IL266935A - Stabilization of sulfur-containing waste for landfiling - Google Patents

Description

38726/19 STABILIZATION OF SULFUR-CONTAINING WASTE FOR LANDFILLING The present invention relates to processing sulfur-rich waste, and particularly to an environmentally friendly process for handling sulfur-containing waste, resulting in a stable solid waste suitable for safe landfilling.

Background of the Invention Hundreds of thousands tons of sulfur-containing waste accumulates from chemical and other industries around the world every year. A significant source of sulfur waste are filter cakes from the massive production of sulfuric acid, resulting from molten sulfur filtered through media based on diatomaceous earth and lime. Controlled burial is necessary in order to prevent the formation and spreading of sulfur compounds, which is cost demanding, particularly in view of the still stricter environmental and safety regulations. When exposed to oxygen, sulfur may undergo slow oxidation creating acidic problematic environment, while anaerobic bacterial reactions may occur in the deeper layers of the landfill which will produce smelly and toxic sulfides. The existing systems are too complicated and do not enable to easily convert sulfur-rich waste to stable material for landfilling. It is therefore an object of this invention to provide an environmentally safe method of converting sulfur-containing waste to a material which can be economically and safely buried by landfilling.

It is another object of this invention to provide an environmentally friendly industrial process for handling sulfur-containing waste and for converting said waste to a material which may be landfilled, while complying with the valid land filling regulations.

Other objects and advantages of present invention will appear as the description proceeds. 38726/19 Summary of the Invention This invention provides a method for safe landfilling sulfur-rich waste, comprising steps of i) mixing said waste with an aqueous liquid and with a bonding agent, the bonding agent comprising one or more components selected from the group consisting of hydroxides of alkaline earth metals, oxides of alkaline earth metals, carbonates of alkaline metals or alkaline earth metals, silicates, or ash obtained from burning a fossil fuel, wherein said bonding agent is added in an amount of between 0.25 and 1.5 weight parts per one weight part of said waste, and ii) transferring said mixture to the site of landfill. Said bonding agent preferably comprises at least one component selected from the group consisting of lime, carbonate, bicarbonate, silicate, cement, slag cement, clinker, coal fly ash, and shale fly ash, and said aqueous liquid preferably comprises waste water, wherein mixing said bonding agent with said waste and with said aqueous liquid provides stabilized sulfur-rich waste mixture, which is transferred to the site of landfill before or after the mixture at least partially solidifies. Said aqueous liquid is preferably waste water in an amount of between 0.1 and 1 weight parts per one weight part of said waste. In one embodiment, the method of the invention comprises steps of mixing one weight part of sulfur-rich waste, 0.25-0.75 weight parts of waste water, and 0.4-1.0 weight parts of said bonding agent, thereby obtaining a mixture of stabilized sulfur-rich waste, which is transferred to the site of landfill in a continuous mode or in a batch mode, thereby obtaining stabilized and solidified waste mixture exhibiting after seven days a compression strength of at least 1 MPa, such as at least 2 MPa, for example at least 3 MPa, for example at least 4 MPa, for example at least 5 MPa, for example at least 6 MPa, for example at least 7 MPa.

The bonding agent at least partially comprises, in one embodiment, cement, such as Portland, slag, or other commercial cement. In other embodiment, the bonding agent comprises ash, for example fly ash, bottom, ash, crushed ash, or a mixture thereof. Said ash may comprise coal ash, shale ash, or other fossil fuel ash. The bonding agent may comprise clinker, sodium silicates, sodium carbonates, alkali metal hydroxides, and alkaline earth metal hydroxides. The aqueous liquid, for example industrial or municipal or other waste water, such as treated industrial, municipal or agricultural waste water, 38726/19 is admixed to the sulfur-rich waste in an amount necessary for obtaining a blendable and homogenizable mixture. Usually, the homogenized mixture is transferred to the site of landfill, where it hardens and results in stable waste safely embedded in a hardened matter, the waste being chemically and mechanically stabilized against eventual move or against oxidation. Said sulfur-rich waste may originate from the oil producing industry or sulfuric acid production, or other industrial and chemical activities. The method for stabilizing sulfur-rich waste and landfilling the stabilized waste may employ, in producing the stabilized mixture, other types of industrial, chemical, biological, agricultural, or other, waste, including sewage sludges, sludges from municipal sanitary wastewater treatment centers, materials from waste and wastewater treatment plants, sludges of lake or river sediments, petroleum refinery sludge, effluent sludges form pharmaceutical production, pulp and paper industry wastes, printing wastes, acrylic latex wastes, sludges from metal surface processing, leather industry wastes, and chemical industry wastes.

Detailed Description of the Invention It has now been found that the known problem of handling sulfur-rich waste can be handled by employing a process which stabilizes the sulfur particles by embedding them in a stable matrix created from said waste and a bonding agent.

