MXPA06006550A - In situ treatment process to remove metal contamination from groundwater - Google Patents

Abstract

The present invention provides a process for enhancing the metal contaminant sorption capacity of mineral compounds within a groundwater-bearing formation by manipulating the pH and the surface acidity of the mineral compounds. The process is useful in removing metal contaminants from groundwater within a groundwater-bearing formation, providing a backstop treatment for groundwater after previous water treatment, and for protection of water sources, for example well-head protection.

Description

IN SITU TREATMENT PROCESS TO ELIMINATE METAL CONTAMINATION OF UNDERGROUND WATER BACKGROUND OF THE INVENTION Groundwater is an important source of water. In consideration of the purity of the water, there are minimum acceptable tolerance values for several metal ions. The amounts of metal ions dissolved in water that are above the desirable or acceptable limits can be considered as contamination. Heavy metal ions are particularly undesirable contaminants in many cases. The present invention provides methods to create an unsatisfied demand for the absorption of metal in water carrier formations in such a manner that the metal contaminants are effectively removed from the ground water passing through the water carrier formation. A water-bearing formation, in many cases referred to as an aquifer, typically consists of areas through which groundwater flows rapidly, as well as deviated areas through which water passes more slowly. The water bearing formations (aquifers) commonly joined by relatively impermeable formations, referred to as semipermeable layers. Metal contamination typically enters an aquifer and flows through the more conductive portions, diverting less conductive semipermeable areas and layers. Metal ions commonly diffuse into the deviated semipermeable areas and layers, and can be absorbed there. In any attempt to flood clean the metal contamination of an aquifer, the metal is gradually released into the main groundwater flow of diverted areas and contiguous semipermeable layers. The clean water passing through said water bearing formation can thus be contaminated over an indefinite period of time. The resulting concentration of contaminants in the water carrier formation may be small, but significantly relative to health standards. There are several sources of heavy metal contamination. These include, but are not limited to, mining district drainage, electrical and electronic manufacturing processes, ammunition production and weapons laboratories, metal shielding processes, battery recycling, coal combustion and very fine ash waste, refinery of oil, production and storage of chemicals and the nuclear industry. Metal carrier fluids having contamination in a water carrier formation are commonly acidic. It has been reported that in the United States, acid mine drainage affects more than 19,000 kilometers of rivers and streams. Some scientists classify toxic mine drainage as the biggest water quality problem facing the Western United States. It is said that only in the state of Colorado, the waste of more than 7,000 abandoned mines contaminates more than 2, 500 km of streams. A significant, but unknown amount of acid drainage has infiltrated the underground surface, acidifying drinking water aquifers there, and contaminating them with metals. The methods known for the remedy of water contaminated with metals include active remedy methods, direct precipitation methods, reactive barriers, and methods of controlled natural attenuation. Active remedy methods for groundwater treatment involve pumping contaminated water from an aquifer and treating contaminated water to remove metal contaminants (for example, through precipitation processes, absorption processes, or electrochemical processes) . In some cases, the water returns to the aquifer where it is withdrawn into the water production well. Such pumping facilities require a long-term commitment and facilities and processes tend to be expensive. Another problem is the disposal of the metal contaminant that has been removed, since the treatment process typically generates large amounts of waste contaminated with metals. One of the difficulties encountered in the art with the metal attenuation active remedy methods is that the methods do not effectively treat the problem of the gradual release of metals from the water carrier formation. For example, metal contaminants can be diffused from deviated low conductivity sediment lenses in areas of high conductivity. In some cases, the water treated by active remedy is pumped back to the aquifer before pumping to be used. If the problem of releasing metals from the water carrier formation itself is not addressed, then the metals can diffuse into the previously treated water, and in this way they can again become unsuitable for immediate use without further treatment. Another persistent problem with the active remedy is that the difficulty in removing a certain amount of metal contaminant increases significantly with the decrease in concentration of metal ions. As a result, it is significantly more expensive, in time and money, to treat a large volume of slightly contaminated water than to treat a small volume of highly contaminated water. Direct precipitation methods for groundwater treatment involve the precipitation of metal contaminants within the water source (eg, aquifer) to keep metals out of groundwater in motion. These methods in some cases involve converting metals into sulfur or other insoluble forms, and both biotic and abiotic proposals have been used. Biotic proposals use detoxification microorganisms to convert metals into insoluble granules; Such proposals may involve introducing sulfur compounds and stimulating sulfate-reducing bacteria. Abiotic proposals use solution methods to provide ligands and suitable reaction conditions to form insoluble precipitates. A disadvantage of this type of proposal is that they are capable of precipitating only the metal ions present in the aquifer at the time of treatment. An additional difficulty of this method is that the precipitated metals are subject to redisol tion (for example, by oxidation of their lfur's granules), allowing the metal ions once again to contaminate the water in the aquifer. Reactive barriers are constructed within a trench dug through an aquifer. The barriers, through which the water can pass, are designed to create a chemical or biological reaction zone where metallic contaminants are immobilized. The disadvantages for reactive barriers include the expense of ding them, the difficulty in applying them to areas where contamination has been or is not limited to shallow depths, the possibility of the water flow diverting them, the possibility that Metal concentrations are not reduced to acceptable levels, and uncertain long-term performance. The methods of monitored natural attenuation for groundwater treatment use the naturally present composition, structure, and microbial content of the aquifer and sediments to immobilize unwanted compounds, such as metal ions. These methods can be used after periods of active remedy. These methods have the potential, when successful, to significantly reduce costs. Such methods for processing groundwater sources run into administrative barriers such as costly environmental monitoring required for process approval, coupled with a costly and lengthy application approval process in the United States. In the United States, there is also political opposition, and the long-term effectiveness of the methods is uncertain. In natural attenuation methods, the removal of metal contaminants may depend on the absorption capacity of the terrestrial structures through which the groundwater moves. When groundwater is infiltrated with acidic fluids, water-bearing formation becomes acidic, markedly decreasing the effectiveness of natural attenuation methods. Groundwater itself is not usually able to rapidly affect the pH of acidified regions in the earth, where the absorption of metals into sediments is hindered. Most groundwater has insufficient alkalinity to rapidly neutralize sediment surfaces. As a result, the surface acidity remains high during the remedy, thus decreasing the effectiveness of the formation in the attenuation of concentration of metal ions. In addition, high surface acidity can allow previously absorbed metals to desorb and re-enter the groundwater flow. Source control refers to processes for the control of pollutants from a wastewater source. For example, such treatments may involve precipitation of heavy metals using alkali, and may also include addition of a precipitation agent such as silica, see, for example, U.S. Patent Nos. 5,370,827 and 3,579,443. These treatments do not occur in an underground water bearing formation, but are carried externally, on the surface of the earth. In the art, flood cleanup techniques are known to flood clean unwanted metals from off-ground formations that are responsible for contaminating groundwater. U.S. Patent No. 5,324,433 and concurrent 5,275,739 describe in situ methods for removing and stabilizing heavy metal contaminants soluble in soil and groundwater. They describe an ion displacement method of introducing an aqueous remedy solution into a soil formation to make soluble, mobilize and remove heavy metal ions from the soil, counteract the retention of ions by charged clays, displace the heavy metal or radioactive ions with harmless ions that occur naturally. The remedy solution described contains at least one remedy ion selected from the group consisting of aluminum, magnesium, calcium, potassium, sodium, hydrogen, chloride, sulfate, carbonate, bicarbonate, hydroxide, or any mixture thereof. After having sufficiently cleaned the soil formation by flooding with the remedy solution to decrease the residual unwanted metal ion content, the soil formation was treated with a stabilization solution consisting essentially of sodium silicate, silicate potassium, and a mixture thereof to co-precipitate remaining metal contaminants and inhibit their removal. The descriptions of any citation in this description are incorporated herein by reference. In summary, there are no methods to treat a water carrier formation to improve or recover its ability to absorb metals. There are no methods that effectively treat the metal problem by diffusing out of diverted regions in the main stream of a water bearing formation. There is a need for an alternative or addition to existing groundwater treatment processes to attenuate the metal contaminant content. There is a great demand for this process that does not require costly absorbing resins or off-site treatment. There is a need for improvement in methods of natural attenuation of groundwater treatment.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a process for enhancing or recovering the metal contaminant absorption capacity of mineral compounds within a water carrier formation by manipulating the pH and surface acidity of the mineral compounds. The process can be useful (i) to provide a water carrier formation capable of more effectively attenuating the content of groundwater metals currently within the formation, as well as groundwater that passes through the formation in the future, (ii) ) to provide a collecting treatment for groundwater after previous water treatment, and (iii) for protection of water sources, for example, well head protection. In a contemplated process, a water carrier formation is exposed to an alkaline flood cleaning solution. With this process, the metals are absorbed in their place in the water carrier formation instead of contaminating the groundwater. Cleaning by alkaline flood causes mobile metals to absorb or precipitate, strengthens the absorption of metals and works against desorption. More importantly, alkaline flood cleaning creates the unmet demand for metal absorption that will continue to remove metal contaminants from the groundwater that passes through the formation. A preferred process for attenuating the groundwater metal content of a groundwater carrier formation is described herein. A groundwater carrier formation typically consists of at least one mineral compound, and often several. Of course, all mineral compounds do not absorb metals to a significant degree. For purposes of discussing the present invention, a contemplated groundwater carrier formation has at least one absorbent mineral compound that is capable of absorbing metals.

