WO2004033732A1

WO2004033732A1 - Method of iron (iii) hydroxide and oxide recovery by bacterial oxidation

Info

Publication number: WO2004033732A1
Application number: PCT/UZ2002/000001
Authority: WO
Inventors: Galina Arkadyevna Babadjanova; Sergey Ivanovich Borminskiy; Lolita Vladimirovna Melikhova
Original assignee: Galina Arkadyevna Babadjanova; Sergey Ivanovich Borminskiy; Lolita Vladimirovna Melikhova
Priority date: 2002-10-10
Filing date: 2002-10-14
Publication date: 2004-04-22
Also published as: EA200500592A1; AU2002335142A1; EA009324B1

Abstract

Recovery of hydroxides and oxides Fe (III) by elementary iron oxidation involving the participation of bacteria, capable to oxidize Fe (II) into Fe (III) in the solution. Process efficiency and recovered products quality are increased by creation of conditions of viable bacteria cells conservation with single temperature maintenance at all process stages, including final product washing. The method of iron hydroxides and oxides recovery comprises in succession oxidation and dissolving of the elementary iron, including a contact of iron containing raw material with sulphuric acid solution, containing bacteria, capable to oxidize Fe (II) into Fe (III), sedimentation of the formed iron hydroxide and oxide suspension, sediment separation, its washing with further drying and in the case of necessity (pigment use etc.) annealing of the recovered product. According to the invention the dissolving of iron containing raw material and iron hydroxides and oxides synthesis is carried out in a reactor -fermenter in aerobic conditions at constant air aeration simultaneously with periodical substitution of a part of the solution by reusable solution from suspension separation carried out into at least one vessel for collection and settlement of iron hydroxide and oxide sediment, wherein the sediment washing using counter flow is carried out with reusable solution formation at constant air aeration of its upper part, whereby all process stages are conducted at similar temperature.

Description

METHOD OF IRON (III) HYDROXIDE AMD OXIDE RECOVERY BY BACTERIAL OXIDATION

The invention relates to iron hydroxide and oxide Fe (III) recovery by elementary iron oxidation using bacteria, capable to oxidize Fe (II) into Fe (III) in the solution.

It is known that ferruginous products are used in many branches of the national economy. Iron hydroxides and oxides are used as iron oxide pigments in pain and varnish, paper, construction, instrument making branches of industry, in production of plastic materials, ceramics and porcelain.

Besides they can be used as iron containing fertilizers in soils impoverished in iron, serve as a initial raw material in. reco ery of: a) iron containing preparations for iron replenishment at human beings and animals; b) powder iron; c) various types steel on the basis of the given powder iron; e) magnetic powder of various modifications; f) coatings, used as antiradar ones.

Lack of iron containing products can be replenished by industrial iron hydroxide and oxide production.

Methods of iron oxide pigments which are ferric hydroxide and oxide Fe (III) by their nature are known.

In particular the method of iron oxide pigments (Patent UZ No 1192, published in 1 94) is known. According to the known method the iron oxide pigments are recovered by bacterial oxidation using ferric oxidizing bacteria, Thiobaccillus ferroxidans BKM-B458, being produced in three stages. Herewith at the first stage the solution iron sulfate (II) is oxidized by bacteria in aerobic conditions during 11-16 hours at pH 1,7-1,8 and temperature 28- 30° C up to 70-90% iron sulfate (III) content with simultaneous pH solution increase up to 2.1-2.2. At the 2-nd stage the main volume of the recovered solution is heated up to 60-70° C. Formed thereby iron oxide pigments are settled in a form of Fe(OH)₃ mixture (9-95%), FeOOH (14-90%) and FeOHS0₄ (1%), pH of the solution is decreased up to 1,7 and bacteria are denatured. Pigments sediment after cooling is separated by filtration, washed out and dried. At the third stage the filtrate, enriched by iron (III) sulfate, comes into contact with the source of elementary iron up to full recovery of Fe (III) into Fe (II) and achievement of the primary sulfate ions concentration (the duration of recovery is not less than 2 hours). The part of bacteria suspension remained after the first stage is brought into the filtrate for the cycle regeneration. The pigments output using this method is 0,5-1,0%, the ratio of main and acid compound of Fe (III) in the raw mass of pigments without the addition of FeOOH at the second stage is 55-85% Fe (OH)₃, 44-14% FeOOH and 1% FeOHS0₄ with FeOOH primer - 9%Fe(OH)₃, 90% FeOOH and 1 % FeOHS0₄. The method of iron oxide pigments recovery is also known (Preliminary

