OA19037A - Interconnected System and Method for the Purification and Recovery of Potash. - Google Patents

Abstract

The present invention provides a kiln for the combustion of agricultural waste. The kiln includes a central cylindrical combustion chamber. The central cylindrical combustion chamber includes a system for the control of combustion air to the combustion chamber. The kiln includes a second concentric cylinder surrounding the central cylindrical combustion chamber. The second concentric cylinder includes a system for the flow of cooling water through the first annulus between the central cylindrical combustion chamber and the second concentric cylinder. The kiln includes a system for the feeding of the agricultural waste into the central combustion chamber. The kiln includes a temperature sensing device to measure and display the temperature within the central combustion chamber during the combustion of the agricultural waste. The kiln includes a system for the recovery of ash from the kiln In operation, the temperature of combustion is controlled to between 550 °C and 650 °C by a combination of increasing the supply of combustion air when the temperature in the central combustion chamber falls to near 550 °C and the introduction of cooling flowing water when the temperature in the central combustion chamber approaches 600 °C.

Description

TITLE INTERCONNECTED SYSTEM AND METHOD FOR THE PURIFICATION AND RECOVERY OF POTASH . ....................TECIINICAL FIELD .......-......’...........' ................................................................’ ....................’ “-------------------............. :......
5 This invention relates to Systems and methods for the purification and recovery of potash. BACKGROUND ART Potash was originally produced by leaching wood ashes and evaporating the solution in an iron pot, thus extracting potassium fertilizer. : Potash is important for agriculture because it improves water rétention, yield, nutritional 10 value texture and disease résistance of food crops. It has wîde application to fruits and vegetables, rice, wheat and other grains, sugar, corn, soybeans, palm oïl and cotton, ail of which benefit from the nutrient’s quality enhancing properties. Economie growth in Asia and Latin America has greatly contributed to the increased use of potash-based fertilizers. Because potash is a fertilizer for the above-mentioned plants, agricultural plant wastes 15 become a réservoir of potassium from which potash can be recovered by extraction from the residue (ashes) which are left from the burning of such agricultural plant wastes. In particular, the agricultural plant wastes which are bumed to ashes and from which potash is extra cted pre.ferah.1y ar.e enenapnd hnsks, plantain (and hanana) pee1s and eola nnt hnsks .................
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Thus, potash may be recovered by extraction from the residue (ashes) left from the burning
20 of the above preferred agricultural plant wastes. There are many patents that deal with the purification of potash from solutions of potash.

Among them are the following:

US Patent No. 7,892,298, issued Feb 22, 2011, to Toagosi Co Ltd for “Method for

Producing High Purity Caustîc Potash” through crystallization by bringing an aqueous solution of caustic potash into a high température zone.

US Patent No. 7,041,268, issued May 9, 2006, to Council of Scientifîc and Industrial

Research for “Process for Recovery of Sulphate of Potash” from sulphate-rich bittern | through the use of lime by fractionation of the bittern to obtain kainite type mixed salts and then reaction with muriate of potash to produce crude sulphate of potash.

US Patent No. 5,456,362, issued Oct 10 1995, to The University of British Columbia for “Rotation Process for the Flotation of Coarse Fraction of Potash Ores”. By using a column flotation device in which air bubbles are generated by a sparger that utilizes high intensity shearing. .

US Patent No. 4,787,506, issued Aug 30 1988, to Kali und Salz Aktîengesellschaft for “Electrostatic Treatment of Milled Crude Potash Salts Containing Kiesserite” by conditioning sequentially with two conditioning agents and feeding the crude potash sait to an electrostatic free fall separator.

US Patent No. 4,198,288 issued Apr 15 1980 to Celanese Polymer Specialties Company for “Desliming of Potash Ores”, by treating pulped potash ore with a polygalactomannan gum flocculant, then with a polyamine collecter and then subjecting it to froth flotation.

SUMMARY OF INVENTION

TECHNICAL PROBLEM '

One technical problem to be solved was that the extraction/purifïcation of potash fromI crude potash slill did not provide pure potash which was substantially free of sodium,;

50---ehleridesrand-heavy-metals-s-ueh-as-iron-chromium-and-mckeL·--------------:-This problem was attempted to be solved by the teachings of the above described US Patent

No. 7,892,298, which, while it was said to provide high purity caustic potash, was silent in regard to the purification of potash (potassium carbonate).|

Hence the problem remains to be solved.

