CA1084291A - Fertiliser solutions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An NPK fertilizer solution is treated with an acid till crystals of a solid solution of monoammonium orthophosphate in monopotassium orthophosphate crystallise out, the crystals are separated from the supernatent liquor and redissolved to form an NPK solution of decreased chloride content, with the supernatent liquor comprising an NPK solution of enhanced chloride content.

Description

L29~.
, T~l~ prcsent invention r~:l.ates to NPK ~ertilisers comprislng ~u~ous solutions oE nitrogenous compounds (e g.
ammonium salts, urea), phosphorus compounds (e,g ammonium s phosphates, phosphoric acid) and potassium compounds (nearly alw~ys potassium chloride) Such NPK fertiliser solutions are w.idely used throughout the world, but in general their plant nutrient levels are severely limited by solubility consiclerations, which place certain restrictions on their . storage, transport and application.
. 10 There have been many ~ttempts to improve the ~` concentrations of such fertiliser solutions by employing raw materials such as ammonium polyphosphates, but these ~ . have hi~herto had very little impact on those grades of .. : fertiliser which contain substantial quantities of potassium ~. chloride Efforts have therefore been directed towards :.~ making use of compounds which contain both potassium and ~`~; phosphorus, but hitherto such materials have not been ~7 available at economic prices, ~:, . We have now discovered that conventional ~PK
; 20 fertilisers con~aining ammonium, phosphate, and potassium ~ ions and comprising aqueous solutions of nitrogenous 7~ ' compounds, phosphorus compounds, and potassium chloride ¦~ under conditi.ons of mild acidulation , will deposit t ' . crystals of a solid solution of mono-ammonium orthophosphate ,~ in monopotassium orthophosphate. These crystals, when separated from the supernatant liquor and dissolved, can .. be mixed with further nitrogen-, phosphorus- and/or potassium-containing plant nutrients, to yield a more concentrated 5~ fertiliser solution than a conventional solution with the 7.. ~ 30 same plant nutirent ratio. This more concentrated solution ~ 2-... .

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contains proportionately less chlorlde than the original sol.ution. It .is a hypochlorid.ic solution and as such may be especially useful for application to crops which are sensitive to chloride~
The acidulated supernatant liquor, after separation of the crystals therefrom, contains more chloride and less potassium than the original s~lution, but its composition can be adjusted by ~he addition ~hereto of further NPK plant nutrients to give a hyperchloridic fertiliser solution suikable for use where the presence of , extra chloride is not detrimental to the crop.
The pre~ent invention accordingly provides a - process for the conversion of a ~PK fertiliser containing ammonium, p~osphate, and potassium ions and comprising an ; a~ueous solution of a nitrogenous compound(s), a phosphorus compound(s) and potassium chloride into a first ~PK
fertiliser fraction having a lower chloride content than the original solution and a second NPK ~ertiliser fraction , having a higher chloride content than the original solution, .
t~: 20 which comprises the steps of treating the solution with an ~ .
,;~ acid, allowing crystals o a solid solution of monoammonium orthophosphate in monopotassium orthophosphate to crystallise . out of the resultant mixture, separating the crystals from the supe.rnatant liquor and redissolving them to form the ;:: ..................................................................... . .
'~ said first ~raction having a lower chloride content than . :the original solution,and the supernatant liquor comprising the second fraction having a higher chloride content than ' the original solution.
,, .~. The acid is suitably phosphoric acid, polyphosphoric i~ 30 acid or a mixture thereof.
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Pre:Eerably, tlle sepa~at~?d crystals ar~ re-, dissolved a:l.ong w.i~h ad~lltional prese].ected plant nutrients ~o produce a more concentrated ~irst fraction which is a hypochloridic NPI~ Eertiliser solution of predet~rmined composition.
Preferably, the supernatant liquor i.s mi.xedwith additional preselected plant nutrients to produce a .i~ second frac~ion which is a hyperchloridic NPK fertiliser .. solution of predetermined composition.
io The invention is hereinafter described with reference to the accompan~ing drawings, wherein:-Fig. 1 is a schematic diagram illustrating the process of the invention; and Fig. 2 is a more complete block diagram illustrating the process of the invention in greater ,~;' detail.
; , Referring to Fig. 1, twelve experiments were .~j .. . .
~ carried out to exemplify the invention, Each experiment '; ~ resulted in one hypochloridic fertiliser and one hyperchlor-. idic fertiliser, making a total of twenty-four. The general procedure followed in the experiments is outlined hereunder, ~- General procedure for Exper:iments 1-12 .i To T gms of a conventional fertiliser solution ~ .:
(composition A-B-C) were added M gms of phosphoric acid , (0-65-0), The resultant mixture was allowed to ~ature for i: at least 20 minutes under ambient conditions before filter-:; .
~ ing off S gms of , . ~
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: which is a hyperchloridic NPK fertiliser solu-tion of predeter-mined compositlon.
The invention is hereinafter described with re~erence to the accompanying drawings, wherein:-Fig. 1 is ~ schematic diagram illustrating the process of the invention; and Fig. 2 is a more complete block diagram ~:
: ~ illustrating the process of the invention in greater detail.
, ~ Referring to Fig~ 1, twelve experiments were carried .~ out to exemplify the invention. Each experiment resulted in one hypochloridic ~ertiliser and one hyperchloridic fertiliser,making a total of twenty-four~ The general procedure followed . .
in the experiments is outlined hereunder~

General procedure for Experiments 1-12 To T gms of a conventional fertiliser solution (com-~ . position A-B-C~ were addea M gms o phosphoric acid (0-65-0).

