CA2523572A1

CA2523572A1 - Treating material for polluted water and methods for production and use thereof

Info

Publication number: CA2523572A1
Application number: CA002523572A
Authority: CA
Inventors: Toru Oishi; Ryouji Takagi; Katsuhiro Yamada; Shozo Ikeda
Original assignee: Individual
Current assignee: Nippon Steel Chemical and Materials Co Ltd
Priority date: 2003-06-05
Filing date: 2004-06-04
Publication date: 2004-12-16
Also published as: WO2004108603A1; AU2004245399A1; AU2004245399B2

Abstract

A treating material for treating a polluted water containing, as a hazardous substance, arsenic, lead, cadmium, antimony, uranium, phosphorus, fluorine or the like, which comprises an oxygen-containing iron compound carried on a material containing a silicic acid based fiber or a silicate based fiber; a method for producing the treating material which comprises contacting and reacting a silicate based fiber, such as rock wool, with an iron-containing acidic water; and a method for treating the polluted water witch comprises contacting the treating material with the polluted water. The treating material has a fine structure wherein the above oxygen-containing iron compound is attached in a sheath form on the surface of a fiber reduced in an alkali component and increased in a silicic acid component as compared to, for example, rock wool. The oxygen-containing iron compounds include schwertmannite, ferrihydrite, akaganeite, amorphous hydrous iron oxide and fired ferric sulfate.

Description

a CA 02523572 2005-10-25 Title of the Invention Treating Material For Polluted Water And Methods For Production and Use Thereof Field of Technolo This invention relates to a material for treating polluted water to remove toxic substances contained therein such as heavy metals and to a method for removing these toxic substances by the use of said treating material.
Background Technology Addition of slaked lime as powder or slurry is used widely for removal of toxic substances from waste water. For example, waste water containing arsenic and sulfuric acid is treated as follows;
the waste water is subjected first to primary neutralization with calcium carbonate, slaked lime or the like, then to an oxidation treatment for oxidation of the arsenic and finally to secondary neutralization with slaked lime, calcium carbonate or the like.
This method has the benefit of low cost of chemicals and marked arsenic-removing ability. However, in the cases where waste water contains sulfate ions and iron ions in large amounts, the iron ions separate as colloidal ferric hydroxide as the pH increases and, moreover, the slaked lime or calcium carbonate reacts with sulfate ions to form sparingly soluble gypsum and precipitates out, together with the unreacted slaked lime used as a neutralizing agent, in the form of a slime which is highly hydrous and difficult to dehydrate. The slime contains toxic substances and its treatment poses a problem.
A treating material for acidic waste water disclosed in W002-079100 uses a solid granular material formed from mineral fibers such as rock wool and an inorganic binder such as blast furnace slag cement. However, this patent discloses only a treating material for acidic waste water containing iron ions in large amounts and does not refer to a treatment of waste water containing toxic substances such as arsenic and phosphoric acid.
Now, a certain kind of oxygen-containing iron compound is known to adsorb arsenic-containing ions. For example, JP2003-112162 A
discloses a method for cleaning polluted soil which comprises adding a chemically synthesized iron compound selected from schwertmannite, geothite, jarosite and ferrihydrite to polluted soil containing arsenic or heavy metals and allowing the iron compound to adsorb and immobilize arsenic or heavy metals. Further, JP2003-112163 A discloses a method which comprises adding a culture solution of iron-oxidizing bacteria to polluted soil to form an iron compound such as schwertmannite and, likewise, allowing this iron compound to adsorb arsenic and the like. However, these patents disclose only the cleaning of polluted soil and do not refer to a treatment of waste water containing toxic substances such as arsenic.
The aforementioned schwertmannite is known to perform adsorptive removal of oxy acids of arsenic, phosphorus, selenium and the like.
Schwertmannite has a composition of Fe808(OH)a_zX(S04)X. Adsorptive removal here means that schwertmannite adsorbs toxic metals or ions and additionally removes them by exchange of metals or ions occurring between them and shwertmannite.
It is reported in Chishitsugaku Zasshi (Journal of Geological Society of Japan), Vol. 107, No. 10 (December, 2001), pp.659-665 that iron- or sulfur-oxidizing bacteria present in acidic waster water discharged from mines cause formation of a film-like substance (biofilm) floating like oil on the surface of water and the substance was identified as schwertmannite.
Disclosure of the Invention An object of this invention is to provide a treating material for polluted water containing toxic substances such as arsenic, lead, cadmium and phosphorus which is effective and easy to maintain. yields highly stable reaction products capable of minimizing re-elution of the adsorbed toxic substances by change with time or acidification and is free of excessive after-treatment and, further, to provide an effective method for producing said treating martial. Another object of this invention is to provide a novel method for producing a treating material containing schwertmannite as an effective component.
A further object of this invention is to provide a method for removing the aforementioned toxic substances which is also effective for the treatment of waster water from mines, industrial waste water, effluent from agricultural land, waste water from animal husbandry, waste water from processing of marine products and river water and to the cleaning of raw city water containing minute amounts of the toxic substances.

