WO2024213945A1

WO2024213945A1 - Adsorbent composition modified by a metal, its preparation method, method of adsorbing phosphorus or phosphate, composition comprising adsorbed phosphorus or phosphate, and its use as a fertilizer

Info

Publication number: WO2024213945A1
Application number: PCT/IB2024/052212
Authority: WO
Inventors: Ariana MACIEL ABRANCHES PINTOR; Cidália BOTELHO; Manuel FERNANDO RIBEIRO PEREIRA; Nuno FERNANDO RODRIGUES E SOUSA; Olivia SALOMÉ GONÇALVES PINTO SOARES
Original assignee: Universidade do Porto
Current assignee: Universidade do Porto
Priority date: 2023-04-10
Filing date: 2024-03-07
Publication date: 2024-10-17
Anticipated expiration: 2025-10-10

Abstract

The invention refers to an adsorbent composition modified by a metal comprising a biochar generated in the pyrolysis of a cork biomass modified by the metal, wherein said metal is selected from a group consisting of magnesium, zinc, barium, nickel, iron, lanthanum or copper, or their mixtures. The adsorbent composition modified by a metal according to the invention presents technical advantages regarding elevated values referred to magnesium fixation, surface area and/or phosphorus or phosphate adsorption capacity, which make it suitable for being used in adsorbing phosphate from liquid compositions, namely wastewater. The compositions comprising adsorbed phosphorus or phosphate are further proper to be used as fertilizers.

Description

ADSORBENT COMPOSITION MODIFIED BY A METAL, ITS PREPARATION METHOD, METHOD OF ADSORBING PHOSPHORUS OR PHOSPHATE, COMPOSITION COMPRISING ADSORBED PHOSPHORUS OR PHOSPHATE, AND ITS USE AS A FERTILIZER

The present invention refers to adsorbent compositions comprising biochar, which is modified by metals, derived from biomass, with the purpose of phosphorus or phosphate adsorption and their use as fertilizers.

In the prior art, biochars modified with magnesium, derived from lignocellulosic biomass are known and are produced with the purpose of phosphorus/phosphate adsorption from water.

Patent application No. WO2013126477A1 of Gao Bin et al., entitled “biochar/metal composites, methods of making biochar/metal composites, and methods of removing contaminants from water” and published on August 29^th, 2013; describes the production of magnesium-modified biochar from sugar beet tailings, with application in phosphate adsorption.

Fang, C. et al. (2014), “Application of Magnesium Modified Corn Biochar for Phosphorus Removal and Recovery from Swine Wastewater”, Int. J. Environ. Res. Public Health 2014, 11(9), 9217-9237; describes the production of magnesium-modified biochars from corn biomass and applies them to the uptake of phosphate from swine wastewater.

Patent application No. CN112169759A of Liao Xuepin et al, entitled “Vinasse biochar and preparation method and application thereof” and published on May 5^th, 2021; reveals a method for the production of magnesium-modified biochar from vinasse to be applied in phosphorus adsorption.

Fang, Y. et al. (2022), “Preparation and characterization of MgO hybrid biochar and its mechanism for high efficient recovery of phosphorus from aqueous media”, Biochar 4, 40 (2022); discloses the production of magnesium-modified biochar from food waste and its application in phosphorus adsorption.

Technical Problem

The adsorbent compositions modified by a metal identified in the prior art have limited and poor results regarding magnesium fixation, surface area, and/or phosphate adsorption capacity.

Still, there is a need to develop adsorbent compositions modified by a metal, and their preparation methods to obtain significant properties that may enhance phosphate adsorption capacity, namely for wastewaters.

Therefore, there is a lack of sustainable solutions referring to biochars able to recover phosphorus from aqueous media, contributing to reducing the eutrophication in a certain ecosystem, besides providing a biochar comprising adsorbed phosphate, which may be used later as a fertilizer.

Solution to Problem

The present invention solves the problems of the prior art by selecting cork as a biomass source for pyrolysis, which is previously impregnated with a salt of a metal selected from a group consisting of magnesium, zinc, barium, nickel, iron, lanthanum, or copper, or their mixtures.

Moreover, in the preferred embodiments of the invention, the pyrolysis of the impregnated cork powder, particulates or granulates is executed under an atmosphere of N₂ and CO₂.

Advantageous Effects of Invention

The adsorbent composition modified by a metal according to the invention presents technical advantages regarding elevated values referred to magnesium fixation, surface area, and/or phosphorus or phosphate adsorption capacity.

Indeed, the operational conditions of the pyrolysis step contribute to the opening of the pore structure, transforming the biomass into a carbon matrix (biochar) with incorporated magnesium oxide particles, resulting in the increase of the surface area, and fixation of magnesium.

To promote an understanding of the principles by the embodiments of the present invention, reference will be made to the embodiments illustrated in the figures and to the language used to describe the same. Anyway, it must be understood that there is no intention of limiting the scope of the present invention to the contents of the figures. Any alterations or later changes of the inventive features illustrated herein, and any additional application of the principles and embodiments of the invention shown, which would occur normally for one skilled in the art when reading this description, are considered as being within the scope of the claimed invention.

