WO2022208432A1 - Method of treatment of hides processing wast - Google Patents

Method of treatment of hides processing wast Download PDF

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Publication number
WO2022208432A1
WO2022208432A1 PCT/IB2022/053015 IB2022053015W WO2022208432A1 WO 2022208432 A1 WO2022208432 A1 WO 2022208432A1 IB 2022053015 W IB2022053015 W IB 2022053015W WO 2022208432 A1 WO2022208432 A1 WO 2022208432A1
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Prior art keywords
optionally
comprised
pyrolysis
equal
char
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PCT/IB2022/053015
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French (fr)
Inventor
Luigi BONANOMI
Giuditta MAURI
Andrea Rizzo
Andrea SALIMBENI
Sara SANTORI
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Phoenix Italy Srl
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Publication of WO2022208432A1 publication Critical patent/WO2022208432A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
    • C10B53/00—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form
    • 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
    • C01B32/324—Preparation characterised by the starting materials from waste materials, e.g. tyres or spent sulfite pulp liquor
    • 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
    • C01B32/342—Preparation characterised by non-gaseous activating agents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/10—Treatment of sludge; Devices therefor by pyrolysis
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
    • C10B57/00—Other carbonising or coking processes; Features of destructive distillation processes in general
    • C10B57/005—After-treatment of coke, e.g. calcination desulfurization
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
    • C10B57/00—Other carbonising or coking processes; Features of destructive distillation processes in general
    • C10B57/16—Features of high-temperature carbonising processes
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/22—Nature of the water, waste water, sewage or sludge to be treated from the processing of animals, e.g. poultry, fish, or parts thereof

Definitions

  • the present invention relates to a method of treatment of hides processing waste, to obtain "char” with a high carbon content, particularly suitable for production of high-quality carbonaceous products, such as activated carbon.
  • char in the present description and in the following claims refers to the result of a pyrolysis process, comprising mainly a carbonaceous residue and ashes.
  • said pyrolysis process can comprise:
  • A.2 starting from ambient temperature, increasing the temperature into said pyrolysis chamber until a pyrolysis temperature comprised between 450°C and 1000°C is reached, wherein said temperature in said pyrolysis chamber is increased until it reaches said pyrolysis temperature with a heating rate comprised between 15°C/min and 25°C/min, optionally equal to 20°C/min;
  • A.3 keeping said pyrolysis temperature for a pyrolysis time interval comprised between 1 hour and 3 hours, optionally equal to 2 hours;
  • said step B can comprise carrying out at least one leaching process of said char with at least one acid reagent, wherein said at least one acid reagent can comprise demineralized water and one mixture of nitric acid and sulphuric acid.
  • said mixture can comprise one percentage quantity by weight between 40% and 60% of nitric acid and one correspondent percentage quantity by weight between 60% and 40% of sulphuric acid, optionally 50% of nitric acid and 50% of sulphuric acid.
  • the percentage weight of said mixture can be comprised between 10% and 30%, optionally between 20% and 28%, more optionally it is equal to 25% and the corresponding percentage weight of said demineralized water can be comprised between 90% and 70%, optionally between 80% and 72%, more optionally it is equal to 75%.
  • the weight ratio between said mixture and said char can be comprised between 1:1 and 2:1.
  • said leaching process can be carried out at a leaching temperature comprised between 90°C and 95°C, for a reaction time interval comprised between 1 and 3 hours, optionally equal 1 hours.
  • said step B can comprise at least one leaching process of said char with at least one basic reagent, wherein said at least one basic reagent can comprise demineralized water and one strong base, optionally caustic soda.
  • the percentage weight of said caustic soda can be comprised between 3% and 10%, optionally between 4% and 8%, more optionally can be equal to 5% and the corresponding percentage weight of said demineralized water can be comprised between 97% and 90%, optionally between 96% and 92%, more optionally can be equal to 95%.