Patent UZ IDP 04992, published on 31.12.2001), including bacterial oxidation Fe (II) into Fe (III), by treatment of iron (II) sulfate solution at the first stage by iron oxidizing bacteria Thiobacillus ferrooxidans BKM-B458 up to the achievement of the 88% of the green vitriol iron oxidation rate. According to the known method the bacterial solution in the amount of 50 1 is brought into the reactor, wherein 0,6 kg of iron oxidizing raw material in grid basket is added, then the raw material solution is aerated and heated from 28°C to 70°C during two hours. Upon the heating process completion, the aeration is stopped and suspension of pigment being settled at 70° C is separated from the spent bacterial solution, washed out by 5 1 of hot water of 60 - 70°C up to neutral reaction (pH = 6,0). 1,2 kg of paste type product with moisture content of 69% is recovered and dried at 100°C.

According to the known method the iron oxide pigment output is 0,5 kg. The worked out bacterial solution with Fe (III) 17 g/1 content is combined with washing water and used for further technological cycle of iron oxide pigments recovery.

The authors consider the known method of iron oxide pigments recovery as he most relevant to the applied one (Preliminary patent UZ IDP 05297, published on 30.08.2002). According to the known method the bacterial oxidation of Fe (II) into Fe (III) by iron sulfate (II) bacterial solution treatment at the first stage using iron oxidizing bacteria Thiobacillus ferrooxidans BKM-B 458, contact and heating of the bacterial solution with iron oxidizing raw material is carried out simultaneously aerobic conditions. The bacterial solution with the temperature from 28°C up to 30°C at pH 1,7-2,4 is continuously supplied into the preliminary heated and further continuously heated reactor (the maintained temperature is 60-70°C), where the bacterial solution comes into contact with iron oxidizing raw material in aerobic conditions, herewith the synthesis of iron oxide pigments takes place in a form of hydroxides in the sediment and Fe (III) is recovered into Fe (11), which serves the basis for pigments being formed. The temperature in the reactor is maintained by the speed of the bacterial solution supply, which is rated to provide the temperature of 60-70°C for the pigment suspension at the output of the reactor. Besides, the rate of bacterial solution supply is determined by the reactor volume, a heat carrier amount and bound to the temperature of the pigment suspension at the output in proportion. It means, if the temperature of the pigment suspension at the output is less than 60°G , then the rate of the bacterial solution supply decreases, if the temperature of the pigment suspension is higher than 70°C , then the rate of the bacterial solution supply increases. The iron oxidizing raw material supply is carried out as iron oxidizes and the pigment suspension is brought out, where it is separated into worked out bacterial solution and pigment mass, which is washed out by hot water at the temperature of 60-70°C and which is directed into a fermenter after washing out the worked out bacterial solution is also directed into the fermenter, herewith its temperature is decreased up to 40- 50°C an it is mixed as a washing out water with main bacterial solution, due whereto the temperature in the fermenter is constantly maintained at the level of 28-30° C without additional waiming up.

According to the result of the analytical study it can be concluded that there is a considerable difference between the temperature of the solution heated up to 60-70°C at the stage of the pigment synthesis without the contact or at the contact with iron containing raw material and the temperature of 25-30°C at the stage of bacteria cultivation and Fe (II) into Fe (III) oxidation in the above mentioned method. But during the solution heating the constant destruction of bacterial cells, coming into the reactor along with solution and sharp change of physical and chemical (pH, Eh) solution parameters takes place, all this leads to the temporary instability of the whole process, which is the serious disadvantage for technologies, related to the microorganisms (biotechnologies) utilization.

In turn the destruction of bacterial cells at the product synthesis stage leads to the large technological difficulties at the iron hydroxide washing out, as the pigment suspension and the paste recovered there from by filtration, contains the large amount of ions Fe (II) due to the high humidity (min 30%), and there are no viable cells, capable to oxidize Fe (II) into Fe (III) in the paste and the part of this iron, despite of water washing out, gets into the finished product, that leads to the product properties deterioration, for example pigment ones both in color and it's behavior in painted coatings.

Besides the existence of stages with various temperature parameters at closed water circulation in one process requires the strict control over the temperature at all stages that is also difficult from the technological point of view.

The considerable disadvantage of known methods is in using of one strain of iron oxidizing bacteria Thiobacillus ferrooxidans BKM-B458 which effectively functions only at the temperature of 25-30°C.

