Effective Use of Platinum Group Metals and Alloys

Abstract

1. 白金族金属の埋蔵量と生産量 白金族金属は、白金（Pt） 、パラジウム（Pd） 、ロジウ ム（Rh） 、ルテニウム（Ru） 、イリジウム（Ir） 、オスミウ ム（Os）の 6種類の金属の総称である。これら 6種類の金 属は、周期律表の 8族に属し、鉄、コバルト、ニッケルの 下に位置する。周期律表のパラジウム、白金の右には銀と 金が存在し、白金族金属と金、銀を総称して貴金属と呼ぶ。 白金族金属の中で、オスミウムは酸素と反応しやすく、生 成する酸化物が有毒であるため、工業的にはあまり使われ ていない。本稿では、オスミウムを除いた 5種類の白金族 金属について解説する。 Fig. 1に 2010年の白金およびパラジウムの主要生産国を 示す 1） 。白金の 76%が南アフリカで生産されており、隣国 のジンバブエからも 5%生産されている。両者を合わせる と白金の 81%がアフリカに偏在していることがわかる。南 アフリカにはブッシュベルトと呼ばれる東西 400km、南 北 300kmもある広大な領域を取り囲むように白金やパラ ジウムを主体とする 20km幅の鉱床が存在する 2） 。この地 域は、隕石に関連した特異なマグマが、非常にゆっくり冷 却されることにより、厚さ数 10cmから数 mの層状に白金 Synopsis: Objective. Platinum group metals (PGMs) have been focused on as typical minor elements. In this paper, the reserves, supply, and demand of PGMs are introduced to clarify the present status of PGMs. Several applications of PGMs are also represented to illustrate their importance in various industries and in daily life and society. Results and Discussion. PGMs have superior physical and chemical properties such as high melting temperatures, good oxidation and corrosion resistance, good catalytic properties, and stability to chemical environments. Thus, PGMs are used in a wide range of application fields such as emission gas purification catalysts in automobiles, catalysts for producing chemical products and for purifying petroleum, electric devices such as magnetic recording materials in hard disks, medical materials, and high-temperature structural and coating materials in the glass and aeronautical industries. On the other hand, the supply of platinum, a representative element of the platinum group metals, is approximately 200 ton per year and PGM resources are concentrated in the Bushveld complex of South Africa, with 75% of PGMs originating from South Africa. The low production and resource concentration in South Africa causes drastic price fluctuations and the unstable supply of PGMs. To maintain a stable supply of PGMs and ensure their effective use, research to extend material life, reduce PGM use, and find alternative materials its being performed. The recycling of PGMs is also very important not only to maintain a stable supply but also to protect the earth from the severe environmental damage caused by mining. The amount of recycling of PGMs has progressively increased since 2004. Conclusions. This paper clarifies the present status of PGMs from the point of view of reserves, supply, demand, and various applications to illustrate their importance in daily life and their problems. To maintain a sustainable and stable supply of PGMs, their reduced use, replacement with alternative materials and recycling are very important.