Daniel Höllen

Landfill mining: Resource potential of Austrian landfills – Evaluation and quality assessment of recovered municipal solid waste by chemical analyses

Since the need for raw materials in countries undergoing industrialisation (like China) is rising, the availability of metal and fossil fuel energy resources (like ores or coal) has changed in recent years. Landfill sites can contain considerable amounts of recyclables and energy-recoverable materials, therefore, landfill mining is an option for exploiting dumped secondary raw materials, saving primary sources. For the purposes of this article, two sanitary landfill sites have been chosen for obtaining actual data to determine the resource potential of Austrian landfills. To evaluate how pretreating waste before disposal affects the resource potential of landfills, the first landfill site has been selected because it has received untreated waste, whereas mechanically–biologically treated waste was dumped in the second. The scope of this investigation comprised: (1) waste characterisation by sorting analyses of recovered waste; and (2) chemical analyses of specific waste fractions for quality assessment regarding potential energy recovery by using it as solid recovered fuels. The content of eight heavy metals and the net calorific values were determined for the chemical characterisation tests.

Landfill mining: Development of a theoretical method for a preliminary estimate of the raw material potential of landfill sites.

In recent years, the rising need for raw materials by emerging economies (e.g. China) has led to a change in the availability of certain primary raw materials, such as ores or coal. The accompanying rising demand for secondary raw materials as possible substitutes for primary resources, the soaring prices and the global lack of specific (e.g. metallic) raw materials pique the interest of science and economy to consider landfills as possible secondary sources of raw materials. These sites often contain substantial amounts of materials that can be potentially utilised materially or energetically. To investigate the raw material potential of a landfill, boreholes and excavations, as well as subsequent hand sorting have proven quite successful. These procedures, however, are expensive and time consuming as they frequently require extensive construction measures on the landfill body or waste mass. For this reason, this article introduces a newly developed, affordable, theoretical method for the estimation of landfill contents. The article summarises the individual calculation steps of the method and demonstrates this using the example of a selected Austrian sanitary landfill. To assess the practicality and plausibility, the mathematically determined raw material potential is compared with the actual results from experimental studies of excavated waste from the same landfill (actual raw material potential).

Zur Fragestellung des Einsatzes von Schlacken als Versatz im Bergbau

ZusammenfassungBergversatz ist die zur Prävention von Bergschäden erforderliche Verfüllung unterirdischer Hohlräume. Die Verfahrensrichtlinie des Bergmännischen Verbandes Österreichs (BVÖ) (Bergmännischer Verband Österreichs, Fachausschuss für Untertagebergbau: Verfahrensrichtlinie – Versatzsysteme im untertägigen Bergbau, 22.05.2013) legt die Anforderungen an die verwendeten Versatzmaterialien fest. Versatzmaterialien aus Sekundärrohstoffen, die aus ressourcenökonomischer Sicht eigens zu diesem Zweck abgebauten Primärrohstoffen vorzuziehen sind, sofern keine bergbaueigenen Materialien in ausreichender Menge zur Verfügung stehen, können diese Anforderungen unter gewissen Voraussetzungen erfüllen. Der Einsatz von Sekundärrohstoffen als Versatzmaterial stellt in diesem Fall eine stoffliche Verwertung im Sinne der Abfallhierarchie (Abfallwirtschaftsgesetz, 2002) dar. Die Zulässigkeit dieser Verwertung hängt maßgeblich von der mineralogisch-hydrogeochemischen Beurteilung der Auswirkungen des Einsatzes sekundärer Versatzmaterialien auf die Umwelt ab. Schlacken der Metallurgie, die aus felsmechanischen Gründen geeignete Versatzmaterialien darstellen, entsprechen unter gewissen Voraussetzungen auch den umweltgeochemischen Anforderungen. Anhand des Beispiels von Chrom in Stahlwerksschlacken wird gezeigt, welche Aspekte bei der Beurteilung dieser Fragestellung im individuell zu beurteilenden Einzelfall zu prüfen sind.AbstractBackfilling of subterraneous cavities is necessary to prevent subsidence damages. The Guideline of the Austrian Mining Association (German: Bergmännischer Verband Österreichs, BVÖ) (Bergmännischer Verband Österreichs, Fachausschuss für Untertagebergbau: Verfahrensrichtlinie – Versatzsysteme im untertägigen Bergbau, 22.05.2013) defines the requirements for the applied backfill materials. Backfill materials from secondary resources, which should be preferred to primary resources if the latter are extracted especially for this purpose, can fulfill these requirements under certain conditions. The application of secondary resources as backfill material represents material recycling in terms of the waste hierarchy (Abfallwirtschaftsgesetz, 2002). The admissibility of this recycling depends significantly on the mineralogical and hydrogeochemical evaluation of the effects of the application of secondary backfill materials on the environment. Metallurgical slags, which represent suitable backfill materials from the point of view of rock mechanics, correspond also to the environmental requirements under certain circumstances. By means of the example of chromium in steel slags it is shown which aspects have to be considered evaluating the application of secondary resources as backfill materials, while every single case has to be judged individually.

POTENTIAL AND MAIN TECHNOLOGICAL CHALLENGES FOR MATERIAL AND ENERGY RECOVERY FROM FINE FRACTIONS OF LANDFILL MINING: A CRITICAL REVIEW

Multiple landfill mining investigations of municipal solid waste landfills have been carried out worldwide in the past decades. Some of these studies have led to the conclusion that landfill mining is not feasible and could represent more of a problem than a solution for old landfill sites. This is the case to a certain extent because, to this day, material and energy recovery in landfill mining has been restricted to the coarse fractions (>10 mm to >60 mm) in most projects, while the fine fractions (<10 mm to <60 mm) have been often re-directed to the landfill with poor or no treatment at all despite their recovery potential. The fine fractions account for 40-80 wt.% of the total amount of the landfill-mined material. Its material composition is characterized by about 40-80 wt.% decomposed organic matter or weathered mineral fractions which cannot be hand-sorted, followed by significant amounts of calorific fractions and a small amount of metals. The main chemical compound found in landfill mining fine fractions is SiO2, mostly present as quartz and minor amounts of sheet silicates, followed by CaO, mostly present in carbonate minerals. MgO, Fe2O3 and Al2O3 represent minor components. Heavy metals are present in concentrations of few to several hundreds of mg/kg without a clear general trend of enrichment compared to the coarse fractions. In contrast, the net calorific value of the fine fractions (about 3-9 MJ/kg DM) can be several times lower than that of the coarse fractions (about 10-30 MJ/kg DM). These data clearly indicate that both a mineral fraction for waste-to-material and a calorific fraction for waste-to-energy might be recovered if suitable mechanical processing technologies can be employed. The potential of the fine fractions for material and energy recovery, as well as the main technological challenges to unlock it, are the main topics discussed in the present review article. This article has been elaborated within the framework of the EU Training Network for Resource Recovery through Enhanced Landfill Mining – NEW-MINE.​