CA2029887A1

CA2029887A1 - Process for manufacturing pelletized materials for use in chemical reactions in industry or agriculture

Info

Publication number: CA2029887A1
Application number: CA 2029887
Authority: CA
Inventors: Zbigniew Boguslawski
Original assignee: Individual
Current assignee: AQUAMOT AG
Priority date: 1989-03-23
Filing date: 1990-03-21
Publication date: 1990-09-24
Also published as: WO1990011264A3; WO1990011264A2; EP0426783A1; CH680586A5

Abstract

ABSTRACT

The present invention concerns pelletized materials for use in chemical conversion processes in industry or agriculture, in which alkaline compounds in powder form are pelletized with hydroxides of substances having highly different solubility products in a manner such that initially in a first stage with the addition of small quantity of pelletizing water nuclei of a size of 0.05 to 0.15 mm are formed and that subsequently the nuclei formed are combined into pellets by the addition of more pelletizing water, and a process for their preparation. To the initial material in the first stage a quantity of pelletizing water sufficient for hydrating, but not substantially exceeding said quantity, is added and following the onset of nucleation the further addition of water is interrupted until the initial materials are completely hydrated. The pelleting water required for the continuation of nucleation is added only after said hydration.
For the preparation of pellets for the elimination of nitrogen impurities and in connection with it of phosphorus impurities and possibly heavy metals, hydrogen-phosphate salts of phosphates of a cation of the second principal and secondary groups of the periodic system are used as the initial active substances.

Description

'9~ 3 l7: ;~c EYER~LINiER P~T ~ 17~ REIEI~H 2 0 2 9 8 8 7 P. ~ i7 MULTILAYER PELLETS

BACKGROU~I~ OF TH~: lNVENTIOrl The prPsent invention concerns pelletizad mate~ial6 for use in chemical conversion processes of industry or agriculture, for example in the purifi~ation o ~omm~nal, in~ust~ial and private sewa~e, or the f~rtilizing or deacidifica~ion o~ soil utilized i~ agriculture or forestry, and a pro¢e~# for their preparation.
Qne of the essential problems of chemi~al conversion proce~ses conæiætæ of the con~rol of the rea~tion rate an~ in particular the regulation of the ~uantity of reagents introduced. Thi6 is partic~larly true in conversion ~rocesses in which water soluble materials are used as rea~ents, the reaction mat~rial i9 p~eæent in an aqueOus solution and ext0nded contact times between the reagents and the solution cannot ~e avoided, This is the case for esample in the deacidification of ~oils in agriculture and forestry and in numerou~ ~h~mical conv~rgion processes, for eYample sewage purification. Materials ~pread to improve soils are conti~uouxly e~posed to di~s41ution by ~he humidity of the soil, which ~articularly in ~ainy weather leads to the excessive dissolution of the soil improvement materialæ. The excessive su~ly of these materials themselves can lsad to damage to the soil, and there is a risk that the materials will be introduced into the ground wat~r. The same is true for chemical conversion proces~es, for example, in sewage purification processes. In order to obtain adequate conversion of the harmful su~stances, reagents are used in great excess on the one h~nd, and on the other, long retention times are required agai~ posin~ the danger of an excessive uptake of the reagents with harm~ul conseguences for the dispo~al o sewage waters .
~ his pro~lem in chemical conversion procos~e~ is es~ecially prevalent in the purification of acidic waste waters wherein acidic sewage waters are defined as all typeæ of sewage with a low pH value, including the ~lue ga~ condensates originating in th~ chimneys of househo~ds and industrial heating installations which are of particular importance.
These condensates have estraordinarily low pH values, and -- as revealèd ~y recent investigations -- Carry apprscia~le proportions of heavy metal~ from the chimney linings in the form of abrasion products or ~olution~ by ~he drippin~ or ~unning condensatos. The neutralization of such sewage waters represents a considerable environmental problem a~ their introduction into public outfalls leads to considerable damage to biological puriication in~tallation~ and subsequently to the environment itself. I~ is therefore increasingly nece~gary in order to prevent such damage, ~o develop chemical ~ewage t~eatment proCe~ses wher~in purification is achiev~d by chemical or phy~iochemical reactions, as a supplement or alternative to biolo~ical purification methodg wherein purification effects are obtained by bac~erial, enzymatically catalyzed metabolic ~eactions.
~ iological processes are limited relative to each other by that only substances that fit into the metabolism of the bacteria are affected and which are taken up during the retention time in the biological system ~activation basin, percolation filter) and reacted, i.e. decomposed. In view of tho increasin~ly complex compo~ition of communal and particularly industrial sewage waters, the ~iologicall~
unreacted residual loads remaining in the biological treatment process will increase in volume, For this reason alone chemical sewaqe treatment methods are particularlY important relativ~ to the future safetY of the aquatic ~art of our ecosystem.