This required mineral compound is referred to in the claims as "a mineral compound" for ease of reference. It should be understood that the use of "a" in the claims is open to have more than one, but at least one, unless specifically referenced. A water carrier formation is provided that is made of groundwater and a mineral compound. The mineral compound has a mineral surface with absorbent sites. Groundwater may contain mobile metal contaminants, immobilization which is desired. In this preferred process, part or effectively all mobile metal contaminants are removed from the groundwater through the next absorption process. An aqueous alkaline solution is applied to the water carrier formation to neutralize the acidity of the groundwater and the surface acidity of the mineral compound. Decreasing the surface acidity of the mineral compound has the effect of enhancing the ability of the absorbent sites provided by the mineral compound to absorb metal ions. In preferred processes, the mineral compounds include ferric oxide, manganese oxide, alumina or silica; each of these compounds can also be composed of hydroxide and / or water, as well as minor amounts of various chemical constituents. The balance of the absorbent sites on the surface of the compound changes by raising the surface pH in such a way so as to enhance the strength and absorption capacity for metal ion contaminants. The mineral compound in the groundwater carrier formation that has been in contact with the alkaline solution is referred to herein as a "treated mineral compound". When groundwater contaminated with metals makes contact with the treated mineral compound, the absorbent sites absorb the mobile metal contaminants. A treated mineral compound has an increased absorption capacity as a result of the treatment. As a result, the groundwater in the treated water carrier formation has an attenuated metal content compared to the groundwater in the water carrier formation before treatment. In an embodiment of the preferred process, the application of the aqueous alkaline solution is achieved by injection of the aqueous alkaline solution into the groundwater carrier formation. In one embodiment of the preferred process, the aqueous alkaline solution includes one or more of hydroxide, carbonate, phosphate, phosphite, or silicate, preferably hydroxide, carbonate or silicate. The cationic composition of the aqueous alkaline solution is discussed in the detailed description. The type of mineral (s) in the water carrier formation affects the preference of aqueous alkaline solution, as discussed in detail below. In one embodiment of the preferred process, the mineral compounds included in the groundwater carrier formation are one or more of ferric oxide, alumina, silica, or manganese oxide (III), which provide absorbent sites, including their hydrated and non-hydrated oxides and hydroxide forms. A contemplated process creates an unmet demand for metal absorption. In addition, in some embodiments of the preferred process, the application of aqueous alkaline solution for groundwater carrier formation inhibits the desorption of metal contaminants from the mineral compounds in the groundwater carrier formation. In some embodiments, the percolation of metals from low conductivity lenses is inhibited to form a new mobile metal contaminant. The present invention has many benefits and advantages, several of which are listed below. A benefit of the invention is that the process can be carried out in the aquifer and does not require removal of the aquifer sediment. An advantage of the invention is that the process also prevents desorption of metals from aquifer sediment in groundwater. Another benefit of the process is that it does not add harmful chemicals to the environment. An advantage of one embodiment of the invention is that it is useful for treating an underground water bearing formation whose metal absorption capacity has been decreased by draining acid water (eg, from mines) that has contaminated groundwater.

