaeta) and hydrogenotrophic (Methanobacterium) methanogens in the stable IBA treatment indicated the importance of Methanofastidiosum as a potential indicator of a healthy and stable reactor.

Isolation of lignocelluloses from the spent liquor of thermomechanical pulping process with fly ash and cationic polymer

In this work, fly ash (FA) and polydiallyldimethylammonium chloride (PDADMAC) were utilized to treat the spent liquor (SL) of thermomechanical pulping (TMP) process in an effort to remove its lignocelluloses. The incorporation of PDADMAC into the system reduced the dosage of FA required for achieving acceptable lignocellulose removals. The maximum lignocellulose removals of 81%, 78%, 56%, 53% and 97% were achieved for lignin, hemicellulose, COD, BOD, and turbidity via treating SL with 100 g/L of FA at 25 °C for 60 min and subsequently treating with 100 mg/L of PDADMAC at 25 °C for 30 min, respectively. Comparing the two-step processes, FA pretreatment with PDADMAC post treatment was more effective than the two step process of PDADMAC pretreatment and FA post treatment. In this case, the FA pretreatment generated metal-organic complexes, and the addition of PDADMAC facilitated the formation of large flocs that could be separated from the system readily. A one stage process of combined PDADMAC and FA was less effective than the two-stage process of FA and PDADMAC treatments in removing lignocelluloses from SL.

Impact of fly ash pretreatment on aerobic treatment of thermomechanical pulping spent liquor.

This study investigated the impact of biomass-based fly ash (FA) pretreatment on the biodegradability of a thermomechanical pulping spent liquor (TMPL) in an aerobic system. In this study, FA was mixed with TMPL under the conditions of 6 wt.% based on TMPL, 25°C and 10 h, which removed a part of recalcitrant organic materials and resulted in 68.0, 40.0, 60.1, 81.2 and 48.3% reductions in chemical oxygen demand (COD), biochemical oxygen demand (BOD), total organic carbon (TOC), lignin and sugar, respectively. FA-pretreated TMPL pressate (FA-TMPL) was biologically treated in an aerobic system of sequencing batch reactor (SBR). The performance of the biological treatment with and without FA pretreatment was studied in two parallel SBRs over three months. The combination of FA and biological treatments removed 97.3% of COD, 98.3% of BOD, 96.3% of lignin, 99.5% of sugar, and 98.1% of TOC. Without FA pretreatment, the biological system removed 87.3% of COD, 89% of BOD, 81.6% of lignin, 98.6% of sugars, and 90.5% of TOC. The results also confirmed that the settling ability of sludge, which was indicated as a sludge volume index, was reduced from 109.3 mL/g to 53.5 mL/g. In addition, the advantages of using FA pretreatment in aerobic systems were discussed in detail. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:370-378, 2018.

Preparation of an Aluminum and Iron‐Based Coagulant From Fly Ash for Industrial Wastewater Treatment

Fly ash was investigated to produce a composite coagulant containing aluminum (Al) and iron (Fe) salts through the calcination and leaching processes. The extraction of Al and Fe oxides from fly ash demonstrated similar results for HCl and H2SO4 leaching. Besides, the calcination pretreatment of fly ash (without any additive) was found to be less effective in extraction. However, the conversion efficiencies of Al and Fe were affected greatly by calcination pretreatment with addition of Na2CO3, and leaching conditions of ratio of solution to fly ash (L/S) and H+ concentration. The maximum concentrations of Al and Fe solubilized from fly ash were 0.21 and 0.04 mol/L, respectively, which were attained by calcination pretreatment using an optimal mass ratio (ca. 1:16.7) of Na2CO3 to fly ash at 805°C. These concentrations correspond to conversion efficiencies of 31.2% for Fe and 18.3% for Al in the fly ash. The slurry was filtrated to obtain a solution containing Al‐ and Fe‐sulfates and silicates. The Al/Fe/Si mole ratio indicated the feasibility of further production of inorganic polymer coagulant. The produced coagulant was determined to be effective for treating soybean wastewater and dairy wastewater in terms of COD and SS removal.

