FIELD OF INVENTION

[0001] The present invention relates to the novel method of separation of exclusive phosphorus-minerals from phosphate rock (PR) ore (sedimentary provenance) in order to obtain heavy-metal free advance phosphorus (P) based products, so that manufactured products and by-products are useful to industries engaged in phosphorus fertilizers and other phosphorus containing products, and products derived from raw materials like gypsum, dolomite, feldspars, apatites, and sepiolites or use them as such. The novel process is more than one sense superior to conventional beneficiation process. It consists of physical breakdown of large rock materials into smaller (sand size) parts accompanied by screening, followed by sink-or- float separation of heavy-metal free phosphorus-minerals from the sand size ore using desired specific gravity liquid that do not dissolve ore-materials. This is based on a set of physical non-destructive process that separate phosphorus- rich materials from Phosphate Rock ore. The phosphorus-rich materials segregated by this process contain 6.6-19.5 percent of elemental phosphorus (P) equivalent to 15.12-44.68 percent of phosphorus pentoxide (also referred as phosphorus (V) oxide with molecular formula as P ₂ 0 ₅ ). Therefore, these materials can be used as raw materials by industries manufacturing phosphorus containing products, including phosphorus-fertilizers. Phosphorus is not-solubilised in this process so that high P-yield is ensured.

[0002] Scientifically, the process is based on the crystal properties observed under Scanning Electron Microscopes (SEM). The SE micrographs showed compactness, clear cut edges, plane crystal faces and shapes, and sharp morpho-structural boundary of P-rich materials, while SE micrographs showed flaky, weathered or, poorly formed and undifferentiating crystal faces of non-P containing (including some P-poor) materials (gangue). The Energy Dispersive Spectroscopy showed that the phosphorus-rich materials are free from toxic heavy metals and radionuclides. The benefit of the novel process is that: (i) it is simple, (ii) eliminates high energy consumption involved at the beneficiation process, and due to use of chemicals that do not dissolve P, the process would be economic, especially for low-grade PRs, and (iii) since, the phosphorus-rich raw materials are free from, toxic heavy metals and radionuclides, the products would be free from such contaminants.

BACKGROUND AND PRIOR ARTS OF THE INVENTION

[0003] The Phosphate Rock scenario: More than 97 percent of the world's phosphate fertilizers are produced from phosphate rock resources, provenance of which is 90 percent from sedimentary deposits, and 10 percent from igneous deposits. About 90 percent of phosphate rock is utilized to manufacture phosphorus fertilizers and remainder is used to produce animal feeds, detergents, chemicals, and other products. Article FAO 2004 (Use of phosphate rocks for sustainable agriculture) discloses use of phosphate rocks for sustainable agriculture.

[0004] Phosphate rock is a non-renewable resource and current global reserves might be depleted by 2035 (Fertilizer and Plant Nutrition Bulletin # 13, Food and Agriculture Organization of the United Nations, Rome, 2004). Globally, prices of PR are rising at a very fast rate, especially since 2002. With the impending shortage of phosphorus fertilizers, and with only one country i.e., Morocco having 85 percent of global high-grade phosphate reserve, the future is bleak for countries like India, until and unless they explore the use of their low-grade PRs, and simultaneously, plan to drastically reduce the consumptions in the next 20-40 years (according to Grantham, J. (2012) Nature. 491 :303).

[0005] Phosphate Rock as such may be used as P-fertilizer in acid soils, and sometimes preferred by marginal or resource poor farmers in alkaline soils for economic reason. Ironically, phosphorus content in Phosphate Rock ores varies from <2 to 17 percent (<5 to 41% P ₂ 0 ₅ ; <1 1 to 89 BPL). Current commercial P- fertilizer manufacturing processes of beneficiation have limitations like they dissolve good amount of phosphorus, which when thrown in river cause eutrophication, consume high level of energy, and they fail to remove heavy metals and radio nuclides fully and therefore, environmentally non-prudent. [0006] Phosphate Rock (PR) contains gangues, impurities along with several non- P minerals. In P-fertilizer manufacturing factories, mined produces are broken in smaller rocks, and then gangues and other impurities are removed to concentrate P. It is followed by reacting P-rich RP with sulfuric acid (H ₂ S0 ₄ ) in the reaction vessels that produces phosphoric acid (¾Ρ0 ₄ ), followed by re-reacting with reaction-products with H3PO ₄ to obtain P-fertilizers. However, at all these stages, heavy metals that are present in the ore are not eliminated completely, and thereby they remain present in the final products.