A benefit of one embodiment of the invention is that it is useful as a pickup treatment for wastewater from a contaminant column after primary treatment, such as a permeable reactive barrier or source control. An advantage of one embodiment of the invention is that it can provide protection from a contaminant column for well water supply.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings forming a portion of this description, Figure 1 illustrates the iron form (u-axis "Number of Surface Sites") in surface structures containing ferric oxide minerals, illustrated as an acid function (x-axis "pH "). The absorption of metal ions (preferably cationic) increases as the pH increases, since the absorption of metal cations on the iron surface (III) releases hydrogen ions (H +). As such, an increase in pH serves to promote the absorption of metal cations, and to cause the cations to be absorbed more tightly. Conversely, environmental acid factors inhibit the absorption capacity of natural water-bearing structures that contain ferrous minerals. Figure 2 illustrates the absorption profiles for the metal ions lead (Pb ++), copper (Cu ++), zinc (Zn ++), and mercury (Hg ++). The graph shows the fraction of metal absorbed as a function of pH. Under non-saturating metal contaminant conditions, when the pH is about 6.5, the ferric mineral is capable of absorbing essentially all of the lead (l l), copper (l l) and zinc (I I), while the mercury is not absorbed. By providing conditions such that the pH is about 9, the absorption of essentially all of the mercury (ll), as well as the other metal ions, is ensured.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a process for enhancing the ability of mineral compounds within a groundwater carrier formation to absorb metal contaminants. The parameters of the contemplated processes are discussed in more detail below. The processes focus on the manipulation of the pH in the local aqueous environments in a groundwater carrier formation and the surface acidity of the mineral compounds. The processes have useful applications in groundwater purification, such as providing a groundwater carrier formation that has enhanced absorption capacity and is therefore effective in attenuating the groundwater metal content, by providing a collecting treatment for groundwater. after previous water treatment, and for the protection of water sources, for example, well head protection.

For groundwater treatment processes of attenuating metal contaminant content, the present invention recognized that the surface acidity of the mineral compounds in the groundwater carrier formation plays an important role. The infiltration of acidic fluids into groundwater bearing formations increases the surface acidity of the mineral compounds, and this decreases the effectiveness of natural attenuation methods and may even exacerbate the contamination of heavy metal ions. Certain negative effects, such as acidic liquid waste, decrease the local pH of the mineral compounds responsible for providing natural absorption sites within the groundwater bearing formation. Under acidic conditions, the affinity of absorption of surface sites for contaminating metal ions decreases considerably. The surface acidity of the mineral compounds also creates a regulated pH region that serves to maintain acid conditions in the underground surface. These negative effects are not found naturally. The majority of groundwater lacks sufficient neutralizing capacity to neutralize surface acidity within a reasonable period of time for the remedy. As a result, the mineral surface acidity remains high during the remedy, thus decreasing the effectiveness of attenuating the content of metal ions.

