Review on high-value utilization of phosphogypsum: Utilization of calcium and oxygen resources present in phosphogypusm

The world's annual production of phosphogypsum (PG) is up to 200 million tons at present. It was found that 15 % of PG produced worldwide is recycled. Therefore, it is imperative to seek a new pathway to recycle PG. This work provides an overview of the state-of-the-art scheme for high-value utilization of PG. Compared with previously published works, this review focuses on the utilization of oxygen (O) and calcium (Ca) resources. The state-of-the-art technology of utilizing O in PG consists of lignite's chemical looping gasification (CLG) with PGbased oxygen carrier. The state-of-the-art technology for utilizing Ca in PG is the low-temperature decomposition of PG for producing CaO and CaCO3 from the reductive decomposition of PG. The process and the reaction mechanism of state-of-the-art technology for application of O and Ca in PG are summarized. Based on current research status, it is suggested to apply two or more solid wastes in cement, bricks and other aspects of largescale. When utilizing PG, the migration transformation of impurities in PG and their reaction mechanisms at the molecular level deserve to be focused on. The key to solving the problems caused by PG large consumption, high value-added utilization and the introduction of policies providing incentives to this end. This research provides guidance for new engineering techniques for PG to achieve high-value and efficient use of resources in the large-scale utilisation of PG.