OA22210A - Production Of Phosphates Using Phosphate Rock. - Google Patents

Abstract

The present disclosure provides a simple process for the production of value-added high purity phosphates from phosphate sources low-grade phosphate sources. Said process comprises treatment of the phosphate source with sulfuric acid in a continuous reactor, filtration of obtained slurry, washing the filtered cake for additional collection of P, Os, followed by treating the obtained solution with a source of calcium oxide so as to precipitate out a calcium phosphate rich in phosphate, and low on impurities. This can be converted to value-add products such as double super phosphate by subjecting it to further downstream processing through acidulation with sulfuric acid, high quality triple super phosphate by treating with merchant grade phosphoric acid, as a feed for the manufacture of merchant grade phosphoric acid. Thus obtained phosphate rich solution has MER less than 8%, and a P20s concentration of upto 24%.

Description

TITLE

PRODUCTION OF PHOSPHATES USING PHOSPHATE ROCK

FIELD OF THE DISCLOSURE

The présent disclosure relates to a process for the production of clean phosphate products.

BACKGROUND OF THE DISCLOSURE

Phosphate is a finite source in the universe and a building block for other compounds. Phosphate products are used to provide phosphorus nutriment to the soit and sustain agricultural yields or for cattle.

It takes hundreds of millions of years for phosphate to form in the earth. The Chemical and physical characteristics of phosphate ore can vary widely depending on the geological history of the ore. Most of the ores of phosphate contain phosphate in the form of apatite, and in a variety of compositions such as fluorapatite, hydroxyapatite, Francolite, etc. where phosphorus is under the form of tricalcium phosphate Ca3(PO4)2 A general formula for apatite can be given as follows: (Ca,Na2,Mg)io(P04)6x(CO3)_xFy(F,OH)2-y, wherein y = 0.33 x to 0. 5 x.

Phosphates are relatively abundant on the earth however the economically available resource tends to décliné overthe last décades with adecrease ofthe P2O5 concentration in the ore and concomitant increase in the level of impurities. Phosphate beneficiation required to increase the P2O5 content in the ore and limit the level of impurities for further processing rejects large amounts of low-grade phosphates which are treated as wastes. No technology exists to process and economically recover useful P2O5 from such resources.

Like in any other ore processing, apatite ore also had to be processed through beneficiation to recover P2O5 in an enriched form and limit the impurities to meet the requirement for downstream processing and products quality. The beneficiated ore is generally referred as concentrate. Phosphate concentrâtes generally contains 28-35%, and plants are generally designed to process a spécifie quality and grade of concentrate. However, as the reserves of high grade ores depleted rapidly, the exports contain concentrâtes with about 30%, and anything less than this, is designated to be of low grade. The continuously depleting reserves, rising costs of mining and beneficiation, and scarce availability of rich ores led the manufacturer to handle or process lower grade materials of 29%, or even less to the extent of 26% and ail such grades are considered low grade phosphates. Attempts are made to work around the processes to extract P2O5 from such resources and the rejects from beneficiation.

However, the problems faced include low grades or sometimes even higher grades containing impurities to such an extent that they are unfit to produce phosphoric acid of adéquate quality for eventually using in the production of fertilizers.

The focus thus far does not seem to be on the impurity of the resources. Phosphate rocks, by their existence, contain large number of impurities such as silica. calcium carbonate in addition to the calcium bound with primary apatite, Fe, Al, F, Mg and a host of other impurities such as Cd, and radioactive éléments.

Silica is a dead load and inert and does not cause process related problems to a large extent but has other implications such as requirement of larger machinery, higher throughputs in ail Systems, wear out etc. Excessive silica causes lower availabiIity of P2O5, causing the grad to be lower, but does not cause problems associated with impurities.

Presence of calcium, generally as a carbonate, results in larger machinery, higher acid consumption, foaming, and other related problems.

Iron is invariably présent in the ores and is removed to some extent during the beneficiation process. The iron présent in the feed concentrate is almost entirely présent in the acid phase during the processing. This impurity affects the quality of the acid being produced.

Aluminum is another impurity that affects the quality of the acid when présent in the phosphate being used, as a substantial quantity of aluminum enters the acid phase.

Fluorine is also present, invariable in almost ail phosphates. However, it is distributed between the acid and gypsum, and is substantially recovered during the concentration of the acid, and also from the émissions.

Magnésium is yet another impurity that must be removed prior to the use of the phosphate in the production of the acid, as it is difificult to remove it subsequently.

The purity of the resource dépends on the presence of the aforementioned éléments, namely, Fe, Al and Mg. These éléments exist in the form of oxides, namely, Fe2O3, AI2O3 which are collectively referred to as R2O3, and hâve a major impact on the purity of the acid. Another ratio called Minor Elément Ratio, (MER) is also used, which is defined as a ratio of (R2O3 + MgO)/P2Os. It is recommended to use phosphate rock with MER<lO-l2% for the production of ammonium phosphate fertilizers, or more precisely, to limit the MER in the acid to 8% for diammonium phosphate (DAP) production, I0% for monoammonium phosphate (MAP) and slightly above for superphosphates. The beneficiation is donc to control the presence of R2O3 in beneficiated ore which is the major reason for rendering a vast P2O5 resource emerging out as mine waste that is unfit for any use due to the presence of MER of even upto 40%.