Another negative effect of high surface acidity is that the acidic conditions allow the previously absorbed metals to desorb and diffuse into the groundwater flow. High acidity also encourages the mobilization of metal ions from low conductivity lenses within the groundwater bearing formation in the main groundwater flow. The processes of the invention provide a means for enhancing the absorption capacity of the metal contaminant of groundwater bearing formations * by manipulating the pH using aqueous alkaline solutions. The goal is to immobilize metal contaminants from the groundwater solution. This is in contrast to U.S. Patent No. 5,324,422, where the goal is to mobilize and thus eliminate the metal contaminants from the soil formations. The processes of the invention are particularly useful for the remedy of a carrier formation of groundwater contaminated with acid. An aqueous alkaline solution is introduced into a carrier formation of acid-contaminated groundwater to neutralize the acidity and convert the mineral compounds within the groundwater bearing formation back to a chemical form having the desired absorption capacity for the mineral compounds. . Although the net effect of a process of the invention is a process to attenuate the content of groundwater metals, a process contemplated in many cases is a remedial process for the groundwater carrier formation itself, restoring the innate ability of the groundwater. mineral compounds there to absorb metal contaminants from groundwater. The introduction of an aqueous alkaline solution into a groundwater carrier formation results in the entry of the aqueous alkaline solution into the groundwater flow, which is often quite slow. The entry typically results in dilution of the aqueous alkaline solution introduced into the groundwater. The mineral compounds in the groundwater carrier formation are treated at the front of the solution of the aqueous alkaline formation, consuming basicity units by neutralizing the acidity within a groundwater carrier formation of acid contamination. The groundwater flowing behind the alkaline front enjoys the benefit of the higher absorption capacity of the metal compounds treated within the formation.

In some cases, it may be advantageous, by introducing aqueous alkaline solution into a ground water carrier formation, also to remove water from the formation. Said elimination can make the introduction of the aqueous alkaline solution more efficient and / or faster. Preferably, the water is removed below gradient (relative to the groundwater flow) of the introduction point (s) of the alkaline solution. A process of the present invention is exemplified by the following embodiment. An aqueous alkaline solution is pumped into an aquifer and begins to migrate in the direction of flow (ie, into a production well). The transit time for the injected solution is possibly weeks, months or years, due to the slow speed at which the groundwater typically migrates through a groundwater bearing formation. As the solution migrates through the aquifer, its alkalinity reacts with sediments, leaving the water more acidic and the sediment surfaces neutralized. The reaction occurs on a "front" that migrates in the direction of groundwater flow, since the alkalinity is cleared from the moving front as it passes through the groundwater bearing formation. Upstream of the alkaline front, the solution is alkaline; downstream, its alkalinity has been consumed. If one considers the process in terms of pore volumes required, it depends on the number of moles of alkalinity that the specific aquifer consumes as it is neutralized., and the moles of alkalinity contained in each pore volume of the applied alkaline solution (concentration dependent). Optimal treatment conditions will vary from one underground water bearing formation to another. Preferably, a sufficient amount of alkaline solution of sufficient strength is injected to drive the reaction front through the affected area of the aquifer (i.e., the contaminated area or area to act as a collector). Carrier formations of groundwater. The contemplated groundwater carrying formations have mineral compounds that provide absorbent sites for metal contaminants. These formations include aquifers, which include water-bearing sediment and water-bearing rock. Water bearing rocks and other groundwater bearing formations include sandstone, which is commonly made of silica-based mineral compounds. The groundwater carrying formations contemplated may include, among other things, sediment, soil and rock. The underground water bearing formations also include those formations from which groundwater can be obtained, although the formation can not rise to the level of being called "aquifer". The term "aquifer" has a functional definition that involves the ability to obtain "useful quantities" of water. Said limitation does not apply to the groundwater carrying formations contemplated in the process of the present invention. Mineral compounds Contemplated mineral compounds that provide absorbent sites for metal contaminants include, but are not limited to, metal oxides, hydroxides, and oxyhydroxides with surface sites that convert between the hydroxy, proton, hydroxy, and oxy forms. Figure 1 shows these forms for ferric oxide, including the number of metal contaminant absorption sites as a function of surface acidity. Examples of preferred mineral compounds are iron, manganese, silicon and aluminum ferrous metals. It should be understood that the surface sites of these mineral compounds exist in equilibrium, depending on their respective pH profile and other environmental factors, in the form of oxide and hydrated oxide form (oxyhydroxide). Metallic contaminants When metal contaminants are immobilized, they are removed from groundwater that moves through a formation that carries ground water. Metal contaminants of interest are dissolved or dispersed in the groundwater, and are referred to herein as mobile metal contaminants. Metal contaminants in groundwater that are of primary interest include heavy metals, such as lead and mercury. Copper and zinc also rise to contaminant levels in certain groundwater. Other significant divalent metal ions that commonly require remedy are Ni2 + and Co2 + (the latter may be radioactive). For the purposes of the present invention, the metal contaminants contemplated are those whose levels are above the desired concentration in groundwater. Metal contaminants that tend to be absorbed by the contemplated mineral compounds are commonly cations. Absorbent sites. For example, a metal oxide surface absorbing site, represented in the equations below as = MOH, which shows the metal in the mineral compound, M, bonded to the coarse ore by three (representing multiple), is bound to oxides for the extended mineral structure, and with an -OH in the absorbent site. The mineral compound absorbs a metal contaminant as shown in the example equations below. Pb2"+ = MOH - - >; = MOPb * + H + Hg2 + + = MOH - - > = MOHg + + H + Cu2 + + = MOH - - > = MOCu + + H + Zn2 + + = MOH - - > = MOZn + + H + In the typical mineral compounds that provide absorbent sites, ferric oxides, manganese oxide (l l l), silica and alumina, M in the above equations represents iron, manganese, silicon and aluminum, respectively. Aqueous alkaline solution. A contemplated aqueous alkaline solution is a solution of high pH, pH of 8 or more, capable of raising the local pH at the surface of the mineral compounds within the groundwater bearing formation. Preferably, said solution is an aqueous solution of a strong base or a mixture of strong bases. Preferred basic anions include, but are not limited to, hydroxide, carbonate, phosphate, phosphite, silicate, with hydroxide, carbonate or silicate being particularly preferred. Two factors must be considered to determine the base concentration to be included in the alkaline solution.