[0007] Reference may be made to an article He et al. 2005 (He ZL, Yang XE and Stoffella; Trace elements in agroecosystems and impacts on the environment, Journal of Trace Elements in Medicine and Biology, 19: 125-140) wherein phosphate Rocks and their derivatives contained high concentrations of heavy metals (e.g., Cd, Cr, Pb, Sb, V, Zn, and Cu), and radioactive elements (e.g., U, and Th), and the presence of heavy metals and radioactive elements in RP was prevalent in all mines spread all over the world. These heavy metals are non- degradabre, persistent and get accumulated in the soil, plants and animals.

[0008] Pan et al. 2010 (Pan J, Plant JA, Voulvoulis N, Oates CJ and Ihlenfeld), Cadmium levels in Europe: implications for human health Environmental Geochemistry and Health. 32: 1 -12 observed that 54-58 percent of the cadmium found in the environment, and almost all arable surface soils of Europe are contaminated with cadmium, the source of which was due to application of mineral phosphate fertilizers to agricultural land.

OBJECT OF THE INVENTION

[0009] The principal object of this invention is to develop a process for segregation of Phosphorus (P) containing minerals free from heavy metal(s) and toxic element(s).

[0010] Another object of this invention is to design a purely physical, cost- effective, and easier for larger scale production and eco-friendly process at normal room temperature for the beneficiation of P-rich minerals without involving any chemical reactions whatsoever. [0011] Yet another object of this invention is to device a process for beneficiation of phosphate rock with minimal wastage by employing reusable components at prescribed set of conditions.

[0012] Further object of the invention is to present a choice of either labour intensive or purely mechanical process, depending on the need of the hour, for manufacturing phosphorus fertilizer(s) and the like(s) from low or extremely low grade phosphate rock (PR), thereby helping in cutting short the import of PR and benefitting the agriculture and strengthening the food security as a whole.

SUMMARY OF THE INVENTION

[0013] The invention discloses a novel method of beneficiation of phosphate rock. It is based on separation of phosphorus-rich (6.6-19.5% phosphorus) materials from phosphate rock (PR) ore by combination of a set of physical non-destructive methods that do not cause dissolution of phosphorus (P). For experimentations, PR ore was collected from the Jhamarkotra mine (Udaipur District) of the Rajasthan State Mines and Minerals Limited, Rajasthan, India. The ore consisted of grey and brown coloured rocks. The P content was 6:375 mg kg ^" (equivalent to 0.1461x10 ^" % of phosphorus pentoxide) in the grey fraction of the ore, and 5.600 mg kg ^" ' (equivalent to 0.1283x10 ^" % of phosphorus pentoxide) in the brown fraction of the ore. The ore consisted of 63 mineral species including micas, feldspars, gypsum, dolomite, apatites, sepiolites and other crystalline and non-crystalline minerals. Some of the minerals (e.g., micas, feldspars) had wide compositional variations implying their occurrence in solid solution phases. Energy Dispersive Spectroscopy data of a phosphorus dominated specimen showed P/O as 0.1340, P/Ca 0.1704, and P/ Mg as 1.2380 by weight ratio, and P/O as 0.0690, P/Ca 0.0221 1 , and P/Mg as 0.9756 by atomic ratio.

[0014] Solid substances were examined under Scanning Electron Microscope (aided with Energy Dispersion Spectroscopy). Materials showed two groups - phosphorus-rich materials were well crystalline, while non-P substances were noncrystalline to quasi-crystalline. This property was used to separate them using a specific gravity solution, where solids were either sank or float. The P-rich fractions separated in the novel process contained 6.6-19.5 percent of elemental phosphorus (P) (equivalent to 15.12-44.68% of phosphorus pentoxide; also referred as phosphorus (V) oxide with molecular formula as P ₂ Os), and were free from toxic heavy metals and radionuclides. The scientific principle of the beneficiation process may remain same, but stages of separations are likely to be different from mines to mines. The Jhamarkotra mine ore was ground to appropriate size at two stages by physical means. First, larger rocks were broken to pebble size with relatively large force, and then pebbles were brought to sand size by relatively small force, but for both steps caution was taken to apply force along the planes of weakness, and finally sieved through 150-250 mesh.