Oil production and sulfuric acid production are the main sources of the waste rich in sulfur. Since sulfur is a flammable material, the sulfur containing waste must be processed before depositing or landfilling. The treatment of such waste may usually include burning or landfilling, the former producing dangerous gases, and the latter requiring special permission and control. Burning is accompanied by producing environmentally complicating materials which, moreover, exhibit strong greenhouse effects. Burying may result in igniting and smouldering. The existing methods usually include some or all of the drawbacks: the methods do not entirely destroy or neutralize the dangerous components, the method steps enhance the final waste volume too much, the method do not prevent the formation of volatile components including dust, aerosols, gases, during the method steps, and an eventual presence of organic 38726/19 contaminants may unacceptably complicate the method. The invention aims at avoiding the known problems and at stabilizing the sulfur-rich waste, while enabling its safe earth deposition, in accordance with the regulations, such as EC-33-2003. Usually practiced land deposition aims at restricting oxygen access to the sulfur-rich waste; the present invention, beside restricting the oxygen access, further aims at isolating sulfur from the oxygen or air environment, thereby restricting both the fire initiation and fire spreading. In order to achieve said aims, the sulfur particles are essentially coated with a cement. The landfilling system according to the invention enables to employ the existing landfilling sites without need of allocating new sites for this purpose, and without necessitating to obtain further permissions required by the regulations relating to starting new sites.

Stabilization by solidification aims at preventing the leakage of the dangerous materials and their seeping out of the controlled area where it may be inadvertently breathed or drunk or otherwise contacted by members of the ecologic chains. Physical and chemical steps may neutralize and/or immobilize the dangerous components. The system and the method of the invention reduce the mobility of the dangerous components by entrapping them within a stable matrix, by reducing their volatility via lowering the content of fine particles, and by enhancing the long-term stability of the processed waste, while employing relatively low-cost means. The stabilization in the process of the invention may include chemical steps modifying some of the components of the processed mixture, reducing the components' volatility and/or toxicity, for example by converting the fluid phase to a solid phase or from a solubilized phase to a solid phase.

The solidification according to the invention includes a step of stirring waste with bonding components, such as cements, in order to form a solid by a chemical reaction between the bonding component and other components in the waste mixture, whereas mechanical elements support the process, including an efficient homogenizing step.

The process advantageously provides uniform blocks, or ceramic or clay-like grains or other solidified objects. 38726/19 The stabilized waste product has a reduced surface/volume ratio compared to the original waste; the penetrability of the contaminants substantially decreases, as well as the horizontal flow. Preferably, the free liquid content of the stabilized waste decreases, and its mechanical strength increases. Water, such as rain, incidentally contacting the processed waste do not solubilize or substantially move the contaminants. The stabilization by solidification in accordance with the invention aims at utilizing reactions between bonding agents and water with other components in the waste in order to at least one of: precipitate, immobilize, encapsulate, neutralize, detoxify, absorb, or adsorb the dangerous material. The process according to the invention preferably employs inorganic, cost-effective, bonding agents, including cements, fly ash, lime, or silicates. Preferably, cement as an important binding agent undergoes hydration and solidifies, optionally including cheap bonding agents obtained as side products in industrial processes, such as for example fly ash, preferably substituting at least a part of more expensive bonding components. In most cases, the cement with waste provides a solid that has sufficient strength to safely hold also the soil above the deposited processed waste. In preferred modifications, the cement is partially substituted or enriched with lime, slag, ash, such as coal ash, or others.

The system and process according to the preferred embodiment of the invention aims at stabilizing a sulfur-enriched waste, such as waste comprising 85% or more elemental sulfur, while complying with the regulations, including EN 12457/2. The processed and stabilized waste complies with the flammability test. In an important embodiment, the sulfur-rich waste is combined with other waste types in order to work like filler materials, but also to assist in disposal of other waste types at landfilling sites. In pilot experiments, batches of a hundred kilograms of sulfur-rich waste were processed, aiming at handling 5000 ton waste in the landfilling site per year, at the first stage.

The materials of processed sulfur-rich waste were tested for flammability potential. The sulfur-rich waste processed according to the invention was found to be not self- flammable; moreover, it did not support spreading fire on its surface when shaped as a 38726/19 cylinder 2-10 cm in diameter and 0.5-5 cm thick. The test was preferably performed according to ASTM standard D4982-12.

The process of the invention, aiming at stabilizing sulfur-rich waste for landfilling, comprises a solidification step stabilizing the elemental sulfur particles against leaching and moving, and also against combining smaller particles to bigger ones, the stabilization being achieved by occluding the sulfur particles and entrapping within a heat stable matrix. The matrix is formed from cement and/or components selected, among others, from lime, ash, blast furnace slag, and silicates, the strength of the matrix depending on several factors, including the degree of hydration and the character of the porous structure which is formed during the process. The process of the invention minimizes the effects of the sulfur-rich waste on the final advantageous physical and chemical properties of the processed waste mixture.