Life cycle inventory, an account of P2O5 in ore and in beneficiated rock shows that the average loss of phosphorus between mining operations, mechanical préparation, and the wet beneficiation is 0.3kg of P2O5 per Ikg of P2O5 being mined. The losses occur mainly during the flotation and other processes. Annually, about 30 million tons of P2O5 is produced and therefore, the quantitative loss of P2O5 is more than 12 million tons in terrns of P2O5, and is estimated to be on an average of 15% P2O5 in the rejects. 80 million tons is piled up every year with a potential value of USD 8 billion of annual loss at current priées, apart from occupying valuable land and environmental pollution due to pond waters. The problem with these rejects is the low grade or low P2O5 in the ore rejects, as well as the presence of very high levels of impurities. There is a strong need to provide a process for the removal of impurities to the greatest extent possible for the production of high grade phosphate concentrate used for the production of merchant grade acid. The total accumulated piles of such mines could be in several billions of tons occupying thousands of hectares of land. Considérable research is being carried out for use of this material for other applications such as in road construction, ceramics etc. While there are processes in vogue for the recovery of phosphates from low grade ores, there do not seem to be any processes for the successful and economical recovery of phosphate from the “impure” resources.

In addition to the above, there are several deposits of phosphates containing good amount of P2O5, but laden with high levels of impurities as R2O3 or MER, thereby rendering them unfit for the production of useful phosphates. Billions of tons of such resources remain underutilized due to constraints of purity.

It is estimated that 90-94% of phosphates produced go into fertilizer industry and manufacture of phosphoric acid is though using sulfuric acid to free P2O5 from bound calcium as the process is simple as gypsum can be separated from liquid phosphoric acid. Sulfuric acid has been found to produce good results in the case of production of phosphoric acid. Nitric acid is not considered as an extracting acid due to its high cost, process associated difficulties, and nonviability.

Aspects of the disclosure may include an economical process for the recovery of phosphate products, and especially high grade phosphate products from phosphate sources such as reject matériel containing high levels of R2O3 or high MER. and conserve valuable phosphate resources. Non-limiting examples of phosphate products include high grade phosphate (HGP), mono calcium phosphate (MCP), dicalcium phosphate (DCP), mono dicalcium phosphate (MDCP), double superphosphate (DSP), triple superphosphate (TSP), and nitro phosphates.

Another aspect ofthe disclosure is to provide a process for the production of phosphate products either as a solid or as phosphoric acid with MER or R2O3/P2O5 less than 8%.

Yet another aspect of the disclosure is to provide a process for the production of high grade phosphate products wherein a single acid is used in the acidulation process.

Further yet another aspect of the disclosure is to provide a process for the production of high grade phosphate products, that does not involve the use of multiple acids such as hydrochloric acid or nitric acid.

Another aspect of the disclosure is to provide a process for the production of high grade phosphate products, that hâve low fluorine content.

Yet another aspect of the disclosure is to provide an integrated process for the 5 production of high grade phosphate products.

Still yet another aspect of the disclosure is to provide a process for the production of high grade phosphate products, wherein the purity is independent ofthe concentration of the phosphate solution.

A further aspect of the disclosure is to provide a process for the production of high grade phosphate products, that can utilize vast resources of phosphate-containing waste or low-grade phosphate sources.

Yet another aspect of the disclosure is to provide a process for the production of high grade phosphate products that can be utilized for the production of valuable end products such as fertilizers, feed additives, downstream products, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the disclosure described herein, together with advantages thereof, may be understood in accordance with the following description taken in conjunction with the accompanying drawings as follows:

Figure l shows the flow chart of the steps involved in the process of the présent disclosure;

Figure 2 shows the MER values of solutions of the sample prepared ïn Example 5 in accordance with the examples of the présent disclosure;

Figure 3 shows the MER values under different conditions of the sample prepared in Example 6 in accordance with the examples of the présent disclosure; and

Figure 4 shows the percentage of P2O5 losses observed in the sample prepared in Example 7 in accordance with the examples ofthe présent disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Aspects of the présent disclosure may provide, among other things, a process for the production of high grade phosphate products from a phosphate source such as phosphate rock or low grade mine sûmes or rejects. In one or more example examples, said process may comprise treatment of a phosphate source, with dilute sulfuric acid or sulfuric acid along with water or recycled solution in a continuous reactor, wherein the solution comprises calcium ion, so as to restrict unacceptable levels of impurities from entering into the solution, recovering the solution (A) in adéquate strength to directly use as phosphoric acid solution, or recover further by filtration, and treat the solution thus obtained with a source of calcium so as to precipitate out calcium phosphate that is rich in phosphate and low on impurities. This can be converted to value-add products such as double super phosphate (DSP) by subjecting it to further downstream Processing through acidulation with sulfuric acid, and high-quality triple super phosphate (TSP) by treating with merchant grade phosphoric acid, and as a reactor feed for the manufacture of merchant grade phosphoric acid. Said process of the présent disclosure also comprises purification of the solution (A) to produce a solution of higher purity by adding a source of calcium, and precipitating impurities along with fluoride salts and some phosphates which are recycled to the first step involving the reaction of rock phosphate with dilute sulfuric acid. Thus obtained pure solution is neutralized to produce feed grade dicalcium phosphate (DCP). Said process of the présent disclosure also comprises acidulation of the feed grade dicalcium phosphate (DCP) with sulfuric acid for production of pure fluorine-free phosphoric acid and gypsum, which are separated, followed by mixing the solution with dicalcium phosphate to produce feed grade mono calcium phosphate (MCP). This process is especially capable of using uneconomical sources such as the low-grade phosphate resources for the production of pure phosphoric acid.

