EP1428228A4 - Particules de carbonne a activation magnetique pour adsorption de solutes a partir d une solution - Google Patents

Particules de carbonne a activation magnetique pour adsorption de solutes a partir d une solution

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Publication number
EP1428228A4
EP1428228A4 EP02706453A EP02706453A EP1428228A4 EP 1428228 A4 EP1428228 A4 EP 1428228A4 EP 02706453 A EP02706453 A EP 02706453A EP 02706453 A EP02706453 A EP 02706453A EP 1428228 A4 EP1428228 A4 EP 1428228A4
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EP
European Patent Office
Prior art keywords
activated carbon
carbon
magnetic
precursor
solution
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP02706453A
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German (de)
English (en)
Other versions
EP1428228A1 (fr
Inventor
Jan D Miller
Gustavo A Munoz
Saskia Duyvesteyn
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University of Utah Research Foundation UURF
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University of Utah Research Foundation UURF
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Publication of EP1428228A1 publication Critical patent/EP1428228A1/fr
Publication of EP1428228A4 publication Critical patent/EP1428228A4/fr
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y25/00—Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D15/00—Separating processes involving the treatment of liquids with solid sorbents; Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28002—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their physical properties
    • B01J20/28009—Magnetic properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C1/00—Magnetic separation
    • B03C1/005—Pretreatment specially adapted for magnetic separation
    • B03C1/01—Pretreatment specially adapted for magnetic separation by addition of magnetic adjuvants
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/30—Active carbon
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/30—Active carbon
    • C01B32/312—Preparation
    • C01B32/318—Preparation characterised by the starting materials
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/30—Active carbon
    • C01B32/312—Preparation
    • C01B32/336—Preparation characterised by gaseous activating agents
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/22—Treatment or purification of solutions, e.g. obtained by leaching by physical processes, e.g. by filtration, by magnetic means, or by thermal decomposition
    • C22B3/24—Treatment or purification of solutions, e.g. obtained by leaching by physical processes, e.g. by filtration, by magnetic means, or by thermal decomposition by adsorption on solid substances, e.g. by extraction with solid resins
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/283—Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/38—Organic compounds containing nitrogen
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • This invention relates to activated carbon with magnetic properties.
  • Activated carbon is used to remove any number of materials from liquids and gasses, for recovery of values or for the purification of a wide range of substances. It is used in the water, food, mining, automotive, chemicals, pharmaceutical and environmental industries. A common application of activated carbon is to adsorb ions, complexes and molecules from aqueous solutions, and the like. Accordingly, activated carbon has been used to extract dissolved metals, either to purify the water, and/or to recover valuable metallic values.
  • activated carbon is commonly used for removing organic molecules and heavy metals.
  • Water is commonly adulterated with pollutants from industrial activity, runoff from polluted sites, and from various other sources. These pollutants, which can range from various organic molecules and heavy metals must be removed to render the water safe and to comply with environmental regulations. This is often accomplished by contacting the polluted water with activated carbon. The treated water and the activated carbon are then separated, and the activated carbon is treated to dispose of the pollutants.
  • the water is often contacted with the carbon by passing the water through fixed beds of the carbon.
  • some operational efficiencies may be derived by mixing the water and carbon in, for example, a stirred tank. However, this requires separation by mechanical screening, or the like, to separate the carbon particles from the treated water.
  • activated carbon Another common application of activated carbon is to extract gold complexes from gold leach solutions.
  • Gold leaching in alkaline cyanide solutions has been studied extensively for more than 200 years, and it has been applied successfully at the industrial level for more than a century. The high recoveries, economics and simplicity of the process have made cyanide leaching the preferred route for gold dissolution from its ores.
  • Conventional gold recovery methods involve crushing and grinding of the gold ores followed by dissolution of the gold in an oxygenated alkaline cyanide solution.
  • Gold, dissolved as the Au(CN) " complex is recovered from solution by several methods, adsorption on activated carbons (carbon-in-pulp, carbon-in-leach and carbon-in-column processes) being a preferred method.