Thus the basis of the applied invention is the aim of increase of the efficiency of products quality and recovery process at the expense of creation of conditions of viable bacteria cells conservation by maintenance of single temperature at all process stages, including the washing of the finished product, at the expansion of the applied bacteria and their strains selection. The given aim is solved by the way wherein the bacterial oxidation

Fe (II) into Fe (III), contact of the solution with the iron oxidizing raw material, oxidation of the elementary iron and Fe (III) hydroxides synthesis is carried out simultaneously in aerobic conditions with constant air aeration, in one vessel at single temperature; the hydroxide mass settlement in the other vessel, settlement separation, its washing out by the method of counter flow, drying and annealing, herewith the air aeration of the upper part of the solution, which makes approximately 1/3 of the whole solution volume is constantly carried out in the vessel for the settled hydroxide mass collection. And the temperature is maintained at the same level as in the reactor-fermenter.

In the vessel which is both a reactor and fermenter simultaneously the following processes are carried out in parallel : a) bacterial oxidation of Fe

(II) into Fe (III); b) chemical oxidation of Fe° into raw material by Fe (III) ions with formation from one atom of Fe° and two ions of Fe (III) of three ions of Fe (II), immediately being oxidized by bacteria; c) Fe (III) hydroxides synthesis at the expense of the reaction between water molecule and formed excess of ions of Fe (III). As a result the iron containing raw material dissolving takes place as well as accumulation of synthesized Fe

(III) hydroxides in the vessel. Taking into account the constant air aeration of the whole volume of the solution, synthesized hydroxides form a suspension in the solution and is poured together with the solution or the part thereof into another vessel, herewith the remain part of the non reacted part of the raw material remains in the reactor-fermenter, and the circulating solution, consisting of filtrate, recovered after hydroxides suspension separation by the filtration of the solution from the suspension washing and recovering of the initial volume of the working solution in the reactor-fermenter is fed into the later one. In the vessel, serving as a receiving vessel for hydroxides suspension collection, coming from the reactor- fermenter, the air aeration of the upper part of the solution (approximately 1/3 of the whole solution volume) is carried out additionally, and the temperature is maintained at the same level as in the reactor-fermenter.

In this vessel, due to the availability of viable bacteria cells in the solution, coming from the reactor-fermenter and lack of iron containing raw material, preeminently reaction of bacterial oxidation Fe (II) into Fe (III) takes place. Besides, here, due to the air supply only to the upper part of the solution the condensation of synthesized hydroxides Fe (III) in the lower part of the vessel. After the vessel filling, the clarified part of the solution (free of heavy settlement) is brought back to the reactor-fermeter, and thickened part for separation of hydroxides off the solution by filtration on the vacuum filter; the filtrate also is brought into the reactor-fermenter, and settlement is brought for washing out (both clarified part and filtrate contain viable bacteria cells). For normal process conduction there must be minimum two vessels- receivers on each rector-fermenter. While the suspension comes into one vessel from the reactor-fermenter, the other serves as a feeder of the same reactor fermenter by circulating solutions. Hydroxide settlement is washed by the counter - flow method in the continuous mode, herewith the settlement, separated at each filtration stage on the vacuum filter, re suspended in the filtrate (solution), obtained at the next washing out stage.

Actually it is carried out by the following way: the hydroxide settlement (A), separated from the working solution by filtration, is re suspended (mixed) in the mixer by the solution, obtained at the washing out of the previous settlement (B), the settlement (B) in turn is re suspended in the mixer by the solution, obtained at the washing out of previous settlement (C) and so on. The fresh water is brought at the re suspension of the first by time settlement separation, and the solution after washing of the last by time settlement separation of hydroxides is mixed with circulating solutions.

The amount of washing stages is determined by the requirement to the chemical purity of resulted recovered hydroxides Fe (III). The additional air aeration of recovered suspensions is carried out at each washing out stage at re suspension, of sediments.

At such washing mode all iron ions, available in the solution (settlements humidity is about 30%), it means that more than 40 kg of washing solution is used for each 100 g (kg) of the final product, recovered after drying at 105 °C during the washing process), are brought again to the reactor-fermenter, herewith the bacteria cells remained viable at re suspension of settlements continue oxidizing ions of Fe (II) which are available in the suspension in various amounts.

To recover more pure final product at the last stage of washing NH OH is brought along with water to the hydroxide suspension pH value higher than 7.0. The amount of added ammonia reacts with SO₄ ions, available in the product and is brought to the reactor- fermenter along with washing water in a formof (NH₄)₂S0₄ .

