Caviglia, Caterina

Confalonieri, Giorgia

Corazzari, Ingrid

Destefanis, Enrico

Mandrone, Giuseppe

Pastero, Linda

Pavese, Alessandro

English

Institutional Research Information System University of Turin

A second life of waste products for a responsible and ethical use of natural resources:evaluations of the use of ashes produced by waste-to-energy plants as aggregated materialsCaterina Caviglia1, Giorgia Confalonieri1, Ingrid Corazzari2 , Enrico Destefanis1, Giuseppe Mandrone1, Linda Pastero1,  Alessandro Pavese11Earth Sciences Department, Università degli Studi di Torino, via Valperga Caluso 35, 10125 Torino, Italy2 Chemistry Department, Università degli Studi di Torino, via Pietro Giuria 7, 10125, Torino, ItalyINTRODUCTIONIn many geographical contexts, the availability of natural mineral resources is not always able to meet the demands and often the supply is carried out athigh energetic and environmental costs. This may not only concern fossil fuels but also raw materials used for the production of aggregates and availability ofmetals for each type of application. It is one of the consequences of the growth of the living standard that involves the construction of an increasing numberof infrastructures. For this reason the figures called to solve the problems of supplying raw materials and their use, as geologists and engineers, arenecessarily faced with problems different from the normal supply of natural resources, increasingly rare and insufficient to cover the demandor available with very high energy costs and in contrast with the environmental protection issues that we try to apply in many countries.The research therefore moves from the traditional retrieval through geological and mineral prospecting to the conversion and re-use of materials consideredwaste or waste deriving from an industrial process.With regard to sustainability, the use of residues from waste-to-energy plants for urban waste is included: after moderate treatments, they can find a role ofraw material-second in the construction of works, reducing the need to find additional natural resources and related problems for their disposal or storage.From the plants Waste to Energy, in 2016 only in Europe, around 19 Mtons of bottom ashes have been produced, thus offering a good opportunity formaterial to be processed to reach the End of Waste condition.The aim of the present study is to characterize the bottom ashes of municipal solid wastes produces in a plant present in northern Italy by means of amultidisciplinary approach and on the basis of the results we have defined the quotas of material available for re-entry into the "portfolio" of raw materials.We have also tested some inertization techniques to reduce polluting substances release in the environment as natural and accelerated carbonation. Thecarbonation process involves the absorption of carbon dioxide by an alkaline material, as bottom ash, decreasing pH and making calcite precipitate.The interaction of carbon dioxide with municipal solid waste incinerator (MSWI) bottom ash has been studied to investigate the resulting changes in pH andbottom ash mineralogy and the impact that these changes have on the mobility of dangerous substances, especially heavy metals. This process can benatural, in an open environment, or accelerated, using laboratories reactors to study the variation of time, temperature and humidity to maximize thecarbonation process. We have compared this two methods to evaluate the possibility of a reuse of bottom ashes, respecting the European legislationthreshold limits.REFERENCES1 Van Gerven T, Van Keer E, Arickx S, Jaspers M, Wauters G, Vandecasteele C. Carbonation of MSWI-bottom ash to decrease heavy metal leaching, in view of recycling. Waste Management, 2005, 25(3):291–300. 2. Speiser C, Baumann T, Niessner R. Morphological and Chemical Characterization of Calcium-Hydrate Phases Formed in Alteration Processes of Deposited Municipal Solid Waste Incinerator Bottom Ash. Environ Sci Technol., 2000;34(23):5030–7. 3. Santos RM, Mertens G, Salman M, Cizer Ö, Van Gerven T. Comparative study of ageing, heat treatment and accelerated carbonation for stabilization of municipal solid waste incineration bottom ash in view of reducing regulated heavy metal/metalloid leaching. Journal of Environmental Management.  2013;128:807–21. 4. C. Speiser, T. Baumann  and, Niessner* R. Morphological and Chemical Characterization of Calcium-Hydrate Phases Formed in Alteration Processes of Deposited Municipal Solid Waste Incinerator Bottom Ash  2000. Available at: https://pubs.acs.org/doi/full/10.1021/es990739c5. Bertos MF, Li X, R. Simons SJ, D. Hills C, J. Carey P. Investigation of accelerated carbonation for the stabilisation of MSW incinerator ashes and the sequestration of CO 2. Green Chemistry, 2004;6(8):428–36. 6. Baciocchi R, Costa G, Lategano E, Marini C, Polettini A, Pomi R, et al. Accelerated carbonation of different size fractions of bottom ash from RDF incineration. Waste Management 2010, 30(7):1310–7. 7 Um N, Ahn J-W. Effects of two different accelerated carbonation processes on MSWI bottom ash. Process Safety and Environmental Protection.  2017, 111:560–8.MATERIALS AND METHODSSome bottom ashes samples were taken from the accumulation deposits of a waste-to-energyplant located in northern Italy. The material leaves the incineration process as it is and israther heterogeneous and contains a significant fraction of metal elements.BA are divided in a fraction over and under 1 mm to perform the best treatments for each grainsize.0%10%20%30%40%50%60%70%80%90%100%0,010,1110100Cumulative (%)Particle size (MM)2,8mm<D50<4mmCHARACTERIZATION OF THE METALLIC FRACTIONWithin the coarser granulometric fraction (> 4mm) ferromagnetic granules have been identified and separated by a magnet. This rate sometimes exceeds 10% of the total weight of thesample. The separated material was analyzed by electronic scanning microscopy with EDS to obtain compositional maps capable of providing preliminary information on the metallic speciespresent.