CN114671421A

CN114671421A - Method and system for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquid

Info

Publication number: CN114671421A
Application number: CN202210472453.9A
Authority: CN
Inventors: 安学斌; 杨刚; 王云山
Original assignee: Institute of Process Engineering of CAS
Current assignee: Institute of Process Engineering of CAS
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2022-06-28
Anticipated expiration: 2042-04-29
Also published as: CN114671421B

Abstract

The invention relates to a method and a system for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquid. Hydrogen chloride generated in the synthesis reaction process at 130-200 ℃ is recycled to obtain regenerated hydrochloric acid with the concentration of 18-21 wt% and suitable for cold rolling and pickling; the aging mother liquor and the washing water formed in the process can be recycled; the invention also provides a system for realizing the method, which comprises an oxidation unit, a synthesis unit, a hydrochloric acid recovery unit, an aging separation unit, a chemical pulp washing unit and a drying discharge unit; the application of the invention can realize the resource utilization of the hydrochloric acid waste liquid, prepare the new energy material ferric phosphate, obviously improve the value and the quality, realize the regeneration cycle of the hydrochloric acid, and has no three wastes discharge and no environmental pollution.

Description

Method and system for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquid

Technical Field

The invention belongs to the field of waste liquid resource utilization and new energy material preparation, and relates to a method and a system for resource preparation of iron phosphate by utilizing iron-containing hydrochloric acid pickling waste liquid.

Background

China has a plurality of production lines of cold-rolled strip steel, acid-pickled strip steel, steel pipes, steel wires and the like, the surfaces of the products need to be pickled to remove iron scales on the surfaces in the deep processing process, wherein the most common pickling solution is hydrochloric acid, so a large amount of hydrochloric acid pickling waste liquid is generated. The hydrochloric acid pickling waste liquid contains a small amount of free acid, ferric iron and a large amount of ferrous iron, and is listed in national hazardous waste records due to the severe corrosiveness of the hydrochloric acid pickling waste liquid. At present, domestic and foreign methods for treating the steel pickling waste liquid mainly comprise a direct roasting method, an evaporation concentration crystallization method, a membrane method and the like, wherein the direct roasting method is undoubtedly the most thorough method for solving the problem of waste acid and can realize the maximum recycling of hydrochloric acid, but the direct roasting method has higher threshold and large device investment, and is difficult to bear by small-sized enterprises, so that the development of the enterprises in the aspect is limited; the product market capacity of the evaporation concentration crystallization method is small, and the product quality is difficult to ensure; the membrane method can only treat relatively dilute waste liquid, cannot treat high-concentration waste liquid, only has the effect of reducing the quantity, and cannot thoroughly solve the problem of large-scale effective utilization of the hydrochloric acid pickling waste liquid.

The ferric phosphate has good application in the fields of agriculture, ceramic glass, steel, surface passivation and the like. Due to the unique catalytic property, ion exchange capacity and electrochemical performance, the lithium iron phosphate has attracted extensive attention in recent years, so that the lithium iron phosphate also has more and more important application in the fields of catalysis, lithium battery electrode materials and the like, for example, the lithium iron phosphate is an important lithium ion power battery anode material and is widely applied to new energy automobiles, and the iron phosphate is an important precursor for synthesizing the lithium iron phosphate; the existing iron phosphate preparation method is mainly a precipitation method, and comprises the steps of reacting by taking ferrous sulfate as an iron source and ammonium dihydrogen phosphate as a phosphorus source or synthesizing by taking ferric chloride as an iron source and phosphoric acid as a phosphorus source, wherein the former can generate a large amount of iron-containing ammonium sulfate by-products, and the latter needs a larger phosphorus-iron ratio.

CN112661129A discloses a method for preparing iron phosphate, which comprises the steps of taking a ferrous sulfate solution as a raw material, firstly generating ferrous phosphate with phosphorus, then removing impurities, complexing and oxidizing to obtain ferric phosphate dihydrate, and finally calcining at high temperature to obtain anhydrous iron phosphate; the method needs to add the phosphorus source for multiple times, and has a long process flow.

CN112479174A discloses a method for synthesizing iron phosphate by using a titanium white byproduct ferrous sulfate as a raw material, and a finished iron phosphate product is prepared.

CN113955732A discloses a method for preparing iron phosphate by using ferric trichloride as a catalyst, in the method, iron phosphate is prepared by circularly dissolving an iron source with ferric trichloride and reacting with phosphoric acid, nitric acid is required to be used as the catalyst, the requirement on equipment is high, and nitrogen-containing wastewater is easily generated.

From the above, it is necessary to develop a new technical method which can not only utilize the hydrochloric acid pickling waste liquid on a large scale to solve the resource problem, but also realize the preparation of the iron phosphate in a low-cost short-flow manner, and the medium can be recycled.

Disclosure of Invention

In view of the problems in the prior art, the invention aims to provide a method and a system for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquid, wherein the method uses the iron-containing hydrochloric acid pickling waste liquid as a raw material, and sequentially performs the processes of oxidation, reaction with phosphoric acid at 130-200 ℃, homogeneous aging, slurrying washing, drying and discharging, so as to obtain the iron phosphate. Hydrogen chloride generated by the synthesis reaction carried out at high temperature can be recovered to obtain regenerated hydrochloric acid suitable for cold rolling and pickling; the aging mother liquor and the washing water formed in the process can be recycled; by applying the method and the system, the recovery rate of hydrochloric acid in the iron-containing hydrochloric acid pickling waste liquid can reach more than 95%, the recovery rate of iron elements can reach more than 95%, and iron phosphate with the purity of 99.5-99.9% can be obtained; therefore, the invention not only can realize the resource utilization of the hydrochloric acid pickling waste liquid, prepare the new energy material ferric phosphate, obviously improve the value and the quality, but also can realize the regeneration cycle of the hydrochloric acid, and has no three wastes discharge and no environmental pollution.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a method for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquid, which comprises the following steps:

(1) adding an oxidant into the iron-containing hydrochloric acid pickling waste liquid for oxidation treatment to obtain a ferric acid liquid;

(2) adding phosphoric acid into the ferric acid solution obtained in the step (1), and performing a synthesis reaction at 130-200 ℃ to obtain a rough ferric phosphate slurry and gaseous hydrogen chloride;

(3) absorbing the gaseous hydrogen chloride obtained in the step (2) by using an absorbent and purifying tail gas to obtain regenerated hydrochloric acid;

(4) adding water into the rough ferric phosphate slurry obtained in the step (2) for homogenizing and aging, and then carrying out solid-liquid separation to obtain a first filter cake and an aging mother liquor; wherein the aging mother liquor returns to the step (2) and is added into the ferric acid liquor;

(5) using water to carry out slurry washing on the first filter cake obtained in the step (4) and filtering to obtain a second filter cake and washing water; wherein the wash water is returned to step (4) and added to the crude iron phosphate slurry;

(6) drying and dehydrating the second filter cake obtained in the step (5) to obtain iron phosphate;

wherein, the step (3) is simultaneously carried out in the process of carrying out the steps (4) to (6).

