纤磷钙铝石类化合物:来自地球具工艺用途的材料(英文)

COMPOUNDS OF THE CRANDALLITE TYPE: MATERIAL FROM THE EARTH ON ITS WAY TO TECHNICAL APPLICATION

纤磷钙铝石类化合物系由自纤磷钙铝石CaAl3 (OH) 6(HPO4) (PO4)本身、经磷钙铝石CaAl3 (OH) 6(SO4) (PO4)到钾明矾石KAl3 (OH ) 6(SO4) 2 等的天然矿物族所组成的。它们表现出具有很大范围的阳离子置换系列 ,其中以Sr2 +和Ba2 +置换Ca2 +,REEs3 +置换Ca2 +和H+,As5 +置换P5 +,S6+/Se6+置换H+P5 +最为重要。随着置换的进行 ,其热动力学稳定性也逐渐增加。由此 ,纤磷钙铝石类化合物成为很能抗风化的矿物 ,在红土中尤其如此。厚的纤磷钙铝石层形成在闪长岩 (富Sr) ,碳酸盐岩 (富REEs)和含金石英脉 (富As)之上 ,从而保护整个磷酸盐红土 ,使之免受风化。以此方式 ,形成了桌状山脉或岛屿 ,他们具有未受覆盖的表面。这些“纤磷钙铝”石化合物为上述及其它元素形成一有效的地球化学障。“纤磷钙铝石”的这种天然地球化学固定作用可以用适当的母体或人工合成晶体来进行模拟 ,即通过金属阳离子交换或就地反应来模拟。这种固定作用还可用于处理天然和人造的放射性裂变产物、有毒的重金属元素、砷酸盐和硒酸盐、硫酸盐等。

Compounds of the crandallite type comprise a natural mineral group reaching from proper crandallite CaAl 3(OH) 6(HPO 4)(PO 4) over woodhouseite CaAl 3(OH) 6(SO 4)(PO 4) to alunite KAl 3(OH) 6(SO 4) 2.They exhibit an extremely wide range of ionic substitutions:Sr 2+ ,Ba 2+ for Ca 2+ ,REEs 3+ for Ca 2+ and H +,As 5+ for P 5+ and S 6+ /Se 6+ for H + + P 5+ are the most important ones.By such substitutions the thermodynamic stabilities are increased and therefore these “crandallites' form very weathering resistant minerals especially in lateritic soils,where sufficient aluminium is available.Thick “crandallitic' layers form on dioritic rocks (Sr),carbonatites (REEs) and gold quartz veins (As) which protect the whole phosphate laterite from weathering.In this way table mountains and islands with an uncovered surface are formed.The “crandallites' form an efficient geochemical barrier for these and other elements.The natural geochemical immobilization of “crandallites' can be imitated by appropriate precursors or/and by synthetic crystals either through ionic exchange or by “in situ' reactions.They can be applied for immobilization of radioactive fission products ,of toxic heavy metals,of arsenate,selenate and sulphate both from natural and artificial sources.