One or more examples of the présent disclosure provide a simple process for the production of high grade phosphate products from phosphate rock.

The varions terminologies and aspects generally used or used in the présent disclosure in particular are presented here for clarity.

R2O3 is the sum of the oxides of iron, aluminum, and magnésium in the form of their respective oxides Fe₂O3 and AI2O3.

MER is the ratio of sum of the oxides stated above to the P2O5 content in any product or source. The MER is considered to be acceptable if it is lower than 8%.

A source of phosphate is considered to be low grade if it contains less than 26% of P2O5. It must be understood that this définition of low grade is dynamic as the reserves of high grades above 32% are depleted.

Any phosphate product or source irrespective of whether the material is of low grade or high grade, is considered to be of adéquate purity when the MER is less than or equal to 8%.

A pure product of calcium phosphate can be a solution of phosphate of a concentration of upto 24%. or a solid HGP is precipitated out of the solution through neutralization, which in turn is used to produce several other products such as DSP, TSP, phosphoric acid, or nitro phosphate. Further purification ofthe pure calcium phosphate obtained in the solution may be used to produce DCP, wherein impurities are precipitated out first, followed by précipitation of high purity DCP feed grade from the filtered solution. The obtained solution comprises HGP and calcium phosphate that are of high purity with MER of less than 8%, and DCP containing a ratio of P to F of more than 180 or more than 250.

For the sake of establishing a reference to the extent of the présent disclosure, the acid required to produce phosphoric acid though a dihydrate wet process phosphoric acid production route is 1.78 times the calcium source content.

According to one or more examples of the présent disclosure, the process comprises production of a phosphate solution with low impurities, from which HGP can be precipitated or can be further purified to produce DCP. Said high grade phosphate (HGP) can be used for the préparation of phosphate products such as double super 10 phosphate (DSP), triple super phosphate (TSP), and nitro phosphates. Said DCP can be further processed and fiItered to obtain feed grade DCP, which can further be treated to obtain mono calcium phosphate or mono dicalcium phosphate (MDCP),

According to one or more examples of the présent disclosure, the process for the 15 recovery of high grade phosphate products from a phosphate source comprises of (a) reacting a phosphate source with sulfuric acid under control led conditions to obtain first a slurry comprising impurities and solution of phosphate containing a MER of 0.5% to 8%; (b) filtering the slurry obtained in (a) to separate high grade phosphoric acid solution (A) comprising 1% to 24% P2O5 and MER of 0.5% to 8%, and filter cake;

and (c) neutralizing the phosphate solution (A) with a source of calcium to obtain highgrade phosphate (HGP) with MER 0.5% to 8%, and feed grade dicalcium phosphate (DCP) with MER 0.5% to 8%. High-grade phosphate (HGP) with MER 0.5% to 8% is obtained by neutralizing the phosphate solution (A) to a pH of 4.5 to 6.5 with a source of calcium. Feed grade dîcalcium phosphate (DCP) is obtained by neutralizing the phosphate solution (A) to a pH of 2.2 to 3.4 with a source of calcium, defluorinating to obtain a solution of dicalcium phosphate dihydrate (DCP DH) and a cake comprising impurities including fluorides, aluminum phosphate, and iron phosphate, neutralizing the solution of dicalcium phosphate to a pH of 5.5 to 6 to precipitate out DCP, and filtering the precipitated DCP. HGP obtained in step (c) is treated with 20-40% sulfuric acid to obtain double super phosphate (DSP), or treated with 25-40% phosphoric acid to produce triple super phosphate (TSP). DCP obtained in step (c) is treated with sulfuric acid to obtain high grade phosphoric acid (B) comprising less than 0.06% of fluoride content. The phosphoric acid solution (B) is treated with DCP to obtain mono calcium phosphate (MCP) or mono dicalcium phosphate (MDCP).

According to one or more examples of the présent disclosure, the production of high grade phosphate (HGP) comprises treating phosphate resource with sulfuric acid under controlled conditions of température, degree of acidulation, and any aid added per unit of phosphate source, wherein the RiOj/PvOs in said solution is reduced to as low as 0.5 to 8%. After completion of the reaction, said siurry is filtered, and the solution is subjected to further treatment. Said solution may contain 2.5% to 24% P2O5. preferably 2.5% to 12% P2O5, more preferably 4% to 6%, and MER. of 0.5% to 8%, and this solution itself could be a value-added product. The dilution does not affect downstream recovery or resuit in any effluent. Said solution may subsequently be neutralized with a calcium source, to precipitate out high grade phosphate (HGP) with MER 0.5% to 8%.

According to one or more examples of the présent disclosure, dicalcium phosphate (DCP) is produced from the phosphoric acid solution (A), wherein said solution contains high fluorine content which is to be removed to render the solution suitable to obtain an acceptable Feed grade DCP. The feed grade product should hâve a P/F of more than 180, preferably 250-300. The pH of the solution is raised to 2.2 to 3.4 and defluorinated to obtain a solution of DCP with MER 0.5% to 8%, and précipitâtes out fluorides predominantly as calcium fluoride along with other phosphates such as iron phosphate, aluminum phosphate, and calcium phosphate. This indicates loss of phosphate from the System, and so, is recovered by recycling it and introducing to the first step of the reaction for producing high grade phosphate. The addition of the residual cake back to the System does not aller the solution phase impurities in the first step as the components of the solution are in equilibrium with the solid phase, and the multi-component solution in the first step suppresses the level of impurities based on the pH. The above obtained DCP DH solution is subjected to further neutralization to a pH of 5.5 to 6 followed by filtration to obtain feed grade DCP.