[0015] The benefit of the novel process is that: (i) it is simple, (ii) eliminates high energy consumption involved at the beneficiation process, and due to use of chemicals that do not dissolve P, the process would be economic to use, especially for low-grade PRs, and (iii) since, the phosphorus-rich raw materials are free from toxic heavy metals and radionuclides, the products would be free from contamination.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Fig. 1 (a) Scanning Electron Micrographs (SEM) of Jhamarkotra mine phosphate rock (PR) ore with different magnification.

[0017] Fig. 1 (b) SEM of grey fraction of PR (with different magnification).

[0018] Fig. 1 (c) SEM of brown fraction of PR (with different magnification).

[0019] Fig. 2. X-ray diffraction of the Jhamarkotra mine phosphate rock (PR) ore.

[0020] Fig. 3. Some broken fractions of the ore.

[0021] Fig. 4. SE micrographs of P-rich minerals of PR showing compactness, clear cut edges planner crystal faces and sharp, morpho-structural boundary (on the left). Energy Dispersive Spectroscopy data showing elemental composition (on the right).

[0022] Fig. 5. SE micrographs of non-P containing minerals of PR showing lack of structural Characteristics.

[0023] Fig. 6. IR spectrum of P-rich mineral fraction. Absorption peaks identified hydroxyapatite. Strong peaks at 1091 -93, 1044-47, 601 , 575 cm ^"1 , small shoulder peaks at 1150, 965 and 471 cm ^" in some species, and presence of carbonate along with some bicarbonate groups were reflected at 1455 and 1377 cm ^"1 peaks.

[0024] Fig. 7. Additional evidences from SEM-EDS and FT-IR data of some of the high P species from both RPB and RPG showed that species rich in phosphorus show compact arrangement and clean edges. Energy Diffractive Spectroscopy coupled with Scanning Electron Microscopy showed that species of URP-Gray (RPG) contain 1.72% to 13.52 % P, and species of URP-Brown contain 5.36% to 13.52 % P. They further confirmed that high P-containing fractions are free from heavy metals. FT-IR spectra and EDS analysis showed that they are often associated with carbonates.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Phosphate Rock beneficiation; Current beneficiation practices involve various processes, depending upon the liberation size of phosphate and gangue minerals and other ore specifications. Good, 1976Beneficiation of un- weathered Indian calcareous phosphate rock by calcination and hydration, US Bureau of Mines; Report No. 8154, Washington DC, and Ray and Robert, 1969, Fluidized bed processing of phosphate rock, Mineral Processing 10: 13-17) discloses different processes like screening, scrubbing, heavy media separation, washing, roasting, calcinations, leaching and flotation may be used. Beneficiation process has disadvantage that it does not effectively remove of heavy metals and some amount of soluble P is lost at this stage.

[0026] Our approach to beneficiation of Phosphate Rock (PR): We used Phosphate Rock ore from the Jhamarkotra mine (Udaipur District) of the Rajasthan State Mines and Minerals Limited, Rajasthan, India. The ore is of sedimentary origin, and consists of grey and brown coloured rock fragments. The very nature of sedimentation causes planes of weakness along 001 planes. We harnessed this property at grinding stage to obtain sand size crystalline materials. We ground URP ore at two stages; first broke them along their planes of weakness with large physical force to pebble size, and then pebbles were reduced to sand size with milder force. Subsequently, we developed beneficiation process on the basis of crystal nature of P-containing minerals and non-P-containing minerals. [0027] The present invention discloses a beneficiation of phosphate rock for the segregation of phosphorus containing heavy metal free minerals comprises the steps of two (2) stage-grinding, screening or sieving, specific gravity separation, and isolation of P-containing minerals from the ore based on crystallinity of the constituent.

[0028] In an embodiment of the present invention the step of 2-stage grinding comprising the usage of rigorous force to break large stones to size of pebbles at the first step.

[0029] In another embodiment of the present invention the step of 2-stage grinding comprising the application of mild force along cleavage planes to break pebbles to sand size crystal in the size range of 0.5-1.0 mm at the second step, followed by screening.

[0030] In yet another embodiment of the present invention the step of screening or sieving involved the collection of the appropriate substrate.

[0031] In still another embodiment of the present invention the step of specific gravity separation" involved the 'Sink' or 'Float'- technique.

[0032] In another embodiment of the present invention the step of isolation of P- containing materials involved transfer of heavier materials to isolation chamber, and drying.

[0033] In an embodiment of the present invention the heavier materials included all the materials having a specific gravity more than 2.82.

