NL2023428B1

NL2023428B1 - Separating phosphate from treated sewer sludge

Info

Publication number: NL2023428B1
Application number: NL2023428A
Authority: NL
Inventors: Carlo Rem Peter; Petrus Maria Berkhout Simon
Original assignee: Univ Delft Tech
Priority date: 2019-07-03
Filing date: 2019-07-03
Publication date: 2021-02-02

Abstract

The present invention is in the field of iron phosphate recovery from an aqueous stream such as waste flow, sewage or another sludge stream, comprising providing an aqueous fluid comprising the phosphate, adding iron, forming iron phosphate, 5 and separating the iron phosphate. The iron phosphate may be vivianite.

Description

Separating phosphate from treated sewer sludge

FIELD OF THE INVENTION The present invention is in the field of a method and system for iron phosphate recovery from an agueous stream such as waste flow, sewage or another sludge stream, comprising providing an aqueous fluid comprising the phosphate, adding iron, forming iron phosphate, and separating the iron phosphate. The iron phosphate may be vivianite.

BACKGROUND OF THE INVENTION A phosphate is a chemical derivative of phosphoric acid. The phosphate ion (P0374) is an inorganic chemical, the conjugate base that can form many different salts. Many phosphates are not soluble in water at standard temperature and pressure. Phosphate is useful for animals and for plants. Phosphates are a naturally occurring form of the element phosphorus, found in many phosphate minerals. Inorganic phosphates are mined to obtain phosphorus for use in agriculture and industry. Depending on source of information the supply of phosphorous at the current rate of consumption is considered to run out the next 100 years. However, large parts of the world already suffer from a shortage of phosphorous resources. Phosphate, or phosphorous is often a limiting nutrient in many environments. It is used widely, and it is also washed out from the environment, such as into waste water and into sewage plants. In waste water phosphorous is often a source of eutrophication.

It is known to remove phosphorus from waste water to prevent eutrophication in effluent receiving surface waters and its phosphate is considered an important compound to be retrieved.

Conventional techniques include enhanced biological phosphorus removal (EBPR) and chemical phosphorus removal (CPR). Phosphate could become at least partly circular by extracting phosphate minerals from waste water streams, such as manure and sewer sludge. This is however typically rather expensive and inefficient.

Conventional phosphorus recovery from waste water may involve the production of struvite (NHsMgPOs -6H20) in EBPR plants and/or phosphorus recovery from sludge ash. It is known that struvite precipitation enables recovery of phosphorus. However, 40 the efficiency to recover phosphorus as struvite is typically only in the range of 10-50% of the total influent phosphorus load. Also, struvite precipitation is limited to plants using EBPR.

In a previous application (WO 2018/169395 Al) a method and system for recovery of phosphate were identified. However, upon further experimentation said method and systems using gravity did not function very well; unexpectedly it was found difficult to retrieve sufficient amounts of phosphorous in high yields as phosphate could not be separated efficiently. For the high- gradient magnetic field concept it was considered that for practical situations, such as for sewer sludge treatment, this concept would be too expensive and too complicated in terms of maintenance.

Some further documents reciting phosphate recovery are mentioned below. In view of the present invention these are considered to relate to background art.

EP 2 666 759 Al recites addition of an iron salt to wastewater containing phosphates. However, the amount of phosphate recovered is relatively low.

CN 104 445 555 A recites a similar process, with good conversion percentages of phosphate into vivianite, but the document seems silent on actual phosphate recovery.

US 5,888,404 A recites a method for phosphate recovery using iron, raising the pH, and recovering an alkali phosphate salt, and then adding HCl. In terms of chemicals this method seems rather expensive.

CA 252 656 Al recites that wastewater from an anaerobic treatment system can be treated to obtain vivianite.

The present invention therefore relates to an improved method and apparatus for recovering iron phosphate, which solves one or more of the above problems and drawbacks of the prior art, providing reliable results, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION It is an object of the invention to overcome one or more limitations of the methods and devices of the prior art and at the very least to provide an alternative thereto. In a first aspect the present invention relates to an apparatus for recovering iron phosphate, or likewise a salt mineral, from an 40 aqueous liquid, or likewise aqueous fluid. The apparatus is adapted to operate in a continuous mode, but can also be operated in a semi-continuous mode, e.g. with intervals between inflowing quantities of aqueous liquid.

An issue with the present invention is that the aqueous liguid has a relatively high dynamic viscosity of >50 mPa*s, such as due to the presence of fibres.

