Flotation concentration of potash accounts for about three-quarters of the potash production worldwide. Leaching and re-crystallization or fractional crystallization processes are also used alone or in conjunction with flotation to produce the final product quality.
The most common potash minerals are sylvite (KCl), carnallite (KMgCl3.6H2O), and kainite (KCl.MgSO4.3H2O). In most cases, the potassium minerals are floated away from halite (NaCl) and other gangue minerals.
Even though the straight flotation of sylvite is the most common process employed worldwide (mainly in Saskatchewan potash fields in Canada and in the U.S., Europe, Russia and South America), the reverse flotation of halite from sylvite is also employed, mainly in the Dead Sea region of Jordan and Israel.
Flotation of potash differs considerably from the standard flotation applications since the minerals to be separated are water-soluble salts and flotation is carried out in saturated brine solution. Temperature is one of the main factors that affects the flotation process. The solubility of NaCl in water, which is much higher than KCl, decreases with decreasing temperature, whereas the solubility of KCl is not affected by temperature. Other important factors are:
- Presence of carnallite in the ore. It has been shown that Mg2+ ions associated with carnallite depress the flotation of KCl with amines, especially in the presence of slimes.
- Presence of clay in the ore. Clays not only compete with sylvite in adsorption of amine, reducing amine adsorption on sylvite, but also crowd the concentrate reducing grade and causing problems in the down-stream operations. Therefore, desliming is generally employed ahead of flotation.
Primary long-chain amines are the usual collectors for the flotation of sylvite. Cytec offers two primary amines with different properties. AEROMINE 3030C and AERO 3035C promoter are fully neutralized, formulated long-chain amine collector which are liquid at 7°C. They are specially formulated to outperform paste amines on a weight-equivalent basis. In addition to its improved selectivity over other paste amines, it is less affected by slimes compared to other amines. Both AEROMINE 3030C and promoter can be prepared as a 5-10% solution. Depending on the type and concentration of KCl ore, its dosage varies from 200 to 500 grams per tonne. AEROMINE 3030C prom AEROMINE 3035C promoter can also be fed neat. In addition to AEROMINE 3030C and AEROMINE 3035C promoters, Cytec offers AEROMINE 3100C promoter as a paste primary amine, which can also be used as an effective sylvite collector.
For the flotation of coarse sylvite, hydrocarbon oils (as extender oils) are used in conjunction with amines to improve the flotation recovery .
The reverse flotation of halite from sylvite is practiced mainly in the Dead Sea region in both Israel and Jordan. Morpholine type collectors are found to be more effective in this process.
A number of sylvite ores with high clay content require additional steps to overcome the harmful effects of these clays on the overall selectivity. Various polymers or modified polymers are used to depress clays ahead of sylvite flotation. Even though common depressants such as CMC, guar, and starch are used in the industry, modified polymers (either anionic or non-ionic) are often more effective clay depressants. These depressants require conditioning ahead of flotation with the amine collector. AERO 8860GL GCA depressant was specifically developed by Cytec to depress talc-like minerals in sulfide flotation and may be applicable to depressing clays in sylvite flotation.
Cytec developed a commercially successful selective flocculation/flotation process to remove clays ahead of potash flotation. This process eliminates the need for mechanical removal of slimes, which is capital and operating cost intensive. In this process, the ground ore is gently conditioned with 25 to 100 g/t of a flocculant such as SUPERFLOC N-100 flocculant and then with 20 to 100 g/t of AERO 870 promoter to float the flocculated clay slimes; the floated clay product is usually low enough in potash to be discarded, but can be refloated in a cleaning stage, if necessary. The flotation tailing is fed to the potash flotation stage and generally requires the use of less clay depressant than in the case of mechanical desliming. The process can also make feasible the treatment of high clay potash ores which, heretofore, could not be treated economically.