The iron-containing hydrochloric acid pickling waste liquid is derived from the cold rolling pickling waste liquid in the steel industry, the method can be used for preparing new energy material iron phosphate from the waste liquid, and can recover hydrogen chloride to generate regenerated hydrochloric acid which can be reused in the cold rolling pickling process, and the formed pickling waste liquid can be recycled; the residual tail gas in the hydrochloric acid recovery process is purified and then discharged up to the standard, three wastes are not discharged in the whole process, the resource utilization rate is high, the added value of products is greatly improved, and the organic coupling of two fields of waste liquid recycling and new energy material preparation can be realized.

According to the method, the synthesis reaction in the step (2) refers to the reaction of ferric chloride and phosphoric acid to generate ferric phosphate and gaseous hydrogen chloride, the synthesis reaction is carried out at a high temperature of 130-200 ℃, the hydrogen chloride can be promoted to volatilize from a solution, and is brought into an absorbent through evaporated water vapor for hydrochloric acid recovery, the reverse reaction of ferric phosphate synthesis can be weakened after a large amount of hydrogen chloride is taken away, the separation rate of the ferric phosphate is improved, and due to the evaporation of a large amount of water, the finally obtained product is slurry which contains crude ferric phosphate and has high viscosity; therefore, the subsequent water adding and aging process is required, so that the iron phosphate crystals are subjected to homogeneous aging again in a liquid phase with a large mass transfer coefficient, the granularity and morphology of the iron phosphate crystals are controlled and optimized, the adsorption of impurities is reduced to a certain extent, and the ferric phosphate dihydrate product is prepared; and removing redundant impurities through chemical pulp washing, improving the product purity, and drying to remove free water from the iron phosphate crystals to obtain the iron phosphate product.

In the step (1) of the method of the present invention, the synthesis reaction is carried out at 130 to 200 ℃, for example, 130 ℃, 135 ℃, 140 ℃, 145 ℃, 150 ℃, 155 ℃, 160 ℃, 165 ℃, 170 ℃, 175 ℃, 180 ℃, 185 ℃, 190 ℃, 195 ℃ or 200 ℃, but not limited to the above-mentioned values, and other values not listed in the above-mentioned range of values are also applicable.

The following technical solutions are preferred, but not limited to the technical solutions provided by the present invention, and the technical objects and advantages of the present invention can be better achieved and realized by the following technical solutions.

As a preferred technical scheme of the invention, the oxidant in the step (1) comprises hydrogen peroxide and/or oxygen.

Preferably, the amount of the oxidizing agent is 1.02 to 1.1 times, for example, 1.02 times, 1.03 times, 1.04 times, 1.05 times, 1.06 times, 1.07 times, 1.08 times, 1.09 times, or 1.1 times, the molar amount of the ferrous iron ions in the iron-containing hydrochloric acid pickling waste liquid, but is not limited to the recited values, and other values not recited in the above range of values are also applicable.

The iron-containing hydrochloric acid pickling waste liquid contains a large amount of iron elements, but most of the iron elements exist in the solution in the form of ferrous ions, the dosage of the oxidant in the invention can be calculated according to the molar quantity of the ferrous ions in the solution, and the dosage of the oxidant is required to ensure that all the ferrous ions are completely oxidized into ferric ions.

Preferably, the oxidation treatment of step (1) is carried out under stirring.

In a preferred embodiment of the present invention, the amount of the phosphoric acid used in the step (2) is 1 to 1.2 times, for example, 1 time, 1.02 time, 1.04 time, 1.06 time, 1.08 time, 1.1 time, 1.12 time, 1.14 time, 1.16 time, 1.18 time, or 1.2 time, the molar amount of the iron element in the trivalent ferric acid solution, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned value range are also applicable.

Preferably, the synthesis reaction of step (2) is carried out under stirring.

Preferably, the synthesis reaction time in step (2) is 3 to 7 hours, such as 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours or 7 hours, but not limited to the recited values, and other values not recited in the above numerical range are also applicable.

The temperature and the time of the synthesis reaction in the step (2) are related, when the temperature of the synthesis reaction used in the range is higher, the reaction time can be properly reduced in the range, but the reaction time cannot be too short, otherwise the volatilization amount of hydrogen chloride can be influenced, the excessive evaporation of water can be caused due to too long reaction time, and the obtained crude iron phosphate slurry is too dry and has poor fluidity, so that the subsequent process is not facilitated.

As a preferred embodiment of the present invention, the absorbent forms an internal circulation in the absorption and the exhaust gas purification, respectively.

Preferably, the absorbent of step (3) comprises water.

Preferably, the internal recycle of the tail gas clean-up produces hydrochloric acid at a concentration of less than 5 wt% and is returned directly to the absorption as absorbent, for example 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 4.9 wt%, etc., but is not limited to the recited values, and other values not recited within the above range of values are equally applicable.

Preferably, the internal circulation of the absorption produces the regenerated hydrochloric acid at a concentration of 18 to 21 wt%, such as 18 wt%, 18.5 wt%, 19 wt%, 19.5 wt%, 20 wt%, 20.5 wt%, 21 wt%, and the like, but is not limited to the recited values, and other values not recited within the above range of values are equally applicable.

When the absorption and tail gas purification of the invention are started, pure water is preferably added as an absorbent, the pure water is used for firstly absorbing the hydrogen chloride gas, and then the pure water is used for further absorbing the residual gas, so that the tail gas purification is realized; after internal circulation of tail gas purification, pure water absorbs hydrogen chloride to generate hydrochloric acid with the concentration of less than 5 wt%, the hydrochloric acid is used as an absorbent to directly flow back to the absorption, after the internal circulation of absorption, regenerated hydrochloric acid with the concentration of 18-21 wt% can be finally obtained, and the regenerated hydrochloric acid can be directly used for cold rolling; it is emphasized that the invention needs to recycle the low-concentration hydrochloric acid generated by tail gas purification to the absorption process, and the concentration of the obtained regenerated hydrochloric acid can meet the requirement through the internal circulation of the absorption, so as to ensure that the hydrogen chloride has higher recovery rate, and the internal circulation of the tail gas purification is also beneficial to realizing the standard emission of the tail gas, if only the absorption is arranged without the purification process, not only the recovery rate of the hydrogen chloride is low, but also the tail gas is difficult to reach the standard.

In a preferred embodiment of the present invention, the amount of the water used in the step (4) is 3 to 5 times, for example, 1 time, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, or 5 times, the mass of the iron phosphate in the crude iron phosphate slurry, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range of values are also applicable; and it should be noted that the mass of the ferric phosphate in the crude ferric phosphate slurry is the theoretical yield of the ferric phosphate, and is calculated according to the molar quantity of the iron element in the ferric acid solution obtained in the step (3) and the conversion yield of 100%.

Preferably, the homogeneous aging of step (4) is performed under stirring.

Preferably, the time for homogenous aging in step (4) is 2 to 6 hours, such as 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, but not limited to the recited values, and other unrecited values within the above-mentioned range of values are also applicable.