  • Activated carbons are used for gold recovery from solutions due to their high capacity for adsorption.
  • the adsorptive properties of activated carbon are a consequence of the highly developed micropore structure and of the surface functional groups generated during the production process.
  • Gold adsorption onto activated carbon is a diffusion- controlled process, where the size of the carbon particles plays an important role. In general, gold adsorption capacity and gold adsorption kinetics increase as the size of the activated carbon particles decrease.
  • powdered activated carbon currently cannot be used in gold recovery circuits, since both the carbon and the solids in suspension will have particle sizes of the same magnitude, thus, separation of the gold-loaded activated carbon from the slurry phase by screening, filtration, or sedimentation are not viable options.
  • a method to separate activated carbon particles from a liquid solution that avoids the problems of mechanical screening would be desirable. Since screening depends upon the particles having a relatively large size, abrasion or other unintended comminution, produces small particles which defeats the screening.
  • An alternative to screening would be magnetic separation, using a magnetic activated carbon. Magnetic carbons have been made by mixing or coating carbon or a carbon precursor with a magnetic material, usually with magnetite, and treating to activate or transform the carbon or carbon precursor. A problem with these materials is that the magnetic material is widely dispersed in the carbon particle or upon its surface. This is inherent in these compositions, since powdered magnetic material (magnetite) is used and in only a minor amount to impart the magnetic property.
  • the magnetic material is dispersed throughout a matrix as small particles of the carbon material, or concentrated upon the surface.
  • carbon fines are usually formed that are free the magnetic material and cannot be magnetically separated.
  • magnetic separation requires that the particles be relatively large to maintain their magnetic properties. Accordingly, the non-magnetic fines formed cannot be recovered.
  • the recovery requires relatively large carbon particles, the same as in mechanical screening, and fine carbon particles cannot be recovered.
  • the abrasion of the prior-art magnetic activated carbon materials also frees the magnetic material. This magnetic material must then be removed by screening. However, unfortunately, this screening also separates the abraded non-magnetic carbon fines with the freed magnetic particles, both of which are then lost.
  • United States Patent 2,479,930 discloses a process of precious metals recovery from ores using a magnetic activated carbon that can be recovered from solution using a magnetic separator.
  • United States Patent 4,260,523 discloses a method for forming a magnetized active carbon composition that consists essentially of mixing 100 parts of active carbon and 5- 100 parts by weight of a magnetized ferromagnetic material, and compressing the mixture to form pellets.
  • the ferromagnetic material has been previously subjected to a saturation magnetization treatment by application of a magnetic treatment prior to preparation of the mixture and the ferromagnetic material. Since these materials retain their magnetism after being subjected to saturation magnetism, they clearly have hard magnetism, which is not desired in separation and purification applications.
  • United States Patent 4,201 ,831 describes a physical mixture of a magnetic particulate material and an organic material that will decompose into "elemental" carbon, to produce a magnetic adsorbent composite.
  • the above patents all disclose magnetic carbons formed from mixtures including magnetic materials. As discussed above, these compositions require that the carbon particles retain a relatively large size to insure that the magnetic property is retained in the particle.
  • the activated carbon materials used in a solution such as in United States Patents 2,479,930 and 4,201,831
  • the handling of the carbon produces carbon fines, as the particles are abraded. These carbon fines usually have not retained any of the magnetic material and cannot be separated by a magnetic field. This results in the loss of the carbon and any material that was adsorbed upon the carbon.
  • the present invention provides a magnetic carbon wherein magnetic material is intimately or essentially homogeneously dispersed through the carbon particles such that even small carbon fines are magnetic.
  • the magnetic carbon of the invention has a soft magnetic property, and is a fine particle size magnetic activated carbon that has improved kinetic properties and adsorbs larger amounts of material per unit mass of carbon.
