By Richard (Rick) Mills
Ahead of the Herd

As a general rule, the most successful man in life is the man who has the best information

Nickel is present in over 3000 different alloys that are used in over 300,000 products for consumer, industrial, military, transport/aerospace, marine and architectural applications.

Nickel's biggest use, about 65%, is in alloying - particularly with chromium and other metals to produce stainless and heat-resisting steels. Its primary function is to stabilize the austenitic (face centered cubic crystal) structure of the steel. Normal carbon steel will, on cooling, transform from an austenite structure to a mixture of ferrite and cementite. When added to stainless steel nickel stops this transformation keeping the material fully austenite on cooling. Austenitic stainless steels have high ductility, low yield stress and high tensile strength when compared to carbon steel - aluminum and copper are examples of other metals with the austenitic structure.

Another 20% is used in other steels, non-ferrous alloys (mixed with metals other than steel) and super alloys (metal mixtures designed to withstand extremely high temperatures and/or pressures or have high electrical conductivity) often for highly specialized industrial, aerospace and military applications.

About 9% is used in plating to slow down corrosion and 6% for other uses, including coins, electronics, in *batteries for portable equipment and hybrid cars, as a catalyst for certain chemical reactions and as a colorant - nickel is added to glass to give it a green color. In many of these applications there is no substitute for nickel without reducing performance or increasing cost.

*Rechargeable nickel-hydride batteries are used for cellular phones, video cameras, and other electronic devices. Nickel-cadmium batteries are used to power cordless tools and appliances.

The U.S. Department of Energy (DOE) has funded a variety of programs designed to encourage more rapid development of renewable energy sources. Specific research and development projects included:

  • domestic manufacturing of advanced batteries
  • development of improved stationary and portable fuel cell power systems
  • development of commercial scale bio-refineries
  • improved design of molten salt storage facilities at power plants that concentrate solar energy
  • design and evaluation of parabolic troughs, dishes, and heliostats for solar power stations
  • construction of demonstration facilities designed to recover and better utilize geothermal energy

All of these expanding subsectors for generating power have the potential to be important users of nickel metal and or nickel-bearing alloys.

Nickel Deposits Come in Two Forms

Nickel deposits are generally found in two forms: sulphide or laterite. About 60% of the world's known nickel resources are laterites. The remaining 40% are sulphide deposits.

Nickel Sulphide Deposits - the principal ore mineral is pentlandite (Fe,Ni)O(OH) - are formed from the precipitation of nickel minerals by hydrothermal fluids. These sulfide deposits are also called magmatic sulfide deposits. The main benefit to sulphide ores is that they can be concentrated using a simple physical separation technique called flotation. Most nickel sulfide deposits have traditionally been processed by concentration through a froth flotation process followed by pyrometallurgical extraction.

Magmas (magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth - Lava is the extrusive equivalent of magma) originate in the upper mantle and contain small amounts of nickel, copper and PGE. As the magmas ascend through the crust they cool as they encounter the colder crustal rocks.

If the original sulfur (S) content of the magma is sufficient, or if S is added from crustal wall rocks, a sulphide liquid forms as droplets dispersed throughout the magma. Because the partition coefficients of nickel, copper, iron and Platinum Group Elements (PGE) favor sulphide liquid these elements transfer into the sulphide droplets in the magma. The sulphide droplets sink toward the base of the magma because of their greater density and form sulphide concentrations. On further cooling, the sulphide liquid crystallizes to form the ore deposits that contain these metals.

There are two main types of nickel sulphide deposits. In the first, Ni-Cu sulphide deposits, nickel (Ni) and copper (Cu) are the main economic commodities - copper may be either a co-product or by product, and cobalt (Co), Platinum Group Elements (PGE) and gold (Au) are the usual by-products.

The second type of deposit is mined exclusively for PGE's with the other associated metals being by products.

Nickel sulphide deposits can occur as individual sulphide bodies but groups of deposits may occur in areas or belts ten's, even hundreds of kilometers long. Such groups of deposits are known as districts. Two giant Ni-Cu districts stand out above all the rest in the world: Sudbury Ontario, and Noril'sk Talnakh, Russia.

The most important platinum-rich PGE district in the world is the Bushveld Complex, South Africa. The second PGE district in importance is the Noril'sk-Talnakh district, which is exceptionally Palladium (Pd) rich as a by-product of its Ni-Cu ores.

Nickel Laterite deposits - principal ore minerals are nickeliferous limonite (Fe,Ni)O(OH) and garnierite (a hydrous nickel silicate) - are formed from the weathering (nickel sulphides are converted to oxide ores) of ultramafic rocks and are usually operated as open pit mines. There is no simple separation technique for nickel laterites. The rock must be completely molten or dissolved to enable nickel extraction. As a result, laterite projects require large economies of scale at higher capital cost per unit of capacity to be viable. They are also generally much higher cash-cost producers than sulphide operations.

Roughly 60 percent of global available nickel is in laterite deposits ? a deposit in which weathering of ultramafic rocks has taken place. The initial nickel content is strongly enriched in the course of lateritization - under tropical conditions fresh rock weathers very quickly. Some metals may be leached away by the weathering process but others, such as aluminum, iron and nickel can remain.

Typically nickel laterite deposits are very large tonnage, low-grade deposits located close to the surface. They tend to be tabular and flat covering many square kilometers. They are most often in the range of 20 million tonnes and upwards, with some examples approaching a billion tonnes of material.

Laterite deposits usually contain both an upper dark red limonite (higher in iron and lower in nickel, magnesium and silica) and lower bright green saprolite zone (higher nickel, magnesium and silica but lower iron content). Due to the different quantities of iron, magnesium and silica in each zone they must be processed differently to cost-effectively retrieve the nickel.

Laterite saprolite (higher nickel, magnesium and silica but lower iron content) orebodies are processed with standard pyrometallurgical technology.

However a laterite limonite zone is higher in iron and lower in nickel, magnesium and silica, which means using High Pressure Acid Leaching (HPAL) technology.

HPAL (which has up to now enjoyed a highly mixed performance record) involves processing ore in a sulphuric acid leach at temperatures up to 270