The aging time of the invention is related to the synthesis reaction carried out in the step (2), and when the synthesis reaction is carried out at a higher temperature, the needed aging time is properly prolonged within the range, so that the iron phosphate crystal is fully aged.

In a preferred embodiment of the present invention, the amount of water used in step (5) is 3 to 5 times, for example, 1 time, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, or 5 times the mass of the first cake, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned numerical range are also applicable.

Preferably, the slurry washing in step (5) is performed under stirring.

Preferably, the temperature for drying and dewatering in step (6) is 80 to 90 ℃, for example 80 ℃, 81 ℃, 82 ℃, 83 ℃, 84 ℃, 85 ℃, 86 ℃, 87 ℃, 88 ℃, 89 ℃ or 90 ℃, but not limited to the recited values, and other values not recited in the above range of values are also applicable.

Preferably, the drying and dewatering time in the step (6) is 1 to 3 hours, such as 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3 hours, but is not limited to the enumerated values, and other unrecited values in the above numerical range are also applicable.

In order to obtain the ferric phosphate dihydrate product, the drying and dehydrating time is set to be 1-3 h, and the reduction of crystal water in the ferric phosphate can be caused by longer drying time or the increase of subsequent heat treatment procedures, but the selection and adjustment can be carried out by a person skilled in the art according to actual needs.

As a preferred technical scheme of the invention, the method comprises the following steps:

(1) adding hydrogen peroxide and/or oxygen as an oxidizing agent into the iron-containing hydrochloric acid pickling waste liquid, wherein the using amount of the oxidizing agent is 1.02-1.1 times of the molar amount of ferrous ions in the iron-containing hydrochloric acid pickling waste liquid, and then performing oxidation treatment under stirring to obtain a ferric acid liquid;

(2) adding phosphoric acid into the ferric acid solution obtained in the step (1), and carrying out synthetic reaction for 3-7 h at 130-200 ℃ under stirring, wherein the use amount of the phosphoric acid is 1-1.2 times of the molar amount of the iron element in the ferric acid solution, so as to obtain rough ferric phosphate slurry and gaseous hydrogen chloride;

(3) using water as an absorbent to absorb the gaseous hydrogen chloride in the step (2) and purify tail gas; the absorbent forms internal circulation in the absorption and the tail gas purification respectively; hydrochloric acid with the concentration of less than 5 wt% is generated by the internal circulation of tail gas purification and directly flows back to the absorption as an absorbent; the absorbed internal circulation generates regenerated hydrochloric acid with the concentration of 18-21 wt%;

(4) adding water into the rough ferric phosphate slurry obtained in the step (2), performing homogeneous aging for 2-6 hours under stirring, wherein the amount of the water is 3-5 times of the mass of ferric phosphate in the rough ferric phosphate slurry, and performing solid-liquid separation to obtain a first filter cake and an aging mother liquor; wherein the aging mother liquor returns to the step (2) and is added into the ferric acid liquor;

(5) under the stirring state, carrying out slurry washing and filtering on the first filter cake obtained in the step (4) by using water, wherein the using amount of the water is 3-5 times of the mass of the first filter cake, and obtaining a second filter cake and washing water; wherein the wash water is returned to step (4) and added to the crude iron phosphate slurry;

(6) drying and dehydrating the second filter cake obtained in the step (5) at the temperature of 80-90 ℃ for 1-3 h to obtain iron phosphate;

In a second aspect, the invention provides a system for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquid, which comprises an oxidation unit, a synthesis unit, an aging separation unit, a slurry washing unit, a drying and discharging unit and a hydrochloric acid recovery unit, wherein the oxidation unit, the synthesis unit, the aging separation unit, the slurry washing unit and the drying and discharging unit are sequentially connected along the material flowing direction; wherein the liquid outlet of the aging separation unit is connected to the inlet of the synthesis unit; the liquid outlet of the slurry washing unit is connected with the inlet of the aging separation unit; the hydrochloric acid recovery unit comprises a hydrochloric acid absorption tower and a tail gas purification tower which are sequentially connected along the gas flow direction.

As a preferred embodiment of the present invention, the oxidation unit includes an oxidation tank.

Preferably, an oxidation tank discharge pump is arranged between the oxidation unit and the synthesis unit; and the inlet of the discharging pump of the oxidation tank is connected with the outlet of the oxidation unit, and the outlet of the discharging pump of the oxidation tank is connected with the inlet of the synthesis unit.

Preferably, the synthesis unit comprises a synthesis kettle; the synthesis kettle is provided with a material outlet and a gas outlet, and the gas outlet is used as a gas outlet of the synthesis unit.

Preferably, a synthesis kettle discharge pump is arranged between the synthesis unit and the aging separation unit; an inlet of the synthesis kettle discharging pump is connected with a material outlet of the synthesis unit, and an outlet of the synthesis kettle discharging device is connected with an inlet of the aging separation unit.

Preferably, the aging separation unit comprises a homogenizing aging tank and an aging filter press which are connected in sequence; the aging filter press is provided with a material outlet and a liquid outlet, and the liquid outlet is used as a liquid outlet of the aging separation unit.

Preferably, an ageing tank discharge pump is arranged between the homogenizing ageing tank and the ageing filter press; the inlet of the ageing tank discharge pump is connected with the outlet of the homogenizing ageing tank, and the outlet of the ageing tank discharge pump is connected with the inlet of the ageing filter press.

Preferably, a screw conveyor is arranged between the aging separation unit and the chemical pulp washing unit; the inlet of the screw conveyer is connected with the material outlet of the aging and separating unit, and the outlet of the screw conveyer is connected with the inlet of the slurry washing unit.

Preferably, the slurry dissolving and washing unit comprises a slurry dissolving tank and a washing filter press which are connected in sequence; the washing filter press is provided with a material outlet and a liquid outlet, and the liquid outlet is used as a liquid outlet of the chemical pulp washing unit.

Preferably, a slurry dissolving tank discharge pump is arranged between the slurry dissolving tank and the washing filter press; the inlet of the slurry melting tank discharging pump is connected with the outlet of the slurry melting tank, and the outlet of the slurry melting tank discharging pump is connected with the inlet of the drying discharging unit.

Preferably, a belt conveyor is arranged between the slurry washing unit and the drying and discharging unit; the inlet of the belt conveyor is connected with the material outlet of the slurry washing unit, and the outlet of the belt conveyor is connected with the inlet of the drying and discharging unit.

Preferably, the dry discharge unit comprises a dryer.

Preferably, the oxidation tank, the synthesis kettle, the homogenizing aging tank and the slurry tank are acid-resistant and oxidation-resistant equipment with stirring modules.

Because the reaction process of the invention is in a strong acid environment, an oxidation tank, a synthesis kettle, a homogenizing aging tank, a slurry tank and the like are required to be acid-resistant and oxidation-resistant equipment, for example, the oxidation tank and the slurry tank are both made of steel-lined PTFE, and the lining of the synthesis kettle is made of graphite; it should be noted that the heating method of the synthesis kettle of the present invention is indirect heating, for example, the synthesis kettle is provided with a jacket, and low-pressure hot steam is introduced into the jacket as a heating source, but the present invention is not limited to this heating method, and other indirect heating methods are also applicable to the present invention, and those skilled in the art can select the heating method according to actual situations.