>4 mm 4 -1 mm <1 mm water content loose bulk density% wt % wt %wt %wt kg/l36 38 26 17 1,095Data of aggregates production  from UEPG “Union Européenne des Producteurs de Granulats” annualreview 2017-2018.Data of aggregates production trend for EU + EFTA (Iceland Liechtenstein, Norway, Switzerland) countries. If European economic growth can be maintained, the EU+EFTA total aggregates production couldreach the milestone of 3bnt by 2019, but this would be still much below the pre-crisis 3.7 bnt of 2006.Accelerated carbonation was performed using 20g of BA, applying different conditions oftemperature, water content, pressure of CO2 and time. The fraction up to 4 mm was excludedfrom carbonation since it doesn’t contain high concentrations of dangerous substances, asalready recognized in previous works (Um et al.,2017), and it only requires moderatetreatments as washing. Accelerated carbonation tests were applied to the grain size fractionbetween 4 mm and 1 mm, and on the fraction <1 mm.The following results are relative to the fraction < 1 mm because most of the heavy metalsand polluting substances concentrates in it . In fact heavy metals detected in the <1 mmfraction of BA are three times higher than in the coarser fraction >1 mm.Different set of parameters were applied in the accelerated carbonation tests, as indicated byprevious work on BA carbonation (Bertos et al., 2004; Van Gerven et al., 2005; Baciocchi etal., 2010; Nam et al., 2012; Pan et al., 2012): the water to solid ratio (L/S) in the samples hasbeen maintained in the range 0,2-0,4 L/S, temperature variation has been set from 25 to 50°C, time from 60 to 120 minutes and P CO2 from 1 to 3 bar.>=4mm 4mm -1 mm< 1 mmWashing AcceleratedcarbonationWashing/AcceleratedcarbonationBOTTOM ASHES TREATMENTSThe comparison between the leaching test after natural andaccelerated carbonation show the decrease in both thesituation of most of the heavy metals , especially copper, zinc,chromium, nickel and lead. In the case of natural carbonationNi, Cr, and Pb decrease by 50%, while Cu by 7%. pH of thesolution decreases, for untreated BA, from 12,5 to 11,5 . In thecase of accelerated carbonation, Cu decrease by 75%, while theNi and Cr by 15%. pH decrease from 11 to 9.5. The decrease ofpH to 9.5 after the accelerated carbonation strongly affectsthe solubilization of some heavy metals like Pb, Zn, Cd, Niwhich are more soluble at lower pH.Metal hydroxide solubility diagram asfunction of pH and concentrations.The acceleratedcarbonation process hasbeen quantified bythermogravimetricanalysis coupled withFTIR, to quantify theamount of carbonatesproduced.Two samples of grain size< 1 mm were chosen, onenot treated and onecarbonated, and wereheated in N2 atmospherefrom 35 to 900 °C (ramp20 °C/min). At 900 °C,they were kept for 15minutes in oxidizingatmosphere(N2/O2 3/1).TGA + FTIR QUANTIFICATION OF ACCELERATED CARBONATIONRESULTS• Weight loss for BA: 6,5%• Weight loss for BA carbonated: 11,5%• The difference of 5% is compatible with the weight increase (measured in laboratory) after carbonation of 4-5 %FTIR profile of the H2O e CO2 releaseby the sample of BA not treated duringheatingH2OCO2H2OCO2FTIR profile of the H2O e CO2 releaseby the sample of the carbonated BAtreated during heatingTG (continuous line) and derivatives (dashed lines) measured in functionof the temperature for BA not treated (red line) e BA carbonated (blueline)BA not treated vs BA carbonatedWeight loss can be due to the CO2 release.Temperature and CO2 release is compatible withthe thermal decomposition of carbonates.LEACHING TESTS BEFORE AND AFTER CARBONATIONElectrolytic conductivity/time diagram of theleaching testThe diagram shows the differencebetween the samples treated withnatural carbonation NC andaccelerated carbonation (AC). Theconductivity of the two carbonatedsamples are very similar. The highconductivity value of the NCsample before treatment isprobably due to the presence of avery fine fraction which is reducedby the carbonation by grainagglomeration.CONCLUSIONSHeavy metals concentrate mainly in the finer grainsize of BA (< 1 mm). The accelerated carbonation iseffective in the reduction of heavy metals butrequires an optimization of the parameters thatinfluence pH in the release in the naturalenvironment.Removing metals from the coarser grain size of ash isessential to improve their reuse and treatments;moreover it can represent a source of metal recoveryAVERAGE HEAVY METALSCONCENTRATION IN WATER AFTERRELEASE TESTS OF BAAfter leaching test concentrates mainly inthe finer fraction <1 mm, especially Cu,Pb, Zn.<1mmThe compositional maps, considered in the total data collected by EDS, provide an elemental metallic set expressed in% of oxides reported in the pie chart.

A second life of waste products for a responsible and ethical use of natural resources:
evaluations of the use of ashes produced by waste-to-energy plants as aggregated materials

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A second life of waste products for a responsible and ethical use of natural resources: evaluations of the use of ashes produced by waste-to-energy plants as aggregated materials

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