Fig.1

shows N₂ adsorption and desorption isotherms regarding samples of biochar generated in the pyrolysis of a cork biomass modified by magnesium and comparative examples;

Fig.2

illustrates the effect of pH on phosphorus adsorption by a composition according to the invention;

Fig.3

illustrates a phosphorus adsorption isotherm using the Langmuir isotherm model fitted to the experimental data;

Fig.4

illustrates a preferred embodiment of a preparation method of an adsorbent composition modified by a metal according to the invention.

The present invention refers, in the first aspect, to a preparation method of an adsorbent composition modified by a metal, wherein said adsorbent composition comprises a biochar generated in the pyrolysis of a cork biomass modified by the metal, and said preparation method comprises the following steps:

a) contacting at least one of powder, particulates, or granulates of cork biomass with an aqueous solution of at least a salt of the metal, obtaining cork biomass impregnated with cations of said metal; and

b) executing a pyrolysis step of said cork biomass impregnated with cations of said metal, obtaining a biochar generated in the pyrolysis of a cork biomass modified by the metal; and

wherein said metal is selected from a group consisting of magnesium, zinc, barium, nickel, iron, lanthanum, or copper, or their mixtures.

In the preferred embodiments of the invention, the preparation method of an adsorbent composition modified by a metal further comprises the following steps executed before the step of contacting at least one of powder, particulates, or granulates of cork biomass with an aqueous solution of at least a salt of the metal:

a1) Washing at least one of powder, particulates, or granulates of cork biomass with water, obtaining washed cork biomass;

a2) Drying said washed cork biomass, obtaining dry washed cork biomass.

The washing step contributes to removing impurities and phenolic compounds which may leach from the cork, wherein water is a preferred solvent for this operation.

In the preferred embodiments of the invention, the preparation method of an adsorbent composition modified by a metal further comprises the following step executed after obtaining cork biomass impregnated with cations of said metal, and before the step of pyrolysis:

b1) Drying said cork biomass impregnated with cations of said method, obtaining dry impregnated cork biomass.

In the preferred embodiments of the invention, the preparation method of an adsorbent composition modified by a metal further comprises the following steps executed after obtaining a biochar generated in the pyrolysis of a cork biomass modified by the metal:

c) Washing said biochar generated in the pyrolysis of a cork biomass modified by the metal, obtaining a washed biochar generated in the pyrolysis of a cork biomass modified by the metal;

d) Drying said washed biochar generated in the pyrolysis of a cork biomass modified by the metal, obtaining a dry biochar generated in the pyrolysis of a cork biomass modified by the metal.

The washing step contributes to removing impurities resulting from the pyrolysis step and excess metals, for instance, magnesium, which were not fixated on the biochar structure wherein water is a preferred solvent for this operation.

Preferably, any one of the washing steps a1) or c) is executed at a temperature in the range from 10ºC to 95ºC for at least 5 minutes. More preferably, any one of the washing steps a1) or c) is executed at a temperature in the range from 20ºC to 60ºC for 5 minutes to 24 hours, even more preferably for 15 minutes to 2 hours.

Preferably, any one of the drying steps a2), b1) or d) is executed at a temperature in the range from 50ºC to 120ºC. More preferably, any one of the drying steps a2), b1) or d) is executed at a temperature in the range from 60ºC to 85ºC for 2 to 48 hours, even more preferably for 10 to 24 hours.

In the preferred embodiments of the invention, in the step of contacting at least one of powder, particulates, or granulates of cork biomass with an aqueous solution of at least a salt of the metal, the concentration of said metal is in the range from 0.05 to 5 M, more preferably in the range from 1 to 3 M.

In the preferred embodiments of the invention, in the step of pyrolysis, the temperature in the step of pyrolysis is in the range from 500 to 1000ºC, more preferably in the range from 600 to 850ºC.

The pyrolysis step is executed in an inert atmosphere, meaning non-reactive atmosphere, comprising an inert gas, for instance nitrogen, argon, helium, or mixtures thereof. Preferably, said inert atmosphere can comprise further gases, for instance carbon dioxide. The inert atmosphere comprises at least 50 % in volume of an inert gas or mixtures thereof, more preferably comprises from 50 to 95 % in volume of an inert gas or mixtures thereof. Preferably, the pyrolysis of the cork biomass impregnated with cations of said metal is executed under an atmosphere of N₂ and CO₂. In these embodiments, the atmosphere composition comprises N₂ in the range from 50 to 95 % in volume, more preferably from 70 to 90 %, and CO₂in the range from 5 to 50 % in volume, more preferably from 10 to 30 %. The pyrolysis step contributes to the opening of the pore structure, transforming the biomass into a carbon matrix (biochar) with incorporated metal oxide particles, for instance, magnesium oxide particles. The pyrolysis promotes the increase of the surface area and the fixation of magnesium.