This makes recovery and separation of particles more difficult in general.

The apparatus comprises at least one input for providing an acueous liguid comprising iron phosphate particles, wherein the input is provided at a side of the apparatus, often the upper side of said apparatus, and is directed towards at least one surface for concentrating iron phosphate particles, wherein said surface has a height of > 10 cm, at least one outlet for the aqueous liquid, wherein the inlet is provided above the outlet, wherein the output is provided below the input , a (main) layer generator disposed between the at least one inlet and the at least one outlet upstream of the at least one surface for generating a layer of aqueous liquid passing along said surface, wherein a force, perpendicuiar to said surface, applied by said generator to said liquid is > 5 N/kg liquid, preferably >100 N/kg, and a divider tor dividing said layer into a first sub-layer comprising iron phosphate particles adjacent to said surface, wherein adjacent may be directly adjacent or with one or more layer between said first sub-layer and said surface, and a second sub-layer comprising mainly aqueous liquid and optionally organic material, wherein the main layer thickness is preferably 2-5 mm, wherein said divider may be located at a distance of < 5mm from said surface, and typically wherein the divider is located at a bottom end of the surface, such as at the bottom.

It was found that the concentration of small phosphate mineral particles of 10 -100 micron that are present in the aqueous liquid, such as a treated sewer sludge, was very efficient, especially as the layer generator provided a relative thin layer.

The phosphate minerals may be concentrated at an outer side of the liquid layer being formed, or at an inner side thereof, depending on the type of apparatus.

In an example the phosphate mineral particles travel only a few millimeters towards the boundary of the liquid layer, such as towards the collecting surface, through the liquid.

Thereafter the mineral was concentrated and

40 separated from the liquid.

In contrast to the above prior art applications, using for instance only gravity to separate the iron phosphate, the iron phosphate could be concentrated and separated adequately. It is considered that in the prior art systems particles could not be separated for instance by hindrance due to fibrous material being inherently present in treated sewer sludge, the fibrous material “capturing” the iron phosphate, and due to too long travel length of the particles. The present apparatus and method are therefore in particular suited for aqueous liquids that comprise impurities, such as fibers and other particles. These fibers may have typical lengths of 0.1-5 mm, such as 0.2-3 mm, and a diameter of 30-500 um, such as 50-250 um. The present apparatus comprising the layer generator overcomes the prior art problems. It is noted that the present apparatus is most suited for liquids comprising small particles, such as iron phosphate.

In the present apparatus a thin layer of an aqueous liquid, such as sewer sludge, was subjected to a force to drive fine iron phosphate mineral to the boundary of the liguid layer where it was collected. A remainder of the aqueous liquid flowed away such as along the surface. The force was thereafter reduced, or absent, the surfaces washed with water, and a concentrate of phosphate mineral was obtained. Also, a flow of liquid, such as the sewer sludge, was processed with an industrial separator. A concentrate of iron phosphate was obtained. In an example an aqueous liquid, such as the treated sewer sludge, flows in a thin layer {or film) along a wall of a centrifugal separator, typically with a vertically oriented axis. The thin layer was split a first part being closer than e.g. 1 mm to the separator wall, and a second part of layer being further away. A good 3C separation of iron phosphate was obtained. An aqueous liquid, such as treated sewer sludge, was in comparison processed in several types of separators, such as a jig and a cyclone, using only gravity. In these latter tests no successful concentration of iron phosphate minerals was cbtained.

It has therefore been shown that concentration of phosphate minerals from an aqueous fluid by converting the liquid into a thin layer of preferably less than 5 mm thick, and creating a differential force on the minerals by the present apparatus, forces the minerals towards at least one of the surfaces of the 40 layer. A large fracticn of the minerals can be collected and therewith separated from the liguid on the magnetic surface.