This invention relates to a treating material for polluted water containing toxic substances such as arsenic and the material comprises a material containing inorganic fibers selected from silicic acid- or silicate-based fibers on which an oxygen-containing iron compound is carried.
The treating material of this invention contains an oxygen-containing iron compound capable of removing toxic substances. The oxygen-containing iron compound includes the one carried on inorganic fibers in the material containing inorganic fibers.
Preferably, the oxygen-containing iron compound is carried on the inorganic fibers in the form of a sheath around the inorganic fibers.
Oxygen-containing iron compounds contain iron and oxygen such as iron oxide and hydrous iron oxide. Additional examples are schwertmannite, ferrihydrite, akaganeite, goethite, lepidocrocite, hematite, magnetite, maghemite, jarosite, calcined schwertmannite, calcined ferrihydrite, calcined akaganeite, calcined geothite, calcined amorphous hydrous iron oxide, calcined ferric sulfate, calcined ferrous sulfate, calcined ferric chloride, calcined ferrous chloride, calcined ferric nitrate and calcined ferrous nitrate and they are used singly or as a mixture of two kinds or more. In the cases where the oxygen-containing iron compound is calcined, the calcination is preferably carried out in air at 150-800°~ for 30 minutes to 2 hours.
The oxygen-containing iron compound is represented by FeOXZY or FeOXZY ~ nH20 (Z is one kind or more of atoms and radicals, x is a number greater than 0 and y is a number equal to or greater than 0). An aggregate of a variety of oxygen-containing iron compounds may be used, but an oxygen-containing iron compound represented by the aforementioned formula is preferably the main component of such an aggregate. Schwertmannite is desirable and its content is controlled so that it accounts for 30 wt% or more, preferably 50 wt% or more, of the oxygen-containing iron compounds.
A material containing inorganic fibers for carrying an oxygen-containing compound may be inorganic fibers alone, a mixture of inorganic fibers and inorganic powders or a mixture of inorganic fibers and an inorganic or organic binder.
Silicic acid-based fibers or silicate-based fibers are used as inorganic fibers. Silicic acid-based inorganic fibers are typically silica fibers which contain silica as the main component. One kind of silicate-based inorganic fibers is inorganic fibers containing the silicates of metals such as alkali metals, alkaline earth metals and aluminum (these metals are hereinafter referred to as alkali component) as the main component. Preferable inorganic fibers are those which are obtained by treating silicate-based inorganic fibers with an acidic aqueous solution containing iron ions thereby removing at least a part, preferably 50% or more, more preferably 70% or more, of the alkali component and increasing the silicic acid component. The inorganic fibers obtained by removing the alkali component are porous with a large surface area and capable of carrying an increased amount of oxygen-containing iron compounds.
Examples of silicate-based inorganic fibers are rock wool, nickel slag wool, glass wool, ceramic fibers and crushed calcium silicate boards that are available as wastes of construction materials and consist of tobermorite fibers and xonotlite fibers.
Of these inorganic fibers, rock wool, nickel slag wool and glass wool are used preferably.

Rock wool or a material containing rock wool is used advantageously. Besides virgin rock wool, wastes of fire-resistant rock wool coverings (sprayed rock wool) containing 50 wt% or more of rock wool and cement or rock wool recovered at the time of spraying may be used. Wastes of rock wool ceiling boards that contain rock wool and calcium carbonate and the like as the main component may also be used. Rock wool is available in several forms such as layered and granular and granular rock wool is preferred. Granular rock wool is obtained by granulating layered rock wool in a granulator or rotary screen and has an average particle diameter of 1-50 mm, preferably 5-40 mm. Moreover, boards molded from a mixture of rock wool, recovered rock wool and a binder may be cut or crushed to granules and used. Rock wool is easy to process into granular products, shows good water permeability and water retention and has gaps suitable for the propagation of microorganisms. Rock wool preferably has the following composition; SiOz 30-50 wt%, A1z03 5-20 wt%, Mg0+Ca0 30-50 wt%, Na20+K20 0-10 wt%, others 0-10 wt%.
In the cases where a material containing inorganic fibers contains components other than inorganic fibers, such other components are preferably silicate-based inorganic powders or binders. When silicate-based inorganic powders are used, the candidate is preferably lower in silicate content and higher in basicity than the inorganic fibers; for example, powders or particles of cement, cement clinker, slag from iron manufacture, slag from non-iron metal manufacture, fly ash and crushed concrete.
Of these, cement or concrete with high basicity is preferred. When the silicate-based inorganic powders is cement which can also serve as an inorganic binder, it is not necessary to use a binder.

