WO2002004139A1 - Method for in-situ purification of contaminated water by means of geochemical barriers of reactive materials - Google Patents

Abstract

The invention relates to a method for in-situ purification of water contaminated with, for example, heavy metals, metals, uranium, the decomposition products thereof and nitroaromatics, by means of geochemical barriers of reactive materials. Purification of contaminated water is achieved by the suitable construction of geochemical barriers, made from a homogeneous mixture and/or in layers of, for example, ferrous materials, non- and/or lightly-alloyed irons and/or waste products and/or residues from the metal processing industry and carbonaceous materials, lignite and/or dull coal and/or vitrain with a ratio of the mass proportion of the ferrous material to the carbonaceous material of from 2: 1 to 1:2. The aim of the invention is to develop an economical, low-energy, long-term and essentially natural process, which guarantees the long-term in-situ purification of water contaminated with for example, heavy metals, metals, uranium, the decomposition products thereof and nitroaromatics, which renders unnecessary the additional use of conventional methods or method steps, which gives sustained prevention of damage to the ecosystem by emission of contaminated water in to the environment and which does not require disposal of conventionally separated toxic materials.

Description

Process for the in-situ cleaning of contaminated water through geochemical barriers made of reactive materials

The invention relates to a method for in situ cleaning with pollutants such as heavy metals, metals, uranium, its natural decay products and nitroaromatics, contaminated water through geochemical barriers made of reactive materials.

Due to natural weathering processes, in particular through the oxidation of sulfidic minerals, and as a result of mining activities (e.g. technically introduced substances), contaminated groundwater occurs in natural systems and remains mine structures, heaps and sedimentation systems worldwide, from which contaminated and often acidic water (leachate, Mine water) leak into the environment. These waters are usually enriched with the soluble metals and radionuclides present in the geological formations.

The range of pollutants in these waters includes heavy metals, metals, nitroaromates and often uranium and its natural decay products.

Since these waters pose a hazard, cleaning is necessary. Treating these waters using conventional methods is cost-intensive and energy-intensive in the long term. Experience to date shows that the decrease in the pollution of such waters often lasts for periods of several years to decades.

In situ processes for pollutant removal in seepage, groundwater and mine water are known, which generally only individual pollutants or groups of pollutants (organic compounds such as halogen and mineral oil hydrocarbons, etc.) or heavy metals (Ni, Cd, Cr, Pb, Cu etc.) from the water. The technical implementation of these processes takes place as:

- geochemical barrier, mostly as a constructed reactive wall (funnel and gate),

- Successive Alkalinity Producing Systems (SAP 's) and

- Wetlands.

Pilot projects are known which treat reactive mine water for the treatment of mine water as it flows underground, taking into account typical geochemical boundary conditions. rieren, especially systems with elemental iron, with a neutralizing and / or reducing effect.

In Langmuir, D., Geochim. Cosmochim. Aca 42, 547-569 (1978) and Venkataramani, B .; Ventateswarlu, K. S .; Shankar, J. III. J. Colloid Interf. Be. 67 (2), 187-194 (1978) describes investigations on the in situ remediation of radionuclide-containing water, which are, however, only carried out on a laboratory scale. The transfer to specific applications only took place in the 1990s. According to Morrison, S. J .; Spangler, R. R, Environ. Be. Technol. 26 (10), 1922-1931 (1992), various industrial products (e.g. hydrated lime, fly ash, titanium oxide, lignite, peat and hematite) are used to separate pollutants in waste water from uranium ore processing, but these are only used to optimize the separation of uranium or molybdenum focus.

The separation of uranium from contaminated groundwater (Oak Ridge Y-12 Plant, USA) by Fe (0) under oxic and anoxic conditions is described in Farell, J .; Bostik, W. D .; Jarabek, R. J .; Fiedor, J.N., Uranium Removal from Ground Water Using Zero Valent Iron Media. Ground Water 37 (4), 618-624 (1999).

Studies on the use of organic materials in "biological" reaction barriers for the remediation of contaminated groundwater in the field of uranium mining (Shiprock, NM, USA) by Thombre, M. S .; Thomson, B. M .; Barton, L.L., Int. Conf. On Containment Technology, St. Petersburg, Abstract, p. 71, Florida, (Feb. 1997). Cellulose, wheat straw, alfalfa hay, sawdust and soluble starch compounds are tested as the reactor material. In addition to the removal of uranium, a decrease in the concentration of sulfate and nitrate is described.

Biotechnological approaches exist for the purification of acidic mine water as on-site technology (Somlev, V .; Tishov, S., Geomicrobiology Journal, 12 (1), 53 - 60, (1994)). With a reaction material made from an easily degradable organic substance and Fe (0) as carrier material, in addition to the reduction of sulfate, degradation or fixation of nitrate, heavy metals and arsenic is also achieved. After Blowes, DW; Ptacek, CJ; Benner, SG; Waybrant, K. R; Bain, JG, Uranium Mining an Hydrogeology II, Proceedings of the Unt. Conference, Freiberg, Germany, (1998) studies of mixtures of various organic materials for the treatment of acidic mine water are known. The mixtures of compost, leftover wood and limestone used resulted in a decrease in the concentration of downstream sulphate and heavy metals and an increase in pH.