In a second aspect the present invention relates to a method of continuously recovering iron phosphate, or likewise a salt mineral, comprising providing an apparatus according to the 5 invention, providing an agueous fluid with a dynamic viscosity > 50 mPa*s ((@20 °C; ASTM D445) comprising iron phosphate particles, optionally adding iron cations to the aqueous fluid, such as Fet and Fe?*, preferably as a chloride salt, forming further mineral iron phosphate particles, passing the fluid as a layer over the surface of the apparatus, forcing iron phosphate particles towards the boundary of the fluid layer, dividing the fluid in at least two sub-layers, wherein a first sub-layer comprises iron phosphate particles adjacent to a surface thereof, and a second sub-layer comprises mainly aqueous liquid, wherein the first sub-layer has a thickness of < 5mm, removing the second sub-layer, and recovering the iron phosphate particles from the first sub-layer. It is preferred to use forces such that a substantially laminar flow is obtained. The iron phosphate is preferably formed and present as vivianite (Fe?*Fe?*; (P04) 2.8H20) . The iron phosphate is typically hardly soluble in water. It is noted that the present method may be performed at the pH of the agueous liquid and thereby keeping the pH substantially constant during the method, such as between 5-9, preferably between 6-8; such is contrary to some prior art methods wherein the pH may be raised, and may be lowered, or both, at the expense of consumption of chemicals and typically also of energy. The concentration of phosphate (in the form of soluble phosphorous) in the fluid may be freely chosen and is typically found to be 1-10000 ppm/l, or 1074-1 mass %, in waste water. By optionaily adding iron and typically forming small particles, such as of 10 um-100 pm size, the phosphate can be removed almost completely from the aqueous liquid. The diameter of the particles formed is typically from 100 nm-500 um, more typically from 1 pum-300 pm, such as 10 pm-109 um. The particles are found to travel towards the surface with a typical speed of

0.1-20 mm/s, such as 0.2-10 mm/s, under the conditions applied. Drag forces limit the speed of the particles. Typical velocities of the aquecus liquid along the surface are between 0.01 m/s and

0.2 m/s (centrifuge) and between 0.5 m/s and 1.5 m/s (spiral). 40 Therewith an efficient and inexpensive method is provided for recovering phosphate. The present apparatus can easily extract a part, such as 5-25%, of treated waste water, e.g. at a rate of 2-20 m?/h, as a concentrate of phosphate.

In a third aspect the present invention relates to a method of continuously recovering mineral salt particles comprising providing an apparatus according to the invention, passing the solution as a layer and forcing the mineral salt towards the boundary of the fluid layer, and recovering the salt. Typical details provided for the iron phosphate recovery method and apparatus as provided throughout the description and claims apply to these salts as well, mutatis mutandis.

The present invention provides a solution to one or more of the above-mentioned problems and overcomes drawbacks of the prior art.

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION In an exemplary embodiment of the present apparatus the thin layer generator is selected from a a hydro cyclone, a centrifugal force generator, a spiral separator, and combinations thereof.

In an exemplary embodiment of the present apparatus the divider comprises a sharp edge, and wherein the divider is preferably provided at a bottom side of the surface.

In an exemplary embodiment of the present apparatus at least two parallel and/or at least serial inputs and outputs are provided.

In an exemplary embodiment the present apparatus comprises a surface cleaner, wherein the surface cleaner is preferably selected from a scraper, a knife, a blade, and combinations thereof, preferably a movable surface cleaner.

In an exemplary embodiment of the present apparatus the surface is selected from an interior of a cylinder, an interior of a cone, an interior of a sphere, an interior of a hemisphere, and combinations thereof, and/or wherein one direction of said surface is adapted to be substantially parallel to the direction of earth gravitation force. The cone may be provided with a surface widening from a top to the bottom, under an angle of e.g. 60-80 degrees. A similar shape may be provided for the 40 sphere or hemisphere,

In an exemplary embodiment of the present apparatus the layer generator is adapted to rotate at a speed of 300-3000 rpm, preferably 500-2000 rpm, such as 600-1500 rpm, e.g. 1200 rpm. The speed may be adapted in view of a radius of the generator, a large radius requiring a relatively lower speed.

In an exemplary embodiment of the present apparatus the input is directed towards an upper side cf said surface, such as the top of the surface.

In an exemplary embodiment of the present apparatus the input comprises at least one nozzle, a sprayer, a tube, and combinations thereof. As such the aqueous liquid is spread out over the surface and a goed concentration with a high flow rate can be obtained.

In an exemplary embodiment of the present apparatus a diameter of the surface is smaller at a top side thereof than at a bottom side thereof.

In an exemplary embodiment of the present method impurities are removed from the iron phosphate and/or at least one surface, such as by washing.

In an exemplary embodiment of the present method the iron phosphate is removed from the surface of the apparatus, such as by the surface cleaner, and thereafter recovering iron phosphate, preferably wherein >50% of phosphate of the aqueous fluid comprising phosphate is removed, typically > 80%, such as > 90%.

In an exemplary embodiment of the present method cycles of (1) forcing iron phosphate to the boundary of the fluid layer, (ii) optionally removing impurities, and (iii) recovering iron phosphate from the first sub-layer, are repeated.

