Titanium dioxide (TiO2) is produced in two major commercial forms worldwide: the traditional - and quantity-wise essential - production of pigment grade, and the innovative ultra-fine or nano grade, which is increasingly being utilized in modern technologies.
As a result of its ability to protect materials against the deleterious influences of sunlight and weather, as well as due to its extreme bleaching and coating power, titanium dioxide is literally present in every facet of modern life. This uniquely white pigment, which is not anticipated to be substituted in either the long- or short-term, is commonly used in the manufacture of paints and coatings of every type, as well as plastics, papers, rubbers, ceramics, welding electrodes, foodstuffs packaging, medicines and toothpastes ...
The nano grade of titanium dioxide is most often used in the production of catalysts, cosmetics (mascaras, lipsticks, powders, eye shadow, and - in particular - sun screen products), as well as remediation of waste waters, plastic packaging and self-cleaning facades. The future of so-called nanocomposite materials appears most promising.
The commercial manufacture of titanium dioxide began in Norway in 1916, and, at present, world consumption of TiO2 pigment amounts to approximately 4.8 million tonnes per annum, whereas the volume of currently installed production capacities amounts to 5.3 million tonnes.
TiO2 pigment may be manufactured using either the older sulphate process (Norway, 1916) or the more contemporary chlorine process (USA, 1951). The global ratio between production capacities of sulphate (SP) and chlorine (CP) is approximately 44:56 in favour of CP, while in Europe the ratio amounts to 69:31 in favour of SP.
Cinkarna Celje has been manufacturing TiO2 pigment based on the sulphate process using French technology since 1973. Between 2001 and 2006 the plant was completely renovated and new technology, emanating from the company’s indigenous knowledge and expertise, was introduced.
The titanium ore is first agitated with concentrated sulphuric acid, which accomplishes the conversion of TiO2 to titanyl sulphate; it is clarified and then hydrolysed through a number of stages. The resultant gel is washed and treated with chemicals that adjust the physical texture (crystal form) through drying and calcination. Although, following this phase, the product already displays the characteristics of a pigment, it still doesn't meet market requirements. The unrefined pigment is consequently surface-treated, usually with a combination of hydrated alumina, silica and/or zirconium deposited into the core of the TiO2 particles using a wet precipitation process. Indeed, the manufacture of this highly sought-after product involves its undergoing a sequence of 22 basic and 18 supporting technological procedures.
In addition to the TiO2 manufacture, the process also results in the production of waste sulphuric acid, which is partially recycled, whereas the remaining portion is neutralised. Chemical gypsum (CaSO4 x 2H2O), is also a by-product of this process, and a portion is marketed, while the residual is a neutral waste which is deposited as landfill.