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SOLUTION TO PROBLEM

The applîcant has discovered that this problem may be solved by way of methods that include the steps of discharging impure potash from whatever source, e.g. agricultural waste ashes, into a warm water leaching zone provided with a steam sparger to provide leached potash. The leached slurry is then passed through at least one thickener zone, e.g., through a cascade ofthickener zones connected in sériés, to provide a partially clarified potash solution. Heavy métal ion complexes in the partially clarified potash solution are then adsorbed in an adsorption zone to provide a clarified potash solution. The clarified potash solution is partially evaporated in an évaporation zone to provide a concentrated clarified solution of potash. The concentrated clarified solution of potash is carbonated in a carbonization zone to convert the potash into potassium bicarbonate. The potassium bicarbonate is crystallized and the potassium bicarbonate ciystals are separated from the mother liquor. Potassium carbonate is then regenerated from the potassium bicarbonate crystals in a heating zone. Finally the potash is ground to provide ground potash which has a purity of about 99%.

Thus by one broad aspect of the présent invention, a method is provided for the purification of impure potash comprising: discharging an impure potash solution in warm water into a leaching zone provided with a steam sparger for leaching potash out of the impure potash, thereby to provide a slurry of leached potash; passîng the leached potash slurry through a thickener zone to remove undissolved matter, thereby providing a potash solution substantially free of undissolved matter; passing that potash solution through an adsorption

------zone-to-adsorb-heavy-metal-ion-eômplexes₅-and-thus4o-pr-o-v-ide-a-clar-ifîed.-pGtash-solution-----------------------substantially-free of heavy métal ion complexes; incompletely evaporating the clarified.

potash solution in an évaporation zone to provide a concentrated potash solution;

carbonating the concentrated potash solution in a carbonization zone to convert the potash into potassium bicarbonate; crystallizing the potassium bicarbonate; separating the potassium bicarbonate crystals from the mother liquor; regenerating potassium carbonate from potassium bicarbonate in a heating zone, thereby producing potassium carbonate of j about 99% purity. p/ ï !

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Preferred aspects of the method aspect of this invention are provided in claims 2 to 12, herein.

Another broad aspect of this invention provides an interconnected system for the purification of impure potash. The system includes the following interconnected apparatus

5—éléments : -a leaching-tank for containing-the impure potash to be purified; the leaching tank _____jii^.ông_aJnwer^ai^Êr;_a^s£didsJnl£tJnljCLth£deaching_tankicMuntrQducingjmpure______ potash to be purified; a water inlet line for introducing water into the leaching tank; a steam inlet line for introducing sparging steam into the sparger in the leaching tank; a thickener tank; a conduit for leading sludge of impure potash from the leaching tank into the thickener tank; an evaporator for receiving overfiow dilute potash solution to provide an effluent of concentrated potash; an inlet line from the thickener tank to the evaporator tank; an adsorption column for being charged with activated carbon or similar adsorbent for absorbing métal complexes from the potash solution; a conduit for leading concentrated potash effluent from the evaporator into the adsorption column to provide an effluent of concentrated potassium carbonate which is substantially-free of métal complexes; a first filter for filtering out solid particles from the concentrated potash solution which is substantially-free of métal complexes and to provide a concentrated potash solution which is substantially free of métal complexes, and which is also substantially free of solid particles; a conduit for leading a concentrated slurry of potash effluent from the adsorption column into the first filter; a carbonation column for converting the concentrated potash solution which is substantially-free of métal complexes and which is also substantially-free of solid particles into a concentrated solution of potassium bicarbonate; a conduit for

and whicITis also substantially free of solid particles from the first filter into the carbonation column; a crystallizer; a conduit for leading the concentrated solution of' potassium bicarbonate from the carbonation column into the crystallizer; a second filter; at conduit for leading a slurry of crystallized potassium bicarbonate into the second filter to‘ provide crystallized potassium bicarbonate which is substantially free of mother liquor; ani oven for converting the crystallized potassium bicarbonate into crystallized potassium carbonate; and a conveyor for conveying a crystallized potassium bicarbonate into the oven, thereby to form crystallized potash.î

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Preferred aspects of the integrated system aspect of this invention are provided in daims 14 to 20.

