KR20150077709A - In-Situ Chemical fixation of metal contaminants - Google Patents

Abstract

Embodiments of the present invention provide treatment of arsenic contaminants in an in-situ environment. According to an embodiment of the present invention, an oxidizing agent stabilized with an aqueous chelate iron solution such as a liquid peroxide agent can be prepared. The stabilized oxidizing agent and the aqueous chelate iron solution can be alternately induced to an in-situ environment polluted with arsenic by an alternate insertion screen to the in-situ environment so as to correct arsenic pollution of the in-situ environment.

Description

In situ chemical fixation of metal contaminants [

Field of the Invention [0002] The present invention relates to the field fixation of metal contaminants in soil and / or groundwater.

Treatment of contaminated soil and groundwater is an important aspect of environmental science and is concerned with neglected hazardous waste disposal sites. The most common methods for site improvement include excavation and landfill disposal. Although these methods are known for removing contaminants, both methods are costly and, in some cases, not impossible, but difficult to perform. More recently, research has focused on the conversion of contaminants contained in soil and groundwater based on the development of field treatment techniques. These techniques focus on the removal of contaminants through physical methods or on-site treatment using chemical or biological methods.

Physical methods to remove metal contaminants focus on pump utilization and treatment techniques. Chemical methods of removing metal contaminants focus on the chemical change of the valence state, ie, reduction or oxidation, to convert metal contaminants to a less or less hazardous state. The use of strong reducing agents has proven to be effective in converting the valence state of chromium VI, a highly mobile and toxic form of chromium, to chromium III, a form of mobility and less toxicity.

Arsenic as a metal contaminant moves freely in groundwater and shows a particularly toxic and more mobile valence state, arsenic III (As ⁺³ ). Thus, field arsenic treatment in soil and groundwater has focused on binding or fixing arsenic to iron complexes that can settle in the soil matrix under field conditions, whether precipitated or filtered from water in a ground treatment system. Conventional arsenic treatment processes are used directly in beverage processing facilities. Specifically, in the conventional arsenic treatment process, the extracted ground water is mixed with the iron solution and the hydrogen peroxide, that is, the peroxide oxidizes As ⁺³ to As ⁺⁵ , the concentration of dissolved oxygen is increased by the addition of peroxide, It uses oxalic oxygen to form oxyhydroxide, and As ^{+ 5} is bound to the iron oxide oxide. This complex is a solid and is filtered from groundwater.

Treatment of arsenic by conventional processes is more difficult under the external or site conditions of a wastewater treatment plant because it is not realistic to dispense and mix separate solutions, iron and peroxides, which is not realistic when contacting the organic material in the soil matrix, And hydrogen peroxide instability. Under field conditions, the reaction occurs rapidly after being injected into the soil matrix saturated with groundwater, and the peroxide rapidly decomposes into oxygen and water to produce an abundance of gas in the soil matrix. Although the treatment program can be carried out by these methods, the distribution radius around the injection position is very limited and the injectable volume is small. These limitations are due to the high rate of reaction that creates a significant amount of gas exposing fluids, groundwater, and injection solutions to the surface or daylight immediately after initiation of injection.

Embodiments of the present invention solve technical deficiencies in the treatment of metal contaminants in paper and provide new and untitled systems and methods for treating arsenic contaminants in the field, e.g., soil, groundwater or rock.

In one embodiment of the present invention, a method of treating arsenic contaminants in an arsenic contaminated field environment comprises preparing an aqueous chelating iron solution and a stabilized oxidizing agent. The method also includes adding an aqueous chelating iron solution and a stabilized oxidizing agent to the site environment in an amount sufficient to promote co-precipitation of iron-arsenic oxyhydroxide. Where the aqueous chelating iron solution and the oxidizing agent may be added alternately before and after the separate water injection into the field environment. Arsenic is then oxidized from As ⁺³ to As ⁺⁵ and iron is oxidized from Fe ⁺² to Fe ⁺³ .

