CET 97 DOI: 10.3303/CET2297027 Paper Received: 15 June 2022; Revised: 3 October 2022; Accepted: 4 October 2022 Please cite this article as: Adiansyah J.S., 2022, Carbon Emission Reduction using Waste Management Strategy Approach for Improving a Mine Site Environmental Performance, Chemical Engineering Transactions, 97, 157-162 DOI:10.3303/CET2297027 CHEMICAL ENGINEERING TRANSACTIONS VOL. 97, 2022 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Jeng Shiun Lim, Nor Alafiza Yunus, Jiří Jaromír Klemeš Copyright © 2022, AIDIC Servizi S.r.l. ISBN 978-88-95608-96-9; ISSN 2283-9216 Carbon Emission Reduction using Waste Management Strategy Approach for Improving a Mine Site Environmental Performance Joni S. Adiansyah* Postgraduate Program of Environmental Sciences, Universitas Muhammadiyah Mataram, Jalan KH. Ahmad Dahlan No.1 Pagesangan, Mataram, Nusa Tenggara Barat, Indonesia joni.adiansyah@ummat.ac.id The mining industry generates various types of waste that could affect environmental quality. One type of waste that is commonly managed by the mine site due to its coal-fired power plant operation is fly ash and bottom ash (FABA). The landfilling system is a worldwide common application strategy to manage FABA generated by a coal-fired power plant. The volume of coal burned for generating electricity determines the volume of coal ash managed in the landfill. This study applied a case study of a 160 MW coal-fired power plant in Indonesia that generates about 16 thousand t of coal ash annually for fulfilling mine site electricity demand. This study aims to compare the carbon emission reduction of three different management strategies associated with fly ash and bottom ash handling. Three scenarios have been developed: on-site landfilling, third-party shipment, and road- based application (internal utilisation). A life cycle assessment (LCA) was applied to compare those scenarios by using a cradle-to-gate boundary system. The functional unit (FU) used was a carbon footprint generated of 1 t of FABA managed using three different scenarios. The result showed that the lowest CO2-eq emitted from the FABA road-based application scenario with 0.90 kg CO2-eq, and the highest carbon footprint generated by the on-site landfilling scenario due to the life cycle of landfill facility. Compared with the on-site landfill and shipment to third party scenario, the road-based application scenario would reduce carbon footprint by about 305.70 kg CO2-eq and 0.32 kg CO2-eq for each t of FABA managed. Network impact analysis indicates that utilisation of diesel is the main environmental hotspot of each scenario. Further fuel efficiency studies should be conducted to create a better environmental performance. 1. Introduction The mining industry is categorised as an energy-intensive industry where mining activities consume about 6.2 % of total global energy, including grinding, haulage, and digging (Holmberg et al., 2017). Energy consumption of each activity varies for open pit and underground mines, commonly determined by total production, type of mineral mined, and type of fuel used. One study indicated that the energy requirements of seven mine sites (four gold and three iron ore) ranged from 10,241 kWh/kt to 33,507 kWh/kt (Jeswiet and Szekeres, 2016). The coal-fired power plant, one of the typical energy sources to fulfil mining's energy demand, would generate waste (fly ash and bottom ash) during the operational stage. One study revealed that coal-fired power plants contributed about 38 % of total power generated worldwide (Zierold and Odoh, 2020). In general, coal combustion for steam generation in coal-fired power plants would generate higher fly ash content (80 %) than bottom ash (20 %). These two types of coal-fired power plant wastes have technical differences in density, physical characteristics, and size. Fly ash has a density that ranges from 1.00 g/cm3 to 2.50 g/cm3 (Feng and Li, 2021), and bottom ash density ranges from 0.89 g/cm3 to 1.06 g/cm3 (Ullah et al., 2020). Fly ash and bottom ash (FABA) have three main similar chemical compositions, namely, calcium oxide (CaO), aluminium oxide (Al2O3), and silica oxide (SiO2). By having these chemical compositions, FABA is widely used in construction projects, including concrete for reducing cement content (Maeijer et al., 2020), highway embankments for backfilling purposes (Rai et al., 2010), road stabilisation (Vestin et al., 2012), backfill material (Lee et al., 2014). Some other studies associated with FABA applications worldwide are presented in Table 1. 