ADVANTAGEOUS EFFECTS OF THE INVENTION

By these aspects of thé présent invention, substantially pure potash is provided which can

S---be-usedûnToüdrproductsvTirdTtharmaceuticalsdreaddftiOnrtorits^primaTyiise^asTrfertilizeT;—;-The potash being purified may be organic potash produced by controlled combustion of agricultural wastes. The potash provided by the présent invention is a substantially pure, premium product which is useful in the production of animal feed suppléments, cernent, fire extinguishers, photographie chemicals, textiles, in brewing beer and as a catalyst for synthetic rubber manufacturing,

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings

Fig 1 is a block flow diagram of the method for the production of potash from agricultural waste ashes; and

Fig 2 as Fig 2A, 2B and 2C is a process flow diagram of the method for the production of potash from agricultural waste ashes

----DETAÏLED DESCRïPTION-O^FIG-1------------------------------As seen in Fig 1, the system and method for the production and purification of potash, preferably from the ashes of agricultural wastes, and more preferably the ashes of coco a pod husks, plantain (and banana) peels and cola nut husks, includes a leaching tank 500 (BLOCK A). The leaching tank is provided with a steam sparger (not seen). In the preferred embodiment the leaching tank 500 includes an ash introduction line 501, a water inlet line 503, a steam sparging tube inlet line 505 and a potash sludge outlet line 507 leading to a first fhickener 502 (BLOCK B). First thickener 502 is provided with an overflow line 509 to lead a dilute potash solution to an evaporator 508 (BLOCK C).

The system and method include several recycle Systems which are shown in Fig 1, One such recycle system comprises a second sludge line 511 from first thickener 502 to a 5 second thickener 504 (BLOCK D). Overflow liquor from second thickener 504 is cycled back to leaching tank 500 through first overflow line 513. Sludge from second thickener 504 is passed to a third thickener 506 (BLOCK E) through third sludge line 515. Overflow liquor from third thickener 506 recycles backto second thickener 504 through second recycle line 517. Waste sludge from third thickener 506 is disposed of to land fill through disposai line 519.

A second such recycle system comprises a first condensate line 521 leading from evaporator 508 both to third thickener 506 through first branch condensate line 523, and directly to boiler 510 (BLOCK F). Boiler 510 is preferably fueled with a mixture of liquid petroleum gas and methane through fuel line 525. Steam effluent from boiler 510 exits through main steam line 527 directly to evaporator 508, and connects to steam inlet sparging line 505 to enter the Iower inlet leaching tank 500. Flue gases, i.e., carbon dioxide, nitrogen and steam, pass from gas outlet of boiter 510 to condenser/economizer 512 (BLOCK G) through main gas line 533. Condenser/economizer 512 is also fed with water through water line 529. Water condensate from condenser/economizer 512 is recycled from Iower outlet ofcondenser/economizer 512 backto boiter 510 through water condensate branch line 531, which merges into first condensate line 521. Effluent gases from -6&ndenser/eeonomi-zer-^-l-2-ex-it-Gondenser/eGonoïnizer-4-l^-and-are-camed-via-sec&nd-gas— line 565 to compressor 514 (BLOCK K) for further use as will be described later.

The concentrated potassium carbonate from evaporator 508 is fed through concentrated potassium carbonate line 535 to adsorption column 516 (BLOCK H), which is loaded with activated carbon through activated carbon loading inlet line 569. The slurry of potassium carbonate from adsorption column 516 is fed to first filter 518 (BLOCK I) through slurry line 537. Spent activated carbon is discharged from first filter 518 through spent carbon filter discharge line 559.

The filtered potassium carbonate from first filter 518 is fedto carbonation column 520 (BLOCK J) via filtered potassium carbonate slurry line 539. As referred to before, the carbon dioxide and nitrogen gases from condenser/economizer 512 leadto compressor 514 (BLOCK K) via second gas line 565. The compressor 514 preferably opérâtes at -37

......5..........degrees C. In compressor 514, carbon dioxide is compressed and nitrogen gas is vented..... through vent line 541. Compressed carbon dioxide gas exits compressor 514 and is fed into carbonation column 520 (BLOCK J) through compressed carbon dioxide line 543.

The potassium bicarbonate which is formed in carbonation column 520 exits carbonation column 520 and is fed into crystallizer tank 522 (BLOCK L) via bicarbonate feed line 545.

A slurry of crystallized potassium bicarbonate then exits from crystallizer tank 522 and is fed into second filter 524 (BLOCK M) via third slurry line 547. The solid potassium bicarbonate exits second filter 524 and is conveyed by conveyor 549 into oven 526 (BLOCK N). The mother liquor from second filter 524 exits second filter 524 and is cycled through mother liquor recycle line 551 backto evaporator 508.

In the oven 526, the potassium bicarbonate décomposés into crystalline potassium carbonate and effluent gases comprising carbon dioxide, nitrogen and steam are released. These effluent gases exit oven 526 and are fed into condenser 558 (BLOCK O) via third gas line 567. Condenser 558 is fed with water through cooling water line 553 to condense the steam to water, which is withdrawn through condensate water line 555. The condensed gases, nitrogen and carbon dioxide, exit condenser 558 and are fed into compressor 514 through gas line 557. Nitrogen gas is vented through second vent 541, and recovered ------gaseous-earban-diOxide-exits-compressorTfrlT-tO-add-furthercarbon-dioxifleunto-carbonatiOn· column 520 through carbon dioxide line 543.

