Heavy mineral sands contain valuable minerals in two core product streams: titanium minerals (ilmenite, leucoxene, rutile), and zircon. Other components include alumina-silicates, magnetite, iron, and tin, as well as occasional inclusions of radioactive elements such as uranium and thorium in small amounts.
The relative content of these minerals vary from deposit to deposit. In some cases, zircon is considered as a by-product, or co-product of titanium minerals production, less frequently, given typical assemblage characteristics, it is the principal product stream.
Zircon (ZrSiO4) usually occurs in a silicate form. Most zircon is recovered from heavy minerals sands deposits, which typically contain higher proportions of titanium bearing elements, including ilmenite and rutile.
Mineral sands deposits are characterised by their grade, by the percentage of heavy mineral (HM) found in the deposit, and by their assemblage. The assemblage of a mineral sands deposit refers to the composition of minerals present, non-valuable factions, and slimes (clay).
The typical composition of a mineral sands deposit has a HM grade ranging from 0.5% to above 20%. Titanium related products are often the most significant component of the valuable heavy minerals in the assemblage relative to zircon, which is usually the minor fraction, if it is present at all. This is where the Donald deposit differentiates itself given the high zircon assemblage.
Revenue:Cash Cost Ratio
Unit cash cost is the measure typically used for most mineral commodities to benchmark a projects relative economics. The grade of valuable mineral, recoveries, scale, mining method, and associated costs are key factors in influencing unit cost.
In mineral sands, given the varying product streams from a deposit and their differing value in use, the economics is influenced as much by the assemblage (composition of the valuable heavy mineral stream which shapes the revenue per tonne characteristics) as the deposit HM grade or the cost of mining.
Most mineral sands mines produce several product streams, with ilmenite usually the predominant component, and lesser quantities of the more valuable minerals of rutile and zircon. Given that the variation between ilmenite pricing and zircon pricing can be 1:6 or more, the revenue to cash cost ratio can be materially influenced by the assemblage characteristics.
Consequently, the industry tends to use a margin curve or revenue:cash cost ratio curve to assess the relative attractiveness of mineral sands deposits.
Zircon has widespread applications across consumer, commercial, industrial, scientific and medical applications. Furthermore, there are a range of emerging R&D technology applications, influenced by the unique characteristics of zircon.
Zircon is hard, abrasive resistant and highly refractive, typically displaying consistent grain size. It has a low thermal expansion co-efficient, is chemical stable, and has a high melting point, making it conducive to chemical application in a wide range of end uses.
The nature of zircon in final applications means that it typically has a low input cost while providing high value, and in many cases there are limited substitutes available.
Zircon’s applications mean that it is typically subject to a low level of recycling or re-use, if any at all.
Zircon – an Array of Applications
Ceramics represents by far the largest end-use sector for zircon, consuming around 55% of all zircon produced.
Zircon has multiple applications as a whiteness and opacity enhancer in ceramics and enhances resistance to abrasion and chemical attack. It is employed as a raw material in the production of ceramic bodies, glazes, enamels, frits and pigments; producing interior and exterior wall and floor ceramic tiles, porcelain tiles, sanitaryware, washbasins, tableware, special porcelains and industrial tiles.
Zircon demand in ceramics is correlated with urbanisation trends, the increase in floor space under construction and the wealth-effect related to modern consumer patterns of improvements in hygiene.
Zirconium oxychloride (ZOC) represents the most important zirconium compound due to its use as a base material for the production of zirconia.
Zirconia is used in the fabrication of special electro-ceramics for a wide range of applications in the automotive, aerospace and telecommunication sectors. It is used in the manufacture of tubes, rings, discs, plates and other complex shapes, in sizes ranging from microns to centimetres, as well as lector-ceramics, structural ceramics, pump components and biocompatible devices, and advanced technical applications such as oxygen sensors and solid oxide fuel cells.
Zirconium chemicals are also used in gemstone production, titanium dioxide coatings, anti-perspirants, paper coatings, and paint driers.
Zirconium metal can be extracted from zircon and further processed to form numerous zirconium chemical compounds employed in manufacturing processes. Zirconium alloys are widely used as structural components in the nuclear industry such as pressure tubes, fuel channels, guide tubes, grid spacers, as well as for fuel cladding, fuel containers, and as the core structural materials of water-cooled nuclear reactors.
