MXPA00009514A - Water treatment product and method - Google Patents

Abstract

A water treatment product which is a particulate material having a specific surface area of at least 1.0 m2/g, or an artefact formed by bonding together such particulate material, and having an insoluble ferric iron coating. Preferably, the particulate material is an alumina-based material. The product is useful in the treatment of water to remove organic materials, cations or anions, and more particularly heavy metals, As, Se or F. Methods of making the water product are also provided.

Description

"PRODUCT AND METHOD OF WATER TREATMENT" As the discharge limits for metals are narrowed, the adsorption processes for the treatment of a high level of metal-bearing waste become increasingly attractive.The adsorption is capable of removing many metals through a further pH scale. In addition, adsorption can often remove metals formed in complex that would not be proven by conventional treatment processes.An adsorbent commonly present in metal treatment processes, is an amorphous iron oxide called ferrihydrite. A disadvantage of this treatment is that the ferrihydrite forms a sludge product from which it is difficult to recover the purified water In order to record this problem, a water treatment product consisting of washed sand coated with ferrihydrite (M) has been described (M Edwards and MM Benjamin, Jnl. Water Poli Control Fed, Volume 61, Part 9, 1989, page 1523-1533). This product has also been tested for the removal of arsenic for drinking water (F G A Vagliasindi et al., Proceedings Water Quality Technology Conference, Part 2, New Orleans, November 12 to 16, 1995, pages 1829-1853).

In Europe and the United States of America the permitted amounts of arsenic in drinking water have been reduced, or will be reduced shortly, from 200 micrograms per liter to 50 micrograms per liter and up to 20 or 10 micrograms per liter. As a water treatment product for removing arsenic, activated alumina has been proposed (Canadian Patent Number 2,090,989). The particles of the activated alumina are robust and easily separable from the treated water. Even though the activated alumina itself is an adsorbent of active arsenic and other heavy metals, there is a need for an even better material. This need has been reported in Patent Number WO 96/37438, which proposes water treatment compositions comprising oxides of lanthanum and alumina. But lanthanum oxides would be prohibitively expensive for the treatment of very large volumes of water. In accordance with the present invention there is provided a water treatment product which is a particulate material having a specific surface area of at least 1.0 square meter per gram, or an artifact formed by ligating this particulate material together, and it has an insoluble ferric iron coating - Preferably, the particulate material is porous and may have through-pores, closed pores, or both. The artifacts formed from the particulate material are typically in cylindrical or brick form. The particulate material is preferably non-metallic and is a mineral or an inorganic material. Preferred materials that can act predominantly as substrates for the ferric iron coating include Zeolites, Ferrierite, Mordenite, Sodalite, clays in the form of pillars and activated clays. The preferred materials are alumina-based including the alumina itself and the bauxite. The particulate material or the device formed therefrom is preferably sturdy, resistant to crushing, and does not form a fine powder or silt during use. The individual particles in the particulate material, which may be accretions of fine particles, need to be large enough to be easily separable from the treated water. The individual particles can be as fine as those having an average size of 5 microns or 10 microns, even though they are more easily separated from the treated water to the coarse particles. Preferably, the individual particles have an average size of 100 micrometers to 5000 micrometers, e.g., 200 micrometers-1000 micrometers. They can be formed by agglomeration or granulation or crushing.