The replenishment of water loss, related to the water molecule participation in the hydroxide formation reaction and natural evaporation at solutions aeration is carried out at the expense of washing water in the reactor fermenter, the amount of iron in the solution is replenished and nitrogen feeding of bacterial cells is carried out at the expense of (NI_₄)₂ S0₄ coming with washing water.

Thus the method applied by authors allows to recover hydroxides and oxides Fe (III) without loss of raw material at long functioning of the device in the closed mode and stable conditions.

Besides in the case of Thiobacillus ferroxidans BKM - B458 strains utilization for temperatures lower than 40° C the economic effect is achieved at the expense of reduction of expenses for additional solution heating at the product synthesis stage, and in the case of thermophile types utilization for temperatures higher than 40°C the effect is achieved at the expense of the product output increase from the solution volume unit. Process temperature and correspondingly the type of used bacteria are determined for each process separately and connected with technological and economic factors: climatic conditions, area, power and heat carries cost, recovered products cost etc. The method is illustrated by the following examples: Example 1.

6.3 kg of green vitriol FeS0₄ • 7H₂ 0 (at the rate of 17 g/1 Fe (II), 285 g Ammonia sulfate (NH₄)₂ S0₄ (at the rate of 3 g/1), 37,5 g of magnesium sulfate MgS0 (at the rate of 0,5 g/1), 37,5 Dipotassium phosphate K₂HP0₄ ( at the rate of 0.5 g/1), are dissolved in 75 1 of water acidified by sulfuric acid pH up to 1,7-1,8 ( acid consumption of 1,84 g/mg density is 75 ml) Thiobacillus ferrooxidans BKM-B458 bacteria cells suspension is brought into the solution and at the stable temperature of 28-30°C in the thermostat and constant medium aeration bacteria are cultivated up to the 85-90-% iron oxidation degree, it means that there must be approximately 2g/l of Fe (II) and 15 g/1 of Fe (III) in the medium. The temperature in all vessels of the device is maintained at 28-30° C level at the expense of the heat carrier, circulating along coil pipes. The finished bacterial medium in the amount of 75 1 is used for iron containing raw material dissolving with recovery of iron (III) hydroxides at continuously functioning device. 50 1 of overgrown medium is poured into the reactor- fermenter and 25 1 into one of the receiving vessels (1) and air is supplied from the compressor. 0,5 kg of iron containing raw material is brought into the reactor-fermenter. In 1- 1,5 hours after the starting of the device Fe (III) hydroxide suspension starts forming as a result of chemical and biological reactions taking place in the reactor-fermenter. In 2 hours after the start 4,16 1 is poured from the upper part of the reactor- fermenter into the free receiving vessel (1), and 4,16 1 of overgrown medium from vessel (1) comes into the reactor- fermenter. Simultaneously the air supply from the compressor into the vessel (II) is switched on. Then the operations are repeated every 2 hours and in 12 hours after the start 25 1 of the working solution, containing hydroxide suspension is collected in the vessel (II).

The air is supplied through the pipe, mounted on the float which lifts as the vessel is filled. In 14 hours after the start of the device next 4,16 1 are poured from the reactor-fermenter into the free receiving vessel (1), and from the clarified part of the vessel (II) 4,16 1 of solution comes into the reactor- fermenter, then every 2 hours 4,16 1 of hydroxide suspension comes from the reactor- fermenter into the vessel (1). Thickened part of hydroxides from vessel (II) is directed for filtration, where the bacterial solution is separated from the hydroxide mass and directed into the free receiving vessel (II), and there from into the reactor-fermenter by portions 4,16 1 each every 2 hours. After the filling of the vessel (I) for successive 12 hours (13-24 hours from the start of the device), the cycle is repeated - pigments suspension is directed into the vessel (II) (25-36 hours from the start) and then into the vessel (I) (37- 48 hours from the start) and so on.

The lack amount of the working solution, formed at the expense of: a) solution, leaving with pigment mass; b) water, spent for Fe (III) hydroxides formation; c) water evaporation from vessels at air bubbling-during first three days of the device functioning they are filled with water, acidified by sulfuric acid pH up to 1,7-1,8. Further the water balance is maintained by solutions, coming with hydroxide washing. Also every day 0,3-0,4 kg of iron containing raw material is loaded into the reactor-fermenter. Thickened and filtered sediment of A hydroxides (further referred to as cake A), recovered for 1 day (0-24 hours) of the device functioning are re suspended in 5 1 of water on the mixer (approximately 1000 rpm) during 1 hour at air aeration and temperature of 28-30° C, then only bubbling remains. In 20 hours the bubbling is stopped and filter cake A is separated from the solution (solution A) by filtration. Hydroxide filter cake (cake B), recovered for second day (25-48 hours) of the device functioning in the solution A is re suspended, and filter cake A is re suspended in fresh water (re suspension modes are similar to the first one). One day later filter cake C, recovered for the third day (49-72 hours) is re suspended in the solution A, separated from the filter cake B. Herewith filter cake B is re suspended in the solution B, got at the separation of filter cake A from this solution. Filter cake A is re suspended in fresh water wherein 0.5 ml of 25% NH₄OH is brought. One day later solution A, separated from the filter cake B comes into the reactor- fermenter (working solution volume correction). Cake B is re suspended in solution B, got at cake A separation from the solution, and cake A is brought for drying at 105° C up to the constant weight and then is weighed. The device operates constantly in such mode of hydroxide cakes washing i.e. every day about 5 1 of washing water come into the reactor-fermenter, in the case of necessity the additional working solution correction is carried out by fresh water without acidification. Selective data on Fe (III) hydroxide output at the device operation during 30 days are given in Table 1 as well as data on Fe_gen(general) and amount of viable Thiobacillus ferrooxidans cells in the solution (amount of cells was calculated by the method of maximum dilutions in 9K medium). Example 2. The preparation of the overgrown medium for the device staring, device operating modes and modes of recovered Fe (III) hydrooxides washing is carried out as in Example 1, but Thiobacillus ferrooxidans bacteria of KSB strain is used, successfully growing and oxidizing Fe²⁺ at temperatures of 15-25 ° C. The device operates at a room temperature (temperature range between night and day time is 16-24°C) without additional preheating and temperature stabilization in vessels. Data are given in Table 2. Example 3.

Device operation and washing modes of recovered hydroxides Fe (III) behave in the same way as in Example 1. The whole process, preparation of the grown over medium up to the operation of the device and 2 stages of cakes washing is carried out at the working temperature of 50-55° C. Herewith the thermophile bacterium Thiobacillus termo- ferroxidans is used. Taking into account the strong evaporation of water at such temperatures and high weight of recovered cakes, the washing solution for these cakes re suspension was 10 1. The last stage of washing is carried out at temperature of about 30° C due to the ammonia volatility . Data are given in Table 3. Example 4.

Used bacteria, process temperature, preparation of grown over medium and washing mode of recovered hydroxides Fe (III) are similar to conditions of Example 1. The device operates in continuous mode. At the device starting the grown over medium is continuously supplied with constant speed of 0,035 1/min (2,08 I/hour) from the receiving vessel (I) into the reactor-fermenter. The solution supply is carried out into the lower part of the reactor-fermenter, and the excess of the solution comes into the receiving vessel (II) by gravity flow along the exhaust pipe. Taking into account that the solution with Fe (III) hydroxides suspension from the reactor- fermenter into the receiving vessel (II) is fed constantly and continuously, i. e in the mode not favorable for the suspension thickening, then for of suspension thickening the buffer vessel (III) with the volume of about 5 1 is used. From the buffer vessel (III) the working solution is fed into the reactor- fermenter, at that time when in 12 hours the vessel (II) is filled by 25 1 of suspension solution and the solution from the reactor- fermenter is fed into the receiving vessel (I), and thickening of hydroxides takes place in the vessel (2) during 2 hours. The further mode of the device operation is the same. The data are given in Table 4. Example 5.

1 1 of the working solution after Fe (III) hydroxides separation by filtration is taken. This solution parameters are as follows Fe (III)- 15,4 g/1; Fe (II)- 2,1 g/1; pH- 2,20; Eh- 640_mv. 11 of fresh prepared medium (without bacteria) is fed into the reactor-fermenter with following parameters: Fe (III) -is not available, Fe (II) - 17,0g/l; pH- 1.85; Eh-450_mv. The iron in the reactor-fermenter is oxidized by bacteria. This substitution doesn't affect general parameters. The selected out solution is fed into the separate vessel, where at air aeration further oxidation of Fe (II) into Fe (III) is carried out. In 2 hours the solution is got with following parameters: Fe (III) - 17,5 g/1; Fe (II) - is not available; pH -2,34; Eh- 810_mvTo the given solution 0,5 1 of solution wherein 100 g of K₄ [Fe(CN)₆]^β3H₂ O - potassium ferrocyanide is diluted is added.