In an exemplary embodiment of the present methed 2-100 cycles are performed.

In an exemplary embodiment of the present method at least three flows are produced, a first output flow comprising recovered iron phosphate, a second flow comprising mainly the aqveous fluid, and a third flow at least partly stripped from iron phosphate.

In an exemplary embodiment of the present method the viscosity of the aqueous fluid is 100%10-3-1 Pa*s, preferably 200*10-3-5%10"1 Pa*s, such as 5*%*10-2-1*10-1 Pa*s, 40 In an exemplary embodiment of the present method an average downward flow speed is 0.5-5 m/s, such as 1-3 m/s.

In an exemplary embodiment of the present method an average residence time is 0.2-10 sec, preferably 1-5 sec,.

In an exemplary embodiment of the present method an average iron phosphate particle size is 100 nm-500 pm, preferably 1 um- 300 pm, such as 10 pm-100 pm.

In an exemplary embodiment of the present method a concentration of iron phosphate is 1-10000 ppm/l, preferably 200-5000 ppm/l, such as 1000-2500 ppm/l.

In an exemplary embodiment of the present method the input flow of a single separation unit is 0.1-10 1l/sec, preferably

0.2- 5 l/sec, such as 0.5-3 l/sec.

In an exemplary embodiment of the present method a Reynolds number of a fluid passing along the at least one surface is maintained between 0.1-100, preferably between 1-50.

In an exemplary embodiment of the present method a diameter of the surface is 10-100 cm, such as 20-50 cm.

In an exemplary embodiment of the present method a height of the surface s 10-1000 cm, such as 20-600 cm.

In an exemplary embodiment of the present method where the surface is rotated, the surface is provided under an angle of 0- 30 degrees with respect to an axis of rotation, preferably 15-20 degrees, that is mostly parallel to the axis of rotation.

In an exemplary embodiment of the present method vivianite is obtained.

In an exemplary embodiment of the present method the aqueous fluid is a processed fluid from an organic digester.

In an exemplary embodiment the present method a pH of the aqueous fluid is maintained, such as the pH of the initial aqueous fluid, before removing and concentrating the iron phosphate, or between 6-9.

In an exemplary embodiment of the present method the layer is thinner than 5 mm, preferably thinner than 3 mm.

In an exemplary embodiment of the present method the first fluid sub-layer is thinner than 2 mm, preferably thinner than

1.5 mm, more preferably thinner than 1 mm, such as 0.1-1.0 mm, and likewise the second fluid sub-layer is thinner than 4 mm, preferably thinner than 3 mm, more preferably thinner than 2 mm, such as 0.5-1.5 mm.

4G In an exemplary embodiment of the present method the aqueous fluid has a has a dynamic viscosity (Q@20 °C; ASTM D445) of 0.01- 1 Pa*s.

In an exemplary embodiment of the present method the aqueous fluid has a kinematic viscosity (@20 °C; ASTM D445) of 10-1000 mm?/s.

In an exemplary embodiment of the present method the agueous fluid has a density of 0.99-1.9 g/cm3.

In an exemplary embodiment of the present method the aqueous fluid comprises fibres, such as fibres with a length of 10-3mm- 10mm, such as 50%1073mm~Imm, and a diameter of 1-100 um, such as 5-80 um. These fibres may be cellulose based fibres, organic fibres, and combinations thereof.

In an exemplary embodiment the present methed further comprises post-treatment of the iron phosphate, such as washing, dissolving, acidifying, and combinations thereof.

The invention will hereafter be further elucidated through the following examples which are exemplary and explanatory of nature and are not intended to be considered limiting of the invention. To the person skilled in the art it may be clear that many variants, being cbvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

SUMMARY QF THE FIGURES Figs. 1-2, 3a-c show some details of the present apparatus.

DETAILED DESCRIPTICN OF FIGURES In the figures: i0 apparatus 1 input 2 output 3 surface 4 divider 5 scraper 6 first sub-layer 7 second sub-layer Figure 1 shows a schematic view of the present apparatus 10 with a cylindrical surface 3, an input 1 and output 2.

Figure 2 shows a schematic view of a conical apparatus 10, with surface 3, gravitational force Fy and centrifugal force Fe. Also a cross-section A-A’ is given.