According to one or more examples of the présent disclosure, feed grade mono calcium phosphate (MCP - anhydrous and mono hydrate) or mono dicalcium phosphate (MDCP) is produced from the above obtained feed grade DCP. The production of mono calcium phosphate requires a relatively pure phosphoric acid to perform the reaction represented by the équation below:

Caj (PO₄)₂+ 3H₃PO₄-> 3Ca (H₂PO₄)₂

Unlike the conventional approach of employing a defluorinated phosphate rock of reasonably high grade and an acid that is purified by removing at least the fluoride content to acceptable level to ensure that the fluorine content in the final product is maintained at an acceptable level, the présent disclosure uses a simple process thereby obviating such complicated steps. DCP produced is acidulated with sulfuric acid in a conventional phosphoric acid producing reactor while permitting rétention of calcium in the solution instead of using additional sulfuric acid. This saves on sulfuric acid, and improves the product quality. Thus obtained phosphoric acid is pure enough to produce MCP. Said high grade phosphoric acid solution comprising less than 0.006% of fluoride content is further treated with feed grade DCP to obtain mono calcium phosphate (MCP) or mono dicalcium phosphate (MDCP). Depending upon the desired grade for the production of mono dicalcium phosphate (MDCP) which is a combination of DCP and MCP, an appropriate amount of acid can be used by maintaining sufficient calcium and PO4. According to one or more examples ofthe présent disclosure, depending upon the end product, if anhydrous material is required, the concentration of the acid used is increased to 40% to 52%, and then pugged in a suitable machine with dry DCP.

According to one or more examples of the présent disclosure, double super phosphate (DSP) is prepared from HGP obtained in accordance with the one or more examples of the présent disclosure. While single super phosphates comprise! 6 to 19% P2O5, it is possible to produce a much higher grade super phosphate using HGP obtained in accordance with the one or more examples of the présent disclosure. Said HGP is treated with sulfuric acid with a dilution of 20% to 40%, and a wet material is obtained. Unlike single super phosphate, the wet material dries fast and cures well in a short period. This can be directly granulated in the wet condition to obtain double super phosphate (DSP) of high grade.

According to one or more examples ofthe présent disclosure, triple super phosphate (TSP) is prepared from HGP obtained in accordance with the one or more examples of the présent disclosure. This process is similar to that of the préparation of DSP from HGP of the présent disclosure. The phosphoric acid with a dilution of 25% to 40% is used to treat HGP. In the production of TSP, the acid required is 15% to 25% lower compared to traditional TSP process which uses rock phosphate as the solid input. In rock phosphate, the mol ratio ofCa:PO4 is 3:2, whereas in HGP, the mol ratio of Ca:PÜ4 is 1:1. Thus, much less calcium has to be converted to mono calcium phosphate in the production of TSP in accordance with the one or more examples of the présent disclosure. As the liquid component is low, the reaction can be achieved with 35% lower phosphoric acid concentration, thereby rendering benefits both from the process as well as the economy perspectives.

According to one or more examples of the présent disclosure, nitro phosphates are prepared from HGP obtained in accordance with the one or more examples of the présent disclosure. Said HGP can also be treated with nitric acid to obtain nitro phosphates.

While there are many variations in the production of nitro phosphate fertilizers, the prédominant route is to acidulate phosphate rock with nitric acid thereby producing a solution comprising mainly of phosphoric acid and calcium nitrate apart from nitrates of the other impurities except silîca. The solution is cooled, and calcium nitrate is separated out before neutralizing with ammonia to obtain higher grade products. Thus, high calcium content with respect to P2O5 gives a product that is low in phosphate, as the ratio of Cao/PCh is generally in excess of 1.6, and goes upto 2 for certain phosphates. The use of HGP gives an excellent product as the Cao/PCh is quite low. Said process offers the benefits of requirement of less nitric acid, and production of a higher grade product.

According to the one or more examples of the présent disclosure, and with reference to Figure I, the process for the production of high-purity phosphate products comprises feeding into a reactor 10, a phosphate source such as low-grade phosphate source, reject material, ores, ore rejects, slime or any other source of phosphate of minerai origin. Said process in accordance with the one or more examples of the présent disclosure may be carried out in one or a plurality of reactors, say 8 reactors, preferably 4 reactors, which may comprise single compartment or multiple compartments. with each compartment or reactor being equipped with an agitator. Said phosphate source can be either low grade or low grade with impurities containing high MER. of upto or more than 30%, and P2O5 of 5% or more. Said reactor 10 is continuously fed with proportionate quantity of sulfuric acid, through stream 102. The proportionate quantity is the pre-determined acid per unit weight of rock phosphate which is decided through an optimization test. The percentage of acid with respect to rock feed ranges between 70% and 95% acidulation. The size of said reactor 10 and agitation System is based on optimized résidence time arrived at during optimization testing. The slurry obtained above is overflown to a filter 11, either directly or through a filtration tank, not shown in the figure. The filtrate is the phosphoric acid solution containing a MER of 0.1 - 8%, and 6 to 12% P2O5, preferably 6 to 24%. The filter cake of gypsum obtained from filter 11 is subjected to washing so as to recover as much phosphate as possible. Alternately, the solution obtained from said washing can be mixed with the primary filtrate taken in tank 12, or recycled by reintroducing it into said reactor 10 if higher concentration of filtrate solution from filter 11 is desired. The solution obtained in tank 12 is the first filtrate, and the product is obtained in a single reaction using a single acid. During said reaction, no effort has been made to heat the slurry, and the température (measured at overflow) ofthe slurry is generally maintained as close to the fixed température ranging between 20 °C to 60 °C.

