Everything You Wanted to Know About Synthetic Iron Oxide Pigments......

                                      .....And Maybe a Bit More Besides

Synergy Pigments Australia Pty Ltd supplies synthetic iron oxide pigments, which are mostly manufactured in China.  Current Chinese industry production levels are around 350,000 - 400,000 metric tonnes  annually, with about half the production being made by a large number of small, independent plants.

Synthetic iron oxide is an inorganic pigment.

The construction sector forms the largest market for iron oxide pigments (both organic and inorganic), which accounts for around 50-55% of production.  The coatings industry takes another 30-35%, with plastics and Ceramics usage forming the bulk of the balance. 

There are three main colours of iron oxide pigment, red, yellow and black.  Browns are sometimes manufactured by controlled reduction of black oxide, but are more often that not produced by blending of the other three.  Blues and Greens are produced by a different process and will be covered later.

Iron - The Base Material.

Iron is the second most abundant metal on Earth (the first being magnesium), and is believed to be the tenth most abundant element in the universe.  Iron is also the second most abundant element by mass, making up 34% of the mass of the Earth.

Nearly all iron produced commercially is used in the steel industry and made using a blast furnace.   This process is one of the most significant industrial processes in history and the origins of the modern process are traceable back to a small town called Coalbrookdale in Shropshire (England) around the year 1773.

The pure metal is not often encountered in commerce, but is usually alloyed with carbon or other metals.

Iron Oxide Manufacture: Raw Material.

In the photos below we can see the raw materials being gathered prior to the crystal seed preparation.  The iron oxide industry is a prolific recycler of scrap iron, in fact some of the iron which is recovered from the process may be reused by the plant.

There are a number of production methods used, most involving the thermal decomposition of iron salts or the reduction of organic compounds by iron.  In the Peniman-Zolph process scrap iron is used to generate Ferrous Sulphate, which is reacted with an alkali, usually Sodium Hydroxide.

Water, as will be seen is a major component of the process, however in the photo (below right) it also provides the medium for the delivery of ship borne chemicals for both the seed preparation and the oxidation process; in this case Ferric Sulphate and Sodium Hydroxide.

Crystal Seed Preparation.

The proper growing speed of the crystal seed and the creation of an even  particle size distribution is controlled via the temperature and dosage of raw materials. The end result should be a product which will have bright color shading, strong tinting strength and good pigment characteristics. Note: I would like to thank Sherry Xie of United Pigments for this photo.

The Oxidisation Process.

 In this process the seed crystals are placed in tanks,  scrap metal is added (at this stage to reduce the acid content), and the tower is heated via steam.

Reaction conditions such as air flow, temperature, ferrous content, PH value of the solution, reaction time etc. are all strictly controlled.  Reaction time, generally speaking varies as, darker colours need a longer time. As an example medium red color takes around 70-80 hours.

Below are photos of the oxidisation tanks at two separate plants.  The one at right is taken on the work platform at the top of the tower; note the steam.  The heat and humidity here is quite intense, as can be imagined.

The resulting "slurry" is then sieved, and piped to the:

Compression Filters.

Here excess water is removed, and the resulting wet "sludge" is placed in trays prior to drying in the ovens.  Below are the empty trays prior to filling, and at right we see them full of wet, caked yellow oxide.

prior to drying in the ovens.

The ovens (at left) are a newer more modern design with better heat sealing; the ones above are at an older plant.

Crushing:
 

(Above) The dried "cake" is seen being  emptied down a chute into a crusher, from where it is  piped blown (by compressed air) into a preliminary bagging machine (right).

This completes the production process, but more activity is required before the customer finally receives their product.

click here for  Page 2