Rising tide for olivine in underwater concretes

By James Sean Dickson
Published: Monday, 27 April 2015

Olivine consumption rising in underwater concretes but refractories remain mineral’s key market.

Olivine, which is sourced from olivine sands, or from peridotite and dunite rock, is seeing an awakening of interest in underwater concrete markets, according to Greece-based refractories producer, Grecian Magnesite.

Pantelis Vetoulas, commercial manager at Grecian Magnesite, told IM that the underwater concrete sector is an expanding market for olivine products.

Underwater concrete, which also utilises limestone, gypsum and sometimes fly ash, is used when a structure needs to be constructed below water lines, where regular concrete can disperse into water forming a cloud of its composite materials.

Uses in this field include port and harbour installations, bridge piers, underground (metro) systems and deep shafts in unstable ground, according to Swiss building conglomerate Sika AG.

Olivine powder, in conjunction with dolomite, limestone, pyroxene, hornblende, feldspar, quartz and other industrial minerals – recipe-dependent – is used to create high density concrete mixtures, which do not "wash out," improving placing security and compaction underwater.

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Peridotite mantle inclusions within a low-silica content igneous rock.
Peridotite rocks are often dominated by the refractory mineral olivine (Source: James St John).


Nano silica: First stop — olivine

While the addition of nano-silica to concrete mixes is less developed than underwater concrete technologies, Vetoulas said that Grecian Magnesite is performing extensive research and development (R&D) work into developing the material as an additive for high performance concretes, in a process that requires olivine and sulphuric acid as raw materials.

High performance concretes are defined by the American Concrete Institute as mixes that meet "special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing and curing practices".

The company currently extracts olivine and dunite from an ophiolite complex – where mantle rocks have been shunted over crustal rocks – in the Halkidiki peninsula in Yerakini, northern Greece.

Grecian Magnesite’s primary business is magnesite, which is extracted from veins of serpentinised – hydrothermally weathered – dunite and harzburgite mantle rocks.

Dunite and olivine is therefore a substantial by product for the company – over 1m tpa is produced as a side to the main magnesite extraction operation.

To increase the refactory performance of its products, Grecian Magnesite is developing a dunite calcination plant, Vetoulas told IM. A low-cost vertical kiln operating at 1,000˚C will decrease the loss on
ignition (LOI) for olivine-based refractory products, leading to greater heat resistance. 

Vetoulas said that Grecian Magnesite’s R&D work has revealed that the magnesite inherently present in the product reacts with free silica to form further forsterite olivine in this process, according to the chemical equations:

Serpentinite → Forsterite Olivine + Silica + Water

2Mg3Si2O5(OH)4 → 3Mg2SiO4 + SiO2 + 4H2O

Magnesite + Silica → Forsterite Olivine

2MgO + SiO2 → Mg2SiO4

Refractories consumption dominates

While speciality concretes are possibly some of the fastest expanding markets for olivine Vetoulas told IM that traditional refractories markets remain the largest source of demand.

Olivine and dunite, a rock comprised almost entirely of olivine, can be mixed with sintered magnesia for the production of tundish working lining materials, both spray and dry. The production of unshaped monolithic refractories for the steel industry typically requires olivine grain sizes of less than 1mm.

Low enstatite pyroxene concentrations are also desirable, as this results in higher refractory performance.

Olivine also has a major end market in eccentric bottom tapping (EBT) filling materials, which are used in electric arc furnaces (EAFs). Grain size requirements of 2-6mm are common here, Vetoulas said.

Less dominant uses are as foundry sand, at 0.1-0.5mm, with fine material of less than 0.1mm requiring processing to remove. Safety lining bricks for EAFs, convertors and thermal accumulators also form smaller but integral olivine end markets.

Finally, olivine rockwool, which performs better than regular glass (silica-based) wool, is an additional end market. Here, Vetoulas said that olivine usage can result in improved insulation, refractory and bio-solubility properties.

Olivine prices expected to remain stable

Owing to an abundance of olivine supply from Norway, Turkey, Spain and Greece, Grecian Magnesite does not expect to see substantial price shifts in the near future.

Most market players are low cost, Vetoulas told IM. Prices are in the range of €80-130/tonne ($85-138/tonne*) for material delivered to refractory procurers’ plants, according to the IM Prices Database, with the variation being mainly due to grain size.

Slag conditioner grade olivine prices are "much lower than for olivine used in refractory applications", Vetoulas said.

For foundry sand, which requires more processing, IM’s prices currently stand at between €160-180/tonne ($171-193/tonne). 

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Forsterite olivine crystals derived
from an igneous complex in Wyoming, US (Source: James St John),


*Conversions made April 2015