Otherwise, inorganic binders or resin-based organic binders are used.
The content of inorganic fibers in a material containing inorganic fibers is in the range of 35-100 wt%, preferably 35-85 wt%. The inorganic fibers preferably have as large an exposed surface area as possible. In case inorganic fibers are used singly, the fibers are formed into a fabric or entwined. When a material containing inorganic fibers is a mixture of inorganic fibers and inorganic powders, the two are mixed, if necessary together with a binder and water, granulated and used.
A material containing inorganic fibers or a treating material of this invention obtained by letting said material containing inorganic fibers carry an oxygen-containing iron compound has a porosity of 50% or more, preferably 60% or more, and a bulk specific gravity of 0.1-1.5, preferably 0.1-0.5.
Of the methods for attaching an oxygen-containing iron compound to a material containing inorganic fibers, the following methods are cited as examples.
1) A material containing inorganic fibers is immersed in iron-containing acidic water to elute the alkali component and increase the silica content by a neutralization reaction and an oxygen-containing iron compound in the hydrous condition is precipitated on the surface of the fibers with an increased silica content in the presence of iron-oxidizing bacteria.
2) A slurry or an aqueous solution of an iron compound capable of producing an oxygen-containing iron compound is prepared in advance, inorganic fibers or the like are immersed in the slurry or the aqueous solution and calcined thereafter, if necessary.
The method 1) is advantageous. However, if carbon fibers or silica fibers showing low reactivity with acids were used here, less oxygen-containing iron compound would be carried on the fibers.
The method 1) is described first. The iron-containing acidic water in which a material containing inorganic fibers is immersed preferably has a sulfate ion content of 500-4000 mg/1, a ferrous ion content of 50-500 mg/1 and a pH of 1.5-3.5. An adequate procedure is to add 1-100 g of the material containing inorganic fibers to 1000 ml of this acidic solution and stir the mixture at room temperature for 1-100 hours thereby forming a material containing inorganic fibers with an increased silicic acid content and, at the same time, attaching an oxygen-containing iron compound to the inorganic fibers. In this case, the reaction is allowed to proceed with stirring until the pH of the acidic solution becomes 3-5 or 7-13. The ability of removing toxic substances may drop in the pH range of 5-7.
The oxygen-containing iron compound to be formed in the hydrous condition according to this method is an aggregate of one kind or more of minerals selected from schwertmannite, ferrihydrite, akaganeite, goethite, lepidocrocite, hematite, magnetite, maghemite and jarosite depending upon the pH or aeration during manufacture.
From the viewpoint of the ability of removing toxic substances, ferrihydrite, schwertmannite, akaganeite and goethite are preferred for their high surface activity and large specific surface area.
Schwertmannite, akagenite, goethite or jarosite forms as a hydrous iron oxide when the treating condition is acidic (the pH
is approximately 2-5) although this depends upon the relationship between the acidic substances in the iron-containing acidic water and the alkaline substances in the material containing inorganic g fibers.
When iron is present as ferrous ions under acidic conditions, the existence of iron-oxidizing bacteria is desirable in order to accelerate the oxidation of iron. The iron-oxidizing bacteria useful for this case include Thiobacillus ferooxidans, Gallionella ferruginea, Leptothrix ochracea, Leptothrix trichogenes, Clonothrix sp., Crenothrin sp., Metallogenium sp., Ochrobium sp.
and Siderocapsa sp. Depending upon the kind of iron-containing acidic water in use, Thiobacillus ferooxidans is suited for strongly acidic water below pH 2 and Gallionella, Leptothrix and the like for others.
On the other hand, when the treating condition is alkaline, iron is oxidized by air in the absence of iron-oxidizing bacteria to form ferrihydrite, lepidocrocite, hematite, magnetite or maghemite as a hydrous iron oxide.
Next, the method 2) is described. An insoluble iron compound such as schwertmannite, ferrihydrite, akaganeite, goethite, amorphous hydrous iron oxide and the precipitated neutralization product of iron-containing acidic waste water from mines is used as a slurry and a water-soluble iron compound such as ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric nitrate and ferrous nitrate is used as an aqueous solution. The concentration of the iron compound in the slurry or aqueous solution is 1000 ppm by weight, preferably 5000 ppm by weight, as iron. The iron compound is used in an amount of 5-100 parts by weight as iron per 100 parts by weight of the material containing inorganic fibers.
The oxygen-containing iron compound obtained in the hydrous condition in the aforementioned manner is used, either as it is or after drying and calcination, to serve as a treating material according to this invention.
In the latter case, the material containing inorganic fibers impregnated with the iron compound is placed in a calcining furnace and heated at 150-800 ~, preferably 250-650, for 30 minutes to 2 hours to give a treating material of this invention.
The proportion of the material containing inorganic fibers in the treating material is in the range of 50-90 wt% while the proportion of the oxygen-containing iron compound is in the range of 10-50 wt%.
The treating material of this invention is not restricted in its shape, but it is preferably granular. A granular treating material is produced as follows: a material containing inorganic fibers is granulated in a ribbon mixer, a rotary granulator or the like, the granulated fibers are treated with iron-containing acidic water or impregnated with an oxygen-containing iron compound and then, if necessary, dried or calcined. The use of granular rock wool as a raw material is advantageous in that the granulating operation can be omitted. In the case of granular rock wool, the average particle diameter is approximately 0.5-100 mm, preferably 1-50 mm.
Where the hydrous material not needing the calcining step is used as it is for a treating material according to this invention, a layered molded product is preferable for use in such cases. This product is composed of an integrated layer of fibers formed by binding inorganic fibers together with a flexible binder resin and, preferably, treated further to provide hydrophilicity. As a flexible binder resin, thermoplastic resins developing adhesive properties upon heating such as PVC, styrene polymers, polyolefins, polyesters, nylon and acrylics can be used in the form of powder, solution or emulsion and hot-melt adhesive fibrous materials can also be used.
An integrated layer of fibers is made by mixing inorganic fibers and a flexible binder resin and forming the mixture by heating into a sheet or felt of a prescribed thickness. Heating during or after forming causes the binder resin to develop its adhesive strength and bind the inorganic fibers together. This fibrous layer has a density of 30-300 kg/m3, preferably 60-250 kg/m3, and a thickness of 1-30 mm, preferably 2-20 mm.
The treating material produced according to this invention has a carrier consisting of inorganic fibers such as rock wool or powders of inorganic fibers and cement and, for this reason, it is high in porosity and low in bulk specific gravity. As the treating material retains the porosity and other properties of fibers even in the presence of inorganic powders, it shows extremely high water permeability and excellent reactivity with toxic substances in waste water and, furthermore, it drains readily after the reaction and dehydration is feasible by merely leaving the treating material standing. The water permeability coefficient is 1X 10-3 cm/s or more, preferably 1 x 10-z cm/s or more. With the use of this material in waste water treatment, it is possible to lower its water content to 90% or less, preferably 80% or less, by simply pulling the material out of water without performing a special dehydrating operation.
The treating material of this invention is applicable to polluted water containing at least one kind of toxic substance selected from heavy metals such as arsenic, lead, cadmium, antimony and uranium, phosphorus, selenium and fluorine. These toxic substances may be present as water-soluble ions or compounds; for example, arsenic may be present as arsenic ions, arsenite ions, arsenate ions, arsenite salts or arsenate salts. Phosphorus or selenium frequently exists as phosphoric acid or selenic acid.
Examples of treatable water are waste water from mines, industrial waste water, effluent from agricultural land, waste water from animal husbandry, waste water from processing of marine products and polluted river and lake waters. In addition, the treating material can be used in after-treatment of reagents and in purification of raw city water and underground water containing minute amounts of the aforementioned toxic substances. The treating material is particularly suited for treating water containing arsenic as a toxic substance and such water ranges from drinking water of a Iow toxic content to industrial water of a high toxic content. Where arsenic is trivalent and present as arsenious ions, arsenite ions or arsenite salts, a convenient procedure is to first oxidize the trivalent arsenic to pentavalent arsenic with air or the Iike and then place it in contact with the treating material of this invention.
In treating polluted water containing toxic substances such as arsenic by the treating material of this invention, it is advantageous to provide a container packed with the treating material and let polluted water flow through the container thereby bringing the water into contact with the treating material. Another procedure is to store polluted water in a container or a pond and place a basket-like container packed with the treating material in the water. For replacement of the spent treating material with a new one, the use of a container offers an advantage. It is also advantageous to use a combination of several treating methods.
The contact between the treating material and polluted water is allowed to occur at room temperature for a period of Z5 minutes or more, preferably 1 hour or more, more preferably 1-10 hours, although the contact time varies with the amount of packed material, amount of water put through, concentration of toxic substances in polluted water and quality required for treated water. The treating material is replaced with a new one at the time when the flow of water becomes physically difficult or it is replaced or supplemented with a new one immediately before the concentration of toxic substances in the treated water reaches the regulation value or the value prescribed in advance.
It is further possible to carry out effectively plural treatments of polluted water by skillfully combining the manufacturing step of the treating material of this invention and the treating step of polluted water.
One mode of such practice is as follows: first, iron-containing acidic waste water is treated with silicate-based inorganic fibers to neutralize the waste water and remove iron and, at the same time, to form a hydrous oxygen-containing iron compound on the silicate-based inorganic fibers; then the hydrous oxygen-containing iron compound carried on the silicate-based inorganic fibers is used as the treating material of this invention and transported to the site of waste water treatment for removal of arsenic, phosphorus and the like.
An example of the aforementioned iron-containing acidic waste water is waste water that is discharged from mines and contains ferrous ions formed by the oxidation of iron sulfide.
However, in the cases where the iron-containing acidic waste water to be initially treated contains oxy acids of arsenic, phosphorus, selenium and the like, S04 contained in the crystal structure of an oxygen-containing iron compound (for example, schwertmannite) formed in the treating material is replaced by arsenic acid, phosphoric acid or selenic acid which is thermodynamically more stable than S04 and, further, the oxygen-containing iron compound in the treating material becomes saturated with arsenic, phosphorus, selenium and the like. The outcome is a decline of the ability to adsorb these toxic substances and no use as the treating material of this invention. In consequence, the step for manufacture of the treating material and that for use is separated clearly in the practice of this invention.
A treating material resulting from the treatment of iron-containing acidic waste water such as waste water from mines contains fibers which have decreased in the alkali component and increased in the silicic acid component after neutralization and besides contain the iron component adhering to the surface as an oxygen-containing iron compound; hence, such a treating material can be used as the treating material of this invention.
The treating material obtained in this manner is dried if necessary, transported and used for treating another waste water or underground water containing toxic substances.
A method for treating acidic waste water from mines containing at least arsenic and iron by the use of the treating material of this invention is described below.
This acidic waste water is submitted to an operation consisting of the following steps: 1) oxidation of arsenic, 2) removal of arsenic, 3) oxidation of iron, 4) removal of iron and adjustment of pH. However, in some cases, the operation may be modified so that it consists of the step a) for the oxidation/removal of arsenic wherein the step for the oxidation of arsenic is omitted and arsenic is simultaneously oxidized and removed in a part or the whole of the steps for the oxidation and removal of arsenic and the step b) for the oxidation/removal of iron wherein iron is simultaneously oxidize and removed in a part of the whole of the steps for the oxidation and removal of iron.
In the step for the oxidation of arsenic, a variety of reactions take place to oxidize ions containing trivalent arsenic such as arsenite ions to ions containing pentavalent arsenic such as arsenate-based complex ions.
The step for the removal of arsenic is the step where ions containing pentavalent arsenic in waste water are removed by the treating material of this invention. In the cases where waste water additionally contains heavy metals such as lead, cadmium, antimony and uranium, phosphoric acid, selenic acid and fluorine, these substances are removed together with arsenic.
The step for the oxidation of iron is provided for accelerating the oxidation of ferrous ions present in waste water after the removal of arsenic to ferric ions and for facilitating the removal of iron in the next step. Increase of oxygen dissolved in waste water and use of iron-oxidizing bacteria are beneficial to acceleration of the oxidation of iron in water under acidic conditions.
Iron-oxidizing bacteria adhere to the surface of a material containing silicate-based inorganic fibers which is used as a material for the removal of iron primarily in the step for the removal of iron, propagate there and oxidize iron and, at the same time, cause iron to separate as an oxygen-containing iron compound.
Thus, the oxidation of iron and the removal of iron progress simultaneously. In this case, the two steps are integrated to a single step for the oxidation and removal of iron.
In the step for the removal of iron where a material containing silicate-based inorganic fibers is used as a material for removing iron and neutralizing bacteria are additionally used, ferric ions in iron-containing acidic water are precipitated and insolubilized as an oxygen-containing iron compound. The spent material containing inorganic fibers carries a large amount of oxygen-containing iron compounds such as schwertmannite and goethite formed under acidic conditions and it is used as a material for adsorbing arsenic, that is, as a treating material in the step for the removal of arsenic.
The effluent from the step for the removal of iron is preferably acidic for the aforementioned reason or its pH is 4.5 or below, preferably 3-4.4.
The step for the adjustment of pH is provided for neutralizing the water treated in the step for the removal of iron before discharge and a variety of neutralizing materials such as slaked lime, quick lime, calcium carbonate and crushed concrete are used.
Brief Description of the Drawincrs Fig. 1 is an SEM image showing the micro structure of the treating material obtained in Example 4. Fig. 2 is a magnification, approximately 100 times, of the central portion of the SEM image shown in Fig. 1. Fig. 3 shows the relationship between the concentration of phosphorus in the untreated lake water (UT-TP) or the concentration of phosphorus in the treated lake water (T-TP) and the collective throughput of water (CTW) determined in Example 16.