As illustrated in , in the preferred embodiments of the invention, the preparation method of an adsorbent composition modified by a metal further comprises the following steps:

a1) Washing (100) at least one of powder, particulates, or granulates of cork biomass (1) with water (2), obtaining washed cork biomass (3); and

a2) Drying (200) said washed cork biomass (3), obtaining dry washed cork biomass (4); and

a) Contacting (300) dry washed cork biomass (4) with an aqueous solution of at least a salt of the metal (5), obtaining cork biomass impregnated with cations of said metal (6); and

b1) Drying (400) said cork biomass impregnated with cations (6), obtaining dry impregnated cork biomass (7); and

b) executing a pyrolysis step (500) of said dry impregnated cork biomass (7), obtaining a biochar generated in the pyrolysis of cork biomass modified by the metal (8); and

c) Washing (600) said biochar generated in the pyrolysis of a cork biomass modified by the metal (8), obtaining a washed biochar generated in the pyrolysis of a cork biomass modified by the metal (9); and

d) Drying (700) said washed biochar generated in the pyrolysis of a cork biomass modified by the metal (9), obtaining a dry biochar generated in the pyrolysis of a cork biomass modified by the metal (10).

The present invention refers, in the second aspect, to an adsorbent composition modified by a metal comprising:

a carbon-containing material, which is a biochar generated in the pyrolysis of a cork biomass modified by the metal; and

the metal is selected from a group consisting of magnesium, zinc, barium, nickel, iron, lanthanum, or copper, or their mixtures.

Preferably, said metal is derived from at least a salt of general formula M_xA_y;

wherein M is a cation selected from a group consisting of magnesium, zinc, barium, nickel, iron, lanthanum, or copper; and

wherein A is an anion selected from a group consisting of chloride, bromide, iodide, hydroxide, sulfate, carboxylate, carbonate, nitrate, or acetate; and

wherein x and y are independent integers of value equal or superior to 1 selected to provide the valence of the cation M according to the valence of the combined anion A; and

wherein said salt is contacted with at least one of powder, particulates, or granulates of cork biomass before the pyrolysis of a cork biomass.

In the most preferred embodiments, M is magnesium, and A is chloride.

Preferably, the dry biochar generated in the pyrolysis of a cork biomass modified by the metal comprises fixed carbon in a mass percentage from 1% to 20% in relation to its overall mass, more preferably from 2% to 10%.

Preferably, the dry biochar generated in the pyrolysis of a cork biomass modified by the metal comprises metal in a mass percentage from 20% to 50% in relation to its overall mass, more preferably from 30% to 40%.

Preferably, the dry biochar generated in the pyrolysis of a cork biomass modified by the metal comprises ashes in a mass percentage from 50% to 80% in relation to its overall mass, more preferably from 55% to 70%. Ashes refers to the inorganic residue that remains after the organic material has been heated and decomposed, which comprises small amounts of inorganic minerals and metals that were present in the original material.

The present invention refers, in the third aspect, to a method of adsorbing compounds containing at least one of phosphorus or phosphate, wherein said method comprises a step of contacting an adsorbing composition modified by a metal, as defined in the second aspect of the invention, with a liquid composition comprising a compound containing at least one of phosphorus or phosphate, obtaining a composition modified by a metal comprising adsorbed phosphorus or phosphate. Preferably, the liquid composition comprises wastewater. In these embodiments, the method of adsorbing phosphorus or phosphate by an adsorbing composition modified by a metal from a liquid composition, namely wastewater, is executed in a pH in the range from about 2 to about 4, more preferably about 3.

The present invention refers, in the fourth aspect, to the composition modified by a metal comprising adsorbed phosphorus or phosphate, which is prepared by the method defined in the third aspect.

The present invention refers, in the fifth aspect, to the use of the composition modified by a metal comprising adsorbed phosphorus or phosphate, which is defined in the fourth aspect of the invention, as a fertilizer.

As it will be understood by a person skilled in the art, the composition modified by a metal comprising adsorbed phosphorus or phosphate, according to the fourth aspect of the invention, is separated from the processed liquid composition or wastewater by a conventional liquid-solid separation, namely filtration, centrifugation, decanting or using a hydrocyclone separator. Optionally, the composition modified by a metal comprising adsorbed phosphorus or phosphate is dried at a temperature in the range from 50ºC to 120ºC, preferably in the range from 60ºC to 85ºC for 2 to 48 h, even more preferably for 10 to 24 h.

Examples

a) Example of a preparation method and obtained product

An exemplary formulation of an adsorbent composition modified by a metal of the present invention is prepared according to the following example:

The preparation method of an adsorbent composition modified by a metal starts with contacting granulates of cork biomass with an aqueous solution of magnesium chloride. The cork powder, particulates, or granulates are obtained from Quercus suber L. and present a particle size equal or below to 8 mm, wherein the particle size refers to the average particle diameter. The use of this biomass as a feedstock for producing biochar contributes significantly to many of the unique characteristics of the adsorbent composition of the present invention.

