In-Situ Leaching of Crownpoint, New Mexico, Uranium Ore: Part 6-Section 9 Pilot Test
Authors: Vogt Thomas C. , Strom E. Thomas , Venuto Paul B. , Winget James E. , Scoggins M.W. 
Published: December 2007

Mobil has successfully recovered uranium by in-situ leaching from a depth of 2,000 ft [610 m] in the Westwater Canyon member of the Morrison formation near Crownpoint, NM. This was the deepest successful in-situ uranium leach carried out in the U.S. and the first in-situ uranium leach in New Mexico. A period of thorough laboratory testing preceded initiation of the pilot. Careful application of conventional petroleum industry drilling procedures and reservoir techniques facilitated project procedures and reservoir techniques facilitated project development. Compared to deep mining, water usage was minimal. After all regulatory approvals were received, the pilot began in Nov. 1979. By using a hydrogen peroxide/alkaline bicarbonate leachate, an average uranium peroxide/alkaline bicarbonate leachate, an average uranium level of slightly greater than 100 ppm was produced during the 10-month leaching phase. The leachate flow was confined to the selected ore zone within the Westwater Canyon member by careful reservoir management. High levels of molybdenum also were produced during leaching. This complicated the functioning of the ion-exchange and precipitation circuits, but methods to control these problems evolved. The leaching demonstration period was insufficient to extract the uranium fully, and period was insufficient to extract the uranium fully, and leaching was terminated after only a part of the uranium resource was recovered so that restoration could proceed. A restoration phase followed the leach phase. During the first 12 months' restoration, all 27 water-quality parameters (New Mexico state standards) except parameters (New Mexico state standards) except molybdenum were reduced below the required limits. In commercial operation, both uranium and molybdenum would be depleted substantially during the leaching phase and should present little problem during restoration. The relatively low front-end capital requirements of in-situ leaching, with its potentialities for development in a step-wise, modular manner, reduce the risk of its implementation in a changing yellowcake market environment.

Introduction

Northwest New Mexico, in particular the Grants mineral belt, contains extensive and diversified uranium ore deposits that have been studied intensively and described in detail. For the most part, uranium resources have been recovered by standard strip or shaft mining techniques followed by conventional milling methods, and this also has been true in New Mexico. We have recently completed a successfull uranium in-situ leach pilot operation near Crownpoint, and the design, operation, and results of this pilot are described in this paper. A number of field projects and commercial scale in-situ uranium leaching operations in south Texas have been described; these include Mobil's El Mesquite plant, 20 with design production capacity of 650,000 plant, 20 with design production capacity of 650,000 lbm/yr [294 835 kg/a] of yellowcake. Several uranium leaching projects in Wyoming have been reported . We are not aware of any other current in-situ uranium leaching activities in New Mexico, although there are two partially completed underground mining projects partially completed underground mining projects near Crownpoint. Among the many potential advantages of in-situ leaching compared to conventional mining, the lower overall environmental impact is paramount. There is significantly less total water required than for underground mining, and less regional hydrological disturbance and aquifer drawdown, since groundwater is recirculated through wells as in petroleum waterflooding. No surface ore handling or tailings ponds are required, and even extensive well-field acreage presents a "low profile." There is no significant radiation exposure with in-situ leaching. It provides great flexibility in developing a wider, more diffuse area of ore resource than mining, which focuses on a more confined ore zone. The overall resource target is expanded to include lower-grade ore zones, and fewer restrictions on both horizontal and vertical continuity are imposed. Manpower requirements are less than for mining, and there are significantly lower front-end capital costs. In contrast to mining, in-situ leaching is not nearly as sensitive to the economy of scale in plant size, and incremental modular expansion from relatively small projects is feasible. Many of the techniques of the petroleum projects is feasible. Many of the techniques of the petroleum industry can be transferred readily to in-situ leaching -i.e., drilling, logging, casing, cementing, perforation, and stimulation, as well as reservoir analysis, perforation, and stimulation, as well as reservoir analysis, large-scale fluids handling, and engineering design. The Crownpoint development sites are in McKinley County on the southern edge of the San Juan basin.

JPT

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