Preferred Embodiments of the Invention Example 1 Rock wool (S-Fiber, granular product with an average particle diameter of 30 mm; available from Nippon Steel Chemical Rockwool Co., Ltd.), nickel slag wool (granular product with an average particle diameter of 30 mm, available from Taiheiyo Kinzoku Kabushiki Kaisha), glass wool (resin-free short fibers), carbon fibers (pitch-based short fibers) and silica fibers (short fibers for use in tissue culture) were respectively used as inorganic fibers. The fibers weighing 75 g were added to 5 liters of an acidic solution with pH 2 containing 340 mg/1 of total iron ions, 250 mg/1 of calcium ions and 2000 mg/1 of sulfate ions prepared from ferrous sulfate of reagent grade, gypsum and sulfuric acid and the reaction was allowed to proceed at room temperature for 28 days.
The amount of the iron component adhering to the inorganic fibers and the pH of the solution after the reaction were determined. Moreover, in order to examine the adhesiveness of the iron component to the surface of fibers, the inorganic fibers containing the iron component were stirred in the solution for 5 minutes and the condition of the fibers and the reaction products was visually observed. Still more, the iron component adhering to the surface of the fibers was analyzed with the aid of a high power X-ray powder diffractometer.
Example 2 The experiment was carried out as in Example 1 with the exception of further adding 15 g of a biomat containing iron-oxidizing bacteria Thiobacillus ferooxidans.
The amount of the iron component adhering to the fibers and the pH of the solution are shown in Table 1. In Table 1, the following abbreviations are used for the inorganic fibers: RW for rock wool, NW for nickel slag wool, GW for glass wool, CF for carbon fibers and SF for silica fibers. In X-ray diffractometry, S+G signifies a mixture of schwertmannite and goethite of low crystallinity and -means that measurements were not possible because of a small amount of products.
(Table 1) Example Example Inorganic R N G C S R N G C S
fibers W W W F F W W W F F

