Decomposition Kinetics of Titania Slag in Eutectic NaOH-NaNO 3 System
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RODUCTION
TITANIUM is usually found in igneous and metamorphic rocks as natural rutile and ilmenite.[1] A survey on the application of titanium indicated that almost 95 pct production of titanium dioxide (TiO2) are employed in paint, coating, filler for plastic and paper, adsorbent, cosmetics, catalyst, and gas sensor.[2–6] The two main commercial technologies for the production of pigment-grade TiO2 include sulfate process and chloride process.[7–10] In the sulfate process, titania slag (Ti-slag, 72 to 87 pct TiO2), or ilmenite (40 to 60 pct TiO2) is used as feed material.[11] The major advantages of this process include low capital costs and flexibility in feed material.[12] The major disadvantage is the production of large amount of wastes or toxic by-products, such as spent sulfate acid and copperas, resulting in serious environmental problems.[7] In the chloride process, rutile (natural or synthetic) and high Ti-slag (85 to 90 pct TiO2) are used as raw materials. The chloride process has some advantages over the traditional sulfate process in terms of product quality and waste management. Ti-slag prepared from ilmenite by carbothermal reduction is a suitable feedstock for pigment-grade TiO2 industries.[13] In the sulfate process, the use of ilmenite as raw material produces more waste than Ti-slag as raw material. With the increasingly strict regulation of environment protection, Ti-slag becomes the main raw material in the sulfate process. On the DONG WANG, Assistant Professor, ZHI WANG and TAO QI, Professors, and LINA WANG and TIANYAN XUE, Vice Professors, are with the Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China, and also with the National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, No. 1 Bei Er Jie, Zhong Guan Cun, Beijing 100190, People’s Republic of China. Contact e-mail: [email protected] Manuscript submitted July 13, 2015. Article published online November 18, 2015. 666—VOLUME 47B, FEBRUARY 2016
other hand, the natural rutile reserves cannot guarantee the feed materials supply in the chloride process, thus high Ti-slag or synthetic rutile is the main feed materials.[14,15] However, upgrading processes for low-grade Ti-slag are usually expensive due to the involvement of multistep of energy-sensitive thermo-reductive conversions and leaching to remove iron impurities.[11] Therefore, the use of Ti-slag as a raw material in developing more environmentally friendly and energy-saving methods to produce titanium dioxide is urgent. For example, Fang reported a novel processes, including alkaline roasting of Ti-slag followed by leaching, solvent extraction, hydrolysis, and calcination.[12] Nayl proposed a process by decomposition of Ti-slag in ammonium hydroxide system.[16] Recently, a novel approach for NaOH decomposition of titanium has been developed using Ti-slag as raw material.[17,18] This technique is c
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