As a preferable technical solution of the present invention, the bottom liquid outlet of the hydrochloric acid absorption tower is connected to the inlet of the regenerated hydrochloric acid storage device and the top liquid inlet of the hydrochloric acid absorption tower, respectively; the tower bottom liquid outlet of the tail gas purification tower is respectively connected with the tower top liquid inlet of the hydrochloric acid absorption tower and the tower top liquid inlet of the tail gas purification tower; a liquid inlet at the top of the tail gas purification tower is connected with a water inlet pipe; and a tail gas outlet is formed in the tower top of the tail gas purification tower.

The liquid inlet at the top of the tower of the tail gas purification tower is connected with a water inlet pipe, and water is added into a hydrochloric acid recovery unit through the water inlet pipe to serve as an absorbent; initially, before the hydrogen chloride gas enters the hydrochloric acid recovery unit, pure water needs to be added through a water inlet pipe, so that the hydrochloric acid absorption tower and the tail gas purification tower reach a working state capable of performing absorption treatment, and then the hydrogen chloride gas enters the hydrochloric acid recovery unit for absorption.

When the hydrogen chloride gas enters the hydrochloric acid absorption tower, pure water in the tower absorbs the gas, the gas is divided into two paths through a tower bottom liquid outlet to be output, and one path enters the hydrochloric acid absorption tower again through a tower top liquid inlet of the hydrochloric acid absorption tower to be absorbed so as to increase the concentration of regenerated hydrochloric acid; the other path outputs a regenerated hydrochloric acid product with the concentration meeting the requirement or stores the regenerated hydrochloric acid product; after unabsorbed gas in the hydrochloric acid absorption tower enters a tail gas purification tower, pure water in the tower is used for purifying and absorbing the gas, the residual tail gas is discharged from a tail gas discharge port on the tower top in a standard-reaching mode, the obtained low-concentration regenerated hydrochloric acid is output in two ways from a liquid outlet on the tower bottom, one way of low-concentration regenerated hydrochloric acid enters the tail gas purification tower again from a liquid inlet on the tower top of the tail gas purification tower to be circulated and is continuously used for purifying gas, and the internal circulation can obtain hydrochloric acid with the concentration of less than 5 wt%; the other path inputs the hydrochloric acid with the concentration less than 5 wt% into the hydrochloric acid absorption tower through the tower top liquid inlet of the hydrochloric acid absorption tower to be used as absorbent; it should be noted that, regarding the flow rate proportional relationship between the branches, those skilled in the art can adjust the flow rate proportional relationship according to actual situations.

The invention realizes the step absorption of the hydrogen chloride through the process, namely, pure water is added into a tail gas purification tower, the concentration of the pure water is increased after the pure water is circulated for many times in the tower, low-concentration hydrochloric acid (the concentration of the hydrogen chloride is less than 5%) is obtained, then the low-concentration regenerated hydrochloric acid is used as an absorbent and is conveyed into a hydrochloric acid absorption tower for many times, and finally high-concentration regenerated hydrochloric acid (the concentration of the hydrogen chloride is 18-21 wt%) is obtained, so that the regeneration and the cyclic utilization of the hydrochloric acid are realized; it should be noted that, after the hydrochloric acid absorption tower outputs a part of regenerated hydrochloric acid products meeting the requirements, the tail gas purification tower should timely deliver low-concentration hydrochloric acid to the hydrochloric acid absorption tower as an absorbent for replenishment, and then should replenish pure water into the tail gas purification tower through a water inlet pipe, so that the whole process maintains dynamic balance; it should be noted that, in the invention, pure water is preferably added as the absorbent at the beginning, and if hydrochloric acid with a concentration of less than 5 wt% is directly added from the water inlet pipe as the absorbent, an alkaline tail gas treatment device needs to be further added after the tail gas purification tower of the invention to solve the problem of tail gas at the beginning.

Preferably, an acid-resistant tail gas fan is arranged between the hydrochloric acid absorption tower and the tail gas purification tower; the inlet of the acid-proof tail gas fan is connected with the gas outlet of the hydrochloric acid absorption tower, and the outlet of the acid-proof tail gas fan is connected with the gas inlet of the tail gas purification tower.

Preferably, an outlet of the tower bottom liquid of the hydrochloric acid absorption tower is connected with an absorption tower circulating pump, an outlet of the absorption tower circulating pump is divided into two branches, a first branch is connected with an inlet of the regenerated hydrochloric acid storage device, and a second branch is connected with an inlet of the tower top liquid of the hydrochloric acid absorption tower.

Preferably, a tower bottom liquid outlet of the tail gas purification tower is connected with a purification tower circulating pump, an outlet of the purification tower circulating pump is divided into two paths, a first path is connected to a tower top liquid inlet of the hydrochloric acid absorption tower, and a second path is connected to the tower top liquid inlet of the tail gas purification tower.

Compared with the prior art, the invention at least has the following beneficial effects:

(1) the invention takes the iron-containing hydrochloric acid pickling waste liquid of the steel cold rolling as an iron source, realizes the separation and recovery of iron and chlorine, changes iron into iron phosphate, changes chlorine into hydrochloric acid and can be recycled, and realizes the resource utilization of the iron-containing hydrochloric acid pickling waste liquid;

(2) according to the invention, the iron phosphate as the new energy material is prepared from the low-cost iron-containing hydrochloric acid pickling waste liquid, so that the value improvement and quality improvement of the product are realized, and the organic coupling of the waste liquid recycling and the new energy material preparation is realized;

(3) the process of the invention adopts the step absorption to recover the hydrochloric acid, and has no three-waste discharge and no environmental hidden trouble.

Drawings

FIG. 1 is a schematic flow chart of a method for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquor according to the invention;

FIG. 2 is a schematic diagram of a system for recycling iron phosphate from iron-containing hydrochloric acid pickling waste liquor adopted in the embodiment of the present invention;

in the figure: 1-oxidation tank, 2-oxidation tank discharge pump, 3-synthesis kettle, 4-hydrochloric acid absorption tower, 5-absorption tower circulating pump, 6-acid-resistant tail gas fan, 7-tail gas purification tower, 8-purification tower circulating pump, 9-synthesis kettle discharge pump, 10-homogeneous aging tank, 11-aging tank discharge pump, 12-aging filter press, 13-screw conveyor, 14-aging tank, 15-aging tank discharge pump, 16-washing filter press, 17-belt conveyor, and 18-dryer.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

The flow schematic diagram of the method for preparing iron phosphate by recycling the iron-containing hydrochloric acid waste liquid is shown in figure 1, and the method comprises the following steps:

(1) adding hydrogen peroxide and/or oxygen as an oxidant into the iron-containing hydrochloric acid pickling waste liquid, wherein the using amount of the oxidant is 1.02-1.1 times of the molar amount of ferrous ions in the iron-containing hydrochloric acid pickling waste liquid, and then carrying out oxidation treatment under stirring to obtain ferric acid liquid;