Effects of Modified Excess Sludge on the Growth of Artemisia ordosica and Transformation of Heavy Metals

A greenhouse experiment was accomplished to investigate the feasibility of excess sludge modified by coal fly ash pretreatment and γ-ray irradiation in soil application for cultivation of Artemisia ordosica. The results showed that modified excess sludge provided a positive effect on the growth of Artemisia ordosica. The modified excess sludge and aeolian sandy soil at the volume ratio of 1:2 was optimal, and nutrient concentrations of Artemisia ordosica reached the highest. In the aeolian sandy soil, the bio-concentration factor values of most heavy metals were less than 1.0 except for Cu, Zn, and Ni. The average bio-concentration factor values of heavy metals in Artemisia ordosica increased in a sequence of Mo < Cd < Fe < V < Cr < Co < Mn < Pb < Cu < Zn < Ni for all samples. Artemisia ordosica could be used to decrease the bioavailability and eco-toxicity of Ni, V, and Mo in all cultivation experiments of artificial soil, and Artemisia ordosica could also reduce the bioavailability and eco-toxicity of Cu, Cd, Cr, and Mn in the artificial soil of modified excess sludge and aeolian sandy soil at the volume ratio of 1:2.

Disintegration of excess sludge enhanced by a combined treatment of gamma irradiation and modified coal fly ash

Abstract In order to improve the disintegration performance and accelerate the disintegration rate of excess sludge, the individual and combined influences of γ-ray irradiation and modified coal fly ash treatment on the disintegration of excess sludge were investigated based on physicochemical properties of excess sludge. The changes in constituents of excess sludge were examined by means of UV/vis spectra and SEM images. The results showed that the disintegration performance of excess sludge was effectively improved by gamma ray irradiation in the presence of modified coal fly ash. A new band from 250 nm to 290 nm appeared on all irradiated sludge samples. The SEM images illustrated the cells surfaces of the sludge by the combined treatment were disfigured. The SCOD, soluble carbohydrate and protein from sludge supernatant increased obviously with increasing modified CFA dosage from 0 to 0.2 g ml −1 and dose from 0 to 10 kGy. The sludge SRF and filter cake moisture declined significantly, and the filtration speed was faster. In conclusion, γ-ray irradiation-modified coal fly ash pretreatment is an effective method to disintegrate excess sludge.

The Heterogeneous Reverse Osmosis Membranes Based Separation of Fluorides with Fly Ash Pretreatment

The Heterogeneous Reverse Osmosis Membranes Based Separation of Fluorides with Fly Ash Pretreatment

Removal of Fluoride from Drinking Water Using Fly Ash after Pre Treatment

The adsorption capacity of fly ash is much higher than the other adsorbents. The Fly ash was an effective adsorbent especially at high concentration of fluoride. This may be because of the presence of unburnt carbon particles in the fly ash which are known to be very efficient adsorbing materials. The main components of fly ash are silica, alumina, iron oxides, calcium oxide and residual carbon. The presence of unburnt carbon and surface area of ash make it a good candidate for utilization as an inexpensive adsorbent. In this method we use fly ash, generate from Chula. The 100 gm ash is mixed with 1 liter fluoridated water and stirs 45 to 60 minutes then leave it for settle down. After 2 hour this solution filters with G-3 crucible in a filtration unit. The fluoride was analyzed by using ions selective electrode method. This method removes fluoride satisfactory from drinking water but also increases some other parameters of water like alkalinity, chloride, TDS, nitrates etc.so after the view of side effects pre treatment of fly ash have been done with distilled water. The results were found very much satisfactory.

