CMA

49 (1300 ⁰C) for MSWI fly ash-amended cements. Special cements containing MSWI ash, like eco-cements, alinite cements, and sulfoaluminate cements, can also be created at considerably lower clinker temperatures of 1100–1200 ⁰C (compared to approximately 1450 ⁰C for traditional materials) (Ashraf et al., 2019). Other studies indicate that the trace element composition of MSWI ash (such as high concentrations of Zn) may lower clinkerization temperature (Ghouleh and Shao, 2018). Huang and Chuieh (2015) found that using washed and chelated fly ash as a cement kiln feed has the lowest environmental impact compared to common disposal options (solidification and landfilling and reuse in bricks and steelmaking) for fly ash. Compared to traditional management methods (solidification and landfilling), beneficially using MSWI bottom ash as a 25% replacement for raw materials in clinker was the preferable recycling scenario with the lowest environmental burden and natural resource consumption; this option was also cheaper than other management options, but transport distances are a key factor in this determination (Margallo et al., 2014). A separate study comparing different management scenarios found that bottom ash recycling in cement production had lower environmental impacts in all categories (abiotic depletion, acidification potential, eutrophication potential, freshwater aquatic ecotoxicity, global warming potential, human toxicity potential, photochemical ozone creation potential, and terrestrial ecotoxicity potential) except for atmospheric acidification potential and photochemical ozone creation potential (Margallo et al., 2013). Similarly, Mao et al. (2020) found that solid waste sourced sulphoaluminate cements manufactured with 35% washed MSWI fly ash had lower life cycle impacts than traditional sulphoaluminate cements for all categories except water depletion and natural land transformation; the fly ash washing process was noted to consume a large amount of water. 4.7 Economic and practical feasibility of recycling MSWI residues The economic feasibility of implementing a practical full-scale recycling practice with MSWI-residues in a cement plant will depend on many factors which has to be evaluated locally. Some important factors that have to be considered in detail, is the following • Existing and current regulation and cement standards for the area of consideration do it allow adding alternative raw materials and what are the limitations and eventually the testing requirements? • What are the volumes and the composition of the MSWI-residues produced in the area within a feasible transport distance transportation might constitute a considerable cost? • What are the current disposal and treatment option practiced in the area, and the associated costs? • What are the raw material chemistry and the cement manufacturing process (chlorine) in the local cement plant and what are the limiting factors for adding MSWI-residues and how much could be added? • What is the experience in the cement plants in question, do they practice co-processing/ recycling, do they have logistics, storage and feeding possibilities? • What kind of process would be most economic and chemical feasible for removing contaminants from the MSWI-residues in question – a broad spectre of technical options needs to be considered. • How should a complete performance verification test be conducted and what will the cost be? Example of Water washing pre treatment of municipal solid waste incinerator fly ash and co-processing in a cement kiln in China Yan et al (2018) conducted full scale experiments with washing of MSWI ash and subsequent co- processing in a cement kiln in China. In this study, toxic HMs, comprising 3 groups, namely volatile HMs (Hg), semi-volatile HMs (Pb, Cd, Tl, and As) and non-volatile HMs, and PCDD/Fs in the input (untreated MSWI-FA (FA), coal, and raw meal (RM)), intermediate (washed MSWI-FA (WFA), washing water, HM sludge, dried-washed MSWI-FA (DWFA), and salt), and output materials (clinker (CK), cement kiln dust (CKD) and ue gas (Flue)) produced during pre-treatment and co-processing in a cement kiln, were systematically measured. The results obtained in this study might provide important knowledge for the control and reduction of heavy metal and PCDD/Fs in cement kilns co-processing MSWI-FA.