The Florida Institute of Phosphate Research was created in 1978 by the Florida Legislature (Chapter 378.101, Florida Statutes) and empowered to conduct research supportive to the responsible development of the state’s phosphate resources. The Institute has targeted areas of research responsibility. These are: reclamation alternatives in mining and processing, including wetlands reclamation, phosphogypsum storage areas and phosphatic clay containment areas; methods for more efficient, economical and environmentally balanced phosphate recovery and processing; disposal and utilization of phosphatic clay; and environmental effects involving the health and welfare of the people, including those effects related to radiation and water consumption. FIPR is located in Polk County, in the heart of the central Florida phosphate district. The Institute seeks to serve as an information center on phosphate-related topics and welcomes information requests made in person, by mail, or by telephone. Research Staff Executive Director Richard F. McFarlin Research Directors G. Michael Lloyd Jr. -Chemical Processing Jinrong P. Zhang -Mining & Beneficiation Steven G. Richardson -Reclamation Gordon D. Nifong -Environmental Services Florida Institute of Phosphate Research 1855 West Main Street Bartow, Florida 33830 (863) 534-7160 Fax:(863) 534-7165 FINAL REPORT William C. Burnett, James B. Cowart, and Paul LaRock Principal Investigators and Carter D. Hull Research Associate with Zigeng Zhang, Jennifer Cherrier, Peter Cable, and Geoffrey Schaefer FLORIDA STATE UNIVERSITY Tallahassee, Florida 32306 Prepared for FLORIDA INSTITUTE OF PHOSPHATE RESEARCH 1855 West Main Street Bartow, Florida 33830 Contract Manager: Gordon D. Nifong May, 1995 DISCLAIMER The contents of this report are reproduced herein as received from the contractor. The opinions, findings and conclusions expressed herein are not necessarily those of the Florida Institute of Phosphate Research, nor does mention of company names or products constitute endorsement by the Florida Institute of Phosphate Research. ii PERSPECTIVE Gordon D. Nifong, Ph. D. Florida Institute of Phosphate Research Since its inception more than fifteen years ago, the Florida Institute of Phosphate Research has stressed research in the environmental aspects of phosphate mining and processing. Included in that emphasis has been the health and safety of industry employees and also the public that live in the vicinity of the industry or who are otherwise affected by its operations. The legislation that created the Institute empowered it in a first directive to conduct or sponsor environmental studies as may be necessary for the health, safety, and welfare of Florida's citizens, especially those in the phosphate region. This directive has been heeded closely in the Institute's mission, as most recently described in the 1995 publication "Strategic Initiatives and Applied Research Priorities." It is recognized that protection of the public health and of the environment are implicit goals of all Institute research, but also there are areas of special interest, including air and water pollution, natural radiation, indoor radon, land reclamation, and the handling and storage (and possible use) of by-product phosphogypsum. Although these areas overlap somewhat, it is the gypsum issue that this current project most directly addresses. Naturally occurring radioactive materials are ubiquitous over all the earth, but are elevated above background in phosphate minerals. Chemically processing phosphate rock into phosphoric acid and phosphogypsum partitions the radionuclides present in the ore in such a way that most radium, and hence its decay products radon, polonium and lead, remain with the gypsum, while uranium and thorium remain with the acid. Largely because of this elevated level of natural radioactivity, little use for phosphogypsum has been found, and indeed the U. S. Environmental Protection Agency currently bans most use and instead requires the material to be left in storage at the plant site. About 700 million tons are currently stockpiled in Florida. Thus over the years the Institute has funded much phosphogypsum research, including the effects of leaving it in storage, and the effects of using it in agriculture, in construction, and in the recovery of sulfur. More recently the risks to health and the environment of using phosphogypsum versus the risks of storing it have been emphasized, along with technical and economic considerations of each alternative. iii This study by investigators at Florida State University addresses the gypsum issue in four ways. A first topic is an expanded characterization of radionuclides present in the material. Part two explores the actual sites in the gypsum where the nuclides are concentrated, a first step in any purification process. A third section examines the impact on near-by groundwater of phosphogypsum storage. Finally any relation between the nuclides, mainly polonium, and certain bacteria, mainly those involved in sulfur cycling, was explored for any potential of using bacteria to release radionuclides from the gypsum or to remove them from process waters. iv MICROBIOLOGY AND RADIOCHEMISTRY OF PHOSPHOGYPSUM EXECUTIVE SUMMARY 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 today. This by-product gypsum precipitates during the reaction of sulfuric acid with phosphate rock and is stored at a rate of about 30 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 impact the environment and which makes its commercial use impossible. Our general approach to this problem was to start the task of detailing exactly where and how radionuclides are hosted within the material. In this way, it is hoped that ultimately one may develop purification schemes for this waste material. Our experimental approaches for characterizing the radiochemistry and microbiology of Florida phosphogypsum has been directed along four specific lines of research. One component of this study involved detailed analyses of the same radionuclides in the phosphate ore rocks and the phosphogypsum. Another component includes preliminary investigations of radionuclides in shallow groundwaters collected from a limited number of monitor wells adjacent to gypsum stacks. The majority of research in the third component of this study involves dissolution and leaching studies of the phosphogypsum and developing techniques to isolate and concentrate specific radionuclides from the phosphogypsum matrix. The ultimate goal of this line of research was to identify the actual sites occupied by individual nuclides and how they are bound in the phosphogypsum. The final research component concerned microbiological studies which endeavored to identify and culture bacteria that either show the ability to release radionuclides from phosphogypsum or have promise of scavenging radionuclides from fluids that are associated with the material. The microbiological research was focused on microbes which metabolize Po and may play a role in the solubility and mobility of Po (and perhaps other radionuclides) in solutions circulating in and through gypsum stacks. This Final Report presents data and discussion of these efforts which have been made since the study was initiated in 1992. The report is organized to show how these V research topics were addressed: Chapter 1 presents general radiological data for phosphate ore rock, phosphogypsum that has been stored on gypsum stacks for various times, and water samples from monitor wells adjacent to phosphogypsum storage areas in Florida. The primary objective of the research described in this chapter was to radiochemically characterize and provide a comprehensive data base of uranium-series nuclides in Florida phosphogypsum and ore rocks. By evaluating all significant nuclides, including ‘**6Ra, *lol?b, and *lol?o in pairs of ore rock feed materials and phosphogypsum , sufficient data were obtained to describe fractionations between the various members of the *38U decay chain during processing. A thorough sampling of phosphogypsum of various ages stored in Florida has also been completed in order to assess whether some radioelements migrate preferentially to others during storage. The actual location of uranium-series radionuclides within phosphogypsum was investigated in more detail in Chapter 2 by several different approaches. The hope here was that if the actual sites within the phosphogypsum that host radionuclides could be identified, this may represent a first step towards radiochemical purification of this material. In this way, a waste material that may potentially contaminate the environment could ultimately be put to some good use. The material presented in Chapter 2 is an extension of the broad-based radiochemical research presented in Chapter 1. We describe methods that have been investigated for fractionating, concentrating, and leaching radionuclides from Florida phosphogypsum by both physical and chemical methods. Our results show that the behavior of radium, and other radionuclides, is often sample dependent, i.e., there are significant differences in the solubility of radionuclides for different samples. In general, about 10-50% of the radium in Florida phosphogypsum is water soluble, although