  • the present invention is a composition and process wherein magnetic material is intimately and essentially homogeneously mixed or combined with an activated carbon material. This allows a magnetic property to be retained even in small powder particles and allows magnetic separation for these small particles.
  • the process of the invention involves the intimate mixing or combining of a carbon precursor and a magnetic material precursor. The carbon precursor is contacted in a manner to form a blend of the carbon precursor and the magnetic material precursor where the carbon precursor and the magnetic material precursor are intimately mixed and integrated together.
  • the carbon precursor and the magnetic material precursor can be integrated together by any suitable method.
  • a preferred embodiment of the invention is where a magnetic precursor in solution is mixed with an organic material, and during the pyrolysis (carbonization) treatment, the ferromagnetic material is formed.
  • the carbon precursor is a porous material that readily absorbs a solution of the magnetic material precursor.
  • the porous carbon precursor is soaked in the solution for sufficient time to integrate enough magnetic material precursor into the porous material so that when the porous material is dried, carbonized and activated it has sufficient magnetic property to permit magnetic separation.
  • the exact magnetization for separation is dependent upon several variables, including exact size, size distribution and composition of the carbon particles, and is within the skill of a practitioner to determine.
  • Suitable porous materials include agricultural wastes that are soft and porous and allow easy impregnation of the magnetic precursor solution. These include pinewood sawdust and shavings, byproducts of lumber mills, sugar cane baggasse, a byproduct of cane sugar manufacturing, and lignin from softwoods, a byproduct of paper manufacturing. Other porous materials, such as porous plastic foams or water swellable plastic materials may also be suitable if they are capable of absorbing sufficient solution.
  • the carbon precursor may also be a carbon containing material that melts and becomes liquid and allows mixture with the magnetic material precursor. The carbon precursor must melt sufficient to allow an intimate mixture of the magnetic material and the carbon material in the final product.
  • Suitable materials include sugars and molasses that are byproducts of sugar manufacturing, and low melting, low density plastics.
  • the carbon-precursor may also be a material that is soluble in water, thus dissolving in the solution of the magnetic material precursor.
  • Such materials include sugars, molasses and other soluble carbohydrates that are byproducts of the food and paper manufacturing industries. Also suitable are water-soluble plastic materials.
  • the magnetic precursor may be any suitable compound that contains iron in any suitable form, which may be, but not limited to ferric iron, ferrous iron, or elemental iron.
  • Suitable magnetic precursors include, for example, compounds that are soluble in water to form iron ions in solution. These include, but are not limited to ferric and ferrous salts, such as ferrous chloride, ferric chloride, ferric nitrate, ferrous sulphate, ferric sulphate, and ferric citrate. These soluble compounds can be dissolved to form a solution and used to soak the carbon material precursor. In this manner it is integrated into porous carbon material precursors by the soaking the carbon precursor in the solution of the soluble compound.
  • solid or liquid iron materials that can be melted together with the carbon precursor material (such as a plastic or a starch) to form a homogeneous solid mixture or solution.
  • the carbon precursor material such as a plastic or a starch
  • solid iron materials are iron oxides (such as hematite (Fe O ) and magnetite (Fe 3 O 4 )), ferrous acetate, ferrous oxalate, or the iron salts listed before (ferrous chloride, ferric chloride, ferric nitrate, ferrous sulphate, ferric sulphate, and ferric citrate).
  • An example of a liquid iron source is iron pentacarbonyl.
  • a homogeneous mixture can also be formed using a water-soluble magnetic material and a water-soluble carbon precursor and dissolving both into homogeneous solution.
  • the requirement is that a homogeneous solution or molten mixture of the magnetic material precursor and the carbon material precursor be formed.
  • the magnetic activated carbon particles of the invention comprise a magnetic activated carbon with the ferromagnetic material nanometrically dispersed throughout the carbon.
  • the dispersion is essentially on a molecular level.
  • the product has a low remanent magnetization, so the application of a saturation magnetization treatment is unnecessary.