3-l1-Z3 17:Z4 E`l'Ei~iLII15ER ~i~T S~ 72 ~ EIEI'~H 2029887 F~4~17 It is known to u~e so-called neutralization ~oxes for the neutra}ization of acid sewage waters; the bos is filled with a basic filler material and the acid solution is drippea into it, thereby reactin~ during the more or less extenxive retention time with t~e reaction mate~ial within the bo~. The known processes have seve~al disadvantages. The one disadvantage is the high consumption rate of neutralizing material due to the complete æaturation o the condensates.
Anothe~ disadvantage is that large proportions of the neutralizing material~ are dissolved in the box during the retention time, leading to eYcessive loa~ing. Finally, there is no ~limination of the heavy metals contained in the wa~te water.

~IEF p~a~IPTION O~ INVENTION

It i8 the o~ject o the present invenSion to provide initial materials for u5e in chemical conversion processes, the consumption of which i8 r~gulated as a function o~ the reactiOn vclocity desired, and a process for thei~ preparation.
Tho P~esent invention utilize~ materi~l ~ w; th varied ~olubility products which are Çormed into layers, preferably with materials of higher solubility on the in~ide of the yellet~ an~ mate~ials o~ ~ower solu~ y on the out~ide of the pellets. Pelletization and the controlled g~anulation desiqnated ~mi~rocoated buildup-agglomoration~ is performed in a nuclei formation step by the initial formation of pelletizing nuclei fol~owed by ~urther pelletization.
In the initial pellet ~ormation st~p, a minimal amount of pelletizing water is used, to allow nucleation of primary m~torials of higher solubility. Upon contact with the solution containing the reactive substances, the pellets of the present invention react in a controlled and quasi-buf~e~ed manner so that the more readily soluble materials are protected against premature dissolution, thereby preventing the e~cessive 636~K

3~ 3 17:25 E`lER~LINSER P~T ~-6~37Z ~REIElCH 2029887 P . 5/17 accumulation of materials o~ low or very low solu~ility. The pellets of the present invention insure that the solution containing the reactive su~st~nces i6 expos~d to large contact surface area, thereby insuring direct contact of the r~acti~e substance usually present in a high dilution, with the reagent and thus it~ convsrsion. In this manne~ it is insured -- for e~ample in the deacidification of sewage waters -- that even in the case of a simple flow of the xewage water through a pile o the pellets prepared according to t~e present in~ention, the quantity o~ reactive material necessary for neutrali~ation is always available to the sewage. Additionally, a Nslow release effect~ is obtained whereby the materials with extremely low solubility ~roducts are concentrated in the outer layers of the nuclei and ~ellets, and a controlled buffer action is obtained preventing eYcessive dissolution ana neutralization whi~h iæ as harmful to the environment as excessi~e acidification. Another siqni~icant advantage of the invention is the complete elimination of heavy metal~ simultaneously with the neutralization of the sewage waters, said metal~ precipitating during the gradual transition of the waters from the acid phase into the baeic ~hase in particle sizes such that they are initially bon~ed phy~ically to the surface ef the pellets an~
may be collected in a special filte~ layer upon being washea out from the ~ellet pile.

