# 【8.2 参考资料 15】The 28th Japan-Korea International Seminar on Ceramics, GO-O-15, 2011 年 11 月, Okayama.

# Phosphorus recovery process from iron- and steel-making slag

Hiroki KAWANISHI $ ^{1} $ , Shinichi SAKIDA $ ^{2} $ , Yasuhiko BENINO $ ^{1} $ and Tokuro NANBA $ ^{1,*} $

$ ^{1} $ Graduate School of Environmental Science, Okayama University

$ ^{2} $ Environmental Management Center, Okayama University

Okayama, 700-8530, Japan

$ ^{*} $ tokuro_n@cc.okayama-u.ac.jp

Keywords: Iron and steel slag, Glass, Phosphorus, Recovery, Recycling

### 1. Introduction

Phosphorus has been widely used in fertilizer, food additive, medicine, and agrichemical, and Japan relies on imports for 100% of phosphorus resources. Recent years, the demand for phosphorus is increasing in a global trend because of population increase. Phosphorus is, however, produced only in the limited countries, such as America, Morocco, and China, and these countries are reducing the exports, which has caused an increase in the price. Thus, the securing of phosphorus resources has become an urgent need for Japan.

Iron- and steel-making slags discharged from the processes of iron manufacture contain small amounts of phosphorus. The total amount of phosphorus contained in Iron- and steel-making slags corresponds to 85% of phosphorus present in the phosphate rock imported $ [1] $ . Various phosphorus recovery processes have been proposed so far. In the authors' research group, chemical recycling process of valuable elements present in inorganic wastes such as granulated blast furnace slag $ [2] $ and municipal waste slag $ [3] $ has been developed by using phase separation of glass. In the present study, the process has been applied to iron- and steel-making slag to examine the possibility of phosphorus recovery.

### 2. Experimental procedures

In this study a dephosphorization slag discharged from an ironworks in Okayama prefecture was used. The chemical composition of the slag is 18.1 mass% $ SiO_{2} $ , 25.0 mass% $ Fe_{2}O_{3} $ , 44.0 mass% CaO, 4.3 mass% $ Al_{2}O_{3} $ , 3.4 mass% MgO, 2.8 mass% MnO, and 1.6 mass% $ P_{2}O_{5} $ . $ SiO_{2} $ and/or $ B_{2}O_{3} $ were added to the slag and the mixture was melted in an alumina crucible at 1500°C for 1 hour. The melt was quenched, obtaining glass. Expecting phase separation, the sample was heat-treated under various conditions. The heat-treated samples were soaked in various solutions, such as acidic, basic and neutral water solutions for 24 hours. The chemical compositions of residual solids not-solved to solution and elutes were determined with X-ray fluorescent (XRF) and inductively-coupled plasma emission (ICP) analyses, respectively. Based on the results, the recovery of phosphorus from dephosphorization slag was considered.

### 3. Result and Discussion

In the case of $ SiO_{2} $ addition, glasses were obtained when $ SiO_{2} $ content was higher than 30 mol%, and when $ SiO_{2} $ content was smaller than 30 mol%, a crystalline phase of Magnesioferrite, $ (\mathrm{Mg}_{0.3}\mathrm{Fe}_{0.7})(\mathrm{Mg}_{0.73}\mathrm{Fe}_{1.27})\mathrm{O}_{4} $ was observed.

Figures 2 shows the SEM photographs of the slag glasses prepared by adding $ SiO_{2} $ and $ B_{2}O_{3} $ , in

Fig. 1 Schematic flow of phosphorous recovery process