Abstract
<title>Abstract</title> <p>With the increasing stringency of environmental regulations, the efficient reclamation of used clay-bonded sand has become a crucial pathway for the sustainable development of the foundry industry. Traditional reclamation processes, which combine high-temperature roasting with mechanical attrition, suffer from prominent issues such as high energy consumption and long processing cycles. To address these challenges, this paper proposes a novel low-temperature and rapid reclamation method for used clay-bonded sand based on catalytic oxidation with potassium nitrate (KNO₃). This method leverages the property of potassium nitrate to release active oxygen upon thermal decomposition. By introducing it as an additive during the roasting process of used clay-bonded sand, the aim is to enhance oxygen mass transfer, thereby promoting the low-temperature oxidative combustion of coal powder components within the clay film coating the sand grains. Experimental results demonstrate that the complete thermal decomposition temperature of coal powder in the used sand is significantly lowered, and the heat treatment time is considerably shortened. The mechanisms by which the additive facilitates oxygen transfer and catalyzes low-temperature decomposition are further elucidated. Under optimized process conditions (KNO₃ concentration of 6%, addition amount of 4%, roasting temperature of 550°C, and roasting time of 30 min), the reclaimed sand exhibits an acid demand value below 5 mL, electrical conductivity below 100 µS/cm, loss on ignition ≤ 0.05%, and the shattering rate decreases from 14.6% for the original used sand to below 3%. These properties fully meet the requirements for cold-box core making processes, enabling the reuse of waste foundry sand, offering an efficient, economical, and feasible pathway for the green and low-carbon transformation of the foundry industry.</p>