The crystalline potassium carbonate (potash) from oven 526 exits onto conveyor 550 to be conveyed to grinders 528 (BLOCK P) where it is ground, preferably to 325 mesh. The ground potassium carbonate (potash) exits grinders 528 onto conveyor 561 to be conveyed to packaging machine 530 (BLOCK Q). The packages so formed may be supplied for local uses or may be sent to export 532 (BLOCK R) via line 563.

BRIEF DESCRIPTION OF FIG 2A FIG 2B and FIG 2C As seen in these figures, the process flow diagram of the method and the System for the production and purification of potash from agricultural waste ashes identifies each of leaching tank 500 (BLOCK A), first thickener 502 (BLOCK B), evaporator 508 5 (BLOCK C), second thickener 504 (BLOCK D), third thickener 506 (BLOCK E), boiler
510 (BLOCK F), condenser/economizer 512 (BLOCK G), adsorption column 516 (BLOCK H), first fïlter 518 (BLOCK I), carbonation column 520 (BLOCK J), compressor 514 (BLOCK K), crystallizer tank 522 (BLOCK L), second fïlter 524 (BLOCK M), oven 526 (BLOCK N), condenser 558 (BLOCK O), grinders 528 (BLOCK P) and packaging 10 machine 530 (BLOCK Q), which will be further identified by reference numbers in the “600” sériés and in the “700” sériés. In addition preferred operating conditions will be specifîed. DETAILED DESCRIPTION OF FIG 2A, FIG 2B and FIG 2C As now seen in Fig 2A, 2B and 2C the process flow diagram as shown is for the method 15 and system for the production and purification of potash from agricultural waste ashes. The process is identified by the general number “600”. In the preferred embodiment, agricultural waste ashes are loaded through tunnel 602 into a screw conveyor 604, preferably at a rate of 4,500 kg/hour at a température of about 25 degrees C and is discharged from the screw conveyor 604 via outlet 601 and through inlet means 603 into 20 leaching tank 606 (BLOCK A), which is provided with an interior stirrer 608. Water,
rhrough upper warer inlei rube 683, is inrroduced rhrough upper inler rube 635 and rhrough	—
-------------:—valve A^Hnto4eaching+ank-606U5+earrns4ntroduced4ntO“leaching“tank“606-through lower steam sparger inlet tube 607 to flow into sparger 611 at the bottom of leaching tank 606.

In the previously described first recycle system in Fig 1, warm sludge of agricultural waste 25 ashes is selectively discharged from lower outlet 613 from leaching tank 606 under the control of valve V2 and through first sludge line 615, into first thickener 609 (BLOCK B), First thickener 609 includes a bottom scraper/mixer 610. Thickened potassium chlorate is discharged from first thickener 609 through lower outlet 617 and first discharge fine 619 and is pumped, via pump PI and first sludge line 701, to inlet 623 of a second thickener

662 (BLOCK D). Second thickener 662 also includes a bottom scraper/mixer 612. Thickened potassium chlorate is discharged through the lower outlet 625 of second thickener 662 through second discharge line 627 and is pumped, via pump P2 and valve

5_______V3. and through extension of discharge line 711 as third slurry line to inlet 629 of third _ thickener 658 (BLOCK E). Third thickener 658 also includes a bottom scraper/mixer 614.

Overflow sludge from second thickener 662 exits through upper outlet 715 and is cycled back to leaching tank 606 via line 616. Overflow sludge from third thickener 631 exits through upper outlet 713 and is cycled back to second thickener 662 through valve V4 and 10 second cycle line 641. Waste sludge from third thickener 658 exits through lower outlet

643 and is disposed of to land fill through disposai line 645 aided by pump P3 and valve V5.

Overflow dilute potassium carbonate from first thickener 609 flows from upper outlet 689 through first overflow line 633 and valve V6 into an evaporator system identified by the 15 general number “622” (BLOCK C). Evaporator system 622 comprises triple effect, cascaded evaporators 622-1, 622-2 and 622-3 connected in sériés. Overflow dilute potassium carbonate line 633 and valve V6 feed the first triple effect evaporator 622-1 to initiate the évaporation procedure. The lower outlet 655 ofthe first triple effect evaporator 622-1 is connected to potassium carbonate holding tank 624 via first outlet line 691, from 20 whence ît is pumped, via lower outlet 665 through line 667, pump P4 and valve V7, to heat exchanger 626 for a purpose to be explained later. The upper outlet 644 ofthe first triple effect evaporator 622-1 is connected to the lower inlet ofthe second triple effect evaporator 622^T2Wiatirst conncctingTincTŸ57. Theupper outlet CSTtofthe secondtriplFêffect evaporator 622-2 is connected to the lower inlet 653 of the third triple effect evaporator 25 622-3 via second connecting line 659.

