Claims:WE CLAIM:
1. A method for preparing hematite-based calcium rich hydroxyapatite (FeCRHA) and Calcium Nitrate from LD slag fines (02), the method comprising:
reacting LD Slag fines (02), with a nitric acid (03) solution to achieve a filtrate (06) and a silica rich residue (05);
neutralizing the filtrate (06) with a lime slurry (07) solution to achieve the hematite-based calcium rich hydroxyapatite (FeCRHA) and a calcium nitrate filtrate (11);
filtering, washing, and drying the hematite-based calcium rich hydroxyapatite (FeCRHA) to achieve final FeCRHA (10); and
evaporating the calcium nitrate filtrate (11) to achieve Calcium Nitrate (CN).
2. The method as claimed in claim 1, wherein composition of the LD slag fines is 35 – 59% CaO, 10 – 20% SiO2, 10 – 20% Fe, 3 – 10% MgO, 1 – 5% Al2O3, 1 – 5% P2O5, 1% TiO2, 0.5 - 1.5% MnO and unavoidable impurities.
3. The method as claimed in claim 1, wherein the filtrate (06) is a mixture of iron nitrate, aluminum nitrate and calcium nitrate and unavoidable impurities.
4. The method of claim 1, wherein the nitric acid (01) is of 60%, SpGr 1.42, 30%(v/v).
5. The method of claim 1, wherein the LD slag fines (02) are of -2mm and is mixed with water prior to addition of nitric acid (01) solution.
6. The method of claim 1, wherein reaction between LD Slag fines (02) and the nitric acid (03) solution is for about 1 hour and at a temperature 100 – 110oC.
7. The method of claim 1, wherein the LD Slag fines (02), is mixed with water, and the nitric acid (03) in a ratio 1 : 1 : 2 respectively.
8. The method of claim 1, wherein pH of a solution between the filtrate (06) and the lime slurry (07) during neutralization is maintained > 7.5 to precipitate the hematite-based calcium rich hydroxyapatite (FeCRHA).
9. The method of claim 8, wherein temperature of the solution is at 80 – 90oC.
10. The method of claim 1, wherein evaporating the filtrate (11) produces the calcium nitrate of specific gravity more than 1.45.
11. The method of claim 1, wherein the hematite-based calcium rich hydroxyapatite (10) is further calcined at 1000oC and powdered to produce the calcined nano sized material.
, Description:A METHOD FOR PREPARING HEMATITE BASED CALCIUM RICH HYDROXYAPATITE FROM LD SLAG
FIELD OF INVENTION
[001] The present invention relates generally to economic utilization of LD Slag fines produced in steel industry processes. More specifically, it relates to series of hydrometallurgical processes of recovering silica rich residue and nano-sized hematite-based calcium rich hydroxyapatite (FeCRHA) from LD Slag waste produced during the recovery of metallic Iron from LD Slag.

BACKGROUND OF THE INVENTION

[002] With the increased costs for dumping the wastes to valuable products is gradually becoming more important. Each non-hazardous waste as well as hazardous wastes has its own set of problems. Issues such as toxicity, pollutant to the environment, and the sizable amount of waste generated cause problems for those with these types of wastes that need to be addressed. For example, nitric acid waste is toxic and is regulated as a hazardous waste. The primary way to dispose of nitric acid of less than 300ml is to dilute with water and the larger quantity of nitric acid needs to be neutralized by using a suitable acid neutralizing agent. Other ways of disposal of, or spent, nitric acid is expensive and there are many regulatory requirements associated with the disposal of it.

[003] Various methods have been used to produce or recover reusable compounds from waste materials, which in turn reduces the amount of waste that needs to be disposed-off and decreases raw material costs for the reusable compound. Slag generated from basic oxygen furnace (BOF) or Linz-Donawitz (LD) converter is one of the recyclable wastes in integrated steel plants. LD slag fines is one such type of waste that is produced during the recovery of metallic Iron from LD Slag produced during steel manufacturing process from LD Converters. Attempts have also been made to recover valuable and rare metal compounds like Vanadium oxide, chromium oxide from the LD Slag fines, in land filling and for acidic soil conditioning which decrease the amount of LD Slag fines that has to be discarded.

[004] With the rapid industrialization, the available land for dispose of large quantities LD slag at a landfill site is reducing the disposal cost becomes increasingly higher in all over the world respectively. The global warming effect and natural resource saving are the general environmental topics nowadays. Besides, the land filled with the waste materials has become a significant source of pollution of air, water and soil, and further adversely affects the human health, and the growth of plant and vegetation etc.