The schematic diagram of the system for preparing iron phosphate by recycling the iron-containing hydrochloric acid waste liquid adopted in the embodiment and the comparative example is shown in fig. 2, and as can be seen from fig. 2, the system comprises an oxidation tank 1 and an oxidation tank discharge pump 2; a synthesis kettle 3; a hydrochloric acid absorption tower 4, an absorption tower circulating pump 5, an acid-resistant tail gas fan 6, a tail gas purification tower 7 and a purification tower circulating pump 8; a synthesis kettle discharge pump 9; a homogenizing ageing tank 10, an ageing tank discharge pump 11, an ageing filter press 12 and a screw conveyor 13; a slurry melting tank 14, a slurry melting tank discharge pump 15, a washing filter press 16, a belt conveyor 17 and a dryer 18; wherein, the outlet of the oxidation tank 1 is connected with the inlet of the discharge pump 2 of the oxidation tank, and the outlet of the discharge pump 2 of the oxidation tank is connected with the inlet of the synthesis kettle 3; a gas outlet of the synthesis kettle 3 is connected with a gas inlet of a hydrochloric acid absorption tower 4, a gas outlet of the hydrochloric acid absorption tower 4 is connected with an inlet of an acid-resistant tail gas fan 6, and an outlet of the hydrochloric acid tail gas fan 6 is connected with a gas inlet of a tail gas purification tower 7; a water inlet pipe is arranged at a liquid inlet at the top of the tail gas purification tower, and a tail gas outlet is arranged at the top of the tail gas purification tower; the liquid outlet at the bottom of the hydrochloric acid absorption tower 4 is connected with the inlet of an absorption tower circulating pump 5, and the outlet of the absorption tower circulating pump 5 is respectively connected with the liquid inlet at the top of the hydrochloric acid absorption tower 4 and a regenerated hydrochloric acid storage device or the regenerated hydrochloric acid is directly used for cold rolling and pickling; a liquid outlet at the bottom of the tail gas purification tower 7 is connected with an inlet of a purification tower circulating pump 8, and an outlet of the purification tower circulating pump 8 is respectively connected with a liquid inlet at the top of the tail gas purification tower 7 and a liquid inlet at the top of the hydrochloric acid absorption tower 4; the material outlet of the synthesis kettle 3 is connected with the inlet of a synthesis kettle discharge pump 9, and the outlet of the synthesis kettle discharge pump 9 is connected with the inlet of a homogenizing aging tank 10; the outlet of the homogenizing ageing tank 10 is connected with the inlet of an ageing tank discharge pump 11, and the outlet of the ageing tank discharge pump 11 is connected with the inlet of an ageing filter press 12; a liquid outlet of the aging filter press 12 is connected with an inlet of the synthesis kettle 3, a material outlet of the aging filter press 12 is connected with an inlet of a screw conveyor 13, and an outlet of the screw conveyor 13 is connected with an inlet of a slurry dissolving tank 14; the outlet of the slurry melting tank 14 is connected with the inlet of a slurry melting tank discharge pump 15, and the outlet of the slurry melting tank discharge pump 15 is connected with the inlet of a washing filter press 16; the liquid outlet of the washing filter press 16 is connected with the inlet of the homogenizing ageing tank 10, the material outlet of the washing filter press 16 is connected with the inlet of the belt conveyor 17, and the outlet of the belt conveyor 17 is connected with the inlet of the dryer 18.

The iron-containing hydrochloric acid pickling waste liquid adopted in the embodiment and the comparative example of the invention is from a cold rolling pickling workshop of a certain steel enterprise in China, and the content of main components in the waste liquid is shown in table 1.

TABLE 1

Example 1

The embodiment provides a method for preparing iron phosphate by recycling iron-containing hydrochloric acid waste liquid, which comprises the following steps:

(1) adding the iron-containing hydrochloric acid pickling waste liquid into an oxidation tank, adding hydrogen peroxide serving as an oxidant, wherein the using amount of the oxidant is 1.05 times of the molar amount of ferrous ions in the iron-containing hydrochloric acid pickling waste liquid, and then carrying out oxidation treatment under stirring to obtain ferric acid liquid;

(2) allowing the ferric acid solution to flow into a synthesis kettle through a discharge pump of an oxidation tank, adding phosphoric acid into the synthesis kettle, and performing a synthesis reaction for 7 hours at 130 ℃ under stirring, wherein the use amount of the phosphoric acid is 1.1 times of the molar amount of iron element in the ferric acid solution, so as to generate rough ferric phosphate slurry and gaseous hydrogen chloride;

(3) adding pure water serving as an absorbent through a water inlet pipe connected to a liquid inlet at the top of the tail gas purification tower to enable the hydrochloric acid purification tower and the tail gas purification tower to reach an absorption treatment state, introducing gaseous hydrogen chloride into the hydrochloric acid absorption tower, absorbing the gaseous hydrogen chloride by the absorbent in the absorption tower to form primary regenerated hydrochloric acid, introducing unabsorbed hydrogen chloride gas into the tail gas purification tower through an acid-resistant tail gas fan, purifying and absorbing to obtain secondary regenerated hydrochloric acid, and discharging the purified residual tail gas through a tail gas discharge port of the tail gas purification tower; at the moment, one part of the secondary regenerated hydrochloric acid is circulated in the tail gas purification tower through a purification tower circulating pump, and the other part of the secondary regenerated hydrochloric acid is conveyed to a hydrochloric acid absorption tower through a purification tower circulating pump to be used as an absorbent for further absorption; at the moment, one part of the primary regenerated hydrochloric acid obtained in the hydrochloric acid absorption tower circulates in the hydrochloric acid absorption tower through an absorption tower circulating pump, the other part of the primary regenerated hydrochloric acid outputs a regenerated hydrochloric acid product through an outlet of the absorption tower circulating pump and is directly used for cold rolling and pickling, and the formed iron-containing hydrochloric acid pickling waste liquid is reused in the method;

(4) conveying the crude ferric phosphate slurry in the step (2) to a homogenizing aging tank through a discharge pump of a synthesis kettle, adding water into the homogenizing aging tank, and carrying out homogenizing aging for 2 hours under stirring, wherein the using amount of the water is 3 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and conveying the obtained system to an aging filter press through the discharge pump of the aging tank for solid-liquid separation to obtain a first filter cake and an aging mother liquor; wherein the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquor;

(5) the first filter cake enters a slurry dissolving tank through a screw conveyor, and water is added to carry out slurry dissolving washing on the first filter cake under the stirring state, wherein the using amount of the water is 3 times of the mass of the first filter cake; then the obtained system is sent into a washing filter press through a discharge pump of a slurry melting tank for filtering to obtain a second filter cake and washing water; wherein the washing water is returned to the homogenizing aging tank in the step (4) and added into the crude iron phosphate slurry;

(6) the second filter cake obtained in the step (5) enters a dryer through a belt conveyor, and is dried and dehydrated for 3 hours at the temperature of 80 ℃ to obtain iron phosphate;