Zircon is widely used as a foundry sand and coating material, mostly for high precision casting and refractory applications where its fine grain characteristics and thermal stability are valued. Stabilised zirconia is used in the manufacture of abrasive materials due to its ultra-hard, tough and dense characteristics. Grinding wheels, sharpening stones, abrasive papers and other high density grinding media, as well as cutting blades and cutting tools can be produced.
Advanced zirconia ceramics have an excellent biocompatibility and an inherent ability to remain biologically inert, making them ideal for use in a range of biomedical applications including the manufacture of medical prosthesis devices such as hip joints or femoral ball heads, pace makers and other medical instruments such as dental implants.
Given the characteristics of zircon and zirconium based products, there are a myriad of potential new uses of zircon and significant R&D based activity on the potential for its application.
Emerging uses include:
- 3D printed advanced ceramics with mechanical properties comparable to those produced using other methods, such as machining
- dye sensitised cells
- memory adaptive alloys – including automotive parts
- smart coatings with enhanced properties: heat resistance, abrasion resistance, stability and durability
- thermal barrier applications for manufacturing of specialty chemicals, steel, aluminium, or other alloys
- zirconia based films for corrosion protection in mild and stainless steel applications
- fuel cells and batteries
- applications in hydrogen production.
The titanium dioxide (TiO2) component of titanium minerals is a dark coloured mineral which, with further processing, becomes a white, opaque powder. Titanium minerals are favoured in a range of applications for their chemical and physical characteristics, which include opacity, non-toxicity, a high refractive index, strength and corrosion resistance.
The main forms of titanium dioxide in titanium minerals are:
|Form of titanium dioxide||TiO2 %|
|Leucoxene (HiTi 70/HiTi 90)||70-90|
|Ilmenite (chloride grade)||58-65|
|Ilmenite (sulphate grade)||45-55|
Upgraded forms of titanium dioxide, where ilmenites are beneficiated to a higher titanium dioxide product, include sulphate or chloride slags (80% to 95%) and synthetic rutile (88% to 95%).
Around 90% of titanium dioxide globally is used as a pigment in the manufacture of paint, plastic, paper and fibre where, in addition to being a non-toxic whitener, it also provides UV and chemical resistance.
The wide range of applications for pigment includes house and car paints, laminates and other coatings, plastic pipes and packaging, fibres, inks, rubber, as well as clothing, sunscreen, toothpaste, food and in cosmetics and pharmaceutical manufacture.
Titanium minerals are also used to produce titanium metal, which has the highest strength to weight ratio of all metals. Titanium metal is chemically resistant, has a high melting point and low conductivity. It is used across a diverse range of applications no limited to aeronautics, medical implants, defence, sporting goods and componentry in the offshore mining and petrochemicals industries.
Welding is a further key market of high grade titanium feedstocks, rutile is used in the manufacture of welding flux wire cord and is used in steel construction and ship building industries.
Rare earth elements can be found in mineral sands deposits. These rare earth elements can be used in an expanding range of high technology consumer goods and low carbon technologies, most notably wind energy turbines and electric vehicles.
Medical science, manufacturing, electronics and renewable energy generation all utilise rare earth elements.
Consumer and other applications in which rare earth elements are needed include smart phones, computers, x-ray machines, medical lasers, plastics, catalytic converters, fibre optics, rechargeable batteries, hybrid cars and wind turbines.
Main Stages of Mineral Sands Mining and Processing
Mineral sands mining involves four main stages: mining, concentration, separation and rehabilitation. Mining can be performed either by dry mining method (employing scrapers, dozers and excavators,typical for dunal deposits), or a wet mining process (emloying floating dredges are used, typically for large unconsolidated deposits). The following provides a generic description of the main stages of the mineral sands mining and separation process.
Clearance And Mining
Clearance and Mining
The first stage is to clear the mine area of vegetation and rocks, followed by removing and stockpiling the topsoil and subsoil separately from the underlying overburden material.
Overburden is stockpiled for rehabilitation purposes, which occurs during progressive mining operations.
A typical dry mining operation consists of depositing the ore into a hopper with the help of dozers, scrapers or excavators, and transferring it to the primary separation process, usually a trommel, where waste material and large particles are screened out of the mix through vibration and rotation. The resulting mix of mineral sand, silt and clay is transferred by slurry to the wet concentrator.