Figs. 3a-c show worked-open views of fig. 2, along section 40 A-A’. A divider 4 and scraper 5 are shown (fig. 3b). Divider 4 is placed at a distance d from surface 3 (fig. 3c), whereas scraper 5 substantially is at a negligible distance from said surface. Divider 4 separates a liquid surface layer into a first sub-layer 6 and second sub-layer 7 (fig. 3a). Examples In a comparative example vivianite is concentrated in a high-gradient magnetic separator, which is a semi-batch process. Vivianite is concentrated on a magnetic surface until it is almost saturated. Then the power supply and the magnet are stopped. The vivianite is then rinsed from the magnetic surface with water. This process is then repeated. If it is stopped too © late, the entire magnetic surface is found to be saturated and the vivianite no longer adheres to the magnetic surface, causing recovery to slow down. If it is stopped too early and the magnetic surface is not yet completely covered, the capacity of the separator is not optimally utilized.

The present gravitational separator with a thin liquid layer can separate continuously. Even if a layer of magnetic material would be applied to the surface of the separator. In the case of a spiral separator a separation force of > 5 N/kg, such as 10 N/kg is used, with a longer residence time; also the divider is located at a bottom end and in view of flow of first and second sub-layers may be rotated over 90 degrees and is located closer to a central part of the spiralseparator. In the case of a centrifugal separator a force of 100 N/kg and 1000 N/kg was used, with a shorter residence time.

Further Experiments Earlier experiments performed at TU Delft seemed to show a successful recovery of Vivianite from sewer sludge with a Jones high-gradient magnetic separator, whereas experiments using “gravity” separators like cyclones and jigs were disappointing. These results were initially interpreted as a sign that Vivianite should be recovered applying magnetic driving forces. However, Jones separators also differ from cyclones and jigs in that the minerals are migrating over very small distances (ca 1 mm), across a flowing layer. In cyclones and jigs minerals travel across a bulk flow with dimensions of ca 0.1 m. Considering the very viscous and fibre-rich sewer sludge, this latter aspect was found to be important. It was found important 40 to only apply the force across a liquid layer flow and to separate the section of the layer in which the driving force has concentrated the minerals from the rest of the layer. This conclusion allows for two major improvement over Jones-type separation in term of cost and complexity of separation, namely to avoid the complex cyclic use of the surface in a Jones-type separator (1. collecting minerals on the steel surface, then 2. switching off the sludge flow and the magnetic force, and 3. washing the minerals from the steel surface with a water flow,

4. starting up the magnetic field and the sludge flow again), and to use cheap gravity forces instead of the more expensive magnetic forces. The improved recovery method of Vivianite recovery then involves a flowing layer of liquid, such as sludge, say 1-5 mm thick, applying a force based on gravity, magnetism, or a combination of the two, driving the Vivianite across the thickness of the layer towards one of its two bounding surfaces, and separation of the part of the layer containing the concentrated Vivianite from the rest of the layer. Two separators that could be used are a centrifuge, in which a layer flows downward along a cylinder’s or cone’s inner surface. The centrifugal force resulting from the rotation of the cylinder or cone around its axis drives the Vivianite towards the inner surface of the cylinder/cone. A scraper then separates the depleted part cf the layer (far from this surface) from the concentrate (near the surface); and a spiral separator (common in mineral processing), in which a layer flows down along a spiral surface. Gravity drives the mineral particles towards the bottom part of the layer. The “secondary flow” continuously moves the bottom part of the layer to the central axis of the spiral, while the top part of layer, which is depleted, moves away from the axis. The two parts of the layer can be collected as flows close and far from the central axis of the spiral. In order to test this analysis, two experiments were done, with a centrifuge and a spiral. Centrifuge sewer sludge was fed at ca 0.5 litre per second into the top of a rotating cylinder with an inner diameter of 240 mm and a height of 400 mm. The rotaticn speed was 1200 RPM. The input sludge contained 4% solids, of which 0.6% was Vivianite with 40 particle sizes (measured by microscope images) mainly in the range 40-150 micron while the rest of the solids was mainly organic and some sand. The film thickness turned out to be slightly over 1 nm. It was observed that while feeding the first 40 litres of the sludge, the two output flows (close to wall and far from the wall of the centrifuge) were both depleted from Vivianite, showing that the centrifugal force concentrates Vivianite across a film flow and make the particles stick to a surface, just as the magnetic force does in a Jones-type separator. More than 90% of the vivianite was recovered, and typically >95% is recovered. Spiral separator A Multotec SGD 1/75 spiral was fed with 1.3 litre per second of input sludge with 4% solids, including ca 1.2% minerals with 10-200 micron particle size. The first splitter was set such that the first product flow (the mineral concentrate} consisted of the output from the ditch of the spiral, about 25% of the volume of the input flow. It contained more than 50% of the mineral content of the input. For the sake of searching the following section is added which represents a translation of the subsequent section.

