Contents lists available at ScienceDirect Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa Depression of the selective separation of rutile from almandine by Sodium Hexametaphosphate Richard M. Kasomo a,c , Hongqiang Li b, *, Huifang Zheng b , Qian Chen a , Xiaoqing Weng b , Akisa D. Mwangi a , Emmanuel Kiamba c , Shaoxian Song a, * a College of Resource and Environmental Engineering, Wuhan University of Technology, Wuhan, 430070, China b Xingfa School of Mining Engineering, Wuhan Institute of Technology, Wuhan, 430205, China c School of Mines and Engineering, Mining and Mineral Processing Engineering Department, Taita Taveta University, Voi, Kenya GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Sodium Hexametaphosphate Rutile Almandine Adsorption mechanism ABSTRACT Sodium Hexametaphosphate (SHMP) is widely used as an inorganic depressant of carbonate minerals. But little information if any exists on the proper mechanism of how SHMP depresses silicate minerals. In the study, flotation separation of rutile and its main gangue mineral almandine using a Sodium Hexametaphosphate is investigated. The study was conducted through micro flotation tests of single and artificially mixed minerals. Adsorption mechanism was analyzed through Zeta potential and X-ray photoelectron spectroscopy (XPS) ana- lyses respectively. The flotation tests for single and artificially mixed minerals show that SHMP is an efficient depressant in the separation of rutile ores from almandine as a possible gangue mineral. Zeta potential mea- surements and XPS analysis indicate that more SHMP was adsorbed on almandine surface as opposed to that of rutile. Fe ions on the surface of almandine were the main active sites for collector adsorption, while the P in (NaPO 3 ) 6 is central to the depression process. The adsorption mechanism of sodium Hexametaphosphate on almandine surface was mainly attributed to the electrostatic interaction and chemical bonding. While on the other hand, SHMP seems to have negligible effect on rutile surface. 1. Introduction Rutile (TiO 2 ) occurs naturally as titanium dioxide. Theoretical TiO 2 content of a rutile ore is 100 %, but it contains impurities such as Fe 2 O 3 and Cr 2 O 2 and others which reduces its purity to 93–95 % [1].Rutile is a critical mineral whose demand is on rise with limited supply, and little https://doi.org/10.1016/j.colsurfa.2020.124631 Received 23 October 2019; Received in revised form 23 February 2020; Accepted 27 February 2020 ⁎ Corresponding authors. E-mail addresses: lhq-18@163.com (H. Li), ssx851215@whut.edu.cn (S. Song). Colloids and Surfaces A 593 (2020) 124631 Available online 28 February 2020 0927-7757/ © 2020 Elsevier B.V. All rights reserved. T