157 Table 1: Various applications of FABA worldwide Application Region Source Reclamation uses: Abandoned mine reclamation Clay mine rehabilitation Soil erosion prevention India Sri Lanka Indonesia (Dube, 2020) (Suloshini et al., 2020) (Matsumoto et al., 2016) Agricultural applications: Soil amendment Soil stabilisation Australia USA (Ukwattage et al., 2013) (Anderson et al., 2004) Manufacturing and other uses: Filler on asphalt Cement substitution Bricks Poland Poland India (Woszuk et al., 2019) (Rutkowska et al., 2021) (Yousuf et al., 2020) The utilisation of FABA, a by-product of pulverised coal in a thermal power plant, is currently also applied in the mining industry. Some applications include soil remediation for reducing soil acidity in minerals mines, road- based material for the mining access road, and concrete for structural and non-structural purposes in the mining area. These applications would assist mining industries in reducing their potential environmental impacts, such as climate change (Adiansyah, 2019), soil and water contamination (Haddaway et al., 2019), and depletion of soil nutrients (Emmanuel et al., 2018). One of the tools that could be used to estimate the environmental impact of activity through its life cycle is life cycle assessment (LCA). A study revealed that three primary commodities (coal, aggregates, and copper ores) were dominating the LCA study in mining (Segura-Salazar et al., 2019). Some studies associated with fly ash utilisation were also found, including fly ash as geopolymer material (Tang et al., 2021), fly ash for partial replacement of cement in concrete (Dandautiya and Singh, 2020), and fly ash carbonation process (Margallo et al., 2018). None of the studies discusses fly ash and bottom ash for road- based mining areas. This study aimed to compare the carbon emission reduction of three different management strategies of fly ash and bottom ash handling using a life cycle assessment approach. A mine site in Indonesia that applies those strategies was taken as a case study. 2. Methods The life cycle assessment (LCA) was applied to estimate the carbon emission of three different coal ash management strategies. Those three coal ash management strategies are landfilling on-site, shipping to the third party for further treatment, and road-based application, as presented in Figure 1. Based on the ISO standard on life cycle management, there are four stages required: 1) goal and scope, 2) inventory analysis, 3) impact assessment, 4) interpretation (ISO, 2006), where SimaPro 9.3.03 (Mark et al., 2016) was used for calculating the environmental impact. 2.1 Case study A mine site that operates a 160 MW coal-fired power plant is taken as a case study where the coal-fired power plant generates two types of waste, namely, fly ash and bottom ash that would be dumped on a dedicated landfill (known as coal ash landfill). Fly ash and bottom ash (FABA) are generated from the combustion of coal in coal grinding equipment (pulverizer). The fine coal is delivered to the furnace by primary air using a pipeline, and burned coal will generate a solid residue (ash). Two pollution management tools are applied to prevent contamination due to coal-fired power plant FABA. These tools are bag-house for collecting the fly ash and submerged chain conveyor for storing the bottom ash. FABA (waste) generated by an internal coal-fired power plant is about 10,000 t/y and is currently managed by operating a landfill and conducting a regular shipment to the third-party that has a permit from the Government of Indonesia for managing the FABA. These management methods are known as business as usual scenarios, as presented in Figure 1 (Scenario 1 and Scenario 2), and more than 60 % of FABA generated were shipped regularly to the third-party. The third scenario is utilising FABA as road-based material in the mining area that aims to apply the reduce, reuse and recycle concepts. Utilising FABA will also reduce mine road maintenance costs and external treatment or management costs of FABA. 2.2 Goal and scope This study aimed to determine the carbon footprint of three different FABA management strategies. In this comparison, the volume of one shipment (8,000 t of FABA) is used as the parameter for collecting the operational data. The functional unit (FU) was 1 t of FABA, and cradle to gate system boundary was applied, 158 as