TiO2 or tai bai fen? China’s dominance to rise

By Mike O'Driscoll
Published: Monday, 26 November 2012

John Ollett reports from the sidelines of this years TZMI conference in Hong Kong, where he finds the conversation has turned to the TiO2 processing route and China’s position in the market.

In the future, will we call it TiO2 or tai bai fen [TiO2 in Chinese]?

That was the question posed by David McCoy, managing consultant and director of mineral sands consultancy TZMI, on the last day of the annual TiO2 conference in Hong Kong

And the point McCoy was making to delegates, following two days of papers, was that China is the future of TiO2, irrespective of its current downturn.

Chinese demand for TiO2 is projected to rise to 35% of the total global market by 2020, from 25% today. Demand from the emerging economies will remain consistent at around 33%, but demand from the advanced economies is projected to fall to 33% from 40% by 2020.






Sulphate route ‘not going away’

“Chinese sulphate is not going away as a process,” McCoy said, adding that, while the global market is now probably equally divided between chloride and sulphate, the latter will begin to rise and by 2020 he expects the split to be 54% sulphate 46% chloride.

This projected rise to 2020 is not simply a beginning to China’s growth, but rather a continuance, as the country’s demand for TiO2 has risen by almost 10% since 2005 to 25% of the world market today.

The country’s production has also rocketed. From being practically non-existent as recently as 1990, it rose to be the world’s second-largest producer, neck-and-neck with the US by 2010, and projected to become the world number one by a substantial margin in the future.

This is being helped by consumers outside of China increasingly opting for Chinese sulphate grade TiO2, McCoy added.

“We are sure that some people have made the decision to go with a different source - still TiO2, just a different area of the world,” he said.

Now China has switched to lower-grade, and therefore lower-priced, feedstock mixes, pigment end-users are unlikely to switch back, which will further boost demand for Chinese sulphate products outside of the country.

“Chinese supply leaving the country has risen, while internal demand has dropped - it is a net exporter now,” he added.

“The majority of Chinese exports go to countries around China - that is the growth area of the world,” he said.

An estimated 37% of production this year has gone to surrounding emerging economies in Asia Pacific, but a high proportion is still going to more established economies, with 13% going to western Europe and 11% going to North America.




The possibility of Chinese chloride production

Official Chinese government policy has seen an increasing number of producers focusing on chloride production. This edict has even gone as far as to refuse sulphate-route companies permission to carry out IPOs.

The country’s first, and currently only, plant was Jinzhou, which entered production in the early 1990s and produces approximately 60,000 tpa with a rumoured ramp up to 100,000 tpa expected.

However, questions remain over the quality of the product.

Yunnan Xinli Nonferrous Metals Co. Ltd has also claimed to have a chloride process bought from a European consultancy business but the authenticity of the claim has been questioned by its peers.

Of the projects in the pipeline, the most promising are in Henan province. Henan Billions Chemicals Co Ltd recently completed a deal with German management consultancy Ti-Cons for processing technology as well as having already completed a deal with paint producer PPG for relevant technology and development aid.

“The [...] agreement between Henan Billions and Ti-Cons is for the delivering of the complete know-how for the erection and operation of a plant for the production of 100,000 tpa of TiO2 using the chloride route,” Christian Weiland of Ti-Cons, said.

Ti-Cons specialises in TiO2 process technology, especially in bringing chloride-route technology online.

Lucha Xiangmao, also in Henan, announced that it will construct a 60,000 tpa chloride plant.

Pangang Group and CYMG have also had projects under construction for some time, but the former has been hampered by accusations of trade-secret theft from DuPont.

DuPont’s Dongying’s project has reportedly been shelved, but may resurface at some time, McCoy said.

Chloride-route technology was invented in the US and is utilised mostly by major western producers such as DuPont (US), Kronos (US), Cristal Global (Saudi Arabia), Huntsman (UK) and Tronox (US).

Despite this activity, two major obstacles stand in the way of chloride, TZMI said.

“The feedstock in the country is not suited to the chloride process,” said McCoy, adding that the majority of internal feedstock produced is either ilmenite or chloride grade slag, both of which are suited to the sulphate process.

The second is the issue of intellectual property, as the chloride process is extremely complicated to apply and most processes are controlled by the leading producers.




TiO2 - the facts

Titanium dioxide, better known by its chemical formula TiO2, is a simple inorganic compound used as a white pigment.