[005] An example of preparing the nano-hydroxyapatite from LD Slag was reported by BAO Steel with Chinese patent publication CN106044734 which discloses a method for preparing nano-hydroxyapatite. The method comprises the following steps of dissolving calcium-containing slag into acid, removing impurities which are not dissolved in the acid by means of filtering, adjusting a pH value to an alkaline level, removing impurities which are not dissolved in alkali by means of filtering again, and obtaining a calcium salt solution; mixing the calcium salt solution with a phosphate solution, adjusting the pH value of the mixed solution to the alkaline level, and reacting to obtain the nano-hydroxyapatite. Compared with the prior art, the nano-hydroxyapatite prepared according to the method provided by the invention has the advantages that factory slag is taken as a raw material, the factory slag is cheap and is easily and widely obtained, the effect of turning waste into treasure is achieved, the nano-hydroxyapatite is friendly and harmless to the environment, and the technology is simple; the dispersity is excellent, the particle diameters are uniform, and the adsorption of heavy metal ions in wastewater is beneficially performed; the prepared nano-hydroxyapatite has a proper mechanical property and an excellent processing property, and the environment can be prevented from secondary pollution during the process of treating heavy metal in the wastewater, therefore the nano-hydroxyapatite is widely used in the field of water treatment.

OBJECTIVE

[006] The prime objective of the present invention is recovering silica rich residue and producing nano-sized hematite-based calcium rich hydroxyapatite from nonmetallic portion of LD Slag fines.

[007] Another object of the invention is to provide alternative methods for utilization of nitric acid and lime fines produced during the production of lime from limestone in an integrated steel plant.

[008] Another object of the invention is to use of the phosphorus content present in LD Slag for synthesizing the novel material. The method also uses the lime fines for adjusting the pH of the solution instead of alkali / ammonia.

PRIOR ART

[009] Chinese patent application CN102502556 from JIANGNAN UNIVERSITY has a method of preparing the nano hydroxyapatite. The method comprises the following steps of: dissolving soluble calcium salt in deionized water to obtain a calcium ion solution; dissolving 0.5 to 7mmol of lauryl sodium sulfate and 1 to 5g of polyvinyl pyrrolidone in each liter of deionized water to obtain a mixed solution; dissolving soluble phosphate in the mixed solution, adjusting the acidity of a system by using hydrochloric acid and ammonia water to ensure that the pH value of the solution is 8.0 to 11.0, and slowly dripping the calcium ion solution into the mixed solution of the lauryl sodium sulfate, the polyvinyl pyrrolidone and phosphate radical ions at a constant temperature to ensure that the molar ratio of Ca to P is 10:6 in a reaction system after the dripping step is finished; and reacting for more than 24 hours, cooling, filtering, washing, drying under vacuum, and thus obtaining a nano hydroxyapatite material.

[0010] BEIJING UNIVERSITY Chinese patent application CN102849700 is related to a hydroxyapatite and a preparation method thereof. According to the invention, hydrolyzed collagen is introduced into a reaction system to realize biomimetic mineralization, and then nanometer hydroxyapatite powder is prepared under a low temperature condition; specifically, the hydroxyapatite is obtained through a chemical precipitation process in the presence of the hydrolyzed collagen, and the weight-average molecular weight of the hydrolyzed collagen is 500 to 20000 Da.

[0011] JAPAN STEEL WORKS patent no JP07002505 provides - to efficiently produce hydroxyapatite excellent in homogeneity and crystallinity by gradually adding an aqueous solution of a calcium salt and an aqueous solution of a phosphoric acid salt to an alkaline aqueous solution adjusted at temperature and pH in specific ratio. An aqueous solution of a calcium salt and an aqueous solution of phosphoric acid salt which are reactional solutions are gradually added to an alkaline aqueous solution adjusted at temperature and pH in a ratio of Ca/P of 1.65 to 1.70 to crystallize hydroxyapatite. The reactional solutions which do not advance the reaction of calcium salt with phosphoric acid salt before adding to the alkaline solution and slowly reacts in the alkali solution are preferably used as these reactional solutions. Furthermore, the rate for adding both reactional solutions are preferably constant. The alkaline aqueous solution is preferably a water-soluble substance obtained by reaction of same kinds of calcium salt and phosphoric acid salt as these reactional solutions. Further, the temperature and the pH are preferably controlled to be constant and the ion concentration is preferably controlled to be constant during reactional period.