The particulate material used herein may be alumina trihydrate as produced by the Bayer process, or calcined alumina. Preferably activated alumina is used, a product formed by heating the alumina triturate at 300 ° C to 800 ° C. Activated alumina has the advantage of a large specific surface area. In this way for example the commercial product AA400G has a specific surface area of 260 to 380 square meters per gram. Alternatively, the porous medium may be bauxite, or another alumina-containing mineral such as zeolite, clay or hydrotalcite. The non-volatile content of bauxite comprises from 40 or 50 percent to 95 percent in that of alumina, along with 3 or 5 - 25 weight percent ferric oxide. Activated bauxite is a preferred material that can be formed by heating the ore to a temperature within the range of 300 ° C to 800 ° C, and can typically have a specific surface area of 100 or 150 to 200 square meters per gram. Because the iron content of the bauxite is present on the surface of the particle rather than on the surface of the particle, it is not generally counted as part of the insoluble ferric iron coating of this invention. Particulate materials that have a high specific surface area show a great ability to adsorb contaminants and remove contaminants from water. The water treatment product of this invention preferably has a specific surface area of from 1.0 to 400 square meters per gram, e.g., at least 10 square meters per gram, particularly at least 100 square meters per gram. The particulate material can be provided with an insoluble ferrous iron coating precipitated by soaking it in a ferrous solution, e.g., an aqueous solution of ferric sulfate or ferric chloride. The water is then removed by evaporation or otherwise and the product is dried at an elevated temperature, eg, from 50 ° to 500 ° C and preferably from 50 ° to 200 ° C, in order to convert the ferric salts into a coating of insoluble ferric iron, probably a ferric oxide hydrate or ferrihydrate. The preparation technique described in the M Edwards reference mentioned above is appropriate. The ferric iron coating may be from 0.01 percent to 50 percent, preferably from 0.1 percent to 10 percent by weight of the water treatment product. Another way of providing a coated particulate material that has been found to be particularly suitable for large scale operation is as follows: an appropriate quality of activated alumina (such as AA400G mesh 28-48) is saturated in a ferric solution, for example of ferric chloride or preferably ferric sulfate with periodic stirring for up to about 6 hours. The sodium hydroxide solution is added to complete the hydrolysis and forms an insoluble ferric iron oxide coating on the activated alumina using a medium such as a pH meter to control the pH up to 7.5 to 8. The product is rinsed completely to remove all fine material and dry either at room temperature or at an elevated temperature. An alternative method for making a water treatment product according to the invention comprises treating a ferruginous ore with liquid acid in order to leach the iron from the ore, and then raising the pH of the liquid in order to form a ferric iron coating. precipitate on the surface of the ore. For example, the ore can be treated with hydrochloric acid at a pH of about 3, and the pH subsequently raised to about 7, by the use of sodium hydroxide. The resulting product is filtered, washed and dried, preferably at elevated temperature as above. Also included within the scope of the invention is a water treatment product which is a ferruginous ore having a coating of ferric iron precipitated on its surface.Preferably the ore is bauxite, particularly activated bauxite.As demonstrated in the examples which are presented below, the water treatment product of this invention has a combination of useful properties: excellent ability and avidity to rapidly adsorb the inorganic contaminants of the water being treated; a robust material that is easily separable from the treated water and that can be treated to recover the inorganic contaminants and thus allow the reuse without losing its structure. The ntion also includes a method of treating water, which method comprises contacting the water to be treated with the water treatment product described herein, and then recovering the treated water containing a reduced concentration of an organic material. or a cation or anion particularly at least one heavy metal such as As or Se or F. Batch or intermittent treatment typically lves stirring the water to be treated with an aliquot of the water treatment product, the amount of which is selects in order to achieve a desired degree of water purification at a desired time, typically less than 1 hour. Continuous methods well known in the art are also possible.

The optimum conditions for the removal of organic materials and inorganic materials are generally different. Depending on the nature of the contaminant to be removed, it may be advantageous to adjust the pH of the water in order to improve the operation of the water treatment product. In this way, for example, arsenic is best removed at a pH of 5 to 7, preferably of 5.5, while fluoride is best removed at a pH of 6 to 8, preferably 7.

Example 1 Pollution Procedure As ferrous salt solutions, chloride and sulfate were initially used. Both ferric chloride and ferric sulfate solutions are classified as potable water qualities, which are appropriate in the treatment of drinking water. The ferric chloride solution was supplied as 10.58 weight percent Fe ion and the ferric sulfate solution was supplied as 12.0 weight percent Fe ion. The activated alumina AA400G (28x48 mesh size; 0.3-0.6 millimeter) ) was contaminated with ferric salt solutions in accordance with the following samples: Sample__l: 9.5 grams of the ferric chloride concentrate was diluted to 1000 milliliters with distilled water. 1000 grams of AA400G was added to this solution and the slurry was stirred to ensure a uniform coating of the salt in the alumina. Once the alumina had adopted (adsorbed) all the liquid, the sample was transferred to a tray and dried in an oven at 160 ° C for 3 hours. After this drying period, all samples flowed freely. After drying, the samples were washed to remove fine dust from the surface. Preferably, they were then immersed in a water / sodium carbonate solution for 24 hours to ensure almost complete hydrolysis of the ferric salt and to prevent any iron salt from being leached. The product contained about 0.15 weight percent of Fe as Fe2? 3- Sample 2: 47.2 grams of a ferric chloride concentrate were diluted in 1000 milliliters of distilled water. 1000 grams of AA400G was added to this solution and the slurry was stirred to ensure a coating of the salt on the alumina. This was then followed as in Sample 1. The product contained 0.61 weight percent of Fe as Fe2? 3.

Sample 3: 8.3 grams of the ferric sulfate concentrate were diluted in 1000 milliliters of distilled water. 1000 grams of AA400G were added to this solution and the slurry was stirred to ensure a uniform coating of the salt on the alumina. This was then followed as in Sample 1. The product contained approximately 0.15 weight percent of Fe as Fe2? 3- Sample 4: 41.2 grams of the ferric sulfate concentrate were diluted in 1000 milliliters of distilled water. 1000 grams of AA400G were added to this solution and the slurry was stirred to ensure a uniform coating of the salt on the alumina. This was then followed as in Sample 1. The product contained 0.63 weight percent of Fe as Fe2? 3 Sample 5: 412 grams of the ferric sulfate concentrate were diluted in 1000 milliliters of distilled water. 1000 grams of AA400G were added to this solution and the slurry was stirred to ensure a uniform coating of the salt on the alumina. This was then followed as in Sample 1. The product contained 6.0 weight percent of Fe as Fe2? 3- Bottle Test Experiments a) A bottle test was carried out at room temperature (~ 20 ° C). The particulate materials used included activated alumina AA400G and iron AA400G contaminated according to the aforementioned procedures. A fixed amount of the particulate material within the scale of 0.05 gram, 0.1 gram, 0.5 gram and 1 gram was weighed into a 250 milliliter conical flask equipped with a magnetic follower. To this 200 milliliters of untreated water (contaminated water) was added and stirred magnetically for a period of time from 10 minutes to several days. After stirring, the solutions were filtered using 0.2 micron membrane filters. b) 5 grams of the particulate material was placed in a flask equipped with a magnetic follower. To this, 1000 milliliters of untreated water (contaminated water) was added and stirred magnetically for a period of 1 hour during which, at intervals of 1, 5 and 10 - minutes, the samples were removed and then filtered using 0.2-icmeter membrane filters.

