Effect of municipal solid waste incineration fly ash on the structure of fired clay materials

Abstract

Increase in the residues from Municipal Solid Waste Incineration (MSWI) residues has become a major concern in many countries. The bottom ash and fly ash generate require appropriate management in order to minimize their effect on the environment. The bottom ash is classified as non-hazardous waste by the European Waste Catalogue [1] and fly ash is classified as hazardous waste owing to its high contents of heavy metals and soluble salts [2]. The studied fly ash (cogeneration power plant UAB “Fortum Klaipėda”) was found to contain a high content of of CaO, which was 45.17, chlorides (mainly KCl, NaCl, MgCl2) – 19.01, sulphate – 7.32, Na2O, K2O, MgO, Al2O3, Fe2O3, TiO2, and heavy metals: lead, cadmium, chromium, copper, mercury, molybdenum, tin, wolfram, strontium, etc. At present, fly ash (FA) from municipal incineration waste are practically not utilized in Lithuania. However, we believe that fly ash or washed fly ash (additional treatment with water) can be used in fired clay building materials production fired at 1000C. Minerals of quartz, hematite, albite-anorthite, spinel, diopside are identified in the control clay samples clay brick. Isomorphic minerals, plagioclases – albite-anorthite, hematite, spinel, diopside, as well as calcium sulphate were identified in clay materials with FA [3]. It should be emphasized that the formation of minerals may be affected by the presence of heavy metals in the FA [4-5]. Heavy metals such as Cu, Zn, Ni, etc. can interfere with the structure of the spinel or/and diopside and thus affect their identification and intensity. The formation of calcium sulphate mineral is influenced by a sufficiently high content of calcium and sulphates in FA. Calcium sulphate mineral is not a preferred mineral in the building ceramics industry, as it can negatively affect the structure of clay materials by increasing porosity due to its properties – sufficiently large volume and the possibility of formation in pores. It was determined that, the chemical composition of fly ash influences the formation of a different structure in the clay body. With the formation of calcium sulphate mineral, evaporation of chlorides, decomposition of CaCO3, more long, large and open pores are formed in the structure (Fig.1 c). Summarizing the obtained results of the study, it is recommended to utilize up to 2.5 fly ash in the production of fired clay bricks. The obtained clay bricks would have the following characteristics: shrinkage after combustion – up to 9.5, bulk density is not less than 1.7 g/cm3, compressive strength is not less than 25 MPa, water absorption is not higher than 15, total porosity is not higher than 31, frost resistance by one-side freeze-thaw method 100–115 cycles.