[0012] MITSUI TOATSU CHEMICALS patent no JP3247896 explains the method of obtaining a hydroxyapatite having a desired atomic Ca/P ratio and a desired secondary particle diameter in good reproducibility. Aqueous solution of phosphoric acid is added drop wise to aqueous slurry of CaO and/or Ca(OH)2 to produce a seed crystal slurry which is a fine particulate hydroxyapatite slurry. While the pH of the slurry is kept constant, the aqueous slurry of CaO and/or Ca(OH)2 and aqueous solution of phosphoric acid are simultaneously added drop wise to the seed crystal slurry to produce the hydroxyapatite.

SUMMARY OF THE INVENTION

[0013] The present disclosure relates to a method for preparing hematite-based calcium rich hydroxyapatite (FeCRHA) and Calcium Nitrate from LD slag fines (02). The method includes reacting LD Slag fines (02), with a nitric acid (03) solution to achieve a filtrate (06) and a silica rich residue (05); neutralizing the filtrate (06) with a lime slurry (07) solution to achieve the hematite-based calcium rich hydroxyapatite (FeCRHA) and a calcium nitrate filtrate (11); filtering, washing, and drying the hematite-based calcium rich hydroxyapatite (FeCRHA) to achieve final FeCRHA (10); and evaporating the calcium nitrate filtrate (11) to achieve Calcium Nitrate (CN).

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0014] Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings of the exemplary embodiments and wherein:
Fig 1: Shows a flow diagram of a process of producing hematite-based calcium rich hydroxyapatite product from LD Slag Waste fines generated by steel plant according to the present invention.

[0015] The figure(s) depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

[0016] The present invention, now be described more specifically with reference to the following specification.

[0017] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.

[0018] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.

[0019] The present disclosure provides a method for recovering silica rich residue and producing nano sized hematite-based calcium rich hydroxyapatite from nonmetallic portion of LD Slag fines whose tentative composition is 35 – 59% CaO, 10 – 20% SiO2, 10 – 20% Fe, 3 – 10% MgO, 1 – 5% Al2O3, 1 – 5% P2O5, 1% TiO2, 0.5 - 1.5% MnO etc., after the recovery of metallic Iron from LD Slag. The invention advantageously provides a method for recovering silica rich residue which can be reused in the iron making process of sinter making. Nanosized hematite-based calcium rich hydroxyapatite used in mainly in nano technology and bio sensors and also in other applications also needs to be explored. The preparation method provided by the invention is environment-friendly, safe and uses low cost material and has a simple process; and the obtained hematite-based calcium rich hydroxyapatite has regular appearance and has important application value in the field of biomedical engineering which needs to be further explored.

[0020] The present invention advantageously provides a method for producing hematite-based calcium rich hydroxyapatite product from LD Slag waste. This invention includes a process of treating LD Slag waste through a digesting process with nitric acid solution, followed by filtration and again treating filtrate with 20% lime slurry solution to get hematite-based calcium rich hydroxyapatite and then concentrating filtrate by evaporation to the desired density and pH resulting in the production of calcium nitrate product, for the subsequent application in bioceramic industries, agriculture, cement setting, water treatment etc.

[0021] As known, LD Slag fine is a mixture of compounds comprised of some or all of the following chemical groupings: carbonates, Silicates of calcium, Magnesium, Oxides of Iron, Aluminium, Phosphorus, hydroxides of calcium and some amount of free lime. LD Slag fine can contain very low concentrations of heavy metals including, cadmium, chromium, lead, mercury, nickel, platinum and palladium. LD Slag fine produces a highly alkaline solution (pH 11-13.5) when mixed with water. This alkalinity is primarily due to the presence of calcium hydroxide in the LD Slag fine or as the slacking of calcium oxide occurs in the solution. LD Slag fine are being generated during the recovery of metallic Iron from LD Slag at Waste recycling plant.

[0022] The LD Slag fine in the size of (-6mm) contains the highest concentration of calcium majorly as Calcium Silicate, Calcium carbonate and Calcium hydroxide. The principal components of LD Slag fine are calcium silicate, calcium carbonate, calcium hydroxide and free lime put together which accounts for between 45% and 55% by weight of LD Slag fine. Other compounds can proportionately vary due to the composition of feed materials to the LD converter, operating temperatures the time of Slag generation during the steel making process. An averaged X-ray fluorescence (XRF) analysis of LD Slag fine taken randomly is provided in Table – 1.

