Lightweight ceramsite made of recycled waste coal gangue & municipal sludge: Particular heavy metals, physical performance and human health.

Large amounts of coal gangue and municipal sludge are generated from coal mining and municipal sewage. Some scholars have studied their use in ceramics, concrete, land reclamation and so on. However, in current study, heavy metals in coal gangue and municipal sludge in utilization have not been safely controlled, and there are potential risks to the ecological environment and human health. Therefore, this study systematically investigated the basic physical and chemical properties of coal gangue and municipal sludge samples, the ecological environment safety risk of heavy metals and other harmful substances (soluble phosphorus and fluorine). The results showed that the main compositions of coal gangue and municipal sludge samples were cristobalite, hematite and anorthite, which can be used as raw material for ceramsite preparation. The characteristic heavy metals in coal gangue and municipal sludge were As, Cd, Cu, Ni and Zn, which had certain environmental risks. When the optimum proportion of coal gangue: sludge = 70: 30, adding clay and blowing agent as auxiliary materials to make ceramsite, its properties, including bulk density, cylinder pressure strength and other physical properties, meet the Chinese standard "light aggregate and its test method" (GB/T 17431). The heavy metal environment and human health assessment model of the product was constructed, in which the risk assessment results are, that the content of characteristic heavy metals in ceramsite was significantly reduced, and this content conformed to the requirements of heavy metals in the Chinese standard "technical specification of cement kiln cooperative disposal of solid waste" (GB/T 30760), riskless to the human body and external environment. The compressive strength of the two kinds of ceramsite concrete can reach LC35, and the density grade was 1400–1650 N/m3, which meets the requirements of Chinese standard "technical specification for lightweight aggregate concrete" (JGJ 51). All the properties of this product meet the corresponding standards and there was no risk to the external environment, to provide theoretical guidance for the harmless and resource utilization of urban sludge and coal gangue. [ABSTRACT FROM AUTHOR]