Device for soil restoration

Description of the Invention

The present invention relates to the field of cleaning of soils, groundwater and other structures or materials containing unwanted or electrically driven particles. This unit can be used to clean soil contaminated by heavy metal ions in various short and long term processes.

Heavy metals can be contaminated with soil for a variety of reasons. Energy, transport, the chemical industry, military landfills are the main polluters of soil. Heavy metal contaminated soil poses a threat to groundwater contamination. Heavy metals removal from soil is still a problem. The main methods for removing heavy metals from soil are soil leaching (using detergents or weak acids), phytoremediation (planting contaminated soil) and soil stabilization. No single method can successfully remove different types of soil from different metals. In addition, there are additional constraints: which soil washing method you choose depends on the mobility of the metal and the type of soil, and is energy and material intensive. Phytoremediation is suitable for cleaning large areas of contaminated surface soil, but only for low concentrations of pollutants. Soil stabilization is a very expensive method and, in addition, its effectiveness can be very short-lived depending on environmental conditions. The advantage of the proposed method is the electric movement of pollutants in the soil from one electrode to another, and the pollutants are adsorbed in a natural mineral medium that does not pollute the environment.

The prototype of the device provided is a device (U.S. Patent No. 6,221,237 JV, Class B01D 59/40), that is, a structure for the accumulation and assembly of electroplated particles, more particularly pollutant particles, in a medium, preferably soil. The essence of the device's operation is to use electric current to move the pollutant particles in and out through a layer adjacent to the electrode (anode) to which the pollutants are moving. The layer consists of a medium conductive adsorbent, which is porous and moistened with water or other solution capable of conducting electricity. The layer material (activated carbon) is easily removed and disposed of. The unit is designed for the removal of contaminated soil from soil.

The disadvantage of this device is that it is only capable of collecting negatively charged particles and many heavy metals (eg Pb, Cu, Ca, Zn, etc.) have a positive charge. The adsorbent layer on a known device is mounted at only one electrode, and to clean the soil,

............... EN 5494 B the adsorbent layer should be at both the anode and the cathode. In a known installation, the adsorbent layer is not separated from the soil by any partition and is therefore difficult to remove. The anode used in this device, an iridium-coated titanium electrode, is very expensive and difficult to obtain.

It is an object of the present invention to provide a device for collecting and collecting electrically polluted particles in soil.

Plant for cleaning heavy metals from soil by electrokinetic method consists of an inorganic glass body consisting of three sections (one filled with contaminated soil) separated by semi-permeable membranes consisting of filter paper and perforated partitions, sections of the metal ion-sorbing material, electrolyte solution supply and disposal vessels, graphite anode, power supply, which would provide a potential difference between the electrode and the stainless steel cathode. By switching on the power supply and starting the electrical current between the graphite anode and the stainless steel cathode, an electric field is created in the middle section and in the sections with zeolites, which causes the movement of contaminants due to electro-osmosis and ion migration. Electrosmosis mobilizes pore fluid in soil media from the anode to the cathode, and ion migration effectively separates the anions and cations, which migrate to the anode and cathode, respectively. This transport of contaminants together with geochemical reactions (desorption and coupling) forms the fundamental mechanism of the electrokinetic process. Due to the sorption properties of zeolite and its ability to bind cation exchangers, contaminants released from the soil are trapped in the zeolite layer and can be easily removed.

The objects are achieved by means of the device, the drawing of which is presented in Fig.1.

The plant for the removal of heavy metals from the soil by electrokinetic methods consists of: inorganic glass housing (1) consisting of three sections (one containing contaminated soil (2)), separated by a semi-permeable membrane consisting of filter paper (3) and perforated partitions (4), a layer of metal ion-sorbent material in the electrode sections ( 5), electrolyte solution supply (8) and discharge (6) vessels, a graphite anode (7), a power supply to provide a potential difference between electrodes (9), and a stainless steel cathode (10).