The invention will be further described and illustrated by the following examples.

Examples Materials Waste containing 1%-100% elemental sulfur from various industries were employed.

Cements of type CEM II and CEM III and other pozzolanic materials (for example burnt shell oil ash) were employed.

Methods Flammability test A sample of sulfur rich processed waste, shaped as a flat cylinder having a diameter of 2-10 cm and a thickness of 0.5-5 cm, was kept in the flame of a gas burner (for example, Bunsen burner); a material comprising the non-processed sulfur waste caught fire, and the fire spread quickly along the surface of the cylinder; a material comprising a sulfur waste processed in accordance with the invention did not start to flame. The cement formed during the process of the invention occludes sulfur particles, thereby preventing the fire spread, whereas the matrix is stable in fire. 38726/19 Ignitability test The test material was formed into a strip 250 mm in length; an ignition source was applied to one end to determine whether combustion will propagate along 200 mm of the strip within a specified period, and if it does – the burning time is measured over a distance of 100 mm and the burning rate is measured in mm/s (Guidelenes for Landfill Disposal of Sulphur Waste, 2011, Government of Alberta).

Example 1 500 g waste from sulfuric acid production, 85% elemental sulfur, was mixed with waste water in an amount of between 30 and 400 g, and with various cements in an amount of between 150 and 600 g. All experimental batches were stirred and allowed to react, and eventually solidify at ambient temperature. Parameters characterizing the stability of the product were measured shortly after the homogenization, and further in 1 week, 1 month, and about 3 months. The measures parameters included DOC (dissolved organic carbon as determined by method EN12457-2), compression strength in MPa (determined by cylindrical sample of 100 mm length and 40 mm radius), TDS (total dissolved solids as determined by method EN12457-2), leaching (as determined by method EN12457-2), pH (as determined by method EN12457-2). The results obtained from 100 batches showed that the sulfur-rich material was safely stabilized if the bonding agent (cements) was employed in an amount of between 0.25 and 1.5 kg per 1 kg of said sulfur-rich waste, and if said water was employed in an amount of between 0.1 and 1.0 kg per 1 kg of said sulfur-rich waste. It was found that cements of the types CEM II and CEM III provided excellent results; for example 200 g CEM II, 600 g CEM III, and 700 g waste water (industrial waste water) per 1 kg sulfur waste (contained over 60% elemental sulfur) resulted in a quickly solidified block exhibiting in 7 days 23 DOC, 14.2 MPa compression strength, 4.9 TDS, 12.2 pH, and in 34 days DOC of 24, 10.6 MPa compression strength, 7.6 TDS. The flammability test showed that the stabilized material did not catch fire and the fire did not spread over its surface (the material is categorized “not flammable”). 38726/19 Example 2 In pilot batches, 1000 kg waste from sulfuric acid production, or an oil refinery, or other sources, 85% elemental sulfur, was mixed with 150 kg to 250 kg cement CEM II, and 550 kg to 650 kg cement CEM III, and water added to the final amount of less than 500 kg.

While the invention has been described using some specific examples, many modifications and variations are possible. It is therefore understood that the invention is not intended to be limited in any way, other than by the scope of the appended claims.

Claims (4)

38726/19 IL266935/2 CLAIMS

1. A method for safe landfilling sulfur-rich waste comprising at least 25% elemental sulfur, comprising steps of i) mixing said waste comprising at least 25% elemental sulfur, with an aqueous liquid and with a bonding agent, the bonding agent comprising one or more components selected from the group consisting of hydroxides of alkaline earth metals, oxides of alkaline earth metals, carbonates of alkaline metals, carbonates of alkaline earth metals, silicates, and ash obtained from burning a fossil fuel, wherein said bonding agent is added in an amount of between 0.25 and 1.5 weight parts per one weight part of said waste, and ii) transferring said mixture to the site of landfill.

2. The method of claim 1, wherein said bonding agent further includes at least one component selected from the group consisting of lime, carbonate, bicarbonate, silicate, cement, slag cement, clinker, coal fly ash, and shale fly ash,; and wherein said transferring occurs before or after the mixture at least partially solidifies.

3. The method of claim 1, wherein said aqueous liquid is waste water in an amount of between 0.1 and 1 weight parts per one weight part of said waste.

4. The method of claim 1, wherein said mixing comprises mixing said waste with 0.25-0.75 weight parts of waste water per 1 weight part of said waste, and with 0.4-1.0 weight parts of said bonding agent per one weight part of said waste, thereby obtaining a mixture of stabilized sulfur-rich waste; and wherein said transferring occurs in a continuous or batch mode; thereby obtaining stabilized and solidified waste mixture exhibiting after seven days a compression strength of at least 1 MPa. 9