Role of Tweens in improved centrifuging of coarse clean coal

To reduce the moisture of coarse clean coal, Tweens involving Tween 20, 40, 60, 80 and 85 were used to improve the centrifugal dewatering of clean coal.The moisture and the contact angle of the dewatered clean coal and the surface tension of the centrifugal liquid were measured for all these surfactants.It was found that all the Tweens show some improving effects on the moisture reduction and increase the contact angle of the coal.Tweens 20, 80 and 85 are better than Tweens 40 and 60 in centrifugal dewatering.The optimum dewatering efficiency is reached at the concentration that decreases the surface tension of the centrifugal fluid to 67 mN/m.The thickness of hydrated layers on the coal particles under different concentrations of Tween 85 were then measured, and the coal particles were scanned by SEM as well after reacting with Tween 85.The results show that the hydration layer outside the particles became thinner after the coal was treated by Tween, and the slimes attached on the surface of the coal particles were significantly reduced with the help of Tween. It can be concluded that the hydrated layer thinning by hydrophobicity modification and the slime-washing function are the main mechanisms contributing to the dewatering improvement effect of Tweens.