Table – 1

LD Slag fines

Components
Weight %
Average Min Max Variance
CaO 51.36 37.35 60.06 7.79
SiO2 15.71 10.97 26.51 2.10
MgO 2.09 0.120 6.16 0.58
Al2O3 0.931 0.520 3.76 0.05
TiO2 1.14 0.600 2.43 0.03
Fe 18.20 10.10 28.67 7.64
S 0.016 0.005 0.177 0.01
MnO 0.446 0.180 4.41 0.03
Cr2O3 0.156 0.040 0.220 0.00
P2O5 3.24 2.06 5.65 0.16

[0023] FIG. 1 provides a simplified flow diagram of a method / process of producing hematite-based calcium rich hydroxyapatite product from LD Slag Waste fines generated by steel plant in accordance with an embodiment of the present disclosure.

[0024] In an embodiment, a chemical composition associated with the LD slag employed in the present invention is provided in Table-2.

Table – 2: Chemical composition of LD Slag fines taken for invention
Parameters Fe(T) CaO SiO2 P2O5 MgO S MnO Al2O3 TiO2 Cr2O3 LoI S Freelime
Values, % 14.70 44.14 13.91 2.70 10.02 0.12 0.60 2.30 0.87 0.16 4.73 0.12 6.80

[0025] Referring to Fig. 1, LD Slag fine of -2mm (02) is mixed with nitric acid (01) of SpGr 1.42, 30%(v/v), conc.60% and above in a reactor (03). In an example, the LD Slag fines (02), water, and the nitric acid (03) are mixed in a ratio 1 : 1 : 2 (ml) respectively. The reaction is exothermic and hence no heating and stirring is required until all the nitrogen dioxide fumes ceases, which takes about maximum one hour. The insoluble portion containing silica is filtered and washed with hot water (04). The silica rich residue (05) obtained is dried in a dryer to produce the silica rich product, whose chemical composition is provided in the Table - 3.
Table – 3: Chemical composition range of silica rich residue
Parameters Fe(T) CaO SiO2 P2O5 MgO MnO Al2O3 TiO2 Cr2O3 LoI
Values,% 20 -28 0.5 – 6.0 40 – 60 0.5 – 2.0 3 – 7 0.5 – 2.0 1 – 3 0.5 – 1.5 0.10 – 0.25 2 – 10

[0026] The filtrate (06) which is a mixture of mainly iron nitrate and calcium nitrate is taken into another reactor (08), where the pH of the solution is raised by using 20% Lime slurry solution (07) to more than 7.5 to precipitate the product called hematite-based calcium rich hydroxyapatite. This is filtered, washed with hot water and dried (09), the resulting residue containing mainly hematite-based calcium rich hydroxyapatite is dried and powdered to produce the final product FeCRHA (10) whose composition is given in the Table - 4.

Table – 4: Chemical composition range of hematite-based calcium rich hydroxyapatite
Parameters Fe(T) CaO SiO2 P2O5 MgO MnO Al2O3 TiO2 Cr2O3 LoI
Values,% 13 – 25 10 – 23 1 – 2 2 – 8 5 – 12 0.5 – 1.5 2 – 8 0.5 – 1.5 0.10 – 0.25 30 – 40

[0027] Another filtrate (11) is taken into CN liquid collector tank (12). This will be then taken to an evaporator and after that to a CN product tank, where the pH of the CN product will be adjusted to 6.5 by using lime slurry solution if required.

[0028] Various steps and chemical reactions associated with the process of producing hematite-based calcium rich hydroxyapatite product from LD Slag Waste fines depicted in Fig. 1 will now be explained in the foregoing description in greater details.

