Here, "phosphorus pentoxide, off-spec" refers to phosphorus pentoxide product that, during the production or refining of phosphorus pentoxide, is judged non-conforming because its purity, particle size, moisture content or other quality indicators fail to meet the product technical requirements. Although such off-spec material no longer meets the usage standard of the original commodity, it still possesses relatively high chemical reactivity and resource value; after recovery, reprocessing or re-refining, it can be reused as a chemical raw material or enter the relevant production processes to achieve resource recovery.