Interparticle interactions and lacunarity of mechano-chemically activated fly ash

A class F fly ash was subjected to high-energy ball milling-induced mechano-chemical activation aided by a surfactant. The resultant nanostructured fly ash was characterized by various techniques. X-ray fluorescence results showed that the amount of iron oxide was reduced from 4.39% to 2.75% after pre-treatment of fly ash by magnetic separation. Ethyl acetate as the milling medium, a ball to powder ratio of 12:1 and 2wt% of surfactant reduced the average particle size of fly ash to 329nm and led to a specific surface area of 8.73m2/g. The decrease in crystallite size of mechano-chemically activated fly ash was confirmed from a reduction in peak intensity with a broadened amorphous phase by X-ray diffraction studies. X-ray photoelectron spectroscopic characterization illustrated that peak area of major elements (O, Si and Al) increased after milling. Morphological and FTIR studies revealed that the smooth and inert surface of the fly ash was converted to a rough and more reactive one after mechano-chemical activation. The surface modification of fly ash with the surfactant was determined from FTIR spectroscopy. Also, a fractal approach was used to characterize the lacunarity of the agglomerates in the nanostructured fly ash.

Effect of water washing pre-treatment on the properties of glass-ceramics from incinerator fly ash using electronic arc furnace

Production of glass-ceramics by sintering the molten slag obtained from electric arc furnace treatment of fly ash was investigated. The effect of washing pretreatment prior to melting the fly ash on the microstructure and properties of the glass-ceramics was examined. The results show that washing pretreatment of fly ash can decrease alkali metal chloride and increase network former in fly ash, which results in the increase of peak crystallization temperature of parent glass and strengthening of properties of bending strength and chemical stability of the glass-ceramics. The optimal heat treatment temperature for parent glass of washed fly ash is 1 173 K, at which the crystalline phase of glass-ceramics is composed of gelignite (Ca2Al2SiO7) and akermanite (Ca2MgSi2O7). Glass-ceramics produced at optimal heat treatment temperature are excellent in term of the physical and chemical properties and leaching characteristics, indicating attractive potential as substitute of nature materials.

Effects of water-washing pretreatment on bioleaching of heavy metals from municipal solid waste incinerator fly ash

Previous studies demonstrated that the bioleaching of municipal solid waste incinerator fly ash by Aspergillus niger was an efficient “green technology” for heavy metals removal, however, it demanded a long operational period. In this study, water-washing was used as a fly ash pretreatment before the bioleaching process (one-step and two-step). This pretreatment extracted 50.6% of K, 41.1% of Na, 5.2% of Ca and 1% of Cr from the fly ash. Due to the dissolution of alkali chlorides which hold particles together, fly ash particles were smashed into smaller granules by the hydraulic flushing action caused by vibration. After the pretreatment, the lag phase and bioleaching period were reduced by 45 and 30%, respectively, in one-step bioleaching of 1% (w/v) fly ash. Meanwhile, the metals extraction yield both in one-step and two-step bioleaching was increased markedly, e.g. in two-step bioleaching, 96% Cd, 91% Mn, 73% Pb, 68% Zn, 35% Cr and 30% Fe was extracted from 1% water-washed fly ash, respectively. The reduction of the bioleaching period and improvement of metals extraction yield will likely allow the practical application of the bioleaching technology for heavy metals removal from fly ash.

Water, Acid, and Calcium Carbonate Pretreatment of Fly Ash: The Effect on Setting of Cement−Fly Ash Mixtures

The treatment of class C, I, and F fly ash (FA) with water, HNO3, and aqueous CaCO3 has been investigated to develop a simple chemical route to change the morphology and surface chemistry of fly ash particles to enhance the setting properties of a cement/fly ash (C/FA) composite. The treatment of C-FA with an aqueous CaCO3 solution results in a dramatic improvement in the setting time and the setting profile on C-class FA; in contrast, the treatment has no effect on the set time for F-FA and reduces the set time and appears to result in an even more nonideal induction setting curve as compared to the untreated C/I-FA. The enhancement observed for the treatment of C-FA with aqueous CaCO3 solution is not a consequence of the water solution since simply washing with water (i.e., C-FAH2O) results in the extraction of Na and Ca with a concomitant increase in surface area and a performance similar to those observed for untreated I-FA and F-FA despite a much higher surface area. The acid (HNO3) treatment of I-FA and F-FA results in the formation of an inert filler-like material, while acid treatment of C-FA results in a material with completely undesirable setting properties. Clearly, the enhancements observed for the aqueous CaCO3 treatment are not as a result of simply either the aqueous or acidic nature of the HCO3 containing CaCO3 solution. Based upon the forgoing, we propose that the efficacy of the aqueous CaCO3 treatment on C-FA is associated with the availability of “reactive calcium”. Exposure of C-FA to dry CO2 does not affect the set time or set profile for C/C-FA mixture, but the retarding effect of the aqueous CaCO3 treatment on C-FA can be replicated by the exposure of the C-FA to a stepwise reaction with water and CO2. Exposure of C-FA to wet CO2 results in the improvement of the setting induction profile without significantly affecting the set time. We propose that this process should allow for the addition of fly ash to cement samples while the induction profile remains flat, providing predictability in pumping for down-hole applications.

