WO2005039702A1 - A method and composition for stabilizing waste mercury compounds using ladle furnace slag - Google Patents

A method and composition for stabilizing waste mercury compounds using ladle furnace slag Download PDF

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Publication number
WO2005039702A1
WO2005039702A1 PCT/SG2004/000245 SG2004000245W WO2005039702A1 WO 2005039702 A1 WO2005039702 A1 WO 2005039702A1 SG 2004000245 W SG2004000245 W SG 2004000245W WO 2005039702 A1 WO2005039702 A1 WO 2005039702A1
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Prior art keywords
furnace slag
ladle furnace
mercury
matrix
slurry
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PCT/SG2004/000245
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French (fr)
Inventor
Darren Delai Sun
Joo Hwa Tay
Hee Kiat Cheong
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Nanyang Technological University
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Publication of WO2005039702A1 publication Critical patent/WO2005039702A1/en

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Classifications

    • A—HUMAN NECESSITIES
    • A62—LIFE-SAVING; FIRE-FIGHTING
    • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
    • A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
    • A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
    • A62D3/33—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents by chemical fixing the harmful substance, e.g. by chelation or complexation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09B—DISPOSAL OF SOLID WASTE
    • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
    • B09B3/20—Agglomeration, binding or encapsulation of solid waste
    • B09B3/25—Agglomeration, binding or encapsulation of solid waste using mineral binders or matrix
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C04B28/08—Slag cements
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/24—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing alkyl, ammonium or metal silicates; containing silica sols
    • C04B28/26—Silicates of the alkali metals
    • A—HUMAN NECESSITIES
    • A62—LIFE-SAVING; FIRE-FIGHTING
    • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
    • A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
    • A62D2101/40—Inorganic substances
    • A62D2101/43—Inorganic substances containing heavy metals, in the bonded or free state
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00758—Uses not provided for elsewhere in C04B2111/00 for agri-, sylvi- or piscicultural or cattle-breeding applications
    • 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
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/91—Use of waste materials as fillers for mortars or concrete

