Study on durability characteristics of solidified sediment in semi-dynamic acid soaking environment

Abstract

In order to achieve the goal of resource utilization of Municipal Solid Waste Incineration (MSWI) fly ash and sediment, the MSWI fly ash and cement are used to solidify sediment as the intermediate cover material in landfill. The engineering properties and evolution of durability characteristics of solidified sediment were studied under semi-dynamic immersion of acid rain and acid leachate simulated by hydrochloric acid by unconfined compressive strength (UCS), direct shear (DS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) tests. The results show that the UCS strength increases with the increase of curing age and the cement content. Strong acid environment (pH = 2) degrades the service performance of the solidified sediment, resulting in secondary slime of the sample leading to reduction in UCS strength, mass, and increase in moisture content. However, weak acidity environment (pH = 4) and neutral environment (pH = 7) lead to increase in UCS strength, stabilization of mass and moisture, and improvement of service performance of the solidified sediment. The main hydration products calcium silicate hydrate (C-S-H), carbonate and calcium sulfate facilitates the development of strength and acid buffering capacity of the solidified sediment. Under soaking in semi-dynamic simulation of acid erosion, the solidified sediment exhibits satisfactory durability. As the intermediate covering material of landfill, it can not only better buffer acid rain and leachate erosion, effectively block the contact between garbage and acid rain, leachate and the ground, reduce the impact on urban climate, but also use MSWI fly ash to replace part of the cement to reduce the use of cement, reduce CO₂ and dust emissions in the production process, with good environmental benefits.