Firstly, the granulates of cork biomass are washed in distilled water, at a proportion of 10 g/L, for 3 cycles of 2 hours each, at 60 ºC. This procedure allows the removal of impurities from the material and leaches water-soluble compounds in cork that might be detrimental in water treatment applications. After washing, the material is then dried in an oven at a temperature in the range from 60ºC to 85ºC for 10 to 24 h.

The dry-washed granulates of cork biomass are then impregnated with the modifier, namely the magnesium, by contacting the dry-washed granulates of cork biomass in a rotating shaker with a magnesium chloride solution of 2.3 mol/L, typically for 2 h, at a solid/liquid ratio of 20 g/L and a temperature of 20 ºC. This step allows the magnesium to penetrate and be fixed in the cork structure during the pyrolysis step. After the time of contact, the impregnated biomass is dried in an oven at a temperature in the range from 60ºC to 85ºC for 10 to 24 h. The mass of dry-impregnated granulates of cork biomass is over 5 times higher than before impregnation.

Afterward, the impregnated biomass is subject to a pyrolysis step under an atmosphere of N₂ and CO_2,wherein the atmosphere comprises N₂ or other inert gas, such as helium (He) or argon (Ar) in the range from 50 to 95 % in volume, preferably between 70 and 90%, and CO₂ in the range of 5 to 50 % in volume, preferably between 10 and 30%. During the pyrolysis step, the flow rate was adjusted to 100 cm³/min and a temperature of 600 ºC or higher (heating ramp 10 ºC/min) was set up, with a typical duration of 1 hour at the highest temperature. Pyrolysis under N₂ rich atmosphere degrades the cork components, transforming them into carbon, and opening the pore structure, substantially increasing the surface area. This process also stabilizes magnesium, incorporating it into the structure and transforming it into magnesium oxide, which is more difficult to solubilize. Fixation of magnesium in the structure is improved by using CO₂ in a small proportion (higher proportions of CO₂ decrease the yield too much, resulting in small quantities of material). The temperature needs to be above 600 ºC for magnesium to react with CO₂ in the atmosphere and for complete degradation of the cork components. The typical material is produced at this temperature, but higher temperatures can be used, with a decrease in yield but an increase in surface area and magnesium fixation.

Finally, the obtained biochar generated in the pyrolysis of a cork biomass modified by magnesium is washed with distilled water for 2 cycles of 15 min, followed by drying in an oven at a maximum temperature of 100 ºC. In this step, the excess magnesium, which was not incorporated in the structure with enough stability, is washed out so as not to interfere with the application in water treatment.

The resulting dry biochar generated in the pyrolysis of a cork biomass modified by magnesium has a particle size below that of the original biomass, even though its total mass increases. The mass yield from cork biomass to the final product is in the range from 113 to 123 %, due to the incorporation of magnesium.

In the preferred embodiments, the dry biochar generated in the pyrolysis of a cork biomass modified by the metal comprises magnesium in a mass percentage from 30.0% to 38.5% in relation to its overall mass. Preferably, the pyrolysis is executed at a temperature in the range from 600 ºC to 850ºC. The yield of pyrolysis alone is in the range from 23.1 to 33.9 %, and from the granulates of cork biomass impregnated with cations of magnesium to the dry biochar generated in the pyrolysis of a cork biomass modified by magnesium is in the range from 18.7 to 22.8 %.

The BET surface area indicates the available surface for adsorption and was calculated to be 109-176 m²/g (range 600 ºC-850ºC of pyrolysis). The pore volume was estimated to be between 0.21-0.30 cm³/g, also by N₂ adsorption.

The dry biochar generated in the pyrolysis of a cork biomass modified by magnesium has the necessary characteristics to be applied for phosphorus adsorption from water, namely wastewater. Its maximum adsorption capacity is estimated to be 232 mg phosphorus /g dry biochar generated in the pyrolysis of a cork biomass modified by magnesium at a pH of 3 and a temperature of 20 ºC.

Comparative examples

b) Synthesis of unmodified cork biochar

Unmodified cork biochar, without impregnation of magnesium, was synthesized in the laboratory to provide a comparison with a biochar generated in the pyrolysis of a cork biomass modified by magnesium, following a similar methodology:

Cork granulates from Quercus suber L. with a particle size in the range from 0.5 to 1 mm were washed in distilled water in a beaker, with mechanical agitation, with a solid/liquid ratio of 10 g/L, for 3 cycles of 2 hours at 60 ºC. They were then dried overnight in an oven at 60 ºC.

The washed cork granulates were then pyrolyzed in a vertical tubular furnace (Termolab) using an N₂:CO₂ mixed flow with a 100 cm₃/min flow rate. The heating ramp was set up at 10 ºC/min until the final temperature of 850 ºC, which was kept for 1 h.

The pyrolyzed cork was then washed with distilled water in a rotating shaker (Stuart, SB3) at 20 rpm, in 50 mL Falcon tubes, for 2 cycles of 15 min each. After each cycle, the biochar was separated by filtration in quantitative filter paper.

