Ever-evolving Flotation Process

The development of the mineral processing technology is like a river of torrent. With the development of science and technology, it also greatly promotes the development of science and technology. The flotation process is a ferry that runs in this river.

The flotation process,which was widely used in the 19th century, can be said to have completely changed the process and production structure of the beneficiation to a great extent, as well as improve significantly the production efficiency of dressing plants. The separation efficiency of flotation process is extremely high, and its application range is also very wide. It is a piece of cake for flotation process to separate non-ferrous metals, ferrous metals or non-metals. Literally,you will think that flotation process uses the density difference of minerals to separate minerals. But in fact, the ups and downs of minerals have almost nothing to do with their own density. Flotation Process utilizes the difference in physicochemical properties of the ore surface, using specific chemicals to separate useful mineral. In the flotation process, the froth is the key; that’s why flotation process is also called froth flotation. There are two type of flotation processes; one is direct flotation process which recovers useful minerals by making the useful mineral in the froth and leaving gauge minerals into the slurry; the other is reverse flotation process which recovers useful minerals by making the gauge minerals in the froth and leaving useful minerals into the slurry. The flotation reagents that are generally used to improve flotation efficiency in the flotation process are: collectors, activators, foaming agents, and so on. The collector is used to promote the lifting of useful ore,the activator is to increase the floating speed of useful ore, and the foaming agent is to increase the number of flotation bubbles.

In fact, people have used goose feathers with grease to extract gold from gold-bearing ore for a longtime. In ancient China, people were used to purifying mineral drugs such as cinnabar and talc by means of the natural hydrophobicity on the mineral surface, so that the fine mineral powder is floated on the surface of the water and separated from the sinking gangue. Evidence was found that oil and bitumen was used to concentrate minerals in ancient Greece and Europe. In the 18th century,it was known that gas can adhere to solid particles and rise to the surface of the water. It’s water vapor or bubbles generated by acid and carbonate that’s used as carriers in the graphite foam flotation process patent produced in 1877.

Later, due to the increasing demand for metals, the mineral resources that can be separated by gravity separation method are decreasing. Therefore, Australia, the United States and some European countries began to use flotation process to separate fine ore. The initial flotation process used were all-oil flotation process and thin film flotation process. The former is to add mineral oil to the slurry to float the oleophilic ore to the surface; the latter is to spray the ore powder on the running water surface of the flotation machine, hydrophobic minerals float on the surface to be recycled. The biggest disadvantage of full oil flotation process is that the consumption of chemicals (petroleum) is large. At the beginning, it is necessary to add 1~ 3 tons of chemicals to per ton of sulfide ore. Due to their practical limitations, full oil flotation process and thin film flotation process were quickly overturned by the raging waves of technology development and are no longer used in the beneficiation industry.

At the beginning of the 20th century, froth flotation process occurred, which separates minerals according to the affinity degree of ore particles to the foam. It has kept evolving along with the developing beneficiation process. A variety of foam flotation processes sprang up like mushrooms, followed by gas flotation process,electrolytic flotation process, vacuum flotation process, positive pressure flotation process and mechanical aerated agitation flotation process. In 1922,a method of suppressing sphalerite and pyrite with cyanide appeared, and apreferential flotation process was developed. In 1925, flotation reagents synthesized with xanthate appeared and greatly reduced the dosage of the agent,which made the flotation process greatly developed and widely used in industrial production.

At present, froth flotation process has become the most widely used foam flotation method. And the process has developed relatively mature. The specific step is to first crush and grind the ore to dissociate the mineral into monomer particles, and the grinding machines discharges the qualified particle size that meets the requirements of the flotation process. Before the flotation, the slurry after grinding and the flotation agent are stirred and blended by using a chemical stirring tank. The adjusted slurry is sent to the flotation cell for separating the useful mineral from the gangue mineral, mechanically scraped or overflowed from the slurry surface, and then dehydrated and dried into a concentrate product.

Modern flotation process mostly adopts mechanical aerated stirring flotation method. According to different ore requirements, different flotation methods are adopted to improve the beneficiation efficiency, such as direct flotation process or reverse flotation process, single flotation process or the combined dressing method using flotation process, gravity separation method and magnetic separation method. On the basis of improving production efficiency, the flotation process is diversified, the flotation equipment is maximize, and the adaptability is also increasing.

The flotation process turns some low-grade deposits that were considered undevelopable into industrially valuable deposits, solves the problem of recovery of useful minerals in many fine ore particles, and easily obtains high-grade and high-recovery concentrates,so that mineral resources can get reasonable and full use. In the mineral processing industry, flotation process has also gained more and more recognition.

With the development of the economy, the status of the flotation process will become more and more important. It is a ferry full of technology and wisdom, which has been and will continue to keep involving with the development of dressing processes.