nE~AILED ~ R~pTION 5~E_E~E PREFERR~ aoDIM~

In practising the present invention, the ~tructure of the nuclei and matri~ ~aterials with dif~erent solubility products, and the choice of tho initial material~ is of doci~ive importance in obtaining the aforementioned efects.
Tho metered addition of pellotizing water i9 the controlling factor in the preparation process. Buildup a~glomeration is the result of the strongly reduced su~ply o pelletiz~n~ water in the nucleation phase. Initially a dissolution of the surface layers of the more rea~ily soluble material particles Z3 17: :~6 E'('ER~LI NSE~ Pf~T ~-~J37~ rjREIE IC:H 2 0 2 9 8 8 7 P . 6 ' 17 takes place, which therefore aq~lomerate preferentially with the bonding of slight proPortions of the less soluble materials. The di~solution of the surfaces of the pa~ticles of the less soluble material takes place a~ a ~i~nificantly later time, so that this material i~ located, following comPletion OT'.
the pelletizing process, mainly in the outer layers of the re~ulting pellets, thus encapsulating the nuclei and residual guantiti~s of not prenucleated material with a higher solubilitY product.
The neutralization of garden, agricultural and forest soils is an example of an especially advsntageous ap~lication of pelletized material~ prepared according to the present invention. ~his application, for e~ample, can be administered usin~ pellets with 40 to 65, pref0ra~1y 45-55~ by weight dolomite, 10 to 25, p~eferabl~ 15-20$ by weight calcium carbonate, 2.5 to 7.5, preferably 4-5~ by weight disodium-monohydrogen-phosphate, 2.5 to 7.7, preerably 4-5~ by weight calcium-hydrogen-phosphate, 10 to 15, preferably 6.5-7~
by weight calcium hydro~ide, 2.5 to 7.5~ preferabl~ 4.5-5.0% 4y w~ight bentonite, 1.5 to 3.0, preferably 2.5-3.0~ by weight feldspar, 1,5 to 5.0, preferably 2.5-3,0~ by weight potassium silicate and 1~5 to 5.0, prefe~ably 3.5~ by weight magnesium oxide. The pelletizing is advantageously carried out in a polydispersod manner, i.e, with hiqhly different sizes, with a proportion of small grain inversely propo~tional to the pH
value of the soil to be treated. The effective period of time an~ the action rato, , the time during which a soil with pH value of for ~ample 2 may be b~ought to a pH value of between 6 and 7 and maintained at this value, may be determined. This action rate is controlled by increasing the small grain size proportion in the case of low pH values and with the controlled selection of the initial materials as a function of their ~olubility pro~ucts. In this Tnanner, for example, the pelletizing of dolomite (calcium-magnesium carbonate) with a ~olubilit~ product Of 2 . 6 ~ 10 5 for 63 ~OK

' ~12J-11 -2S 17: 27 E~'ER~LII ISE~ P~T ~ 72 Il~E IE I I~H 2 0 2 9 8 8 ~ P . 7/17 magnesiu~ carbonate and 4.7 x 10 7 for aalcium carbonat~, may be buffered ~y use of aalci~m hydro~ide (solubility product ~.9 ~ 10 6) magnesium hydroxide (1.5 x 10 12~ aluminum hydroxide (1.9 x 1~ 31) or iron hydro~i~e (5.0 Y lo 38), thereby obtaining in a controlled manner a more or less strong 4uffering of the active material, whereby the dissolution of the material (in this e~ample the dolomite) is corresPondingly delayed.
Further activ~ substanceæ may be added to the initial material, æ~ch as for eY~mple activated ~entonite or sodium-sulfate-d~cahydrate to regulate the water content of the soil. Activated bentonite i~ capable of storing water in a quantity of 30 times of its wei~ht, while sodium-sulfate-decahydrate cleaves off its wat~r of ~ry~allization congruently at temperatu~e~ ov~r 30C. In a similar manner, an active sub~tance m~y be added to the ~ellets, where~y the ozone taken up by the plant as the result of the action of s~n light on the loaves may be eliminated, tog~ther with it~ ha~mful effe~ts. This may con~ist either of a ~uffer causinq a mildly al~aline reaction -- pHC7 -- the sap o the plant, o~ an agrotechnically acceptable metalizer, or exa~pl~ manganese sulfate (MnS04), which decomposes the ozone, whe~ein the rate of decompo~ition decrea6es with the inCrea~in~ alkalinity o the solution (plant sap).
A~other em~odiment is a process for making ~ollets for the eliminatio~ of nitrogen impurities, and in combination with it, of phosphorus impurities, possibly together with the removal of heavy metals. This ombodiment contains hydroyen phosphate salts of a cation of the second principal and secondary groups of the Periodic Syste~, p~eferably magnesium-hydrogen-phosphate ~MgHP04) and/or phosphate salts, in par~icular the ortho-phos~hate salt~ of a cation of the second principal (Be, Mg, Ca, Sr, Ba and Ra) and secondary (Zn, 'ge~ 3 l7:c~ EYEf~LINSER G~T ~ EIr2 ~ EIEII::H 2~29887 P.~/17 . .