illustrated in Figure 1. The life cycle impact that estimated base on the operational data of 8,000 t of FABA would be transformed into 1 t of FABA as discussed in sub-section 3.1. Figure 1: System boundaries 2.3 Inventory analysis (LCI) The three FABA management scenarios, namely, landfilling on-site, shipping to the third party for further treatment, and road-based application, are summarised in Table 2 – Table 4. The first scenario, as presented in Table 2, covers some activities: transportation of FABA from a coal-fired power plant to a disposal area (landfill), landfill re-contouring, and leaching water treatment. Coal bottom ash collected from a submerged chain conveyor was transported to a landfill using a dump truck with a load capacity of 5 t. A dump truck with a load capacity of 10 t was used for transporting fly ash from the fly ash silo to the disposal area (landfill). Beside diesel fuels, chemicals (sulphuric acid), water, and electricity for the dosing pump are required in the FABA landfill scenario. Table 2: Data inventory – FABA landfill on-site scenario Main activities Sub-activities Total material input Unit Transporting bottom ash to landfill Diesel for dump truck 272 kg Landfill re-contouring Diesel for dozer 3,188 kg Water for dust suppression 3.5 m3 Transporting fly ash to landfill Diesel for dump truck 194 kg Landfill re-contouring Diesel for dozer 3,188 kg Water for dust suppression 3.5 m3 Wastewater treatment Dosing sulphuric acid 1,472 kg Dosing pump 200 kWh Database approach (ecoinvent database) was used in landfill on-site scenario to estimate the impact of FABA landfill facility. Based on the government of Indonesia regulation, FABA is categorised as a waste that shall be managed properly. One of the strategies is transporting to the third party with a hazardous waste management license. Therefore, the second management strategy is shipping the FABA to other company that has hazardous waste management facility. The third party company is located about 350 nautical miles from where FABA is generated. There are four activities within the scope of the second scenario: FABA transporting and handling, tug-boat services, and shipment process, as presented in Table 3. Fossil fuel consumption (diesel) for loading 159 and hauling activity is the main material input of the second scenario. A small volume of water is required for dust suppression during the barge's FABA handling. Table 3: Data inventory – FABA shipment to the third-party scenario Main activities Sub-activities Total material input Unit Transporting FABA to barge Diesel for dump truck 217.60 kg Diesel for loader 446.25 kg FABA handling at the barge Diesel for dozer 1,062.5 Diesel for excavator 807.5 kg Water for dust suppression 2.0 m3 Tug-boat services Diesel for two tug-boats 1,275 kg Shipment to the third-party Diesel for tug-boat 1200 HP 13,458.90 kg The internal data record showed that more than 50 % of the total FABA generated was transported to the third party from the Year 2010 to the Year 2017. FABA utilisation scenario is proposed for increasing the volume of FABA utilisation internally. A total of 8,000 t FABA is mixed with 8,000 t of mine soil or 50 % FABA and 50 % mine soil composition. The mixture materials are spread out into five layers with 40 cm height for each layer as road-based in the mining area. There are four activities involved in road-based work, namely, transportation, FABA mixing and spreading, and compacting road-based layers. These all activities consume fossil fuel (diesel) as the main input material, as presented in Table 4. Table 4: Data inventory – FABA road-based application scenario Main activities Sub-activities Total material input Unit Transporting FABA for site application Diesel for dump truck 2,992 kg Diesel for loader 446 kg FABA mixing with soil Diesel for excavator 1,857 kg Diesel for loader 1,466 kg Spreading of mixed material Diesel for dozer 1,594 kg Diesel for grader 842 kg Compacting Vibrator compactor 238 kg 3. Results and discussion 3.1 Life cycle impact assessment (LCIA) Life cycle impact assessment applied ReCiPe midpoint methods and Hierarchist version where global warming as the impact category focused. Table 5 compares the CO2 equivalent (CO2-eq) emissions that were released from handling 1 t of FABA material for each scenario. It can be seen from Table 5 that the lowest CO2-eq emitted from the FABA handling with 0.90 kg CO2-eq is the road-based application