The combined intermediate outlets 716 and 717 ofthe triple effect evaporators 622-2 and 622-3, respectively, are led via outlet lines 669 and 677 to connected line 679 and then to lower inlet 681 of potassium carbonate pretreatment tank 628. The upper outlet 661 of potassium carbonate pretreatment tank 628 leads, via line 685 to the lower inlet 651 of 30 boiler 636 (BLOCK F). Most ofthe steam produc ed in boiler 636 is dîrected via steam inlet i

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' [ ' ί sparging tube 649 leading to steam sparger inlet tube 607 to the sparger 611 at the bottom of leaching tank 606. The principal gascons outlet fromboiler 636, namely carbon dioxide, nitrogen and any residual steam, îs led via gas line 663 into the condenser 638 whose outlet 693 is connected to the inlet 695 of the connected economizer 640 by inlet line 697.

.....Condenser 638 and connected economizer 640 together constitutc (BLOCK G)............... In the condenser 638, water is condensed out of condenser 638 and is discharged through ^: outlet 675 to water condensate discharge line 647 which includes a branch line 639 leading to the upper inlet 605 of leaching tank 606 and a main water line 683 for unspecified use which may, for example, be for irrigation purposes. The outlet 699 from connected economizer 640 containing carbon dioxide and nitrogen leads via line 703 to the compresser 642 (BLOCK K), then via outlet 637 and line 707 to the lower inlet 787 of carbonation column 664 (BLOCK J).

The lower outlet line 673 from the third triple effect evaporator 622-3 is pumped, via pump

P5, through concentrated potassium carbonate line 705 to the upper inlet 720 of adsorptîon tank 630 (BLOCK H). Activated carbon from screw conveyor 668 is charged into adsorptîon tank 630 through activated carbon loading line 725. Adsorptîon tank 630 is çquipped with a stirrer 670.

A slurry of potassium carbonate is led from the lower outlet 727 of adsorptîon tank 630 via line 729 and pump P6 to the intermediate inlet 721 of first filter 671 (BLOCK I). The clarifîed slurry of potassium carbonate so formed is pumped by pump P7 from lower outlet

735 of first filter 671 and through line 737 and valve VI3 to the uppet¹ inlet 783 of —.......

------previously-meiTÎioned-car‘bonation-column-664—ΐΰΓ(ΒΕΘθΚ-Κ)-ίο^_ίοηη-»-81ιΐΓΓγ-οΐ----------------------------l· potassium bicarbonate.

The slurry of potassium bicarbonate produced in carbonation column 664 exits carbonation column 664 through the lower outlet 747 and is led through outlet line 739 and by pump P8 ί and valve V12 to crystallizer 672 to provide crystalline potassium bicarbonate. The | crystalline potassium bicarbonate exits through the lower outlet 743 of crystallizer 672 and ί is led through outlet line 745 and by pump P9 and valve V14 to filter 674 (BLOCK Μ). ί . i

The fîltered crystalline potassium bicarbonate is conveyed by conveyor 749 into oven 768 I

I (BLOCK N). The mother lîquor from filter 674 is fedby filtrate line 755 to inlet 723 of heat exchanger 626 where it is combined with slurry from first thickener 609 via slurry line 761 to inlet 759. In heat exchanger 626, the slurry and mother liquor are cooled and are retumed to the third thickener 658 from outlet 733 of heat exchanger 626 to inlet 731 of

5_______third thickener 658 via line 719 and valve V9..............................................................................................................

In the oven 768, the potassium bicarbonate is decomposed into crystalline potassium carbonate (potash) and gaseous carbon dioxide, nitrogen and steam. Such stream of gaseous carbon dioxide, nitrogen and steam exits through upper outlet 763 of oven 768 and is fed, via line 772 to a condenser 660 (BLOCK O). The description of condenser 660 is not duplicated in Fig 2 A but its fonction is completely described in Fig 1.

The crystalline potassium carbonate (potash) from oven 768 exits through outlet 765 and is conveyed by conveyor 769 to grinder 656 (BLOCK P) where it is finely ground, e.g. to 325 mesh. The ground potassium carbonate (potash) is conveyed by conveyor 753 to packaging machine 678 (BLOCK Q). The packages so formed may be supplied for local use or may be conveyed by conveyor 771 to be exported 676 (BLOCK R).

