IAEA-TECDOC-1239 Manual of acid in situ leach uranium mining technology August 2001 The originating Section of this publication in the IAEA was: Nuclear Fuel Cycle and Materials Section International Atomic Energy Agency Wagramer Strasse 5 P.O. Box 100 A-1400 Vienna, Austria MANUAL OF ACID IN SITU LEACH URANIUM MINING TECHNOLOGY IAEA, VIENNA, 2001 IAEA-TECDOC-1239 ISSN 1011–4289 © IAEA, 2001 Printed by the IAEA in Austria August 2001 FOREWORD An important part of the IAEA programme for reactor fuels involves eliciting and circulating information on innovative uranium production technologies. As compared with conventional mining, in situ leach (ISL) technology is both innovative and relatively young. It is recognized as having economic and environmental advantages when properly employed by knowledgeable specialists to extract uranium from suitable sandstone type deposits. In recent years ISL uranium mining has been producing about 13 to 15 per cent of world output. Because of its potential for both low cost recovery and having environmental advantages, the use of the technology will very probably increase. This may occur because sandstone hosted uranium deposits amenable to ISL recovery are relatively widespread in the world. ISL technology recovers uranium using two alternative chemical leaching systems — acid and alkaline. Acid leach is the more widely employed and has historically produced a majority of the world’s ISL production. This technology, with its origins in the 1960s, was developed and employed in the former Soviet Union and the successor states, as well as in central and eastern Europe. The report describes operational practices developed under the economic systems, together with the governmental policies and programmes prevailing over this period. The United States of America is the only other country with an extended history of ISL uranium production. In the USA, both acid and alkaline leach systems were tested before alkaline technology was exclusively adopted for environmental reasons. As with all mining technology, any project must be planned, developed, operated and closed, only when appropriate consideration is made for environmental impacts. This report brings together information from several technical disciplines that are an essential part of ISL technology. They include uranium geology, geohydrology, chemistry, as well as reservoir engineering and process engineering, It is not intended as a how to do it manual. However, it does provide insights into many of the considerations related to the technical feasibility of planning, operating and closing ISL uranium mining projects. No comprehensive report exits for either acid or alkaline ISL uranium mining. Furthermore, while there is a significant amount of literature on alkaline leach systems, almost no English language literature is available for acid technology. Therefore this manual is the first report published in English providing an extensive description of acid ISL uranium mining technology. It should also be noted that much of the material may also be of value for planning or operating alkaline ISL projects. The IAEA wishes to thank the consultants who took part in the preparation of this report for their valuable contributions. The IAEA is also grateful to the Member States and individual organizations for their generous support in providing experts to assist in this work. In particular it expresses its appreciation to the staff of the All Russian Research Institute of Chemical Technology for its major contribution. The IAEA officer responsible for this publication was D.H. Underhill of the Division of Nuclear Fuel Cycle and Waste Technology. EDITORIAL NOTE The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA. CONTENTS CHAPTER 1. INTRODUCTION AND THEORY OF IN SITU LEACH (ISL) URANIUM MINING TECHNOLOGY................................................1 1.1. Introduction .......................................................................................................................1 1.2. Geochemical characteristics of ISL sites...........................................................................3 1.3. Reactants — chemistry of leaching ...................................................................................5 1.3.1. General information on reactants...........................................................................5 1.3.2. Chemical reactions in sulphuric acid leaching ......................................................8 1.3.3. Chemical reactions in alkaline leaching ..............................................................10 1.3.4. Criteria for choosing leaching chemistry.............................................................11 1.4. Theoretical background of the uranium ISL process.......................................................12 1.4.1. Principal processes for ISL..................................................................................12 1.4.2. General mechanism of ISL in unconsolidated sedimentary deposits ..................13 1.5. Characteristic features of solution flow in ISL................................................................22 1.5.1. Physical properties of solutions affecting migration in the aquifer; density stratification in the aquifer ......................................................................22 1.5.2. Solution flow with pore plugging........................................................................28 1.5.3. Solution flow with gas formation........................................................................42 1.5.4. Dilution of solutions during leaching ..................................................................46 1.5.5. Lag of production solutions behind flow.............................................................49 References to Chapter 1 ............................................................................................................50 CHAPTER 2. GEOLOGIC AND HYDROGEOLOGIC CONDITIONS FOR IN SITU LEACH (ISL) MINING.................................................................51 2.1. Classification of deposits amenable to ISL mining .........................................................51 2.2. Hydrogeological conditions for ISL ................................................................................56 2.3. Influence of composition of ores and rocks on the ISL process......................................59 2.3.1. General.................................................................................................................59 2.3.2. Influence of mineral composition of ores on the ISL process .............................60 2.3.3. Effect of host rock composition on the ISL process............................................60 2.4. Uranium ores and ore-forming minerals..........................................................................63 2.5. Minerals formed during ISL and their influence on the process .....................................65 References to Chapter 2 ............................................................................................................67 CHAPTER 3. GEOLOGY OF SANDSTONE TYPE URANIUM DEPOSITS..................69 3.1. Lithology and facies of deposits. Classification by lithology and permeability of ore and host rocks...................................................................................69 3.2. Investigation of geochemical features of deposits and epigenetic alteration...................72 3.3. Study of the morphology of ore bodies and parameters of uranium mineralization .......73 3.3.1. Orebody morphology...........................................................................................73 3.3.2. Mapping uranium mineralization ........................................................................76 3.4. Study of the composition of ores and host rocks.............................................................80 3.5. Exploration for uranium deposits for ISL........................................................................86 3.5.1. Exploring and delineating uranium deposits for ISL extraction..........................86 3.5.2. Parameters for resource evaluation for ISL extraction ........................................88 3.6. Geophysical studies used in uranium ISL........................................................................91 3.6.1. General.................................................................................................................91 3.6.2. Investigations of ore and host rocks using logging methods ...............................94 3.6.3. Surveying drift, drill hole diameter and geothermal characteristics of measurements ..........................................................................94 References to Chapter 3 ............................................................................................................95 Bibliography to Chapter 3.........................................................................................................95 CHAPTER 4. HYDROGEOLOGICAL EVALUATION OF URANIUM DEPOSITS................................................................................97