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Leaching of wood ash products aimed for spreading in forest floors: influence of method and L/S ratio
University of Kalmar, School of Pure and Applied Natural Sciences.
University of Kalmar, School of Pure and Applied Natural Sciences.
University of Kalmar, School of Pure and Applied Natural Sciences.
University of Kalmar, School of Pure and Applied Natural Sciences.
2008 (English)In: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 28, no 11, p. 2235-2244Article in journal (Refereed) Published
Abstract [en]

Use of biofuels in the form of logging residues is increasing in the European countries. This intensive forestry, where entire trees are removed from the felling sites, may contribute to a negative nutrient balance in the forest soil. Recycling of ash from the combustion of clean wood fuel, sometimes in combination with limestone or additives/binders, back into the forest soil could maintain the soil nutrient reservoir intact. Before spreading ash, it is important to determine its contents and, particularly, its decomposition pattern using reliabl laboratory leaching tests. In this study, mineralogy and the leaching of Na, Ca, K, Mg, Mn, Al, Cu, Fe, P, and Zn from wood ash pellets and granules, produced both from green liquor sludge and fly ash, are examined by XRD and by subjecting these substances to three different laboratory leaching tests: upflow percolation (CEN/TS 14405), batch leaching (SS-EN12457), and a new Swedish leaching test using a magnetic stirrer. Mineral phases such as quartz, ettringite, calcite, gehlenite, and aphtitalite were identified in the ash granules and in the ash/green liquor sludge granules, by means of XRD. Six additional minerals were detected in the granules of ash only, and another six in the ash/green liquor sludge granules. At L/S 2, the batch leaching test resulted in the highest amounts of elements leached and the upflow percolation test the lowest. At L/S 10, both the batch leaching test and the upflow percolation test resulted in high amounts of elements leached. The batch leaching test at L/S 10 complies quite well with the percolation test and could be suitable for ash/green liquor sludge granule evaluation in daily practice. The magnetic stirrer test seems to underestimate the release potential of elements from granules. The batch test is simple to perform, and has the ability to dissolve 70–80% of the elements with the highest mobility from the materials under study.

Place, publisher, year, edition, pages
Elsevier, 2008. Vol. 28, no 11, p. 2235-2244
National Category
Natural Sciences
Research subject
Natural Science, Environmental Science
Identifiers
URN: urn:nbn:se:hik:diva-613DOI: 10.1016/j.wasman.2007.09.037OAI: oai:DiVA.org:hik-613DiVA, id: diva2:1862
Available from: 2007-10-08 Created: 2009-09-16 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Ash Products for Nutrient Recycling in Forestry: Leaching and Drying Characteristics
Open this publication in new window or tab >>Ash Products for Nutrient Recycling in Forestry: Leaching and Drying Characteristics
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

As the demand for carbon dioxide neutral energy sources increases, forestry becomes more intensive. Entire trees are removed from the felling sites threatening the nutrient balance of the forest soils. By recycling wood ash produced from the combustion of clean wood biofuels back to the forest, it is possible to maintain the nutrient balance of the soil and also to counteract its acidification. To avoid negative effects, e.g. burn damage on mosses and lichens caused by the high pH of the ash, it is important that the ash is treated and hardened in order to lower its reactivity and to prolong its dissolution rate. The ash chemicals content are determind and the reactivity and dissolution properties are evaluated by laboratory leaching tests. Pulp and paper industries generate not only ash but green liquor sludge also as residual material. These nutrient-rich materials could be put together into granules and be recycled on forest soil. The applied leaching tests vary in their performance and duration. Therefore the focus of this work is put on both making granules of ash and green liquor sludge and developing a method for the testing of these.

The aims of this thesis are: to investigate how leaching tests influences the dissolution of ash products; to find out how drying techniques affect the product's leaching behaviour and to find an appropriate technique for mixing and agglomerating wood ash and green liquor sludge in suitable proportions.

The leaching tests compared were: up-flow percolation, batch leaching and leaching using a magnetic stirrer. This study includes analyses of pH and concentrations of Na, Ca, K, Mg, Mn, Al, Cu, Fe, P and Zn in the eluate from each leaching test. The results show that the batch leaching test at L/S 10 has the ability to dissolve 70-90 % of K and Na from the ash products. The upflow percolation test releases 55-100 % K and Na, but takes several weeks to perform. The leaching test with a magnetic stirrer results in low leached amounts of elements and underestimation of the dissolution potential of the material. The test seems to be best suited for its original purpose, i.e. control of the reactivity of wood ash.

Four drying techniques were applied on wood ash pellets: drying at room temperature, drying by hot air (60 and 130 C) and drying by flue gas. The ash pellets dried in flue gas showed the significantly lowest values of pH and electric conductivity. This makes flue gas drying an advantageous method, for ash products intended for spreading in forest. Regarding the elements studied, the flue gas drying does not contaminate the ash material.

Processing the ash and green liquor sludge using an intensive mixer offers effective blending and a quick granulation with a short process line. With the intensive mixer it is possible to granulate a mixture of maximum 65 % sludge (wet weight basis) and 35 % ash (dry weight basis).

Series
Dissertation series / University of Kalmar, Faculty of Natural Science, ISSN 1650-2779
Keywords
Ash products, Wood ash, Leaching, Drying, Nutrient;, Sustainable forestry
National Category
Forest Science
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:hik:diva-25 (URN)978-91-89584-77-8 (ISBN)
Presentation
2007-08-22, A137, Landgången 4, Kalmar, 10:00 (English)
Opponent
Supervisors
Available from: 2007-10-08 Created: 2007-10-08 Last updated: 2010-03-09

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Sarenbo, SirkkuStålnacke, OlofClaesson, Tommy

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