In-Situ Leaching Materials Considerations
Authors: Huff Ray V. , Davidson Donald H. 
Published: December 2007

This paper presents a review of materials considerations associated with in situ mining processes for copper and uranium. Because the lixiviants employed are corrosive to ordinary oilfield equipment, special materials of construction for both surface and subsurface hardware are required. Surface equipment may be subjected to either low or high pressures. Low pressure equipment may be constructed of polyvinyl pressure equipment may be constructed of polyvinyl chloride or chlorinated polyvinyl chloride and other materials. High pressure will require the use of equipment constructed of stainless steels, fiberglass reinforced plastics (FRP), etc.

Down-hole equipment presents similar problems. Depending upon depth of the hole plastic, FRP, or combination carbon steel/stainless steel tubulars are required. Cements for corrosive environments are available and are reviewed. Other down-hole hardware such as packers, tailpipes, seating nipples, liners, etc., must be fabricated from suitable materials. Equipment for use in production wells will be similar to that used in injection wells. In addition, materials of construction for lift systems are discussed.

Various types of materials are reviewed including steels, plastics, elastomers, coatings, liners, and lubricants. Some suggestions for testing these materials in both the laboratory and the field are presented. presented. Special problems arise because oxidants are often incorporated into the leach solution. The oxidants may be hydrogen peroxide, sodium chlorate, oxygen or others. The concern for handling fluids containing oxidants is indicated.

Introduction

In-situ mining and in-situ leaching are synonymous processes employed to extract mineral values from the earth without removal of the ore body. These processes are, in fact, a combination of petroleum processes are, in fact, a combination of petroleum technology, ground water hydrology, corrosion chemistry, and hydrometallurgical engineering. The operational aspects of the process involve injection of a suitable fluid into the ore deposit in order to dissolve the valuable mineral and lifting the mineral laden fluid to the surface for extraction. The petroleum engineer is already familiar with most of petroleum engineer is already familiar with most of these activities, since they involve drilling and completion of wells and evaluation of the fluid flow characteristics of the ore deposits. In short, the major part of in-situ mining depends on the design of well fields, injection, and lift equipment. These activities are not unlike those used in waterflooding.

A major element that makes in-situ mining distinctly different from waterflooding is that highly corrosive fluids, often called lixiviants, are injected. These lixiviants are chosen to dissolve portions of the ore body. Any lixiviant capable of reacting with and dissolving copper or uranium minerals usually is very corrosive to conventional oilfield hardware. This suggests that the in-situ mining engineer must understand not only borehole technology and flow of fluids through porous media, but also hydrometallurgy. In addition, because corrosive fluids are employed, the engineer must select appropriate materials for constructing the system and fabricating equipment. The system can be divided as follows:Processing Plant A. Lixiviant Preparation B. Metal ExtractionInjection FacilitiesWell FieldProduction Facilities

This paper will address only the latter three elements of the system.

CHEMICAL NATURE OF FLUIDS

Aqueous fluids are employed in the leaching process for recovery of both copper and uranium. These process for recovery of both copper and uranium. These fluids may be either acidic or basic and may contain an oxidizing agent. The choice of fluid depends primarily upon the mineralization and the nature of primarily upon the mineralization and the nature of gangue. Oxidants are incorporated in the mineral to be leached must first be oxidized.