p H 4.0 3.5 2.4 2.3 2.4 4.4 4.3 2.2 2.1 2.1 Adhesion of 57 82 33 5 9 87 100 40 29 30 iron %

X-ray S+G S+G S+G - - S+G S+G S+G S+G S+G
diffraction Example 3 A mixture of 60 wt% of rock wool (S-Fiber, granular, average particle diameter 30 mm) and 40 wt% of blast furnace slag cement (B grade, available from Nippon Steel Blast-Furnace Slag Cement Co., Ltd.) was stirred in a ribbon mixer to give a granular mixture with an average particle diameter of 20 mm, a bulk specific gravity of 0.15 and a porosity of 94%. The chemical composition of the granular mixture was as follows: Si02 33.0%, . CA 02523572 2005-10-25 A1203 10.2%, Ca0 47.8%, Mg0 4.2%, Fe203 1.4%, TiOz 0.5%, Mn0 0.2%, and S03 0.7%. The ignition loss was 1.2%.
Separately, an acidic solution with pH 2.5 containing 1080 mg/1 of sulfate ions, 137 mg/1 of total iron ions and 250 mg/1 of calcium ions was prepared from ferrous sulfate, gypsum and sulfuric acid.
A synthetic resin column with a diameter of 10.4 cm was packed with 100 g of the granular mixture so that the thickness became 6.8 cm and the bulk specific gravity became 0.174 and the acidic solution was passed through the column at a rate of 5 1/day for 10 days. The amount of the iron component adhering to 1 kg of the granular mixture after passage of water was 68.5 g as metallic iron. When the effluent after completion of the reaction was tested for pH and concentration of the iron component, the pH was 10.0 and the concentration of total iron ions was 0.01 mg/1.
Moreover, the granular mixture after the reaction became a treating material carrying oxygen-containing iron compounds. This treating material was tested for water permeability and found to show a water permeability coefficient of 4.0 X10-1 cm/sec and a water content of 76%. The iron component adhering to the surface of fibers was ferrihydrite of low crystallinity.
Example 4 The experiment was carried out as in Example 3 with the exception of using portland cement in place of blast furnace slag cement and passing the acidic solution to which iron-oxidizing bacteria Thiobacillus ferooxidans had been added at a rate of 5 1/day for 6 days. The effluent at the end of the reaction showed a pH of 4.0 and contained 1.4 mg/1 of total iron ions, 1000 mg/1 of sulfate ions, 16 mg/1 of silicic acid and 297 mg/1 of calcium ions. The amount of the iron component adhering to 1 kg of the treating material was 407 g as metallic iron. The treating material showed a water permeability coefficient of 7.0x10-2 cm/sec and a water content of 78%.
When the treating material carrying an oxygen-containing iron compound was observed under an electron microscope, protuberance-like products (schwertmannite) were deposited in the form of a sheath on rock wool fibers as shown in Figs. 1 and 2 and each protuberance-like product was an aggregate of sub-micron needle-like particles. The fibers contained in the treating material were chemically composed of 98.3% of Si02, 0.8% of A1203 and 0.0% of Ca0 and the rock wool became porous silica fibers retaining the fibrous shape. The oxygen-containing iron compound was chemically composed of 85.6% of Fe203, 2.8% of SiOz, 0.2% of Ca0 and 11.0% of S03 and it was schwertmannite of low crystallinity.
Examples 5-6 An aqueous solution acidified by nitric acid to pH 3.6 and containing 15 mg/1 of trivalent arsenic ions, 15 mg/1 of cadmium ions and 15 mg/1 of lead ions was prepared and 9 g of the treating material obtained in Example 3 or 4 was added to 1 liter of this acidic solution. The reaction was allowed to proceed at room temperature for 1 hour and the reaction mixture was filtered. The concentration of the ions in the filtrate and the pH of the filtrate were determined. The results are shown in Table 2.

