鉄鋼中に含まれるイオウの重量分析法における硫酸バリウムの形成と溶解

抄録

Sulfur is one of the five ubiquitous elements of steel, and the presence of sulfur reduces the performance of steel. Therefore, the sulfur content in steel must be strictly controlled. This paper focuses on the gravimetric method after separation of iron (JIS G 1215-1) specified in the Japanese Industrial Standards (JIS) as an absolute analysis method for sulfur content in steel. The precipitation formation process of BaSO₄ and the rinse process of the formed precipitate had a major influence on the recovery. In the formation process of BaSO₄, it was confirmed that the precipitation was almost completely formed under the conditions specified in JIS G 1215-1. However, the coexistence of manganese ions (Mn²⁺) significantly reduced the precipitation recovery. Ethylenediaminetetraacetic acid (EDTA) was effective for masking Mn²⁺. In JIS G 1215-1, the BaSO₄ formed is rinsed in two steps: first, barium chloride solution (BaCl₂) is used to remove foreign substances, followed by hot water to remove the BaCl₂. Mn²⁺ not only inhibited the precipitation of BaSO₄ but also reduced the recovery during rinsing with hot water. Sulfur recovery in the entire JIS G 1215-1 process exceeded 100 % regardless of the addition of EDTA. This indicates loss of sulfur during the precipitation process much less contributed the recovery of sulfur in the total process of JIS G 1215-1.