.,.

Cd and Hg) groups of the Periodic System, preerably tri-magnesi~m-di-phosphate. Optionally, the ~hosphate salt, in particular the ortho-phosphate ~onstituting one o~ the active substancec, may be ~ynt~e~i~ed in the fir~t pelletizing stage in a manner such that initiallg a partial ~uantity of the m~tal oxide i8 reacted with phoæphoric acid in a guantitY necessary for conversion, after which more maqnesium o~ide i~ added, whereupon followinq the comPlete con~ersion, pelletizing takes place usin~ the magnesium hydroxi~e formed in the seeond rea~tion step a~ the binder, in combina~ion with the excess re~ction water formed in the ~irst reaction ~tep. In this manner, the control of the addition of p~lletizing wat~r is made po~æible in the fir~t pelletizing stage in a particularly #imple manner, since in the reaction of magnesium oxide with pho~phoric acid an ~xaes~ ~uantity of reac~ion water i~
released suffi~ient for the hydrating of the sub~e~uently added magnesium o~ide, A metere4, ~light quantity o~ water i~
required for the formation o~ t~e nuclei preferably ~ro~ the more soluble active materials. The less ~oluble materials ~ake part later only in the agglomeration and encapsulate a~ the matrix material in a mix~ure the the ~ore soluble nucl~i.
The present invention may be applied with great advantage in the preparation of pellets for the neutralization of a~ids, with the ~imultaneous elimination of heavy metals.
In ~his case pHlletizing is carried out ~onveniently in a manner such that initially nuclei are formed with a core consisting essentially of bases of the second principal group o~ the periodic sy~tem, in particular magnesium hydroxide, an~
an encapsulation by iron-III h~droxide, The nuclei are subsequently pelletized in a matrix, wherein pellets of different composition, i~Çl in ~axticular pellet~ with a different magnesium hydroxide/iron-III hydro~ide ratio, may ~e formed. The pellets c~ntaining a high proportion of magnesium hydroxide are used for the rapid neutralization of the acids ~ contained in the liquid being treated, while the pellets ,.~

, ', r9QI-11-2:~ 17:29 E`'EI~LIN5ER F'~T ll-S13,2 DREIEICH 202988~ P.~'17 containing a higher proportion of iron-III hydro~ide pro~iae a stronger encapsulation of the magnesium hydroxide, with the effect of reducing to about 7.5 the pH value which had been increased to over 9 in the neutralization phase with the purpose o precipitating the heavy metals. This lowered pH of about 7. 5 is more compatible with the environment.
The iron hydroxide is present in the form of a trivalent hydrated iron ion which Convert~ gradually from Fe(H20~63 to Fe(~20)2(OH)4, The hydrogen ions thus produced re~ult in a slightly acidic ~roperty of the iron hydro~ide. In addition to this advantageous effect of the regulation o~ the pN value, the pellets prepared in this manner have the ~urther advantage that in the phase of the increa~ed pH val~e (~9~ the heavy metals conta~nea in the ~ol~tion are precipitated and the precipitate is absorbed on the iron hydroxi~e pre~ent in the colloidal form.
T~e invention will become more apparent ~rom the ~ollowing esam~les:

~XAMPLE 1s 15 kg dolomite 18~23, 5 kg calcium carbonate, 0.5 kg each of di~odium-mon~hydrogon-~hosphate and calcium-hydrogen-phosphate, ~.5 kg calcium hydroxide, 1.5 kg ~1dspar, 1.0 potassium silicat~, 3.0 kg active bentonite and 1 kg mangane~e sulfate, i8 placed into a ~elletizing mixer.
The mi~ture is homogenized intensively. Subg~quently, 2.5 k~ water, 2.5 kg magnesium oxide and 5.0 kg white li~e are added and mi~ed intensively. Following the completion of the e~oth~rmic reac~ion of lime ~laking, the ~i~ture is pelletized with the addition of 4.5 kg ~elletizing water to the nucleation #tage~ whereupon ~inal pelletizin~ takes ~lace with the a~dition o another 0.5 to 0.6 kg water, until the microcoated, nuclei-based pellet~ desired are obtained with a grain size distributio~ between 3 and 6 mm, T~ey contain water in .. : .