According to one or more examples of the présent disclosure, said solution in tank 12 could be considered as a product by itself predominantly as a phosphate comprising phosphoric acid of a concentration of upto 24%. The solution from said tank 12 is then subjected to neutralization with a source of calcium, such as but not limited to calcium carbonate, powder of minerai carbonate, precipitated calcium oxide, calcium hydroxide, hydrated lime, or combinations thereof, from stream 104, preferably in the form of a slurry with a consistency of a solid of 2 to 6 times of diluent, which could be wateror any ofthe final effluent solutions obtained in the process such as a stream from any of the filters, namely, filters 14 or 19. Said diluted slurry of the calcium source is continuously fed into a HGP precipitator 13, and allowed to overflow with a pH of 4.5 to 6.5.The filter cake obtained in stream 104 is HGP cake, which is a calcium phosphate product, possessing a definite punty of MER less than 8%. The fluonde content of said product HGP is normaliy high and has very low P/F value.

According to one or more examples of the présent disclosure, the solution from tank 12, is received in tank 15, a defluorinator, in which the calcium source from tank 13 is continuously fed to tank 15 along with the solution from tank 12 while maintaining the overflow at a pH of 2.2, or preferably even higher upto 3.4, or inost preferably to a pH that renders the solution from tank 15 a P/F of more than 180. The overflow from tank 15 is continuously collected, and filtered in a polishing filter 16 to recover a cake comprising impurities such as calcium fluoride, calcium phosphate, aluminum phosphate, and iron phosphate. The cake from said filter 16, is recycled by réintroduction to reactor 10, and processed to recover value-added phosphate products. The solution from the process from the clean phosphate storage 17 is further processed in a neutralizer 18, wherein the solution from the storage 17 and source of calcium from tank 13, neutralize the pH to 2.2 to 3.4 and defluorinated to obtain a slurry of dicalcium phosphate dihydrate (DCP DH) and a solution or effluent containing traces of P2O5. The above filtration is carried ouf in filter 19, and DCP DH is separated out. Thus obtained product is dried for use as feed grade DCP from stream 106, and comprises phosphorous of not less than 18%, and a P/F value of more than 180 to 200. The dried DCP obtained from stream 107 can be directly used as the final product - DCP feed grade. DCP obtained as slurry can further be used for the production of high grade mono calcium phosphate by first producing a fluoride-free phosphoric acid. Said DCP slurry is introduced continuously into reactor 20, either from stream 106 or directly as a wet cake, and it can also be continuously fed with concentrated sulfuric acid in a ratio of 1.02 mole of H2SO4 calculated on the basis of 100% for every mol of DCP estimated on dry basis. Said reactor 20 is operated by recycling wash obtained from filter 21, preferably a vacuum filter but not limited to using a vacuum filter, or any form of apparatus for solid liquid séparation. Said reactor 20 is equipped with a suitable agitator, and the reactor slurry is maintained at a température range of 75°C to 85 °C, and comprising a solid content not exceeding 30% by weight on slurry weight basis, preferably not exceeding 25% or 20%. This consistency ofthe slurry is maintained by recycling ail the wash water obtained through filtration from filter 21, and if required, from wash collection tank 50. The cake obtained from filter 21 is gypsum of high purity and a dihydrate form which can be used to produce valuable downstream products such as Plaster of Paris, from stream 201. The phosphoric acid obtained from filter 21 is stored in tank 22, which has a P/F of more than 200, and approximately 30-32% P2Û5.The phosphoric acid obtained therein is mixed with DCP from stream 106 along with phosphoric acid from tank 22 in an apparatus such as a paddle mill. Pug mill, ribbon blender, or such other equipment 23, is used for thorough mixing so as to produce a wet or semi-solid product of calcium phosphate, which can be mono calcium phosphate, mono dicalcium phosphate, or a product comprising a ratio of MCPto DCP. Thus obtained product is dried in a dryer 24 to produce a product that can be acceptable in the market.

According to the présent disclosure, not shown in Figure I, the acid from tank 22 can be further concentrated by methods known in the prior art or used in the industry, such as a concentrator of phosphoric acid, and an acid of 48% can be used to obtain a final product of MCP, MCP-DCP, or MDCP that is fairly dry, which could be crushed and bagged for dispatch.

According to one or more examples of the présent disclosure, HGP cake can also be recycled and subjected to further processing in a DSP mixer 30 or TSP mixer 40, to obtain phosphate products. The HGP obtained in stream 105 is admitted into a paddle type mixer which is generally used in the production of super phosphates along with sulfuric acid of concentration between 20% and 40%, and mixed in a mixer 30. The wet product obtained is granulated in a granulator 31, to produce granular double super phosphate (DSP) comprising high P2O5 compared to single super phosphate.

According to one or more examples of the présent disclosure, HGP obtained through the process of the présent disclosure. is treated with merchant grade phosphoric acid obtained through stream 301 into a mixer 40, and the obtained wet product is granulated in a granulator41, producing a high-quality triple super phosphate (TSP).

