Use of residual materials for synthesis of lightweight granulates by thermal treatment process

• We studied the isothermal behaviour of various residual materials up to 1200 °C.
• Mixtures of kaolin waste, sewage sludge, schist and wasted glass were formulated.
• Thermal synthesis of lightweight granulates of various mixtures was performed.
• Lightweight materials synthesis is an alternative route for kaolin waste minimization.

The general scope of this paper is to explore the formulation and the production, by thermochemical transformations, of expanded lightweight granulates incorporating residual materials as kaolinitic waste, sewage sludge, schist fines and wasted glass. The possible application fields are light concretes, road engineering, water treatment and hydroponic agriculture. The benefits can be multiple: creation of new resources from wastes; preservation of primary resources; humid zones on the river banks and the natural course of rivers; management of hazardous residual materials.Tests on the thermal treatment and the thermochemical expansion were conducted in horizontal experimental set-up including a static electrical furnace. Raw material mixtures and treatment products were examined by visible microscopy, scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), X-ray diffraction (XRD) and infrared spectroscopy (IR) in order to understand the thermal behaviours of the chosen samples. Data analysis of the experimental results showed the possibility of obtaining the expanded granulates at temperatures lower than or equal to 1100 °C for a firing time of a few minutes. The optimal temperature for their synthesis is a function of fluxes content and decreased significantly with increase of the wasted glass amount. Obtained granulates have a density lower than unity and they have good mechanical strength fulfilling the conditions for their use as building materials.Sewage sludge, wasted glass as well as incinerator ashes can be used as alternative materials, among other industrial solid wastes, in the formulation of lightweight clay and schist based granulates. Results of this work try to meet the principles of sustainable mining and decreased pressure on the environment.