  • the weight ratio between said caustic soda and said char can be comprised between 1:1 and 2:1, optionally can be equal to 1:1.
  • said leaching process can be carried out at a leaching temperature lower or equal to 95°C, optionally equal to 90°C, and for a reaction time interval comprised between 50 min and 1,5 hours, optionally equal to 1 hour.
  • Figure 1 shows a flow chart of the main steps of the method of the present invention
  • FIG 2 illustrates the main sub-steps of step A for the method depicted in Figure 1;
  • Figure 3 is a table showing the concentration of some metals found in the char, based on the pyrolysis temperature.
  • Figure 4 shows a table reporting porosity of char obtained with the above said pyrolysis, as a function of the pyrolysis temperature.
  • a method of treatment of hides processing waste according to the present invention is particularly suitable for being applied to hides scraps coming from processing of natural leather, i.e. animal skin, mainly goatskin or bovine skin such as calves and bulls, also superficially treated and, for example, comprising one or more of ethylene vinyl acetate, diethylene adipate, nitrocellulose.
  • That method represented in the attached Figure 1 and indicated therein with reference number 1, comprises a first operating step (step A) wherein starting from a quantity of such processing waste, by means of a pyrolysis process in absence of oxygen, char is obtained, and a second step (step B) wherein metals and other pollutants are removed from the ashes of the so obtained char, by means of a leaching process.
  • the pyrolysis process carried out at step A requires placing the above mentioned quantity of hides processing waste into a pyrolysis chamber (sub-step A.l) and increasing the temperature in that pyrolysis chamber (sub-step A.2), starting from an ambient temperature, until a pyrolysis temperature between 450°C and 1000°C is reached.
  • the amount of hides processing waste can be shredded, so that each piece of waste has a (surface) dimension lower than 1 cm, optionally lower than or equal to 5mm.
  • the temperature is increased with a heating rate between 15°C/min and 25°C/min, optionally equal to 20°C/min, until the pyrolysis temperature is reached.
  • the pyrolysis temperature can be one selected from the group comprising the following temperatures: 450°C, 550°C, 700°C, 900°C or 1000°C.
  • step A of the method of the present invention comprises (sub-step A.3) maintaining the pyrolysis temperature in the pyrolysis chamber for a time interval between 1 hour and 3 hours, optionally equal to 2 hours and, then (sub-step A.4) reducing the temperature in the pyrolysis chamber until it reaches back the ambient temperature.
  • step A of the method according to the invention provides for extracting the so obtained char (sub-step A.5).
  • method 1 of the present invention comprises, at the end of step A, one step B of removal of metals and other pollutants from the char obtained at previous step, the metals and other pollutants being substantially present in the ashes thereof and resulting from the processing of the hides before being subjected to pyrolysis.
  • the metals contained in the char ashes the most present is chromium Cr with its oxide Cr2C>3, followed by Potassium K, Zinc Zn, Lead Pb, Magnesium Mg and other metals in smaller quantities.
  • traces of Nitrogen (N) and Chlorine (Cl) are found, whose concentration is the lower the higher the pyrolysis temperature selected at step A.
  • this comprises in particular carrying out at least one leaching process of the char, which char can optionally be reduced to powder, for this purpose.
  • the above-mentioned leaching process makes use of at least one acid reagent, wherein that acid reagent comprises demineralized water and a mixture of nitric acid and sulphuric acid.
  • Said mixture advantageously comprises one percentage quantity by weight between 40% and 60% of nitric acid and one corresponding percentage quantity by weight between 60% and 40% of sulphuric acid, optionally 50% of nitric acid and 50% of sulphuric acid.
  • the percentage weight of the nitric and sulphuric acid mixture is comprised between 10% and 30%, optionally between 20% and 28%, more optionally is equal to 25%, the percentage weight of the demineralized water being correspondingly comprised between 90% and 70%, optionally between 80% and 72%, more optionally equal to 75%.