In one aspect of this embodiment, the aqueous chelating iron solution comprises an effective amount of iron selected from the group consisting of Fe (II) salts, Fe (III) salts, Fe (II) chelates, Fe . In another aspect of this embodiment, the stabilized oxidant source is a peroxide selected from the group consisting of hydrogen peroxide, sodium peroxide, and calcium peroxide. In another aspect of this embodiment, the aqueous chelate iron solution is maintained at a pH of about 5 to 8. [ In another aspect of this embodiment, the stabilized oxidant source is stabilized with a stabilizer selected from the group consisting of, for example, an acid, a salt and a mixture of acid and salt, and in yet another example, phosphoric acid, potassium phosphate and phosphate, ≪ / RTI > and combinations thereof.

Further aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. These and other aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. While the embodiments shown herein are presently preferred, it is understood that the invention is not limited to the precise arrangements and means shown.
Figure 1 is an illustration of a process for treating arsenic contaminants in a field environment.
2 is a flow chart illustrating a process for treating arsenic contaminants in a field environment;

Embodiments of the present invention provide for the treatment of arsenic contaminants in a field environment. According to one embodiment of the invention, a stabilized oxidizing agent, for example a stabilized liquid hydrogen peroxide oxidizing agent, can be prepared with an aqueous chelating iron solution. To stabilize arsenic contaminants in the site environment by oxidizing and anchoring the arsenic present in the site environment, stabilized oxidant and aqueous chelating iron solution can be alternately introduced into the field environment through the injection screen.

In the drawings, FIG. 1 schematically illustrates a process for treating arsenic contaminants in a field environment. As shown in FIG. 1, the peroxide agent 160A can be prepared by adding water 110 to the peroxide source 120 and the dry stabilizer 130. At the same time, the aqueous iron solution 160B can be prepared by adding water 110 to the dried or liquid iron 140 and the chelate 150. The peroxide activator 160A and the aqueous iron solution 160B are then introduced into the on-site environment (e.g., by injection screening, for example, by injection wells connected directly to a wellhead or injection wells connected to a source of water) 170). The implant screen 180 may serve to oxidize arsenic +3 100 present in the field environment 170 to arsenic +5190, which may be adhered to iron-oxyhydroxide.

In another embodiment, Figure 2 is a flow chart illustrating a process for treating arsenic contaminants in a field environment. Beginning at block 210A, a peroxide agent is prepared. Peroxide agents may include, for example, peroxides such as hydrogen peroxide, sodium peroxide or calcium peroxide. The peroxide source may also be stabilized using, for example, stabilizers such as acids, salts or mixtures of acids and salts. More specifically, the stabilizer may be a potassium phosphate or a combination of phosphoric acid and potassium phosphate.

At the same time, an aqueous chelating iron solution is prepared in block 210B. The aqueous iron solution may comprise an effective amount of iron selected from the group consisting of Fe (II) salts, Fe (III) salts, Fe (II) chelates, Fe (III) chelates and combinations thereof. The aqueous iron solution can be maintained at a pH of about 5 to 8, for example, by adding a pH adjusting agent comprising water or a chelating agent to the aqueous iron solution.

Thereafter, both the peroxide agent and the aqueous iron solution can be added to the field environment, such as soil, ground water or crushed rock. In this regard, the field environment can be a soil or groundwater with moderate to high permeability. Alternatively, the field environment can be a soil or groundwater having a low or intermediate permeability. In either case, the peroxide agent can be added to the site environment in an effective concentration and in an amount sufficient to promote co-precipitation of the iron arsenic oxy-oxide.