It has a very high refractive index of 2.7, which compares with values of only 2.0 and 1.6 for zinc oxide and china clay respectively. This high refractive index gives the potential for producing much greater opacity or hiding power, making TiO2 a much better pigment.

It can be produced in either an anatase or rutile crystalline structure. Rutile is more stable under high heats than anatase TiO2. At over 700°C the structure of anatase crystals changes to that of rutile.

The rutile crystalline structure is also more compact which gives it a higher specific gravity (4.23-4.25 v 3.8-4.0) and a higher measurement on the Mohs Hardness scale (6-7 v 5.5-6). Rutile also has a higher refractive index than anatase (2.76 v 2.55).




Feedstock

TiO2 is not found in nature, but must be made from the feedstock minerals rutile, ilmenite, and leucoxene. It can also be made from the synthetic feedstocks, synthetic rutile and titanium slag, which are themselves made from natural feedstocks.

Rutile is the best and most expensive of the natural feedstocks whereas ilmenite can only be used in the sulphate process or upgraded into a synthetic feedstock. While rutile is sourced only from mineral sand deposit, ilmenite can come from either hard rock or mineral sand deposits.

Synthetic rutile is produced by reducing the iron oxide in ilmenite to metallic iron using carbon monoxide, followed by reoxidation and separation from the TiO2 rich fraction (Becher process) or leaching with hydrochloric acid (Benelite process).

Slag feedstocks are produced by the smelting of ilmenite with coal at high temperature. The process is adjusted to produce the different particle size requirements for sulphate or chloride use.

Leucoxene tends to have a high titanium percentage (70%-80%), but is exceedingly rare.




The industry

The titanium dioxide feedstock supply is dominated by Australia and South Africa. Pigment production, however, is centred on several major companies in the US and Europe.

China also has a large centre of production, but the majority is sulphate-route products. Only the Jinzhou plant, which was recently expanded to 60,000 tpa and is now majority owned by the Citic Group, produces using the chloride-route.

Several more may come on stream by 2015. The Pangang Group has claimed to be developing a 100,000-150,000 tpa chloride-route plant, but is in a dispute with the US government over the alleged theft of DuPont trade secrets.

Henan Billions is also developing chloride technology and has partnered with leading paint producer PPG Industries, which produced chloride-route TiO2 itself in the 1970s, to develop a 100,000 tpa chloride-route plant.

The processes

Titanium dioxide (TiO2) is mainly refined using one of two processes. The newest is a process that uses hydrochloric acid, but the technology is not widely available and supply is restricted to several large companies.

There are other companies that have chloride technology, but the most modern technology is highly patented and protected. ISK Japan also produces chloride-route TiO2.

The other process, which is more widely available, involves the use of sulphuric acid and is used throughout the US, Europe and China.

Major producers include Rockwood Specialties and its European segment Sachtleben, and Cinkarna Celje, Crimea Titan, Precheza AS, and Zaklady Chemiczne Police SA.

As of 2012, Rockwood is attempting to divest its TiO2 assets in order to focus on lithium.

Other processes do exist, such as Argex Mining’s CTL process, which creates TiO2 straight from ilmenite, but the chloride- and sulphate-route processes account for nearly all of the world’s production.

Advantages of the chloride process

The chloride process has several key advantages over the more widely available sulphate process. The first is that it gives a better quality of pigment that has better hiding powers and tinting strength and gives better coverage when used.

The chloride process is also much more environmentally friendly. However, the environmental impact of TiO2 production is mostly a factor of the raw materials used, the effluent treatment processes and the degree of by-product development a particular plant has.

A key difference between the processes is the choice of feedstocks that can be used. Ilmenite, the cheapest of the feedstocks, is rarely used by chloride-route producers because the low TiO2 content leads to high chlorine losses and high volumes of waste products.

Instead, chloride-route producers prefer to use natural rutile, synthetic rutile and chloride grade titanium slag. The most expensive of these, rutile, has the highest TiO2 content so gives the lowest waste volumes, followed by synthetic rutile and chloride-grade slag.

The sulphate process, on the other hand, thrives on the cheaper feedstocks as rutile-based compounds cannot be digested in sulphuric acid. The actual feedstock used by the plant, depending on whether it is sulphate-grade slag or ilmenite, will be determined by overall costs and environmental regulations (especially regarding waste discharge) and usually decided at the plant design stage.

How the chloride process works

The chloride process chemistry uses heat, chlorine gas and titanium feedstocks to create a bright, white TiO2.

