Soil remediation composition

Abstract

Soil remediation composition containing: - Water, - at least a two-layer or three-layer clay mineral, - at least one cation consisting of a group of Al 3+ , Fe 3+ , Fe 2+ , Ca 2+ , Mg 2+ or monovalent cations are chosen - at least a restructuring plan, - where the cation is a component of the remediation agent and / or is present as a component of a soluble salt.

Description

TECHNICAL AREA

[0001] The invention relates to a composition for soil remediation. Soil remediation involves removing pollutants from contaminated soils or converting them into non-toxic forms to enable the affected areas to be used again. STATE OF THE ART

[0002] For the remediation of contaminated sites ("legacy sites"), in-situ chemical-physical methods can be employed. These methods can extract pollutants such as halogenated and non-halogenated solvents, mineral oils, PAHs (polycyclic aromatic hydrocarbons), and other organic compounds from the affected soils or convert them into harmless substances. Furthermore, heavy metals can also be converted into less hazardous species via redox reactions. Depending on the pollutant, oxidative or reductive methods can be used for decontamination. In certain cases, these processes can offer significant economic and environmental advantages compared to traditional methods such as soil replacement or groundwater control.

[0003] During the chemical oxidation of pollutants by introducing suitable oxidizing agents into the subsurface, a significant portion of the naturally occurring carbon and other oxidizable soil constituents is also oxidized, in addition to the pollutants themselves. In some cases, this background consumption (Natural Oxidant Demand, NOD) can consume more than 80% of the oxidizing agent used, leaving less than 20% of the reagents available for pollutant oxidation. Therefore, the achievable concentration of oxidizing agents in an aqueous solution may not be sufficient to achieve complete oxidation of all pollutants.If, on the other hand, the oxidizing agents are used as solids - especially in the form of suspensions - they can accumulate in the mixing and storage tanks or in the pipes, so that too little oxidizing agent is available for the reaction with the pollutants and blockages occur in the systems. PRESENTATION OF THE INVENTION

[0004] Based on this prior art, the invention aims to provide an improved composition for soil remediation that enables simple and efficient application.

[0005] The composition according to the invention for the remediation of soil is defined by the features of main claim 1. Further developments of the invention are the subject of subsequent claims.

[0006] The composition according to the invention for the remediation of soil contains water, at least one two-layer or three-layer clay mineral and at least one cation consisting of a group of Al 3+ , Fe 3+ , Fe 2+ , Ca 2+ , Mg 2+ or monovalent cations are chosen. Furthermore, at least one remediation agent is included. The cation can be present as a component of the remediation agent and / or added to the remediation agent as a soluble salt.

[0007] Clay minerals are layered silicates named for their layered crystal structure composed of silicon and oxygen, hydrogen, magnesium, and aluminum. Clay minerals consist of tetrahedral layers with corner-sharing SiO₄ tetrahedra and octahedral layers with edge-sharing Al(OH)₆ octahedra. Depending on the arrangement of these layers, they are classified as two-layer clay minerals (tetrahedral layer-octahedral layer) or three-layer clay minerals (tetrahedral layer-octahedral layer-tetrahedral layer). Examples of two-layer clay minerals include kaolinite and attapulgite, while examples of three-layer clay minerals include illite, smectite, bentonite, and vermiculite. In the tetrahedral layers, silicon may be partially substituted by aluminum, and in the octahedral layer, aluminum may be partially substituted by magnesium. Synthetic layered silicates also fall under the category of clay minerals for the purposes of these claims.

[0008] Such clay minerals are available commercially under names such as Acti-Gel 208° and Cimgel 2080. ® , Min-U-Gel ® ATTAGEL ® VEEGUM ® or PANGEL ® S9 available.

[0009] When suitable cations are added to aqueous dispersions of clay minerals, they can act as thickening agents. The cations cause the silicate particles to aggregate and agglomerate, forming a gel. The interactions between the silicate particles and the cations induce an association via secondary bonds, such as ionic or hydrogen bonds, resulting in a three-dimensional network that leads to gelation. Multivalent cations, such as Al⁻¹, are particularly effective in this process. 3+ , Fe 3+ , Fe 2+ , Ca 2+ , Mg 2+They are particularly efficient at crosslinking the silicate particles. This allows gel formation at lower concentrations compared to monovalent cations. However, suitable gels can also be formed with monovalent ions.

[0010] The gel formed in this way has special properties due to its cross-linked internal structure. For example, it can keep high concentrations of solids in suspension for extended periods without the solids settling at the bottom. The remediation agent can therefore be used as a solid, allowing for a significantly larger quantity to be introduced and then diffusely distributed throughout the subsurface. In this way, up to 1,300 kg of remediation agent can be suspended in 1,000 liters of gel.