Example 2

(1) adding the iron-containing hydrochloric acid pickling waste liquid into an oxidation tank, introducing oxygen serving as an oxidant, wherein the using amount of the oxidant is 1.04 times of the molar amount of ferrous ions in the iron-containing hydrochloric acid pickling waste liquid, and then carrying out oxidation treatment under stirring to obtain ferric acid liquid;

(2) allowing the ferric acid solution to flow into a synthesis kettle through a discharge pump of an oxidation tank, adding phosphoric acid into the synthesis kettle, and performing a synthesis reaction for 6 hours at 150 ℃ under stirring, wherein the use amount of the phosphoric acid is 1 time of the molar amount of iron element in the ferric acid solution, so as to generate rough ferric phosphate slurry and gaseous hydrogen chloride;

(3) adding pure water serving as an absorbent through a water inlet pipe connected to a liquid inlet at the top of the tail gas purification tower to enable the hydrochloric acid purification tower and the tail gas purification tower to reach an absorption treatment state, introducing gaseous hydrogen chloride into the hydrochloric acid absorption tower, absorbing the gaseous hydrogen chloride by the absorbent in the absorption tower to form primary regenerated hydrochloric acid, introducing unabsorbed hydrogen chloride gas into the tail gas purification tower through an acid-resistant tail gas fan, purifying and absorbing to obtain secondary regenerated hydrochloric acid, and discharging the purified residual tail gas through a tail gas discharge port of the tail gas purification tower; at the moment, circulating one part of the secondary regenerated hydrochloric acid in the tail gas purification tower through a purification tower circulating pump, and conveying the other part of the secondary regenerated hydrochloric acid to a hydrochloric acid absorption tower through the purification tower circulating pump to be used as an absorbent for further absorption; at the moment, one part of the primary regenerated hydrochloric acid obtained in the hydrochloric acid absorption tower circulates in the hydrochloric acid absorption tower through an absorption tower circulating pump, the other part of the primary regenerated hydrochloric acid outputs a regenerated hydrochloric acid product through an outlet of the absorption tower circulating pump and is directly used for cold rolling and pickling, and the formed iron-containing hydrochloric acid pickling waste liquid is reused in the method;

(4) conveying the crude ferric phosphate slurry to a homogenizing aging tank through a discharge pump of a synthesis kettle, adding water into the homogenizing aging tank, and carrying out homogenizing aging for 3 hours under stirring, wherein the using amount of the water is 4 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and conveying the obtained system to an aging filter press through the discharge pump of the aging tank for solid-liquid separation to obtain a first filter cake and an aging mother liquor; wherein the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquor;

(5) the first filter cake enters a slurry dissolving tank through a screw conveyor, and water is added to carry out slurry dissolving washing on the first filter cake in a stirring state, wherein the using amount of the water is 4 times of the mass of the first filter cake; then the obtained system is sent into a washing filter press through a discharge pump of a slurry melting tank for filtering to obtain a second filter cake and washing water; wherein the washing water is returned to the homogenizing aging tank in the step (4) and added into the crude iron phosphate slurry;

(6) the second filter cake obtained in the step (5) enters a dryer through a belt conveyor, and is dried and dehydrated for 2 hours at 85 ℃ to obtain iron phosphate;

Example 3

(1) adding the iron-containing hydrochloric acid pickling waste liquid into an oxidation tank, adding oxygen serving as an oxidant, wherein the using amount of the oxidant is 1.02 times of the molar amount of ferrous ions in the iron-containing hydrochloric acid pickling waste liquid, and then carrying out oxidation treatment under stirring to obtain ferric acid liquid;

(2) allowing the ferric acid solution to flow into a synthesis kettle through a discharge pump of an oxidation tank, adding phosphoric acid into the synthesis kettle, and performing a synthesis reaction for 4 hours at 170 ℃ under stirring, wherein the use amount of the phosphoric acid is 1.2 times of the molar amount of the iron element in the ferric acid solution, so as to generate rough ferric phosphate slurry and gaseous hydrogen chloride;

(4) conveying the crude ferric phosphate slurry to a homogenizing aging tank through a discharge pump of a synthesis kettle, adding water into the homogenizing aging tank, homogenizing and aging for 4 hours under stirring, wherein the using amount of the water is 5 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and conveying the obtained system to an aging filter press through the discharge pump of the aging tank for solid-liquid separation to obtain a first filter cake and an aging mother solution; wherein the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquor;

(5) the first filter cake enters a slurry dissolving tank through a screw conveyor, and water is added to carry out slurry dissolving washing on the first filter cake under the stirring state, wherein the using amount of the water is 5 times of the mass of the first filter cake; then the obtained system is sent into a washing filter press through a discharge pump of a slurry melting tank for filtering to obtain a second filter cake and washing water; wherein the washing water is returned to the homogenizing aging tank in the step (4) and added into the crude iron phosphate slurry;

(6) the second filter cake obtained in the step (5) enters a dryer through a belt conveyor, and is dried and dehydrated for 1 hour at the temperature of 90 ℃ to obtain iron phosphate;

Example 4

(1) adding the iron-containing hydrochloric acid pickling waste liquid into an oxidation tank, adding hydrogen peroxide serving as an oxidizing agent, wherein the using amount of the oxidizing agent is 1.08 times of the molar amount of ferrous ions in the iron-containing hydrochloric acid pickling waste liquid, and then carrying out oxidation treatment under stirring to obtain ferric acid liquid;

(2) allowing the ferric acid solution to flow into a synthesis kettle through a discharge pump of an oxidation tank, adding phosphoric acid into the synthesis kettle, and performing a synthesis reaction for 3 hours at 190 ℃ under stirring, wherein the use amount of the phosphoric acid is 1.1 times of the molar amount of the iron element in the ferric acid solution, so as to generate rough ferric phosphate slurry and gaseous hydrogen chloride;

(4) conveying the crude ferric phosphate slurry to a homogenizing aging tank through a discharge pump of a synthesis kettle, adding water into the homogenizing aging tank, homogenizing and aging for 5 hours under stirring, wherein the using amount of the water is 5 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and conveying the obtained system to an aging filter press through the discharge pump of the aging tank for solid-liquid separation to obtain a first filter cake and an aging mother solution; wherein the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquor;

(6) feeding the second filter cake obtained in the step (5) into a dryer through a belt conveyor, and drying and dehydrating for 3 hours at the temperature of 80 ℃ to obtain iron phosphate;

Example 5

(1) adding the iron-containing hydrochloric acid pickling waste liquid into an oxidation tank, adding hydrogen peroxide serving as an oxidant, wherein the using amount of the oxidant is 1.1 times of the molar amount of ferrous ions in the iron-containing hydrochloric acid pickling waste liquid, and then carrying out oxidation treatment under stirring to obtain ferric acid liquid;

(2) allowing the ferric acid solution to flow into a synthesis kettle through a discharge pump of an oxidation tank, adding phosphoric acid into the synthesis kettle, and performing a synthesis reaction for 3 hours at 200 ℃ under stirring, wherein the use amount of the phosphoric acid is 1.1 times of the molar amount of the iron element in the ferric acid solution, so as to generate rough ferric phosphate slurry and gaseous hydrogen chloride;

(4) conveying the crude ferric phosphate slurry to a homogenizing aging tank through a discharge pump of a synthesis kettle, adding water into the homogenizing aging tank, and carrying out homogenizing aging for 6 hours under stirring, wherein the using amount of the water is 4 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and conveying the obtained system to an aging filter press through the discharge pump of the aging tank for solid-liquid separation to obtain a first filter cake and an aging mother liquor; wherein the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquor;

(5) the first filter cake enters a slurry dissolving tank through a screw conveyor, and water is added to carry out slurry dissolving washing on the first filter cake under the stirring state, wherein the using amount of the water is 4 times of the mass of the first filter cake; then the obtained system is sent into a washing filter press through a discharge pump of a slurry melting tank for filtering to obtain a second filter cake and washing water; wherein the washing water is returned to the homogenizing aging tank in the step (4) and added into the crude iron phosphate slurry;

wherein, the step (3) is simultaneously carried out in the processes of the steps (4) to (6).