The primary advantage of the process of the présent disclosure in accordance with the various examples to produce DSP and TSP from HGP, is that the process needs less quantity of the acids as Cao/PÛ4 of the input HGP is less than l, or about 0.8 to I.

The HGP obtained through the process of the présent disclosure, can also be used as feedstock for the manufacture of high-quality nitro phosphates, by treating HGPwith adéquate quantity of nitric acid in required concentration as per known industry techniques.

HGP can be used for the production of high-quality merchant grade phosphoric acid using less amount of sulfuric acid compared to phosphate rock concentrate, as Cao/PO4 ratio is much less compared to the eommercially available phosphate rock concentrate.

One of the novel features of the process is that the intermediate cake obtained in the defluorinator from filter 16 can be put to multiple uses to produce valuable byproducts such as hydrogen fluoride, by treating the product obtained in filter 16 with sulfuric acid. While gaseous HF can be collected, the solid residue contains valuable phosphate that can be recycled by réintroduction into the process, or into products such as TSP, DSP, etc., or mixed with HGP.

The acid used in the process in accordance with one or more examples of the présent disclosure, is 1.06 to 1.78 times of the calcium source content, and the température is maintained in the range of 20 - 60 °C, so as to ensure control of R2O3 and the MER to a range of 0.5% to 8%.

In accordance with the various examples of the présent disclosure, reactors used in this disclosure, comprise suitable agitator units, pumps, and other apparatus required to complété such unit operations. The reactor system can be a single reactor or a plurality of reactors, say 8 reactors, preferably 4 reactors, of any shape such as circular, ellîptical or rectangular cross-section, with single compartment or multiple compartments in the rector or reactors, such reactors operating in sériés or parallel.

The advantages achieved by the présent disclosure hitherto not possible by any ofthe processes in the prior art, include recovery of valuable phosphates from sources containing high MER, minimal losses even during defluorination step for the production of DCP by utilizing the intermediate byproduct to even recover fluorine and also due to reuse ofthe impure filtered cake, operation of the reactors at températures such that there are negligible fluorine émissions, use of only one acid during the process, absence of génération of liquid effluents, and high cost-effectiveness of material of construction (MOC) of equipment as operation températures are very low. Also, broadly fîxingthe important parameters of operations such as température, degree of acidulation, and résidence time to achieve a desired MER is not dépendent on unworkable broad ranges such as température varying between 30°C to IOO°C, reaction times varying from 5 minutes to 180 minutes, as observed in the processes available in the prior art. Such unworkable propositions are dispensed with by the présent disclosure which teaches a simple method that can be easily operated by a person skilled in the art through the various examples of the présent disclosure.

The efficacy of the results obtained through the various examples of the présent disclosure are presented herein, for better understanding.

EXAMPLES

For the study, in the examples presented herein, the source of phosphate is low-grade impure phosphate source comprising MER higher than 8%, and generally upto 30% or above. The typical analysis is reported below in Table l.

Table l

Parameter	Sample 1	Sample 2	Sample 3	Sample 4
P2O5	16.49%	23.94%	12.60%	25.10%
CaO	19.80%	31.58%	16.90%	33.34%
Fe2O3	2.83%	4.02%	2.78%	4.33%
AI2O3	2.39%	5.68%	2.02%	2.37%
MgO	0.11%	0.17%	0.14%	0.21%
MER	32.32	41.23	39.21	27.53
Calculated acid requirement for the production of merchant grade phosphoric acid	0.596	0.356	0.565	0.302

EXAMPLE I

100 gms of phosphate rock from Sample 4 of Table l on dry basis comprising 25.1% 10 of P₂O₅, 4.33 % of Fe₂O3, 2.37% of AI2O3, and 33.34% of CaO was added along with 450 gms of water. 50 gms of 98.5% concentration sulfuric acid was slowly added over a period of one hour. After completion of the addition of the acid, the slurry is filtered thereby separating gypsum and phosphate solution. The pH of the solution was 1.04. Gypsum on dry basis weighed 106 gms, and showed a P2O5 content of 1.21%, thereby indicating nearly 95% of phosphate recovery. Said solution was then neutralized to a pH of 6.2, and HGP was precipitated out. Said precipitate showed 39.2% P2O5, 0.65%

FeîOs, 0.16% Α1?Ο₃, and 1.01% of F content. This indicates that along with high recovery of P2O5, a product having low impurities could be obtained.

EXAMPLE 2

A reaction between phosphate and sulfuric acid was carried out in a manner as conducted in Example 1, and a phosphate solution was obtained. Said solution was treated with lime to achieve a pH of 2.85. The solids produced were separated, and the solution was then neutralized with lime to a pH of 6.2.DCP was precipitated out which comprised 0.092% fluorine and 39.2% P2O5, with fluorine well within acceptable limits. DCP obtained herein, on dry' basis, weighed 24.9 gms. The separated out cake comprising 19% fluorine and 27.36% P2O5 weighed 4.76 gms. This indicates that 12% of P2O5 is to be recycled to reaction stage to recover entire P2O5. This cake can also be further routed for the production of Double super phosphate (DSP) or Triple super phosphate (TSP), effectively recovering P2O5.

EXAMPLE 3

DCP obtained in EXAMPLE 2 was treated with 27 gms of sulfuric acid per 100 gms of DCP on dry basis and the sulfuric acid was diluted to 34%. The résultant product showed 29.5% water soluble P2O5, 31% neutral ammonium citrate soluble P2O5, and 2.2% free acid P₂Os, thereby indicating a high grade double super phosphate (DSP).

