CHAPTER 10 URANIUM PRODUCTION METHODS AND ECONOMIC CONSIDERATIONS

• Jurisdiction: United States

Uranium Exploration and Development
(Nov 1976)
CHAPTER 10
URANIUM PRODUCTION METHODS AND ECONOMIC CONSIDERATIONS
Douglas J. Lootens
Dames G. Moore
Park Ridge, Illinois

TABLE OF CONTENTS

SYNOPSIS

INTRODUCTION

PRODUCTION OF URANIUM OXIDE (YELLOWCAKE)

Basic Mining Concepts

Open-Pit Versus Underground Mining

Open-Pit Mining

Underground Mining

Basic Processing Techniques

Solution Mining

ECONOMIC CONSIDERATIONS

Capital Costs

Operating Costs

Solution Mining

NOVEL URANIUM RECOVERY SYSTEMS

Uranium in Copper Deposits

Uranium in Phosphate Deposits

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LIST OF TABLES AND PLATES

Table 10-1	Comparison of Major Process Stages of Typical Uranium Mine-Mill Complexes and Solution Mining
Table 10-2	Capital Cost Estimate Summary — Hypothetical Uranium Processing Operations — New Mexico and Wyoming
Table 10-3	Capital Investment Estimate for Surface Mine Plant — New Mexico
Table 10-4	Estimated Capital Requirements for Stripping & Ore Mining Fleets — New Mexico
Table 10-5	Uranium Ore Processing — Mill Capital Construction Cost Estimates
Table 10-6	Operating Cost Estimate Summary — Hypothetical Uranium Processing Operations — New Mexico and Wyoming
Table 10-7	Estimated Cost Summary — New Mexico Open-Pit Uranium Mine
Table 10-8	Solution Mining System Capital Costs — 750,000 lbs. U3O8 Annually
Table 10-9	Solution Mining System Operating Costs — 750,000 lbs. U3O8 Annually
Figure 10-1	Schematic Diagram of the Uranium Production Cycle
Figure 10-2	Cross Section of a Typical Open-Pit Mine
Figure 10-3	Plan of a Hypothetical Underground Mine
Figure 10-4	Basic Uranium Processing Steps
Figure 10-5	Yellowcake Production Cost
Figure 10-6	Hypothetical Cross-Section of a Solution Mining System

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INTRODUCTION

I'd like to thank you for the opportunity to speak to you this morning on the very practical matter of actually producing uranium. During the course of this meeting we have been looking at various elements related to uranium development. In a sense, all of these elements: claim location, mining titles, exploration permits, joint venture arrangements, exploration programs and the like are a necessary prologue to the main event, namely, mining and processing of uranium ore to produce uranium oxide or yellowcake, the primary saleable commodity of the uranium industry.

Yesterday, Jim Davis described to you how uranium deposits are identified and evaluated. I'd like to pick up the thread of his story and look at what happens after a presumably economic deposit has been delineated. I say "presumably" because, until detailed engineering and economic feasibility studies have been carried out, it is often not possible to determine whether a given deposit is, in fact, economic. We cannot arbitrarily say that a reserve of one million pounds, contained in a deposit whose average grade is 0.2 percent U₃O₈, is economic; neither can we arbitrarily say that a reserve of 250,000 pounds at an average grade of 0.03 percent U₃O₈ is uneconomic.

Each case must be examined on its own merits. A given reserve may be economic in one setting and uneconomic in another. Likewise, a deposit which was uneconomic when uranium brought $6 per pound may be very attractive with uranium prices hovering around their current level of $40 per pound. The operator's aim in developing a property is to derive as much profit as possible from that development and to show the best return on invested capital that he can. To do this, he seeks to maximize the amount of product recovered and, at the same time, minimize capital investment and operating expenditures necessary to produce that product. The balance of my discussion will be directed to an exposition of various mining and processing methods in current use, with some comments on the approximate costs and economic implications of each system.

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PRODUCTION OF URANIUM OXIDE (YELLOWCAKE)

First, I'd like to give you a brief overview of the uranium production process (Figure 10-1). Basically, the problem is to liberate and concentrate or upgrade the uranium from its host rock. Generally, we are dealing with ores containing one to six pounds of uranium per ton of ore. In a conventional mining system, the ore is mined, either by open pit or underground methods, mechanically crushed to expose more uranium-bearing surfaces, chemically leached to take the uranium into solution, from which solution the uranium is precipitated in a more concentrated form.