[0011] Furthermore, due to its exceptional adhesive properties, the gel encapsulates the soil to be remediated, including individual soil particles, and holds the remediation agent in place. Additionally, the liquid (low-viscosity) application benefits from infiltration of the composition, allowing both preferential and non-preferential flow paths to be treated equally. This enables the decontamination of soils even in the unsaturated zone.

[0012] In a first embodiment, the remediation agent can be an oxidizing agent or a reducing agent. When an oxidizing agent or a reducing agent is used as the remediation agent, it can, due to the special adhesive forces of the gel, encapsulate the pollutant adsorbed onto the soil grain as completely as possible and react with it – even when introduced into the unsaturated soil zone.

[0013] In this case, the remediation agent can be a water-soluble salt, with the cation of the remediation agent consisting of a group of Al 3+ , Fe 3+ , Fe 2+ , Ca 2+ , Mg 2+ or monovalent cations are chosen.

[0014] If an oxidizing agent is to be used as a remediation agent, it could be, for example, potassium permanganate (KMnO4), potassium persulfate (K2S2O8) or various percarbonates or peroxides.

[0015] If a reducing agent is to be used as a remediation agent, it can be, for example, ferrous sulfate (FeSO4), iron(II) carbonate (FeCO3), or various thionates. This allows, for example, chromium(VI) to be reduced to chromium(III), which is sparingly soluble in water and less toxicologically relevant. Elemental iron can also be used as a reducing agent and, with the composition according to the invention, introduced into the subsurface in finely dispersed form. There, the elemental iron can react with a range of pollutants, which are thereby converted into harmless products.

[0016] In principle, all oxidizing agents or reducing agents used for soil remediation can be used in the composition according to the invention.

[0017] If the remediation agent contains no free cations or too few due to insufficient water solubility, a suitable cation in the form of a corresponding water-soluble salt can be added to induce gel formation. The cation of the water-soluble salt is from a group consisting of Al 3+ , Fe 3+ , Fe 2+ , Ca 2+ , Mg 2+ or monovalent cations. Without the presence of another suitable cation in sufficient concentration, the mixture might be too thin (low viscosity), meaning the composition wouldn't remain in the soil long enough. In this case, the remediation agent wouldn't have enough time to react with the pollutants present in the subsurface.

[0018] In addition to or as an alternative to an oxidizing or reducing agent, the remediation agent can be sand. Using the composition according to the invention, the sand can be distributed evenly and effectively in the subsoil. This increases the permeability of the soil, allowing subsequent processing steps to be carried out more effectively.

[0019] Additionally or alternatively, the remediation agent can, for example, be a nutrient or trace element for bacteria. In this way, nutrients and / or trace elements can be introduced into the soil using the composition according to the invention. Mixtures of organic acids or oils, optionally with other carbon sources such as lactic acid or molasses, can also be introduced into the soil in this way. This promotes microbial activity in the soil, enabling the pollutants to be broken down by microbial activity.

[0020] Further advantages and features of the invention can be seen in the features further specified in the claims and in the exemplary embodiments below. WAYS TO IMPLEMENT THE INVENTION

[0021] The ratio of water to clay mineral can be in the range of 1:0.01 to 1:0.35 wt%. In this case, the composition would contain approximately 1 to 35 wt% clay mineral to water. Preferably, the ratio of water to clay mineral can be in the range of 1:0.05 to 1:0.30 wt%. In this case, the composition would contain approximately 5 to 30 wt% clay mineral to water.

[0022] In a subsequent remediation application, the composition can be applied to the soil to be remediated in such a way that approximately 0.1 to 6 percent by weight of clay mineral is present in relation to the soil mass.

[0023] For effective reduction of chromium(VI), the FeSO4 / soil mass ratio in grams per kilogram can be approximately 0.02 to 5 percent by weight.

Claims

[1] Soil remediation composition containing: - Water, - at least a two-layer or three-layer clay mineral, - at least one cation consisting of a group of Al 3+ , Fe 3+ , Fe 2+ , Ca 2+ , Mg 2+ or monovalent cations are chosen - at least a restructuring plan, - where the cation is a component of the remediation agent and / or is present as a component of a soluble salt. [2] Composition according to claim 1, - characterized by , that - the remediation agent is an oxidizing agent, for example potassium permanganate (KMnO4) or potassium persulfate (K2S2O8). [3] Composition according to claim 1, - characterized by , that - the remediation agent is a reducing agent, for example iron sulfate (FeSO4) or iron(II) carbonate (FeCO3). [4] Composition according to any one of the preceding claims, - characterized by , that - the renovation agent is sand. [5] Composition according to any one of the preceding claims, - characterized by , that - that the remediation agent is a nutrient or trace element for bacteria. [6] Composition according to any one of the preceding claims, - characterized by , that - the ratio of water to clay mineral is approximately 1 : 0.01 to 1 : 0.35 percent by weight, preferably approximately 1 : 0.05 to 1 : 0.30 percent by weight.