Technical note The importance of mechanical scrubbing in magnetite-concentrate reverse-flotation Wencai Zhang ⇑ , Rick Honaker, Yonggai Li, Jinxiang Chen Mining Department, University of Kentucky, KY 40502, USA article info Article history: Received 2 January 2014 Accepted 24 July 2014 Available online 28 August 2014 Keywords: Magnetite concentrate Cationic reverse flotation Coagulation Scrubbing DVLO calculation abstract Getting magnetite concentrate with extremely high Fe grade using reverse flotation method has become increasingly important due to the enhanced requirement of iron making industry. The coagulation in magnetite-concentrate flotation system may impose negative effect on flotation performance. This paper combined the DLVO calculation and microscope observation to study the coagulation behavior in the sys- tem. The result shows that the coagulation between fine magnetite and coarse silica particle is very likely to occur with energy barrier 1.5  10 18 J at pH 10.0, which is much smaller than 1.6  10 17 J and 3.3  10 17 J for fine magnetite and fine magnetite-coarse magnetite particles. The coating of fine mag- netite particle on silica surface was observed under microscope. Mechanical scrubbing increases the con- centrate Fe grade and recovery by 1.5% and 8.5% respectively. Magnetite concentrate of 67.9% Fe grade and 71.5% Fe recovery was finally obtained. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The dependence of magnetic force, gravity and hydrodynamic force on particle size and the entrapment caused by magnetic floc- culation severely limit the use of magnetic separation in ultra-fine iron-ore enrichment (John, 1974; Arol and Aydogan, 2003). Tradi- tional magnetic separation process was difficult to separate the iron-ore particle less than 100 lm(Svoboda and Fujita, 2003). Get- ting magnetic concentrate with high Fe grade via reverse flotation is very efficient (Cao et al., 2013; Bada et al., 2012). Concentrate with 69.8% Fe and 2.0% SiO 2 has been obtained with a combined process of low-intensity magnetic-separation and cationic reverse-flotation (Bada et al., 2012). People have noticed that some coagulation behavior in magnetite-concentrate flotation system can impose negative influence on flotation performance. To avoid this influence, Bada et al. (2012) agitated the feed magnetite mate- rial with stirred mill; concentrate with 4.3% higher Fe grade can be obtained compared with direct flotation. However, few papers pro- vide deeper insight for this method. To systematically study the role of scrubbing play in magnetite- concentrate reverse-flotation system, this paper first measured the zeta-potential of magnetite and silica. According to the data obtained from zeta-potential test, this paper explained and pre- dicted the interaction among particles in the system through DLVO theoretical calculation and the results were verified via microscope observation. Finally, this paper compared the physical dispersion (scrubbing) and chemical dispersion (hexametaphosphate sodium) in terms of improving flotation performance. 2. DLVO theory DLVO theory was used to evaluate the total interaction energy between mineral particles in terms of electrostatic repulsion (V E ) and Van-der-Waals force (V W ). This approach was written as V D T ¼ V W þ V E V W means the Van der Waals energy, J, V E means the electrostatic energy, J, V D T means the total interaction energy, J. For two particles with radius R 1 and R 2 respectively, V W equals V W ¼ A 6x R 1 R 2 R 1 þ R 2 A means the Hammaker constant in vacuum, and x means the distance between two particles. For two different types of particles with radius R 1 and R 2 respec- tively, V E equals V E ¼ 4pe 0 e r R 1 R 2 R 1 þ R 2 u 2 01 þ u 2 02   2u 01 u 02 u 2 01 þ u 2 02 p þ q   http://dx.doi.org/10.1016/j.mineng.2014.07.020 0892-6875/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Address: 320, Clay Ave., Lexington, KY 40502, USA. Tel.: +1 8593516264. E-mail address: wzh257@g.uky.edu (W. Zhang). Minerals Engineering 69 (2014) 133–136 Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng