Classifications

• • C—CHEMISTRY; METALLURGY
  • C05—FERTILISERS; MANUFACTURE THEREOF
  • C05B—PHOSPHATIC FERTILISERS
  • C05B13/00—Fertilisers produced by pyrogenic processes from phosphatic materials
  • C05B13/02—Fertilisers produced by pyrogenic processes from phosphatic materials from rock phosphates

Definitions

• This invention relates to making a fertilizer material from apatite.
• Apatite is an insoluble phosphorus-containing mineral, approximating to Ca 5 (PO 4 ) 3 (F,OH,CI,1 ⁇ 2CO 3 ), and the phosphate content must be rendered soluble for fertilizer use.
• Apatite the most abundant terrestial form of phosphorus, is conventionally treated with a strong acid such as nitric or sulphuric acid to render the phosphate soluble. This requires a capital-intensive industry.
• apatite Another known way of treating apatite is the 'Rhenania process' described in British Patent Specification 301022.
• the apatite is mixed with Na 2 CO 3 to give a molar ratio of
• the reactants are ground together and calcined in a rotary kiln at 1100C - 1200C for approximately 2 hours. Fluorine is said to be retained in the process, although steam is sometimes admitted to the kiln before 1000C is reached in an attempt to remove at least part of the fluorine.
• the sintered product may be used directly as a slow- release source of P or it may be subsequently extracted with hot aqueous Na 2 CO 3 solution, giving either Na 3 PO 4 or Ca 3 (PO 4 ) 2 .
• Rhenania process and without using acid without using acid. Sri Lanka is understood to have an indigenous alkali (NaOH) industry. (although it does also produce hydrochloric acid, this is not a suitable acid for treating apatite.)
• the alkali is readily convertible to sodium carbonate.
• siliceous material and this is also widely available as quartz, sand or potash felspar (an alkali metal aluminosilicate). Addition of the last-named in small proportions also has the advantage of introducing available K 2 O, and the same might be said of mica.
• the present invention is a method of making a fertilizer material from apatite, by roasting apatite at up to
• apatite (as P 2 O 5 ): alkali metal is 1: at least 3 and in the presence of sufficient siliceous material to keep the free-lime content of the fertilizer material below 2 weight % and to inhibit formation of tetracalcium phosphate.
• the molar ratio apatite : alkali metal is preferably from
• the molar ratio apatite : siliceous material is preferably from 1:0.75 to 1:1.0.
• the roasting temperature is preferably below 1000C, and desirably at least 800C, more preferably at least 85OC, most preferably from 880C to 950C, for example 900C.
• the duration of roasting need not exceed 2 hours, and is preferably at least 1 hour.
• the apatite, the siliceous material and the carbonate and/or aluminosilicate are pressed together (e.g. pelletised) before the roasting. This appears to enhance the rate of reaction.
• the invention extends to the fertilizer material made as set forth above, optionally admixed with other agriculturally acceptable components.
• the reasons for avoiding excessive free lime and tetracalcium phosphate are as follows: Free lime is capable of causing skin burns, reacts with moisture thereby causing caking and may make the fertilizer, and hence the soil, too alkaline.
• the phosphate in tetracalcium phosphate Ca 4 P 2 O 9 is all soluble, i.e. it is at first sight an ideal fertilizer material.
• Ca 4 P 2 O 9 is liable to conversion in the presence of water vapour, which is likely in a fossil- fuel-fired tunnel kiln, to CaO (or Ca(OH) 2 ) plus insoluble hydroxyapatite, one of the very materials which the present invention was devised to solubilise.
• the quantities of Na 2 0/K 2 0 and SiO 2 are desirably the minimum, as an excess would result in too much dilution of the phosphate phases.
• a way of determining these is to consider the CaO- and P 2 O 5 -rich regions of the system CaO-Na 2 O-P 2 O 5 -SiO 2 .
• the plane of compositions lying between Ca 2 SiO 4 , Ca 3 (PO 4 ) 2 and CaNaPO 4 just fulfils the condition that CaO and Ca 4 P 2 0 9 should be absent and, furthermore, we find that this plane of compositions constitutes a true ternary system at subsolidus temperatures. Its position within the quaternary system is shown in the accompanying drawing.
• Table 1 records the results of solubility determinations made on pure single-phase preparations. For present purposes availability is defined by the relation:
