Burnett W C, Elzerman A W
Environmental Radioactivity Measurement Facility, Department of Oceanography, Florida State University, Tallahassee, FL 32308, USA.
J Environ Radioact. 2001;54(1):27-51. doi: 10.1016/s0265-931x(00)00164-8.
Phosphogypsum, a waste by-product derived from the wet process production of phosphoric acid, represents one of the most serious problems facing the phosphate industry in Florida today. This by-product gypsum precipitates during the reaction of sulfuric acid with phosphate rock and is stored at a rate of about 40 million tons per year on several stacks in central and northern Florida. The main problem associated with this material concerns the relatively high levels of natural uranium-series radionuclides and other impurities which could have an impact on the environment and prevent its commercial use. We have studied the potential release of radionuclides from phosphogypsum by: (i) analysis of stack fluids, groundwaters, and soils associated with gypsum stacks; and (ii) geochemical modeling. Stack fluids were observed to be very high in dissolved uranium and 210Pb with only moderate concentrations of 226Ra. Underlying soils tend to be enriched in U and 210Pb indicating precipitation when acidic stack fluids enter a buffered environment. Modeling results showed significant increases in radionuclide complexes with sulfate and phosphate, resulting in relatively mobile uncharged or negatively charged solution species within the stacks with likely precipitation of multicomponent solids with increasing pH below the stack. Our evidence thus suggests that, while phosphogypsum stacks do contain significant quantities of dissolved radionuclides, removal mechanisms appear to prevent large-scale migration of radionuclides to the underlying aquifer.
磷石膏是湿法生产磷酸过程中产生的一种废弃物副产品，是当今佛罗里达州磷酸盐工业面临的最严重问题之一。这种副产品石膏在硫酸与磷矿石的反应过程中沉淀下来，每年以约4000万吨的速度储存在佛罗里达州中部和北部的几个堆场中。与这种物质相关的主要问题是天然铀系放射性核素和其他杂质的含量相对较高，这可能会对环境产生影响并阻碍其商业用途。我们通过以下方式研究了磷石膏中放射性核素的潜在释放情况：（i）分析与石膏堆场相关的堆体渗滤液、地下水和土壤；（ii）进行地球化学建模。观察到堆体渗滤液中的溶解铀和210Pb含量非常高，而226Ra的浓度仅为中等水平。下层土壤往往富含铀和210Pb，这表明当酸性堆体渗滤液进入缓冲环境时会发生沉淀。建模结果表明，放射性核素与硫酸盐和磷酸盐的络合物显著增加，导致堆体内相对易迁移的不带电荷或带负电荷的溶液物种增加，随着堆体下方pH值升高，可能会形成多组分固体沉淀。因此，我们的证据表明，虽然磷石膏堆场确实含有大量溶解的放射性核素，但去除机制似乎可以防止放射性核素大规模迁移到下层含水层。