First, the pH of the aqueous alkaline solution needs to be high enough to allow, once the solution is mixed with the ambient groundwater flow, that the absorbing mineral compounds in the groundwater carrier formation absorb the metal contaminants. Please refer, for example, to the pH profile for iron oxide in Figure 2. Second, the alkaline flood should be designed so that as much alkalinity as possible will be used to neutralize the surface acidity. For this second factor, it is important to avoid the mineral precipitation of the base, which then could consume the majority of the alkalinity of the aqueous alkaline solution (and thus, neutralize the energy). The last criterion can also be related to the selection of the cationic composition of the aqueous alkaline solution to be used for alkaline flooding. For example, a calcium solution should not be used in an underground water bearing formation where precipitation of carbonate minerals (eg, CaCO3) is possible. Preferably, when introducing the aqueous alkaline solution and mixing with the ambient groundwater flow, the pH of the mixture is not greater than about 12, in order to prevent the precipitation of the pH controlling base from the solution or the dissolution of the absorbent mineral compounds. For example, the alumina will dissolve at a very high pH, such as pH above 12. Examples of a strong base contemplated include, but are not limited to, metal hydroxide, metal carbonate, or metallic silicate; wherein the metal is a highly prevalent low valence metal ion, such as sodium or potassium, although magnesium and calcium of divalent cations are also useful, and preferably the metal ion is abundant in uncontaminated groundwater that occurs naturally; and where the anion (basic) portion is a mineral anion that occurs naturally. The concentration of the pH controlling base in the aqueous alkaline solution must be sufficiently high that the alkalinity is not consumed by reactions within the water carrier formation immediately. Preferably, the concentration before mixing with ambient groundwater is at least 0.1 N base, more preferably 1 to 5 N. The cationic composition of the aqueous alkaline solution can be any cation, preferably inorganic in nature. The cationic composition of the aqueous alkaline solution is not a metal ion whose elimination may be desired, but preferably is a standard cation, such as an alkali metal or alkaline earth metal of the lA group or HA group of the periodic table, preferably rows 2 to 4 (for example, K +, Na +, Ca ++, Mg ++), or a typical inorganic cation such as ammonium ion (NH4 +), among others. Particularly preferred examples are alkali metal ions such as K +, Na +, Ca ++ and Mg ++. Also particularly preferred is the ammonium ion, N H4 +, which also serves as a nitrogen source for some bacteria that can also enhance the water purifying properties of aquifers. The type of mineral (s) in the water carrier formation affects the preference of aqueous alkaline solution, as discussed in more detail below.

The anionic composition of the aqueous alkaline solution is a strong base, preferably an inorganic base. Such bases include, but are not limited to, hydroxide ion, silicate ion, aluminate, phosphate and carbonate. In one embodiment of the preferred process, the aqueous alkaline solution comprises one or more of NaOH, Na2CO3, or NaS03. The nature of the mineral composition of the water-bearing formation should be considered when selecting a base and against ion to prepare the aqueous alkaline solution. For example, if a water-bearing formation contains a high concentration of calcium-laden minerals, the use of carbonate ions in the aqueous alkaline solution will cause the precipitation of calcium carbonate within the water-bearing formation., consuming alkalinity and possibly preventing the flow of groundwater. As another example, if a water-bearing formation contains a high concentration of alumina-based minerals, such as kaolinite, the mineral compounds will react with a KOH solution to make an unwanted potassium clay. In order to evaluate the risk of mineral precipitation, calculations (on the basis of mineral solubility) and / or experiments are preferably used. The type of experiment commonly used to assess the risk of mineral precipitation is a column experiment in which a large tube is filled with sediment from the groundwater bearing formation, the solution is pumped slowly through the column, and observed and analyzes the chemistry of the waste. Application of the alkaline solution. The alkaline solution can be introduced into the groundwater carrier formation by a suitable means. For example, it can be introduced by injection wells. In order to encourage the flow in the groundwater bearing formation, it may be useful to remove the groundwater at another location at the same time, for example, by pumping downstream. For example, injection systems can be used as defined by any suitable well arrangement for the particular application (groundwater treatment, protection or well head collector). The injection wells can be arranged in any convenient pattern, for example, a conventional five-site pattern in which a central well is surrounded by four injection wells located in some symmetrically way. Alternatively, other suitable patterns include, among others, in-line drilling, sautéed line drilling, four sites, and seven sites. The term "pore volume" is generally understood in the geological technique. ASTM International D44404-84 (1998) e1 describes a standard test method for determining pore volume and soil pore volume distribution by mercury intrusion porosimetry. The pore volume is used herein as applied to a groundwater carrier formation as the volume of water required to replace or flush the water in a certain volume of the formation. Although there may be substantial heterogeneity in a groundwater carrier formation, the amount applied need not be precise in order to successfully carry out the present invention. In addition, as the aqueous alkaline solution passes through the acidic groundwater bearing formation, basic equivalents are lost in the front as neutralization occurs, so that the alkaline front is delayed further and further behind the front extending from the solution introduced as it progresses. As a result, the concept of introduced pore volumes does not directly reflect the number of pore volumes of alkaline solution that are actually in the groundwater bearing formation at a given time, depth or area. As a result, the "pore volumes" referred to herein are used in a very general manner. In a preferred embodiment, at least a few pore volumes of aqueous alkaline solution are applied to the portion of the groundwater bearing formation to be treated. The aqueous alkaline solution rapidly balances with the absorption surface compared to the time it typically takes for water to migrate through the underground surface of an underground water bearing formation. Acid-based reactions tend to be very rapid (eg, limited diffusion). Typically, the absorbent sites immediately equilibrate with the pH of the aqueous alkaline solution.

