Preparationoftitanium_省略_lagbymoltenNaOH

International Journal of Minerals, Metallurgy and Materials Volume 19, Number 3, Mar 2012, Page 205 DOI: 10.1007/s12613-012-0539-9

Corresponding author: Tao Qi E-mail: tqgreen@home.ipe.ac.cn © University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg 2012

Preparation of titanium dioxide from titania-rich slag by molten NaOH method

Yan-fang Han1,2,3), Ti-chang Sun1), Jie Li2,3), Tao Qi2,3), Li-na Wang2,3), and Jing-kui Qu2,3) 1) School of Civil and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China 2) National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China 3) Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China (Received: 22 February 2011; revised: 19 April 2011; accepted: 26 April 2011)

Abstract: Preparing titanium dioxide from titania-rich slag (TiO2 73wt%) by molten NaOH method has been developed. The effects of tem-perature and reaction time on the titanium conversion were investigated. The results showed that temperature had significant influence on the titanium conversion as well as the structure of the product. About 92% of titanium in the titania-rich slag could be converted after reacting with NaOH at 500°C for 1 h. Metatitanic acid was formed through the steps of washing treatment, acid dissolution, and hydrolysis. Well-dispersed spherical titanium dioxide particles with an average size of 0.1-0.4 μm can be obtained by calcination of metatitanic acid. In addition, the content of titanium dioxide in the product is up to 98.6wt%, which can be used as pigments after further treatment of coating and crushing.

Keywords: slags; titanium dioxide; molten salt method; pigments

[This work was financially supported by the National Key Technologies R & D Program of China (No. 2006BAC02A05), the National Basic Research Program of China (No. 2007CB613501), the Knowledge Innovation Program of the Chinese Academy of Sciences (No. KGCX2-YW-214), and the Special Funds of “Mountain Tai Scholar” Construction Project.]

1. Introduction Titanium dioxide pigments are the most frequently ap-plied white pigments, commonly used in the paint, plastic, rubber, paper, ceramic, and cosmetic products [1-2], due to their inert, nontoxic, and thermodynamically stable properties [3]. Appropriately sized TiO2 particles provide more light

scattering and are of a lower cost than other materials [4].

The industrial production of titanium dioxide pigments generally employs the sulfate process and the chloride proc-ess. The sulfate process is a relatively low-technology batch manufacture. Titanium-bearing ore is dissolved in sulfuric acid, followed by thermal hydrolysis of titanium ions in highly acidic solutions, and then, the precipitate of hydrous

titania is calcined to grow titanium dioxide crystals to pig-mentary dimensions [5-6]. This method is relatively simple in operation, but the conversion rate of Ti from the ore to ti-tanium oxide is relatively low (about 80%). Aside from that a large amount of wastes are produced in the sulfate process, resulting in serious environmental problems [7-8]. In the production of titanium dioxide pigments by the chloride process, titanium tetrachloride (TiCl4) is first produced as an

intermediate product and then subsequently oxidized at high temperature above 1000°C [9-10], which is a high-en-ergy consuming process. In addition, the raw material to be used is required to have a high grade and good fluidity be-cause of passing such processes as chlorinating the tita-nium-containing feed material by the fluidized bed chlorina-tion process and separating impurities for obtaining the tita- 206 Int. J. Miner. Metall. Mater., Vol.19, No.3, Mar 2012 nium tetrachloride, and a naturally occurring rutile ore has hitherto been mainly used as the raw material [11]. Recently, a novel metallurgical process for pigmentary TiO2 produc-

tion with high titanium slag (TiO2 92wt%) as a material has

been developed by Xue et al. [12]. In this process, the high titanium slag was decomposed in a molten NaOH system with an NaOH-to-high titanium slag mass ratio of 1.5:1. In comparison with the sulfate process, this method has the advantages of high reaction activity, high conversion of Ti, and less waste emission to the environment. The key point of this process is the liquid phase decomposition of titanium slag in the molten NaOH medium at 500°C. The unique re-action system has been proved to have a high reaction activ-ity and high Ti conversion rate, which can reach up to 99%. Using lower-grade titania-rich slag as a raw material is a good prospect for better application, because the material is of lower cost and easier to obtain compared with high tita-nium slag. Feng et al. [13] has conducted exploratory re-search to produce titanium oxide by the same process using acid dissolved titanium slag (TiO2 73wt%) as a raw material.