What do paint, sunscreens, paper, toothpaste, plastic windows and catalytic converters have in common?

The answer is E Number 171, aka titanium dioxide.

Titanium dioxide (TiO₂₎ is a common mineral found in many parts of the world, it has a wide range of uses but is mostly used as a pigment, especially for creating white due to its outstanding opacity and a high refractive index. As much as 25% of a tin of brilliant white paint may be made up of TiO₂. It replaces the toxic lead oxide which was once a common constituent in paint.

It is also a key component in the manufacture of catalytic converters, cosmetics and even food colouring. 4.2 million tons are used worldwide each year. Ultrafine particles of TiO₂ have been found to absorb certain types of air pollution through photocatalytic reaction, when used as a coating on pavements and roads in cities.

TiO₂ nanoparticles have been developed for use in sunscreens, however, there is some evidence that at this size the particles can enter human cells, cause DNA damage resulting in cancer [1]. Other research has raised concerns over inhalation of fine dust leading to respiratory diseases.

The problem with TiO₂ is that the extraction of pure material from the natural mineral deposits is destructive to the landscape, hugely energy intensive and polluting at every stage.

TiO₂ is found in minerals known as rutile, ilmenite and anatase. The largest mines are in Australia, Canada, and Norway, with other deposits found in India, Ukraine, Brazil, Madagascar and South Africa. Rutile is the purest form but most scarce.

Open cast mining is common. In some cases the mineral only contains 5% TiO₂, resulting in vast swathes of land being destroyed, only to return 95% of the material, but devoid of the ecosystem it once supported. This is happening in sensitive locations such as Madagascar.

 

Pic Fort Dauphin, Rio Tinto’s Ilmenite mine in Madagascar. By Ed Kashi, Prix Pictet.

 

There are two main manufacturing methods. The sulphate method involves dissolving the mineral in strong sulphuric acid, then heating the material to 1000°C. This process results in 5kg of CO₂ per kg of TiO₂, as well as emissions of SO₂, NOx, methane, and VOC’s to atmosphere and sulphates to water along with small amounts of chromium, lead, cadmium, and mercury. Energy consumption is estimated at 54 to 76 MJ/kg. [2].

The chloride method is cleaner but is more expensive, using either ilmenite or rutile. Heating the mineral to 1000°C in the presence of chlorine creates a vapour which crystallises during cooling. Combustion produces TiO₂, the chlorine is recycled. The process emits less CO₂ at 4.1kg per kg of material, but a similar amount of energy is consumed.

The acidic wastes from some TiO₂ production plants are dumped in the sea, the alkaline seawater quickly neutralises the waste, but the process de-oxygenates the water decimating sea life. Waste is also landfilled or neutralised by adding chalk, but land and air pollutions still results.[3]

As chartered surveyors at Conker Conservation Ltd, we have promoted sustainable construction and avoidance of damaging chemicals since the early 1990’s.  We believe it is important to consider the constituents of paints and other building products, even if they are not harmful themselves, as the manufacturing process has a major impact on the environment.

Choosing products which are not pure white, avoiding PVC, choosing low tech paints such as clay paint, lime wash and casein, are ways to avoid TiO₂. We also recommend using the website GreenSpec as a wonderfully useful resource for designers and specifiers wanting to check out the true green credentials of materials and products.

 

So remember, to be green, avoid white.