1. Apparatus for continuously recovering iron phosphate from an aqueous liquid with a dynamic viscosity >50 mPa*s comprising at least one input for providing the aqueous liquid comprising iron phosphate particles, wherein the input is provided at a side of the apparatus and is directed towards at least one surface for concentrating iron phosphate particles, wherein said surface has a height of > 10 cm, at least one outlet for the aqueous liquid, wherein the output is provided lower than the input, a layer generator disposed between the at least one inlet and the at least one outlet upstream of the at least one surface for generating a layer of aqueous liquid passing along said surface, wherein a force, perpendicular to said surface, applied by said generator to said liquid is > 5 N/kg, preferably >10 N/kg, and a divider for dividing said layer into a first sub-layer comprising iron phosphate particles adjacent to said surface, and a second sub-layer comprising mainly aqueous liquid, wherein sald divider is preferably located at a distance of < 5mm from said surface. 40 2. Apparatus according to embodiment 1, wherein the layer generator is selected from a hydro cyclone, a centrifugal force generator, a spiral separator, and combinations thereof.

3. Apparatus according to any of embodiments 1-2, wherein the divider comprises a sharp edge, and wherein the divider is preferably provided at a bottom side of the surface.

4. Apparatus according to any of embodiments 1-3, wherein at least two parallel and/or at least serial inputs and outputs are provided.

5. Apparatus according to any of embodiments 1-4, comprising a surface cleaner, wherein the surface cleaner is preferably selected from a scraper, a knife, a blade, and combinations thereof, preferably a movable surface cleaner.

6. Apparatus according to any of embodiments 1-5, wherein the surface is selected from an interior of a cylinder, an interior of a cone, an interior of a sphere, an interior of a hemisphere, and combinations thereof, and/or wherein one direction of said surface is adapted to be substantially parallel to the direction of earth gravitation force.

7. Apparatus according to any of embodiments 1-6, wherein the layer generator is adapted to rotate at a speed of 300-3000 rpm, preferably 500-2000 rpm, such as 600-1500 rpm.

8. Apparatus according to any of embodiments 1-7, wherein the input is directed towards an upper side of said surface.

9. Apparatus according to any of embodiments 1-8, wherein the input comprises at least one nozzle, a sprayer, a tube, and combinations thereof.

10. Apparatus according to any of embodiments 1-9, wherein a diameter of the surface is smaller at an top side thereof than at a bottom side thereof.

11. Method of continuously recovering iron phosphate, comprising providing an apparatus according to any of embodiments 1-10, providing an aqueous fluid with a dynamic viscosity > 50 mPa*s ((@20 °C; ASTM D445) comprising iron phosphate particles, optionally adding iron cations to the agueous fluid, such as Fe? and Fe?*, preferably as a chloride salt, forming further mineral iron phosphate particles, passing the fluid as a layer over the surface of the apparatus, forcing iron phosphate particles towards a boundary of the fluid 40 layer,

dividing the fluid in at least two sub-layers, wherein a first sub-layer comprises iron phosphate particles adjacent to a surface thereof, and a second sub-layer comprises mainly agueous liquid, wherein the first sub-layer has a thickness of < 5m, removing the second sub-layer, and recovering the iron phosphate particles from the first sub- layer.

12. Method according to embodiment 11, wherein impurities are removed from the iron phosphate particles and/or at least one surface, such as by washing.

13. Method according to any of embodiments 11-12, wherein the iron phosphate is removed from the surface of the apparatus, such as by the surface cleaner, and thereafter recovering iron phosphate, preferably wherein >50% of phosphate of the aqueous fluid comprising phosphate is removed.

14. Method according to any of embodiments 11-13, wherein cycles of (i) forcing iron phesphate to the boundary of the fluid layer, (ii) opticnally removing impurities, and (iii) recovering iron phosphate from the first sub-layer, are repeated.

15. Method according to embodiment 14, wherein 2-100 cycles are performed.

16. Method according to any of embodiments 11-15, wherein at least three flows are produced, a first output flow comprising recovered iron phosphate, a second flow comprising mainly the aqueous fluid, and a third flow at least partly stripped from iron phosphate.

