<p>Steel slag, a major byproduct of the steel industry, poses a significant environmental challenge due to its low utilization rate and the risk of heavy metal leaching. Nevertheless, it is also a valuable reservoir of critical elements, such as calcium, phosphorus, and vanadium. This review provides a critical and comprehensive analysis of hydrometallurgical pathways to unlock the potential of steel slag as a secondary resource. We systematically evaluate conventional leaching methods (including acid, alkaline, and ammonium salt leaching) detailing their mechanisms, efficiencies, and environmental trade-offs. Beyond established techniques, the review explores emerging technologies, such as ultrasonic-assisted, microwave-assisted, and high-pressure leaching, which offer enhanced kinetics and a greener footprint. By synthesizing a vast body of literature, this work establishes a clear comparative framework based on operational parameters and extraction performance. Finally, we outline the pressing challenges and prospects, emphasizing the imperative for integrated approaches that advance the steel industry toward a circular economy. This review serves as a strategic guide for researchers and engineers aiming to transform steel slag from a waste liability into a valuable asset.</p>