Recycling of TiO2 Pigments from Waste Paint: Process Development, Surface Analysis, and Characterization
Doctoral thesis, 2018

Pigments are commonly used in paint, plastic and paper products and titanium dioxide (TiO2), the most important white pigment, accounts for approximately 70 % of the total volume of all pigments used today. Minerals containing TiO2 are relatively abundant in the earth’s crust. However, the production of TiO2 is energy intensive and carries a high environmental burden. Therefore, the paint industry is seeking replacements for the virgin TiO2 pigment used extensively in paint formulations today. The research work presented in this thesis was carried out to investigate the possibility to use secondary TiO2 pigments, recycled from waste paint, as an alternative to virgin pigments.
Typically, commercial grade pigments are not pure TiO2. Rather, they are surface treated in order to make the pigments more compatible with the paint matrix and to facilitate optimum dispersion. Waste paint feedstock for a recycling process will therefore contain TiO2 pigments having different chemistries due to the variety of surface coatings. In this research three pigments, coated with different combinations of aluminium, silicon, and zirconium oxides were investigated.
The TiO2 was recovered from paint in a three-step recycling process. First, the paint was pyrolysed at 500 °C in a nitrogen atmosphere to remove the volatile organic fraction. Next, the inorganic pyrolysed residues were oxidized in air at 500 °C to remove any residual organics and black carbon. After pyrolysis and oxidation the inorganic fraction was found to be contaminated with ionic salt residues from the decomposition of paint components during the recycling process. Therefore, the final step in the recycling process was to wash the residues in the presence of a mixture of ion exchangers yielding a pure secondary TiO2 product.
In order to clarify the extent to which the pigment was affected by the recycling process, the characteristics of the recycled pigments were studied using techniques such as powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and measurement of the dynamic electrophoretic mobility. Of the three pigments studied, it was shown that a pigment coated with a combination of silicon and aluminium oxides was more prone to degradation in the recycling process compared to pigments coated with a combination of aluminium and zirconium oxides or only aluminium oxide.
In addition, recycled pigment was used as a replacement for virgin pigment in a paint formulation. Results showed that the paint made from recycled TiO2 had a minor decrease in opacity, and that the effect on whiteness was insignificant when compared to a paint containing virgin pigment. However, surface defects due to poorly dispersed pigments decreased the gloss of the paint film. Even though the performance of the recycled pigment was lower than that of the virgin




Titanium dioxide


Municipal solid waste handling




Mikael Karlsson

Chalmers, Chemistry and Chemical Engineering, Energy and Material

Vem har inte en skvätt överbliven gammal färg hemma som står och samlar damm? I bästa fall dyker något nytt projekt upp där färgen kan återanvändas. Med största sannolikhet hamnar dock färgen på en återvinningsstation där den skickas till förbränning och blir till aska. Det uppskattas att
3 100 000 000 L dekorativ färg tillverkas globalt varje år. Ungefär 10 % av denna färg kommer aldrig till användning. Även i dagens samhälle där återvinning och resurseffektivisering är i fokus så saknas processer där färgavfall kan tas till vara på bästa sätt.

Det vita pigmentet titandioxid (TiO2) är i dagsläget det överlägset mest använda pigmentet i produkter såsom färg, plast och papper. Framställningen av TiO2 är dock energiintensiv och har en hög miljöbelastning. Därför söker färgindustrin efter alternativ till konventionellt framställd TiO2. I denna avhandling beskrivs hur TiO2 kan utvinnas från färgavfall med hjälp av en pyrolysprocess. Det återvunna pigmentet karakteriseras efter återvinningen och används sedan vid tillverkning av ny färg.

Who does not have a splash of old paint at home that is collecting dust? In the best situation, a new project arises where the paint can be reused. However, most likely the paint ends up at a recycling station where it is sent for combustion and becomes ash. It is estimated that 3 100 000 000 L decorative paint is manufactured globally every year. About 10 % of this paint will never be used. Even in today's society where recycling and resource efficiency are in focus, there are no processes where paint waste can be handled in the best possible way.

The white pigment titanium dioxide (TiO2) is currently the most widely used pigment in products such as paint, plastic and paper. However, the production of TiO2 is energy intensive and has a high environmental impact. Therefore, the paint industry is constantly looking for alternatives to conventionally produced TiO2. This thesis describes how TiO2 can be extracted from paint waste using a pyrolysis based process. The recycled pigment is characterized after recycling and is then used in the fabrication of new paint.

Driving Forces

Sustainable development

Areas of Advance

Building Futures (2010-2018)


Materials Science

Subject Categories

Chemical Process Engineering

Materials Chemistry

Other Chemical Engineering



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4403


Chalmers University of Technology

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