Definitions

  • the present invention generally relates to stabilization of heavy waste metals.
  • the invention relates to a method for stabilization of heavy waste metals such as mercury using waste ladle furnace slag.
  • Waste materials contaminated with heavy metal ions and other inorganic ions requires complex and costly processes before these waste materials can be properly disposed of.
  • One of the most difficult forms of waste to be disposed of are the mercury contaminated materials.
  • the present invention seeks to provide a method for stabilizing and encapsulating waste mercury compounds using ladle furnace slag.
  • a method for stabilizing and encapsulating mercury compounds using ladle furnace slag comprising the steps: preparing a matrix slurry having a cementitious matrix, the matrix slurry comprising of ladle furnace slag particles and at least one alkaline activator; precipitating mercury ions of the mercury compounds into the cementitious matrix of the matrix slurry by adding and mixing the mercury compounds into the matrix slurry; and enhancing precipitation of the mercury ions via thermal treatment.
  • the present invention provides, a method for stabilizing and encapsulating waste mercury compounds comprising the steps: preparing a matrix slurry having a cementitious matrix, the matrix slurry comprising about 55% by weight ladle furnace slag particles, about 18% by weight of 2M sodium hydroxide solution and about 27% by weight of sodium silicate; adding and mixing waste mercury compounds amounting to about 1% by weight of ladle furnace slag particles into the matrix slurry; and autoclaving the matrix slurry at 180°C for 12 hours.
  • the present invention provides, a method for stabilizing and encapsulating waste heavy metal compounds comprising the steps: preparing a matrix ' slurry having a cementitious matrix, the matrix slurry comprising about 61% by weight ladle furnace slag particles, about 8% by weight of 2M sodium hydroxide solution and about 31% by weight of sodium silicate; adding and mixing waste heavy metal compounds amounting to about 0.5% by weight of ladle furnace slag particles into the matrix slurry; and autoclaving the matrix slurry at 180°C for 12 hours.
  • a cementitious matrix composition for stabilizing and encapsulating waste heavy metal compounds comprising: about 55% by weight ladle furnace slag particles, about 18% by weight of 2M sodium hydroxide solution and about 27% by weight of sodium silicate; wherein the ladle furnace slag particles are of 45 ⁇ m and below.
  • a cementitious matrix composition for stabilizing and encapsukting waste heavy metal compounds comprising: about 61% by weight ladle furnace slag particles, about 8% by weight of 2M sodium hydroxide solution and about 31% by weight of sodium silicate; wherein the ladle furnace slag particles are of 250 ⁇ m and below.
  • FIG.l illustrates a flowchart for a method for stabilizing waste heavy metal compounds using ladle furnace slag in accordance with the present invention
  • a method for stabilizing waste heavy metal compounds using ladle furnace slag with a preferred embodiment is described.
  • details are provided to describe the preferred embodiment. It shall be apparent to one skilled in the art, however that the invention may be practiced without such details. Some of the details may not be described at length so as not to obscure the invention.
  • the present invention advantageously utilizes one waste from one industry to stabilize waste heavy metal compounds and reduce the leachability of these waste heavy metal compounds to acceptable levels.
  • ladle furnace slag is used to form an activated matrix slurry for stabilizing waste heavy metal compounds such as mercury compounds.
  • Ladle furnace slag under normal conditions is a non-reactive material comprising mainly of gamma dicalcium silicate ( ⁇ -Ca 2 SiO 4 ), gehlenite (Ca 2 Al 2 SiO 7 ) and bredigite (Cai 4 Mg 2 (SiO ) 8 ).
  • ⁇ -Ca 2 SiO 4 gamma dicalcium silicate
  • Ca 2 Al 2 SiO 7 gehlenite
  • SiO bredigite
  • the non-reactive ladle furnace slag undergoes a chemical reaction and forms a durable cementitious matrix capable of advantageously stabilizing mercury ions.
  • the mercury ions are precipitated into stable heavy metal compounds like mercury sulfides and are encapsulated by the matrix slurry as the matrix slurry sets into a monolith structure.
  • ladle furnace slag In addition to the above compositions, ladle furnace slag also differs in the amounts of impurities and additives found in the slag due to the various processes and practices in various countries.
  • ladle furnace slag used in the production of construction products in the publication by Caijun Shi and Shunfu Hu, "Cementitious properties of ladle slag fines under autoclave curing conditions", Cement and Concrete Research 2430 (2003) (uncorrected Proof Copy) uses ladle furnace slag that contains substantial amounts of fluorides which were added as fluxing agents.
  • the ladle furnace slag used in the present invention uses calcium aluminate as a fluxing agent and therefore differs from the ladle furnace slag as used in the "Cementitious. properties" publication.