  • the weight ratio between the mixture (of nitric and sulphuric acid) and the char to be subjected to leaching is between 1:1 and 2:1.
  • the temperature at which the leaching process takes place is comprised between 90°C and 95°C.
  • the demineralization of char is extremely reduced.
  • the char incorporated in a known way in the acid reagent, at the aforementioned temperature is kept under stirring for a reaction time interval between 1 and 3 hours, optionally equal to 1 hour.
  • step B it has been possible to experimentally verify how, at the end of step B, the demineralization efficiency was globally comprised (i.e. taking into account the reduction in the concentration of all the metals contained in the char) between 57% and 62%, calculated according to the formula:
  • the aforementioned method 1 can be implemented according to the following process conditions:
  • step B when the pyrolysis temperature of step A is equal to or higher than 900°C, optionally equal to 1000°C, step B, alternatively or in addition to what has been described above, can comprise one leaching process of char with at least one basic reagent, wherein the basic reagent comprises at least demineralized water and a strong base, for example caustic soda NaOH.
  • the basic reagent comprises at least demineralized water and a strong base, for example caustic soda NaOH.
  • the percentage weight of said caustic soda is comprised between 3% and 10%, optionally between 4% and 8%, more optionally is equal to 5% and the percentage weight of said demineralized water is correspondingly comprised between 97% and 90%, optionally between 96% and 92%, more optionally is equal to 95%.
  • the caustic soda and the char With reference to the weight ratio between the caustic soda and the char, it is comprised between 1:1 and 2:1, optionally is equal to 1:1.
  • the basic leaching process takes place at a process temperature lower than or equal to 95°C, optionally equal to 90°C, for a reaction time interval, during which the char incorporated in a known way into the basic reagent is kept under stirring at the above said temperature, comprised between 50 min and 1.5 hours, optionally equal to 1 hour.
  • Method 1 of treatment of the hides processing waste described above achieves the goals set out in the introduction.
  • the hides processing waste thanks to the method of the present invention, can be converted into char having a reduced inorganic fraction, which could therefore be used as base carbon for the production of high-quality carbonaceous products.
  • Figure 4 which shows the porosity of char obtained at the end of step A as a function of the selected pyrolysis temperature, pyrolysis at 700°C already produces a char with a high porosity, while the char produced at 900°C and 1000°C shows an even higher surface area, a feature that makes it suitable for the production of activated carbon.
  • the leaching step B can comprise the execution of a first acid leaching step and a subsequent basic leaching step or vice versa.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Environmental & Geological Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Water Supply & Treatment (AREA)
  • Treatment And Processing Of Natural Fur Or Leather (AREA)
  • Processing Of Solid Wastes (AREA)

Abstract

Method (1) of treatment of hides processing waste, comprising the following operational steps: A. obtaining char from a quantity of said hides processing waste by means of a pyrolysis process, in absence of oxygen; and B. removing metals and other pollutants from said char thus obtained, by means of a leaching process.

Description

METHOD OF TREATMENT OF HIDES PROCESSING WASTE
* * *
The present invention relates to a method of treatment of hides processing waste, to obtain "char" with a high carbon content, particularly suitable for production of high-quality carbonaceous products, such as activated carbon.
Before going into the merit of the present invention, it is specified that the term "char" in the present description and in the following claims refers to the result of a pyrolysis process, comprising mainly a carbonaceous residue and ashes.
Currently, the waste obtained from hides processing in the tanning industry are destined to be disposed of according to complex and expensive procedures, since they often contain pollutants that cannot be freely released in nature.
However, such waste could be recycled, to obtain, on the one hand, reusable materials also in other technical areas and, on the other, a reduction in the fraction destined to landfill. The scientific magazine article by H.S. MURALIDHARA ER AL: "Conversion of tannery waste to useful products", RESOURCES AND CONSERVATION, vol. 8, no.l, 1 March 1982 (182 -03-01), pages 43-59, XP055596508, ISSN: 0166-3097, DOI: 10.1016/0166-3097 (82) 90052-9, documents US 4332584 A and CN 104261646 B and the article by Porter John ET AL: "OFR 82- 84 Chromium recovery from tanning wastes by pyrolysis and sulfuric acid leaching", 1 June 1987 (1987-06-01) all teach procedures for processing waste from hides processing according to the known art.