(Table 2) Treating As Cd Pb p H
material Example Example 3.7mg/1 0.05mg/1 0.01mg/1 9.4 Example Example 2.4mg/1 0.75mg/1 3.45mg/1 3.0 Example 7 When artificial waste water containing 50 mg/1 of trivalent arsenic ions was treated with the treating material obtained in Example 4, addition of 5 g of the treating material to 1 liter of the waste water removed 45.2% of arsenic. Likewise, addition of 5 g of the treating material to 1 liter of artificial waste water containing 98 mg/1 of phosphoric acid removed 99.5% of phosphorus or addition of 100 g of the treating material to 1 liter of artificial waste water containing 3.6 mg/1 of fluorine removed 40%
of fluorine.
Fibrous silica on the surface of the treating material after the waste water treatment is enclosed by a sheath of schwertmannite and arsenic and others are taken in this schwertmannite and exist stably. For this reason, it was possible to take out the treating material as it was and submit it to an after-treatment.
Example 8 A granular mixture with an average particle diameter of 20 mm, a bulk specific gravity of 0.2 and a porosity of 95% was prepared by mixing 50 parts by weight of nickel slag wool (granular, average particle diameter 30 mm), 50 parts by weight of a hydrous iron oxide selected from schwertmannite (S), magnetite (MG), goethite (G) and ferrihydrite (FH) and 2 parts by weight of an acrylic .. CA 02523572 2005-10-25 emulsion in a ribbon mixer.
The schwertmannite used here was obtained by preparing an acidic solution with pH 2.5 containing 1080 mg/1 of sulfate ions, 137 mg/1 of total iron ions and 250 mg/1 of calcium ions from ferrous sulfate, gypsum and sulfuric acid, adding iron-oxidizing bacteria Thiobacillus ferooxidans to the solution, and stirring the mixture at room temperature for 7 days while blowing air into the mixture at a rate of 1 1/min. Commercial materials (available from Tetsugen Co., Ltd.) were used for magnetite, goethite and ferrihydrite.
The treating materials thus obtained were respectively used for treating artificial waste water containing 50 mg/1 of trivalent arsenic ions or 98 mg/1 of phosphoric acid while adding 10 g of the treating material to 1 liter of the waste water and they performed excellently in the removal of arsenic or phosphorus as shown in Table 3. The treating materials after the waste water treatment did not become slimy and could be taken out as they were and submitted to an after-treatment.
(Table 3) S MG G FH

Removal of arsenic % 3 0 . 2 9 . 4 6 . 2 3 .

Removal of phosphorus 6 5 . 5 7 . 4 0 . 5 9 .
% 0 1 8 2 Example 9 A mixture of 40 wt% of rock wool (granular, average particle diameter 30 mm) and 60 wt% of blast furnace slag cement (B grade) was agitated in a ribbon mixer to give a granular mixture with an average particle diameter of 20 mm, a bulk specific gravity of 0.15 and a porosity of 94%. A synthetic resin column, 120 cm in width, 90 cm in height and 16 cm in thickness was packed with 20 kg of the granular mixture so that the thickness became 60 cm and the bulk specific gravity became 0.174.
Acidic waste water with pH 2.8 from an iron sulfide mine which contains 875 mg/1 of sulfate ions, 124 mg/1 of total iron ions and 226 mg/1 of calcium ions and in which iron-oxidizing bacteria Thiobacillus ferooxidans live was passed through the column at a rate of 1 1/day for 10 days.
The granular mixture after passage of the waste water became a treating material carrying oxygen-containing iron compounds. The amount of the iron component adhering to 20 kg of the treating material was approximately 6 kg as metallic iron. The effluent at the end of the reaction showed a pH of 4.1 and contained 0.09 mg/1 of total iron ions. The water permeability coefficient was 0.6x102 cm/sec and the water content was 78%. When dried at 100 ~, the material showed a bulk specific gravity of 0.18. The iron component adhering to the material was a mixture of schwertmannite and goethite of low crystallinity.
Next, waste water with pH 6.9 containing 1.07 mg/1 of arsenic ions, 0.07 mg/1 of total iron ions and 0.003 mg/1 of lead ions was passed through the column at a rate of 0.5 1/day until the collective throughput became 10 liters. According to an analysis of the treated water conducted at that time, the pH was 3.9, the concentration of arsenic ions was 0.01 mg/1, the concentration of total iron ions was 2.3 mg/1 and lead ions were not detected.
Moreover, the treating material showed a water permeability coefficient of 0.5 x102 cm/sec after the reaction and a water content of 77% at the time of completion of the reaction. When .. CA 02523572 2005-10-25 dried at 100 ~, the material showed a bulk specific gravity of 0.19.
Example 10 A mixture of 60 parts by weight of rock wool (granular, average particle diameter 30 mm) and 40 parts by weight of blast furnace slag cement was stirred in a ribbon mixer to give a granular mixture with an average particle diameter of 20 mm, a bulk specific gravity of 0.15 and a porosity of 94%.
Next, 5 parts by weight of the granular mixture was mixed with 5 parts by weight as iron of ferrous sulfate, ferric sulfate or ferrous chloride and placed in a porcelain crucible, 5 parts by weight of water was added and the resulting mixture was stirred and left standing for 1 hour.
The crucible and its contents were calcined in an electric furnace in an oxidizing atmosphere at 350 ~ for 1 hour, cooled and the contents were taken out and ground coarsely in a mortar with a pestle to give a treating material A, B or C.
To 1000 ml of a phosphoric acid solution (approximate concentration 100 mg/1) was added 1.25 g of the treating material A, B or C, the mixture was stirred for 30 minutes and the removal of phosphorus was determined to calculate the phosphorus-removing ability per 1 g of the treating material (P04-mg/g). Moreover, 1.25 g of the treating material A, B or C was added to 1000 ml of a sodium arsenate solution (concentration 15 mg/1), the mixture was stirred for 30 minutes and the removal of arsenic was determined to calculate the arsenic-removing ability per 1 g of the treating material (As-mg/g). Still more, the presence or absence of the outflow of the iron component (whether iron-red water is generated -- _, CA 02523572 2005-10-25 or not) at the time of removal of phosphorus or arsenic was examined by inspecting the coloring of the solution after filtration. The results are shown in Table 4.
(Table 4) Treating material A B C

Iron compound Ferrous Ferric Ferrous sulfate sulfate chloride Arsenic-removing 3 0 . 1 4 0 . 2 3 7 . 9 ability m g / g Phosphorus-removing3 8 . 2 5 1 . 0 4 8 . 0 ability m g / g Outflow of iron no no no component Example 11 The rock wool (RW) or blast furnace slag cement (BC) used in Example 10, ferrous sulfate or ferric sulfate and water were mixed according to the formulation shown in Table 5 and the mixture was stirred in a procelain crucible and left standing for 1 hour.
Next, the crucible and its contents were calcined in an electric furnace in an oxidizing atmosphere at 350 ~C for 1 hour, cooled and the contents were taken out and ground coarsely in a mortar with a pestle to give a treating material D or E. The numericals in Table are in the unit of part by weight.