The reaction starts after the addition of this solution: 2Fe₂(S0₄)₃ +3K₄ [Fe(CN)₆] → Fe₄ [Fe(CN)₆]₃i+6K₂S0₄, the precipitated fine disperse sediment is the pigment "Prussian blue". The pigment is separated by filtration and brought for washing, and the solution is evaporated up to precipitation of the salt K₂ S0 _; the pigment weight is 72 g; at solution evaporation 57 g K S0 is recovered (70% of theoretical). The remained solution is used at dissolving of potassium ferrocyanide for the further cycle. "Prussian blue" is widely used for dyes and enamel production for various purposes, in particular for production of polygraphic dyes, dyes for leather, colored pencils production etc. "Prussian blue" is resistant to weak and neural acids. Thus the applied method of iron oxides and hydroxides recovery allows to recover hydroxides and, or oxides Fe (III), which are iron oxide pigments and widely used in productions related to iron containing products recovery. In particular, paint and varnish, paper, construction, instrument making branches of industry, in the production of plastics, ceramics and porcelain.

Besides, opportunities . of utilization in production of iron containing fertilizers, medicines, in production of powder iron, various types of steel on the basis of powder iron, magnetic powders of various modifications, in the production of coatings, used as and radar etc. The method is economically profitable and can be recommended for industrial production.

Fe (HI) hydroxides output and working solution parameters change at continuous process on Example 2

Fe Q Ϊ) hydroxides output and working solution parameters change at continuous process on Example 3

Fe (HI) hydroxides output and working solution parameters change at continuous process on Example 4

FeCHI) hydroxides output indices and specific power expenses at continuous device operation on applied method in comparison with known

Table 5.

Note: the summary power consumption includes the consumption for solution heating, theπnostating, air supply, pumps operation.

Claims

1. The method of iron hydroxides and oxides recovery by oxidation and dissolving of elementary iron, including contact of iron containing raw material with solution, containing bacteria capable to oxidize Fe (II) into Fe (III), sedimentation of formed suspension of iron hydroxides and oxides, sediment separation, its washing with further drying and in the case of necessity annealing of the final product, wherein all process stages are conducted at the same temperature and dissolving of iron containing raw material and iron hydroxides and oxides synthesis is carried out simultaneously in one vessel with periodically substitution of the part of the solution for circulating solution at simultaneous suspension separation with iron oxides and hydroxides recovery.

2. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the temperature of all process stages is set by the type and, or strain of used bacteria.

3. The method of iron hydroxides and oxides recovery as set forth in claim 2 wherein Thiobacillus ferrooxidans BKM-B458 bacteria are used. At the temperature lower than 40°C.

4. The method of iron hydroxides and oxides recovery as set forth in claim 2 wherein at temperature higher than 40°C thermophile bacteria are used, for example Thiobacillus termo-ferrooxidans.

5. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the process is conducted continuously with constant circulating solutions supply into the reactor.

6. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the suspension is additionally aerated by air before separation.

7. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the iron hydroxide and oxide suspension after separation from the solution is re suspended by water, which after iron hydroxides and oxides separation is used as a circulating solution.

8. The method of iron hydroxides and oxides recovery as set in claim 7 wherein the water is supplied by counter flow.

9. The method of iron hydroxide and oxide recovery as set forth in claim 7 wherein at re suspension of iron hydroxides and oxides by water, the suspension is additionally aerated by air.

10. The method of iron hydroxides and oxides recovery as set in claim 7 wherein at re suspension alkali is brought into the solution, for example NH₄ OH, up to the acidity index pH > 7,0.

11. The method of iron hydroxide s and oxides recovery as set forth in claim 1 wherein recovered iron hydroxides and oxides are used as additives to iron containing fertilizers.

12. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the recovered iron hydroxides and oxides are used as additives to iron containing preparations for iron deficit replenishment at animals and human beings.

13. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the recovered iron hydroxides and oxides are used at powder iron production.

14. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the recovered iron hydroxides and oxides are used at steel production.

15. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the recovered iron hydroxides and oxides are used at magnetic powders production.

16. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the iron hydroxides and oxides depending on annealing temperature are used as pigments of various colors.

17. The method of iron hydroxides and oxides recovery as set forth in claim 1 wherein the part of circulating solution after the settled iron hydroxides and oxides separation are treated by the solution of potassium ferrocyanide, separated and washed the formed sediment ("Prussian blue"- blue pigment) and the filtrate is evaporated and K₂ S0 is separated.