In recent years, some methods have also been proposed for the treatment of waste deriving from hides processing, for production of activated carbon or hierarchical porous carbon which, however, have not yet taken hold given the high costs and long implementation times required.
There is therefore a need to improve the state of the art in the area of treatment of hides processing waste and the main purpose of the present invention is to allow in a simple, efficient and economical way transforming a hides processing waste into a product of high added value, which can also be used in other technical areas.
It is a specific object of the present invention a method of treatment of hides processing waste, comprising the following operational steps:
A. obtaining char from a quantity of hides processing waste by means of a pyrolysis process, in absence of oxygen; and B. removing metals and other pollutants from said char thus obtained, by means of a leaching process.
According to another aspect of the invention, said pyrolysis process can comprise:
A.l arranging said quantity of said hides processing waste into one pyrolysis chamber;
A.2 starting from ambient temperature, increasing the temperature into said pyrolysis chamber until a pyrolysis temperature comprised between 450°C and 1000°C is reached, wherein said temperature in said pyrolysis chamber is increased until it reaches said pyrolysis temperature with a heating rate comprised between 15°C/min and 25°C/min, optionally equal to 20°C/min;
A.3 keeping said pyrolysis temperature for a pyrolysis time interval comprised between 1 hour and 3 hours, optionally equal to 2 hours;
A.4 reducing the temperature into said pyrolysis chamber until it reaches said ambient temperature; and
A.5 extracting said char thereby obtained.
According to a further aspect of the invention, said step B can comprise carrying out at least one leaching process of said char with at least one acid reagent, wherein said at least one acid reagent can comprise demineralized water and one mixture of nitric acid and sulphuric acid.
According to an additional aspect of the invention, said mixture can comprise one percentage quantity by weight between 40% and 60% of nitric acid and one correspondent percentage quantity by weight between 60% and 40% of sulphuric acid, optionally 50% of nitric acid and 50% of sulphuric acid.
According to another aspect of the invention, in said acid reagent the percentage weight of said mixture can be comprised between 10% and 30%, optionally between 20% and 28%, more optionally it is equal to 25% and the corresponding percentage weight of said demineralized water can be comprised between 90% and 70%, optionally between 80% and 72%, more optionally it is equal to 75%.
According to a further aspect of the invention, the weight ratio between said mixture and said char can be comprised between 1:1 and 2:1.
According to an additional aspect of the invention, said leaching process can be carried out at a leaching temperature comprised between 90°C and 95°C, for a reaction time interval comprised between 1 and 3 hours, optionally equal 1 hours. According to another aspect of the invention, when said pyrolysis temperature is equal to or greater than 900°C, said step B can comprise at least one leaching process of said char with at least one basic reagent, wherein said at least one basic reagent can comprise demineralized water and one strong base, optionally caustic soda.
According to a further aspect of the invention, in said basic reagent the percentage weight of said caustic soda can be comprised between 3% and 10%, optionally between 4% and 8%, more optionally can be equal to 5% and the corresponding percentage weight of said demineralized water can be comprised between 97% and 90%, optionally between 96% and 92%, more optionally can be equal to 95%.
According to an additional aspect of the invention, the weight ratio between said caustic soda and said char can be comprised between 1:1 and 2:1, optionally can be equal to 1:1.
According to another aspect of the invention, said leaching process can be carried out at a leaching temperature lower or equal to 95°C, optionally equal to 90°C, and for a reaction time interval comprised between 50 min and 1,5 hours, optionally equal to 1 hour.