(Table 5) Treating material D E

Iron compound Ferrous sulfate Ferric sulfate 9.0 9.0 RW 5 p Water 5 5 To 1000 ml of a phosphoric acid solution (approximate concentration 100 mg/1) was added 1.25 g of the treating material D, the mixture was stirred for 30 minutes and the removal of phosphorus was determined to calculate the phosphorus-removing ability per 1 g of the treating material (P04-mg/g). Furthermore, 1.25 g of the treating material D was added to 1000 ml of a sodium arsenate solution (concentration 15 mg/1), the mixture was stirred for 30 minutes and the removal of arsenic was determined to calculate the arsenic-removing ability per 1 g of the treating material (As-mg/g). Still more, the presence or absence of the outflow of the iron component at the time of the removal of phosphorus or arsenic was examined. Similar experiments were carried out using the treating material E and the treating materials F and G that were obtained by calcining respectively ferrous sulfate and ferric sulfate alone. The results are shown in Table 6.

(Table 6) Treating material D E F G

Arsenic-removing ability mg / 5 8 2 7 4 7 5 6 g . 7 . . 2 . 1 Phosphorus-removing ability mg/g7 4 3 4 5 9 7 1 . 4 . . 8 . 1 Outflow of iron component n o n o y a y a s s Experiment 12 According to the formulation shown in Table 7, the rock wool used in Experiment 10, the precipitates consisting of a mixture of schwertmannite and goethite formed by neutralizing iron-containing acidic waste water from a mine (15 parts by weight of the precipitates corresponds to 5 parts by weight of metallic iron) and water were mixed so that the iron component becomes roughly equal in weight to the rock wool and the resulting mixture was placed in a porcelain crucible, stirred and left standing for 1 hour. The crucible and the mixture were calcined in an electric furnace in an oxidizing atmosphere at the calcining temperature shown in Table 7 for 1 hour, cooled and the contents were taken out and ground coarsely in a mortar with a pestle to give treating materials H to K.
(Table 7) Treating material H I J K

Precipitates 5 15 1 5 1 5 Water 5 5 5 5 Calcining 1 0 0 1 5 0 7 0 0 3 5 0 ~ ~ rC C

The treating materials H to K were respectively tested as follows. To 1000 ml of a phosphoric acid solution (approximate concentration 100 mg/1) was added 1.25 g of the treating material, the mixture was stirred for 30 minutes and the removal of phosphorus was determined to calculate the phosphorus-removing ability per 1 g of the treating material (P04-mg/g). Moreover, 1.25 g of the treating material was added to 1000 ml of a sodium arsenate solution (concentration 15 mg/1), the mixture was stirred for 30 minutes and the removal of arsenic was determined to calculate the arsenic-removing ability per 1 g of the treating material (As-mg/g). Still more, the presence or absence of the outflow of the iron component at the time of the removal of phosphorus or arsenic was examined by inspecting the coloring of the solution after filtration. The results are shown in Table 8.
(Table 8) Treating material H I J K

Arsenic-removing ability3 9 . 3 4 . 1 0 . 2 8 .
mg/g 1 9 3 2 phosphorus-removing 4 9 . 4 4 . 1 3 . 3 5 .
ability mg / g 6 3 0 7 Outflow of iron componentn o y a s n o n o Although Examples 10 to 12 refer to the removal of arsenic and phosphorus, it was confirmed that other toxic substances such as lead, cadmium, antimony, uranium, selenium and fluorine could be removed.
Example 13 Iron-containing acidic waste water with pH 2.7 from a mine which contains 956 mg/1 of sulfate ions, 116.4 mg/1 of total iron ions and 0.68 mg/1 of total arsenic ions and shows an acidity of 768 mg ~ CaC03/1 at pH 4. 8 and an acidity of 830 mg ~ CaC03/1 at pH 8.3 and in which iron-oxidizing bacteria Thiobacillus ferooxidans live was used as raw water and it was treated for the removal of arsenic and iron by feeding it a rate of 1 t/day to an equipment provided with the steps for the oxidation of arsenic, removal of arsenic, oxidation of iron and removal of iron. The granular mixture obtained in Example 3 was used in the step for the removal of iron and the precipitation of oxygen-containing iron compounds and partial neutralization took place simultaneously here. The rock wool on which iron compounds precipitated sufficiently and which decreased in the alkali component was used as a treating material in the step for the removal of arsenic to effect adsorptive removal of arsenic.
The quality of water treated for the removal of arsenic was as follows: pH 2.8, concentration of sulfate ions 965 mg/1, concentration of total iron ions 117.9 mg/1, and concentration of total arsenic ions 0.014 mg/1. The water treated for the removal of arsenic was treated further for the removal of iron and the quality of water after this treatment was as follows: pH 4.1, concentration of sulfate ions 938 mg/l, concentration of total iron ions 0.09 mg/1, concentration of total arsenic ions 0.007 mg/1, acidity (pH 4.8) 2 mg ~ CaC03/1, and acidity (pH 8.3) 117 mg ~
CaC03/1 .
The treating material used in the step for the removal of arsenic or the granular mixture used in the step for the removal of iron was added to the artificial waste water (a solution of metals, each as its nitrate) shown in Table 9 at a rate of 9 g to 1 liter, the concentration of each metal was determined after 1 hour and the results are shown in Table 9. The numerals in Table 9 designate the concentration of metal in the unit of mg/l.
(Table 9) Fe Mn Cu Zn Pb Cd As As (III) M