  • the method 100 in accordance with the present invention starts with the steps of preparing 110 a matrix slurry comprising the durable cementitious matrix.
  • the matrix slurry comprises of ladle furnace slag particles mixed with at least one alkaline activator, examples of which are sodium silicate and sodium hydroxide solution.
  • the matrix slurry is mixed with both sodium silicate and sodium hydroxide solution.
  • the ladle furnace slag particles have first been sieved before being added into the matrix slurry.
  • the sieved ladle furnace slag particles are sieved according to at least two sizes. Non-limiting examples of possible sieved sizes are 250 ⁇ m and below, 75 ⁇ m and below and 45 ⁇ m and below.
  • the step of precipitating 115 the heavy metal ions is performed by adding and mixing the mercury waste compounds into the durable cementitious matrix of the matrix slurry.
  • the mercury ions begin to advantageously precipitate 115 into the matrix slurry forming mercury oxides, mercury hydroxides and mercury sulphides.
  • Sulfur is bonded in ladle furnace slags during steel desulfurization in the slag reaction process. Most of this sulfur is found in the ladle furnace slag as calcium sulfides and also free form sulfur.
  • the presence of sulfur and sulfur compounds in the ladle furnace slag particles advantageously aid in the precipitation 115 of the mercury ions into the durable cementitious matrix of the matrix slurry. This advantageously omits the step of adding additional sulfur or sulfur additives into the matrix slurry.
  • the step of setting 120 the matrix slurry is performed to improve the manageability of the matrix slurry.
  • the matrix slurry may be left to stand in a mold or in a container. Once the matrix slurry has set into a relatively manageable state or into a slurry block, i.e. the matrix slurry has set sufficiently to allow manipulation and ease of transport, the slurry block is demolded from its mold or removed from the container.
  • the slurry block then undergoes the step of enhancing 125 of precipitation of the mercury ions into the durable cementitious matrix via thermal treatment.
  • a preferred means of the thermal treatment is by way of autoclaving.
  • the slurry block is placed in an autoclaving unit and undergoes autoclaving treatment at about 180°C for about 12 hours. This autoclaving process helps to further release the sulfur from the ladle furnace slag particles into the durable cementitious matrix of the slurry block for further precipitating 115 of any remaining mercury ions in the slurry block.
  • the final product after autoclaving is a solid monolith resembling a block of concrete.
  • the solid monolith may then be used as substitute aggregate for replacing natural aggregate in land reclamation projects.
  • a matrix slurry is first prepared using 30 g of ladle furnace slag having particle size of 45 ⁇ m and below, 15 g of undiluted laboratory grade sodium silicate solution (Na 2 SiO 4 ) and 10 g of 2M sodium hydroxide solution (NaOH) as the alkaline activator.
  • Mercury nitrate of up to 0.3 g is used to simulate mercury waste and is added to the matrix slurry and well mixed.
  • the matrix slurry is allowed to harden and set for about 24 hours before being autoclaved for 12 hours at an autoclaving temperature of 180°C.
  • the resulting solid monolith (cylindrical in shape for this present example) was found to have a compressive strength of around 12 N/rnm 2 .
  • a Toxicity Characteristics Leachate Procedure (TCLP) test was performed on the resultmg monolith and results showed that amount of teachable mercury present was less than 0.2 ppm.
  • composition of the materials used amounted to about 55% by weight of ladle furnace slag particles of 45 ⁇ m and below, about 18% by weight of 2M sodium hydroxide solution and about 27% by weight of sodium silicate.
  • the amount of waste heavy metal compounds to be encapsulated by the matrix slurry amounts to about 1% by weight of the ladle furnace slag particles.
  • a matrix slurry is first prepared using 30 g of ladle furnace slag particles having particle size of 250 ⁇ m and below, 15 g of undiluted laboratory grade sodium silicate solution (Na 2 SiO 4 ), and 4 g of 2M sodium hydroxide solution (NaOH) as the alkaline activator.
  • Mercury nitrate of up to 0.15 g is used to simulate mercury waste and is added to the matrix slurry and well mixed.
  • the matrix slurry is allowed to harden and set for about 24 hours before being autoclaved for 12 hours at an autoclaving temperature of 180°C.
  • the resulting solid monolith (cylindrical in shape for this present example) was found to have a compressive strength of around 15 N/mm 2 .
  • a Toxicity Characteristics Leachate Procedure (TCLP) test was performed on the resulting monolith and results showed that amount of teachable mercury present was less than 0.2 ppm.
  • composition of the materials used amounted to about 61% by weight of ladle furnace slag particles of 250 ⁇ m and below, about 8% by weight of 2M sodium hydroxide solution and about 31% by weight of sodium silicate.
  • the amount of waste mercury compounds to be encapsulated by the matrix slurry amounts to about 0.5% by weight of the ladle furnace slag particles.