The overall chemistry of this process can be represented as:

TiO2 + C + 2Cl2 = TiCl4 + CO +CO2

TiCl4 +O2 = TiO2 + 2Cl2

Chlorination is carried out at a temperature of between 800° and 1200° in a fluidised bed reactor in the presence of coke. The resulting gas stream contains titanium tetrachloride (TiCl4), oxides of carbon (CO, CO2) and all the impurity metals from the feedstock in the form of metal chlorides.

The gas stream is cooled, which allows the other metal chlorides to separate out as solids, and the TiCl4 goes onto the next stage where it is further cooled and condensed as a liquid and then fed to a high-temperature oxidation reactor.

Here, it is reacted with oxygen in a plasma reactor or toluene burner to reform into titanium dioxide and the chlorine is released and filtered off back to the beginning of the process. The only chlorine consumed is that which reacts with impurities.

This TiO2 is then processed using a range of chemical surface treatments, milling and drying operations to give a range of products, such as dispersion and durability, which make it more suitable for its particular end-use applications.

This “finishing” stage of the process can include chemical surface modification, filtration washing and drying, grinding, slurry makeup and additives to give it other properties.

The sulphate process

The sulphate process is a slightly more complicated process in terms of the number of stages involved, but it produces either rutile or anatase TiO2.

If ilmenite is used, a reduction step is required in which iron is added to convert any ferric iron to the ferrous form to aid separation later in the process.

The overall chemistry of the process can be represented as:-

FeTiO3 + 2H2SO4 = TiOSO4 + FeSO4 + H2O

TiOSO4 + H2O = TiO2n.H2O + H2SO4

TiO2n.H2O = TiO2 = n.H2O

The feedstock is first digested in strong sulphuric acid, which converts the titanium components into titanyl sulphate (TiOSO4) and the iron into sulphates (FeSO4). This creates a liquor that the rest of the process will work with.

This is followed by a clarification step to remove any undigested material from the liquor. For an ilmenite process, crystallisation typically follows, which separates out co-product ferrous sulphate heptahydrate (copperas), although it is also possible to extract copperas later in the process.

The liquor passes forward to a hydrolysis stage in which the oxysulphate is reacted with water to produce a hydrated titanium dioxide product and releases sulphuric acid. The hydrated TiO2 passes forward to a rotary kiln, where it is calcined to produce the anhydrous titanium dioxide product.

The TiO2 product then undergoes mostly the same finishing as product produced by the chloride process, that is chemical surface modification, filtration washing and drying, grinding, slurry makeup and additives to give it other properties.

The acid that is released at hydrolysis is not strong enough to be recycled and used directly at the digestion stage earlier in the process, so it must be either concentrated, to make usable acid, or neutralised to produce gypsum.

Making anatase crystals

To produce the anatase form of the titanium dioxide, a small portion of the liquor is neutralised with an alkali to produce anatase microcrystals. These microcrystals are then introduced into the main liquor, which is then hydrolysed under controlled conditions to produce anatase crystals.

To produce the rutile form of the titanium dioxide, a small portion of the liquor is neutralised in the presence of hydrochloric acid (or another monohydric acid), which is then reintroduced when the main liquor is hydrolysed.

The market

The consensus at this year’s TZMI conference was that the skies remain cloudy for both zircon and titanium dioxide pigment (TiO2) markets.

The boom of 2011 that led to such a positive conference last year has now faded.

“What a difference 12 months makes,” Philip Murphy, TZMI managing director, told the conference.

Last year was a year of two halves for both the zircon and TiO2 industries, he added, and this year seems to be following a similar pattern, with a global slowdown showing clearly in the second half of 2012.

The main cause of this has been destocking by end-users and reciprocal drops in plant utilisation rates.

Most zircon markets, in particular, are remaining weak and a short-term turn around seems unlikely, he said.

The short-term future appears bleak.

“We see surpluses [in supply] for the next couple of years [...] if supply reacts to market weakness, we could see further cutbacks [in production],” he said.

Demand will also weaken and 2012 is likely to show a decrease of 9%, he added.

This will hit zircon especially, where he believes there are “inventory excesses of 200 days - maybe even 250 - [...] and that will take some time to unwind”.

“Trading conditions [for zircon] are going to remain tough for a while,” he said.

For TiO2, on the other hand, Murphy could see improvement as early as the second half of 2013.

“A real return to growth we only expect in the second half,” said Murphy.

The current downturn could also affect new projects as investment capital dries up, which will delay their production schedules.

“The grey clouds will not disappear anytime soon and there are a couple of darker ones in the background,” Murphy added.