EXAMPLE 4

DCP obtained in EXAMPLE 2 was treated with 47 gms of phosphoric acid calculated based on 100% P2O5 solution of 45% concentration, thoroughly mixed, and allowed to cure. The product obtained after 48 hours comprised 54.6% total P2O5, 48.4% water soluble P2O5, and 2.8% free acid phosphoric acid. This indicates the high-quality Triple super phosphate (TSP) that can be obtained through this process.

EXAMPLE 5

Phosphate from Sample 2 of Table 1 was treated with an acidulation of 60%, 70%, 80%, and 90%, with addition of 400 gms of water per 100 gms of rock phosphate used, and the MER of the solutions were measured, and presented in Figure 2.

The test was conducted at a steady reaction température of 45 °C. As can be seen in Figure 2, MER is dépendent on the degree of acidulation.

EXAMPLE 6

Sample 3 of Table 1 was taken, and acidulated at 85% with températures ranging from 40,50, 60, and 70 °C. The MER values under different conditions are presented in Figure 3. It is évident from Figure 3 that for the same amount of acid used, the MER goes up with température thereby indicating that the process is température dépendent.

EXAMPLE 7

The cake obtained from Example 5 was subjected to assessment of recovery efficacy with respect to sulfuric acid used. This was done by assessing the residual insoluble P2O5 after thorough washing to remove soluble P2O5, estimating the losses based on the weight of the input rock, the content of P2O5 in said rock, the dry weight of the cake, and corresponding P2O5 values. The percent losses of P2O5 are presented in Figure 4 which shows the recovery eflficiency of P2O5 with respect to the acid used.

EXAMPLE 8

Concentration of P2O5 was increased by repeated recycling of the solution obtained from Example 7 back into the reactor, and the MER of the solutions obtained under different concentrations are shown in Table 2. This indicates that the MER is more or less stable, and is not influenced by either recycling or the alteration in the 10 concentration, as long as the other parameters, namely, sulfurtc acid and température of reaction, are maintained the same.

Table 2

MER	Concentration of P2Oy(%)
6.77	4.80
6.87	6.76
6.21	9.20
7.05	11.80
6.55	14.30

The above examples clearly establish that MER is dépendent on critical parameters such as degree of acidulation, température and résidence time. While it is possible to produce a product with acceptable MER by using more amount of acid and lower température, or higher température and less amount of acid, P2O5 losses are observed. The process of the présent disclosure présents a unique method to optimize parameters based on the local conditions. For instance, when the source phosphate is of near zéro value and the acid is expensive, compromise can be made on the recovery of P₂Os while using reduced amount of acid.

The présent disclosure provides a process for the recovery of high grade phosphate products from a phosphate source comprising reacting a phosphate source with sulfuric acid under controlled conditions to obtain a high-grade phosphate (HGP) solution, fiItering the slurry obtained from the reaction to separate the phosphoric acid solution (A) and filter cake, neutralizing said phosphate solution (A) to a pH of 4.5 to 6.5 to obtain high-grade phosphate (HGP) with MER of 0.5% to 8%. A calcium source may be used to obtain said high-grade phosphate (HGP) cake. The concentration of the sulfuric acid used in the reaction is in the range of 70% to 95%. Said HGP can be treated with sulfuric acid diluted to 20%-40% to obtain a wet material which is granulated to obtain high grade double super phosphate (DSP). Said HGP can be treated with 25%40% phosphoric acid to obtain triple super phosphate (TSP). The initially obtained phosphate solution (A) may be subjected to neutralization with a source of calcium to a pH of 2.2 to 3.4, and defluorinated to obtain a solution of DCP DH which is further subjected to neutralization to a pH of 5.5 to 6, to precipitate feed grade dicalciuin phosphate which is filtered and dried. Said feed grade dicalcium phosphate can be subjected to further processing to obtain a product with desired characteristics. Said filter cake is subjected to filtration to remove impuritîes such as fluorides such as calcium fluoride, and phosphates such as calcium phosphate, aluminum phosphate, and iron phosphate, and said product acid solution comprises l% to 24% P2O5. Said product

acid solution is neutralized to precipitate dicalcium phosphate (DCP) possessing a minor element ratio (MER) of 0.5% to 8%, and a P/F ratio of 180 to 300. The feed grade DCP obtained from the reaction of the phosphate source with sulfuric acid is utilized for the production of various phosphate-based products such as mono calcium phosphate (MCP), dicalcium phosphate (DCP), and mono dicalcium phosphate (MDCP), The feed grade DCP obtained through the process of the present disclosure comprises not less than 18% phosphorous and a P/F value of more than 180, preferably upto 300. The filter cake is reintroduced along with the initially obtained phosphoric acid solution and calcium source, passed through a mixer and dried to obtain mono calcium phosphate (MCP) with a minor element ratio (MER) of less than 8%. Alternately, above obtained DCP can be fed to a mixer, and dried to obtain mono calcium phosphate (MCP) with MER of less than 8%. DCP can be acidulated with sulfuric acid, MCP obtained from phosphoric acid is combined, and the amount of acid is adjusted by increasing the concentration to 40% to 52% to obtain mono dicalcium phosphate (MDCP). The recycling of the various intermediate byproducts obtained during the process can be directly used for the production of various valuable end products, or reintroduced into the process for the recovery of phosphate products.