The biochar was dried overnight in an oven at 60 ºC and stored in an airtight container. We will refer to this sample as P850.

c) Synthesis of magnesium-modified cork biochar with only N₂

Magnesium-modified cork biochar was synthesized in the laboratory using only N₂ gas for pyrolysis. This biochar provided a comparison to highlight the effect of CO₂ on the atmosphere composition. We used the following steps:

Cork granulates from Quercus suber L. having a particle size in the range from 0.5 to 1 mm were washed in distilled water in a beaker, with mechanical agitation, with a solid/liquid ratio of 10 g/L, for 3 cycles of 2 hours at 60 ºC. They were then dried overnight in an oven at 60 ºC.

The washed cork granulates were then put in contact with a magnesium chloride solution (prepared from MgCl₂.6H₂O, VWR International) with a concentration of 2.3 mol/L in 50 mL Falcon tubes in a rotating shaker at 20 rpm. The temperature was kept at 20 ºC, the solid/liquid ratio was 20 g/L, and the contact time was 2 h. After this time, the cork granulates were separated from the liquid and dried for 48 hours in an oven at 60 ºC.

The impregnated cork granulates were subject to pyrolysis in a vertical tubular furnace, using an N₂ flow with a total flow rate of 100 cm₃/min. The heating ramp was 10 ºC/min until the final temperature of 850 ºC, which was kept for 1 h.

The biochar was dried overnight in an oven at 60 ºC and stored in an airtight container. We will refer to this sample as N850.

d) Synthesis of magnesium-modified cork biochar using according to the invention

The biochar generated in the pyrolysis of a cork biomass modified by magnesium was synthesized in the laboratory according to the preparation method according to the invention, using two different pyrolysis temperatures: 600 ºC and 850 ºC. The following steps were used:

Cork granulates from Quercus suber L. having a particle size in the range from 0.5 to 1.0 mm were washed in distilled water in a beaker, with mechanical agitation, with a solid/liquid ratio of 10 g/L, for 3 cycles of 2 hours at 60 ºC. The washed granulates of cork biomass were then dried overnight in an oven at 60 ºC.

The dry-washed granulates of cork biomass were then put in contact with a magnesium chloride solution with a concentration of 2.3 mol/L in 50 mL Falcon tubes in a rotating shaker at 20 rpm. The temperature was kept at 20 ºC, the solid/liquid ratio was 20 g/L, and the contact time was 2 h. After this time, the cork granulates were separated from the liquid and dried for 48 hours in an oven at 60 ºC.

The dry-impregnated granulates of cork biomass were subjected to pyrolysis in a vertical tubular furnace using an N₂:CO₂ mixed flow with a 100 cm³/min flow rate. The heating ramp was 10 ºC/min until the final temperature of 600 ºC or 850 ºC, which was kept for 1 h.

Each batch of biochar generated in the pyrolysis of a cork biomass modified by magnesium was washed with distilled water in a rotating shaker at 20 rpm, in 50 mL Falcon tubes, for 2 cycles of 15 min each. After each cycle, the samples of washed biochar generated in the pyrolysis of a cork biomass modified by magnesium were separated by filtration in quantitative filter paper.

The samples of washed biochar generated in the pyrolysis of a cork biomass modified by magnesium were dried overnight in an oven at 60 ºC and stored in an airtight container. We will refer to these samples as C600 and C850.

e) Calculation of yields

Yields of the produced biochar generated in the pyrolysis of a cork biomass modified by the metal were calculated using the following formulas:

The yield from the initial product (granulates of cork biomass) to the final product (washed biochar):

The yield of pyrolysis, from impregnated cork to pyrolyzed cork (before washing):

The yield from impregnated cork to the final product (washed biochar):

The yield results are shown in Table 1.

Sample
P850	14.0 %	15.0 %	-
N850	107.0 %	22.7 %	22.1 %
C600	112.9 %	33.9 %	22.8 %
C850	123.5 %	21.4 %	18.7 %

f) Determination of magnesium content

The magnesium content in the biochars was determined by acid digestion of the solid using a mixture of distilled water, nitric acid (HNO₃), and hydrochloric acid (HCl). The mixture was heated to 150 ºC with a ramp of 10 ºC/min and kept at this temperature for 2 hours to solubilize all metallic components. Before the acid digestion, the mass of the biochar was measured (m_biochar).

The liquid was then vacuum filtered using cellulose acetate filters (pore size 0.45 µm) and completed to 100 mL with distilled water. The concentration of magnesium (C_Mg) was analyzed in the volume of liquid (V_liquid) using flame atomic absorption spectroscopy (equipment GBC 932 Plus). Before analysis, the metal was stabilized using a lanthanum oxide modifier in a 1:10 (v/v) proportion. The analysis was carried out at a wavelength of 202.6 nm, with a lamp current of 3 mA and a slit width of 1 nm. The concentration range was 0.5-15 mg/L, and dilutions were performed whenever necessary.

The magnesium content in the biochar was then calculated by the following equation:

The determination was not carried out for the unmodified cork biochar, as magnesium is assumed to be inexistent in this sample. For the other samples, the achieved results are presented in table 2.

