Novel process for the production and purification of phosphoric acid

Abstract

The invention relates to a process for the production and purification of phosphoric acid from a precursor referred to as acid natural phosphate (PNA), including, in particular, treatment of the filtrate (LPNA) produced by acid attack by means of starch functionalized with sulfur (NaHS). This process enables the production of phosphoric acid with a low level of impurity and efficient recovery of the metals initially present in the raw materials.

Description

[0001] NEW PROCESS FOR THE PRODUCTION AND PURIFICATION OF PHOSPHORIC ACID

[0002] FIELD OF INVENTION

[0003] The present invention relates to the field of purified phosphoric acid, said to be high quality, and derived products such as metal sulfides, high quality gypsum, silica and clay, as well as purified liquid fertilizer LPNA(p).

[0004] EARLIER ART

[0005] According to study [1], a process for the production of phosphoric acid is known. This process employs a device comprising various elements and several steps that allow the preparation of phosphoric acid by wet attack using different acids.

[0006] One of the technical problems encountered when using this process is the difficulty of obtaining high-purity phosphoric acid with a limited level of heavy metals (Cd, As, Pb, Cu, Hg) relative to its P2O5 content. Furthermore, existing processes for producing pure acid are costly due to energy consumption in the thermal phase and the use of expensive reagents in the liquid-liquid extraction.

[0007] The aim of the present invention is to present an innovative process that overcomes the drawbacks mentioned above and simultaneously improves the performance of known prior art processes. In particular, this invention aims to propose a new process for producing high-quality phosphoric acid, while optimizing process performance and minimizing any potential negative environmental impacts.

[0008] BRIEF DESCRIPTION OF THE INVENTION

[0009] The invention relates to the production of high-quality phosphoric acid by a novel purification and demetallization process. The present invention also incorporates a device comprising various elements that promote the precipitation of the metallic sulfides obtained during this process.

[0010] The device in question uses different raw materials: calcium sources (calcium carbonates or lime) or a combined source of calcium and phosphorus (natural phosphate, low-grade natural phosphate or phosphate washing sludge) and unpurified phosphoric acid (29% or 54% P2O5).

[0011] The invention consists of adding phosphoric acid (ACP29 or ACP54) to these different calcium sources to obtain a slurry called the precursor PNA (Natural Acid Phosphate). Control of the PNA precursor preparation is essential in the invention presented. The pH of the preparation medium must be between 1.5 and 2.5 to promote the precipitation of metal sulfides during the purification step with a pH ≤ 1.5 (step 2 of the process) and to prevent the precipitation of calcium phosphate (pH < 2.5).

[0012] The resulting PNA slurry is then filtered to obtain a liquid (filtrate) and a solid:

[0013] - The solid, consisting of silicates and clay with a low P2O5 content, can be used in the field of ceramics, pottery or refractory bricks.

[0014] - The resulting liquid filtrate, called LPNA (Liquid Natural Acid Phosphate), is then treated with a solution of NaHS and starch, which allows (1) the precipitation of metallic sulfides (CdS, AsS, PbS, CuS, HgS) and (2) the formation of purified liquid (CaxH3-3x(PO4)2 with x so.25, designated LPNA(p), Purified Liquid Natural Acid Phosphate), which can be more or less enriched with trace elements and used as a high-quality liquid fertilizer.

[0015] The foregoing shows that the preparation stage is one of the key points of the present invention.

[0016] Next, attacking the purified LPNA(p) liquid with sulfuric acid yields (i) purified phosphoric acid free of Cd, As, Pd, Cu and Hg, and (ii) high-quality pure gypsum with a CaSO4 content greater than 98% wt.

[0017] The diagram in Figure 1 summarizes the steps of the new process that is the subject of this invention.

[0018] DETAILED DESCRIPTION OF THE INVENTION

[0019] The described process consists of several stages in the production of purified phosphoric acid from the precursor PNA.

[0020] Description of the different stages:

[0021] Step a: Preparation of the PNA precursor A source of calcium carbonate is added to a solution of unpurified phosphoric acid which comes from the production line of the Moroccan phosphoric acid industry (ACP29OU ACP54).

[0022] The source of calcium carbonates is derived from the washing sludge of natural phosphate, phosphate rich in P2O5, natural phosphate poor in P2O5 or other raw materials such as lime or calcium carbonates or a combined source of calcium and phosphorus, having a particle size between 65 and 80 pm,

[0023] The reaction of attacking the phosphoric acid solution used with one of the sources of calcium carbonates mentioned above takes place for 30 min under stirring and at the temperature of the acid as such, and the pH is adjusted between 1.5 and 2.5, preferably between 1.5 and 2, depending on the amount of calcium source added.

[0024] Step b: Liquid / solid separation

[0025] The slurry (PNA precursor) is then subjected to filtration accompanied by rinsing of the solid phase to recover maximum phosphorus in the filtrate.

[0026] The solid phase obtained after this filtration is called the "residue." This residue represents between 5 and 17% of the initial total weight and is mainly composed of SiO2, P2O5, and CaO. The resulting liquid phase (filtrate) is called LPNA (Liquid Natural Acid Phosphate). Elemental analysis performed by ICPA revealed that LPNA contains high levels of phosphorus and calcium. It also contains low levels of iron and magnesium, ranging from 0.02% to 1%. Heavy metals (cadmium (Cd), lead (Pb), cobalt (Co), copper (Cu), nickel (Ni), arsenic (As), and mercury (Hg)) were also detected in LPNA, with concentrations ranging from 10 to 200 ppm, previously present in the starting acid or the calcium sources used.