17. Method according to any of embodiments 11-16, wherein the viscosity of the aquecus fluid is 100*10-3-1 Pa*s, and/or wherein an average downward flow speed is 0.5-5 m/s, and/or wherein an average residence time is 0.2-10 sec, and/or wherein an average iron phosphate particle size is 100 nm-500 pm, preferably 1 pm-300 um, such as 10 pm-100 um, and/or wherein a concentration of iron phosphate is 1-10000 ppm/l, and/or wherein an input flow is 0.1-10 l/sec, preferably 0.2-5 l/sec, such as 0.5-3 1/sec, and/or wherein a Reynolds number of the flow is maintained between 0.1- 10, preferably between 1-3, and/or wherein a diameter of the surface is 10-100 cm, and/or 40 wherein a height of the surface s 10-100 cm, and/or wherein the surface is provided under an angle of 0-30 degrees with respect to an axis of rotation, preferably 15-20 degrees.

18. Method according to any of embodiments 11-17, wherein a pH of the aqueous fluid is maintained.

19. Method according to any of embodiments 11-18, wherein a Reynolds number of a fluid passing along the at least one surface is maintained between 0.1-10.

20. Method according to any of embodiments 11-19, wherein the fluid layer is thinner than 5 mm, preferably thinner than 3 mm, more preferably thinner than 2 mm, such as 0.1-1.5 mm, and/or wherein the first fluid sub-layer is thinner than 2 mm, preferably thinner than 1.5 mm, more preferably thinner than 1 mm, such as 0.1-1.0 mm.

21. Method according to any of embodiments 11-20, wherein the aqueous fluid is a processed fluid from an organic digester, and/or wherein the aqueous fluid has a has a dynamic viscosity (820 °C; ASTM D445) of 0.01-1 Pa*s, and/or wherein the agueous fluid has a kinematic viscosity (@20 °C; ASTM D445) of 10-1000 mm2/s, and/or wherein the aqueous fluid has a density of 0.99-1.9 g/cm, and/or wherein the aqueous fluid comprises fibres, such as fibres with a length of 1073mm-10mm and a diameter of 1-100 um.

22. Method according to any of embodiments 11-21, further comprising post-treatment of the iron phosphate, such as washing, dissolving, acidifying, and combinations thereof.

23. Method of continuously recovering a mineral salt comprising providing an apparatus according to any of embodiments 1-10, providing an agueous solution comprising the mineral salt as particles, passing the solution as a layer and forcing the mineral salt towards the boundary of the liquid layer, and recovering the salt.

Claims

CONCLUSIONS

An apparatus for continuously recovering iron phosphate from an aqueous liquid having a dynamic viscosity> 50 mPa * s comprising at least one input for providing the aqueous liquid comprising iron phosphate particles, the input being provided and directed on one side of the apparatus is to at least one surface for concentrating iron phosphate particles, the surface having a height of> 10 cm, at least one outlet for the aqueous liquid, the output being provided lower than the input, a layer generator disposed between the at least one inlet and the at least one outlet upstream of the at least one surface for generating a layer of aqueous liquid passing along said surface, where a force, perpendicular to said surface, applied by said generator to said liquid is> 5 N / kg , preferably> 10 N / kg, and includes a divider for dividing said layer into a first sub-layer The iron phosphate particles adjacent to said surface, and a second sublayer comprising predominantly aqueous liquid, said distributor being preferably located at a distance of <5 mm from said surface.

Device according to claim 1, characterized in that the layer generator is selected from a hydrocyclone, a centrifugal force generator, a spiral separator, and combinations thereof.

3. Device as claimed in any of the claims 1-2, wherein the divider comprises a sharp edge, and wherein the divider is preferably arranged on an underside of the surface.

Device according to any one of claims 1-3, wherein at least two parallel and / or at least serial inputs and outputs are provided.

Apparatus according to any one of claims 1-4, comprising a surface cleaner, wherein the surface cleaner is preferably selected from a scraper, a knife, a blade, and combinations thereof, preferably a movable surface cleaner.

A device according to any one of claims 1 to 5, wherein the surface is selected from an interior of a cylinder, an interior of a cone, an interior of a sphere, an interior of a hemisphere, and combinations thereof, and / or one direction of said surface is adapted to be substantially parallel to the direction of gravity.

Device according to any one of claims 1-6, wherein the layer generator is adapted to rotate at a speed of 300-3000 rpm, preferably 500-2000 rpm, such as 600-1500 rpm.