The present invention will be now described, for illustrative but not limiting purposes, according to its preferred embodiments, with particular reference to the Figures of the accompanying drawings, wherein:
Figure 1 shows a flow chart of the main steps of the method of the present invention;
Figure 2 illustrates the main sub-steps of step A for the method depicted in Figure 1;
Figure 3 is a table showing the concentration of some metals found in the char, based on the pyrolysis temperature; and
Figure 4 shows a table reporting porosity of char obtained with the above said pyrolysis, as a function of the pyrolysis temperature.
Before going into the merits of the present description, it is noted that a method of treatment of hides processing waste according to the present invention is particularly suitable for being applied to hides scraps coming from processing of natural leather, i.e. animal skin, mainly goatskin or bovine skin such as calves and bulls, also superficially treated and, for example, comprising one or more of ethylene vinyl acetate, diethylene adipate, nitrocellulose.
That method, represented in the attached Figure 1 and indicated therein with reference number 1, comprises a first operating step (step A) wherein starting from a quantity of such processing waste, by means of a pyrolysis process in absence of oxygen, char is obtained, and a second step (step B) wherein metals and other pollutants are removed from the ashes of the so obtained char, by means of a leaching process.
More particularly, the pyrolysis process carried out at step A requires placing the above mentioned quantity of hides processing waste into a pyrolysis chamber (sub-step A.l) and increasing the temperature in that pyrolysis chamber (sub-step A.2), starting from an ambient temperature, until a pyrolysis temperature between 450°C and 1000°C is reached. According to one aspect of the invention, before being placed in the pyrolysis chamber, the amount of hides processing waste can be shredded, so that each piece of waste has a (surface) dimension lower than 1 cm, optionally lower than or equal to 5mm.
According to another aspect of the invention, in the pyrolysis chamber the temperature is increased with a heating rate between 15°C/min and 25°C/min, optionally equal to 20°C/min, until the pyrolysis temperature is reached.
According to a preferred embodiment of the invention, the pyrolysis temperature can be one selected from the group comprising the following temperatures: 450°C, 550°C, 700°C, 900°C or 1000°C.
Once the pyrolysis temperature in the pyrolysis chamber is reached, step A of the method of the present invention comprises (sub-step A.3) maintaining the pyrolysis temperature in the pyrolysis chamber for a time interval between 1 hour and 3 hours, optionally equal to 2 hours and, then (sub-step A.4) reducing the temperature in the pyrolysis chamber until it reaches back the ambient temperature.
Finally, step A of the method according to the invention provides for extracting the so obtained char (sub-step A.5).
As already mentioned above, method 1 of the present invention comprises, at the end of step A, one step B of removal of metals and other pollutants from the char obtained at previous step, the metals and other pollutants being substantially present in the ashes thereof and resulting from the processing of the hides before being subjected to pyrolysis. Among the metals contained in the char ashes, the most present is chromium Cr with its oxide Cr2C>3, followed by Potassium K, Zinc Zn, Lead Pb, Magnesium Mg and other metals in smaller quantities. Moreover, in the char also traces of Nitrogen (N) and Chlorine (Cl) are found, whose concentration is the lower the higher the pyrolysis temperature selected at step A.
Therefore, with reference to step B of method 1 of the present invention, this comprises in particular carrying out at least one leaching process of the char, which char can optionally be reduced to powder, for this purpose. The above-mentioned leaching process, according to a particularly advantageous aspect of the invention, makes use of at least one acid reagent, wherein that acid reagent comprises demineralized water and a mixture of nitric acid and sulphuric acid.
Said mixture, according to a preferred embodiment of the invention, advantageously comprises one percentage quantity by weight between 40% and 60% of nitric acid and one corresponding percentage quantity by weight between 60% and 40% of sulphuric acid, optionally 50% of nitric acid and 50% of sulphuric acid. In the acid reagent, the percentage weight of the nitric and sulphuric acid mixture is comprised between 10% and 30%, optionally between 20% and 28%, more optionally is equal to 25%, the percentage weight of the demineralized water being correspondingly comprised between 90% and 70%, optionally between 80% and 72%, more optionally equal to 75%.
