KEY FACTORS FOR THE SEPARATION OF SILICON AND IRON DURING PHOSPHORUS RECOVERY FROM SLAG DISCHARGED FROM THE DOUBLE-SLAG REFINING PROCESS

In the present study, we developed a technology for concentrating and recovering phosphorus from slag-like phosphorus-containing unused resources and applied it to slag discharged during the latest steelmaking process, that is, double-slag refining process (DRP). The technology we developed consists of the following four processes: Process (1) is the initial acid elution; Process (2) involves alkali precipitation; Process (3) is the second acid elution; and, Process (4) utilizes ion-exchange. In Process (1), the addition of DPR slag to 0.5 M of a nitric acid solution for 24 min resulted in sufficient phosphorus dissolution. In Process (2), ammonia was added to the dissolved solution, and phosphorus was precipitated with high efficiency. The timing of the addition of ammonia significantly influenced the removal of silicon and iron, which would have been inconvenient to accomplish in subsequent processes. In Process (3), the precipitation obtained in Process (2) was re-dissolved in a nitric acid solution. The dissolution of phosphorus together with other elements progressed sufficiently, and we confirmed that silicon could be completely separated as silica by using high-concentration nitric acid at this stage. The fact that silicon could be removed during Process (3) was an important finding, since silicon could not have been separated in the Process (4). In Process (4), by passing the phosphorus-containing solution obtained in Process (3) through an ion exchange resin, elements other than phosphorus and silicon could be removed, which confirms that the range of applications for this technology could be expanded.