[0027] Step c: Purification of the LPNA precursor

[0028] The LPNA is then purified by adding a mixture of NaHS and starch to remove heavy metals. The resulting LPNA(p) (purified acidic natural phosphate liquid) filtrate exhibits improved purity due to the precipitation of metals as sulfides (CdS, AsS, PbS, CuS, HgS).

[0029] The purification step is carried out as follows: the LPNA filtrate is stirred for 30 min with a NaHS / starch mixture (10 g of starch suspended in 100 ml of a 10% aqueous NaHS solution) as a purification reagent to remove heavy metals from the medium. This purification reagent is added at a rate of 1 to 2 grams per kilogram of P2O5.

[0030] After 30 minutes of stirring, the mixture is filtered. The resulting residue is rich in heavy metal sulfides such as cadmium (2.36 wt.), arsenic (4.569 wt.), zinc (0.242 wt.), and copper (3.572 wt.). The resulting LPNA(p) filtrate has the advantage of being free of heavy metals such as Cd, As, P, Cu, and Hg.

[0031] Step d: preparation of phosphoric acid

[0032] The LPNA(p) solution is reacted with sulfuric acid for 10 to 15 minutes at room temperature. This yields high-purity phosphoric acid with a low heavy metal content. The recovered acid exhibits a very low impurity level, with Cd, As, Pb, Cu, and Hg undetectable by ICP analysis. High-quality calcium sulfates (gypsum) are also obtained (CaSO4 greater than 98%).

[0033] INDUSTRIAL APPLICATION

[0034] The process of the invention is specifically designed for industrial applications in the field of high-quality phosphoric acid production:

[0035] Five high-quality end products are obtained through this process:

[0036] - Silicates and clays

[0037] - Metallic sulfides (CdS, AsS, PbS, CuS, HgS)

[0038] - Purified liquid fertilizer LPNA(p)

[0039] - Purified acid LPNAS(p)

[0040] - High-quality gypsum

[0041] This innovative process allows for the recovery of various calcium sources without generating waste during the different stages of the process. All operations and stages of this process are carried out at ambient temperature.

[0042] REFERENCES

[0043] [1] Schorr, M., Valdez, B., 2017. Phosphoric Acid Industry: Problems and Solutions. BoD - Books on Demand.

[0044] [2] Gilmour, R., 2013. Phosphoric Acid: Purification, Uses, Technology, and Economics. CRC Press.

[0045]

[0046] 10.1201 / b16187.

[0047] [3] Kouzbour, S., Gourich, B., Gros, F., Vial, C., Allam, F., Stiriba, Y, 2019.

[0048] Comparative analysis of industrial processes for cadmium removal from phosphoric.

[0049] [4] Zhou, Y, Zheng, G., Long, Y, Liu, Z., Tao, C., Liu, R., 2022. Advanced oxidation processes for wet-process phosphoric acid: enhanced phosphorus recovery and removal of organic matters. Hydrometallurgy 210, 105842. https: / / doi.org /

[0050] 10.1016 / j. hydromet.2022.105842.

[0051] [5] Qamouche, K., Chetaine, A., El Yahyaoui, A., Moussaif, A., Frohlich, ” R, Bertau, M., Haneklaus, N., 2021. Uranium and other heavy metal sorption from Moroccan phosphoric acid with argan nutshell sawdust. Miner. Eng. 171, 107085 https: / / doi. Org / 10.1016 / j.mineng.2021.107085

Claims

DEMANDS 1. A process for the production and purification of phosphoric acid from a precursor, Natural Phosphate Acid (NPA), characterized in that it comprises the following steps: a. Obtaining the NPA precursor by combining different raw materials and sources of calcium (calcium carbonates or lime) or a combined source of calcium and phosphorus (natural phosphate, low-grade natural phosphate, or phosphate washing sludge) and phosphoric acid as such b. Filtration and recovery of the filtrate (LPNA) accompanied by rinsing of the solid phase to recover a maximum of phosphorus in the filtrate. c. Purification of the LPNA filtrate obtained according to step b) by addition of starch functionalized with NaHS, followed by solid / liquid separation by filtration leading to the obtaining of purified filtrate (LPNA(p)) free of heavy metals and of a solid residue rich in metal sulfides (CdS, AsS, PbS, CuS, HgS); d. Treatment of the filtrate (LPNA(p)) obtained according to step "c" with sulfuric acid, followed by solid / liquid separation by filtration leading on the one hand to (i) obtaining a solid residue composed of high quality gypsum and, on the other hand, to (ii) recovery of purified phosphoric acid free of heavy metals.

2. A process according to claim 1, wherein different raw materials used in step "a" comprise different raw materials and sources of calcium (calcium carbonates or lime) or a combined source of calcium and phosphorus (natural phosphate, low-grade natural phosphate or phosphate washing sludge) and having a particle size between 65 and 80 pm.

3. A process according to claim 1, characterized in that the attack of the PNA precursor with phosphoric acid as such is carried out at pH values ​​between 1.5 and 2.5, preferably between 1.5 and 2, in order to promote the precipitation of metal sulfides during the purification step.

4. A process according to any one of claims 1 to 3, wherein the starch is functionalized with NaHS used according to step c) leading to obtaining an LPNA(p) filtra with low levels of heavy metals and a residue rich in heavy metal sulfides such as cadmium.

5. The process according to any one of claims 1 to 4, wherein the purified phosphoric acid attacked by the sulfuric acid produced according to step d) has undetectable levels of heavy metals (Cd, As, Pb, Cu and Hg).

6. The process according to any one of claims 1 to 5, wherein the high-quality gypsum produced in step d) has a calcium and sulfate content greater than 98% by weight.

7. Use of phosphoric acid obtained by means of the process according to any one of claims 1 to 6 in the energy, pharmaceutical and food industries.

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