However, due in part to the volume of an underground water bearing formation and the flow velocity, a typical process carried out in accordance with the present invention uses a large volume of aqueous alkaline solution (eg, approximately 189 to 378,540 liters). ) applied over a long period of time (for example, several hours to several months). A person skilled in the art is able to immediately appreciate the range of variation both in volume and time that will be useful for various applications, depending on the particular groundwater carrier formation that is to be treated. The approximate pore volume suggestions provide sufficient guidance to a person skilled in the art, who is also very familiar with the acceptable flow rates through the different groundwater bearing formations and thus the application time necessary to enter the desired volume. . Treated mineral compound. The exposure of a mineral compound present in a ground water carrier formation to an aqueous alkaline solution returns the absorbent sites there to a basic form having a higher affinity for absorbing metal contaminants than the mineral compound absorbing sites at low pH. See, for example, Figure 2. In a contemplated process, the metal contaminant absorption capacity is enhanced or recovered through the application of the alkaline solution to the groundwater carrier formation. After the treatment, the mineral compound is referred to herein as the "treated mineral compound". Dimmed metallic content. The goal of the present invention is to reduce the level of contaminants in the groundwater that passes through an underground water bearing formation. Relative to the initial metallic content of groundwater of an untreated groundwater bearing formation, the methods of the present invention result in a lower concentration of contaminants in the accumulated groundwater of the treated groundwater bearing formation. This is referred to as attenuated metal content. An alternative use in the art relates to the attenuation of metal by passing contaminated groundwater through a soil formation carrying groundwater containing absorbent clay and / or other minerals. This is the natural process of contaminant attenuation by fa land. For the natural process, attenuation of metallic content refers to the concentration of metal before and after the water passes through the soil. For a process of the invention, attenuation refers to the concentration of metal in the ground water that passes through the soil after treatment in accordance with the present invention relative to without (or before) treatment. As applied to the natural process, the invention has been termed "accelerated attenuation" of the metallic content, since the treatment according to the invention allows the groundwater carrier formation to more effectively reduce the metallic content of the groundwater passing through. the formation. De-absorb and filter. When metal contaminants that have already been absorbed into mineral compounds within the groundwater carrier formation release those metal contaminants in the groundwater, that is called "desorption". At a higher pH, the binding constant (absorption affinity) is higher for metal cations. The acid contamination of the groundwater causes the pH, and thus the affinity of absorption, to fall, so that the metal contaminants are desorbed. Filtration refers to metal contaminants that move in groundwater from within the minerals of the groundwater bearing formation. Dissolved metallic species. In some modalities, groundwater contains other metallic species that are capable of precipitating and providing additional absorbent sites. In preferred modalities, the metal species are iron (11), aluminum (11) or silicon (IV) which can be precipitated to form iron oxide, alumina or silica having the preferred absorbent sites. In addition, iron (II) and manganese (ll) can be oxidized to (l 1 l) in the presence of fluids with high pH, and then precipitated as additional absorbent mineral. Applications of the process The processes of the invention are useful for treating groundwater bearing formations in situ. Due to the altering nature of the pH of the treatment, its application is more useful in formations that have been exposed to acidic conditions that have altered the nature of the contaminant that sequesters the formation. The processes according to the invention are also useful as a local treatment for attenuating metal concentrations, for example, to reduce contaminants in groundwater that move away from a source of contamination or that approach a source of water that must be protected. . The following examples of the invention are provided to explain in detail the applications of selected embodiments of the invention, and should not be limiting. Example 1. Remedy for acid contamination. An aquifer is contaminated by metal-rich acid drainage from a mining operation. The mine is located upstream of an underground water bearing formation that has a slow but generally downward direction of flow. The acid contamination of the groundwater carrier formation decreases the metal absorption capacity of the mineral compounds within the groundwater bearing formation. The current, sporadic release of acid contamination results in several columns of heavy metal contamination that extend up to approximately 914 meters downhill from the mining operation.

The groundwater carrier formation contains a significant portion of kaolinite (alumina-based) mineral compounds, but little calcium. The drainage of the mining operation is modified, so that water contaminated with metals no longer enters the aquifer. An extraction well is drilled approximately 914 meters downstream from the mining operation to assist in cleaning by flooding the water through the contaminated portion of the aquifer, and to serve as a control well. The extraction well initially produces groundwater samples that have a high metallic content. An injection well is drilled in the mining operation, near the original source of contaminated water. For an initial period, approximately 1 1, 356 liters of clean water per day are injected into this well, and an equivalent amount produced from the extraction well. The water removed from the extraction well is treated to remove metal contaminants and neutralize the acidity, and is injected back into the injection well. After a period of three months, the injected water has displaced the original contaminated water from the highly conductive portion of the aquifer. At this time, the metal concentration observed in the extraction well falls sharply, although it remains in excess of environmental standards and continues to require treatment.