[0029] Once the LD Slag fines (02) is in the reactor (03), reacts with the nitric acid solution (01). The reactor (03) is preferably agitated and maintained at a temperature between 100 – 110-degree C to allow for optimum reaction conditions for a particular time preferably 1 hour till the Calcium silicate breaks in to soluble Calcium nitrate and Silica by the reaction with nitric acid and other impurities partially forms the soluble nitrates. Given the range of calcium oxide and its associated oxide, silicate and hydroxide concentrations in the LD Slag fine (02), the amount of dry weight nitric acid (01) required to achieve the conversion to FeCRHA and other products varies according to stoichiometry. In an embodiment, the reactions of nitric acid (01) with the calcium compounds present in LD Slag fine (02) yield the following:

Ca2SiO4 + 4HNO3 = 2Ca(NO3)2 + 2H2O + SiO2

4FeO + 12HNO3 + O2 = 4Fe(NO3)3 + 6H2O

2Fe(NO3)3 + 3Ca(OH)2 = 2Fe(OH)3 + 3Ca(NO3)2

[0030] The reaction is complete once the effervescence of the product slurry (04) stops, which is preferably happens after 45 mins. Once the reaction halts, the product slurry (04) is allowed sufficient residence time within the reactor (03) to cool. The initial slurry (04) is then conveyed, preferably by pumping, to filtration and water washing step (04). The LD Slag fines derived mixed slurry is filtered and washed with hot water and silica rich residue is dried between 100 – 110-degree C.

[0031] The product slurry (04) is discharged from the reactor (03) once it is cooled and taken to filtrate tank (08) after passing through suitable filtration media to produce the silica rich residue (05) which is washed with hot water and later dried in a dryer to produce the dried silica rich residue (05). Thus, the process has three products namely silica rich residue (05) which can be reused in the iron making process to be precisely in sinter making process and hematite-based calcium rich hydroxyapatite (010) for possible applications in pigment or HPPI (High phosphorus pig iron production.

[0032] When the metal oxide is calcium, the result is Calcium nitrate. Other metal oxides, hydroxides and carbonates react with the nitric acid solution but are considered side reactions for the purpose of this invention and forms soluble nitrates with the exception of silica and other sparingly soluble metal ions like Titanium, chromium etc. These soluble nitrates along with excess nitric acid are neutralized with lime slurry solution, filtered and washed (09), residue (010) is dried (09) and hematite-based calcium rich hydroxyapatite is (010) formed. The filtrate (011) is taken to CN liquid storage tank and feed to evaporator (012) after which it is collect ed in CN product tank, where the pH is finally adjusted to desired level. Finally, the (CN) calcium nitrate (012) which is used in the agriculture as liquid fertilizer.

[0033] While the present invention is described as a batch process, process modifications can be made to perform the present invention as a continuous operation without departing from the scope of the present invention. The process modifications required for continuous operation will be known to those skilled in the art. The liberation of various vapors occurs as a result of the reaction between the hydrogen ion and calcium oxide molecule. This primary reaction between the hydrogen ion from the nitric acid and the metal oxides in an aqueous environment produces nitrogen dioxide, carbon dioxide gas and the associated metal ion complex. The metal ion complex then forms an ionic bond with the resulting nitrate ion from the dissociation of the nitric acid in solution. The result is an often hydrated metal ion nitrate.

[0034] Besides carbon dioxide, the various vapors that are emitted during the reaction can also include water vapor, nitric acid mist, and inherent volatile organic compounds from the slurry (03). The nitric acid mist contained within the vapor stream contains traces of organic vapors, which can be neutralized by sending the vapor stream to a caustic / lime scrubber/mist eliminator system.

[0035] Since the composition and amount of calcium within LD Slag fines varies because of presence of various types of oxide along with calcium, a more accurate manifestation of the reaction, based upon experimentation, is as follows:

Ca2SiO4 + 4 HNO3 = Ca(NO3)2 +SiO2 + 2H2O
172.2391 + 53.012 = 164.08 + 60.084 + 18.015

Ca(OH)2 + 2 HNO3 = Ca(NO3)2 + 2 H2O
74.092 + 63.012 = 164.08 + 18.015
CaCO3 + 2 HNO3 = Ca(NO3)2 + CO2 + H2O
100.086 + 63.012`` = 164.08 +44.00 + 18.015