Synthesis of Faujasite from Fly Ash and its Applications for Hydrocracking of Petroleum Distillates

The synthesis of faujasite from fly ash and its application for hydrocracking catalyst of heavy petroleum distillates have been performed. Faujasite was synthesized from fly ash by hydrothermal reaction in alkaline solution via combination of reflux pretreatment of fly ash with HCl and fusion with NaOH. The preparation of nickel containing catalysts by ion exchange method under similar initial concentration of nickel resulted higher amount of nickel loaded on faujasite than those on zeolite Y, however, the structural damage of faujasite was higher than those of zeolite Y. In the hydrocracking of heavy petroleum distillates over Ni-faujasite and Ni-zeolite Y catalysts, the conversion of heavy gas oil fraction was the most pronounced. The selectivity toward hydrocarbons in the range of gasoline and kerosene obtained over Ni-faujasite catalyst was lower compared to those of Ni-zeolite Y reference catalyst. © 2007 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Cytotoxicity and Mutagenicity Study of Waste and Purified Water Samples from Electroplating Industries Prepared by Use of Ferrous Sulfate and Wood Fly Ash

Toxicological safety of the new purification method for electroplating wastewaters (EWW) has been assessed. Method utilizes waste by–product ferrous sulfate and wood fly ash to scavenge heavy metals from EWW. Energy dispersive X–ray fluorescence (EDXRF) analysis of all samples met the law requirements for safe depositing of waste into the environment. The toxicity study consisted of determination of frequency of bacterial and human cell lines survival and the Ames assay (plate incorporation assay and the preincubation assay). Unexpectedly, data obtained indicate cytotoxicity and slight mutagenic potential of purified water. Ames assay showed that combination of alkalis and heavy metals present in the water purified with original fly ash and eluates of fly and waste ash were metabolically activated and conjugated with glutathione, resulting in new metabolites active and toxic for the cell. In order to reduce this effect pretreatment of fly ash (partial removal of highly soluble compounds) are necessary prior to its usage for neutralization /coagulation/flocculation processes.

Disposal of MSWI fly ash through a combined washing-immobilisation process

The objective of this work was to investigate the feasibility of a combined washing-immobilisation process as a means of optimising the disposal of fly ash resulting from municipal solid waste incineration (MSWI) in cementitious matrices. Two different types of Italian MSWI fly ash and an ordinary Portland cement (ASTM Type I) were used. Washing pre-treatment of fly ash with water always produces a wastewater that can be successfully treated by reducing the pH to values of 6.5–7.5. This treatment is capable of removing the detected contaminants (Al, Cd, Pb, Zn) through two different mechanisms: precipitation of aluminium hydroxide and adsorption of cadmium, lead and zinc ions onto floc particles of Al(OH) 3. Setting and leaching tests on cementitious mixes prove that the hazardous sludge produced from wastewater treatment can be completely mixed with washed fly ash and this mixture can be incorporated into cementitious matrices to a great extent (75 wt.% of total solid) without the risks of an unacceptable delay of cement setting and an excessive heavy metals leachability from solidified products. The better performance of the combined washing-immobilisation process as compared to the immobilisation process of unwashed fly ash may be ascribed primarily to the ability of the washing step in promoting the formation of hydrate phases that incorporate and/or convert heavy metal compounds into less reactive forms and, secondarily, to its ability of removing significant amounts of alkali chlorides and sulphates from fly ash. As a result, MSWI fly ash is transformed into a material that adversely affects cement hydration to a much lower extent than unwashed fly ash.