Abstract

A Method and Composition for Stabilizing Waste Mercury Compounds Using Ladle Furnace Slag The present invention advantageously utilizes one waste from one industry to stabilize waste heavy metal compounds and reduce the leachability of this heavy metal compound to acceptable levels. Particularly, ladle furnace slag is used to form an activated matrix slurry for stabilizing waste heavy metal compounds such as mercury compounds. The method comprises the steps: preparing a matrix slurry comprising of ladle furnace slag particles, at least one alkaline activator, precipitating mercury ions of the waste mercury compounds by adding the waste mercury compounds into the matrix slurry; setting the matrix slurry into a slurry block to improve manageability; and enhancing precipitation of the mercury ions via thermal treatment.

Description

A METHOD AND COMPOSITION FOR STABILIZING WASTE MERCURY COMPOUNDS USING LADLE FURNACE SLAG
Field of the Invention
[0001] The present invention generally relates to stabilization of heavy waste metals. In particular, the invention relates to a method for stabilization of heavy waste metals such as mercury using waste ladle furnace slag.
Background of the Invention
[0002] Disposal of contaminated waste materials is a major problem throughout the world. Waste materials contaminated with heavy metal ions and other inorganic ions requires complex and costly processes before these waste materials can be properly disposed of. One of the most difficult forms of waste to be disposed of are the mercury contaminated materials.
[0003] Treatment of mercury bearing waste by encapsulation is well-known in the prior art. Rechichi in U.S. Patent No. 6,399,848 discloses a method of encapsulating mercury by adding the mercury to a settable slurry composition comprising of calcium carbonate and a caustic magnesium oxide. Upon the setting of the slurry composition, the slurry composition encapsulates the mercury and provides low level of leaching.
[0004] The addition of sulfur or sulfur compounds to stabilize mercury waste is also not new. In U.S. Patent No. 4,844,815, Ader et al describes a method for reducing the leachability of mercury containing waste to an acceptable level by using a mixture of elemental sulfur and cement kiln dust [0005] Similarly, Kaczur et al. in U.S. Patent No. 4,354,942 discloses a process for stabilizing soluble mercury deposits by using inorganic sulfur compounds including sulfides, alkali metal thiosulfates, alkaline earth thiosulfates, iron thiosulfates, alkali metal dithionites, and alkaline earth metal dithionites. By using these inorgamc sulfur compounds, the soluble mercury is converted to insoluble mercury compounds which is less prone to leaching and thereby reducing the leachability of the final products.
[0006] Heat treatment of some sulfur treated mercury wastes have further proved to be more effective in producing insoluble mercury compounds. Adams in U.S. Patent No. 5,347,072 and in U.S. Patent No. 5,562,589 discloses a method to stabilize a mixture of inorganic substrates containing metals, metals ions, inorganic ions and up to 10 % organic chemicals with sulfur by heat treatment at an elevated temperature greater than the melting point of sulfur to produce an inert carbon sulfur polymer.
[0007] In U.S. Patent No. 6,399,849, Kalb et al. mixed mercury-contaminated waste with a sulfur polymer cement under an inert atmosphere before heating the mixture to produce a molten product as a monoUthic final waste form. In order to improve the leaching properties of the final product, additional sulfur polymer cement could be added as additive.
[0008] Autoclaving is a well-known process used for various applications such as sterilizing of equipments. However, since autoclaving involves the increasing of temperatures via steam, it can be also be used for enhancing the properties of materials. Suzuki et al in Patent publication No.2002-255671 provide a method for producing inorganic hardened body from fiber and cement by using an autoclavmg process. [0009] Ladle furnace slag is currently a waste material available at no cost and is a by product of steel manufacturing processes. Ladle furnace slag is considered one of the most difficult waste products to dispose of. Current practices simply disposes of ladle furnace slag by burying them in landfills. While this may appear a simple solution, this practice can create problems for regions where land is a highly priced commodity like in the island state of Singapore.
[0010] There have thus been several attempts at recycling ladle furnace slag by re- introducing ladle furnace slag as a raw material in construction industry. Caijun Shi and Shunfu Hu in the publication "Cementitious properties of ladle slag fines under autoclave curing conditions", Cement and Concrete Research 2430 (2003) (uncorrected Proof Copy) disclosed the use of ladle slag fines in production of construction products. Particularly, the publication disclosed that ladle slag fines when combined with siliceous materials, Portland cement and hydrated lime and after undergoing a hydrothermal process forms a high strength cementitious monolith compound suitable for the construction industry.
[0011] However, such processes disadvantageously involves several steps and requires the addition of several additives and raw materials (e.g. Portland cement and hydrated lime) before a high strength monolith compound is achieved. Purchasing such additives and raw materials can disadvantageously add to the cost of recycling.