Sample	Mg _biochar (mg/g)	Mg content
N850	239.1	23.9 %
C600	299.6	30.0 %
C850	385.4	38.5 %

g) Determination of moisture, ash, fixed carbon, and volatile content

The moisture, ash, fixed carbon, and volatiles content were determined through thermogravimetric analysis (TGA) (equipment Netzsch STA 409 PC). This analysis was carried out for the samples of biochar generated in the pyrolysis of a cork biomass modified by magnesium and for the raw biomass.

A small sample mass was heated under a flow rate of 30 cm³/min of N₂ from 50 ºC to 900 ºC, with a ramp of 10 ºC/min, while the mass loss (ml) was measured. At the temperature of 100 ºC, the mass loss was registered as the humidity/water content of the sample (ml_100ºC). At the maximum temperature of 900 ºC, two isothermal steps were carried out: a first one during 7 min under a flow rate of 30 cm³/min of N₂(ml_after _N2), and a second one during 13 min under a flow rate of 40 cm³/min of air (ml_after _air). The moisture was calculated relative to the initial mass (m_initial), and the ash, fixed carbon, and volatiles content were calculated relative to the dried mass (without moisture), using the values of mass loss registered at each of these steps:

The results regarding moisture, ash, fixed carbon, and volatiles contents are shown in table 3.

Sample	Moisture	Ash	Fixed carbon	Volatiles
Cork biomass	0.75 %	1 %	3 %	96 %
N850	0.33 %	56 %	16 %	28 %
C600	0.58 %	56 %	2 %	42 %
C850	0.26 %	70 %	8 %	22 %

h) Determination of BET surface area and pore volume

The specific surface area and pore volume were determined using N₂ adsorption isotherms at -196 ºC, acquired in the equipment Quantachrome NOVA 4200e. Each sample was submitted first to a degasifying step at 150 ºC for 3 h. Afterward, they were contacted with liquid nitrogen at -196 ºC with increasing partial pressure, enabling the retrieval of the N2 adsorption isotherms in terms of partial pressure vs adsorbed amount. The desorption branches were also registered as the partial pressure decreased afterward. All the biochar samples and the raw cork biomass were analyzed according to this technique.

Using the software Quantachrome NovaWin, the data from N₂ adsorption isotherms were used to calculate the BET surface area in the partial pressure range between 0.05 and 0.3, and the total pore volume was quantified at the partial pressure of 0.99.

The adsorption/desorption isotherms registered for the abovementioned conditions are shown in .

The estimated BET surface areas and pore volumes are presented in table 4.

Sample	BET surface area (m ² /g)	Pore volume (cm ³ /g)
Cork biomass	25	0.02
P850	280	0.16
N850	59	0.21
C600	109	0.21
C850	176	0.30

i) Determination of BET surface area and pore volume

The phosphorus adsorption was tested by batch adsorption tests using the produced materials. The batch adsorption tests were carried out in 50 mL Falcon tubes, where 45 mL of phosphorus solution (prepared by dilution of a VWR standard solution of 1000 mg/L of phosphate in H₂O) at pH 3 (adjusted using HCl) with a concentration of 25 mg P/L were put in contact with 90 mg of biochar (corresponding to a solid/liquid ratio of 2 g/L), and shaken in a rotating shaker at 20 rpm for 24 hours at 20 ºC. After this time, the aqueous solution was filtered in syringe acetate cellulose filters (0.45 μm pore size) and analyzed for P. A control test without biochar was carried out simultaneously.

Analysis of P in the solution was carried out using a colorimetric method with ascorbic acid (Standard Methods 4500-P E) in the range from 0.11 to 1.00 mg/L. Dilutions were performed whenever necessary. The developed color by the addition of combined reagent was measured at 880 nm in a UV-Vis molecular absorption spectrophotometer (Unicam Helios α).

The results for the adsorbed amount of P in these conditions are presented in table 5.

Sample	Adsorbed P (mg/g)
Cork biomass	0
P850	0
N850	4.9
C600	12.3
C850	12.4

Because the difference between the samples using the invention methodology (C600 and C850) was minimal in these conditions, the test parameters were changed to test if the materials could adsorb higher amounts and whether a difference could be observed in such conditions. The P concentration was increased to 100 mg/L in the aqueous solution, and the biochar mass was decreased to only 22.5 mg (corresponding to a solid/liquid ratio of 0.5 g/L).

In these new conditions, the results for the adsorbed amount of P are presented in table 6.

Sample	Adsorbed P (mg/g)
C600	174
C850	175

j) Effect of pH on adsorption

Since the previous results showed that the biochar generated in the pyrolysis of a cork biomass modified by the metal, produced using the invention’s preparation method, has a similar capacity for phosphorus adsorption from a pyrolysis temperature of 600 ºC to higher, further studies were conducted, with the magnesium-modified biochar produced at 600 ºC.

Batch adsorption tests were carried out in similar operating conditions as before, but at different pH levels, from 3 to 9, to confirm that the pH of about 3 is a preferred pH for phosphorus adsorption. The pH was adjusted using HCl or NaOH. The initial P concentration was 100 mg/L, the solid/liquid ratio was 0.5 g/L, and the contact time was 24 h.

