Titanium is not a rare element on earth. The oxide, TiO
2 is widely used in paints and a host of other applications, including in sunscreens and in photocatalytic materials. The price of purified TiO
2 is in the neighborhood of $150/ton.
Titanium
metal on the other hand, which is used mostly in aerospace applications, including famously the SR-71 Blackbird spy plane, is very expensive and often difficult to obtain.
This has been a shame, since the metal is superior to steel inasmuch as it is refractory (wrt steel) and light weight (wrt steel). If the frame of the World Trade Center had been titanium rather than steel, the building may have withstood the attack by dangerous fossil fuel terrorists with comparatively minor damage.
The reason that the metal is expensive while the ore is cheap is the same reason that Napoleon III had
aluminum dinner service at his palace as a display of his wealth. In former times, the reduction of alumina (the ore) to aluminum was very difficult and therefore very expenive. After the electrolytic molten salt Hall process was discovered, aluminum became cheap and Napoleon's expensive dinnerware became rather ordinary.
I have been aware of a new titanium reduction process that is electrolytic, and was patented about 8 or 10 years ago. This should improve access to titanium metal in the long run.
A recent paper in the scientific literature that I had cause to contemplate touches on this subject.
The paper is "Molten salt applications in materials processing" and the reference is
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TXR-4F0GBHM-1&_user=10&_coverDate=02%2F01%2F2005&_alid=1358633357&_rdoc=1&_fmt=high&_orig=search&_cdi=5597&_sort=r&_docanchor=&view=c&_ct=22&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=582a706845855d201e50f0481dfbec1c">Journal of Physics and Chemistry of Solids 66 (2005) 396–401
Mostly the paper refers to the refining of
calcium metal, using a novel porous ceramic sheath around the annode.
Some excerpts of the paper beginning with the introduction:
Molten salt processing provides a unique opportunity to process and produce metals where gas-based pyro-reduction, metallothermic reduction, hydrometallurgical methods or aqueous electrochemical techniques are not feasible due to thermodynamic or kinetic constraints. Industrial applications of molten salts have been well recognized for more than century. In spite of the use of high temperature corrosive liquids, molten salts offer unique opportunities. The steel and other non-ferrous metal industries make use of molten salts and slags for refining and precision heat treatment.
Commercial production of aluminum, magnesium, sodium, potassium, lithium, beryllium, etc. make use of molten salt reduction or electrolysis, since any other method is technoeconomically not feasible. Several other reactive metals, such as lanthanides and actinides make use of molten salt processing for extraction and refining. Additionally, the high temperature carbothermic or metallothermic smelting reduction methods for metal production are associated with the generation of significant quantity of waste as slags. There’s a need to develop alternative processes that have low waster ideally a ‘zero-waste’ generation. Low temperature multicomponent molten salts <1>, as well as room temperature ionic liquids <2> have been developed for materials processing. Molten salts are also finding applications in fuel cell technology. The process described in this paper for producing metals is primarily aimed at complete recycling of process waste. It is also anticipated that the suggested scheme will lower the production cost, since the reductant is electrolytically generated. Significant research effort has been invested in recent times for producing titanium and other refractory metals by molten salt processing. Implementation of this scheme with respect to titanium production is demonstrated <3–5>...
Further on:
...A number of research studies have been initiated to prepare a waste-minimization strategy <6–9>. This work describes two aspects of the overall metal production program: (a) electrolytic recovery of calcium metal from theDOR process effluent salt comprising calcium oxide and calcium chloride and (b) use of electrolytically recovered calcium metal in situ as a reductant in a hybrid reactor. There are several advantages of the suggested hybrid process. The process ideally produces ‘zero’ waste and themetals can be recovered from inexpensive oxides/chlorides without the need for an expensive reductant. Oxygencarbon dioxide and chlorine gases are the only process effluent which can be easily contained. Operational costs include graphite anode, electric power and recyclable salt only. The process is also amenable to alloy production directly by incorporating co-reduction of respective oxides...
The paper ends thusly.
...The process could be conducted under a cover ofnitrogen gas in the electrowinning and reduction chamber, since the metals are not exposed to high temperature atmosphere and are always contained within the salt phase.Fig. 4 shows two such possible designs that have been adopted to produce titanium metal (OS Process) byelectrolytically winning calcium and using it simultaneously to reduce titanium oxide <11>. In Fig. 4a, the calcium chloride salt with electrodeposited calcium is transferred into another reactor where the reduction of titania takes place. In the design shown in Fig. 4b, titania is introduced in the same chamber and the reduction idaffected by the calcium deposited on the iron cathode.
6. Conclusion
Calcium can be electrolytically produced by dissociating calcium oxide in a molten calcium chloride electrolyte. Aporous ceramic diaphragm around the anode is essential for separating the anolyte and catholyte to be able tocathodically deposit calcium. The cell temperature, fluidity of salt and porosity of the sheath are critical in recovering calcium. Ionic diffusion through the sheath is the rate controlling step. A diffusion coefficient in the range of 10K5to 10K6 cm2/s is obtained for a 30% porous alumina sheath for cell temperatures between 800 and 9008C.A hybrid process is investigated consisting of electrowinning calcium from calcium oxide and in situ utilization of calcium as a reductant within the same reactor. Silver, tin, lead and bismuth can be produced by pyrochemical reduction of their respective chlorides and/or oxides with calcium in a calcium chloride medium. These metals were produced as a surrogate for a certain radioactive metal.
Cool. I cite this paper as a demonstration of two of the three R's they teach kids Recyle and Reduce.
We can make
better materials cheaper and more sustainably if we invest in intellectual capital.