strategy, and the highest carbon footprint is generated by the landfilling on-site scenario. Compared with the first and second scenarios, the road- based application strategy would reduce carbon footprint by about 305.70 kg CO2-eq and 0.32 kg CO2-eq for each t of FABA managed. Table 5: Global warming of 1 t FABA – based on scenario applied Impact Category Unit Scenario 1 Scenario 2 Scenario 3 Global Warming kg CO2-eq 306.60 1.22 0.90 Figure 2 shows that utilisation of diesel is the main environmental hotspot of each scenario. On-site landfill scenario generated the highest environmental hotspot (99.8 %) from the life cycle of the landfill facility, as seen in Figure 2a. The FABA shipment scenario (see Figure 2b) shows that diesel consumption of vessels that transport FABA to the third party contributes 77.9 % of the total carbon footprint. Scenario 3 for FABA on-site application, as seen in Figure 2c, shows that more than 50 % of the total carbon is emitted by FABA mixing activity. There are also other impact categories such as terrestrial acidification, marine eutrophication, terrestrial ecotoxicity, marine ecotoxicity, human carcinogenic toxicity, human non-carcinogenic toxicity, and water consumption that compare each scenario's environmental impact magnitude. The highest environmental impact of all impact categories would be the on-site landfill scenario, where most of the lowest environmental impacts are generated by applying a road-based scenario. 160 Figure 2: Network impact analysis of (a) on-site landfill scenario, (b) shipment to third part scenario, (c) on-site application scenario 3.2 Limitations The availability of a local database would create a less reliable and accurate result for life cycle impact assessment. Some assumptions about fuel consumption have been made due to the limitation of data access. Database reference applies due to a lack of field data availability. The LCA analysis was limited to the impact categories associated with the selected method (ReCiPe). 4. Conclusions A coal-fired power plant is currently the main energy source that supports mining activities in Indonesia. The coal combustion process would generate waste, namely, fly ash and bottom ash. These coal-fired power plant by-products should be managed properly based on the government of Indonesia's regulations. Some commonly applied management strategies are on-site landfilling, third-party handling, and internal utilisation. Each strategy generates carbon emissions mainly emitted by operational equipment, including dump trucks, dozers, excavators, and vessels. The application of on-site landfilling strategy generates the highest carbon emission for 1 t of FABA handling compared to other management strategies. The FABA utilisation strategy through road-based application indicates as the lowest carbon footprint with 305.70 kg CO2-eq lower than on-site landfill scenario and 0.32 kg CO2-eq lower than shipment to Scenario 3. The environmental hotspot of those three strategies indicates that the efficiency of diesel fuel usage should be considered to reduce the current carbon footprint. Further fuel efficiency studies should be conducted to create a better environmental performance. References Adiansyah J.S., 2019, Improving the environmental performance of a copper mine site in Indonesia by implementing potential greenhouse gas emissions reduction activities, Chemical Engineering Transactions, 72, 55–60. SCENARIO-1 Bottom Ash Handling 0.0798% Fly Ash Handling 0.078% Waste Water Treatment 0.016% FABA Landfill System 99.8% Transpor ting bottom ash to landfill Recontour ing landfill (bottom Recontouri ng landfill (fly ash) Sulphuric acid production Electricity (IDN) Residual material landfill Diesel (RoW) SCENARIO-2 FABA handling at barge 14.7% Tug-boat services 7.38% Shipment to third party 77.90% Diesel (RoW) Transporti ng FABA to barge a) b) SCENARIO-3 Transporting FABA for site application 26.90% On-site application 73.10% Compacting Mix material spreading FABA mixing with soil Diesel (RoW) c) 161 Anderson V., Buckley T., Stewart A., 2004, Instructions for Use of Fly Ash to Stabilize Soil in Livestock Facilities - AS1258, North Dakota State University ND Agricultural Experiment Station, North Dakota, USA. Dandautiya R., Singh A.., 2020, Life-Cycle Assessment of Production of Concrete Using Copper Tailings and Fly Ash as a Partial Replacement of Cement. In: Pancharathi, R., Sangoju, B., Chaudhary, S. (Eds.), Advances in