Preparation of recycled sand from excavated soil based on microwave drying technology: Experiment and energy consumption analysis

The treatment of excavated soil using the dry sieving method to produce recycled sand is an effective approach for resource utilization. Currently, the hot-air drying process used in this method exhibits high energy consumption. To address this issue, this study proposes a microwave drying technology to dry the excavated soil. Comparative experiments on microwave (1–6 kW) and hot-air (105–205 °C) drying of the excavated soil were conducted. The drying behavior and specific energy consumption of the excavated soil were investigated. The Weibull–Fick combined method was recommended for the segmental determination of the effective moisture diffusion coefficient, and the question of whether microwave drying adversely affects sand particles in the excavated soil was answered. The results revealed the following: Compared with hot-air drying, microwave drying demonstrated shorter drying time (3.5–38 min vs 75–1200 min), lower specific energy consumption (6.2–11.5 MJ/kg vs 22.3–55.4 MJ/kg), and a higher range of effective moisture diffusion coefficient (10⁻⁸–10⁻⁷ m²/s vs 10⁻⁹–10⁻⁸ m²/s). With increasing microwave power (3–6 kW), the time required for complete drying of the sample was reduced by up to 56 %. Under microwave drying, relaxing the termination moisture content criterion from 0 to 0.01 resulted in a 17 %–32 % reduction in specific energy consumption, accompanied by a 24 %–36 % decrease in drying time. Microwave drying did not damage sand particles within the excavated soil.