Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2000-03-30
2001-11-06
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C075S743000
Reexamination Certificate
active
06312500
ABSTRACT:
The present invention relates to a method of operating a heap leach for leaching nickel-containing ore to recover nickel. In particular, the present invention is directed to a method of heap leaching nickel-containing ore having a tangible clay component (i.e., greater than about 10%, by weight, of clay). More particularly, the present invention is directed to an economical method of heap leaching nickel-containing laterite ores that have a tangible clay content.
Laterite ore deposits have historically been overlooked in favor of higher-grade sulfide deposits, although they are an abundant source of low-grade nickel ore. Now, easily mined sulfide ore bodies are beginning to disappear and, in combination with the growing environmental concerns of processing these ores, lateritic deposits will become an increasingly important source of the world's nickel and cobalt.
To date, the processes for extracting nickel from laterite ores has been confined to expensive and/or energy intensive methods. For example, it is known to smelt the laterite ore, which is quite energy intensive. It is also known to pressure leach the laterite ore with sulfuric acid, which requires expensive autoclaves, flash tanks, etc. and is highly corrosive. Thus, there is a need for an economical effective method for obtaining nickel from laterite ores.
Heap leaching is a conventional method for economically extracting metals from low-grade ores. Generally, it simply involves piling raw ore, taken directly from an ore deposit, into heaps that vary in height. The leaching solution (lixiviant) is introduced upon the top of the heap to percolate down through the heap. The effluent liquor passes into, for example, perforated drainpipes arranged on the surface of the base beneath the heap. The drainpipes direct the effluent liquor into a header for transport to a processing plant where the metal values are separated from the effluent and recovered.
Although heap leaching has been successfully used to recover metal values such as copper, gold, silver, and uranium, the heap leaching process has not been proposed for recovering nickel from particular laterite ores that contain a tangible clay component. Besides being a generic term for specific clay minerals, “clay ” also implies particle size. According to John Bichard (Oil Sands, Composition and Behaviour; Alberta Oil Sands Technology and Research Authority, Edmonton 1987, pp. 3-7), “clay” is frequently defined as material less then 325 mesh (<44 micron) in size.
One problem hindering the heap leaching of laterite ores is the substantial clay component present in such ores. The clay minerals have a number of common characteristics. Their structural classification is based on composite layers built from components with tetrahedral and octahedral coordinated cations. Most of them occur as platy particles in fine-grained aggregates, which when mixed with water yield materials that have varying degrees of plasticity. The clay minerals are generally classified into four layered mineral groups and they are kaolinite, smectite (montmorillonite), vermiculite, and illite. The chemical composition of clay minerals is principally hydrous silicate minerals of aluminum or magnesium.
The type of clay mineral formation is dependent on parent rock and the physico-chemical environment of clay formation. For example, clay minerals associated with porphyry copper mineralization are distinctly different from clay minerals associated with the lateritic nickel mineralization. The clay minerals associated with porphyry copper are primarily acidic and intermediate rocks (high silica), which suffered intense hydrothermal alteration to form kaolinite, illite and montmorillonite. In contrast, the clay associated with nickel saprolite and limonite is formed by near surface weathering of relatively unstable parent rocks like basic or ultrabasic (low silica).
It has been reported that when the laterite ore is piled dry, the leach solution percolation was poor to impossible. This poor percolation observation has been explained as being the result of the absorbent nature of the clay constituents that, when wetted with the leach solution, swelled and closed the established porosity. Because of the poor permeability, a low irrigation rate is required so that the leach solution can effectively leach the nickel and thus, the leaching will require an undesirably long time.
The method of the present invention solves that problem by pre-treating the ore with a concentrated acid to physically and/or chemically agglomerate the fine clay particles. It is believed that the concentrated acid breaks down the clay minerals and metal silicates and solubilizes the silica gel so that reprecipitated silica as well as precipitated metal sulfates will act as a binding agent that, upon curing, will produce a rather strong pellet. Advantageously, these pellets, when formed into a heap, allow a high percolation flux rate. Consequently, the leach time is economical.
BACKGROUND
In general, it has been found that most deposits of nickel-cobalt laterites contain three major zones based on morphology, mineralogy, and chemical composition. These three zones from the base to the surface atop weathered parent bedrock materials are the saprolite zone, the transition zone, and the limonite zone with large variations in total thickness of the deposit, as well as individual zone thickness. The saprolite zone consists of three separate subzones: rocky saprolite, saprolite, and ferruginous saprolite. This saprolite zone consists predominantly of “saprolitic serpentine” and a large variety of nickel-magnesium silicate minerals that belong to the septochlorite group of minerals as defined in “An introduction to the Rock Forming Minerals” by Deer, Howie and Zussman; Longman Group Limited, London, UK, 1983. Septochlorites (general chemical formula: A
6
(B
4
O
10
)(OH)
8
wherein A represents Mg, Fe, Ni, and/or Al and wherein B represents Si, Fe, and/or Al) are characterized by serpentine like layers, with each layer having a tetrahedral (Si Al)
2
O
5
component linked to it by a tri-octahedral brucite-type (MgO) compound. Various arrangements of layer stacking are possible and they give the laterite deposits its layered and clayey structure. The weathering process or serpentinization of the ultrabasic bedrock (a low nickel (~0.2%) and high (~5%) iron containing magnesium olivine mineral) is characterized by a decrease of Mg in the ultrabasic and an increase in Ni and Fe upward. The resulting saprolite zone contains between 0.5 and 4% Ni.
The not-well-defined transition zone is composed essentially of nontronite-type clays (smectite group) and quartz. It also commonly contains Ni in the range from 1.0 to 3.0% with coexisting Co ranging from 0.08% up to 1% Co (associated with asbolane, a hydrated manganese oxide). The limonite zone (with nickel ranging from about 0.5 to 1.8%) consists of an upper hematite-rich section and a lower goethite-rich section and is rich in Fe, Al, and Cr. Sometimes the weathering has not been fully completed and either the hematite or the goethite rich sections are not present. Alternatively, depending upon the climatic condition the limonite zone will still contain residual iron-aluminum silicates, such as chlorite that are nickeliferous.
While heap leaching copper ores is well known as a unit operations, there are several differences between heap leaching of copper containing ores that also contain some clay components and the lateritic ores that have a substantial clay component.
The laterization process occurs mainly in tropical or subtropical environments, where warm, humid, and good drainage environments are prevalent. This process occurs with slow dissolution of olivine and pyroxene along micro-fractures and grain-boundaries of these minerals usually removing soluble metal like magnesium and leaving porous silicate-(serpentine), silica-(chalcedony, tridymite) and iron- skeleton (sieve texture) or box-work or sometimes called mesh texture especially for serpentine.
In tropical wet-dry climates, clay
Davis Michael J.
Duyvesteyn Willem P. C.
Liu Houyuan
BHP Minerals International Inc.
Brinks Hofer Gilson & Lione
King Roy
McGuthry-Banks Tima
Nichols G. Peter
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