.

2~ 17:S~l EYER~.LIN-,ER Pf~T D~ REIEICH 2~2 98 ~7 P. 1~17 quantitie~ of abou~ 2.0 to 2.2 kg, have a deactivating effect on o~on~ sol~tions and have a pH val~es of approximately 11.6 in water and in acidic water -- initial v~lue 3.8 -- ~ buf~ered value of 7.35.

EXAMPLE 2:
100 kg magne~ium o~ide with a degree of purity in e~ceæs of 98~ and a calcium ion content o l~s~ than 0.5~ by weight ~re weighted into the pellstizer, together with 10 kg iron oxide -- again of a purit~ in e~esæ of 98%. A~ter intensive mi~ing for about lO min, 48.4 kg deionized ~softened di~tilled water) are addea, which is ~ufficient for the conversion of the oYides to hydroxides, ~n excess Of about 0.5% to 1% by weignt should not be increased further. The reaction i8 carried ou~ under intensive cooling to remove the reaction heat so that the rea~tion t~mperature o~ 35~ is n~
e~ceeded. Following the completion of the intensive reaction phase, the misture is allowed to a~e fo~ between 30 and 120 min.
More pelletizing water i8 then added in three ste~s to the cool~d rea~tion ma~s with continuou~ pelletizing, i.e.
initial}y a quantit~ of about 2.75 kg, then after lO min another 1.35 kg. After a ~elletizing time of another lO min, pellet nucl~i have been ormed, whi~h followin~ the addition of another 1.35 kg water are pelletized into final pellets with dim~nsio~s between 3 and 6 mm. ~he wet pellets are ~owdered with abo~t 2.5 kg magnesium o~ido and dried in air for 12 h.

~XAMPLE 3:
lO0 k~ iron oxide with lO kg ma~nesium ox~de, are ~rocessed wit~ the addition o~ 34.0 kg hydratin~ water and -- in three part~ -- of 2.0 ~ 0.95 + 0.95 kg pelleti~ing water, into pellets suita~le or pH value adj~stments. ~h~ pellets are prepared in the manner described in the foregoing exarnples, un~er the ~ame conditions.

_ g _

Claims

We claim:

1. A process for the pelletizing materials of varied solubility products for use in chemical conversion processes comprising formation of nuclei 0.05 to 0.15 mm in diameter, said nuclei having a high proportion of material with a relatively high solubility product;
and subsequently formation of pellets from said nuclei, said pellets having a high proportion of material with a relatively low solubility product in said pellet's outer layers.

2. A process according to claim 1, wherein in said nuclei formation step pelletizing water is added not substantially more than is sufficient for hydration, and in said pelletizing step the further addition of pelletizing water required for pelletization is delayed until after said hydration is complete.

3. A process according to claim 2, wherein said material is chosen from a group consisting of the hydrogen-phosphate salts of the second principal and secondary groups of the periodic table, and the ortho phosphate salts of the second principal and secondary groups of the periodic system.

4. A process according to claim 3, wherein said material is magnesium-hydrogen-phosphate or trimagnesium-di-phosphate.

5. A process according to claim 3, wherein in said nuclei formation step a partial quantity of metal oxide is reacted with a sufficient quantity of phosphoric acid, and then more metal oxide is added, and in said pellet formation step pelletization is carried out using the metal hydroxide formed as the binder in combination with the excess reaction water formed in the nuclei formation step.

6. A process according to claim 2, wherein in said steps of nuclei formation and pellet formation, said materials consist essentially of magnesium hydroxide and Fe (OH)3.

7. A process according to claim 2, wherein in said nuclei formation step and said pellet formation step said material is comprised essentially of:
40% to 65% dolomite by weight:
10% to 25% calcium carbonate by weight;
2.5% to 7.5% disodium-monohydrogen-phosphate by weight;
2.5% to 7.7% calcium-hydrogen-phosphate by weight;
10% to 15% calcium hydroxide by weight;
2.5% to 7.5% bentonite by weight;
1.5% to 5% feldspar by weight;
1.5% to 5% potassium silicate by weight; and 1.5% to 5% magnesium oxide by weight.

