Contents lists available at ScienceDirect Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa Characterization of coal particles wettability in surfactant solution by using four laboratory static tests Yinping Chen a , Guang Xu a, ⁎ , Jinxin Huang a , Jacques Eksteen a , Xiaofei Liu b , Zidong Zhao a a WA School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, Kalgoorlie, Australia b School of Safety Engineering, China University of Mining and Technology, Xuzhou, China GRAPHICALABSTRACT ARTICLEINFO Keywords: Coal wettability Surfactant Contact angle Coal dust suppression Sink test ABSTRACT Coaldustisahealththreattoundergroundcoalminers,andthecurrentcommonpracticeistousewatersprayto controlit.Thecoalwettabilityplaysasignifcantroleinstudyingtheefectiveness ofcoaldustsuppression,and theadditionofsurfactanttowatercangreatlyimprovethecoalwettability.Theaimofthispaperistoevaluate thereliabilityoffourmethodsthatarecommonlyusedtoquantifythecoalwettabilityinpresenceofsurfactant, they are the sessile drop measurement, the sink test, the capillary rise test and the drop penetration test. The advantagesanddisadvantagesofthesefourmethodsweredetailed.Theresultsindicatedthatthesinktestisthe most reliable method in terms of its simplest operation and the highest accuracy. It also has the ability to quantitatively compare the wettability of diferent coal particle sizes, which the other three methods failed to identify. The addition of surfactant resulted in smaller contact angles, less sink time, less drop penetration time andmorecapillaryriseweightgainscomparedwithusingwateronly,whichindicatedthatthecoalwettabilityis improvedbysurfactants.Ofthetwostudiedsurfactants,SDBSperformedbetterthanSDS.Thisstudyprovideda guideline on both evaluation method and surfactant selection when studying the wettability of coal particles. 1. Introduction Inthepresenceofsomeimmiscible fuids,thetendencyofoneliquid to adhere to, or spread on a solid surface is referred to the wettability [1].Thewettabilityinvolvestheinteractionbetweenliquidphase,solid phase and gas phase. Coal wettability is one of the most important surfacepropertiesofcoal.Itrefectstheabilityofcoalsurfacetocontact with liquid resulting in an interaction of intermolecular [2]. Understanding the coal wettability is crucial for the development of efcient coal dust suppression system by using water spray. The coal wettability is generally pictured in terms of the contact angle of a liquid on the coal surface. The contact angle, shown as in Fig. 1, is formed by the interaction of the liquid-solid interface and liquid-air interface. Geometrically, it is obtained by applying a tangent line from the contact point along the liquid-air interface in the liquid profle[3].Asmallcontactanglegenerallyimplieshighwettability.For https://doi.org/10.1016/j.colsurfa.2019.01.068 Received 19 December 2018; Received in revised form 30 January 2019; Accepted 30 January 2019 ⁎ Corresponding author. E-mail address: guang.xu@curtin.edu.au (G. Xu). Colloids and Surfaces A 567 (2019) 304–312 Available online 31 January 2019 0927-7757/ © 2019 Elsevier B.V. All rights reserved. T