  • the small particle size of the magnetic activated carbon results in higher loading capacity of the adsorbed material and faster adsorption kinetics than prior-art activated carbon that cannot be manufactured with such a small size.
  • particle sizes can be much smaller.
  • a particle size between about 50 ⁇ m and 110 ⁇ m has been found suitable for magnetic separation, but particles sizes well outside of this range may be suitable depending upon the application. This size is generally included in the range considered powdered. Smaller sized particles are expected to be subject to magnetic separation, but smaller sizes become difficult to work with in industrial applications, and are not preferred.
  • a particle size between 53 and 106 ⁇ m has been used, as well as a particle size range of 150-
  • the present invention will result in higher gold loading capacity and faster gold adsorption kinetics than that of the traditional activated carbon currently used in industry. It is expected that the magnetic properties of the activated carbon will permit gold-loaded activated carbon recovery from slurry by any suitable magnetic separation method, such as a wet high intensity magnetic separator or magnetic drum separator, instead of the current screening process.
  • practice of the present invention will introduce more flexibility in how the activated carbon is contacted with the water, allowing mixed systems, instead of fixed bed systems, and dramatically reduce the amount of activated carbon required to achieve the desired purification. Separation of the activated carbon from the water can be achieved by known magnetic separation technologies.
  • the advantages of the present invention derive from the reality first, the very small particle size of the magnetic activated carbons results in higher adsorption kinetics than that of conventional granular activated carbon. Second, because the activated carbon is magnetic, it can easily be separated from streams to which it has been added, even from those that contain solids. Such improvements are expected to have significant economic impact on plant design and operation.
  • the improved adsorption capacity and kinetics can also result in further advantages.
  • concentration of the material in solution will be reduced much quicker, and in a continuous process the concentration will typically be much lower. Based on chemical principles, this will alter the equilibrium and the driving forces for reactions involving the adsorbed material.
  • gold extraction using cyanide solutions it is expected that the driving force from gold to the formation of the dissolved gold-cyanide complex will be increased. This in turn leads to further process efficiencies, such as lower reactor size, and lower cyanide requirements.
  • the magnetic activated carbon particles of the invention may be used in any application where activated carbon is required and where separation of the activated carbon is required.
  • the magnetic activated carbon may also be used in gas treatment applications where separations of the carbon from another process material, such as another particulate adsorbent or catalyst, are required.
  • Figure 1 is a graph showing weight loss and temperature profile during carbonization of an 18 x 30 mesh pinewood sample with no iron impregnation.
  • Figure 2 is a graph showing char yield vs. pyrolysis time for pinewood with different iron contents.
  • Figure 3 is a flow sheet showing a method for production of two magnetic activated carbon compositions of the invention and a comparative non-magnetic composition.
  • Figure 5 is a graph showing the magnetization curve of magnetite with a particle size of minus 5 mm.
  • Figure 6 is a graph showing the magnetization curve of FeCl 3 used as a precursor for the preparation of magnetic activated carbon (MAC).
  • Figure 7 is a graph showing the magnetization curve of Pinewood MAC with a particle size of 53 - 106 mm and 2.8 % Fe.
  • Figure 8 is a graph showing the magnetization curve of steel wool used as a magnetic matrix.
  • Figure 9 is a graph showing an XRD scan of pinewood.
  • Figure 10 is a graph showing an XRD scan of char from pmewood. Amount of Fe in char: 0%.
  • Figure 11 is a graph showing an XRD scan of char from pinewood. Amount of Fe in char: 1.1%.
  • Figure 12 is a graph showing an XRD scan of char from pmewood with the magnetite XRD spectra overlapped. Amount of Fe in char: 1.1%.
  • Figure 13 is a graph showing an XRD scan of MAC from pinewood. Amount of Fe in MAC: 1.4%.
  • Figure 14 is a graph showing an XRD scan of MAC from pinewood with the magnetite XRD spectra overlapped. Amount of Fe in MAC: 1.4%.