GENERALIZED DESCRIPTION OF FIGURES 1,2A, 2B AND 2C

As previously described in Figures 1, 2A, 2B and 2C, the first step in the extraction/purifïcation of the potash, which preferably is organic potash produced by controlled combustion of agricultural wastes, preferably the ashes of cocoa pod husks,

2Û plantmnJiimLbananaLpeHsreJl·d cofomuthusks.comsistsJ^£dischargingJl<ίashcs, containing typically about 77% potash, into water in preferably one or more stainless steel leaching tanks connected in sériés, which are of the CS TR type, each of which is equipped with a steam sparger. The impeller speed is set at a predetermined rpm. The température of the leaching is set to between 90°C and 100 °C.

Next, the leached slurry is sent preferably through a cascade of thickeners to remove undissolved matter and to form a clarified potash solution. The ash waste is then thoroughly washed until it contains practically no potash. 1

Next, the clarified potash solution is sent into an evaporator to concentrate the potash solution to saturation, i.e., about 60.8% potash concentrate.

Next, the potash concentrate is mixed, preferably in a stainless steel tank, with an adsorbent, preferably activated carbon, the quantity being about 3% of its mass to the potash concentrate. The activated carbon adsorbs ferrie ion complexes and clarifies the solution. Next, the spent carbon is fîltered out of the concentrated clarified solution with the aîd of a filter and the filtrâte is sent to a packed carbonation column. In the packed carbonation column, the fîltrate is carbonated to potassium bicarbonate. The packing is preferably an Intalox ™ packing.

Next, the bicarbonate solution is sent into a crystallizer operating from a maximum of about 90°C down to a minimum of 30°C, from where it is sent to another filter to separate the crystals from the mother liquor. The mother liquor is retumed into the evaporator while the bicarbonate crystals obtained are sent to an oven to regenerate the potash and to release carbon dioxide. The carbon dioxide is returned for reuse.

The potash which is obtained and which is of about 99%+ purity, is ground into powder for market. This final product potash Is wîdely used in the fcrtilizcr, soap, petrochemical, glass, food and pharmaceutical industries among others.

20.

In summary, the benefît of achieving this ability to produce substantially-pure potash, preferably from organic potash produced from the ashes of agricultural wastes by contmlled-comhustiQn-o.f-agr.iculWaLwasics,-a.ad-pEcfcrably4hc-ashcs-of-c.QGoa-pQd-husks_T plantain (and banana) peels and cola nut husks. is that it generates a finished potash product, which unlike unpurified mined potash, is substantially fiee from arsenic, and is therefore useable in the food and the pharmaceutical additives industries.

EXAMPLE 1

This is an example of the controlled combustion of cocoa pod husks to form ashes, although it is equally applicable to the controlled combustion of the other agricultural wastes, e.g. plantain (and banana) peels and cola nut husks.

The controlled combustion is preferably carried out in the kiln which is disclosed and claimed in co-pending PCT application filed on even date herewith by the présent applicant. Briefly, the kiln includes a central combustion chamber. The central combustion chamber includes a System for the control of combustion air to the combustion chamber.

........5 The kiln includes a s ccond cyl indrical chamber s urro unding the central combustion.................................................... chamber. The second cylindrical chamber includes a System ofthe flow of cooling water through the first annulus between the central combustion chamber and the second cylindrical chamber. The kiln includes a System for the feeding of the plant waste into the central combustion chamber. The kiln includes a temperature-sensing device to measure and display the température within the central combustion chamber during the combustion of the waste plant material. The kiln includes a System for the recovery of ash from the ashes.

In operation, the température of combustion is controlled to between 550 °C and 650 °C by a combination of increasing the supply of combustion air when the température in the central combustion chamber faits to near 550 °C and the introduction of cooling flowing water when the température in the central combustion chamber approaches 650 °C. The cocoa pod husks are formed into ashes in the above-described portable kiln at an average température of about 600 °C (i.e. between about 550 °C and about 650 °C).

To achieve the leaching of the potash from. the so-produced ashes, the ashes are transported to a leaching facility, preferably as described with respect to Fig 1, Fig 2A, Fig 2B and Fig

2C. At this facility, the leaching ofthe potash from the ash is carried out using warm water,

------Ue^at-about^O-^G-to-abeut-dOO—G7-The4eaehed-potash-gees4hrOugh-sever-al-leaehing------------------------purification processes, as described with respect to Fig 1 and Fig 2 until it attains a purity of over 99%.

