Chemistry: fertilizers – Processes and products – Inorganic material
Patent
1981-04-30
1982-12-14
Lander, Ferris H.
Chemistry: fertilizers
Processes and products
Inorganic material
71 45, 71 47, 71 51, 71 53, C05B 1300
Patent
active
043636500
DESCRIPTION:
BRIEF SUMMARY
This invention relates to making a fertilizer material from apatite. Apatite is an insoluble phosphorus-containing mineral, approximating to Ca.sub.5 (PO.sub.4).sub.3 (F,OH,CI,1/2CO.sub.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.
Another known way of treating apatite is the `Rhenania process` described in British Patent Specification 301022. The apatite is mixed with Na.sub.2 CO.sub.3 to give a molar ratio of Na.sub.2 CO.sub.3 /P.sub.2 O.sub.5 .perspectiveto.1.0, while at the same time sufficient SiO.sub.2 is also added to combine with excess CaO. The reactants are ground together and calcined in a rotary kiln at 1100 C.-1200 C. for approximately 2 hours. Fluorine is said to be retained in the process, although steam is sometimes admitted to the kiln before 1000 C. 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.sub.2 CO.sub.3 solution, giving either Na.sub.3 PO.sub.4 or Ca.sub.3 (PO.sub.4).sub.2. This process requires high temperatures, and hydroxy-rich apatite, which is indigenous to central Europe and occurs in a few other regions of the world, some of which are of questionable reliability.
Hard mineral apatite (richer in chlorine/fluorine) is widely available in Sri Lanka, India and East Africa and is often a by-product from other mining operations. The present invention seeks to make fertilizer material from such apatite at a lower temperature than the 1100 C.-1200 C. required in the Rhenania process and without using acid. Sri Lanka is understood to have an indigenous alkali (NaOH) industry. (While it does also produce hydrochloric acid, this is not a suitable acid for treating apatite). The alkali is readily convertible to sodium carbonate. To make fertilizer material from apatite according to the present invention requires 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.sub.2 O, and the same might be said of mica.
Accordingly, the present invention is a method of making a fertilizer material from apatite, by roasting apatite at up to 1100 C. with a carbonate and/or aluminosilicate of an alkali metal in an amount such that the molar ratio apatite (as P.sub.2 O.sub.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 1:3 to 1:10, more preferably 1:3 to 1:5, for example 1:4.
The molar ratio apatite:siliceous material (as SiO.sub.2) is preferably from 1:0.75 to 1:1.0.
The roasting temperature is preferably below 1000 C., and desirably at least 800 C., more preferably at least 850 C., most preferably from 880 C., to 950 C., for example 900 C. The duration of roasting need not exceed 2 hours, and is preferably at least 1 hour.
Preferably 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 (i.e. why siliceous material is added) 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.sub.4 P.sub.2 O.sub.9 is all soluble, i.e. it is at first sight an ide
REFERENCES:
patent: 1799882 (1931-04-01), Brenek
patent: 2916372 (1959-12-01), Schytil
patent: 3552944 (1971-01-01), Hauschild et al.
patent: 4106922 (1978-08-01), Hauschild et al.
Glasser Fredrik P.
Gunawardane Richard P.
Lander Ferris H.
National Research Development Corporation
LandOfFree
Fertilizer material from apatite does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fertilizer material from apatite, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fertilizer material from apatite will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1200450