  • Figure 15 is a graph showing gold adsorption onto two different samples of powdered magnetic activated carbon with a particle size of minus 74 ⁇ m and on a conventional activated carbon. Adsorption conditions: 10 mg/L Au, 1 g/L NaCN, 1 g/L activated carbon, pH 11, 23 °C, 200 rpm.
  • Figure 16 is a graph, which is a magnification of the left-top corner of the graph shown in Figure 15.
  • Figure 17 is a graph showing the effect of burnoff degree and iron content of the different chars.
  • Figure 18 is a graph showing the loading capacity of a conventional activated carbon used for gold recovery.
  • Figure 19 is a graph showing the loading capacity of an activated carbon and a magnetic activated carbon.
  • MAC powdered magnetic activated carbon
  • the raw material was placed in a tube furnace at 300°K (27 °C ), and the temperature was raised to 900°K (627 °C) at a heating rate of 12 °K/min.
  • the pyrolyzed material was kept at that temperature to achieve 60 minutes of total heat treatment.
  • the pyrolyzed material was then transferred to another tube where it was cooled down to room temperature at a rate of 60 °K/min under a fixed N flow of 1.56 L/min calculated at STP.
  • the temperature of 900 °K was selected for wood pyrolysis based on published data and on experimental tests.
  • Figure 1 shows the weigh loss due to carbonization and temperature profile for a pinewood sample without iron impregnation.
  • Char is defined as the solid product resulting of a pyrolysis process applied to a carbon-containing material
  • char yield is defined as the percentage of char obtained from the dry carbon-containing material. In this particular process, char yield was found to be dependent on the concentration of iron solution used for impregnation, as can be seen on Figure 2.
  • the char produced was activated using a CO /N 2 atmosphere at 1200 °K.
  • the partial pressures of both gases were fixed at 0.42 atm., and flows for both gases were fixed at 1.56 L/min calculated at STP.
  • the char samples were left inside the tube furnace for enough time to produce a weight-loss of 21% to 50%. (burnoff degree).
  • the activated material was then transferred to another tube where it was cooled down to room temperature at a rate of 60 °K/min under a fixed N flow of 1.56 L/min calculated at STP.
  • the magnetic activated carbon (MAC) produced has a particle size of about 300- 600 ⁇ m. In order to make it powdered, it was wet-ground and sieved, and the particle size between 53 -106 ⁇ m used for gold recovery analysis and further characterization.
  • Figure 3 describes the MAC synthesis process.
  • Dry carbon 0.100 g was placed in 100 mL of a solution that contained 0.5 g/L NaCN and 10 mg/L Au at pH 11.
  • the carbon gold-cyanide slurry was placed in a 150-mL plastic bottle, and shaken at 200 rpm for 2 hours.
  • the solution was filtered and the gold content in solution was determined by inductively-coupled plasma emission spectroscopy (ICP).
  • ICP inductively-coupled plasma emission spectroscopy
  • Figure 5 shows the magnetization curve of magnetite. It shows that magnetite has a very high value of initial magnetic susceptibility, and exhibits saturation magnetization (J reaches a maximum value). After the magnetic field H is removed, magnetite shows remanent magnetization. This curve is characteristic of semipermanent or semihard magnets.
  • Figure 6 shows a magnetic curve for FeCl 3 , used as a precursor for the preparation of MAC. It shows a small value of magnetic susceptibility and does not show hysterisis. This behavior is characteristic of paramagnetic materials.
  • Figure 7 shows magnetization curves of pinewood magnetic activated carbon with 2.8% Fe. It shows hysterisis and has a high value of initial magnetic susceptibility. The plot also shows that it has a low value of remanent magnetization (J r ).
  • Figure 8 shows the magnetization curve for steel wool. It is used in the magnetic separator device as a matrix for magnetic separation. It has high values of initial magnetic susceptibility and saturation magnetization, and it has a low value of remanent magnetization. This behavior is characteristic of non-permanent or soft magnets.