Ash yield from the dried husks consisted of about an average of 7.2%. The resulting ash contained about 75% potash as potassium carbonate.I

Unlike mined potash which is contaminated with heavy metals (e.g. arsenic) the main 1%| . ...... , . .i of impurities in this organic potash are iron, calcium and magnésium. This makes thel i

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organic potash a premium product which is suitable for the pharmaceutical and food industries. This potash is also useful in the production of animal feed suppléments, cernent, fine extinguishers, photographie chemicals, textiles, in brewing beer and as a catalyst for synthetic rubber manufacturing. 5 INDUSTRIAL APPLIC ABILITY
Potash is important for agriculture because it itnproves water rétention, yield, nutritional value, texture and disease résistance of food crops. It has wide application in the farming of fruits, vegetables, rice, wheat and other grains, sugar, corn, soybeans and cotton, ail of which benefit from the nutrient’s quality enhancing properties. Potash-based fertilizers 10 hâve greatly contributed to économie growth in Africa, Asia and Latin America.
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19037
CITATION LIST
PATENT LITERATURE
US Patent No 3,842,762;
US Patent No 4.037.543;
5 US Patent No. 4,091,228
US Patent No 4, 092,098;
US Patent No. 4,198,288;
US Patent No 4,418,893;
US Patent No. 4,584,180;
10 US Patent No. 4,199,652;
US Patent No. 4,206, 312;
US Patent No. 4,787,506;
US Patent No 4,793,269;
US Patent No 4,973,246;	—
15 US Patent No 5,230, 617;
US Patent No. 5,350,296;
US Patent No. 5,456,362;
US Patent No. 6,315,976; and
US Patent No. 7,041,268;
15

]

NON PATENT LITERATURE “Chemical studies of some plant wastes from Ghana” E.K. Ankrah Journal of the Science of Food and Agriculture, Vol28, issue 10, pages 1229 - 1232,1984,

...............“Extraction of potash from cocoa pod husks’ B. K.. Simpsion et al Agricultiiral Wastes, Vol

5----J3-issue-l-pages-69-73^-1-9-85^--------------------------------------------------------------“Effect of rîpening on the chemical composition of plantain peels and pulp “L.Welford Abbey, et al Journal of the Science of Food and Agriculture, Vol 45, issue 4, pages 233-336 1988.

“Extraction and potential application of caustic potash from kola husk, ugwu pod husk and plantain peels” A.A. Taiwo et al Scientific Research and Essay Vol 3 (10) pages 515 -517, October2008.

Claims (12)

1) A method for the purification of impure potash from whatever source, e.g. from the controlled combustion of agricultural wastes, preferably the ashes of cocoa pod husks,________________ plantain (and banana) pcels and cola nut husks, comprising:

discharging impure potash in an aqueous warm water solution into a leaching zone provided with a steam. sparger, for leaching potash out of the impure potash;

passing the léached potash slurry through at least one thickener zone to provide a thickened potash solution;

partially-evaporating the thickened potash solution in an évaporation zone to provide a concentrated thickened potash solution;

passing the concentrated thickened potash solution through an adsorption zone to adsorb heavy métal ion complexes, and thus to provide a clarified concentrated thickened potash solution;

passing the clarified concentrated thickened potash solution through a first filter zone to fîlter out solid particles_: and to provide a concentrated potash solution;

carbonating the concentrated potash solution in a carbonization zone to couvert the potash ititô potassium bicarbonate;------------------------------------------------------------crystallizing the potassium bicarbonate;

separating the potassium bicarbonate crystals from the mother liquor in a second filter zone; and regenerating potassium carbonate from the potassium bicarbonate in a heating zone thereby to produce potash of about 99% purity. J

2) The method of daims 1, wherein the water is at a température of about 90°C to about

100° C.

3) The method of claim 1 or claim 2, wherein the concentrated potash solution contains about 60% potash concentration.

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4)-Lhe-niet-hod-of-aiiy-one-ofdaims-l-toB7-iùdud-vey-w4ierein.-the-eiystal-lization-zoneds^t-aminimum température of about 30°C to a maximum température of about 90 °C .

5) The method of any one of daims 1 to 4, inclusive, including the step of washing the agricultural waste ashes thoroughly untii it contains substantially no potash, and combining such wash water with water which îs introduced into the leaching zone.

6) The method of any one of daims 1 to 5, inclusive, wherein at least one thickener zone comprises a cascade of a plurality of thickener zones connected in sériés.

7) The method of daim 6, including at least one of: a recycle stream from a third zone of the plurality of thickener zones to the second zone of the plurality of thickener zones; or a recycle stream from the second zone of the plurality of thickener zones to the leaching zone; or a discharge zone for sludge from the third zone of the plurality of thickener zones to land fill.

