Flotation tests generally consist of grinding, slurry preparation, flotation (scraping), and product processing. Properly mastering these techniques is essential for the normal conduct and accuracy of the test.
(1) Grinding. First, run the grinding mill idle for a few minutes to clean it. Then add part of the water required for grinding, followed by the ore sample and reagents to be added. Finally, add the remaining water. During grinding, pay attention to the mill’s rotation speed and the sound to ensure the balls or rods are moving normally within the mill. Accurately control the grinding time. When pouring out the slurry, place a ball screen on the receiving container and rinse the mill’s inner wall and bottom with a fine, rapid stream of water. Pour the slurry into the receiving container, lift the ball screen, and rinse it thoroughly with a rapid stream of water. Finally, fill the mill with water and cover it for future use.
During cleaning, be careful not to use too much water, as this may overwhelm the flotation cell. If there is excess water, it can be drawn out using a suction bulb or siphon after clarification and used as replenishment water for flotation.
(2) Stirring and Slurry Preparation. The purpose of stirring is to suspend the mineral particles and ensure effective contact between the particles and air bubbles. Slurry preparation is done after adding reagents and before introducing air, with the aim of uniformly dispersing the reagents and allowing them to interact with the mineral particles.
Aqueous solutions of reagents can be added using pipettes, graduated cylinders, or measuring cups. For non-water-soluble reagents, such as No. 2 oil or oleic acid, direct dropwise addition with a syringe is used, but the actual mass of each drop must be determined beforehand. This is done by adding dozens of drops of reagent to a small beaker (of known mass), weighing the drop, and then dividing by the number of drops to obtain the weight per drop.
(3) Flotation Foam Scraping. By observing the size, color, solidity, toughness, and brittleness of the foam during the flotation process, and by adjusting the amount of frother, aeration, slurry level, and strict operation, the quality and amount of foam scraped off can be controlled.
The aeration rate is adjusted by controlling the valve opening and the flotation machine speed. Once the aeration rate is determined, it should be kept constant to avoid affecting the comparability of the tests. The thickness of the foam layer in the laboratory flotation machine is generally controlled at 25-50 mm, and the slurry should not overflow from the flotation cell on its own. Due to the continuous scraping of foam, the slurry level drops. To ensure continuous foam scraping, water should be added continuously. If the pH value of the slurry has little effect on flotation, tap water can be added. Otherwise, a supplementary water with the same pH value as the slurry should be prepared in advance. Foam adhering to the wall of the flotation cell must be frequently rinsed back into the cell. The pH value and temperature of the slurry must be measured and recorded at the beginning and end of foam scraping. After flotation, the tailings should be poured out and the flotation machine cleaned.
(4) Product processing. The flotation product should be dewatered, dried, weighed, and sampled for chemical analysis.
If the product is very fine or contains a lot of mud, a coagulant can be added to accelerate sedimentation. When drying sulfide ore, the temperature should be controlled below 110℃ to prevent oxidation and changes in product grade.