  • MAC and the matrix show low values of remanent magnetization (the remaining magnetic forces are significantly small when compared to the forces applied in an effective magnetic separation), and the MAC can be separated from the matrix simply by gravity or with the aid of a water flush.
  • Figure 9 shows an XRD scan of pinewood.
  • the peaks at 2 ⁇ values of 15°, 16.5° and 22.8° are characteristic of cellulosic material.
  • the broadness of these peaks is characteristic of amorphous materials or material with short-range order.
  • Figure 10 shows an XRD scan of char obtained from pinewood with no iron impregnation.
  • the broad region in the 2 ⁇ region of 5°-35° is characteristic of the highly amorphous nature of the char.
  • Figure 11 is an XRD scan of a char from pinewood.
  • the amount of Fe in the char is 1.1 %.
  • the highly disorganized structure, characteristic of amorphous materials is evidenced in the broad peak region between the 2 ⁇ values of 5° to 30°. At 2 ⁇ values of 30.1°, 35.4°, 56.94°, and 62.51°, the peaks that correspond to magnetite are present. This can be visualized overlapping the magnetite XRD pattern as it is shown in Figure 12.
  • Figure 13 is an XRD scan of MAC from pinewood.
  • the amount of Fe in MAC is 1.4 %.
  • the highly disorganized structure, characteristic of amorphous materials is evidenced in the broad peak region between the 2 ⁇ values of 5° to 30°. At 2 ⁇ values of 30.1°, 35.4°, 56.94°, and 62.51°, the peaks that correspond to magnetite are present. This can be visualized overlapping the magnetite XRD pattern as it is shown in Figure 14.
  • Figures 15 and 16 show that the use of powdered magnetic activated carbon for gold recovery from cyanide solutions increases significantly the loading kinetics from solution in the gold recovery process and is expected to provide significant savings in equipment and operating costs. Separation of this loaded carbon from the pulp magnetically, rather than by screening of granular carbon, should offer significant capital and operating cost savings.
  • Figure 17 shows the effect of burnoff degree and iron content of the different chars produced from pinewood and ferric chloride for a particle size range of 53-106 ⁇ m on gold adso ⁇ tion kinetics.
  • the first group at no activation, shows a carbon with no iron and two magnetic carbons with different iron contents.
  • the three samples show the same trend with respect to gold adso ⁇ tion kinetics.
  • the second group at a burnoff degree of 21%, shows an activated carbon with no iron and two magnetic activated carbons with different iron contents.
  • the three samples show the same trend with respect to gold adso ⁇ tion kinetics.
  • the third group at a burnoff degree of 45%, shows an activated carbon with no iron and two magnetic activated carbons with different iron contents.
  • Powdered magnetic activated carbons for gold recovery have been produced using two different raw materials and one magnetic precursor.
  • the carbons produced have enough magnetic content to be recovered with a magnetic separator.
  • the particle size of the MACs is in the range of 150-600 ⁇ m.
  • carbon sources pinewood dust with a particle size of 250 - 600 ⁇ m, and cornstarch, with a particle size of minus 25 ⁇ m have been used. These two products were chosen because they have different behaviors during the pyrolysis stage, and because the inco ⁇ oration of the magnetic source into the carbon structure is also done in different manner.
  • the magnetic precursor chosen for this research was ferric citrate tetrahydrate (C 6 H 5 O 7 Fe-4H 2 O).
  • An organic iron salt was chosen over inorganic salts, such as iron chlorides, nitrates or sulfates, to avoid the generation of species, such as Cl , dioxins, NO x , SO 2 , and other compounds during synthesis.
  • the pulp was placed in a Nalgene ® HDPE bottle, covered with a lid, and agitated using a VWR ® orbital shaker at 200 rpm for 24 hours. Afterwards, the pulp was transferred to a vacuum filter, and the remaining pinewood impregnated with iron citrate was dried in a Blue M ® oven at 400 °K for 12 hours.
  • the gas flowrate was kept constant at 700 mL/min (measured at 273 °K and 1 atm).