[0034] The current industrial methods being used for beneficiation and fractionation of P-rich minerals from PR are costly, environment degrading, energy and labour intensive. The technology discussed in the present patent is a non complicated, cost-effective, three steps physical method for enrichment of the rock-P which can further be used for preparation of phosphatic fertilizers, thereby reducing import load of rock-P and/or costly enrichment procedure carried out in industry.

Examples [0035] The present invention is described herein-below with references to the following examples, which are illustrative and should not be constructed as limiting the scope of invention in anyway.

Example 1

Crushing/Grinding and sieving the rock sample:

[0036] The Phosphate Rock was collected from the Jhamarkotra mine (Udaipur District) of the Rajasthan State Mines and Minerals Limited, Rajasthan, India was crushed in stainless steel pestel mortar applying minimal force and keeping it wet with acetone to avoid abrasion. First, large rocks were broken to pebble size, and then pebbles were crushed to 0.5-1.0 mm size particles using suitable sieves. Dusts generated in the process were discarded.

Example 2

Enrichment/ Beneficiation Process

[0037] Particles of 0.5-1.0 mm size were poured into a separating funnel containing bromoform (specific gravity of 2.82). Any liquid that do not dissolved P, but having- specific gravity of 2.82 would serve the purpose of separation (floatation) of P-rich mineral species from PR. Phosphorus-rich mineral species float, while non-P mineral species sank.

Example 3

Characterisation of Phosphorus-rich mineral species

[0038] All P-rich mineral species obtained by the above method were separately viewed under Scanning Electron Microscope (SEM) with various magnifications, elemental analysis was done using Energy Dispersion Spectroscopy (EDS), and absorption spectra were analysed through the Fourier Transformed infra-Red Spectroscopy (FT-IR) techniques. The phosphorus-rich materials segregated by this process contain 6.6-19.5 percent (by atom; EDS data) of elemental phosphorus (P) equivalent to 15.12-44.68 percent of phosphorus pentoxide (also referred as phosphorus (V) oxide with molecular formula as P ₂ 0 ). For FT-IR analysis the particles were ground to a fine powder in agate pestle mortar and diluted using spectroscopic grade potassium bromide (KBr) in the ratio 1 : 100. The mixture was compressed to a clear pellet using a dye-set in hydraulic press. All measurements were carried out in the range of 100-4000 cm ^"1 at a resolution of 4 cm ^"1 . FTIR spectrum of samples showed an intense broad band in the vicinity of 1 100-1000 cm ^"1 and 630-510 cm ^"1 which could be attributed to P0 ₄ ^3" vibrations.

Example 4

Further Beneficiation

[0039] There is opportunity to further concentrate the P-rich minerals. This could be done by removal of carbonates by weak acetic acid (0.01M). The resulting particles, when viewed under SEM showed an improvement in structural features, while EDS data showed increased content of P, and FT-IR spectra enumerated reduced level or no peaks of C0 ₃ ^2" and sharp (most often single) peak pertaining to P0 ₄ ^3" .

[0040] Advantages/ Industrial application of the invention:

Advantages of the process claimed in the present invention are:

(i) This is a purely physical, single-stage two-step (grinding and floatation), method for fractionation and beneficiation of P-rich minerals, especially applicable to Jhamarkotra mine (Udaipur District) Phosphate Rock ore.

(ii) It does not involve any chemical reactions, and P is not flotation chemical does not dissolve phosphorus or heavy metals.

(iii) All processes occur at environmental temperature, eco-friendly and cost- effective.

(iv) This process of beneficiation of PR ore is easy for large scale industrial manufacturing.

(v) The process yields segregation of P-rich PR mineral species that are free from heavy metals and toxic elements.

(vi) The process segregates gangue materials (residual, and lighter than 2.82 specific gravity), which could be dumped easily at safe places eliminating cost of environmental clean-up. Gangue materials may be used as raw material for manufacturing of quartz, gypsum and some rare earth elements. (vii) The flotation liquid being volatile leaves no trace on the surface of particles. Moreover, if the process is carried out in dark, flotation liquid could be reused many times (economic advantage).

(viii) Current methods practiced in industry have many drawbacks like high consumption of energy at beneficiation process, dissolution of P and heavy metals and subsequent disposal of waste flotation liquid.

(ix) Our process could be followed entirely mechanically or, by engaging labour. Thereby, it would be convenient for industrial applications.

(x) The technology discussed herein can be effective for manufacturing phosphorus fertilizers from low or, extremely low grade Phosphate Rock.

This is futuristic and provides great advantage to countries like India who do not have good PR resource, but burdened with sustaining high agricultural productivity. This may eventually reduce import of PR.