:~ ~ The resultant mixture was allowed to mature or at least 20 min~

., utes under ambient conditions before filtering of S gms of ~; ' ' .
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., , Z~ 28376 1(~84;~:9 ~' ;i crystalline monoammonium phosphate-monopotassium phospha-te solid solution ~composition D-E-F) from a ~upernatant liquor (composition J-K-~) weighing gm8.
~- To the S gms of wet cxystals were added Vl gms of = onium phosphate solution (8-24-0), Wl gms of urea, ~1 gm8 of po-tassium chloride, hl gms of -~ aqueou~ ammonia (26-o-o) and nl gms of water, producing 100 gm~ of a more concentrated, hypochloridic fertiliser eolution (co~position P-Q-R).
Similarly, to the ~ gms of supernatant liquor were added V2 gms of ` ammonium pho=phate solution (8-24-0) or = onium polypho~phate =olution (10-34-0~, W2 gm~ of urea, ~2 gms of potassium chloride, h2 gme of aqueous am~onia (26-o-o) and n2 gm~ of water thereby producing 100 gms of a hyperchloridic .~ fertiliser ~olution (compo~ition X-Y-Z).
Numerical values of the parameters A, ~, C, etc. are summarised in the ~ followin~ ~able 1.
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~L~8'~291 t will b~a observed th~-t, in these samples the chlo-. ride content o the hypochloridic solution P-Q-R has been decreased by up to about one-third as compared with the original .. solution A-B-C, whereas the chloride content of the hyperchlo-ridic solution X-Y-Z has been increased by an average of about . 30%.
The weight and composition of the raw materials added ; to the wet crystals and supernatant li~uor may be varied as required to provide final hypochloridic and hyperchloridic solutions of predetermined compositionf.
- In the block diagram of Fig. 2 the upper portion illustrates a conventional method of preparing a conventional .,.
;........... NPK fertiliser solution (i.e. the solution A-B-C). Phosphoric ~.
.. or polyphosphoric acid is neutralised with ammonia in a neutra-liser, gaseous ammonia is dissolved in water, and these two ~ constituents are mixed, together with additional water, potas-f sium chloride and urea in a mixer A. ~ ~
The mixture ~rom mixer A is led to a crystalliser : :
' . where it is treated with phosphoric or polyphosphoric acid, and ~ 20 the resultant mixture is allowed to mature for at least 20 min- :
.~ utes at ambient temperature, during which time a solia solution of monoammonium orthophosphate in monopotassium orthophosphate crystallises out. The wet crystals are separated from the .~ mother liquor, and are led to a mixer B, the mother liquor ; being led to a mixèr C. To each of these two mixers there are added, in preselected quantit.ies, plant nutrients from the . earlier stages of the process, for example phosphoric or poly-: phosphoric acid~ ammonium phosphate or ammonium polyphosphate, ~.
aqueous ammonia, potassium chloride, urea, together with further -~:
water. As shown, s~me of the original fertiliser solution :, . (A~B-C) produced in mixer A can be added to mixer B and/or mixer C.

Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the conversion of an NPK
fertiliser containing ammonium phosphate and potassium ions and comprising an aqueous solution of a nitrogenous compound (s),a phosphorus compound (s) and potassium chloride into a first NPK fertiliser fraction having a lower chloride content than the original solution and a second NPK fertiliser fraction having a higher chloride content than the original solution, which comprises the steps of treating the solution with an acid, allowing crystals of a solid solution of monoammonium orthophosphate in monopotassium orthophosphate to crystallise out of the resultant mixture, separating the crystals from the supernatant liquor and redissolving them to form the said first fraction having a lower chloride content than the original solution, and the supernatant liquor comprising the second fraction having a higher chloride content than the original solution.

2. A process as claimed in Claim 1, wherein the acid is phosphoric acid, polyphosphoric acid or a mixture thereof.

3. A process as claimed in Claim 2, wherein the separated crystals are redissolved along with additional preselected plant nutrients to produce a more concentrated first fraction which is a hypochloridic NPK fertiliser solution of predetermined composition.

4. A process as claimed in Claim 1, wherein the supernatant liquor is mixed with additional plant nutrients to produce a second fraction which is a hyperchloridic NPK
fertiliser solution of predetermined composition.

5. A process as claimed in Claim 3 or Claim 4 wherein the additional plant nutrients comprise ammonia, phosphoric acid, polyphosphoric acid, ammonium phosphate, ammonium polyphosphate, urea and/or potassium chloride, together with water.

6. A process as claimed in Claim 3 or Claim 4 wherein the additional plant nutrients comprise pre-selected quantities of the original solution.