The device of any one of claims 1-7, wherein the inlet is directed to a top of said surface.

The device of any of claims 1 to 8, wherein the inlet comprises at least one nozzle, a nozzle, a tube, and combinations thereof.

Device according to any of claims 1-9, wherein a diameter of the surface is smaller at a top side thereof than at a bottom side thereof.

A method for the continuous recovery of iron phosphate, comprising providing an apparatus according to any one of claims 1 to 10, providing an aqueous liquid having a dynamic viscosity> 50 mPa * s ((@ 20 ° C; ASTM D445) comprising iron phosphate particles, optionally adding iron cations to the aqueous liquid, such as Fe? t and Fe, preferably as a chloride salt, thereby forming further iron phosphate mineral particles, passing the fluid as a layer over the surface of the device, forcing iron phosphate particles to a boundary of the liquid layer, dividing the fluid into at least two sub-layers, a first sub-layer comprising iron phosphate particles adjacent a surface thereof, and a second sub-layer comprising predominantly aqueous liquid, the first sub-layer having a thickness of <5 mm removing the second sublayer, and recovering the iron phosphate particles from the first sublayer.

The method of claim 11, wherein 40 impurities are removed from the iron phosphate particles and / or at least one surface, such as by washing.

A method according to any one of claims 11-12, wherein the iron phosphate is removed from the surface of the device, such as by the surface cleaner, and thereafter recovering iron phosphate, preferably wherein> 50% phosphate of the aqueous liquid comprising phosphate is used. deleted.

A method according to any one of claims 11 to 13, wherein cycles of (i) forcing iron phosphate to the boundary of the liquid layer, (ii) removing any contaminants, and (iii) reclaiming iron phosphate from the first sublayer, are repeated .

The method of claim 14, wherein 2-100 cycles are performed.

A method according to any one of claims 11-15, wherein at least three streams are produced, a first output stream comprising recovered iron phosphate, a second stream mainly comprising the aqueous fluid, and a third stream at least partially depleted of iron phosphate.

A method according to any one of claims 11-16, wherein the viscosity of the aqueous liquid is 100 * 1073-1 Pa * s, and / or wherein an average downward flow velocity is 0.5-5 m / s, and / or where an average residence time is 0.2-10 sec, and / or where an average iron phosphate particle size is 100 nm-500 µm, preferably 1 µm-300 µm, such as 10 µm-100 µm, and / or where a concentration of iron phosphate is 1- 10000 ppn / l, and / or where an input flow is 0.1-10 l / sec, preferably 0.2-5 l / sec, such as 0.5-3 l / sec, and / or where a Reynolds number of the flow is maintained between 0.1-10, preferably between 1-3, and / or where a diameter of the surface is 10-100 cm, and / or where a height of the surface s is 10-100 cm, and / or wherein the surface is provided at an angle of 0-30 degrees to an axis of rotation, preferably 15-20 degrees.

A method according to any of claims 11-17, wherein a pH of the aqueous liquid is maintained.

40

The method of any of claims 11-16, wherein one

Reynolds number of a fluid passing the at least one surface is maintained between 0.1-10.

A method according to any one of claims 11-19, wherein the liquid layer is thinner than 5 mm, preferably thinner than 3 mm, more preferably thinner than 2 mm, such as 0.1-1.5 mm, and / or wherein the first liquid sublayer is thinner than 2 mm, preferably thinner than 1.5 mm, more preferably thinner than 1 mm, such as 0.1-1.0 mm.

A method according to any of claims 11-20, wherein the aqueous liquid is a processed liquid from an organic digester, and / or wherein the aqueous liquid has a dynamic viscosity (@ 20 ° C; ASTM D445) of 0.01- 1 Pars, and / or wherein the aqueous liquid has a kinematic viscosity (820 ° C; ASTM D445) of 10-1000 mm? / S, and / or wherein the aqueous liquid has a density of 0.99-1.9 g / cm? and / or wherein the aqueous liquid comprises fibers, such as fibers having a length of 1073 mm-10 mm and a diameter of 1-100 µm.

The method of any of claims 11-21, further comprising post-treating the iron phosphate, such as washing, dissolving, acidifying, and combinations thereof.

A method of continuously recovering a mineral salt comprising: providing an apparatus according to any one of claims 1 to 10, providing an aqueous solution comprising the mineral salt as particles, passing the solution as a layer and leaving the solution in a layer. forcing mineral salt to the boundary of the liquid layer, and reclaiming the salt.