Al2O3 + 6 HNO3 = 2 Al(NO3)3 + 3 H2O
101.96 + 63.012 = 212.99 +18.015

Cr2O3 + 6 HNO3 = 2 Cr(NO3)3 + 3 H2O
151.99 + 63.012 = 238.010 + 18.015

MnO + 6 HNO3 = 2 Mn(NO3)2 + 3 H2O
70.937 + 63.012 = 178.94 + 18.015

P2O5 + 2 HNO3 = 2 HPO3 + N2O5
141.944 + 63.012 = 79.97 + 108.015

MgO + 2 HNO3 = Mg(NO3)2 + H2O
40.30 + 63.012 = 148.314 + 18.015

FeO + 2 HNO3 = Fe(NO3)2 + H2O
71.84 + 63.012 = 179.85 + 18.015

Fe2O3 + 6 HNO3 = 2 Fe(NO3)3 + 3 H2O
159.68 + 63.012 = 241.85 +18.015

2 Fe(NO3)3 + 3 Ca(OH)2 = 3 Ca(NO3)2 + 2 Fe(OH)3
241.85 + 74.092 = 164.08 + 106.86

2 HNO3 + Ca(OH)2 = Ca(NO3)2 + 2 H2O
63.012 + 74.092 = 164.08 + 18.015

Fe(NO3)2 + Ca(OH)2 = Ca(NO3)2 + Fe(OH)2
179.85 + 74.092 = 164.08 + 89.85

[0036] The details of the materials used and process parameters associated with the process of Fig. 1 are provided in the Table – 5.

Table – 5
Sr. No Materials Quantity
1 LD Slag fines (-2.0mm) 100gm
2 Nitric acid (1.45 Sp.Gr) 200ml
3 Water 100ml
4 Temperature 100 – 110 o C
5 Duration of digestion 1Hrs
6 Filter paper porosity 2.5µm
7 Vacuum 20 cm Hg
8 Lime slurry solution (20%) 41gm

[0037] The amount of nitric acid required to leach the calcium from LD Slag fines and to reduce the PH on the average 100gms of LD Slag fines solution from 11.0+/-0.5 to 1.0+/-0.5 is 200 ml+/-0.14 along with 100ml of water for one Hr. digestion at 100 – 110-degree C. The sample of LD Slag fines, as shown in above Table 2. The results of Table – 6 (CN) are based upon ten digestions of -2.0mm LD Slag fines (Table – 2) using nitric acid and water at 100 – 1100C and neutralization with lime slurry solution (20% solution.) after removing the silica rich residue (Table – 3) and FeCRHA (Table – 4) to collect the filtrate CN (calcium nitrate) after evaporation. The filtration steps were performed the through a 2.5 µm filter paper using a 150 mm diameter Buchner funnel operating under 28.5 inches Hg vacuum.

Table – 6: Composition of lime fines used for making slurry for neutralization
Parameters Fe(T) CaO SiO2 P2O5 MgO Al2O3
Values,% 0.20 – 0.40 80 – 97 0.2 – 10 0.10 0.3 – 10.0 0.1 – 10.0

[0038] One limitation to the treatment of LD Slag fines with nitric acid to manufacture FeCRHA by process mentioned in Fig.1 is the yield of the FeCRHA produced. Due to the nature of LD Slag fines, the constituents of the LD Slag fines vary both qualitatively and quantitatively and also depends up on the quantity of nitric acid used for treating the LD Slag fines. Increase in the quantity of nitric acid needs more quantity of lime slurry solution for neutralization in the process and thus increasing the ratio of Ca/P. Thus, the limitation can be converted to advantage to obtain the FeCRHA products of different Ca/P ratios. Also, the FeCRHA of lesser Ca/P ratio can be produced by further addition of phosphoric acid to the filtrate of reactor (08) before addition of lime slurry for PH adjustment.

[0039] FeCRHA produced is a unique nano material whose applications in different areas like bio sensors, for production of high phosphorus pig iron(HPPI) to be explored and Calcium nitrate (CN) which is another product obtained in the process is used as a fertilizer has many advantages viz., it is completely water soluble and provides calcium, nitrate nitrogen to the plants. It can be used for all types of crops produced in all seasons. Calcium, the king of elements, supports cellular growth stimulated by nitrogen application, enhance cell wall development of the new tissues/growth to resist fungal infections, and triggers many biochemical reactions leading to better growth and productivity of crops. Calcium also displaces sodium in soils for better penetration and distribution of water. Calcium also improves soil structure.

[0040] The advantages of this invention apply to both the producers of LD Slag fines and the producers of by-product nitric acid solution. To the agriculture industry, the LD Slag fines derived Calcium nitrate (CN) product from process mentioned in Fig – 1 will offset / reduce costs associated with purchasing commercially available fertilizers as it is a very good nitrate fertilizer.

[0041] It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention. For example, it is envisioned that the process can be carried out in batch operations or on a continuous operation basis with only the reactors working in a batch mode. Other variations, such as different types of process equipment, can be utilized and are to be considered within the scope of the present invention. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims.