Method and system for purifying water containing heavy metal ions

Abstract

This invention provides a method for purifying water containing heavy metal ions and a corresponding purification system that can maintain a sustained pH increase and high heavy metal removal capacity over a long period of time. [Solution] A purification method comprising the steps of passing water to be treated containing heavy metal ions through a reaction vessel equipped with a packing material containing a mixture of solid granular alkaline material and fine grain husks, and removing the heavy metal ions from the water to be treated.

Description

[Technical Field]

[0001] This invention relates to a method and system for purifying water containing heavy metal ions. In particular, this invention relates to a method and system for purifying water by removing heavy metal ions using a reaction vessel equipped with a packing material containing a mixture of an alkaline material and grain husks. [Background technology]

[0002] Mining-derived wastewater, such as mine wastewater from metal mines, and various types of wastewater, such as industrial wastewater, generally contain ions of various heavy metals, and also sulfate ions (SO4). 2- ) may also be present. In particular, abandoned mines generate acidic mine wastewater containing ions of various heavy metals such as Zn (zinc), Cu (copper), Pb (lead), Cd (cadmium), and Fe (iron) due to the oxidative dissolution of metal sulfides. Many of these heavy metal ions are harmful to the natural environment and to animals and plants, including humans. Therefore, when discharging water containing these heavy metal ions, treatment is required to meet established wastewater standards.

[0003] To remove heavy metal ions from treated water containing heavy metal ions, such as acidic mine wastewater, so-called active treatment has been employed, which involves directly treating the treated water by administering chemicals that react with heavy metal ions. For example, in acidic mine wastewater, chemicals such as quicklime or slaked lime are added, and the sludge, which is coagulated and settled by neutralization, is separated into solid and liquid phases before being discharged into rivers, etc. Such active treatment requires chemicals, electricity, and management personnel at all times, and frequent maintenance is also required, resulting in high costs. Therefore, in recent years, research has been conducted on so-called passive treatment technologies that treat treated water by utilizing natural purification processes, minimizing the use of machinery and chemicals that require electricity, with the aim of reducing treatment costs and energy consumption.

[0004] Passive treatment methods include various types such as aerobic wetlands that utilize vegetation and sulfate-reducing bacterial reaction tanks that utilize microbial activity. Among these, open lime channels with a simple structure using limestone are commonly used to remove and purify heavy metal ions from treated water such as acidic mine wastewater containing heavy metal ions such as Zn, Cu, Pb, and Cd. While such open lime channels are useful when large-scale water channels can be installed, they have the disadvantage that if sufficient retention time cannot be ensured in a wide water channel, the pH may rise and heavy metal removal may be insufficient.

[0005] Therefore, as a method for removing and purifying heavy metal ions from treated water such as acidic mine wastewater containing heavy metal ions such as Zn, Cu, Pb, and Cd, an attempt has been made to combine an open lime channel with a water channel made of waste concrete material mainly composed of highly alkaline slaked lime, which has a stronger neutralizing ability (see Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Guidance on the Introduction of Naturally Restoring Mine Wastewater Treatment Systems (Passive Treatment) in Closed and Abandoned Mines (Supplementary Volume): Collection of Introduction and Test Cases, Ministry of Economy, Trade and Industry, December 2021. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Thus, by combining an open lime channel with a waste concrete channel, it is possible to raise the pH of the treated water containing heavy metal ions such as Zn, Cu, Pb, and Cd, thereby achieving the removal and purification of heavy metals. However, even with this method, it was not easy to sustain the effect of raising the pH of the treated water and the resulting high heavy metal removal capacity over a long period of time.

[0008] Therefore, the problem that the present invention aims to solve is to provide a method for purifying water containing heavy metal ions that can sustain the effect of raising the pH of the water to be treated and the high removal capacity of heavy metals therefrom over a long period of time, and a corresponding purification system. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have discovered that by filling a reaction vessel with a mixture of solid granular alkaline material and fine grain husks, and passing water to be treated containing heavy metal ions through this reaction vessel, it is possible to stably remove and purify heavy metal ions from the water to be treated, thus completing the present invention.

[0010] One aspect of the present invention for achieving the above objective is as follows: A method for purifying water to be treated that contains heavy metal ions, A method comprising the steps of passing the water to be treated through a reaction vessel equipped with a packing material containing a mixture of solid granular alkaline material and fine grain husks, and removing the heavy metal ions from the water to be treated.

[0011] Furthermore, another aspect of the present invention for achieving the above objective is as follows. A water purification system for water containing heavy metal ions, A reaction vessel equipped with a packing material containing a mixture of solid granular alkaline material and fine grain husks, A supply system for supplying the water to be treated to the reaction tank, and A system including a discharge system for discharging treated water, from which the heavy metal ions have been removed from the treated water, from the reaction tank. [Effects of the Invention]

[0012] According to the method and purification system for purifying treated water containing heavy metal ions of the present invention, by passing the treated water containing heavy metal ions through a reaction tank filled with a mixture of an alkaline material of solid granular matter and fine grain husks, the advantage that heavy metal ions can be removed and purified from the treated water stably in the long term can be obtained.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a schematic diagram of a purification treatment device for treated water containing heavy metal ions according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of a purification treatment device for treated water containing heavy metal ions according to another embodiment of the present invention. [Figure 3] FIG. 3(a) is a graph plotting the change in the pH of the treated water after treatment against the number of elapsed days in the purification methods of the treated water in Example 1 and Comparative Example 1. FIG. 3(b) is a graph plotting the change in HRT (hydraulic retention time) against the number of elapsed days in the purification methods of the treated water in Example 1 and Comparative Example 1. [Figure 4] FIG. 4(a) is a graph plotting the change in the amount of dissolved Zn (zinc) in the treated water (filtered) after treatment against the number of elapsed days in the purification methods of the treated water in Example 1 and Comparative Example 1. FIG. 4(b) is a graph plotting the change in the total amount of Zn (zinc) in the treated water after treatment against the number of elapsed days in the purification methods of the treated water in Example 1 and Comparative Example 1. [Figure 5] FIG. 5(a) is a graph plotting the change in the amount of dissolved Cu (copper) in the treated water (filtered) after treatment against the number of elapsed days in the purification methods of the treated water in Example 1 and Comparative Example 1. FIG. 5(b) is a graph plotting the change in the total amount of Cu (copper) in the treated water after treatment against the number of elapsed days in the purification methods of the treated water in Example 1 and Comparative Example 1. [Figure 6]FIG. 6(a) is a graph plotting the change in the amount of dissolved Pb (lead) in the treated water (filtered) with respect to the number of days elapsed in the method for purifying the treated water of Example 1 and Comparative Example 1. FIG. 6(b) is a graph plotting the change in the total amount of Pb (lead) in the treated water with respect to the number of days elapsed in the method for purifying the treated water of Example 1 and Comparative Example 1. [Figure 7] FIG. 7(a) is a graph plotting the change in the amount of dissolved Cd (cadmium) in the treated water (filtered) with respect to the number of days elapsed in the method for purifying the treated water of Example 1 and Comparative Example 1. FIG. 7(b) is a graph plotting the change in the total amount of Cd (cadmium) in the treated water with respect to the number of days elapsed in the method for purifying the treated water of Example 1 and Comparative Example 1.

MODE FOR CARRYING OUT THE INVENTION

[0014] Hereinafter, an embodiment for carrying out the present invention will be described. The present invention is not limited by the description of the following embodiments. Note that the purification system for treated water containing heavy metal ions according to the present invention is a system including components for realizing the method for purifying treated water according to the present invention. Since both have substantially common technical matters, hereinafter, the description will be mainly made from the viewpoint of the purification method.

[0015] The method for purifying treated water containing heavy metal ions according to the present embodiment includes a step of passing the treated water through a reaction tank provided with a filler containing a mixture of an alkaline material of solid particulate matter and fine grain husks, and a step of removing the heavy metal ions from the treated water. In the layer of the filler containing the mixture of the alkaline material of solid particulate matter and fine grain husks in the reaction tank, usually, the alkaline material of solid particulate matter and the fine grain husks exist in a substantially uniform mixed state. The biological purification method for treated water containing heavy metal ions according to the present embodiment can usually remove heavy metal ions from the treated water by passing the treated water through the layer of the filler in the reaction tank from above to below. At this time, the treated water passing through the layer of the filler in the reaction tank can form a vertical downward flow following gravity.

[0016] In this specification, when "water to be treated containing heavy metal ions" is referred to, it means water before purification treatment in the reaction tank (supply water to the reaction tank), water before carbonate ion supply in the pretreatment reaction tank described later (supply water to the pretreatment reaction tank), or water being subjected to any of these treatments. Furthermore, in this specification, "post-treatment water" means water after it has been subjected to purification treatment in the reaction tank. Examples of treated water containing heavy metal ions include mine-derived wastewater such as mine wastewater from metal mines, and industrial wastewater. The heavy metal ions to be removed from the treated water by the purification method according to this embodiment typically include one or more of the following: Zn (zinc) ions, Cu (copper) ions, Pb (lead) ions, and Cd (cadmium) ions.

[0017] The pH of the water to be treated supplied to the reaction vessel is not particularly limited, but is usually about 2.5 to 8.0, about 3.0 to 7.8, about 3.5 to 7.6, about 4.0 to 7.4, about 4.5 to 7.2, or about 4.7 to 7.0 at room temperature. The pH of the water to be treated may be increased by supplying it to a pretreatment reaction vessel prior to supplying it to the reaction vessel. The pretreatment reaction vessel may be installed for the purpose of supplying carbonate ions to form carbonate precipitates of Pb (lead) ions and Cd (cadmium) ions, which can only form hydroxides at considerably high pH, ​​in order to enhance the removal function of these ions. In the pretreatment reaction vessel, carbonate ions are supplied from a substance that has carbonate ion supply capacity (e.g., limestone), and these carbonate ions are converted into bicarbonate ions (HCO3) in water. - This can lead to an increase in pH. When such a pretreatment reactor is provided, the pH of the water to be treated supplied to the pretreatment reactor is not particularly limited, but is usually about 2.5 to 7.0, about 3.0 to 6.8, about 3.2 to 6.6, about 3.5 to 6.4, about 3.6 to 6.2, or about 3.7 to 6.0 at room temperature. These upper and lower limits of the pH of the water to be treated may be combined in any way.

[0018] The solid granular alkaline material constituting the packing material of the reaction vessel is not particularly limited, as long as it is an alkaline substance that provides pH-raising ability. As the solid granular alkaline material, for example, one of limestone, dolomite, concrete waste, and semi-calcined dolomite, or a mixture of any combination thereof, may be used. Furthermore, a mixture of one of limestone, dolomite, concrete waste, and semi-calcined dolomite, or a mixture of any combination thereof, may be further mixed with any other solid granular alkaline material. The proportion of solid granular alkaline material other than limestone, dolomite, concrete waste, and semi-calcined dolomite in the solid granular alkaline material may be, for example, 20% by mass or less, 10% by mass or less, 5% by mass or less, or 1% by mass or less. Examples of alkaline materials other than limestone, dolomite, concrete waste, and semi-calcined dolomite include, but are not limited to, materials containing at least one alkaline earth metal-containing compound, such as calcium and magnesium oxides, hydroxides, carbonates and silicates, calcium silicate minerals or artificial materials, tobermorite, xonotlite, rock wool, glass wool, nickel slag wool, mortar, iron slag, non-ferrous slag, fly ash, zeolite, and any mixture of two or more of these waste materials. The particle shape of these solid granular alkaline materials is not particularly limited, but is usually amorphous.

[0019] As the solid granular alkali material, from the viewpoint of high pH-raising ability, concrete waste and semi-calcined dolomite, or a mixture thereof, may preferably be used. In addition to high pH-raising ability, concrete waste may more preferably be used as the solid granular alkali material from the viewpoint of a large degree of freedom in particle size and low procurement cost. In one preferred embodiment, the ratio of the total amount of concrete waste and semi-calcined dolomite to the total mass of the solid granular alkali material may preferably be 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably substantially 100% by mass. In another preferred embodiment, the ratio of the amount of concrete waste to the total mass of the solid granular alkali material may preferably be 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably substantially 100% by mass.

[0020] Limestone, which can be used as a solid granular alkaline material, is a natural mineral whose main component is calcium carbonate (CaCO3), and may contain small amounts of magnesium oxide (MgO), silica (SiO2), aluminum oxide (Al2O3), iron oxide (Fe2O3), etc. The calcium content of limestone is usually between 67% and 73% by mass. The particle size of the limestone particles is usually about 10 mm to 50 mm, preferably about 20 mm to 40 mm, from the viewpoint of balancing sufficient pH-raising ability and suppression of clogging by precipitates (ensuring the flow path of the treated water). The equilibrium pH of limestone in water at room temperature may be about 7 to 7.5. In this specification, the particle size of solid granular alkaline materials such as limestone can be measured according to the dry sieving method of the sieving test method in accordance with JIS Z8815-1994.

[0021] Dolomite, which can be used as a solid granular alkaline material, is a natural mineral that mainly contains a double salt structure represented by the general formula CaMg(CO3)2, in which the molar ratio of limestone CaCO3 and magnesite MgCO3 is approximately 1:1. In this double salt structure, CO3 2- Ca 2+ Ions and Mg 2+ The ions are arranged in alternating layers. The calcium content of dolomite can be approximately 51% by mass. The particle size of the dolomite particles is usually about 3 mm to 30 mm, preferably about 5 mm to 20 mm, from the viewpoint of balancing the ability to raise pH and suppress clogging by precipitates. The equilibrium pH of dolomite in water at room temperature may be about 7.5 to 8.

[0022] Semi-calcined dolomite, which can be used as a solid granular alkaline material, is a substance obtained by calcining dolomite (CaMg(CO3)2) and can be represented by the general formula CaMg(CO3)2. When dolomite is calcined, it undergoes a decomposition reaction represented by CaMg(CO3)2 → MgO + CaCO3 + CO2. The conditions for this thermal decomposition reaction are not particularly limited, but include, for example, a temperature of 600°C to 1000°C and a time of 1 hour to 10 hours. It is thought that the resulting semi-calcined dolomite has enhanced adsorption performance for heavy metal ions and the like due to the formation of pores resulting from this thermal decomposition reaction of dolomite. Semi-calcined dolomite has a structure in which the dolomite phase (CaMg(CO3)2 phase), MgO phase, and CaCO3 phase coexist. In partially calcined dolomite, although not particularly limited, the content of the MgO phase may be about 5% to 40% by mass, the content of the CaCO3 phase may be about 40% to 60% by mass, and the content of the residual CaMg(CO3)2 phase may be the remainder of these. The compositional analysis of partially calcined dolomite can be performed by known methods based on the Rietveld method by powder X-ray diffraction. The particle size of the partially calcined dolomite is usually about 3 mm to 30 mm, preferably about 5 mm to 20 mm, from the viewpoint of balancing the ability to raise pH and suppress clogging by precipitates. The equilibrium pH of partially calcined dolomite in water at room temperature may be about 10 to 11.

[0023] As concrete waste that can be used as a solid granular alkaline material, concrete waste whose main component is Ca(OH)2 can preferably be used. Furthermore, concrete waste materials that can be used as solid granular alkaline materials may also be waste materials derived from structures formed with ordinary concrete containing coarse aggregate, fine aggregate, and cement. In addition to waste materials derived from structures formed with concrete, concrete waste materials also include solid granular materials separated from concrete sludge, which is waste derived from excess fresh concrete generated at ready-mix concrete plants and concrete product manufacturing plants. The cement that is a component of concrete waste materials in this form is mainly composed of tricalcium silicate (CaO)3 (SiO2), dicalcium silicate (CaO)2 (SiO2), tricalcium aluminate (CaO)3 (Al2O3), and tetracalcium iron aluminate (CaO)4 (Al2O3) (Fe2O3). The particle size of the concrete waste material is usually about 3 mm to 40 mm, preferably about 4 mm to 30 mm, and more preferably about 5 mm to 20 mm, from the viewpoint of balancing the ability to raise pH and suppress clogging by precipitates. The equilibrium pH of the concrete waste material in water at room temperature may be about 11.5 to 12.5.

[0024] The fine grain husks that make up the packing material of the reaction vessel are not particularly limited as long as they are obtained from grains, but the following grain husks are examples: Grasses belonging to the Poaceae family, such as rice, wheat, barley, rye, oats, millet, barnyard millet, and foxtail millet; legumes belonging to the Poaceae family, such as soybeans, adzuki beans, mung beans, kidney beans, peanuts, and peas; buckwheat of the Polygonaceae family; quinoa of the Chenopodiaceae family; and senna of the Amaranthaceae family.

[0025] Among these examples of grain husks that can be used as fine-grained grain husks, rice husks are preferred because they are widely consumed (i.e., readily available) and inexpensive. Rice husks typically have a flattened ellipsoidal shape, with an average length of the long axis being approximately 3 mm to 10 mm, or approximately 4 mm to 9 mm. Using rice husks of this size promotes substantially uniform mixing of solid granular material with alkaline material, thereby capturing precipitates, such as hydroxides of heavy metal ions formed under elevated pH conditions, with the packing material in the reaction vessel, while also ensuring sufficient flow of the treated water and suppressing clogging by precipitates. The average length of the long axis of the rice husks can be determined by measuring the length of the long axis of 10 arbitrarily selected granular materials using a standard measuring tape and calculating the average value.

[0026] The volume ratio of fine grain husks to solid granular alkaline material constituting the packing of the reaction vessel is usually 1:0.01 to 1:10. By having a volume ratio of fine grain husks to solid granular alkaline material within this range, the pH-raising ability is fully exhibited, and precipitates, which are reaction products such as hydroxides of heavy metal ions formed under the elevated pH, can be efficiently captured by the packing in the reaction vessel, while clogging by precipitates can also be significantly suppressed. The volume ratio of fine grain husks to solid granular alkaline material is preferably 1:0.05 to 1:9, 1:0.1 to 1:8, 1:0.2 to 1:7, or 1:0.4 to 1:6, and more preferably 1:0.6 to 1:5, 1:0.8 to 1:4, or 1:1 to 1:3.

[0027] The packing material of the reaction vessel may include, in addition to a mixture of solid granular alkali material and fine grain husks, wood-based materials such as wood chips in an amount of 10% or less by volume of fine grain husks, or 5% or less by volume. For example, wood chips from coniferous trees such as cedar and pine can be used. Waste wood chips can also be recycled. The size of the wood chips is not particularly limited, but the average length of the longest individual particle (the average length of 10 arbitrarily selected particles) may be approximately 3mm to 10mm, or approximately 4mm to 9mm.

[0028] The packing layer of the reaction vessel may normally be a single layer, but alternatively, it may be formed from multiple layers with different volume ratios of fine grain husks to solid granular alkaline material. When the packing layer of the reaction vessel is formed from multiple layers with different volume ratios of fine grain husks to solid granular alkaline material, it is preferable that the upper layers have a lower volume ratio of fine grain husks to solid granular alkaline material (i.e., the upper layers have a higher volume ratio of solid granular alkaline material to fine grain husks) from the viewpoint of balancing sufficient pH raising ability and suppression of clogging by precipitates (ensuring the flow path of the treated water).

[0029] The passage of water to be treated into a reaction vessel equipped with a packing material containing a mixture of solid granular alkaline material and fine grain husks is not particularly limited as long as the water to be treated passes through the packing material of such a reaction vessel. However, it is usually possible to pass the water to be treated from top to bottom through the layers of packing material of the reaction vessel. When the water to be treated passes through the layers of packing material of the reaction vessel from top to bottom in this way, the water to be treated can form a vertical downward flow due to gravity. As the water to be treated passes through the layers of packing material of the reaction vessel, precipitates, which are reaction products such as hydroxides of heavy metal ions contained in the water to be treated, are formed under the pH level raised by the solid granular alkaline material, and these can be trapped in the packing material, mainly the fine grain husks. According to the water purification method of this embodiment, since the precipitates are mainly captured by fine grain husks, the surface of the solid granular alkaline material is continuously exposed without being completely covered by the precipitates, thus maintaining a high pH-raising ability over a long period of time. Furthermore, the flow path of the water to be treated is secured, and clogging can be suppressed, thereby reducing the need to interrupt operation due to maintenance work to remove clogging, and enabling continuous and stable operation. In a preferred embodiment, according to this water purification method, the water flow process and the heavy metal ion removal process can be carried out continuously and without interruption for 90 days or more, preferably 180 days or more, 270 days or more, 360 days or more, or 450 days or more, without lowering the pH to 9 or less, preferably to 10 or less, without performing maintenance work to remove clogging.

[0030] Prior to the step of passing the water to be treated, which contains heavy metal ions, through a reaction tank equipped with a packing material containing a mixture of solid granular alkaline material and fine grain husks, the water to be treated may be passed through a pre-treatment reaction tank having a carbonate ion supply capacity. The pre-treatment reaction tank may be installed for the purpose of supplying carbonate ions to form carbonate precipitates of heavy metal ions, from the viewpoint of enhancing the removal function of Pb (lead) ions and Cd (cadmium) ions, which can only form hydroxides in the subsequent reaction tank at considerably high pH levels. For example, if the capacity for post-treatment to reduce the pH of the high-pH treated water discharged from the reaction tank to below the environmental standard of 8.6 is small, or if it is difficult to install post-treatment equipment, providing such a pre-treatment reaction tank has the advantage of promoting the removal of Pb (lead) ions and Cd (cadmium) ions while controlling the pH rise in the reaction tank to an appropriate level.

[0031] The material that provides carbonate ion supply capacity to be filled into the pretreatment reaction vessel is not particularly limited, but any one of the solid granular alkaline materials exemplified above—limestone, dolomite, concrete waste, and semi-calcined dolomite—or any combination thereof can be used. From the viewpoint of high carbonate ion supply capacity, the material that provides carbonate ion supply capacity is preferably limestone and / or dolomite, and more preferably limestone because, in addition to its high carbonate ion supply capacity, it is readily available at low cost.

[0032] The water to be treated supplied to the reaction vessel or pretreatment reaction vessel may be water that has undergone a precipitation and removal treatment of iron ions (iron removal as a primary treatment) in a reaction vessel separate from the reaction vessel or pretreatment reaction vessel, for example, using the action of iron-oxidizing bacteria, prior to being supplied to them. In this case, it is preferable that the concentration of iron(II) ions is reduced to, for example, 1000 mg / L or less, 700 mg / L or less, 500 mg / L or less, 300 mg / L or less, 200 mg / L or less, 100 mg / L or less, 70 mg / L or less, or 50 mg / L or less.

[0033] Regarding the pH standard when discharging treated water into the environment, when discharging into public water areas other than the sea area, it is defined to be 5.8 or more and 8.6 or less. Therefore, when the pH of the treated water rises too much by passing water through the reaction tank, it is necessary to lower the pH to 8.6 or less. In such a case, for the treated water discharged from the reaction tank, for example, any known pH reduction treatment can be performed, such as discharging it into the environment after passing through constructed wetlands planted with reeds, sedges, cattails, and Canada thistles, etc.

[0034] The reaction tank that can be used in the purification method of the water to be treated in this embodiment is not particularly limited in terms of shape, material, capacity, etc., as long as the method can be implemented and the reaction treatment can proceed while the water to be treated moves inside the reaction tank. The material of the reaction tank is not particularly limited, but for example, it may mainly be made of resin or concrete, and some members may contain metal, ceramics, rock, clay, etc. The shape of the reaction tank is not particularly limited, but it may be vertically long or flat, substantially rectangular parallelepiped, substantially cubic, substantially spherical, substantially cylindrical (substantially tubular), or a combination thereof, etc. Also, the reaction tank can be an artificial pond, constructed wetland, large tank, etc. The volume of the reaction tank actually used outdoors is not limited, but for example, it may be 10 m 3 ~1×10 5 m 3 、50 m 3 ~5×10 4 m 3 Or 100 m 3 ~1×10 4 m 3 or so. The examples regarding the shape, material, and capacity of the reaction tank described here can also be similarly applied to the pretreatment reaction tank.

[0035] The reaction tank is provided with an inlet for the water to be treated and an outlet for the treated water. Also, when the water to be treated is groundwater, the reaction tank can be a permeable reaction wall buried underground, and the groundwater flow can also be utilized for the flow paths of the supply system of the water to be treated and the discharge system of the treated water and the supply and discharge energy. The same may apply to the pretreatment reaction tank.

[0036] In the reaction tank used in the water purification method of this embodiment, the thickness of the packing layer can be appropriately set depending on the characteristics of the water to be treated and the treatment scale. The thickness of the packing layer in the reaction tank is not particularly limited, but for example, it may be 0.01m to 2m, 0.02m to 1.5m, 0.03m to 1m, 0.04m to 0.8m, or 0.05m to 0.6m. When the packing layer consists of multiple layers, the thickness of each layer may be the same or different. If the packing layer of the reaction tank is formed from multiple layers with different volume ratios of fine grain husks to solid granular alkaline material, and the upper layer has a lower volume ratio of fine grain husks to solid granular alkaline material, it is preferable that the upper layer has a thinner thickness from the viewpoint of balancing the ability to sufficiently remove heavy metal ions from the water to be treated, to stably maintain the liquid properties of the water to be treated within a desired range, and to ensure sufficient flow of the water to be treated.

[0037] To prevent the packing layer of the reaction tank from being exposed to the outside air and the grain husks from drying out when the water to be treated is passed through, it is preferable to provide a water seal layer for the water to be treated with a predetermined thickness above the packing layer. The thickness of the water seal layer is not particularly limited, but may be, for example, 0.01m to 2m, 0.02m to 1m, 0.03m to 0.5m, or 0.04m to 0.4m.

[0038] Furthermore, it is preferable to provide a crushed stone layer at the bottom of the reaction vessel to support the packing layer and as a means to prevent the outflow of solid matter from the reaction vessel and to prevent clogging of the drainage system. The crushed stone is not particularly limited as long as it performs the function, but for example, it may be limestone as exemplified above for the packing layer. The thickness of such a crushed stone layer at the bottom is not particularly limited, but for example, it may be 0.01m to 2m, 0.02m to 1m, 0.03m to 0.5m, or 0.04m to 0.3m.

[0039] In the water treatment purification method according to this embodiment, it is preferable that the water to be treated, such as mine wastewater, is continuously introduced into the reaction tank and then continuously discharged from the reaction tank as a natural downward flow after a predetermined time. This allows for the continuous removal and purification of heavy metal ions from the water to be treated. Even when such a continuous water treatment process is adopted, it may be permissible to temporarily interrupt the continuous water treatment and perform batch processing for operational reasons, such as for periodic or irregular inspection, maintenance, or repair of the equipment.

[0040] In the case of continuous flow of treated water such as mine wastewater, the flow rate (supply and discharge flow rate of treated water to the reaction tank) is not particularly limited, as long as the treated water remains in the reaction tank for a period of time sufficient to adequately remove the desired heavy metal ions. The flow rate in the case of continuous flow of treated water such as mine wastewater is not particularly limited, as it depends on the reaction scale, the type and characteristics of the treated water, etc., but for example, the lower limit may be 1 L / min or more, 3 L / min or more, 5 L / min or more, 10 L / min or more, or 20 L / min or more, and the upper limit may be 1000 L / min or less, 500 L / min or less, 300 L / min or less, 200 L / min or less, 100 L / min or less, or 50 L / min or less. These upper and lower limits of the continuous flow rate of treated water may be combined arbitrarily.

[0041] The water purification method according to this embodiment can be used with water at any temperature, as long as the neutralization reaction and the formation of hydroxides, etc., occur in the reaction tank. Therefore, this purification method can be implemented in environments where water at a wide range of temperatures is used (for example, in natural environments such as high-latitude regions or high-altitude regions where temperatures are low in winter).

[0042] The method of supplying the water to be treated is not particularly limited, as long as it can be set and adjusted so that it can be supplied to the reaction tank (treatment vessel for carrying out the purification method) or pretreatment reaction tank at a desired constant flow rate. The water to be treated can be supplied to the reaction tank or pretreatment reaction tank through a transfer path such as piping. In a natural passive treatment system, from the viewpoint of saving labor and reducing costs, it is desirable to configure the system so that the water to be treated, from supply to treatment and discharge, can move according to gravity, using as little electricity as possible. Therefore, in actual application fields, it is preferable to set the height of the transfer path such as piping and the inlet of the reaction tank or pretreatment reaction tank so that electric pumps are not used.

[0043] Figure 1 shows a non-limiting example of an apparatus for implementing the purification method / purification system for water containing heavy metal ions according to this embodiment. In Figure 1, the reference symbols are as follows: 1 is the reaction tank (a treatment vessel for purifying the water to be treated), 2 is the water seal layer inside the reaction tank, 3 is the packing layer inside the reaction tank, 3a is the solid granular alkaline material (typically concrete waste) that makes up packing layer 3, 3b is the fine grain husk (typically rice bran) that makes up packing layer 3, 4 is the crushed stone layer located below the packing layer in the reaction tank and supporting the packing layer, 4c is the crushed stone that makes up crushed stone layer 4, 5 is the introduction pipe for introducing (transferring) the water to be treated into the reaction tank, 6 is the discharge pipe for discharging (transferring) the treated water from the reaction tank, and 10 refers to the entire water purification treatment system.

[0044] In Figure 1, the reaction vessel 1 is a resin or concrete container with a roughly rectangular prism (cuboid or cube) or roughly cylindrical outline. In addition to resin or concrete, the material of the surrounding wall of the reaction vessel 1 may include metal, ceramics, rock, clay, glass, etc., in whole or in part.

[0045] In Figure 1, a crushed stone layer 4 is formed in the reaction tank 1 at the bottom, covering the area above the discharge port, and a packing layer 3 is positioned above it, supported by the crushed stone layer. The packing layer 3 is composed of a uniform mixture of solid granular alkaline material (typically concrete waste) 3a and fine grain husks (typically rice bran) 3b that make up the packing layer 3. The crushed stone layer 4 has the function of preventing the outflow of solid matter from the container, thereby preventing clogging of the drainage system. The crushed stone c in the crushed stone layer 4 may typically be limestone.

[0046] In the purification apparatus shown schematicly in Figure 1, the water to be treated (which may be wastewater from an iron removal treatment device) containing heavy metal ions is continuously introduced into the reaction tank 1 from the supply source along the direction of arrow F through the introduction pipe 5. The water to be treated descends through the water seal layer 2 and packing layer 3 of the reaction tank 1 by gravity, and the neutralization reaction with alkali and the formation of reaction products (precipitates) such as hydroxides of heavy metal ions under the elevated pH conditions gradually proceed. In other words, as the water to be treated descends through the packing layer 3 of the reaction tank 1, neutralization by solid granular alkaline material (typically concrete waste) 3a and the formation of precipitates such as hydroxides of heavy metal ions occur, and the water is purified by the capture and filtration of these precipitates in the packing layer 3, particularly by fine grain husks (typically rice bran) 3b. The water to be treated undergoes such reaction and capture treatment in the packing layer 3, then passes through the crushed stone layer 4 and reaches the bottom of the reaction tank 1. After treatment, the water is discharged through the outlet and out the discharge pipe 6 in the direction of arrow D.

[0047] In this method of purifying water to be treated using such a device, a uniform mixture of solid granular alkaline material (typically concrete waste) 3a and fine grain husks (typically rice bran) 3b is placed in the packing layer 3 of the reaction tank 1. Water to be treated containing heavy metal ions is passed through this in a vertical downward flow manner. Under the pH level raised by the solid granular alkaline material 3a, precipitates, which are reaction products such as hydroxides of heavy metal ions, are formed, and these precipitates are mainly captured by the fine grain husks 3b in the packing layer 3. Because the precipitates are mainly captured by the fine grain husks 3b, the surface of the solid granular alkaline material 3a is continuously exposed without being completely covered by the precipitates, and the pH-raising ability, i.e., neutralization performance, of the solid granular alkaline material 3a is maintained at a high level for a long period of time. Furthermore, by using a uniform mixture of solid granular alkaline material 3a and fine grain husks 3b, precipitates adhere to the grain husks, ensuring a clear flow path for the treated water and suppressing clogging. This reduces the need to interrupt operations for maintenance work to remove blockages, enabling stable and continuous operation over a considerably long period.

[0048] Figure 2 shows another non-limiting example of an apparatus for implementing the purification method / purification system for water to be treated containing heavy metal ions according to this embodiment. This apparatus is used when water to be treated containing heavy metal ions is passed through a pre-treatment reactor with carbonate ion supply capacity prior to being passed through the reactor. Therefore, the right half of the apparatus shown in Figure 2, i.e., the apparatus for the later treatment in chronological order, is the same as the apparatus shown in Figure 1.

[0049] In Figure 2, the reference numerals indicate the following: 11 is the pretreatment reactor (a reactor for pretreatment performed prior to the purification of the water to be treated in reactor 1), 12 is the water seal layer in the pretreatment reactor, 13 is the packing layer in the pretreatment reactor, 13c is the carbonate ion supply material (typically limestone) that makes up packing layer 13, 14 is the introduction pipe for introducing (transferring) the water to be treated for pretreatment into the pretreatment reactor, and 15 is the discharge pipe for discharging (transferring) the pretreated water. The meaning of the reference numerals for the apparatus shown in the right half of Figure 2 is the same as described above for Figure 1.

[0050] In the purification apparatus shown schematicly in Figure 2, the water to be treated (which may be wastewater from an iron removal treatment device) containing heavy metal ions is continuously introduced into the pretreatment reaction tank 11 from the supply source along the direction of arrow F0 through the introduction pipe 14. The water to be treated descends through the water seal layer 12 and packing layer 13 of the pretreatment reaction tank 11 by gravity, and the carbonate formation reaction between carbonate ions supplied from the carbonate ion supply material (limestone as a typical example) 13c and heavy metal ions gradually proceeds. In other words, as the water to be treated descends through the packing layer 13 of the pretreatment reaction tank 11, a precipitate of carbonates formed from carbonate ions supplied from the carbonate ion supply material 13c and heavy metal ions is formed, and this precipitate passes through the packing layer 13 made of carbonate ion supply material and is accumulated and captured at the bottom of the pretreatment reaction tank 11. The water to be treated in this way is discharged from the bottom of the pretreatment reaction tank 11 through the discharge port and out the discharge pipe 15 along the direction of arrow D0. The treated water discharged from the discharge pipe 15 is sent to the inlet pipe 5 of the reaction tank 1.

[0051] The pretreatment reactor 11 may be installed prior to treatment in the reaction reactor 1 to enhance the removal function of Pb (lead) ions and Cd (cadmium) ions, which can only form hydroxides at considerably high pH levels, by supplying carbonate ions to form carbonate precipitates (deposits) of these ions. Pb (lead) ions and Cd (cadmium) ions can only form hydroxides at high pH levels, such as approximately 9 or above, or approximately 9.5 or above. On the other hand, due to factors such as the type of solid granular alkaline material 3a used in the packing layer 3 of the reaction reactor 1, fluctuations in the pH properties of the water to be treated, and the small treatment capacity for pH reduction following the reaction reactor 1, it may be difficult to raise the pH of the water to be treated in the reaction reactor 1 to a level where hydroxides of Pb (lead) ions and Cd (cadmium) ions can be formed, or the level of pH increase may be insufficient. Even under these circumstances, by providing a pretreatment reactor with carbonate ion supply capabilities, the removal of carbonate-based precipitates (deposits) such as Pb (lead) ions and Cd (cadmium) ions can be promoted and reinforced, supplementing the function of the reactor. Consequently, it becomes possible to achieve more stable removal of various heavy metal ions, including Zn (zinc) ions, Cu (copper) ions, Pb (lead) ions, and Cd (cadmium) ions, over a long period of time in such an entire apparatus. [Examples]

[0052] The present invention will be further explained below with reference to examples, but there is no intention to limit the present invention to these examples. The following examples should be understood as illustrative.

[0053] Preparation of the reaction vessel A reaction tank was prepared indoors (inside the tunnel) that was configured to allow the water to be treated to be introduced from above, and had an outlet for the treated water at the bottom. The reaction tank was a roughly rectangular container with transparent plastic walls and an open top, measuring 30 cm wide x 22 cm deep x 60 cm high.

[0054] Example 1 In the above-mentioned reaction vessel, a crushed stone layer approximately 5 cm thick, consisting of limestone with a particle size of about 20-40 mm, was laid at the bottom. On top of the crushed stone layer, a 30 cm thick packing layer was placed, consisting of a homogeneous mixture in a 1:1 volume ratio of "PAdeCS" (registered trademark), a concrete waste material containing alkaline materials with a particle size of 10-20 mm obtained from Nippon Concrete Industry Co., Ltd., and rice husks, which are grain husks. The rice husks used were procured from farmers. The average length of the long axis of the rice husks used was about 5 mm. A pre-treatment reaction vessel with a limestone packing layer was installed in front of the reaction vessel.

[0055] The water supplied to the above-mentioned reaction vessel is treated after passing through a pretreatment reaction vessel equipped with a packing layer made of limestone as described above, and has an average pH of 6.12 and an average concentration of approximately 16.9 mg / L of Zn ions (Zn 2+ ), Cu ions (Cu) with an average concentration of approximately 6.5 mg / L 2+ ), Pb ions (Pb) with an average concentration of approximately 1.67 mg / L 2+ ), and Cd ions (Cd) with an average concentration of approximately 0.18 mg / L 2+ Acidic mine wastewater (iron-removed) containing the following heavy metal ions was used. The concentrations of these heavy metal ions were measured using ICP-AES. pH was measured at room temperature using a glass electrode manufactured by Toa DKK Corporation. (The same procedure was followed for measuring heavy metal ion concentrations and pH below.)

[0056] The water to be treated was continuously passed through the reaction tank from above at a flow rate of 15 mL / min, and allowed to naturally descend through a packing layer consisting of a homogeneous mixture of concrete waste material "PAdeCS" (registered trademark) and rice husks in a 1:1 volume ratio. The thickness of the water seal layer was 5 cm (the thickness of the water seal layer was the same in subsequent examples). The hydraulic residence time (HRT) of the water to be treated in the packing layer was adjusted to 12 hours according to the design. As the water to be treated descended through the packing layer of the reaction tank, it was purified by the neutralization reaction of the alkaline material concrete waste material "PAdeCS" (registered trademark) and the gradual formation of reaction products (precipitations) such as hydroxides of heavy metal ions under the elevated pH. After treatment, the water passed through the crushed stone layer and reached the bottom of the reaction tank, and was then discharged through the outlet and discharge pipe. Table 1 below shows an overview of the packing layer configuration and the water supply conditions for this example, along with other examples. Furthermore, in the water purification method for treated water in this example (and Comparative Example 1 described later), Figure 3(a) shows a graph plotting the change in pH of the treated water against the number of days elapsed, and Figure 3(b) shows a graph plotting the change in HRT (hydraulic residence time) against the number of days elapsed.

[0057] Comparative Example 1 Except for placing a packing layer consisting solely of "PAdeCS" (registered trademark), a concrete waste material with a particle size of 10-20 mm obtained from Nippon Concrete Industries Co., Ltd., on top of the crushed stone layer of the above-mentioned reaction tank, setting the flow rate of the water to be treated through the reaction tank to 26 mL / min, and adjusting the hydraulic residence time (HRT) of the water to be treated in the packing layer to 6 hours as designed, the water purification method was carried out in the same manner as in Example 1. Table 1 below shows an overview of the packing layer configuration and the water supply conditions for this example, along with other examples. Furthermore, in the water purification method for treated water in this example (and Example 1 described above), Figure 3(a) shows a graph plotting the change in pH of the treated water against the number of days elapsed, and Figure 3(b) shows a graph plotting the change in HRT (hydraulic residence time) against the number of days elapsed.

[0058] Examples 2-6 As shown in Table 1 below, Examples 2 to 6 were carried out in the same manner as Example 1, except that the volume ratio of concrete waste material "PAdeCS" (registered trademark) to rice husks, the particle size of concrete waste material "PAdeCS" (registered trademark), the design hydraulic residence time (HRT) of the treated water, and the supply flow rate of the treated water were changed.

[0059] [Table 1]

[0060] In the water purification methods of Example 1 and Comparative Example 1, the change in the amount of soluble Zn (zinc) in the treated water (filtered) with respect to the number of days elapsed, and the change in the total amount of Zn (zinc) in the treated water with respect to the number of days elapsed were measured and recorded, and the graphs for each are shown in Figures 4(a) and (b). Here, "amount of soluble Zn (zinc)" refers to the amount of zinc measured from the liquid portion (dissolved portion) after the solid portion of the treated water has been removed by filtration using a filter with a pore size of 0.45 μm, and "total amount of Zn (zinc)" refers to the amount of zinc measured from all of the solid and liquid portions (dissolved portion) in the treated water. (The same applies to the measured amounts of other metals thereafter.) Furthermore, in the water purification methods of Example 1 and Comparative Example 1, the change in the amount of soluble Cu (copper) in the treated water (filtered) with respect to the number of days elapsed, and the change in the total amount of Cu (copper) in the treated water with respect to the number of days elapsed were measured and recorded, and the graphs for each are shown in Figures 5(a) and (b). Furthermore, in the water purification methods of Example 1 and Comparative Example 1, the change in the amount of soluble Pb (lead) in the treated water (filtered) with respect to the number of days elapsed, and the change in the total amount of Pb (lead) in the treated water with respect to the number of days elapsed were measured and recorded, and the graphs for each are shown in Figures 6(a) and (b). Furthermore, in the water purification methods of Example 1 and Comparative Example 1, the change in the amount of soluble Cd (cadmium) in the treated water (filtered) with respect to the number of days elapsed, and the change in the total amount of Cd (cadmium) in the treated water with respect to the number of days elapsed were measured and recorded, and the graphs for each are shown in Figures 7(a) and (b).

[0061] From the above-described matters and the comparison of the results shown in the graphs in Figures 3 to 7, it can be seen that, according to the embodiment of the present invention, Example 1 was able to stably raise the pH of the treated water over a long period of time compared to Comparative Example 1, and that precipitates and dissolved components of various heavy metal ions such as Zn (zinc) ions, Cu (copper) ions, Pb (lead) ions, and Cd (cadmium) ions could be reliably and stably removed and purified over a long period of time. Furthermore, in Examples 2 to 6 according to the embodiments of the present invention, the pH of the treated water could be stably increased over a long period of time at a level similar to that obtained in Example 1, and precipitates and dissolved components of various heavy metal ions, such as Zn (zinc) ions, Cu (copper) ions, Pb (lead) ions, and Cd (cadmium) ions, could be reliably and stably removed and purified over a long period of time. [Explanation of Symbols]

[0062] 1: Reaction vessel 2: Hydraulic layer 3: Filling layer 3a: Solid granular alkaline material (typical example: concrete waste) 3b: Fine grain husks (rice bran is a typical example) 4: Crushed stone layer 4c: Crushed stone 5: Inlet pipe for treated water 6: Discharge pipe for treated water F: Direction of introduction of water to be treated D: Discharge direction of treated water 10: Purification treatment equipment (overall) 11: Pretreatment reactor 12: Hydraulic layer 13: Filling layer 13c: Carbonate ion supply material (limestone is a typical example) 14: Inlet pipe for water to be treated for pretreatment 15: Discharge pipe for pre-treated water to be treated F0: Direction of introduction of the water to be treated during pretreatment. D0: Discharge direction of treated water after pretreatment

Claims

1. A method for purifying water to be treated that contains heavy metal ions, The process involves passing the water to be treated through a reaction vessel equipped with a packing material containing a mixture of solid granular alkaline material and fine grain husks, A step of removing the heavy metal ions from the water to be treated, Methods that include...

2. The method according to claim 1, further comprising the step of passing the water to be treated, which contains heavy metal ions, through a pretreatment reaction tank having carbonate ion supplying capacity, prior to the step of passing the water to be treated, which contains heavy metal ions, through the reaction tank.

3. The method according to claim 1, wherein the fine grain husks include rice husks.

4. The method according to claim 1, wherein the solid granular alkaline material comprises concrete waste and / or semi-calcined dolomite.

5. The method according to claim 1 or claim 2, wherein the volume ratio of the fine grain husks to the solid granular alkaline material is 1:0.01 or more and 1:10 or less.

6. The method according to claim 1 or claim 2, wherein the heavy metal ion comprises at least one heavy metal ion selected from the group consisting of Zn ions, Cu ions, Pb ions, and Cd ions.

7. The method according to claim 1 or claim 2, wherein, in the step of removing the heavy metal ions from the water to be treated, the neutralization reaction product of the heavy metal ions formed under pH conditions raised by the alkaline material of solid granules is captured on the surface of the packing material.

8. A water purification system for water containing heavy metal ions, A reaction vessel equipped with a packing material containing a mixture of solid granular alkaline material and fine grains of grain husk, A supply system for supplying the water to be treated to the reaction tank, and A system including a discharge system for discharging treated water, from which the heavy metal ions have been removed from the treated water, from the reaction tank.

9. The system according to claim 8, further comprising a pretreatment reactor having carbonate ion supply capability prior to the aforementioned reactor.

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