In one aspect of the invention, the peroxide agent and the aqueous iron solution can be added to the field environment using an injection screen. Note that the injection screen can be introduced into the field environment, into the unsaturated vadose zone of the field environment or into the capillary fringe of the saturated zone. The injection may be performed at a high pressure of about 5 to 100 pounds per inch where the peroxide agent and the aqueous iron solution, as shown in blocks 230 to 250, are passed through the water source to the field environment alternately after an initial water flush After receiving the inflow, they receive additional water. It should be understood, however, that the peroxide agent and the aqueous iron solution can be introduced into the field environment in any order, and that in an embodiment of the invention both can be continuously introduced into the field environment.

The corresponding structures, materials, acts, and equivalents and functional elements of all means or steps in the following claims are to include any structure, material or act for performing the function with other elements specifically claimed. The description of the present invention is presented for purposes of illustration and description and is not intended to limit the invention in the form presented herein. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The embodiments are chosen and described to illustrate the principles and practical application of the invention and to enable others skilled in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be obvious that modifications and variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims (21)

A method of treating arsenic contaminants in a field environment,
Preparing an aqueous chelating iron solution;
Adding a stabilized oxidizing agent source to the field environment at an effective concentration and further adding the aqueous iron solution to the field environment in the presence of an oxidizing source in an amount sufficient to promote co-precipitation of iron-arsenic oxyhydroxide step; And
Oxidizing arsenic in a field environment and oxidizing iron in a field environment. The aqueous chelating iron solution according to claim 1, wherein the aqueous chelating iron solution comprises iron selected from the group consisting of Fe (II) salts, Fe (III) salts, Fe (II) chelates, Fe Lt; / RTI > effective amount. 2. The method of claim 1, wherein the stabilized oxidant source is a peroxide selected from the group consisting of hydrogen peroxide, sodium peroxide, and calcium peroxide. The method of claim 1, wherein the stabilized oxidant source is stabilized with a stabilizer selected from the group consisting of an acid, a salt, and a mixture of an acid and a salt. 5. The method of claim 4, wherein the stabilizing agent is selected from the group consisting of phosphoric acid, potassium primary phosphate and a combination of phosphoric acid and primary potassium. The method of claim 1, wherein the stabilized oxidant source is a hydroperoxide in water having a concentration of 70 wt% or less. 2. The method of claim 1, further comprising the step of adding a pH adjusting agent to the aqueous iron solution to maintain the aqueous chelating iron solution at a pH of about 5 to 8. 8. The method of claim 7, wherein the pH adjusting agent is selected from water and a chelating agent. 2. The method of claim 1, comprising adding the stabilized oxidant source and the aqueous chelating iron solution alternately to the field environment. 10. The method of claim 9, wherein the aqueous chelating iron solution is first added to the field environment and then a stabilized oxidant source is added. 10. The method of claim 9, wherein the aqueous chelating iron solution is added after the stabilized oxidant source is first added to the field environment. 2. The method of claim 1, comprising continuously adding said stabilized oxidant source and said aqueous chelating iron solution to a field environment. 2. The method of claim 1, wherein the field environment comprises at least one of soil and groundwater having moderate to high permeability. 2. The method of claim 1, wherein the field environment comprises at least one of soil and groundwater with low or medium permeability. 2. The method of claim 1, wherein the field environment is selected from the group consisting of soil, groundwater, and crushed rock mass. 16. The method of claim 15, wherein the stabilized oxidant source and the aqueous chelating iron solution are added to a zone within the field environment known as capillary fringe. 16. The method of claim 15, wherein the stabilized oxidant source and the aqueous chelating iron solution are added to a zone within the field environment known as an unsaturated vadose zone. 16. The method of claim 15, wherein the stabilized oxidant source and the aqueous chelating iron solution are added to a field environment zone that includes a saturated zone. 16. The method of claim 15, wherein the oxidant source and the aqueous chelating iron solution are added to the field environment multiple times. 2. The method of claim 1, wherein the oxidant source and the aqueous chelate iron solution are added to the field environment at high pressure. 21. The method of claim 20, wherein the high pressure is about 5 to 100 psi.

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