Hola

SME Annual Meeting
Feb. 19 - 22, 2012, Seattle, WA

Preprint 12-119
INSIGHTS INTO HEAP LEACH TECHNOLOGY
N. Dhawan, Univ. of Utah, Salt Lake City, UT
M. S. Safarzadeh, Univ. of Utah, Salt Lake City, UT
J. D. Miller, Univ. of Utah, Salt Lake City, UT
R. K. Rajamani, Univ. of Utah, Salt Lake City, UT
M. S. Moats, Univ. of Utah, Salt Lake City, UT
ABSTRACT

circuits (Hiskey, 1983). Risingcosts of milling and concentration forces
more low to medium grade ores to be available for heap leaching
(McCleland, 1985; Hiskey, 1986; Miller, 2003).

With ever-increasing demand, low-grade complex ores and strict
environmental regulations, metallurgical processing options have
become limited. Heap leach technology provides several benefits to
combat these issues including low cost,flexibility and diversified
process conditions. This paper provides an overview of heap leaching
technology with specific emphasis on chemical aspects. Hence,
influencing factors, advantages and disadvantages, testing approaches
and some fundamentals will be discussed. Finally, heap leach
technology for different ore types (copper, nickel, uranium and gold)
will be briefly compared.

Whileheap leaching is a well established technology which
continues to grow in use, there are certain criteria that justify its
selection over other treatment options. Ore grade and mineral
leachability are two of these criteria. For example for gold ores, heap
leach is preferred if the gold content of the ore is less than 0.04 troy
ounces per ton (1.2 g-Au/t of ore). For copper ores, theintegration of
heap leaching with SX-EW is essential. The most efficient SX-EW
plants in the world will be hindered if the target metal cannot be
dissolved and recovered within the heap (Ulrich et al., 2003).

INTRODUCTION

INFLUENCING FACTORS

Heap leaching was first practiced by piling up heaps of copper ore
and irrigating them with leach solution (Kappes, 1978). Heap leaching
can be defined asthe practice of piling a large tonnage of mineralbearing material over a liquor collection system and feeding a leaching
solution onto the surface of the heaped pile (Mashbir, 1964; Ralph,
2007). Modern heap leaching is a controlled process whereby a
complex or low-grade ore is stacked in short lifts (under 10 m in most
cases), usually crushed and often agglomerated, on a carefully
preparedcontainment system (the leach pad) and irrigated in a
controlled manner with a solution to extract the optimum amount of
metal from the ore (usually copper, gold, silver, uranium and nickel).
The first commercial modern-day style of heap leaching was probably
introduced to the uranium industry in the 1950’s (Scheffel, 2002). The
application of heap leaching technology revolutionized goldproduction
in the United States, Peru and other countries in the 1970’s and 1980’s
(Brunk, 1997). The rapid expansion of the heap leach-solvent
extraction-electrowin (L-SX-EW) copper production occurred in Chile
during 1990’s (Taylor, 2007). In the past decade, heap leaching of
nickel laterites (Taylor, 2009; Readett and Fox, 2010) and mixed metal
sulfide ores (Taylor, 2009; Vanhanen, 2010) havebeen demonstrated
and appear to be moving into commercial practice. Biological heap
leaching (also known as bio-mining) for nickel and copper recovery has
further expanded the use of the process (Harder, 2011). It has also
been proved that successful heap leaching operations are
accomplished not in just temperate climates but also from the Arctic to
the Equator (Alta, 2011). Heap leachingis now being considered for
the processing of uranium and nickel ore also (Kyle, 2010).

Upon first glance, heap leaching appears simple in nature.
However, in fact, heap leaching is a very complex process. A family of
technologies such as material handling, environmental control,
analytical techniques (Smith, 2004; Steemson and Smith, 2008; Alta,
2011), process chemistry, hydrology and...