Addition of chemical agents to inhibit the CaCO3 precipitation process is a potential way to solve the blocking problem in the industrial in situ leaching process for uranium recovery. This research investigated the role of P(V) added as sodium hexametaphosphate ((NaPO3)6), anhydrous sodium pyrophosphate (Na4P2O7), and sodium tripolyphosphate (Na5P3O10) as inhibitors for the precipitation of CaCO3 in supersaturated solutions of Ca2+ and HCO3−. The results indicated that the three inhibitors prevented the formation and growth of CaCO3 and Na5P3O10 showed the best performance. In the aqueous phase Ca2+ coordinated with P(V) ions to form complex anions of Ca-phosphates including CaHP2O7—, CaP2O72−, CaHP3O102−, and CaP3O103−. The role of P(V) as an inhibitor was attributed to the adsorption of P(V) species including CaP complex anions and phosphate anions on the calcite surface to form an amorphous protective layer which prevented further precipitation of CaCO3 phase. Moreover, dosage threshold of Na5P3O10 was experimentally determined to be 2 mg/L. This dosage gave a CaCO3 precipitation inhibition efficiency higher than 90 %. Injection of inhibitors had no negative effect on the in situ leaching of uranium by CO2 and O2 and subsequent ion exchange adsorption process for uranium recovery.

中文翻译：

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P（V） 盐在使用 CO2 和 O2 的铀原位浸出过程中抑制 CaCO3 沉淀的作用


添加化学试剂以抑制 CaCO3 沉淀过程是解决工业原位浸出铀回收过程中阻塞问题的潜在方法。本研究研究了添加为六偏磷酸钠 （（NaPO3）6）、无水焦磷酸钠 （Na4P2O7） 和三聚磷酸钠 （Na5P3O10） 作为抑制剂在 Ca2+ 和 HCO3− 过饱和溶液中沉淀 CaCO3 的作用。结果表明，3 种抑制剂阻止了 CaCO3 的形成和生长，其中 Na5P3O10 表现出最佳性能。在水相中，Ca2+ 与 P（V） 离子配位形成 Ca-磷酸盐的复合阴离子，包括 CaHP2O7—、CaP2O72−、CaHP3O102− 和 CaP3O103−。P（V） 作为抑制剂的作用归因于 P（V） 物质（包括 CaP 络合阴离子和磷酸阴离子）在方解石表面的吸附，形成无定形保护层，阻止 CaCO3 相进一步沉淀。此外，实验确定 Na5P3O10 的剂量阈值为 2 mg/L。该剂量使 CaCO3 沉淀抑制效率高于 90 %。注入抑制剂对 CO2 和 O2 对铀的原位浸出以及随后的离子交换吸附过程没有负面影响以回收铀。