Sustainable Construction Materials, Springer, Singapore. Dube S.K., 2020, Strategic plan for ash disposal in abandoned mines filled with acid mine drainage, International Journal of Scientific and Research Publications, 10, 709-717. Emmanuel A.Y., Jerry C.S., Dzigbodi D.A., 2018, Review of environmental and health impacts of mining in Ghana, Journal of Health and Pollution, 8, 43–52. Feng S., Li Y., 2021, Study on coal fly ash classified by bulk density, Journal of Physics: Conference Series, 1732. Haddaway N.R., Cooke S.J., Lesser P., Macura B., Nilsson A.E., Taylor J.J., 2019, Evidence of the impacts of metal mining and the effectiveness of mining mitigation measures on social – ecological systems in Arctic and boreal regions : a systematic map protocol, Environmental Evidence, 1–11. Holmberg K., Kivikytö-Reponen P., Härkisaari P., Valtonen K., Erdemir A., 2017, Global energy consumption due to friction and wear in the mining industry, Tribology International, 115, 116–139. ISO, 2006, Environmental Management - Life Cycle Assessment - Principles and Framework ISO 14040, Geneva, Switzerland. Jeswiet J., Szekeres A., 2016, Energy Consumption in Mining Comminution, Procedia CIRP,48, 140–145. Lee K.J., Kim S.K., Lee K.H., 2014, Flowable backfill materials from bottom ash for underground pipeline, Materials (Basel), 7, 3337–3352. Maeijer P.K. De, Craeye B., Snellings R., Kazemi-Kamyab H., Loots M., Janssens K., Nuyts G., 2020, Effect of ultra-fine fly ash on concrete performance and durability, Construction Building Material, 263, 120493. Margallo M., Cobo S., Muñoz E., Fernández A., Santos E., Dominguez-Ramos A., Aldaco R., Irabien Á., 2018, Life cycle assessment of alternative processes to treat fly ash from waste incineration, Chemical Engineering Transactions, 70, 883–888. Mark G., Oele M., Jorrit L., Tommie E.M., 2016, Introduction to LCA with SimaPro, Netherlands. Matsumoto S., Ogata S., Shimada H., Sasaoka T., Kusuma G.J., Gautama R.S., 2016, Application of Coal Ash to Postmine Land for Prevention of Soil Erosion in Coal Mine in Indonesia : Utilization of Fly Ash and Bottom Ash, Earth Materials and Environmental Applications, 2016, 1–9. Rai A.K., Paul B., Singh G., 2010, A Study on Backfill Properties and Use of Fly Ash for Highway Embankments, Journalof Advanced Laboratory Research in Biology, 1, 110–114. Rutkowska G., Chalecki M., Żółtowski M., 2021, Fly ash from thermal conversion of sludge as a cement substitute in concrete manufacturing, Sustainability, 13, 1-23. Segura-Salazar J., Lima F.M., Tavares L.M., 2019, Life Cycle Assessment in the minerals industry: Current practice, harmonization efforts, and potential improvement through the integration with process simulation, Journal of Cleaner Production, 232, 174–192. Suloshini S., Ranathunga A.S., Kulathilaka S.A.S., Gunawardana W.B., Mapa M.M., 2020, Utilization of Bottom Ash for Clay Mine Rehabilitation, the 11th International Conference on Sustainable Built Environment, 10- 12 December, Sri Lanka. Tang W., Pignatta G., Sepasgozar S.M.E., 2021, Life-cycle assessment of fly ash and cenosphere-based geopolymer material, Sustainability, 13, 1–23. Ukwattage N.L., Ranjith P.G., Bouazza M., 2013, The use of coal combustion fly ash as a soil amendment in agricultural lands (with comments on its potential to improve food security and sequester carbon), Fuel, 109, 400–408. Ullah A., Kassim A., Abbil A., Matusin S., Rashid A.S.A., Yunus N.Z.M., Abuelgasim R., 2020, Evaluation of coal bottom ash properties and its applicability as engineering material, Earth and Environmental Science,1– 6. Vestin J., Arm M., Nordmark D., Lagerkvist A., Hallgren P., Lind, B., 2012, Performance Record of Fly Ash As a Construction Material,WASCON 2012, 30 May - 1 June, Gothenburg, Sweden,300–320. Woszuk A., Bandura L., Wojciech F., 2019, Fly ash as low cost and environmentally friendly filler and its effect on the properties of mix asphalt, Journal of Cleaner Production, 235, 493–502. Yousuf A., Manzoor S.O., Youssouf M., Malik Z.A., Sajjad Khawaja K., 2020, Fly Ash: Production and Utilization in India-An Overview, Journal of Materials and Environmental Science,11, 911–921. Zierold K.M., Odoh C., 2020, A review on fly ash from coal-fired power plants: Chemical composition, regulations, and health evidence, Reviews on Environmental Health, 35, 401–418. 162 027.pdf Carbon Emission Reduction using Waste Management Strategy Approach for Improving a Mine Site Environmental Performance