Several landfill mining (LFM) studies have been carried out in recent years all around the world. From these studies qualitative and quantitative information regarding the composition and characteristics of the different fractions excavated from landfills has been obtained. This information comprises data from various landfill sites around the globe from which useful correlations for future LFM projects can be identified. Of particular interest to this paper is the information regarding the fine fractions, which represent to this day a crucial obstacle in the implementation of LFM and enhanced landfill mining (ELFM). The fine fractions make up a considerable portion of the total amount of waste disposed of in landfills. Depending on the particle size chosen as upper limit to define the fines fraction, the portion of this fraction can be as high as 40-80 wt.% of the total excavated waste. These fractions consist of decomposed organic substances, e.g. humic substances, partly weathered mineral waste, e.g. sand, brick fragments, concrete, but also of fine metal particles, especially non-ferrous metals, and still a significant amount of plastics, paper and other calorific fractions. However, although calorific fractions might be used for energy recovery and inorganic fractions for material (especially metal) recovery, current LFM studies are discarding the fine fraction due to lacking or too expensive processing routes. Therefore, it is of critical interest to LFM and ELFM projects to reduce the particle size down to which the excavated material can be processed. This paper, which was elaborated within the framework of the EU Training Network for Resource Recovery through Enhanced Landfill Mining -NEW-MINE, aims to review the obtained data from different LFM studies from municipal solid waste (MSW) landfills, concerning the fines fraction, in order to identify key aspects to be taken into consideration while designing the processing approach in future LFM and ELFM investigations.

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 redirected 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 SiO 2 , mostly present as quartz and minor amounts of sheet silicates, followed by CaO, mostly present in carbonate minerals. MgO, Fe 2 O 3 and Al 2 O 3 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.

Within the framework of the "EU Training Network for Resource Recovery through Enhanced Landfill Mining -NEW-MINE", around 374 Mg of waste were excavated from a landfill site in Mont-Saint-Guibert, Belgium. Parameters such as bulk density, water content, particle size distribution and material composition of the fine fractions (material <90 mm) were determined and analyzed. The present investigation has the main objective to document and disseminate the findings on the material characterization of the fine fractions obtained in this case study, since such information is of critical relevance for the design of an effective and efficient mechanical processing in (enhanced) landfill mining projects. Additionally, the potential of the fine fractions for material and energy recovery is discussed. The fine fractions in question were obtained through the implementation of a ballistic separation process with simultaneous screening directly after excavation, from which about 77 wt.% of the total amount of processed material in raw state corresponded to the fine fractions. These fractions presented an overall bulk density range of 720-1000 kg/m 3 in raw state and a total water content range of 25-30 wt.%. In dry state, the material showed a more uniform particle size distribution than in raw state, and results confirm that water content has a large impact on the particle size distribution of the fine fractions, as well as on the content of impurities in the material fractions "Combustibles", "Inert", "Total metals" and "Others" and on the presence of agglomerates. Results on the material composition in dry state reveal that amounts of 2.1-19.7 wt.% "Combustibles", 31.1-35.4 wt.% "Inert" and 0.6-1.8 wt.% "Total metals" could be recovered from the fine fractions 90-10 mm, while 37.8-55.6 wt.% "Fine fractions <10 mm" could be processed further in order to increase the recovery amounts of the previous material fractions and produce a substitute material for soil in construction applications.

For decades, ballistic separators have been used in Europe as a means of sorting waste to separate mixed waste material streams at material recovery facilities and municipal solid waste treatment plants. Currently, with the growing need to remediate landfill sites, ballistic separators can be employed to recover calorific fractions from excavated landfill material within the framework of enhanced landfill mining. Ballistic separators provide multiple separation steps in one machine: they sort flat two-dimensional materials from rigid three-dimensional materials, while the material is screened to a selected particle size at the same time. The present study shows the results obtained during an investigation performed at the landfill in Mont-Saint-Guibert, Belgium. The main objectives were to acquire first-hand information regarding the efficiency of the ballistic separator in relation to processing old and untreated landfilled material and to study the potential of the landfill as a reservoir of secondary resources. The excavated material was processed through a pre-treatment chain of steps, including material classification and separation, as well as particle size reduction. As a first step, the material was processed with a ballistic separator using two different mesh sizes, 200 mm and 90 mm. Subsequently, the performance of the separator in question was evaluated, especially regarding its effectiveness in the production of refuse derived fuel. The two-dimensional flow was characterized by combustible materials from municipal solid waste and the three-dimensional by construction and demolition waste. As a result, 46% (dry basis) of the input material were fines particles <20 mm, 3% had a calorific value of 22.4 MJ kg -1 , 1% 16.0 MJ kg -1 and approximately 1% were magnetic metals that could be recovered by mechanical processes. The results of processing and valorising the potential resources disposed in landfills are essential for the implementation of enhanced landfill mining since revenues from material and energy recovery could contribute to the economic feasibility of the project.

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