(652g) Enhancement of Fluorite Flotation Process with the Combination of in-Situ Modification By Ball-Milling and Gas-Liquid Microdispersion

Fluorite is the most important upstream raw material of fluorine industry. As main and the most economical source of fluorine, high grade fluorite (CaF₂>97%) is of great demand in order to obtain high performance fluorine-containing solar cell film, ionic superconducting materials and other kinds of fluoropolymers. However, complex association is quite common in fluorine ore, effective fluorite content of which could only reach 7 % to 20 % in the nature. As the most universal separation method, higher request has been put forward to froth flotation to get fluorite concentrate. Facing challenges due to the similar Ca site of fluorite and calcium carbonate and the easiness of quartz to be activated by the existence of calcium, countless improvements have been contributed to froth flotation during decades, mainly focused on mixture of novel additives, effective equipment and so on. However, rarely did the investigators focus on the problem of high energy consumption caused by times of scavenging and mechanical agitation. What is more, it is still lacks a green method to separate the fine and complex paragenetic particles without expensive additives and high emission.

In this study, we realized the separation of fine fluorite particles with the help of micro-bubbles and in-situ modification during the ball-milling. Instead of traditional water milling, we directly added oleic acid and Na₂CO₃ into the ball-milling jar, which was found to be the optimal feeding and modification mode by contrast. Firstly, owing to the regulation of pH caused by Na₂CO₃, an appropriate zeta potential was achieved, effectively preventing the aggregation of the fine particles. Secondly, due to the mechanical force of the milling, adsorption of oleic acid onto the surface of the particles was intensified, leading to a superior dispersion of the initial suspension under minimum amount of surfactant. In addition, it was proved by the size analyzer that the selectivity and accuracy of the adsorption between surfactant, fluorite and quartz particles was remarkably enhanced. Furthermore, a controlled and high efficient gas-liquid microdispersion technology was introduced to intensify the froth flotation process in terms of productivity and selectivity. Within the limited space less than 8 cubic millimeter, due to sufficient dispersion of membrane and strong shear of continuous phase of suspension, we obtained gas bubbles swarm with average diameter of 1 mm. Compared with traditional flotation where bubbles are usually in the size of centimeter level, the contact area of the gas-liquid-solid system in our work was expanded by thousand fold, which maximized the interaction between hydrophobic fluorite and the bubbles, decreased the concentration of the depressant and reduced gas consumption at the same time. Thanks to the combination of the approaches mentioned above, the grade of fluorite could reach 98 % in one time flotation just within a palm-sized blocked swiftly, which notably increased the flotation efficiency. Besides, the density and size of the bubble group could be precisely controlled by the gas flux along with mechanical equilibrium of each single bubble, which brings good adaptability to various particles with different size, concentration or surface characteristics.

In a word, with the coupling of in-situ modification of ball-milling and membrane dispersion flotation, instead of utilizing other complex combination of additives, we obtained a satisfactory grade and recovery only with the most fundamental and cheapest long-chain fatty acids oleic acid as collector and sodium silicate as depressant. Owing to the accurate interaction between tiny particles and additives, usage of the additive was minimized and the flotation could be once completed without times of selection, which cut down the consumption of water treatment, energy and fixed investments to a great extent. Moreover, it is worth noting that the simplified process is of huge potential to be applied to the separation of different kinds of tiny solid compounds effectively through the adjustment of micro bubbles flexibly.