Materials Science and Engineering A271 (1999) 485 – 490 Increased dissolution of ilmenite induced by high-energy ball milling Y. Chen a,b, *, J.S. Williams a , S.J. Campbell c , G.M. Wang c a Research School of Physical Sciences and Engineering, Institute of Adanced Studies, The Australian National Uniersity, Canberra, ACT 0200, Australia b Department of Engineering, FEIT, The Australian National Uniersity, Canberra ACT 0200, Australia c School of Physics, Uniersity of College, Uniersity of New South Wales, Australian Defence Force Academy, Canberra, ACT 2600, Australia Received 14 December 1998; received in revised form 14 June 1999 Abstract High-energy ball milling treatment leads to full dissolution of natural ilmenite sands containing both FeTiO 3 and Fe 2 Ti 3 O 9 phases in a sulphuric acid solution at 100°C. The ilmenite material has been milled for various times in two environments (vacuum and air), and characterised by X-ray diffraction, Mo ¨ ssbauer spectroscopy and surface area analysis. It is found that after milling for only 10 h, 50% of the sample can be dissolved as a result of the increased surface area, nanocrystalline structure and high level of lattice distortion present in the milled sample. Complete dissolution of the ilmenite is obtained on extended milling (200 h) in an oxygen free atmosphere. This occurs as a result of a gradual reduction of the Fe 3 + phase (Fe 2 Ti 3 O 9 ) to the relatively more soluble Fe 2 + phase (FeTiO 3 ) on milling in vacuum. The results overall show that the chemical reactivity of milled materials can be affected significantly by the milling conditions and environment. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Ilmenite; Ball milling; Dissolution www.elsevier.com/locate/msea 1. Introduction The increased chemical reactivity induced in solids by mechanical treatments such as ball milling or grinding is generally referred to as mechanical activation. As reviewed by Lin et al. [1] and Boldyrev [2], the in- creased chemical reactivity of solids is linked with the increased surface area, small particle size and structural defects which are produced by mechanical treatment. However, it has been observed recently that the chemi- cal reactivity of materials increases continuously on milling time for extended periods (more than 100 h), while the surface area of the treated material decreases because of agglomeration effects [3,4]. In addition, ex- tended milling often causes structural changes in the materials as well as introducing high levels of contami- nation [5,6]. Chemical reactions between the milled materials and the contaminants and milling atmo- spheres can also take place during long-term milling [5 – 8]. However, the influence of structural changes, contaminations and milling atmospheres (especially in air) on the chemical reactivity of the materials has not yet been investigated thoroughly. Here, we present the results of an investigation of the chemical reactivity of mineral ilmenite (FeTiO 3 ) after different high-energy ball milling treatments. The reactivity has been moni- tored in terms of the dissolution of the milled products in an acid solution. This investigation also has strong industrial links and potential applications. In industry, high purity titanium dioxide (TiO 2 ) is obtained from ilmenite by using a chemical leaching process, the so-called sulphate process [9,10] in which ground mineral sands are digested with strong sul- phuric acid at 160 – 180°C for several hours. This yields a titanium sulphate solution that is later hy- drolysed and precipitated to form a TiO 2 pigment and a solid waste material consisting mostly of ferrous sulphate septahydrate crystals. Because of the low dis- solution of natural ilmenite sands, this process has to * Corresponding author. Present address: Department of Engineer- ing, FEIT, The Australian National University, Canberra ACT 0200, Australia. Tel.: +61-2-62490380; fax: +61-2-62490511. E-mail address: ying.chen@anu.edu.au (Y. Chen) 0921-5093/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0921-5093(99)00441-4