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Leaching of Metal(loid)s From Ashes of Spent Sorbent and Stabilisation Effect of Calcium-Rich Additives
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.ORCID-id: 0000-0001-5375-8825
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.ORCID-id: 0000-0002-2319-0906
Visa övriga samt affilieringar
2020 (Engelska)Ingår i: Environmental Science and Pollution Research, ISSN 0944-1344, E-ISSN 1614-7499Artikel i tidskrift (Refereegranskat) Epub ahead of print
Abstract [en]

Contaminated water with multiple contaminants, including As, Cr, Cu and Zn, was treated with a sorbent prepared by coating peat with Fe oxides. Because As has a relatively little explored market, the regeneration of the spent sorbent was not feasible. Meanwhile, the disposal of As wastes in landfills can cause landfill leachate treatment problems. Under the reducing conditions prevailing at landfills, As(V) is reduced to As(III), which is a toxic and more mobile form. In this study, incineration was explored as a management option to treat the spent sorbent that was loaded with As, Cr, Cu and Zn. The first objective of this study was to evaluate the leaching of these metal(loid)s from the ashes and compare it with the leaching from the spent sorbents before incineration. The second objective was to evaluate the leaching behaviour when the spent sorbent was co-incinerated with a Ca-rich additive (lime). To achieve these objectives, the obtained ashes were subjected to leaching tests, sequential extraction, and X-ray diffraction analyses. After the incineration, the ash content ranged from 9 to 19% of the initial mass of the spent sorbents. The leaching of As, Cu and Zn decreased compared with that from the spent sorbents before the thermal treatment because of the high incineration temperatures and/or co-incineration with lime. However, the leaching of Cr increased, which would hinder the disposal of the obtained ashes in a landfill because the limit value for disposal at a landfill for hazardous wastes was exceeded by 50 times. However, co-incineration with 10 wt% lime significantly decreased the leaching of Cr as a result of the formation of water-insoluble Ca-Cr compounds.

Ort, förlag, år, upplaga, sidor
Springer, 2020.
Nyckelord [en]
Arsenic, Heavy metals, Lime, Incineration, Iron-coated peat, Thermochemical equilibrium calculations
Nationell ämneskategori
Annan naturresursteknik Energiteknik
Forskningsämne
Avfallsteknik; Energiteknik
Identifikatorer
URN: urn:nbn:se:ltu:diva-76322DOI: 10.1007/s11356-020-09269-zPubMedID: 32436093OAI: oai:DiVA.org:ltu-76322DiVA, id: diva2:1359398
Tillgänglig från: 2019-10-09 Skapad: 2019-10-09 Senast uppdaterad: 2020-05-27
Ingår i avhandling
1. Peat Coated with Iron Oxides: Purification of Metal(loid)-Contaminated Water and Treatment of the Spent Adsorbent
Öppna denna publikation i ny flik eller fönster >>Peat Coated with Iron Oxides: Purification of Metal(loid)-Contaminated Water and Treatment of the Spent Adsorbent
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

In Sweden due to the industrial activities, such as wood impregnation, multiple point sources of arsenic (As) contamination in soil and water bodies are scattered over the country. Metals, such as chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), cadmium (Cd) or zinc (Zn) at varying concentrations are usually present as well. Since adsorption is a common method to purify contaminated water, research and development of adsorbents have been actively carried out in the last few decades. However, seldom spent sorbent is safely handled afterwards and often end up in landfill, thus creating new problems and posing new risks to humans and environment.

The aim of this study was to develop a waste-based adsorbent for simultaneous removal of As and associated metals: Cr, Cu and Zn, and to analyse sustainable ways how to manage the spent adsorbent without creating secondary pollution.

In the model system two well-establish adsorbents: Fe oxides (deriving from FeCl3) and peat (waste-based), were combined and the concept of simultaneous removal of cationic and anionic contaminants was tested in a batch adsorption experiment. Due to Fe coating, removal of As and Cr increased by 80% and 30%, respectively, as compared to non-coated peat. Removal of Cu and Zn was higher (up to 15%) on non-coated peat than on Fe-coated peat. Similar results were obtained in the up-scaled column adsorption experiment, where Fe salt was substituted with a waste-based Fe hydrosol. Within the same pH environment (pH=5), Fe-coated peat effectively adsorbed all four investigated contaminants (As, Cr, Cu and Zn). Non-coated peat was effective for Cr, Cu and Zn. While, Fe oxides (coated on sand) adsorbed only As.

Three management strategies for spent adsorbents, obtained after column adsorption experiment, were investigated in this study. i) Long-term deposit in a landfill was simulated by exposing spent adsorbents to a reducing environment and evaluating metal(loid) leaching. Leaching of As increased manifold (up to 60% in a 200-day experiment) as compared to the standardized batch leaching experiment under oxidizing conditions. It was determined that about one third of As(V) was reduced to As(III), which is more mobile and toxic. ii) Valorisation of the spent adsorbent was attempted through hydrothermal carbonisation. It was expected that obtained hydrochar could be used as a beneficial soil amendment. However, treatment resulted in the process liquid and the hydrochar both having high loads of As, Cu and Zn. Additional treatment of process water and hydrochar imply higher management costs for spent adsorbents. iii) Possibility of thermal destruction was investigated by combusting spent adsorbents. After the treatment volume of the waste (ash) was by 80-85% smaller as compared to spent adsorbents. Combustion at higher temperature (1100 °C vs 850 °C) resulted into a weaker metal(loid) leaching from ashes. Furthermore, co-combustion with calcium (Ca)-rich lime (waste-based) decreased leaching of all four investigated elements, Cr in particular, below the limit values for waste being accepted at landfills for hazardous waste. Therefore, combustion enabled possibility of safe and long-term deposit of As-bearing ashes. At the same time, less As would be circulating in society. 

For the future work, studies that could broaden the spectrum of contaminants targeted by Fe-coated peat would be beneficial. At the same time it is important not only to find alternative utilisation methods for Fe-coated peat, but also investigate other management options for the spent adsorbents.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2019
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nyckelord
iron-peat, adsorption, arsenic, metals, combustion, hydrothermal carbonisation, landfilling
Nationell ämneskategori
Miljöledning Annan naturresursteknik
Forskningsämne
Avfallsteknik
Identifikatorer
urn:nbn:se:ltu:diva-76325 (URN)978-91-7790-462-5 (ISBN)978-91-7790-463-2 (ISBN)
Disputation
2019-12-05, D770, Luleå, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2019-10-09 Skapad: 2019-10-09 Senast uppdaterad: 2019-11-14Bibliografiskt granskad

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Kasiuliene, AlfredaCarabante, IvanSefidari, HamidÖhman, MarcusKumpiene, Jurate

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