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Peat Coated with Iron Oxides: Purification of Metal(loid)-Contaminated Water and Treatment of the Spent Adsorbent
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.ORCID iD: 0000-0001-5375-8825
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords [en]
iron-peat, adsorption, arsenic, metals, combustion, hydrothermal carbonisation, landfilling
National Category
Environmental Management Other Environmental Engineering
Research subject
Waste Science and Technology
Identifiers
URN: urn:nbn:se:ltu:diva-76325ISBN: 978-91-7790-462-5 (print)ISBN: 978-91-7790-463-2 (electronic)OAI: oai:DiVA.org:ltu-76325DiVA, id: diva2:1359453
Public defence
2019-12-05, D770, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2019-10-09 Created: 2019-10-09 Last updated: 2019-11-14Bibliographically approved
List of papers
1. Removal of metal(oid)s from contaminated water using iron-coated peat sorbent
Open this publication in new window or tab >>Removal of metal(oid)s from contaminated water using iron-coated peat sorbent
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2018 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 198, p. 290-296Article in journal (Refereed) Published
Abstract [en]

This study aimed at combining iron and peat to produce a sorbent suitable for a simultaneous removal of cations and anions from a solution. Peat powder, an industrial residue, was coated with iron by immersing peat into iron salt solutions. The adsorption efficiency of the newly produced sorbent towards As, Cr, Cu and Zn was tested by means of batch adsorption experiments at a constant pH value of 5. Coating of Fe on peat significantly increased the adsorption of As (from <5% to 80%) and Cr (from <3% to 25%) in comparison to uncoated peat. Removal of cations on coated peat slightly decreased (by 10–15%), yet remained within acceptable range. Electron Microscopy combined with X-Ray Energy Dispersive Spectroscopy revealed that iron coating on the peat was rather homogenous and As and Cr were abundantly adsorbed on the surface. By contrast, Cu and Zn displayed a sparing distribution on the surface of the iron coated peat. These results indicate that iron-peat simultaneously target sufficient amounts of both cations and anions and can be used for a one-step treatment of contaminated groundwater

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Other Environmental Engineering
Research subject
Waste Science and Technology
Identifiers
urn:nbn:se:ltu:diva-67545 (URN)10.1016/j.chemosphere.2018.01.139 (DOI)000427338800033 ()29421741 (PubMedID)2-s2.0-85041488356 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-02-07 (andbra)

Available from: 2018-02-07 Created: 2018-02-07 Last updated: 2019-10-09Bibliographically approved
2. Treatment of metal (loid) contaminated solutions using iron-peat as sorbent: is landfilling a suitable management option for the spent sorbent?
Open this publication in new window or tab >>Treatment of metal (loid) contaminated solutions using iron-peat as sorbent: is landfilling a suitable management option for the spent sorbent?
2019 (English)In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 26, no 21, p. 21425-21436Article in journal (Refereed) Published
Abstract [en]

This study firstly aimed to investigate the potential of simultaneous metal (loid) removal from metal (oid) solution through adsorption on iron-peat, where the sorbent was made from peat and Fe by-products. Up-flow columns filled with the prepared sorbent were used to treat water contaminated with As, Cu, Cr, and Zn. Peat effectively adsorbed Cr, Cu, and Zn, whereas approximately 50% of inlet As was detected in the eluent. Iron-sand was effective only for adsorbing As, but Cr, Cu, and Zn were poorly adsorbed. Only iron-peat showed the simultaneous removal of all tested metal (loid)s. Metal (loid) leaching from the spent sorbent at reducing conditions as means to assess the behaviour of the spent sorbent if landfilled was also evaluated. For this purpose, a standardised batch leaching test and leaching experiment at reducing conditions were conducted using the spent sorbent. It was found that oxidising conditions, which prevailed during the standardised batch leaching test, could have led to an underestimation of redox-sensitive As leaching. Substantially higher amounts of As were leached out from the spent sorbents at reducing atmosphere compared with oxidising one. Furthermore, reducing environment caused As(V) to be reduced into the more-toxic As (III).

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Arsenic, metals, trace elements, sorption, landfill leachate, low redox
National Category
Other Environmental Engineering
Research subject
Waste Science and Technology
Identifiers
urn:nbn:se:ltu:diva-74016 (URN)10.1007/s11356-019-05379-5 (DOI)000482211100030 ()31119550 (PubMedID)
Note

Validerad;2019;Nivå 2;2019-09-09 (johcin)

Available from: 2019-05-23 Created: 2019-05-23 Last updated: 2019-10-09Bibliographically approved
3. Hydrothermal carbonisation of peat-based spent sorbents loaded with metal(loid)s
Open this publication in new window or tab >>Hydrothermal carbonisation of peat-based spent sorbents loaded with metal(loid)s
2019 (English)In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 26, no 23, p. 23730-23738Article in journal (Refereed) Published
Abstract [en]

Hydrothermal carbonisation (HTC) is a wet and relatively low-temperature process where, under autogenous pressures, biomass undergoes a chain of reactions leading to the defragmentation of organic matter. As well as its other uses (e.g. for producing low-cost carbon-based nano-compounds), HTC is utilised for the treatment of wet wastes, such as manure and biosludge. This study aimed to determine if hydrothermal carbonisation is a feasible treatment method for spent sorbents that are highly enriched with arsenic, chromium, copper, and zinc. The chemical properties of hydrochar and process liquid were evaluated after HTC treatment, where peat-based spent sorbents were carbonised at 230 °C for 3 h. Analysis of Fourier transform-infrared spectra revealed that during HTC, the oxygenated bonds of ethers, esters, and carboxylic groups were cleaved, and low-molecular-weight organic fragments were dissolved in the process liquid. A large fraction of arsenic (up to 62%), copper (up to 25%), and zinc (up to 36%) were transferred from the solids into the process water. Leaching of these elements from the hydrochars increased significantly in comparison with the spent sorbents.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Metals, Adsorption, Thermal treatment, Iron-peat, Post-sorption management, HTC
National Category
Other Environmental Engineering
Research subject
Waste Science and Technology
Identifiers
urn:nbn:se:ltu:diva-75121 (URN)10.1007/s11356-019-05653-6 (DOI)000477958300045 ()31203552 (PubMedID)
Note

Validerad;2019;Nivå 2;2019-08-20 (johcin)

Available from: 2019-06-28 Created: 2019-06-28 Last updated: 2019-10-25Bibliographically approved
4. Leaching of metal(loid)s from ashes of spent sorbent and stabilization effect of calcium-rich additive
Open this publication in new window or tab >>Leaching of metal(loid)s from ashes of spent sorbent and stabilization effect of calcium-rich additive
Show others...
(English)Manuscript (preprint) (Other academic)
Keywords
Fe oxide, peat, combustion, lime, arsenic, adsorption
National Category
Environmental Management
Research subject
Waste Science and Technology
Identifiers
urn:nbn:se:ltu:diva-76322 (URN)
Available from: 2019-10-09 Created: 2019-10-09 Last updated: 2019-10-30

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