Patent GB-740675-A (GB)
Title: Process of extracting potassium from dilute potassium salt-containing solutions as nitrate
IPC: C01D9/04
Filed: 1954-02-12
Abstract: In the extraction of potassium from dilute solutions such as seawater, a highly nitrated secondary aromatic amine is added as a soluble salt (calcium or magnesium).  Potassium aminate is precipitated and separated from the mother lye.  Amine is recovered from the aminate by the addition of nitric acid or a nitric acid/nitrate solution from another stage of the process, and from the mother lye by adding a mineral acid produced by passing a chloride solution such as aqueous potassium chloride, or seawater, through a nitric acid-regenerated cation exchange resin. Amines referred to are 2,4,6,31x1-pentanitro diphenylamine (x1 may be 21,41,51,61), 2,4,6,3161-pentanitro - 41 - methyl - diphenylamine, 2,4,6,2141-pentanitro diphenylamine, 2,4,6,2141 - pentanitro - 61 - methyl - diphenylamine, 2,4,6,2141-pentanitro - 51 - chloro - diphenylamine, 2,4,6,2141 - pentanitro - 61 - chloro - diphenylamine, 2,4,6,2141 - pentanitro - 61 - methoxydiphenylamine, 2,4,6,2141 - pentanitro - 51,61-dimethyl - diphenylamine, 2,4,6,2141 - pentanitro - 3, 61 - dimethyl - diphenylamine, 2,4,6,2141 - pentanitro - 31, 61 - dimethyl - diphenylamine, 2,4,6,2141 - pentanitro - 31 - chloro - 61 - methyl - diphenylamine, 2,4,6,2141 - pentanitro - 5 - methyl - 5 - carboxy - diphenylamine, 2,4,6,2161 - pentanitro - 41 - chlorodiphenylamine, 2,4,6,2161 - pentanitro - 41 - methyl - diphenylamine, 2,4,6,2161 - pentanitro - 3, 41 - dimethyldiphenylamine, 2,4,6,2161 - pentanitro - 41-ethoxy - diphenylamine, 2,4,6,213141 - hexanitro diphenylamine, 2,4,6,214161 - hexanitro diphenylamine, 2,4,6,214161 - hexanitro - 3-methyl - diphenylamine, 2,4,6,214161 - hexanitro - 3 - chloro - diphenylamine, 2,4,6,213161-hexanitro - 41 - methyl - diphenylamine.  Highly nitrated derivatives of phenyl-naphthyl-amine and dinaphthylamine, for instance, 2,4,6-trinitro-phenyl-nitro-a -naphthtlamines may also be used. Specifications 605,694, 642,472 and 668,735 are referred to.ALSO:Potassium nitrate is extracted from dilute solutions such as seawater, as nitrate, by precipitating with a highly nitrated secondary amine, separating the aminate from the mother lye, and treating it with nitric acid to form a potassium nitrate solution and free amine, recovering further amine from said mother lye by addition of mineral acid to a pH of 2-6, preferably 3-5, and separating the precipitated free amine, said mineral acid being produced by passing a chloride-containing aqueous solution through a nitric acid-regenerated cation exchanger. The chloride containing aqueous solution may contain one or more alkalimetal-(e.g. sodium, potassium), ammonium-, or alkaline earth metal-(e.g. magnesium, calcium) chloride or may be seawater, water from saline springs or salt lakes, or mother lyes from salt works or the precipitation of magnesium hydroxide or carbonate from seawater.  On regenerating with nitric acid, valuable nitrate solutions are produced.  If a solution of potassium chloride is used, that part of the potassium nitrate solution containing nitric acid produced in regeneration of the exchanger may be used to treat the precipitate of potassium aminate to give free amine and potassium nitrate, or after evaporation if desired and after addition of nitric acid e.g. by contact with nitrous gases (whereby potassium nitrate precipitates) to regenerate the exchanger.  With the use of other solutions, further quantities of nitrate may be obtained by neutralizing, the acid-containing products of regeneration with a base corresponding to the salt therein (e.g. sodium hydroxide, ammonium hydroxide, calcium carbonate &c.); when seawater is employed for acid production, the solution obtained on regenerating may be treated, e.g. with calcium carbonate or calcium hydroxide to neutralize and precipitate magnesium hydroxide, and the solution remaining fractionally crystallized to obtain potassium nitrate and calcium nitrate.  Preferred ion exchangers are resins containing sulphonic acid groups.  The free amine may be converted by means of a base, e.g. calcium hydroxide or magnesium hydroxide to an easily soluble salt for use in further precipitations.  A number of suitable amines are specifically referred to, of which, 2, 4, 6, 21, 41-pentanitro diphenylamine, 2, 4, 6, 21, 61-pentanitro 41-ethoxydiphenylamine, and 2, 4, 6, 21, 41, 61-hexanitro-3-chlorodiphenylamine are typical: highly nitrated derivatives of phenylnaphthyl-amine and dinaphthylamine may also be used.  The ion exchange may if desired be carried out at temperatures above ordinary room temperatures e.g. at 30-40 DEG C, whereby more highly concentrated nitric acid may be used for regeneration due to the increased solubility of the salt produced.  Preferred linear liquid velocities of 1-10 m./hr. preferably 2-8 m./hr. calculated on an empty column are suitable.  In the examples which illustrate ionexchange procedures to obtain hydrochloric acid for use in the invention about 4m./hr. (=3.6 1./hr.) is used.  In the first example a 3.85 N aqueous sodium chloride solution is passed into the top of a first column and hydrochloric acid collected until sodium chloride passes out: the discharge is then connected to a second column and the hydrochloric acid collected until sodium chloride again passes out, when the discharge is connected to the top of a third column and a further 1 litre of sodium chloride solution is passed into the top of the first column.  Water is then passed in until sodium chloride passes out from the third column.  By this means the hydrochloric acid is always taken from a layer of hydrogen-saturated exchanger. By employing a suitably large number of columns e.g. a series operated cyclically, the number of equivalents of exchanger converted becomes equal to the number of salt equivalents required for attaining this conversion.  Other examples illustrate the production of hydrochloric acid from aqueous potassium chloride and seawater, regeneration in a similar manner (with consequent production of nitrate), and washing the exchanger after production of acid. Sodium chloride washed out before regeneration may be fed back into the exchanger after regeneration, to produce more hydrochloric acid. Specifications 605,694, 642,472 and 668,735 are referred to.