Example 6

This example provides a method for preparing iron phosphate from iron-containing hydrochloric acid waste liquid as a resource, which is the same as example 5 except that the synthesis reaction time in step (2) is adjusted from 3h to 1 h.

Example 7

This example provides a method for preparing iron phosphate from iron-containing hydrochloric acid waste liquid as a resource, which is the same as example 1 except that the synthesis reaction time in step (2) is adjusted from 7h to 9 h.

Example 8

This example provides a method for preparing iron phosphate from iron-containing hydrochloric acid waste liquid by recycling, which is the same as example 1 except that the time for homogenous aging is adjusted from 2h to 1h in step (4).

Example 9

This example provides a method for preparing iron phosphate from iron-containing hydrochloric acid waste liquid by recycling, which is the same as example 5 except that the time for homogenous aging is adjusted from 6h to 7h in step (4).

Comparative example 1

The comparative example provides a method for preparing iron phosphate by recycling hydrochloric acid waste liquid containing iron, wherein the method does not carry out homogeneous aging, namely the method comprises the following steps (4): conveying the rough ferric phosphate slurry obtained in the step (2) to a homogenizing aging tank through a discharge pump of a synthesis kettle, and conveying the rough ferric phosphate slurry to an aging filter press through a discharge pump of the aging tank for solid-liquid separation to obtain a first filter cake and an aging mother liquor; wherein the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquor; except for this step, the other conditions were exactly the same as in example 5.

Comparative example 2

The comparative example provides a method for preparing iron phosphate by recycling hydrochloric acid waste liquid containing iron, and the method is completely the same as the method in the example 1 except that the temperature of the synthesis reaction in the step (2) is adjusted from 130 ℃ to 100 ℃.

Comparative example 3

The comparative example provides a method for preparing iron phosphate by recycling hydrochloric acid waste liquid containing iron, and the method is completely the same as the method in the example 5 except that the temperature of the synthesis reaction in the step (2) is adjusted from 200 ℃ to 220 ℃.

The concentrations of the regenerated hydrochloric acids obtained in the examples and the comparative examples were tested according to the analytical method of GB/T622-.

TABLE 2

Item	Regenerated hydrochloric acid concentration	Recovery rate of Cl in waste liquid	Recovery rate of Fe in waste liquid	Purity of iron phosphate
					Example 1	18wt％	96.6wt％	98.9wt％	99.77wt％
Example 2	19wt％	95.5wt％	98.3wt％	99.76wt％
					Example 3	20wt％	98.3wt％	99.7wt％	99.84wt％
Example 4	21wt％	98.1wt％	99.3wt％	99.85wt％
					Example 5	21wt％	98.0wt％	99.2wt％	99.83wt％
Example 6	19wt％	95.7wt％	97.9wt％	99.81wt％
					Example 7	18wt％	97.2wt％	99.1wt％	99.46wt％
Practice ofExample
	8	18wt％	96.6wt％	97.1wt％	99.45wt％
Example 9						21wt％	98.1wt％	99.3wt％	99.85wt％
	Comparative example 1	21wt％	98.1wt％	76wt％	99.88wt％
Comparative example 2						3wt％	10wt％	0wt％	/
	Comparative example 3	21wt％	98.5wt％	96.6wt％	97.91wt％

As can be seen from table 2:

(1) compared with the example 1, in the step (2) of the example 7, the time of the synthesis reaction is adjusted to 9 hours from 7 hours, and is higher than the preferable range of 3-7 hours; compared with the embodiment 5, in the step (2) of the embodiment 6, the time of the synthesis reaction is adjusted to 1h from 3h, and is lower than the preferable range of 3-7 h; the time of the synthesis reaction is related to the reaction temperature, the reaction temperature is high, the needed synthesis time is short, and otherwise, the synthesis time is long; the longer the synthesis time is, the yield of Cl and Fe is not deteriorated, but the production efficiency is reduced and the energy consumption is increased; when too short synthesis time is adopted, hydrogen chloride gas can not be completely escaped from the slurry to volatilize, so that the yield of Cl and Fe is relatively low;

(2) compared with the embodiment 1, the embodiment 8 adjusts the time of the homogenizing and aging in the step (4) from 2 hours to 1 hour, which is lower than the preferable range of 2-6 hours; compared with the embodiment 5, the embodiment 9 adjusts the time for homogenizing and aging in the step (4) from 6 hours to 7 hours, which is higher than the preferable range of 2-6 hours; the aging reaction is a key step for preparing the yield and the crystal form size of the iron phosphate, the longer the aging reaction time is, the higher the yield of phosphorus and iron is, the yield of the iron phosphate can be improved, but iron phosphate crystal grains can be agglomerated, the crystal grain size is increased, the purity is influenced to a certain extent, impurity removal is not facilitated, and the product performance is influenced; too short an aging reaction time may result in iron phosphate grains not being formed in time or being formed smaller and being transported to the next stage, and thus the yield of the product may be affected; comparative example 1 was not aged as compared with the Fe yield (99.2 wt%) obtained in example 5, and thus the Fe yield was severely decreased to only 76 wt%, and thus it was necessary to set homogeneous aging for increasing the yield of phosphoric acid product;

(3) compared with the example 1, the temperature of the synthesis reaction in the step (2) is adjusted to be 100 ℃ from 130 ℃ in the comparative example 2, and is lower than the preferable range of 120-200 ℃; compared with the example 5, the temperature of the synthesis reaction in the step (2) is adjusted to 220 ℃ from 200 ℃ in the comparative example 3, and is higher than the preferable range of 120-200 ℃; too low synthesis reaction temperature can cause that slurry in a synthesis system can not reach boiling point, so that the volatilization rate of hydrogen chloride gas is seriously influenced, even the hydrogen chloride gas can not escape from the slurry and volatilize, the reaction can not be carried out, the iron phosphate can not be prepared, and high-concentration regenerated hydrochloric acid can not be recovered; however, the use of an excessively high synthesis reaction temperature causes side reactions in the synthesis reaction to generate ferric pyrophosphate, iron hydroxychloride and the like, which reduces the purity of the iron phosphate product, for example, the purity of the iron phosphate obtained in comparative example 3 is only 97.91 wt%, and in addition, the volatilization of hydrogen chloride gas may carry phosphoric acid, thereby reducing the product yield.