[0012] Alternative methods for stabilizing and disposing of heavy metals such as mercury and ladle furnace slags in ways which comply with environmental regulations are always in constant need. It can thus be seen that there exists a need for a simple and effective method for stabilizing waste heavy metal compounds that can overcome the disadvantages of the existing prior art. Summary of the Invention
[0013] The present invention seeks to provide a method for stabilizing and encapsulating waste mercury compounds using ladle furnace slag.
[0014] Accordingly, in one aspect, a method for stabilizing and encapsulating mercury compounds using ladle furnace slag, comprising the steps: preparing a matrix slurry having a cementitious matrix, the matrix slurry comprising of ladle furnace slag particles and at least one alkaline activator; precipitating mercury ions of the mercury compounds into the cementitious matrix of the matrix slurry by adding and mixing the mercury compounds into the matrix slurry; and enhancing precipitation of the mercury ions via thermal treatment.
[0015] In another aspect, the present invention provides, a method for stabilizing and encapsulating waste mercury compounds comprising the steps: preparing a matrix slurry having a cementitious matrix, the matrix slurry comprising about 55% by weight ladle furnace slag particles, about 18% by weight of 2M sodium hydroxide solution and about 27% by weight of sodium silicate; adding and mixing waste mercury compounds amounting to about 1% by weight of ladle furnace slag particles into the matrix slurry; and autoclaving the matrix slurry at 180°C for 12 hours.
[0016] In a further aspect, the present invention provides, a method for stabilizing and encapsulating waste heavy metal compounds comprising the steps: preparing a matrix' slurry having a cementitious matrix, the matrix slurry comprising about 61% by weight ladle furnace slag particles, about 8% by weight of 2M sodium hydroxide solution and about 31% by weight of sodium silicate; adding and mixing waste heavy metal compounds amounting to about 0.5% by weight of ladle furnace slag particles into the matrix slurry; and autoclaving the matrix slurry at 180°C for 12 hours. [0017] In yet another aspect, a cementitious matrix composition for stabilizing and encapsulating waste heavy metal compounds comprising: about 55% by weight ladle furnace slag particles, about 18% by weight of 2M sodium hydroxide solution and about 27% by weight of sodium silicate; wherein the ladle furnace slag particles are of 45 μm and below.
[0018] In yet a further aspect, a cementitious matrix composition for stabilizing and encapsukting waste heavy metal compounds comprising: about 61% by weight ladle furnace slag particles, about 8% by weight of 2M sodium hydroxide solution and about 31% by weight of sodium silicate; wherein the ladle furnace slag particles are of 250 μm and below.
Brief Description of the Drawings
[0019] A preferred embodiment of the present invention will now be more fully described, with reference to the drawings of which:
[0020] FIG.l illustrates a flowchart for a method for stabilizing waste heavy metal compounds using ladle furnace slag in accordance with the present invention; '
Detailed description of the Drawings
[0021] A method for stabilizing waste heavy metal compounds using ladle furnace slag with a preferred embodiment is described. In the following description, details are provided to describe the preferred embodiment. It shall be apparent to one skilled in the art, however that the invention may be practiced without such details. Some of the details may not be described at length so as not to obscure the invention. [0022] The present invention advantageously utilizes one waste from one industry to stabilize waste heavy metal compounds and reduce the leachability of these waste heavy metal compounds to acceptable levels. Particularly, ladle furnace slag is used to form an activated matrix slurry for stabilizing waste heavy metal compounds such as mercury compounds.
[0023] Ladle furnace slag under normal conditions is a non-reactive material comprising mainly of gamma dicalcium silicate (γ-Ca2SiO4), gehlenite (Ca2Al2SiO7) and bredigite (Cai4Mg2(SiO )8). However, when subjected to an alkali-activated process with thermal treatment, the non-reactive ladle furnace slag undergoes a chemical reaction and forms a durable cementitious matrix capable of advantageously stabilizing mercury ions. The mercury ions are precipitated into stable heavy metal compounds like mercury sulfides and are encapsulated by the matrix slurry as the matrix slurry sets into a monolith structure.
[0024] In addition to the above compositions, ladle furnace slag also differs in the amounts of impurities and additives found in the slag due to the various processes and practices in various countries. For example, ladle furnace slag used in the production of construction products in the publication by Caijun Shi and Shunfu Hu, "Cementitious properties of ladle slag fines under autoclave curing conditions", Cement and Concrete Research 2430 (2003) (uncorrected Proof Copy) uses ladle furnace slag that contains substantial amounts of fluorides which were added as fluxing agents.
[0025] The ladle furnace slag used in the present invention, however uses calcium aluminate as a fluxing agent and therefore differs from the ladle furnace slag as used in the "Cementitious. properties" publication. [0026] Referring to FIG.l, the method 100 in accordance with the present invention starts with the steps of preparing 110 a matrix slurry comprising the durable cementitious matrix. The matrix slurry comprises of ladle furnace slag particles mixed with at least one alkaline activator, examples of which are sodium silicate and sodium hydroxide solution. In the present description of the invention, the matrix slurry is mixed with both sodium silicate and sodium hydroxide solution. The ladle furnace slag particles have first been sieved before being added into the matrix slurry. The sieved ladle furnace slag particles are sieved according to at least two sizes. Non-limiting examples of possible sieved sizes are 250μm and below, 75μm and below and 45μm and below.