At this time, approximately 757 liters of a 1 N sodium carbonate solution per day are injected into the soil below the surface in each well of a five-well linear arrangement penetrating the aquifer, evenly separated over the pollutant column , from the mining operation to approximately 457 meters upstream of the extraction well. After six months of injection of the alkaline solution, the concentration of metals in water produced from the extraction well is observed to fall within environmental standards, and the pH is observed to have risen above 8. At this time, they cease the injection of the alkaline solution and the pumping of the extraction well. Samples of water are taken from the extraction well each week for a period of three years and monitored to ensure that the concentration of metals meets or exceeds environmental standards. Example 2. Picker for Source Control A mine operator performs several processes to recover precious metals from gold-laden earth using acid solutions. Some of these acid solutions sneak into an aquifer, creating a column of metal pollution that migrates gradually downhill. Mine operators complete recovery processes and carry out treatments, such as sulfur precipitation from acid washes, to remove hazardous heavy metals from contaminated groundwater. The treatments are effective, but not completely effective, and the contaminating metals continue to migrate down the aquifer in small but important concentrations. In addition, there is concern that some of the previously immobilized metals will be mobilized at a future date. The invention is applied as a source control to minimize the continuous movement of contaminants over the aquifer. A 2N aqueous solution of sodium hydroxide is pumped into the earth in a linear arrangement of ten injection wells that spans a range of the aquifer below the polluting column. The wells are constructed approximately 46 meters below the current position of the foot of the column, separated approximately 18.30 meters, and placed to intercept the column as it advances. Aqueous alkaline solution is pumped into the injection sites until the high pH front crosses an observation well approximately 91 meters downstream from the injection wells. The mineral compounds of the groundwater carrier formation between the injection sites and the observation well are thus treated according to the invention. The result is an effective absorption zone in situ that protects the pending aquifer below the mining operation from the source of contamination.

The monitoring of metal content in groundwater downstream of the treatment area shows that contaminating metals are present at concentrations that meet or exceed environmental standards. Example 3. Pick-up for permeable reactive barriers. A chemical waste site provides a source of metal contamination. Industrial waste buried in underground containers is subject to leakage as old, buried containers deteriorate. The waste site lies above an aquifer through which water is migrating in a certain direction. The contamination of metals enters the aquifer and forms a column that migrates downhill. A reactive barrier is placed so that it covers approximately the width of the metal contaminant column (as determined from the sample test) and is placed below the source of metal contamination. The permeable reactive barrier serves as a first protective stage that prevents pollution from migrating off-site. To enhance the effectiveness of the cleaning properties of the groundwater bearing formation, injection points are instituted in a linear pattern downstream of the chemical waste site and reactive barrier. A volume of a 5N solution of sodium hydroxide is pumped at the injection points which is sufficient to displace the pore volume several times by approximately 91 meters surrounding the disposal site approximately 15 meters in depth, or a volume of approximately 1, 394 square meters per linear foot around the injected perimeter of the site. The mineral compounds treated in this way are formed for approximately 91 meters from the region sloping down from the site. The groundwater below is not removed to make room for the aqueous alkaline solution that has been applied. Instead, the solution is allowed to diffuse further into the groundwater carrier formation to create an expanded treated zone, although the alkali concentration is decreased due to the previous passage through the formation. The treated zone serves to immobilize the metal ions that pass through or bypass the reactive barrier. Groundwater monitoring is carried out in several locations near the chemical waste site. Example 4. Protection of the wellhead. A well is located in a formation that carries groundwater. As a result of pumping from the well, groundwater flows from the groundwater carrying formation generally into the well. In a circular pattern surrounding the well, approximately 27 meters from the well site, a 2N aqueous solution of sodium carbonate is injected into the groundwater bearing formation. The well is pumped to remove the alkaline solution through the groundwater carrier formation until a sharp rise in pH is noticed. The reaction of the alkaline solution with the mineral compounds creates a wide band of approximately 27 meters of groundwater bearing formation surrounding the well head containing treated mineral compounds. The wellhead is thus protected from contamination by metal ions. From the foregoing, it will be noted that numerous modifications and variations can be made without departing from the true spirit and scope of the present invention. It should be understood that no limitation with respect to the specific examples presented is intended or should be inferred. The description is designed to cover the modifications of the appended claims as they fall within the scope of the claims.

Claims (19)

RECIPI N D ICAC IO NES

1 .- A process to enhance the absorption capacity of an underground water bearing formation comprising the steps of: a. providing a carrier formation for groundwater and a mineral compound, wherein said mineral compound has a mineral surface comprising absorbent sites with an initial metal contaminant absorption capacity, wherein said groundwater may contain mobile metal contaminants; b. apply an aqueous alkaline solution to the groundwater carrier formation; and c. contacting said mineral compound with said aqueous alkaline solution to convert the mineral compound to a form having a metal contaminant absorption capacity more than the initial metal contaminant absorption capacity so as to form a mineral compound treated within said formation carrier of groundwater.

2. The process according to claim 1, wherein the application step is achieved through injection of the aqueous alkaline solution into the groundwater carrier formation.

3. The process according to claim 1, wherein said aqueous alkaline solution comprises one or more of NaO H, Na2CO3, or Na2SiO3, or a combination thereof.

4. - The process according to claim 1, wherein said mineral compound comprises one or more of ferric oxide, manganese oxide, alumina, silica or their respective hydrated forms, hydroxy not hydrated or sxihydroxy.

5. The process according to claim 1, wherein said aqueous alkaline solution application inhibits the desorption of metals from the mineral surface to form new mobile metallic contaminant.

