Immobilization enhancement of heavy metals in lightweight aggregate by component regulation of multi-source solid waste

Abstract

Integrated recycling of solid waste containing heavy metals is a critical environmental challenge. In this study, a green solution to reduce heavy metal leaching from solid waste is demonstrated by combining contaminated soil, industrial sludge and lithium slag in pairs to produce lightweight aggregates (LWAs). The physical properties and heavy metal leaching behavior of LWA samples were systematically investigated and characterized. The results showed that industrial sludge reduced the density and water absorption of LWA, while the high content of lithium slag was detrimental to the physical properties. LWA containing 80% contaminated soil and 20% lithium slag had the lowest particle density of 1.47 g/cm³ due to the hollow structure caused by the low viscosity and violent generation of SO₂. LWAs with lithium slag leached excessive Cu and Cr relatively, while heavy metals were immobilized well in LWAs with contaminated soil and industrial sludge as the main components. Because the flux components of industrial sludge could enhance the encapsulation of heavy metals by glass phase. In addition, the co-immobilization of multiple heavy metals was observed in the spinel phase. This study provides an efficient and safe method for the synergistic recycling of solid waste.

Keywords: Heavy metal; Hollow structure; Immobilization; Lightweight aggregate; Solid waste; Thermal treatments.