8) The method of any one of daims 1 to 7, inclusive, including a boiler zone connected to the èvaporator zone for converting effluent from the évaporation zone into flue gases comprising carbon dioxide, nitrogen and steam. and condensing the tlue gases to provide

TT into the carbonation zone.

9) The method of any one of daims 1 to 8, inclusive, wherein the mother liquor provided during the filtration séparation of the potassium bicarbonate crystals is retumed to the évaporation zone. : .

10) The method of any one of daims 1 to 9, inclusive, wherein the régénération of potassium carbonate from the potassium bicarbonate in a heating zone simultaneously 18 produces carbon dioxide which is charged into the compresser zone for supplying additional carbon dioxide for the carbonation zone.

11) The method of any one of daims 1 to 10, inclusive, including the step of grinding the so-produced potassium carbonate to provide ground potash of about 99% purity.

-l-TjdThe-method-of-any-one-oFdaims-l-to-Hy-indusiveT-wherein-potash-is-contained-in---agricultural waste ashes from coco a pod ash and comprises about 77% potash content.

13) An interconnected system for the purification of impure potash comprising:

a leaching tank for containing the impure potash to be purified, the leaching tank including a lower sparger;

a solids inlet for introducing impure potash to be purified, the leaching tank;

a water inlet line for introducing water into the leaching tank;

a steam inlet line for introducing sparging steam into the sparger in the leaching tank;

a thickener tank;

a conduit for leading sludge of impure potash from the leaching tank into the thickener tank;

çin puanaraicir fnr notajoh caliitiAti ιλ«λχςιζ1α an Afflnpnt a-F .. . . concentrated potash; an inlet line from the thickener tank to the evaporator tank; an adsorption column for being charged with activated carbon or similar absorbent for absorbing métal complexes from the potash solution; 19

a conduit for leading concentrated potash effluent from the thickener tank into the adsorption column to provide an effluent of concentrated potassium carbonate which is substantially-free of métal complexes;

a first fîlter for filtering out solid particles from the concentrated potash solution which is substantially-free of métal complexes andto provide a concentrated potash solution which

is substantially-free of métal complexes, and which is also substantially-free of solid particles; . . . a conduit for leading a concentrated slurry of potash effluent from the adsorption column into the first fîlter; a carbonation column for converting the concentrated potash solution, which is substantially free of métal complexes, and which is also substantially free of solid particles, into a concentrated solution potassium bicarbonate; a conduit for leading the concentrated potash solution which is substantially free of métal complexes, and which is also substantially free of solid particles from the first fîlter into the carbonation column; a crystallizer; a conduit for leading the concentrated solution of potassium bicarbonate from the carbonation column into the crystallizer; a second, fîlter: a conduit for leading a slurry of crystallized potassium bicarbonate into the second fîlter to provide crystallized potassium bicarbonate which is substantially free of mother liquor; an oven for converting the crystallized potassium bicarbonate into crystallized potassium carbonate; and 20

a conveyor for conveying a crystallized potassium bicarbonate into the oven, thereby to form crystallized potash. 14) The interconnected system as claimed in claim 13, including: at least one thickener; a recycle line from the thickener back to the leaching tank; and a sludge discharge line from the thickeners for use as land fill. 15) The interconnected system as claimed in claim 13 or claim 14, wherein the at least one thickener comprises a plurality of thickeners connected in a cascading sériés. 16) The interconnected system as claimed in any one of claims 13 to 15, inclusive, further including: a condensate line from the evaporator to a boiler; and a steam line from the boiler to the steam inlet sparging line to the leaching tank. 17) The interconnected system as claimed in any one of claims 13 toi6, inclusive further including: a condenscr/economizer for receiving effluent gases comprising carbon dioxide, nitrogen and «team and for erinvi-yinu c.artian diax.idç anr| nitroaen fiinm ttiçJhniler ta a çapiprecgaj·· — and a compressed carbon dioxide line for leading compressed carbon dioxide to the carbonization column to convert potassium carbonate into potash. 18) The interconnected system as claimed in any one of claims 13 to 17, inclusive further including: a condenser for receiving effluent gases comprising carbon dioxide, nitrogen and steam

from the oven; and a line for conveying carbon dioxide and nitrogen from the condenser to the carbonation column.

19) Ί hc intcrconnccted system as clainicd in any one of daims13“tô T7“'indusive,“further including:-------------------------^:------------------------------------------------------------------a grinder for grinding the crystallized potash.

20) The interconnected system as claimed in claim 11, claim 12 or claim 13, further including a packaging machine for packing ground potassium carbonate, and including a conveyor for conveying ground potassium carbonate to the packaging machine,