Disadvantages of the known methods are:

- the restricted application of the processes to individual organic substances or groups of substances or to individual heavy metals,

- No suitability for the simultaneous cleaning of contaminated water and unproblematic separation of heavy metals, metals, uranium, its natural decay products and nitroaromatics as well as an increase in the pH value and

- The use of further conventional processes or process steps for the necessary purification of the water described.

The object of the invention is to develop an inexpensive, low-energy, long-term effective and natural process that guarantees permanent in-situ cleaning with pollutants such as heavy metals, metals, uranium, its natural decomposition products and nitroaromatics, contaminated water and the separation of pollutants, which the additional use of conventional processes or process steps is superfluous, the damage to ecosystems due to the escape of contaminated water into the environment is permanently prevented and no landfill of conventionally separated pollutants is required.

According to the invention, the object is achieved by a process for the in-situ cleaning of contaminated water by geochemical barriers made of reactive materials, that the water contaminated with pollutants such as heavy metals, metals, uranium, its natural decay products and nitroaromatics, by geochemical barriers which are present in and / or or technically created cavities are introduced into the flow paths of the waters and / or in technical facilities to which the waters are supplied, from a homogeneous mixture and / or in layers of or from ferrous materials, non-alloyed and / or low-alloyed iron materials and / or waste products and / or residues of metal processing manufacturing industry, and carbonaceous materials, brown coal, matt coal and / or bright coal, with a ratio of the mass fraction of the iron-containing materials to the mass fraction of the carbon-containing materials of 2: 1 to 1: 2, which are made of a homogeneous mixture and / or geochemical barriers created in layers have a water permeability coefficient of greater than 10 ^"2 m / s and a porosity of 50% to 95%.

Non-alloyed and / or low-alloyed iron materials and / or waste products and / or residues from the metalworking industry with a bulk density of 0.3 t / m ³ to 2.0 t / m ³ , a piece length of up to 50 cm, are used as ferrous materials Piece thickness up to 50 cm and a specific surface area of 0.05 m ² / kg to 0.5 m ² / kg and as carbonaceous materials, brown coal and / or matt coal and / or bright coal with an ash content of up to 25%, a sulfur content of 1% , and a grain size of up to 10 cm, which is mechanically stable and does not tend to form sludge.

The iron-containing materials lead to the formation of a low redox potential and a first step in raising the pH. In this process step, uranium is primarily removed. The carbonaceous materials cause a further pH increase and thus the hydrolysis of iron and aluminum. A number of heavy metals are excreted with the hydroxides. At the same time, further pollutants are sorptively bound to the carbonaceous materials.

Surprisingly, it was found that the combined use of the two reactive materials synergistically leads to significantly better results than can be expected from the addition of the effects of the individual components. The process cleans the water adequately, separates the pollutants and raises the pH. Other conventional cleaning processes can be omitted.

The two reactive materials are used as a homogeneous mixture and / or in layers in the direction of flow in a hydraulic element, eg. B. a natural cavity, a stretch, a diaphragm wall or a container through which the water is passed, introduced and flowed through by the water to be cleaned.

The introduction of the two reactive materials is carried out taking into account the specifically occurring water so that the required reactivity is ensured with a sufficient flow. A suitable ratio is used to set the required reactivity the mass fractions of the iron-containing materials to the mass fractions of the carbon-containing materials from 2: 1 to 1: 2, the geometry and the bulk densities of the reactive materials.

Embodiment 1

In an underground column test, an iron-lignite mixture with a ratio of the mass fractions of iron, which is used in the form of iron filings with a length of 1 cm to approx. 20 cm, to the mass fractions of lignite with a grain size of 0.5 cm to 2 cm of 1: 1 with a sulfuric acid mine water (1). The flow through the column (2) - PVC column with a diameter of 30 cm and a filling height of approx. 60 cm - takes place under saturated conditions.

FIG. 1 shows the schematic structure of the standing column (2) of the underground test facility.

The mine water used (1) is characterized by the following parameters: pH value 2, Eh value 700 mV, sulfate 7200 mg / 1, iron 2200 mg / 1 and aluminum 280 mg / 1 and the heavy metals cobalt 2.5 mg / 1 , Nickel 5.2 mg / 1, copper 2.8 mg / 1, arsenic 3.5 mg / 1, lead 0.2 mg / 1, cadmium 0.6 mg / 1, chromium 0.9 mg / 1, uranium 75 mg / 1, radium 12 Bq / 1, nitro aromatics 0.1 mg / 1. The dwell time of the pit water (1) during the test period was adjusted to the expected natural conditions and averages 5 days. After leaving the column, the percolate is fed through a gas-tight hose to a flow measuring cell (4), in which - just like in the mine water inlet - temperature, conductivity, pH value and redox potential are measured and sampled and analyzed at intervals and via a collecting container with overflow ( 5) derived. The reaction gases are collected via separate collection devices, the gas bag (3).

