Chloride

Extraction of potassium salts occurs mainly by mining (in the Federal Republic of Germany currently to a depth of ca. 1200 m), but leaching processes (solution mining, with one plant each in Canada and Utah/USA) and direct extraction from lakes (Dead Sea; Great Salt Lake, Utah; Searles Lake, California; Lake McLoed, Australia) are also utilized.

The solid salt has to be more or less strongly ground, depending upon the degree of fusion, before it can be further processed. can be separated from the salt mixtures by:
(1) dissolution processes;
(2) flotation;
(3) electrostatic fractionation;
(4) gravitational (dense medium) separation.

These processes are also combined with one another. In dissolution processes, the differences in solubility of the various constituents of the raw salt in water are exploited to attain high percentage potassium chloride. The particular process used depends upon the type of salt mixture, but energy consumption, disposal of byproducts etc. are also important.

Flotation or a combination of flotation with dissolution processes are currently used for processing 50% of the sylvinite. An important precondition for the use of flotation processes is the availability of coarsely intergrown minerals (predominantly in Canada, USA and the former States of the USSR) is. There is also one plant in the Federal Republic of Germany which uses this process.

In electrostatic fractionation, the fact that the various components of a salt mixture (in particular sylvinite, kieserite and rock salt) become differently charged upon contacting one another under particular conditions. The process consists of the following steps:
(1)dry grinding of the raw salt
(2)conditioning
(3)heating and drying
(4)(triboelectrical) charging and adju\tment of the relative humidity of the air
(5)(multistage) separation

Grinding reduces the raw salt to a size of < ca. 1 to 2 mm, depending upon the composition. Fines and dust interfere with this process. Conditioning entails the addition of organic compounds, mostly carboxylic acids, in quantities of 50 to 200 g/t raw salt. The salt is then dried e.g. by passing hot air over it. The (triboelectrical) charging takes place in so-called "fluidized bed salt warmers" in which the various salt components become oppositely charged. The residence time of the salt in this unit is less than one minute.

Separation of the charged salt mixture takes place (multistage, with partial recirculation) in so-called "plate separators". In the 2 m high and up to 10 m wide unit, particles fall unimpeded, are deflected sideways by an electric field of 4 to 5 kV/cm and are separated according to the sign of the charge. The electrodes rotate at 10 to 30 rpm against brushes which remove the deposited particles. Energy consumption is low. The throughput of a separation unit is several thousand t per day. 10^.10⁶ t are currently separated annually using this process.

Dense medium separation can only be carried out with coarsely intergrown minerals. It has found only limited industrial application (Canada). Salt solutions containing ferrosilicon serve as the gravitational liquids.

The potassium chloride produced for use as a fertilizer or in fertiliLer mixtures is mostly granulated or compacted.

Much of the salt mined together with potassium chloride cannot be industrially utilized. Solid residues can to some extent be disposed of as infill in mines, however, there are limits to this procedure in that the bulk volume of the material being returned is much greater than the volume of salt originally present in the bed. A further possibility is tipping, which is not without its problems due to the solubility of the salt in water. If geological conditions permit, dissolved residues can be injected under pressure into impermeable subterranean strata. Discharge into mains drainage is only possible to a limited extent and has encountered considerable resistance in some cases (salt problems in the rivers Werra, Weser and Rhine in the Federal Republic of Germany for example).

Potassium sulfate is manufactured from potassium chloride by reacting sulfuric acid with a mixture of sulfur dioxide, air and water (Hargreaves process):

Alternatively potassium sulfate is manufactured by metathesis of potassium chloride with the sulfate of another metal, particularly magnesium sulfate. This reaction takes place in two steps:

The double sulfate is separated and reacted with additional potassium chloride:



Worldwide over 1^.10⁶ t/a of potassium sulfate (as K₂O) is manufactured by this process.

Potassium

is produced by reacting potassium chloride with nitric acid:

The process is in fact much more complex than this equation indicates.

In analogy with the manufacture of potassium sulfate, potassium nitrate can also be manufactured by metathesis with other nitrates, e.g. with sodium, calcium or ammonium nitrate, as follows: