| 1. |
- Camerani, Maria Caterina, et al.
(författare)
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Determination of the cd-bearing phases in municipal solid waste and Biomass single fly ash particles using SR-mu XRF Spectroscopy
- 2007
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 79:17, s. 6496-6506
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Tidskriftsartikel (refereegranskat)abstract
- By using an excitation energy of 27.0 keV, synchrotron radiation-induced micro-X-ray fluorescence (SR-mu XRF) is employed to extract information regarding the composition and distribution of Cd-bearing phases in municipal solid waste (MSW) and biomass fly ashes. Significance of observation is based on statistics of totally more than 100 individual MSW and biomass fly ash particles from a fluidized bed combustion (FBC) plant. Cd concentrations in the parts-per-million range are determined. In general, although previous leaching studies have indicated Cd to be predominant in the smaller-size ash particles, in the present study Cd is more evenly distributed throughout all the particle sizes. For MSW fly ashes, results indicate the presence of Cd mainly as CdBr2 hot-spots, whereas for biomass fly ashes, which exhibit lower CdX2 concentration, a thin Cd layer on/in the particles is reported. For both ashes, Ca-containing matrixes are found to be the main Cd-bearing phases. Support for this observation is found from independent first-principles periodic density functional theory calculations. The observations are condensed into a schematic mechanism for Cd adsorption on the fly ash particles.
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| 2. |
- Davidsson, Kent, 1967, et al.
(författare)
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Countermeasures against alkali-related problems during combustion of biomass in a circulating fluidized bed boiler
- 2008
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Ingår i: Chemical Engineering Science. ; 63, s. 5314-5329
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work was to study different ways to mitigate alkali-related problems during combustionof biomass in circulating fluidized beds. Wood chips and wood pellets were fired together withstraw pellets, while the tendency to agglomerate and form deposits was monitored. In addition to areference case, a number of countermeasures were applied in related tests. Those were addition of elementalsulphur, ammonium sulphate and kaolin to a bed of silica sand, as well as use of olivine sand andblast-furnace slag as alternative bed materials. The agglomeration temperature, composition and structureof bed-ash samples were examined. The flue-gas composition, including gaseous alkali chlorides, wasmeasured in the hot flue gases and in the stack. Particles in the flue gas were collected and analysed forsize distribution and composition. Deposits were collected on a probe in hot flue gases and their amountand composition were analysed. Addition of kaolin was found to be the best method to counteract theagglomeration problem. The deposition problem is effectively counteracted with addition of ammoniumsulphate, while kaolin is too expensive to be used commercially against deposits, and sulphur is lesseffective than ammonium sulphate.
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| 3. |
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| 4. |
- Herstad-Svärd, S., et al.
(författare)
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Ramprogram – Åtgärder för samtidig minimering av alkalirelaterade driftproblem, Etapp 2
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Combustion of an increasing amount of biofuel and waste woods has resulted in certainenvironmental advantages, including decreased emissions of fossil CO2, SO2 andmetals. On the other hand, a number of chloride and alkali related operational problemshave occurred which are related to combustion of these fuels.Alkali related operational problems have been studied in a project consisting of twoparts. The overall scope has been to characterise the operational problems and to studymeasures to minimise them. The first part was reported in Värmeforsk report 997 wherethe results were summarised in a table of different measures. In part two, additionalmeasures have been included in the test plan and initial corrosion has been studiedlinked to the different measures. The tests have also in part two been carried out at the12 MW CFB boiler at Chalmers. The effect of the selected measures has beeninvestigated concerning both deposit formation and bed agglomeration, and at the sametime emissions and other operational conditions were characterised.The second part of the project has among other things focused on:• To investigate measures which decrease the content of alkali and chloride in thedeposits, and consequently decrease the risk for corrosion (by investigating theinitial corrosion). Focus was also on trying to explain favourable effects.• To investigate if it is possible to combine a rather low dosage of kaolin and injectionof ammonium sulphate. This was done in order to reduce both bed agglomerationand problems from deposits during combustion of fuels rich in chlorine.• To investigate if co-combustion with sewage sludge, de-inking sludge or peat withhigh ash content, could give similar advantages as conventional additives.• Investigate if ash from PFBC is possible to use as an alternative bed material.By comparing the different measures in part two, it could be concluded that cocombustionof sewage sludge gave the best overall effect. The judgement was based onthe effects concerning bed agglomeration, level of alkali chloride in the flue gas,deposits and initial corrosion. Simultaneous addition of kaolin and ammonia sulphatealso had a favourable impact both in the bed and on the alkali chlorides in the gas phase.Dosage of kaolin did not reduce the effect of injected ammonium sulphate. Cocombustionof peat could also be a very attractive alternative, but it is critical to select asuitable peat type. It is of special concern to avoid peat with a high content of calcium,since it can increase the level of alkali chlorides by reacting with available sulphur.Change of bed material to ash from PFBC can decrease problems with bedagglomeration, but there is a risk of increased deposit formation and corrosion. A boileroperated with high steam data should consequently combine the change of bed materialwith injection of ammonium sulphate or another source of sulphur.Co-combustion of de-inking sludge from pulp and paper production can reduceproblems with bed agglomeration. There is, however, an increased chance of corrosiondue to the high content of calcium. Injection of sulphates may improve the situationconcerning corrosion. The results also showed that low potassium chlorine content in the flue gas decreasesthe risk of corrosion. Increased amount of potassium chlorine content in the flue gaswill not necessary give a high amount of chlorine content in the deposits if there is sulphur in the system.Key words: agglomeration, deposits, corrosion, alkali, kaolin, ammonium sulphate,sludge
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| 5. |
- Kalmykova, Yuliya, 1981, et al.
