Titanium dioxide, also known titania, is the naturally occurring oxide of titanium, the ninth most abundant element in the Earth’s crust and the seventh most abundant metal. About 95percent of titanium ore extracted from the Earth is destined for refinement into titanium dioxide and some 5.7mtonnes of this is sold every year. From medicine to make-up, plastics to paper – hardly a day goes by when we do not use titanium dioxide.
Now researchers at the University of Leeds, UK, have developed a simpler, cheaper and greener method of extracting higher yields of one of this most useful and versatile of minerals.
In powder form titanium dioxide is widely used as an intensely white pigment to brighten everyday products such as paint, paper, plastics, food, medicines, ceramics, cosmetics – and even toothpaste. Its UV ray absorption qualities make it perfect for sunscreen lotions too.
Titanium dioxide is also a precursor material for titanium metal production. In metal form it is strong and lightweight and is used in the aerospace and electronics industries as well as being used to strengthen golf clubs and fishing rods. It is also inert and biocompatible, making it suitable for medical devices and artificial implants.
As such, it’s hardly surprising that the global market for this important mineral is some £7billion per year.
Unfortunately, despite its relative abundance in nature, it’s natural occurrence is never pure, being bound with contaminant metals such as iron, aluminium and radio-active elements.
Pigment grade titanium dioxide is produced from mineral ore by smelting, then treating the slag with chlorine, or by directly introducing it into a sulphuric acid solution. These two processes generate toxic and hazardous wastes. The treatment of such wastes is expensive and complex.
The patented process developed by professor Animesh Jha of the Faculty of Engineering at Leeds consists of roasting the mineral ore with alkali to remove the contaminants, which are washed and leached with acid to yield valuable by-products for the electronics industry. The coarse residue left behind is then reacted with 20times less than the usual amount of chlorine to produce titanium dioxide powder.
The Leeds process gives an average yield of up to 97percent titanium dioxide, compared with the current industry average of 85percent. This level of purity will reduce production costs of pigment grade materials and waste disposal costs (Fig.1).
Furthermore, Jha is confident that the process can be further refined to yield 99percent pure titanium dioxide: “Researchers have sought a sustainable replacement for current processes for many years. Our aim was to develop new technology for complex minerals of titanium dioxide that are particularly
low-grade and whilst readily available in the world market, can’t yet be extracted economically.
“Our process is a real world breakthrough, because it can be used for both lower and richer grades of ores and it overcomes major environmental concerns about having to neutralise and discharge wastes generated in the process that end up going into contamination ponds.” he concluded.
Jha and his colleagues have formed an industrial partnership with Millennium Inorganic Chemicals to develop this technology. The research was jointly funded by the Sustainable Technology Initiative Programme of the UK’s Department of Trade and Industry, in collaboration with the Engineering and Physical Science Research Council (EPSRC) and Millennium Inorganic Chemicals.l