Kroll process, steps

TaMe 4.40. Specific-energy-consumption breakdown of Hunter and Kroll processes Step... 

The form of the Kroll process used in this plant is believed to be generally sinular to the process used at the Bureau of Mines plant, which has been described in detail by Shelton et al. [S3]. The principal steps in the Kroll process as practiced in the Bureau of Mines plant are own in Fig. 7.11. 

Zirconium is prepared from ZrCLj by the Kroll process (chemical reduction of the chloride by hquid magnesium at 900 °C), but the electrochemical route in molten salts is considered as a good alternative. As for Ta and Nb, pure chloride melts are not appropriate for the electrowinning to yield the metal because of too complex cathode process. The addition of fluoride ion source (KF) allows to stabilize Zr ions in the form of K2ZrFg which is reduced in one step to Zr [23]. 

For hafnium electrowinning, electrolysis process is readily preferred to Kroll process Cezus developed the process in pure chloride media from HfCl4, reduced in Hf in a one single step [24]. However, the mechanism is controversial, other authors proposing two steps in pure chloride and a single step in chloride-fluoride melts [25]. 

Zirconium production with the Kroll process is carried out by the following steps [19.4] ... 

Titanium is produced by chlorination of rutile (Ti02, 95%), synthetic rutile prepared from ilmenite or titanium slug of a high content with cokes at 1000 C to give crude TiCU, which is then purified by distillation and by reduction of the purified TiCU with Mg at about 900 °C under argon atmosphere (Kroll process), or by two step reduction with sodium metal (Hunter process) [2-5]. 

The most well-known method of titanium production is the Kroll process, which involves the reduction of TiCl4 by magnesium. The first step in the process is the preparation of the tetrachloride itself, which is carried out by the chlorination of a mixture of carbon with rutile or il-menite. The Kroll magnesium-reduction reaction takes place in a closed heated reactor vessel under an inert atmosphere. Liquid TiCU is introduced to the liquid magnesium already present in the vessel, thereby initiating the reaction 2Mg + nCl4 —> 2MgCl2 + Ti. The reaction prod-... 

The bismuth that is found in the lead ore accompanies the lead through the smelting operation right up to the last refining steps. The removal of bismuth then requires special techniques, the most common being the Betterton-Kroll and the Betts processes (5). 

During smelting, calcium reports exclusively to slag, but is subsequently introduced into lead bullion as calcium metal additions during removal of bismuth by the Kroll Betterton process. The residual calcium is readily removed by oxidation in the final caustic refining step with the addition of sodium... 

William Kroll (1889-1973) from Luxembourg described an economically and technically feasible way of producing titanium on a largescale [18.2]. This opened the way to the exploitation of titanium. The first step in the KroU process is the manufacture of titanium chloride. Chlorine gas is passed through a mixture of titanium oxide and carbon in high towers at a temperature of 900°C. 

A closed system for removing naphthalene from coke-oven gas in the final cooler is described by Kroll and Barry (1991). In this system, recycled water and fresh water are sprayed into the process gas at high flow rates to cool and saturate the gas with water. Naphthalene is condensed and collected with the water. The naphthalene is removed from the water by contact with liquid tar in a liquid-liquid extraction step at the bottom of the spray contactor. After naphthalene removal the water is pumped through an indirect heat exchanger (cooler) and recycled with fresh water makeup to the spray nozzles. 

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