According to an aspect of the present invention, the weight ratio between the mixture (of nitric and sulphuric acid) and the char to be subjected to leaching is between 1:1 and 2:1.
With reference, then, to the temperature at which the leaching process takes place, according to a particularly advantageous aspect of the invention, it is comprised between 90°C and 95°C. In fact, experimental studies have shown that at temperatures lower than those indicated above, the demineralization of char is extremely reduced. During step B, the char incorporated in a known way in the acid reagent, at the aforementioned temperature, is kept under stirring for a reaction time interval between 1 and 3 hours, optionally equal to 1 hour.
With that method, it has been possible to experimentally verify how, at the end of step B, the demineralization efficiency was globally comprised (i.e. taking into account the reduction in the concentration of all the metals contained in the char) between 57% and 62%, calculated according to the formula:
(% ashes in char before leaching — % ashes in char after leaching) % ashes in char before leaching
With reference to the Chromium content, it was experimentally verified in particular that the reduction has been very high, around 77% of the initial content. Lower results in terms of demineralization efficiency and reduction of the Chromium concentration were instead obtained, under the same conditions, with a leaching process performed with an acid reagent comprising only hydrochloric acid, or only sulphuric acid or only oxalic acid or only nitric acid (not mixed with other acids).
According to a particularly preferred embodiment of method 1 of the present invention, the aforementioned method 1 can be implemented according to the following process conditions:
Pyrolysis temperature between 450°C and 700°C;
Pyrolysis time interval 2 hours;
Acid mixture with 50% by percentage weight of nitric acid and 50% of sulphuric acid;
Mixture concentration, in the reagent, at 25%;
Leaching temperature 95°C;
Acid mixture/char weight ratio 1:1; and
Reaction time interval 2 hours.
According to a variant of method 1 of the present invention, when the pyrolysis temperature of step A is equal to or higher than 900°C, optionally equal to 1000°C, step B, alternatively or in addition to what has been described above, can comprise one leaching process of char with at least one basic reagent, wherein the basic reagent comprises at least demineralized water and a strong base, for example caustic soda NaOH.
According to a preferred embodiment of the present invention, in said basic reagent the percentage weight of said caustic soda is comprised between 3% and 10%, optionally between 4% and 8%, more optionally is equal to 5% and the percentage weight of said demineralized water is correspondingly comprised between 97% and 90%, optionally between 96% and 92%, more optionally is equal to 95%.
With reference to the weight ratio between the caustic soda and the char, it is comprised between 1:1 and 2:1, optionally is equal to 1:1.
According to this preferred embodiment of the method of the present invention, the basic leaching process takes place at a process temperature lower than or equal to 95°C, optionally equal to 90°C, for a reaction time interval, during which the char incorporated in a known way into the basic reagent is kept under stirring at the above said temperature, comprised between 50 min and 1.5 hours, optionally equal to 1 hour.
Experimental tests have shown that the demineralization of char obtained with the basic leaching process described above is less efficient than that obtained by the acid leaching process, since the basic demineralization is only between 10% and 17%. However, a lower AEX efficiency achieved by basic leaching can be compensated for by a lower weight percentage of minerals contained in the char before execution of the leaching process, if pyrolysis has been carried out at elevated temperatures (> 900°C). In fact, it has been experimentally verified that at pyrolysis temperatures between 900°C and 1000°C, the concentration in the char of some metals such as Lead and Zinc is significantly reduced compared to the char obtained with lower pyrolysis temperatures (Fig. 3).
Method 1 of treatment of the hides processing waste described above achieves the goals set out in the introduction. In fact, it has been experimentally proved that the hides processing waste, thanks to the method of the present invention, can be converted into char having a reduced inorganic fraction, which could therefore be used as base carbon for the production of high-quality carbonaceous products. As can be seen in Figure 4, which shows the porosity of char obtained at the end of step A as a function of the selected pyrolysis temperature, pyrolysis at 700°C already produces a char with a high porosity, while the char produced at 900°C and 1000°C shows an even higher surface area, a feature that makes it suitable for the production of activated carbon.