(författare)
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Adsorption materials for removal of heavy metals and petroleum hydrocarbons from contaminated leachates
- 2006
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Ingår i: proceedings of the 9th International FZK/TNO Conference on Soil-Water Systems, ConSoil 2005, 3-7 October 2005, Bordeaux.
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Konferensbidrag (refereegranskat)abstract
- Adsorption function and capacities, for heavy metals and selected hydrocarbons, of several low-cost and alternative bio-sorption materials have been investigated. The materials studied were residual products from the forest industry (saw dust, pine bark and fiber ash) and natural materials (peat moss, shrimp shells and seaweed). Batch tests and column experiments were carried out with both artificial solutions and highly contaminated leachate from an industrial landfill. Fiber ashes and peat showed the highest sorption capacity for metals among the materials studied in comparative batch tests. In these tests, artificial single metal solutions in concentration ranges of 1−10 mg/l, and liquid to solid ratios of 20 and 200 were used. The fiber ash removed lead by 99%, copper by 100%, zinc by 99% and chromium by 82%. Peat removed lead by 98%, copper by 94%, zinc by 73% and chromium by 88%. Metal removal from the landfill leachates was also studied in batch tests, where lead was reduced by ash and peat by 99% and 96% respectively, copper by 100% and 92%, zinc by 95% and 33%, cadmium by 88% and 40%. A net release of Al, Cr, Ca, Ba and K from ash was observed, whereas the peat removed chromium by 66% and aluminium by 85%. The lower performance of the adsorbents for complex solutions as real leachates, suggests competitive sorption of ions although the mechanisms of sorption are not yet fully understood.In initial batch studies for organic pollutants, the adsorption for diesel oil by ash and peat was 98% and 97% respectively, 97% and 92 % for the n-alkane C16, and 91% for n-C12 for both materials. Bark adsorbed diesel oil by 83%, and the lower value could be explained by the larger particle size of the bark.Several column tests with peat, a peat-ash mixture and bark have been carried out to investigate the adsorbents’ behavior and sorption capacity under flowing conditions. Both simulated contaminated groundwater and real landfill leachates were used as eluents. Sorption capacities for the metals and break-through volumes of the solutions were obtained. For most of the metals studied (Cd, Pb, Zn, Cu, Ni) ground peat appeared to be the best adsorbent, both in degree of sorption and service time. The column with peat-ash mixture adsorbed Cd, Ni and Pb to a lower degree, but retained the metals for a longer time than the peat column. The adsorption rate was significantly higher when artificial solutions were used and the metals were adsorbed for a longer time: Cu and Ni for approximately 20% and Zn for 50% longer time. These results point out that laboratory tests can overestimate adsorbent’s performance and experiments should be specific and using real leachates. High iron content showed no effect on the sorption capacity of Cd and Cu, but other metals as Ni, Pb, Zn were sorbed for a shorter time. To better understand the basic mechanisms and processes, column tests need to be complemented with batch tests for basic studies of adsorption and competitive mechanisms.
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| 6. |
- Kalmykova, Yuliya, 1981, et al.
(författare)
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Adsorption of Cd, Cu, Ni, Pb, and Zn on Sphagnum peat from solutions with low concentrations
- 2007
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Ingår i: Journal of Hazardous Materials. - : Elsevier BV. - 1873-3336 .- 0304-3894. ; 152:152, s. 885-891
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates adsorption of metal ions on Sphagnum peat from solutions with environmentally relevant concentrations of metals. The peat moss is intended as an alternative, low-cost filter material for contaminated waters. Adsorption of Cd, Cu, Ni, Pb and Zn was studied in batch tests, and adsorption isotherms were determined. The kinetics of adsorption was analyzed using a second-order model and rate constants were calculated. An empirical model for predicting adsorption of metal ions at a given time was derived from these constants. Metal ions were removed in the descending order Pb > Cu > Ni > Cd > Zn. Relationship between the affinities of the metals to the peat active sites with chemical properties for the metals were indicated by the results. In addition, equilibration studies were performed at constant pH and ionic strength. The experimental data fitted the Freundlich equation. Both the uptake of metals and the Freundlich constants increased in line with increasing pH. The Freundlich exponent declined with higher initial concentrations, suggesting adsorption to sites with lower activity.