Contaminated soil is poured into the middle part of the unit (2) and will be separated from the electrodes and adsorbent by semi-permeable membranes on each side. Semi-permeable membranes consist of filter paper (3) adjoining organic glass partitions with multiple holes (4) to ensure permeability. The purpose of filter paper in the unit is to prevent the movement of solids, ie so that the flow of water in the electrified soil does not remove soil particles. In static conditions with no thermodynamic gradients, particle movement would be caused by the electrophoretic pull of the soil particles on the anode side and on the cathode side by the erosion caused by the flow of pure water to the cathode in negatively electrified soils (electro-space). Filter paper should be resistant to acids and alkalis. The filter paper shall be chosen so that its «

pores would be smaller than soil particles. Because of the reactions caused by the electrodes, the main condition for the selection of the filter paper was its resistance to pH changes. Adsorption - Zeolite (5) is added to the lateral sections of the device where the electrodes are attached. The material of the cathode (10) is stainless steel, in the form of a perforated plate, which is attached to the inner side of the unit wall. Anode (7) - 50 mm diameter graphite rod. Power electrode materials - graphite and stainless steel - are selected based on their electrochemical properties. The electrode-based materials can influence the quality and quantity of electrochemical and electrokinetic processes in soil. Therefore, it is very important that the electrode material chosen is as inert as possible so that the particles separated from it do not get into the soil and the zeolite leaching liquid. Graphite has such properties when used as both an anode and cathode. The carbon forming the electrode does not participate in the reactions that occur, even those occurring in acidic media. For these reasons, granite is chosen as the anode. The same condition applies to the cathode. When cleaning contaminated soils, most metals are suitable for the cathode, so stainless steel is chosen.

The anode and the cathode are wired to the respective inputs of the power supply (9) (cathode to - and anode to +). The soil and zeolite are moistened to 15% by weight. Of this 15% moisture level, 10% should be distilled water and 5% - 0.1 M sodium sulfate solution to assist specific soil permeability. To ensure continuous soil irrigation and removal of contaminated electrolyte, which reduces the cleaning efficiency, a contacting vessel is equipped with an irrigation and drainage system. The electrolyte solution supply vessels (8), filled with electrolyte solution, are mounted higher than the unit, from which drainage hoses are inserted into the zeolite sections of the unit (to control the flow rate). Spent electrolyte disposal vessels (6) are installed lower than the unit and are provided with hose clamps for draining zeolite sections from the unit. The electrolyte can be supplied and disposed of continuously or at certain time intervals. Part of the soil at the cathode is occasionally wetted with acetic acid solution to help form an acidic front.

Turning on the power supply (9) and starting the electrical current between the graphite anode (7) and the stainless steel cathode (10) creates an electric field in the middle section and the zeolite sections which causes the movement of contaminants due to electro-space in soils) and ion migrations. Electrosmosis mobilizes pore fluid in soil media from the anode to the cathode, and ion migration effectively separates the anions and cations, which migrate to the anode and cathode, respectively. This transport of contaminants, together with geochemical reactions (desorption, dissolution, and coupling), forms the fundamental mechanism of the electrokinetic process. Due to the sorption properties of zeolite and its ability to bind cations, contaminants released from the soil are trapped in the zeolite layer and can be easily removed.

Natural zeolite is used at the electrodes to collect pollutants. Zeolites are crystalline aluminosilicates of rock formations, the main active components of which are clinoptilolite and montmorillonite. One of the unique properties of the zeolites, which determined the choice was resistance to high temperatures, aggressive media, ionizing radiation, alkalinity, alkaline earth and some heavy metal coarse cations. Zeolites exhibit ion-exchange and adsorption properties. The zeolite lattice contains open passage-connected cavities. The diameter of the canals ranges from 2.8 to 8.0 angstroms. They are therefore free to enter water and other polar molecules such as NH3, SO2, H₂S, CO₂ and etc. Due to its specific structure, zeolites have a number of useful properties: adsorbent - effectively adsorbs various substances from gas mixtures and solutions; Molecular Grids - sorb only molecules of appropriate size; cationic - weakly bonded cations on the inner surfaces of pore and open channels can be replaced by other cations; the activation energy of the molecules in the pores of the catalytic - crystalline lattice is reduced in some reactions. Zeolites are ecologically clean, inert and non-toxic material. It is recommended to use 3-5 mm fraction of zeolite in the device.

The proposed installation is used to clean soils heavily contaminated with heavy metals when the pollution is not widespread. If necessary, larger sections of the unit, similar to those described above, can be installed when larger volumes of soil need to be cleaned.