In the foregoing the preferred embodiments were described, and some modifications of the present invention were suggested, but it should be understood that those skilled in the art can make modifications and changes without departing from the relative scope of protection, as defined by the appended claims. Thus, for example, in a particularly advantageous embodiment of the invention, the leaching step B can comprise the execution of a first acid leaching step and a subsequent basic leaching step or vice versa.

Claims

1. Method (1) of treatment of hides processing waste, comprising the following operational steps:
A. obtaining char from a quantity of said hides processing waste by means of a pyrolysis process, in absence of oxygen; and
B. removing metals and other pollutants from said char thus obtained, by means of a leaching process, wherein said leaching process is carried out at a leaching temperature comprised between 90°C and 95°C, for a reaction time interval comprised between 50 min and 3 hours.
2. Method (1) according to claim 1, wherein said pyrolysis process comprises:
A.l arranging said quantity of said hides processing waste into one pyrolysis chamber;
A.2 starting from ambient temperature, increasing the temperature into said pyrolysis chamber until a pyrolysis temperature comprised between 450°C and 1000°C is reached, wherein said temperature in said pyrolysis chamber is increased until it reaches said pyrolysis temperature with a heating rate comprised between 15°C/min and 25°C/min, optionally equal to 20°C/min;
A.3 keeping said pyrolysis temperature for a pyrolysis time interval comprised between 1 hour and 3 hours, optionally equal to 2 hours;
A.4 reducing the temperature into said pyrolysis chamber until it reaches said ambient temperature; and
A.5 extracting said char thereby obtained.
3. Method (1) according to claim 1 or 2, wherein said step B comprises carrying out at least one leaching process of said char with at least one acid reagent, wherein said at least one acid reagent comprises demineralized water and one mixture of nitric acid and sulphuric acid.
4. Method (1) according to claim 3, wherein said mixture comprises one percentage quantity by weight between 40% and 60% of nitric acid and one correspondent percentage quantity by weight between 60% and 40% of sulphuric acid, optionally 50% of nitric acid and 50% of sulphuric acid.
5. Method (1) according to claim 3 or 4, wherein in said acid reagent the percentage weight of said mixture is comprised between 10% and 30%, optionally between 20% and 28%, more optionally is equal to 25% and the corresponding percentage weight of said demineralized water is comprised between 90% and 70%, optionally between 80% and 72%, more optionally is equal to 75%.
6. Method (1) according to any claim 3 to 5, wherein a weight ratio between said mixture and said char is comprised between 1:1 and 2:1.
7. Method (1) according to any claim 3 to 6, wherein said leaching process is carried out at a leaching temperature of 95°C, for a reaction time interval equal to 1 hour.
8. Method (1) according to claim 2, wherein when said pyrolysis process has a pyrolysis temperature equal to or greater than 900°C, said step B comprises at least one leaching process of said char with at least one basic reagent, wherein said at least one basic reagent comprises demineralized water and one strong base, optionally caustic soda.
9. Method (1) according to claim 8, wherein in said basic reagent the percentage weight of said caustic soda is comprised between 3% and 10%, optionally between 4% and 8%, more optionally is equal to 5% and the corresponding percentage weight of said demineralized water is comprised between 97% and 90%, optionally between 96% and 92%, more optionally is equal to 95%.
10. Method (1) according to claim 8 or 9, wherein a weight ratio between said caustic soda and said char is comprised between 1:1 and 2:1, optionally is equal to 1:1.
11. Method (1) according to any claim 8 a 10, wherein said leaching process is carried out at a process leaching temperature equal to 90°C and for a reaction time interval comprised between 50 min and 1,5 hours, optionally equal to 1 hour.
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