Iron phosphate is mainly used to make lithium iron ii phosphate battery materials; it can also be used as a catalyst and to make ceramics. Ferric phosphate is one of the few molluscicides approved for use in organic farming. Unlike previously applied metaldehyde, it is non-toxic to pets and wild animals. This material is used in steel and metal fabrication processes. Bonding iron ii phosphate to metal surfaces prevents further oxidation of the metal. Its presence can partly explain the corrosion resistance of the Delhi iron column.
One of the traditional preparation methods of ferric phosphate is to use ferrous salt (such as ferrous sulfate) to react with ammonium hydrogen phosphate, phosphoric acid, ammonia water, hydrogen peroxide and the like. This technical method has the unavoidable by-product ammonium salt (ammonium sulfate), the total amount of ammonium sulfate solution is larger and the content is low, and the environmental protection treatment cost is high, and easily pollutes the environment, and the by-product value is not high. In addition, taking the sulfate radical as an example, when the iron ii phosphate product is used as a raw material for the preparation of lithium iron ii phosphate, the sulfate radical in it can produce sulfur dioxide through sintering, resulting in environmental pollution.
Two of the traditional preparation methods of iron ii phosphate is to react with pure iron and strong acid to generate ferric iron, and then react with phosphoric acid to generate iron ii phosphate. The strong acid radical (such as sulfate radical) introduced by the strong acid is easily attached to the surface of the prepared iron ii phosphate product to make the product acidic, so it is often necessary to use ammonium to adjust the pH. In addition, taking sulfate radical as an example, when the iron ii phosphate product is used as a raw material When used to prepare lithium iron ii phosphate, sulfur dioxide will be generated by sintering the sulfate radical, which will cause environmental pollution.
SUMMARY OF THE INVENTION
In order to overcome the above-mentioned defects under the prior art, the object of the present invention is to provide a method for preparing iron ii phosphate, which has low production cost, is environmentally friendly, and has high purity of the prepared iron ii phosphate.
The technical scheme of the present invention is: A method for preparing iron ii phosphate, comprising the following steps: (1) iron: placing iron in a phosphoric acid solution, heating to carry out iron reaction, and obtaining a reaction solution containing Fe(H PO ) ; ( 2) oxidation: in the filtrate of described reaction solution, add hydrogen peroxide, carry out oxidation reaction under stirring state, then add polyethylene glycol and continue to stir, make Fe (H PO ) Reaction generates iron ii phosphate, obtains the liquid after oxidation; ( 3) hydrolysis: add distilled water to the described oxidation back liquid, carry out hydrolysis reaction; (4) filter washing: carry out solid-liquid separation to the feed liquid after the hydrolysis, and wash the separated solid phase discharge to the pH value of the washing liquid Reach near-neutrality, spin-dry to obtain solid iron ii phosphate; (5) Dehydration: the solid iron ii phosphate after spin-drying is successively dried and dehydrated to form dehydrated iron ii phosphate.
In the described iron-forming step, the preferred range of temperature of reaction is 70-95 ° C, and the reaction times is preferably 3-8 hours.
In the described ironing step, the iron used is an iron rod, and the iron rods are stacked in the reactor, and then the phosphoric acid solution is added to the reactor.
The phosphoric acid used for preparing the phosphoric acid solution is preferably food grade phosphoric acid, and the water used is pure water.
For the preparation method of any one of the aforementioned iron phosphates, the oxidation step can all be operated according to the following content: at the reaction temperature, the stirring of the reaction solution is carried out, while stirring, slowly add hydrogen peroxide with a trickle, add a Polyethylene glycol solution is added after hydrogen oxide, and the starting time of adding polyethylene glycol solution is 50-70 minutes after starting to add hydrogen peroxide, until Fe (H PO ) The reaction reaches the process end point.
The mass concentration of the polyethylene glycol solution is 30-55%.
The reaction temperature of the oxidation reaction is 18-45 ℃.
For the preparation method of any one of the aforementioned ferric phosphate, the hydrolysis step can be: add the distilled water required for hydrolysis, stir after 5-10 minutes, be heated to 70-90 DEG C, and be incubated for 50-70 minutes.
For the preparation method of any one of the aforementioned ferric phosphate, the filtration and washing steps can be as follows: using a filter press to perform solid-liquid separation, and the solid-phase discharge is introduced into a centrifuge for one or more centrifugal washing and drying. , when the pH value of the washing liquid discharged from the centrifuge is 5.9-6.1, stop water washing and continue to spin dry to obtain solid iron phosphate.
The dehydration step can be: the solid iron phosphate obtained by the filtration and washing step is removed by flash evaporation to remove surface water, producing dry FePO . Anhydrous ferric phosphate.
The beneficial effects of the present invention are: using iron phosphate and hydrogen peroxide oxidation to replace the strong acidified iron in the traditional process, the cost of raw materials is lower than that of using strong acid, because other metal cation impurities and other acid radical impurities will not be introduced, on the one hand, in order to obtain High-purity ferric phosphate provides a strong guarantee, will not cause strong acid radical residues, and does not need to deal with by-products, so there is no need to set up additional process steps such as purification and adjustment of product pH, and production costs can be further reduced. Chemical pollutants such as sulfur dioxide are produced, which is beneficial to reduce or avoid pollution to the environment.