• phase A is not completely soluble unless it too contains silica in solid solution; Phase A is explained in the footnote to Table 3. Both ⁇ and ⁇ Ca 3 (PO 4 ) 2 give less than 100% available P 2 O 5 . Moreover, while
• Ca 4 P 2 O 9 has 100% availability, it is (as- already mentioned) readily converted to hydroxyapatite by annealing in air, whereby the available P 2 0 5 falls to 20%. Attempts to form a solid solution, substituting two Na + ions for Ca ++ ions, in the hope that Ca 4-x Na 2x P 2 o 9 would be less reactive to water vapour than the Ca 4 P 2 O 9 , were unavailing.
• CaNa 6 P 2 0 9 was found to be 100% extractable, but is hygroscopic and therefore undesirable.
• ss solid solution
• Sri Lanka apatite sample (1) is a sample of pure apatite from the "leached zone" in the deposit at Eppawela, Sri Lanka.
• Sample (2) is a commercially beneficiated sample of apatite from Eppawela, Sri Lanka.
• Phase A see footnote to Table 3.
• the invention will now be described by way of example.
• the accompanying drawing shows a corner of the quaternary system CaO-Na 2 O-P 2 0 5 -SiO 2 .
• the plane Ca 3 (PO 4 ) 2 -Ca 2 SiO 4 -CaNaPO 4 has been marked out. Compositions on this plane contain neither CaO nor Ca 4 P 2 O 9 , and accordingly are desirable.
• Reaction batches were prepared by blending these raw materials and firing following a heating rate of 5C/min at a constant temperature for 2 hours.
• Table 3 records the results of the annealing treatments. The phases present were determined by X-ray powder diffraction but the limit of detection of unreacted apatite was as high as 5%.
• SiO 2 fulfils this-rble.
• apatite : alkali metal from 1:3 to 1:4 gave the most rapid reaction at low temperatures. These batch proportions correspond to a weight percentage of Na 2 CO 3 between 20 and 27%. Some excess sodium carbonate was tolerable. If the optimum proportions of all three components are considered, molar ratios of apatite : Na 2 CO 3 : SiO 2 close to 1:2:1 are favourable for reaction. If the SiO 2 content is reduced slightly below this optimum, for example to 1:2:3 ⁇ 4, a high yield of available phosphorus is obtained, but free CaO is also developed.
• Examples 1 to 3 are according to the invention.
• Examples A to J are not according to the invention. It will be seen that few of Examples A to J gave any significant reaction below 1100oC, and of those which did, either inadequate phosphate was solubilised (as H) or free lime and sometimes a hygroscopic product resulted (as C and D).
• Phase A tricalcium phosphate.
• Phase A is believed to approximate to Ca 5 Na 2 (PO 4 ) 4 and is the crystalline phase defined by Ando and Matsuno (J. Ando and S..Matsuno, Bull. Chem. Soc. Japan 41 (1968) 342.)
• Phase A solid solutions may also contain silicon.
• APPENDIX Determining the 2%-citric-acid-soluble P 2 O 5 in a sample: The sample is ground to pass a 100 mesh BS sieve. A 1.0 g sample is extracted with 100 ml of 2% citric acid in a mechanical shaker operating at 260 oscillations per minute for 30 minutes at 18C. The resultant solution is filtered under vacuum using a sintered glass crucible (porosity No. 4) and the filtrate P 2 0 5 content is determined by the vanadomolybdate method, in which the following reagents are used:
• Ammonium metavanadate solution prepared by dissolving 1.12 g of ammonium metavanadate in a mixture of 240 ml of concentrated HC10 4 acid and 260 ml of water.
• Ammonium molybdate solution prepared by dissolving 35 g of ammonium molybdate in 500 ml of water,
• Standard phosphate solution 0.2 mg/ml P 2 O 5 , prepared by dissolving 0.3835 g of dried potassium dihydrogen phosphate in 1 litre of water. Solutions (i) and (ii) are stable and will keep for some months.
• the resultant solution is diluted with water in a 100 ml volumetric flask.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Fertilizers (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10507678

Family Applications (1)

Country Status (5)

Families Citing this family (3)

Citations (7)

Family Cites Families (3)

• 1980
  • 1980-09-08 JP JP50195380A patent/JPS56501086A/ja active Pending
  • 1980-09-08 DE DE8080901660T patent/DE3068215D1/de not_active Expired
  • 1980-09-08 EP EP80901660A patent/EP0041504B1/en not_active Expired
  • 1980-09-08 US US06/261,162 patent/US4363650A/en not_active Expired - Fee Related
  • 1980-09-08 WO PCT/GB1980/000139 patent/WO1981000711A1/en not_active Ceased
• 1982
  • 1982-07-30 US US06/406,713 patent/US4436546A/en not_active Expired - Fee Related

Patent Citations (7)

Also Published As

Similar Documents

Legal Events