(4) According to the analysis comparison, the method for preparing the iron phosphate by recycling the iron-containing hydrochloric acid pickling waste liquid can separate iron and chlorine in the hydrochloric acid pickling waste liquid, so that the preparation of the iron phosphate and the reproduction and recycling of hydrochloric acid are realized.

The present invention is described in detail with reference to the above embodiments, but the present invention is not limited to the above detailed structural features, that is, the present invention is not meant to be implemented only by relying on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims

1. A method for preparing iron phosphate by utilizing a resource of iron-containing hydrochloric acid pickling waste liquid is characterized by comprising the following steps:

(1) adding an oxidant into the iron-containing hydrochloric acid pickling waste liquid for oxidation treatment to obtain ferric acid liquid;

2. The method of claim 1, wherein the oxidizing agent of step (1) comprises hydrogen peroxide and/or oxygen;

preferably, the dosage of the oxidant is 1.02-1.1 times of the molar weight of ferrous ions in the iron-containing hydrochloric acid pickling waste liquid;

preferably, the oxidation treatment of step (1) is carried out under stirring.

3. The method according to claim 1 or 2, wherein the phosphoric acid in the step (2) is used in an amount of 1 to 1.2 times the molar amount of the iron element in the ferric ferrite solution;

preferably, the synthesis reaction of step (2) is carried out under stirring;

preferably, the time of the synthesis reaction in the step (2) is 3-7 h.

4. The method according to any one of claims 1 to 3, wherein the absorbent of step (3) forms an internal circulation in the absorption and the tail gas purification, respectively;

preferably, the absorbent of step (3) comprises water;

preferably, the internal recycle of tail gas cleanup produces hydrochloric acid at a concentration of less than 5 wt% and is returned directly to the absorption as absorbent;

preferably, the internal circulation of absorption generates the regenerated hydrochloric acid with the concentration of 18-21 wt%.

5. The method according to any one of claims 1 to 4, wherein the amount of water used in step (4) is 3 to 5 times the mass of the iron phosphate in the crude iron phosphate slurry;

preferably, the homogeneous aging of step (4) is performed under stirring;

preferably, the time for homogenizing and aging in the step (4) is 2-6 h.

6. The method according to any one of claims 1 to 5, wherein the amount of water used in step (5) is 3 to 5 times the mass of the first filter cake;

preferably, the slurry washing in the step (5) is carried out under stirring;

preferably, the temperature for drying and dehydrating in the step (6) is 80-90 ℃;

preferably, the drying and dehydrating time in the step (6) is 1-3 h.

7. The method according to any one of claims 1 to 6, characterized in that it comprises the steps of:

8. The system for preparing the iron phosphate by utilizing the recycling of the iron-containing hydrochloric acid pickling waste liquid is characterized by comprising an oxidation unit, a synthesis unit, an aging separation unit, a chemical pulp washing unit, a drying and discharging unit and a hydrochloric acid recovery unit, wherein the oxidation unit, the synthesis unit, the aging separation unit, the chemical pulp washing unit and the drying and discharging unit are sequentially connected along the material flowing direction; wherein the liquid outlet of the aging separation unit is connected to the inlet of the synthesis unit; the liquid outlet of the slurry washing unit is connected with the inlet of the aging separation unit; the hydrochloric acid recovery unit comprises a hydrochloric acid absorption tower and a tail gas purification tower which are sequentially connected along the gas flow direction.

9. The system of claim 8, wherein the oxidation unit comprises an oxidation tank;

preferably, an oxidation tank discharge pump is arranged between the oxidation unit and the synthesis unit; an inlet of the oxidation tank discharging pump is connected with an outlet of the oxidation unit, and an outlet of the oxidation tank discharging pump is connected with an inlet of the synthesis unit;

preferably, the synthesis unit comprises a synthesis kettle; the synthesis kettle is provided with a material outlet and a gas outlet, and the gas outlet is used as a gas outlet of the synthesis unit;

preferably, a synthesis kettle discharge pump is arranged between the synthesis unit and the aging separation unit; an inlet of the synthesis kettle discharging pump is connected with a material outlet of the synthesis unit, and an outlet of the synthesis kettle discharging device is connected with an inlet of the aging separation unit;

preferably, the aging separation unit comprises a homogenizing aging tank and an aging filter press which are connected in sequence; the aging separation unit is provided with a material outlet and a liquid outlet, wherein the material outlet and the liquid outlet are arranged on the aging filter press;

preferably, an ageing tank discharge pump is arranged between the homogenizing ageing tank and the ageing filter press; an inlet of the ageing tank discharge pump is connected with an outlet of the homogenizing ageing tank, and an outlet of the ageing tank discharge pump is connected with an inlet of the ageing filter press;

preferably, a screw conveyor is arranged between the aging separation unit and the chemical pulp washing unit; the inlet of the screw conveyer is connected with the material outlet of the aging separation unit, and the outlet of the screw conveyer is connected with the inlet of the slurry washing unit;

preferably, the slurry dissolving and washing unit comprises a slurry dissolving tank and a washing filter press which are connected in sequence; the washing filter press is provided with a material outlet and a liquid outlet, and the liquid outlet is used as a liquid outlet of the chemical pulp washing unit;

preferably, a slurry melting tank discharge pump is arranged between the slurry melting tank and the washing filter press; an inlet of the slurry melting tank discharging pump is connected with an outlet of the slurry melting tank, and an outlet of the slurry melting tank discharging pump is connected with an inlet of the drying discharging unit;

preferably, a belt conveyor is arranged between the slurry washing unit and the drying and discharging unit; the inlet of the belt conveyor is connected with the material outlet of the slurry washing unit, and the outlet of the belt conveyor is connected with the inlet of the drying and discharging unit;

preferably, the dry discharge unit comprises a dryer;

10. The system according to claim 8 or 9, wherein the bottom liquid outlet of the hydrochloric acid absorption column is connected to an inlet of the regenerated hydrochloric acid storage device and an overhead liquid inlet of the hydrochloric acid absorption column, respectively; the tower bottom liquid outlet of the tail gas purification tower is respectively connected with the tower top liquid inlet of the hydrochloric acid absorption tower and the tower top liquid inlet of the tail gas purification tower; a liquid inlet at the top of the tail gas purification tower is connected with a water inlet pipe; a tail gas outlet is formed in the tower top of the tail gas purification tower;

preferably, an acid-resistant tail gas fan is arranged between the hydrochloric acid absorption tower and the tail gas purification tower; an inlet of the acid-proof tail gas fan is connected with a gas outlet of the hydrochloric acid absorption tower, and an outlet of the acid-proof tail gas fan is connected with a gas inlet of the tail gas purification tower;

preferably, an outlet of the tower bottom liquid of the hydrochloric acid absorption tower is connected with an absorption tower circulating pump, an outlet of the absorption tower circulating pump is divided into two branches, a first branch is connected with an inlet of the regenerated hydrochloric acid storage device, and a second branch is connected with an inlet of the tower top liquid of the hydrochloric acid absorption tower;