[0027] Next, the step of precipitating 115 the heavy metal ions is performed by adding and mixing the mercury waste compounds into the durable cementitious matrix of the matrix slurry. The mercury ions begin to advantageously precipitate 115 into the matrix slurry forming mercury oxides, mercury hydroxides and mercury sulphides.
[0028] Sulfur is bonded in ladle furnace slags during steel desulfurization in the slag reaction process. Most of this sulfur is found in the ladle furnace slag as calcium sulfides and also free form sulfur. The presence of sulfur and sulfur compounds in the ladle furnace slag particles advantageously aid in the precipitation 115 of the mercury ions into the durable cementitious matrix of the matrix slurry. This advantageously omits the step of adding additional sulfur or sulfur additives into the matrix slurry.
[0029] Subsequently, the step of setting 120 the matrix slurry is performed to improve the manageability of the matrix slurry. The matrix slurry may be left to stand in a mold or in a container. Once the matrix slurry has set into a relatively manageable state or into a slurry block, i.e. the matrix slurry has set sufficiently to allow manipulation and ease of transport, the slurry block is demolded from its mold or removed from the container.
[0030] The slurry block then undergoes the step of enhancing 125 of precipitation of the mercury ions into the durable cementitious matrix via thermal treatment. A preferred means of the thermal treatment is by way of autoclaving. The slurry block is placed in an autoclaving unit and undergoes autoclaving treatment at about 180°C for about 12 hours. This autoclaving process helps to further release the sulfur from the ladle furnace slag particles into the durable cementitious matrix of the slurry block for further precipitating 115 of any remaining mercury ions in the slurry block.
[0031] At this stage, recrystallization of the less soluble mercury compounds occur, which results in these less soluble mercury compounds being encapsulated within the durable cementitious matrix.
[0032] The final product after autoclaving is a solid monolith resembling a block of concrete. The solid monolith may then be used as substitute aggregate for replacing natural aggregate in land reclamation projects. s
[0033] The following non-limiting examples further serve to illustrate the preferred embodiments in accordance with the present invention and it will be appreciated that various modifications and improvements can be made by a person skilled in the art without departing from the scope of the present invention.
Example 1
[0034] A matrix slurry is first prepared using 30 g of ladle furnace slag having particle size of 45 μm and below, 15 g of undiluted laboratory grade sodium silicate solution (Na2SiO4) and 10 g of 2M sodium hydroxide solution (NaOH) as the alkaline activator.
[0035] Mercury nitrate of up to 0.3 g is used to simulate mercury waste and is added to the matrix slurry and well mixed. The matrix slurry is allowed to harden and set for about 24 hours before being autoclaved for 12 hours at an autoclaving temperature of 180°C. The resulting solid monolith (cylindrical in shape for this present example) was found to have a compressive strength of around 12 N/rnm2. A Toxicity Characteristics Leachate Procedure (TCLP) test was performed on the resultmg monolith and results showed that amount of teachable mercury present was less than 0.2 ppm.
[0036] The composition of the materials used amounted to about 55% by weight of ladle furnace slag particles of 45 μm and below, about 18% by weight of 2M sodium hydroxide solution and about 27% by weight of sodium silicate. The amount of waste heavy metal compounds to be encapsulated by the matrix slurry amounts to about 1% by weight of the ladle furnace slag particles.
Example 2
[0037] A matrix slurry is first prepared using 30 g of ladle furnace slag particles having particle size of 250 μm and below, 15 g of undiluted laboratory grade sodium silicate solution (Na2SiO4), and 4 g of 2M sodium hydroxide solution (NaOH) as the alkaline activator.
[0038] Mercury nitrate of up to 0.15 g is used to simulate mercury waste and is added to the matrix slurry and well mixed. The matrix slurry is allowed to harden and set for about 24 hours before being autoclaved for 12 hours at an autoclaving temperature of 180°C. The resulting solid monolith (cylindrical in shape for this present example) was found to have a compressive strength of around 15 N/mm2. A Toxicity Characteristics Leachate Procedure (TCLP) test was performed on the resulting monolith and results showed that amount of teachable mercury present was less than 0.2 ppm.
[0039] The composition of the materials used amounted to about 61% by weight of ladle furnace slag particles of 250 μm and below, about 8% by weight of 2M sodium hydroxide solution and about 31% by weight of sodium silicate. The amount of waste mercury compounds to be encapsulated by the matrix slurry amounts to about 0.5% by weight of the ladle furnace slag particles.
[0040] The above description and examples serve to illustrate the preferred embodiments in accordance with the present invention and it will be appreciated that various modifications and improvements can be made by a person skilled in the art without departing from the scope of the present invention.

