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Phosphogypsum refers to the gypsum formed as a by-product of the production of fertilizer from phosphate rock. It is mainly composed of gypsum (CaSO4·2H2O). Although gypsum is a widely used material in the construction industry, phosphogypsum is usually not used, but is stored indefinitely because of its weak radioactivity. The long range storage is controversial.〔Ayres, R. U., Holmberg, J., Andersson, B., "Materials and the global environment: Waste mining in the 21st century", MRS Bull. 2001, 26, 477. 〕 ==Production== Phosphogypsum is a side-product from the production of phosphoric acid by treating phosphate ore (apatite) with sulfuric acid according to the following reaction: :Ca5(PO4)3X + 5 H2SO4 + 10 H2O → 3 H3PO4 + 5 CaSO4 · 2 H2O + HX :where X may include OH, F, Cl, or Br Phosphogypsum is radioactive due to the presence of naturally occurring uranium and thorium. Marine-deposited phosphate typically has a higher level of radioactivity than igneous phosphate deposits, because uranium is present in seawater. Phosphogypsum also can contain high levels of cadmium.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「phosphogypsum」の詳細全文を読む スポンサード リンク
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