In the in-situ or solution mining system, the ore is not mined in the conventional sense. Instead, solutions pumped into the ground dissolve the uranium and take it into solution. These "pregnant" solutions are then recovered and the uranium is precipitated much as it is in a conventional milling operation.

With this very generalized description of the uranium production process as background, I'd now like to examine some of the major elements of the process in greater detail.

Basic Mining Concepts

Having defined a potentially economic reserve of uranium by exploration and development drilling, the mine operator must develop the most efficient, cost-effective scheme for converting that uranium in the ground to yellowcake in the can. About 98 percent of the 1975 production utilized conventional mining and milling technology.

Open-Pit Versus Underground Mining

The decision as to whether to mine a deposit by open pit or underground methods is largely dictated by physical factors: how deeply-buried is it and what is its three-dimensional configuration.

The economics of overburden removal and handling effectively limit open pit mining to depths of about 500 feet or less. This can be easily seen in Figure 10-2 which shows the basic geometry of an open pit mine. As depth to ore increases, the amount of overburden to be removed increases dramatically because of the angle of the pit slopes. The break-even stripping ratio, or the point at which the over-burden removal costs equal the ore revenues, determines the ultimate economic extent of the open-pit mine.

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If a deposit is too deeply-buried to be recoverable by strip mining techniques, an underground mining system must be utilized. Generally speaking, such a system includes at least one production shaft for hoisting ore, a shaft for movement of men and equipment, and one or more ventilation shafts designed to force fresh, non-radioactive air through the underground workings to provide healthy working conditions for the miners.

While a great variety of underground mining methods are employed, their description is beyond the scope and intent of this discussion.

A commonly-used system is known as "room-and-pillar" mining (Figure 10-3). This technique involves removal of the ore in a systematic fashion, while leaving a series of posts or "pillars" in place to support the roof of the workings. This approach is particularly suitable for deposits which are relatively flat-lying and two-dimensional in nature, as are many uranium deposits. One disadvantage to most underground mining systems is the necessity to leave as much as 20-30 percent of the total reserve in the ground for support purposes, as, for example, the pillars in room and pillar mining.

There are underground mining systems, such as long-wall or panel retreat methods, by which 100 percent of the ore can be recovered. These methods, however, tend to be substantially more expensive and require a rather particular set of mining conditions to be used.

Open-Pit Mining

While each open pit mining operation varies in detail, the basic approach is the same. The orebody is exposed by stripping off the overburden. Depending on the hardness of the rock, this is accomplished by large scrapers, bulldozers or combinations of shovels, front-end loaders and haulage trucks.

Having exposed the ore, the removal process is much the same, except that instead of the material being placed on a waste dump, ore-grade materials are trucked to a mill for processing.

The ratio of waste rock which must be moved to ore mined varies, of course, from mine to mine, but a ratio of 40 tons or more of waste to one ton of ore is not uncommon. Thus, for a mine producing 1,000 tons per day of ore, an additional 40,000 tons of waste must be moved. In some cases,

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this waste rock is not a total loss, however. If it contains uranium in concentrations too low to be recovered by conventional milling technology, it may be placed on a speciallyprepared "pad" to allow recovery of the low-grade uranium values by leaching through the percolation of solutions through the material. This is known as "heap" or "dump" leaching.

One of the key elements in open pit mining is grade control. Uranium deposits often consist of interlayered bands of ore and waste material, sometimes as little as one foot thick. In order to maintain a relatively constant grade of material being fed into the mill, it is necessary to be extremely conscious of whether material being mined should go to the dump (waste), the leaching pads (low-grade ore) or to blending stockpiles (ore grade). This requires constant sampling of the active mining areas and frequently involves blending or mixing of higher grade ore from one area of the mine with lower grade ore from another area. In many mines, each truckload of material is scanned with scintillometers and the driver directed to specified dumping areas based on the scintillometer readings of uranium content.

Underground Mining

While each mine varies in specifics, a typical underground mine is developed by a series of shafts through which ore, men and materials, and fresh air are carried. These shafts vary from a few feet to 25 feet in diameter and are sunk either with large-diameter shaft-boring equipment or by drilling, blasting and hoisting of the rock.

Once the orebody has been reached by shafts from the surface...