8. A process according to claim 2, wherein in said nuclei formation step and said pellet formation step said material is comprised essentially of:
45% to 55% dolomite by weight;
15% to 20% calcium carbonate by weight;

4% to 5% disodium-monohydrogen-phosphate by weight;
4% to 5% calcium-hydrogen-phosphate by weight;
6.5% to 7% calcium hydroxide by weight;
4.5% to 5% bentonite by weight;
2.5% to 3% feldspar by weight:
2.5% to 3% potassium silicate by weight; and approximately 3.5% magnesium oxide by weight.

9. Process accordinq to claim 7, wherein in said nuclei formation step and said pellet formation step, said material is chosen from the group consisting of:
dolomite, calcium carbonate, disodium -monohydrogen-phosphate, calcium hydrogen phosphate, calcium hydroxide, bentonite, feldspar, potassium silicate, magnesium oxide, active bentonite, and sodium sulfate-decahydrate.

10. Process according to claims 7, 8 and 9, wherein in said nuclei formation step and said pellet formation step, active bentonite and/or sodium sulfate-decahydrate (Na2SO4 x 10H2O) having a water storage function are used.

11. Process according to claims 7, 8 and 9, wherein additionally ozone decomposing material with a low solubility product is added.

12. Process according to claim 7, wherein in said nuclei formation step, said material contains less than 0.5 dry weight percentage calcium.

13. Process according to claim 8, wherein in said nuclei formation step, said material contains less than 0.5 dry weight percentage calcium.

14. Process according to claim 9, wherein in said nuclei formation step, said material contains less than 0.5%
dry weight percentage calcium.

15. Process according to claim 2, wherein in said nuclei formation step said material contains 0.05 to 0.25%
weight percent manganese II salts.

16. Process according to claim 2, wherein the solubility products of said materials differ by approximately three powers of ten or more.

17. Process according to claim 2, wherein in said nuclei formation step said materials are chosen individually or in combination, from: the group consisting of zinc hydroxide, magnesium hydroxide, aluminum hydroxide, manganese II hydroxide, Iron III hydroxide; the group consisting of zinc sulfide, tin sulfide, manganese II
sulfide or Iron III sulfide; and zinc carbonates and calcium carbonates.

18. Process according to claim 16, wherein in said nuclei formation step, said materials include: 3.0 - 8.0% by weight Mg(OH)2, 3.0 - 8.5% by weight Zn(OH)2 and 3.0 to 17.5% by weight Fe(OH)3.

19. Process according to claim 16, wherein in nuclei formation step, the calcium content of said materials is less than 0.5 dry weight percent.

20. A process for the formation of pelletized materials for use in ehemical conversion processes comprising a first nuclei formation step during which primarily materials with relatively higher solubility products are concentrated into nuclei, and a second pellet formation step during which primarily materials with relatively lower solubility products are concentrated into outer layers encapsulating a plurality of nuclei.

21. A process according to claim 20, wherein said first nuclei formation stage is performed with cooling to room temperature.

22. A process according to claim 20, wherein in said first nuclei formation stage, said materials contain 0.5% to 3.0% dry weight kaolin, and after said pellet formation step the pellets are heat treated at 260° to 350°C and cooled slowly to room temperature.

23. A process according to claim 20, wherein in said nuclei formation step, said materials contain soluble salts with acids of carbonates and hydrogen carbonates, of Na2CO3 or k2CO3 alone or together.

24. Pellets for use in chemical conversion processes formed according to claim 20 with a porosity of 0.05 to 0.20; a specific surface area of 65 square meters/gram; and a settled apparent density of 1.1 to 1.25.

25. Pellets for use in chemical conversion processes wherein primarily materials with relatively higher solubility products are concentrated in said pellet's inner layers and materials with relatively lower solubility products are concentrated in said pellet's outer layers.

26. Pellets for use in chemical conversion processes according to claim 25, wherein said materials are chosen from a group consisting of the hydrogen-phosphate salts of the second principal and secondary groups of the periodic table and the ortho phosphate salts of the second principal and secondary groups of the periodic system.