Urban ores can be classified into two types—those made up of items that were in the possession of consumers, such as end-of-life home appliances, and those that were not, such as manufacturing wastes. The dephosphorization slag generated at some steelmaking plants is an example of a manufacturing waste. In this study, the potential for this slag to become a new phosphorous resource is evaluated in terms of total material requirement (TMR). To do this, we compare two types of TMR—natural ore TMR (NO-TMR) and urban ore TMR (UO-TMR)—defined respectively as the TMR to obtain or recycle 1 kilogram of phosphoric acid from natural phosphate ore or dephosphorization slag.
In the dephosphorization slag process, the slag is magnetically separated into a phosphorous-rich (PR) phase and an iron-rich (IR) phase, and the phosphorous in the PR phase is subsequently converted to phosphoric acid. We included case studies that considered generation of potentially useful by-products, such as phosphogypsum and the IR phase. The effect of declines in natural phosphate ore grade on the potential recyclability of phosphoric acid from dephosphorization slag was also explored. In addition, the effect of changes in the slag's contribution to the UO-TMR of phosphoric acid was considered.
We found that, in many scenarios, the UO-TMR for phosphoric acid was lower than its NO-TMR. This indicates that dephosphorization slag has the potential to be a new phosphorous resource. We also found that recycling of the IR phase by recharging it to the blast furnace plays an important role in improving the potential feasibility of slag as a new phosphorous resource. The value of the slag stream, relative to the value of the pig iron stream, is also a key parameter, with low relative values improving the potential for production of phosphoric acid. Evaluating the UO-TMR of materials recovered from manufacturing waste streams promises to be a useful tool for assessing the potential of these waste streams to serve as urban ores.