6. The process according to claim 1, wherein said groundwater may also contain dissolved metal species, said process comprising an additional step of: d. that the groundwater makes contact with the aqueous alkaline solution to precipitate the dissolved metal species to form precipitated metal species, where the precipitated metal species provide absorbent sites of additional metal ion contaminants.

7. The process according to claim 6, wherein said dissolved metal species is selected from the group consisting of iron (III), iron (II), manganese (III), manganese (II), aluminum ( III) and silicon (III).

8. A process for the remedy of groundwater contaminated by metal ions through attenuation of the metallic content there, wherein said groundwater is in a formation carrying ground water, which comprises the steps of: a. providing a ground water supply formation, wherein said groundwater carrier formation comprises groundwater and a mineral compound, "and wherein said mineral compound has a mineral surface comprising absorbent sites with an initial metallic contaminant absorption capacity, and where sub-terrain water may contain mobile metal contaminants, b) apply an aqueous alkaline solution to the underground water-seeker formation in a manner that penetrates the aquifer areas from which water flows rapidly: c. When the mineral compound is contacted with said aqueous alkaline solution to convert the mineral compound to a form with a higher metal contaminant absorption capacity than the initial metal contaminant absorption capacity to form a mineral compound treated within said formation carrier of groundwater; and contact said c This mineral is treated with groundwater that can contain mobile metallic contaminants to allow the mineral compound to absorb mobile metal contaminants to form water with a metal content attenuated.

9. The process according to claim 8, wherein the application step is achieved through injection of the aqueous alkaline solution into the groundwater carrier formation.

10. - The process according to claim 8, wherein said aqueous alkaline solution comprises one or more of NaOH, Na2CO3, or Na2SiO3, or a combination thereof.

11. The process according to claim 8, wherein said mineral compound comprises one or more of ferric oxide, manganese oxide, alumina, silica or their respective hydrated, hydroxy non-hydrated or oxyhydroxy forms.

12. A process for the protection of the well head of melamic contaminants, wherein said well head is in a formation carrying ground water, comprising the steps of: a. providing a wellhead in a groundwater bearing formation, wherein said groundwater carrier formation comprises groundwater and a mineral compound, and wherein said mineral compound has a mineral surface comprising absorbent sites with a contaminant absorbing capacity. initial mephalic, and wherein said sub-terrain water may contain mobile metallic contaminants; b. apply an aqueous alkaline solution to the groundwater bearing formation in such a way that at least some groundwater reaching the wellhead has had to pass through the portion of the groundwater bearing formation that has the mineral compound traiate formed in step c; c. said mineral compound making contact with said aqueous alkaline solution to convert the mineral compound to a form with a metal contaminant absorption capacity higher than the initial metal contaminant absorption capacity to form a mineral compound within said water carrier formation underground d. that said treated mineral compound makes contact with groundwater which may contain mobile metal contaminants to allow the mineral compound brought to absorb mobile melamic condensers to form groundwater with an attenuated metal content thus proving the wellhead of melamine contaminants.

13. The process according to claim 12, wherein the application step is achieved by injection of the aqueous alkaline solution into the porous formation of groundwater.

14. The process according to claim 12, wherein said aqueous alkaline solution comprises one or more of NaOH, Na2CO3, or Na2SiO3, or a combination thereof.

15. The process according to claim 12, wherein said mineral compound comprises one or more of ferric acid, manganese oxide, alumina, silica or their respective hydrated forms, hydroxy non-hydrated or oxyhydroxy.

16.- A process to provide a collector for a permeable reactive barrier water treatment method or a water source control method to eliminate more meiálicos conaminaníes, where the sub-irrigation in a subsurface water supply formation has It has been previously prepared by a method of water permeable reactive barrier analysis or a water source control method, a collector that includes the steps of: a. provide an underground water carrier formation, where there is a subterranean water carrier formation comprising a mineral compound and groundwater that has been previously irrigated by a water treatment method of a permeable reactive barrier or a control method water source, and wherein said compound has a mineral surface that comprises absorbent sites with an initial metal contaminant absorption capacity, and wherein said groundwater can contain mobile metal contaminants; b. applying an aqueous alkaline solution to the groundwater carrier formation in such a way that at least some of the groundwater reaching the portion of the water bearing formation its groundwater having the treated mineral compound formed in step c has previously been treated by a method of water permeable reactive barrier irrigation or a water source control method; c. That said mineral compound makes contact with said aqueous alkaline solution to convert the mineral compound to a form with a metal contaminant absorption capacity higher than the initial metallic coniraminanie absorption capacity to form a mineral compound brought therein. subsurface water supply formation; d. that said traverted mineral compound makes contact with groundwater which can coniine mobile meiallic devices to allow the ore compound to absorb mobile metal contaminants to form ground water with an attenuated metal content thus providing a collector for a barrier water treatment method. permeable reactive or a water source control method to eliminate more meíálicos contaminaníes.

17. The process according to claim 16, wherein the application step is achieved by injecting the aqueous alkaline solution into the groundwater carrier formation.

18. The process according to claim 16, wherein said aqueous alkaline solution comprises one or more NaOH, Na2CO3, or Na2SiO3, or a combination thereof.

19. The process according to claim 16, wherein said mineral compound comprises one or more of ferric oxide, manganese oxide, alumina, silica or their respective hydrated forms, hydroxy not hydrated or oxyhydroxy.