Artificial 90.4 15 15 15 15 15 15 15 waste water Treating 92.59 15.44 15.90 15. 3.45 0.75 2.42 0.01 material Granular 0.01 0.09 0. 0.01 ND. 0.05 13.66 3.68 mixture Example 14 A column with a diameter of 75 mm was packed with 50 g of the treating material prepared in Example 9 to a packing thickness of 50 mm and raw water containing 0.1 mg/1 of phosphoric acid prepared by diluting a liquid fertilizer (OKF2 available from Otsuka Chemical Co., Ltd.) was passed through the column at a rate of 15 ml/min for 30 days.
The concentration of phosphoric acid in the treated water was measured 1 day, 15 days and 30 days after the start of passage of water and it was 0.005 mg/1 or less in each measurement. The volume of the treating material at this time was 220.8 cm3 and the residence time was approximately 15 minutes.
Example 15 The treating material B prepared in Example 10 has the chemical composition (wt%) shown in Table 10. This treating material was a pumice-like material showing a porosity of approximately 75% and a water permeability coefficient of 1.4 X10° cm/sec.
(Table 10) Ca0 Mg0 S i A Fez03 T Na20 KZO Mn0 S03 Total OZ 1203 i OZ

13.2 1.8 14.7 4.3 25.9 0.2 0.1 0.1 0.1 39.5 99.9 In order to understand the phosphorus-removing ability of this treating material against solutions of low phosphoric acid concentrations, OKF2 was diluted to prepare two kinds of raw water, one containing 0.1 mg/1 of phosphoric acid and another containing 1.0 mg/1 of phosphoric acid. To 200 ml of the raw water was added 0.2 g of the treating material, the mixture was stirred at room temperature for 15 minutes and filtered and the concentration of phosphorus in the filtrate was determined. It was 0.005 mg/1 or less for the raw water containing 0.1 mg/1 of phosphoric acid and 0.01 mg/1 for the raw water containing 1 mg/1 of phosphoric acid.
Example 16 A column with a diameter of 150 mm was packed with 100 g of the treating material prepared in Example 9 to a packing thickness of 50 mm, moderately polluted lake water was passed through the column continuously at a rate of 60 ml/min, the concentration of phosphorus in the untreated water (UT-TP) and that in the treated water (T-TP) were determined and the results are shown in Fig. 3.
In Fig. 3, the abscissa shows the collective throughput of water (CTW) and the ordinate the concentration of total phosphorus (TP).
At this time, the volume of the treating material was 883.1 cm3, the superficial velocity was 0.34 cm/min and the residence time was approximately 15 minutes.

Examples 14 to 16 indicate that the treating materials of this invention show stable and continuous performance in the removal of phosphorus even from lake and marsh waters containing low concentrations of phosphorus.
Industrial Applicability The treating material of this invention is capable of removing toxic substances from a variety of polluted waters and raw city water by a simple method with high efficiency and ease of maintenance. The material maintains its water permeability after use and is suited for use over a long period of time. The treated products are stable, do not allow toxic substances to elute again by changes with time or acidification, and their after-treatment is simple.

Claims

What is claimed is:

(1) A treating material for polluted water containing at least one kind of toxic substance selected from arsenic, lead, cadmium, antimony, uranium, selenium and fluorine which comprises an oxygen-containing iron compound carried on a material containing inorganic fibers having an increased silicic acid content as a result of the reaction of at least a part of silicate-based fibers reactive with acids with an acid and shows a porosity of 50% or more and a bulk specific gravity of 0.1-1.5.

(2) A treating material as described in claim 1 wherein the inorganic fibers having an increased silicic acid content as a result of the reaction of at least a part of them with an acid are silicate-based fibers which have increased in the silicic acid content by removal of 50% or more of the alkali component.

(3) A treating material as described in claim 1 wherein the silicate-based fibers reactive with acids are at least one kind selected from rock wool, nickel slag wool and glass wool.

(4) A treating material as described in claim 1 wherein the material containing inorganic fibers is a mixture or an integrated body of inorganic fibers, inorganic powders and an inorganic or organic binder.

(5) A treating material described in claim 1 or 2 wherein the oxygen-containing iron compound is carried on the inorganic fibers in the form of a sheath.

(6) A treating material as described in claim 1 wherein the oxygen-containing iron compound is at least one kind selected from schwertmannite or its calcined product, ferrihydrite or its calcined product, akaganeite or its calcined product, goethite or its calcined product, lepidocrocite, hematite, magnetite, maghemite, jarosite, calcined amorphous hydrous iron oxide, calcined ferric suflate, calcined ferrous sulfate, calcined ferric chloride, calcined ferrous chloride, calcined ferric nitrate and calcined ferrous nitrate.

(7) (Deleted) (8) A treating material as described in claim 1 wherein the toxic substance is arsenic and arsenic is present as a water-soluble arsenic compound or ions generated therefrom.

(9) A method for producing a treating material described in claim 1 which comprises treating a material containing inorganic fibers with iron-containing acidic water to give inorganic fibers on which an oxygen-containing iron compound is carried.

(10) A method for producing a treating material as described in claim 9 wherein the acidic water containing iron is water containing sulfuric acid and iron or acidic waste water containing iron and a material containing inorganic fibers is treated with the iron-containing acidic water to effect neutralization and formation of an oxygen-containing iron compound thereby yielding an oxygen-containing iron compound carried on inorganic fibers.

(11) A method for producing a treating material as described in claim 9 wherein iron-oxidizing bacteria are further added at the time of the treatment with the iron-containing acidic water.

(12) (Deleted) (13) A method for treating polluted water which comprises contacting a treating material described in claim 1 with polluted water containing at least one kind of arsenic, lead, cadmium, antimony, uranium, phosphorus, selenium and fluorine as a toxic substance.

(14) A method for treating polluted water as described in claim 13 wherein polluted water containing trivalent arsenic as a toxic substance is submitted to an oxidation treatment to convert trivalent arsenic to pentavalent arsenic and then the polluted water is contacted with the treating material.