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| 7. |
- Kalmykova, Yuliya, 1981, et al.
(författare)
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ALTERNATIVE MATERIALS FOR ADSORPTION OF HEAVY METALS AND PETROLEUM HYDROCARBONS FROM CONTAMINATED LEACHATES
- 2008
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Ingår i: Environmental Technology. ; 29, s. 111-122
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, waste products from forest industries (sawdust, pine bark and fibre sludge ash), as well as some biological materials (peat, shrimp shells and seaweed), have been investigated with respect to their capacities to adsorb metals and hydrocarbons from contaminated waters. Batch and column experiments were carried out with artificial metal ion solutions and contaminated leachates from an industrial landfill. The fibre sludge ash and the Sphagnum peat showed the highest sorption capacities for metals among the materials studied in batch experiments with single-metal solutions. The uptake of metals by the fibre ash for the metals studied was: Cu and Pb 112 µg g-1, Zn 115 µg g-1 and Cr 97 µg g-1. For peat the uptake was: Pb 109 µg g-1, Cu 105 µg g-1, Zn 100 µg g-1 and Cr 99 µg g-1. These materials were also effective in adsorption of diesel oil, and the n-alkanes C16 and C12. Peat and ash adsorbed respectively 36.6 and 36.4 mg g-1 of C12, 1.84 and 1.94 mg g-1 of C16 and for both 0.98 mg g-1 of diesel oil. Bark adsorbed diesel oil to 0.83 mg g-1. In the column experiments, the removal of metals from a contaminated landfill leachate by ash and peat was lower than from artificial solutions with only a few metals. The results suggest interference from other components in the leachates, such as competition of ions for the same active sites. It is quite clear that laboratory tests can overestimate the performance of adsorbents and that experiments should be specific for the intended application. For most of the metals studied in columns, peat appeared to be the best adsorbent, with respect to both sorption capacity and service time. The addition of 10 % by weight of fibre ash to the peat gave higher adsorption capacities for Cd, Ni and Pb but lower for the Cu and Zn.
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| 8. |
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| 9. |
- Karlfeldt Fedje, Karin, 1977, et al.
(författare)
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Addition of kaolin as a potassium sorbent in the combustion of wood fuel- effects on leaching of metals from the resulting fly ash
- 2007
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Ingår i: 4th Biennial Meeting of the Scandinavian-Nordic Section of the Combustion Institute hosted by Åbo Akademi, November 5-6 2007.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Combustion of biomass is a way to decrease the use of fossil fuels and thereby decrease the emissions of for instance the green house gas CO2. Earlier the forest felling residues, i.e. branches, needles and treetops, were left in the forest, but nowadays it is common to use forest felling residues as fuel. Consequently, there is a risk that the supply of nutrients and essential trace elements to the new generation of trees will be limited in the long perspective. Recycling of biomass ashes to the forest soil as fertilizers is common practice in many places. However, the ash spreading may cause some problems, such as a large initial pH increase that the forest soil may be exposed to from the strongly alkaline ash. The alkalinity is mainly caused by the oxides and hydroxides of potassium and calcium present in the ash. Kaolin has been shown to adsorb and react with vaporous alkali metal species from the flue gas and therefore addition of kaolin to bio fuel was tested in a full scale boiler in this project. Since no information about how kaolin addition in the boiler affects the leaching properties of nutrients and trace elements from the ashes this study was undertaken. Fly ash from combustion cases with and without kaolin were investigated in leaching tests in original form and in self-hardened form, i.e. mixed with water and left to react for a number of months. The leaching tests were carried out in order to compare the different ashes and to simulate the possible release of nutrients and trace elements. The ashes were leached according to EN 12457-2 as well as at two constant pH-values, 7 and 4, using a pH-stat titration system. Preliminary results suggest that some of the investigated trace elements (Cd, Cu, Mn, Pb and Zn) only to low content are found in compounds that are soluble at high pH values. Hardening seems to slightly decrease the leaching of these metals at high pH values, whereas addition of kaolin did not affect the release much. The leaching behaviour of trace elements at lower pH values is under evaluation and the results will be included in the presentation. The consumption of acid to achieve neutral and acidic pH values, respectively, during the titrations was highest in the unhardened ashes without kaolin. Both addition of kaolin and hardening of the ashes decreased the acid demand.
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| 10. |
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