As a result, which is shown in Table 1, it is found that the iron-lignite mixture used fixes virtually all potential pollutants almost quantitatively. This also applies to the relatively mobile elements U, Co, Zn and Ni. The pH value increased from 2 in the mine water inlet to 5 to 6 in the percolate over the total test period of 14 months. Parameters As Pb Cu Ni Zn Co Cr Cd Mo U AI SO ₄ NitroRa aromate

Degree of retention in% 99 87 10 68 81 40 54 99 99 96 83 98 67

Table 1: Fixed quantities based on the quantities supplied via the mine water inlet

The retention remained at approximately the same level throughout the test phase, i. H. the iron-lignite mixture used has a large retention capacity.

Sequential extractions of the iron-brown coal mixture loaded with the pollutants from the underground columns (2) very clearly show the element-specific binding properties. Only very small proportions of the metals examined are remobilized.

Embodiment 2

This example describes an underground experiment that realistically simulates the conditions of a pit. The hydraulic and geochemical behavior of the iron-lignite mixture with a ratio of the mass fraction of iron to the mass fraction of lignite of 1: 1 is tested in a horizontal column (2). The iron is used in the form of iron filings with a length of 1 cm to approx. 20 cm and the brown coal with a grain size of 1 cm to 4 cm.

The schematic structure of the horizontal column is shown in FIG. 2.

The lying column (2) has a length of 2 m and a diameter of 0.5 m. The hydraulic conditions thus correspond to the conditions in a staggered section and ensure a saturated flow through the iron-lignite mixture. The percolation speed corresponds to a dwell time of the pit water of approx. 5 days. The lying column (2) is flowed through with a pit water of the following parameters: pH value 3, Eh value 550 mV, sulfate 1800 mg / 1, iron 350 mg / 1, aluminum 70 mg / 1 and the heavy metals cobalt 0.4 mg / 1, nickel 1.0 mg / 1, copper 0.05 mg / 1, arsenic 0.3 mg / 1, cadmium 0.1 mg / 1, chromium 0.15 mg / 1, uranium 13 mg / 1. The three installed tapping points (A, B, C), some of which serve as drains at the same time, enable several sampling options to determine the parameters of the percolate during or after the flow through the iron-lignite mixture. After a six-month test period, the present results, Table 2, show extensive separation of the pollutants contained in the mine water even under these realistic flow conditions.

Table 2: Fixed quantities based on the quantities ^J) Pb supplied via the mine water inlet in the inlet below the analytical detection limit

Buffering the acid raises the pH from 3 to 4 to 6. Together with the reduction of the redox potential to an Eh value of -200 mV to -500 mV, environmental conditions are created that lead to the immobilization of heavy metals, arsenic, aluminum, nitroaroamten and natural radionuclides. Under the generated environmental conditions, water constituents can be sorbed onto the brown coal.

The resulting reaction gases are quantitatively captured and analyzed over the entire duration of the experiment using a gas bag (3). Over time, there is a tendency for the resulting gas quantities to decrease.

Claims

claims 1. Process for the in-situ cleaning of contaminated water through geochemical barriers made of reactive materials, characterized in that the contaminated water such as heavy metals, metals, uranium, its natural decay products and nitroaromatics, contaminated water through geochemical barriers that exist in naturally existing and / or technically created Cavities are introduced into the flow paths of the waters and / or in technical facilities to which the waters are fed, from a homogeneous mixture and / or in layers of or from ferrous materials, non-and / or low-alloyed ferrous materials and / or waste products and / or residues of the metalworking industry, and carbon-containing materials, lignite and / or matt coal and / or bright coal, with a ratio of the mass fraction of the iron-containing materials to the mass fraction of the carbon-containing materials of 2: 1 to 1: 2, are conducted, whereby the a homogeneous a mixture and / or geochemical barriers created in layers have a water permeability coefficient of greater than 10 ^"2 m / s and a porosity of 50% to 95%. 2. The method according to claim 1, characterized in that non-alloyed and / or low-alloyed iron materials and / or waste products and / or residues of the metalworking industry with a bulk density of 0.3 t / m ³ to 2.0 t / m as ferrous materials ³ , a piece length of up to 50 cm, a piece thickness of up to 50 cm and a specific surface area of 0.05 m ² / kg to 0.5 m ² / kg and as carbonaceous materials brown coal and / or matt coal and / or bright coal with an ash content up to 25%, a sulfur content of up to 1%, and a grain size of up to 10 cm, which are mechanically stable and do not tend to form sludge.