  • Activation time was varied to obtain activated carbons from 10% to 50% burnoff.
  • the sample to be activated was placed in a clay crucible, forming a monoparticle bed. After gasification, the crucible was transferred to an alumina tube, where the samples were cooled to room temperature under a N atmosphere at a flowrate of 1.56 L/min, measured at 273 °K and 1 atm.
  • Heat treatment of the MACs Selected samples of magnetic activated carbons produced as described previously were heat-treated to alter the adso ⁇ tion characteristics of the carbon surface. A heat treatment in N atmosphere at 1200 °K and a heat treatment in an O 2 atmosphere at 700 °K were used.
  • Figure 18 shows the loading capacity of a conventional activated carbon used for gold recovery. At its original size 1,400 - 3,350 ⁇ m, it has a loading capacity (K value) of 40.2 Kg of gold per metric ton of activated carbon. When the carbon is ground to a particle size of 53 - 106 ⁇ m, its loading capacity (K value) increases to 54 Kg of gold per metric ton of activated carbon.
  • the loading capacity K is defined as the amount of gold per metric ton of carbon that is in equilibrium with a solution containing 1 milligram of Au per liter of solution, starting with an initial solution containing 100 milligrams of Au per liter of solution.
  • FIG. 19 shows the loading capacity of an activated carbon and a magnetic activated carbon produced with pinewood and ferric citrate, with a particle size of size 250 - 600 ⁇ m.
  • Loading capacities (K values) are 43 and 35 Kg Au/ ton carbon, respectively. It can be seen that the K values are in the same magnitude as conventional activated carbon used for gold recovery (compare to Figure 18).

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Abstract

Cette invention concerne une composition et un procédé permettant d'obtenir un carbone activé doté de propriétés magnétiques en vue de la séparation magnétique du carbone activé et d'un liquide en cours de traitement. Ce procédé consiste à mélanger intimement ou à adsorber un précurseur magnétique de fer en solution dans un précurseur de carbone poreux, ou bien à le mélanger à un précurseur de carbone fusible pour obtenir un mélange ou une solution essentiellement homogène qui, après séchage et pyrolyse, forme des particules de carbone activé dispersées uniformément au sein de la matière carbonée activée. Les particules carbonées activées peuvent être de très petite taille, voir se présenter sous forme de poudre et conserver néanmoins de propriétés magnétiques suffisantes pour une séparation magnétique. Selon un aspect particulier de l'invention, un précurseur du carbone fait de bois tendre est immergé dans une solution de sel ferrique, séché, pyrolysé et activé.
EP02706453A 2001-02-26 2002-02-26 Particules de carbonne a activation magnetique pour adsorption de solutes a partir d une solution Withdrawn EP1428228A4 (fr)

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PCT/US2002/006065 WO2002069351A1 (fr) 2001-02-26 2002-02-26 Particules de carbone a activation magnetique pour adsorption de solutes a partir d'une solution

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HU229789B1 (hu) * 2008-04-15 2014-07-28 Hm Elektronikai Logisztikai Es Vagyonkezeloe Zartkoerueen Muekoedoe Reszvenytarsasag Eljárás és berendezés szorbens elõállítására, elsõsorban ivóvíz arzénmentesítéséhez
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EP4219660A3 (fr) 2011-04-15 2023-10-18 Carbon Technology Holdings, LLC Procédés pour la production de réactifs biogéniques à haute teneur en carbone
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US11413601B2 (en) 2014-10-24 2022-08-16 Carbon Technology Holdings, LLC Halogenated activated carbon compositions and methods of making and using same
EP4217520A1 (fr) 2020-09-25 2023-08-02 Carbon Technology Holdings, LLC Bioréduction de minerais métalliques intégrés à la pyrolyse de biomasse
JP2024508270A (ja) 2021-02-18 2024-02-26 カーボン テクノロジー ホールディングス， エルエルシー カーボンネガティブ冶金製品
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