The results for the adsorbed amount of P are reflected in , wherein it is confirmed that in the preferred embodiments, the pH of a liquid composition in the method of absorbing phosphate is in the range from 2 to 4, wherein most preferably the pH 3 is more favorable for phosphorus adsorption in the 3-9 range.

k) Phosphorus adsorption isotherm

The phosphorus adsorption isotherm was also drawn based on equilibrium batch adsorption tests using the biochar generated in the pyrolysis of a cork biomass modified by magnesium produced at 600 ºC in similar conditions. The solid/liquid ratio was 0.5 g/L, the contact time was 48 h, the initial pH was 3, and the initial concentration of P was varied between 10 and 100 mg/L.

The Langmuir isotherm model was fitted to the experimental data to estimate the maximum adsorption capacity achievable by the biochar:

Where q_e (mg/g) is the adsorbed amount of P at equilibrium with the concentration of P in the aqueous solution C_e (mg/L), K_L is the Langmuir constant (L/mg) and q_max (mg/g) is the maximum adsorption capacity.

The isotherm in graphical form is presented in . The Langmuir model was fitted using the software CurveExpert Professional 2.6.4. with the following results presented in table 7.

Parameter	Value
K _L (L/mg)	0.17 ± 0.06
q *_max* (mg/g)	232 ± 36
R ²	0.972
SE (standard error)	12

l) Specifications of an example of a dry biochar generated in the pyrolysis of a cork biomass modified by magnesium

The specifications of a biochar produced from cork biomass is presented in table 8, which has a residual honeycomb structure observable by microscopy and incorporated magnesium in its structure (for example, in the form of magnesium oxide particles).

Parameter	Value
Particle size	< 1 mm;
Yield from cork biomass to final product	113-123 %
Yield of pyrolysis	23.1-33.9 %
Yield from impregnated biomass to final product	18.7-22.8 %
Magnesium content	30.0-38.5 %
Ash content	56-70 %
Fixed carbon	2-8 %
Volatiles	22-42 %
Moisture content	0.26-0.58 %
N₂ BET surface area	109-176 m²/g
Pore volume	0.21-0.30 cm³/g
Experimental maximum P adsorbed amount	174-175 mg/g
Estimated Langmuir maximum P adsorption capacity	232 mg/g

As used in this description, the expressions “about” and “approximately” refer to a range in values of roughly 10% of the specified number.

As used in this description, the expression. “substantially” means that the real value is within an interval of about 10% of the desired value, variable or related limit, particularly within about 5% of the desired value, variable or related limit or particularly within about 1% of the desired value, variable or related limit.

Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is unless specified otherwise, or clear from the context, the phrase “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B.

In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form.

Further, as used herein, the term “exemplary” is intended to mean serving as an illustration or example of something and is not intended to indicate a preference.

The subject matter described above is provided as an illustration of the present invention and must not be interpreted to limit it. The terminology used with the purpose of describing specific embodiments, according to the present invention, must not be interpreted to limit the invention. As used in this description, the definite and indefinite articles, in their singular form, aim to include in the interpretation the plural forms, unless the context of the description explicitly indicates the contrary. It will be understood that the expressions “comprise” and “include”, when used in this description, specify the presence of the characteristics, the elements, the components, the steps, and the related operations, but do not exclude the possibility of other characteristics, elements, components, steps, and operations from being also contemplated.

All modifications, providing that they do not modify the essential features of the following claims, must be considered within the scope of protection of the present invention.

100. a washing step of cork biomass with water;

200. a first drying step;

300. a contacting step of at least one of powder, particulates, or granulates of cork with an aqueous solution of at least a salt of the metal;

400. a second drying step;

500. a pyrolysis step;

600. a washing step of biochar with water;

700. a third drying step;

1. powder, particulates, or granulates of cork biomass;

2. water;

3. washed cork biomass;

4. dry-washed cork biomass;

5. an aqueous solution of at least a salt of the metal;

6. cork biomass impregnated with cations

7. dry impregnated cork biomass;

8. a biochar generated in the pyrolysis of cork biomass modified by the metal;

9. washed biochar generated in the pyrolysis of a cork biomass modified by the metal;

10. dry biochar generated in the pyrolysis of a cork biomass modified by the metal.

Patent Literature

patent application No. WO2013126477A1 of Gao Bin et al., entitled “biochar/metal composites, methods of making biochar/metal composites, and methods of removing contaminants from water” and published on August 29th, 2013;

patent application No. CN112169759A of Liao Xuepin et al, entitled “Vinasse biochar and preparation method and application thereof” and published on May 5th, 2021;

Non Patent Literature

Fang, C. et al. (2014), "Application of Magnesium Modified Corn Biochar for Phosphorus Removal and Recovery from Swine Wastewater", Int. J. Environ. Res. Public Health 2014, 11(9), 9217-9237; https:/doi.org/10.3390/ijerph110909217;

Fang, Y. et al. (2022), "Preparation and characterization of MgO hybrid biochar and its mechanism for high efficient recovery of phosphorus from aqueous media", Biochar 4, 40 (2022). https:/doi.org/10.1007/s42773-022-00171-0.

