Potential of Steelmaking Slag as New Phosphorous Resource in terms of Total Materials Requirement

Despite of importance of phosphorous for agricultural food production and for the chemical industry, it is present in nature only as a trace element, and what is worse is that high-quality ores are drastically decreased.It is therefore important to consider the quantity and availability of untapped phosphorous resources. One of the possible candidates would be some steel-making slags because the total amount of phosphorous in such slags in Japan is comparable to the imported amount. Such the slags consist of phosphorous rich (more than 10 mass%) and free phases, the each of which can be separated under the strong magnetic field after pulverization. The separated phosphorous-rich phase is possibly utilized as a new phosphorous resource and the residual matrix can be recycled to iron and steel-making processes as flux.One of authors has proposed the novel evaluation method of recyclability of materials in urban mine in terms of total materials requirement (TMR), that is, the TMR for recycling (urban ore TMR, UO-TMR).In many of industry, phosphoric acid is rather preferable to elemental phosphorous. Thus the aim of this study is to evaluate the quality of phosphoric acid derived from a steel-making slag compared with that from natural ore from the viewpoint of TMR.The TMR of phosphoric acid produced from natural phosphorous ore (NO-TMR) and recycled from a steel-making slag (UO-TMR) using strong static magnetic field were estimated and compared. Furthermore, not only TMRs of phosphoric acid but also those of by-products such as gypsum were estimated as well.As the results of estimation, the NO-TMR of phosphoric acid was estimated to be 6.0~11.8 kg/kg and UO-TMR was 5.6~29.4 kg/kg. The fluctuation is ascribed to utilization efficiency of by-products. These results mean that the steelmaking slag has potential as new phosphorous resource in terms of TMR.TMR can be thought of as the indicator that can evaluate how much mining sites are developed to obtain resources. This means that the degree of self-sufficiency of phosphorous from two resources can be evaluated by analyzing the country-by-country breakdown of TMR for these materials.