Claims

Claims
1. A method for stabilizing and encapsulating mercury compounds using ladle furnace slag, comprising the steps: a. preparing a matrix slurry having a cementitious matrix, the matrix slurry comprising of ladle furnace slag particles and at least one alkaline activator; b. precipitating mercury ions of the mercury compounds into the cementitious matrix of the matrix slurry by adding and mixing the mercury compounds into the matrix slurry; and c. enhancing precipitation of the mercury ions via thermal treatment
2. The method in accordance with claim 1, wherein the at least one alkaline activator comprises one or both of the following: sodium silicate and sodium hydroxide solution.
3. The method in accordance with claim 2, wherem the sodium hydroxide solution is of concentration 2M.
4. The method in accordance with claim 1, wherein setting of the matrix slurry into a slurry block to improve manageability is performed before the step c:
5. The method in accordance with claim 1, wherein the step d. further comprises autoclaving the matrix slurry for 12 hours at 180°C.
6. The method in accordance with claim 1, wherein the mercury ions in the step b. form mercury oxides, mercury hydroxides and mercury sulfides.
7. The method in accordance with claim 1, wherein the mercury ions in the step d. form mercury sulfides.
8. The method in accordance with claim 1, wherein the ladle furnace slag particles are sieved into sizes of 45 μm and below and 250 μm and below.
9. A method for stabilizing and encapsulating waste mercury compounds comprising the steps: preparing a matrix slurry having a cementitious matrix, the matrix slurry comprising about 55% by weight ladle furnace slag particles, about 18% by weight of 2M sodium hydroxide solution and about 27% by weight of sodium silicate; b. adding and mixing waste mercury compounds amounting to about 1% by weight of ladle furnace slag particles into the matrix slurry; and c. autoclaving the matrix slurry at 180°C for 12 hours;
10. The method in accordance with claim 9, wherein the step of setting the matrix slurry into a slurry block to improve manageability is performed before the step c.
11. The method in accordaiice with claim 9, wherein the ladle furnace slag particles are of 45 μm and below.
12. A method for stabilizing and encapsulating waste heavy metal compounds comprising the steps: a. preparing a matrix slurry having a cementitious matrix, the matrix slurry comprising about 61% by weight ladle furnace slag particles, about 8% by weight of 2M sodium hydroxide solution and about 31% by weight of sodium silicate; b. adding and mixing waste heavy metal compounds amounting to about 0.5% by weight of ladle furnace slag particles into the matrix slurry; and c. autoclaving the matrix slurry at 180°C for 12 hours.
13. The method in accordance with claim 12, wherein setting of the matrix slurry into a slurry block to improve manageability is performed before the step c.
14. The method in accordance with claim 12, wherein the ladle furnace slag particles are of 250 μm and below.
15. A cementitious matrix composition for stabilizing and encapsulating waste heavy metal compounds comprising: about 55% by weight ladle furnace slag particles, about 18% by weight of 2M sodium hydroxide solution and about 27% by weight of sodium silicate; wherein the ladle furnace slag particles are of 45 μm and below.
16. A cementitious matrix composition for stabilizing and encapsulating waste heavy metal compounds comprising: about 61% by weight ladle furnace slag particles, about 8% by weight of 2M sodium hydroxide solution and about 31% by weight of sodium silicate; wherein the ladle furnace slag particles are of 250 μm and below.
PCT/SG2004/000245 2003-10-28 2004-08-13 A method and composition for stabilizing waste mercury compounds using ladle furnace slag WO2005039702A1 (en)

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WO2006087484A2 (en) * 2005-02-21 2006-08-24 Philippe Pichat Fabrication d ' un matériau solide à partir d' un hydroxyde alcalin
KR100752327B1 (en) 2006-09-12 2007-08-27 재단법인 포항산업과학연구원 Removal method of mercury contained in emission gas from incinerator by blast furnace slag and apparatus of the same
CN104001709A (en) * 2014-05-19 2014-08-27 上海大学 Solidifying and stabilizing method of mercury in desulfurized gypsum by employing chemical bond phosphatic ceramic combined with sulfide
JP2014198642A (en) * 2013-03-29 2014-10-23 住友大阪セメント株式会社 Hydraulic composition

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JP2014198642A (en) * 2013-03-29 2014-10-23 住友大阪セメント株式会社 Hydraulic composition
CN104001709A (en) * 2014-05-19 2014-08-27 上海大学 Solidifying and stabilizing method of mercury in desulfurized gypsum by employing chemical bond phosphatic ceramic combined with sulfide

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