Claims

A preparation method of an adsorbent composition modified by a metal, characterized in that, said adsorbent composition comprises a biochar generated in the pyrolysis of a cork biomass modified by the metal and said preparation method comprises the following steps:
a) Contacting at least one of powder, particulates, or granulates of cork biomass with an aqueous solution of at least a salt of the metal, obtaining cork biomass impregnated with cations of said metal; and
b) executing a pyrolysis step of said cork biomass impregnated with cations of said metal, obtaining a biochar generated in the pyrolysis of a cork biomass modified by the metal; and
wherein said metal is selected from a group consisting of magnesium, zinc, barium, nickel, iron, lanthanum or copper, or their mixtures.
The preparation method of an adsorbent composition modified by a metal, according to the previous claim, wherein it further comprises the following steps executed before the step of contacting at least one of powder, particulates, or granulates of cork biomass with an aqueous solution of at least a salt of the metal:
a1) Washing at least one of powder, particulates, or granulates of cork biomass with water, obtaining washed cork biomass;
a2) Drying said washed cork biomass, obtaining dry washed cork biomass.
The preparation method of an adsorbent composition modified by a metal, according to any of the previous claims, wherein it further comprises the following step executed after obtaining cork biomass impregnated with cations of said metal, and before the step of pyrolysis:
b1) Drying said cork biomass impregnated with cations of said method, obtaining dry impregnated cork biomass.
The preparation method of an adsorbent composition modified by a metal, according to any of the previous claims, wherein it further comprises the following steps executed after obtaining a biochar generated in the pyrolysis of a cork biomass modified by the metal:
c) Washing said biochar generated in the pyrolysis of a cork biomass modified by the metal, obtaining a washed biochar generated in the pyrolysis of a cork biomass modified by the metal;
d) Drying said washed biochar generated in the pyrolysis of a cork biomass modified by the metal, obtaining a dry biochar generated in the pyrolysis of a cork biomass modified by the metal.
The preparation method of an adsorbent composition modified by a metal, according to any of the previous claims, wherein in the step of contacting at least one of powder, particulates, or granulates of cork biomass with an aqueous solution of at least a salt of the metal, the concentration of said metal is in the range from 0.05 to 5 M.
The preparation method of an adsorbent composition modified by a metal, according to any of the previous claims, wherein the temperature in the step of pyrolysis is in the range from 500 to 1000ºC.
An adsorbent composition modified by a metal characterized by comprising:
a carbon-containing material, which is a biochar generated in the pyrolysis of a cork biomass modified by the metal; and
the metal is selected from a group consisting of magnesium, zinc, barium, nickel, iron, lanthanum or copper, or their mixtures.
The adsorbent composition modified by a metal, according to the previous claim, wherein said metal is derived from at least a salt of general formula M_xA_y;
wherein M is a cation selected from a group consisting of magnesium, zinc, barium, nickel, iron, lanthanum, or copper; and
wherein A is an anion selected from a group consisting of chloride, bromide, iodide, hydroxide, sulfate, carboxylate, carbonate, nitrate, or acetate; and
wherein x and y are independent integers of value equal or superior to 1 selected to provide the valence of the cation M according to the valence of the combined anion A; and
wherein said salt is contacted with at least one of powder, particulates, or granulates of cork biomass before the pyrolysis of a cork biomass.
The adsorbent composition modified by a metal, according to any of the claims 7 to 8, wherein the dry biochar generated in the pyrolysis of a cork biomass modified by the metal comprises fixed carbon in a mass percentage from 1% to 20% in relation to its overall mass.
The adsorbent composition modified by a metal, according to any of the claims 7 to 9, wherein the dry biochar generated in the pyrolysis of a cork biomass modified by the metal comprises metal in a mass percentage from 20% to 50% in relation to its overall mass.
The adsorbent composition modified by a metal, according to any of the claims 7 to 10, wherein the dry biochar generated in the pyrolysis of a cork biomass modified by the metal comprises ashes in a mass percentage from 50% to 80% in relation to its overall mass.
The adsorbent composition modified by a metal, according to any of claims 7 to 11, wherein it is prepared by the method defined in any one of claims 1 to 6.
A method of adsorbing compounds containing at least one of phosphorus or phosphate, characterized by the said method comprising a step of contacting an adsorbing composition modified by a metal, as defined in any of the claims 7 to 12, with a liquid composition comprising a compound containing at least one of phosphorus or phosphate, obtaining a composition modified by a metal comprising adsorbed phosphorus or phosphate.
The method of adsorbing compounds, according to the previous claim, wherein the liquid composition comprises wastewater.
A composition modified by a metal comprising adsorbed phosphorus or phosphate, characterized by being prepared by the method defined in any one of the claims 13 to 14.
A use of the composition modified by a metal comprising adsorbed phosphorus or phosphate, characterized by being defined in the previous claim, as a fertilizer.