To obtain the desired phosphate products with reduced R2O3 thereby leading to an MER of 0.1 to 8%, the amount of the sulfuric acid used is in the range of 1.06 to 1.78 times the calcium source content, and the température is maintained in the range of 20 to 60 O/-

The process of the présent disclosure has the merits of controlling the distribution of R2O3 when the ore source contains high MER, i.e,, more than 8%, and upto more than 30% MER; it is a continuous process with résidence time that could be as low as 5 minutes or even lower which dépends on other factors such as reactor shape, speed of 5 the agitation etc.; no requirement of any acid other than sulfuric acid; no limitation on the concentration of the available acid and strength of solution of phosphate that could be produced, the only limitation being the physical limitation of recycling large acid quantities while using low grade resource. For instance, while using a low-grade resource of say 8%, enormous recycling has to be done to obtain 20% P2O5 acid. Also, 10 there is no limitation on the lower side ofthe reaction température, but not freezing conditions, and it is préférable to avoid températures in excess of 60 °C. Additionally, there is no limitation on the ratio of Ca to PO₄ while alleviating the need for the use of any source of calcium irrespective of the amount of CaO and PO₄ being présent. The step involving the recycling of phosphate solution containing P2O5 has no impact on 15 the process thereby eliminating the need for any other ion from any other acid source to produce pure phosphates having low MER.

The process of the présent disclosure provides a simple method that can be easily adopted for the production of pure phosphate products either in solution form in 20 sufficient strength for downstream use, or in solid form for use for downstream

Processing, or as finished products that can be readily sold. This disclosure alleviates the complex process of estimating acid requirement or need for multiple acids thereby simplifying the estimation of the required amount of the acid and température for said process. The présent disclosure also provides the possibility of optimizing the conditions for optimal économie gain, generates no effluent stream, does not introduce any additional undesirable acid streams into the process, opérâtes at low températures, reduced construction costs due to low operation or reaction températures, and relatively much fewer gaseous émissions. The process of the présent disclosure offers multiple possibilities without restrictions, and ensures production of phosphates, both as liquids and solids, with MER of less than 8% consistently, possibility of recycling solutions thereby minimizing P2O5 losses, and use in a wide range of applications.

It is to be understood, however, that the présent disclosure would not be limited by any means to the techniques, and approaches that are not specifically described, and any change and modifications to the techniques and approaches can be made without departing from the spirit and scope described in the présent disclosure.

Claims (10)

1. I. A process for the recovery of one or more phosphate products from a phosphate source comprising:

   (a) reacting the phosphate source with sulfuric acid under controlled conditions to obtain a first slurry comprising impurities, and a solution of phosphate containing a MER. of 0.5% to 8%;

   (b) fïltering the slurry obtained in (a) to separate the phosphate solution (A) comprising 1% to 24% P2O5 and fïlter cake;

   (c) neutralizing the phosphate solution (A) with a source of calcium to obtain high grade phosphate (HGP) with MER 0.5% to 8%, and feed grade dicalcium phosphate (DCP) with MER 0.5% to 8%.
2. 2. The process as claimed in claim 1, wherein high grade phosphate (HGP) with MER 0.5% to 8% is obtained by neutralizing the phosphate solution (A) to a pH of 4.5 to 6.5 with a source of calcium.
3. 3. The process as claimed in claim 1, wherein feed grade dicalcium phosphate (DCP) is obtained by neutralizing the phosphate solution (A) to a pH of 2.2 to 3.4 with a source of calcium; defluorinating to obtain a solution of dicalcium phosphate dihydrate (DCP DH) and a cake comprising impurities including fluorides, aluminum phosphate, and iron phosphate; neutralizing the solution of dicalcium phosphate to a pH of 5.5 to 6 to precipitate out DCP, fïltering the precipitated DCP, and dry ing.
4. 4. The process as claimed in claim l, wherein HGP obtained in step (c) is treated with 20-40% sulfuric acid to obtain double super phosphate (DSP).
5. 5. The process as claimed in claim l, wherein HGP obtained in step (c) is treated with 25-40% phosphoric acid to produce triple super phosphate (TSP).
6. 6. The process as claimed in claim l, wherein DCP obtained in step (c) is treated with sulfuric acid to obtain high quality phosphoric acid (B) comprising less than 0.06% of fluoride content.

   Ί. The process as claimed in claim I and claim 6, wherein the phosphoric acid solution (B) is treated with DCP to obtain mono calcium phosphate (MCP) or mono dicalcium phosphate (MDCP).
7. 8. The process as claimed in claim l, wherein the phosphate source is a low-grade phosphate source, reject material, ores, ore rejects, taîling, slime, or any other source of PjOî of minerai origin.
8. 9. The process as claimed in claim l, wherein said calcium source is selected from calcium carbonate, powder of minerai carbonate, precipitated calcium oxide, calcium hydroxide, hydrated lime, and combinations thereof.

   I0. The process as claimed in claim l, wherein R2O3, a combination of FeiCh and AI2O3 is controlled, and minor element ratio (MER) is reduced by using sulfuric acid in the range of 1.06 to I.78 times the calcium source content, and maintaining the température in the range of 20 to 60 °C.
9. 11. The process as claimed in claim l, wherein the concentration of the sulfuric acid used in the reaction is in the range of 10% to 98.5%.

   I2. The process as claimed in claim l, wherein dicalcium phosphate (DCP) comprises

   10 a fluorine content of 0.06% to 0.1 %, and phosphorous content of not less than 18%.
10. 13. The process as claimed in claim 1, wherein said DCPpossesses a P/F (Phosphorous to Fluorine) ratio of 180 - 300.