Slime coatings in froth flotation: A review

- The slime coatings on value minerals in froth flotation are reviewed.
- Mechanisms responsible for slime coatings are summarized.
- Current techniques to detect and quantify slime coatings are described.
- Methods to mitigate slime coatings are reviewed and discussed.
- Further research directions are suggested.

Slime coating is a significant phenomenon in froth flotation. The adverse effects of slime coating, by which a value mineral is covered by slimes and prevented from direct contact with collectors and/or air bubbles, have been recognized for decades. It happens ubiquitously in the flotation of various minerals, including sulfide minerals (sphalerite, galena, chalcopyrite, pentlandite, etc.), oxide minerals (hematite, wolframite, scheelite, etc.), salt minerals (fluorite, potash, etc.), coal and bitumen. In this paper, an attempt was made to present a comprehensive review of slime coatings in froth flotation including particle adhesion mechanisms, slime coating measurement techniques, influencing factors, control methods and mitigation measures. It was shown that the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and the extended DLVO theory, are the mainstream mechanisms underpinning slime coatings. According to their sources, the slimes can originate from gangue minerals and value-gangue composite particles, or from colloidal compounds formed during ore dressing due to grinding, mineral surface oxidation and chemical precipitation. The origin and property of the slimes, the types and concentrations of electrolytes, and solution pH are the main factors influencing slime coatings. Current techniques employed to study slime coatings are mainly focused on the interactions between two particles in a static and ideal environment, which cannot account for slime coatings under commercial froth flotation conditions. Physical mitigation methods such as ultrasonic treatment and high intensity conditioning are often more effective than chemical mitigation methods that usually entail the use of dispersants. Gaps in the existing literature are discussed and potential research directions are suggested.