Analysis Arsenic in solution was measured by atomic absorption spectrometry (atomic absorption-hydride generation method), which can detect the trace limit of 2 micrograms per liter or under favorable conditions as low as 0.5 micrograms per liter.

Example 2 Use of iron oxide coated with activated alumina to remove fluoride To examine the effectiveness of the activated alumina coated with iron oxide to remove the fluoride compared to the untreated activated alumina, the following test was carried out. 1. A solution containing ~20 milligrams per liter F was prepared and analyzed for the fluoride concentration using a selective ion electrode. 2. Samples of 0.05 gram, 0.1 gram and 0.5 gram of the different particulate materials were placed in containers. 3. 200 milliliters of fluoride solution was added to each container. 4. Using magnetic stirrers, the containers were stirred overnight at room temperature. 5. Approximately 50 milliliters of the slurry from each package was supplied with syringe and filtered. 6. The fluoride concentration of each filtered solution was analyzed using a selective ion electrode. The media tested were • Commercially-activated AA400G-alumina obtainable.

• Sample 2 • Sample 4 • Sample 5.

Results The starting fluoride concentration was 21 milligrams per liter F. The results shown in the table below are the final concentrations of F in milligram per liter.

Addition of Material in Particles 0. 05 g 0.1 g 0.5 g AA400G 19.5 19.0 17.3 Sample 2 15.9 11.9 12.5 Sample 4 19.0 18.1 13.2 Sample 5 19.3 18.1 11.4 Conclusions The use of activated alumina coated with iron allowed the greater removal of fluoride than untreated activated alumina particularly at medium addition levels of 0.1 gram and above. By increasing the amount of iron oxide present on the surface of activated alumina, the amount of fluoride removed was increased.

Example 3 A bottle test experiment was carried out as described in Example 1. The water tested was wastewater containing 26 milligrams per liter of arsenic. The particulate materials tested were the product of sample 5 (Example 1 containing 6.0 weight percent of Fe as Fe2 ?3) which is referred to herein as AAFS50, and (for comparison) commercial activated alumina AA400G. 1.5 grams or 2 grams of the particulate material was kept in contact with 200 milliliters of residual water for 30 or 60 minutes. The results are shown in Table 1, which is presented below.

Table 1: Removal of arsenic from wastewater using activated alumina coated with iron Average weight of the material Concentration Time in Contact Final particle Arsenic (grams) (minutes) (mg / liter) AAFS50 1.5 30 0.58 AA400G 1.5 30 3.32 AAFS50 60 0.35 AA400G 60 0.78 Example 4 Bottle test experiments were carried out as described in Example 1, using a well borehole water containing an initial arsenic content of concentration of 14.7 micrograms per liter. Samples of 200 milliliters of water were stirred with different amounts of the particulate material during different contact times. The results are shown in Table 2.

Table 2: Removal of arsenic from borehole water using activated AA400G alumina or iron oxide coated with AAFS50 Weight of material Time of AA400G AAFS50 in particles Contact ConcentraConcentra (grams) (minutes) End Final arsenic arsenic (μg / liter) (μg / liter) 0. 1 10 < = 0.5 0. 1 20 < = 0.5 0. 1 30 1.7 < = 0.5 0.1 60 0.6 < = 0.5 0. 1 960 0.5 < = 0.5 0. 5 10 0.97 < = 0.5 0-5 20 < = 0.5 < = 0.5 0. 5 30 < = 0.5 < = 0.5 0. 5 60 < = 0.5 < = 0.5 0. 5 960 < = 0.5 < = 0.5 1 10 0.56 < = 0.5 1 20 < = 0.5 < = 0.5 1 30 < = 0.5 < = 0.5 1 60 < = 0.5 < = 0.5 1 960 < = 0.5 < = 0.5 Example 5 Bottle test experiments were carried out as described above, using water splashed with from about 31 to 33 micrograms per liter of arsenic as sodium arsenate. The two particulate materials were those described above, activated alumina AA400G, and an activated alumina coated with iron oxide AAFS50. Different amounts of each particulate material (0.1 gram, 0.5 gram and 1.0 gram) were stirred with 200 milliliters of the test water for different periods of time (10, 20, 20, 60 minutes and 16 hours (960 minutes)). The results are indicated in the accompanying Figures 1 and 2 which are graphs showing the final arsenic concentration against the contact time.

Example 6 Bottle test experiments were carried out as described above using water splashed with up to 1700 micrograms per liter of arsenic as sodium arsenate. The two particulate materials were those described in Example 5 and used at 0.05 gram of the material per 1000 milliliters of the arsenic solution and which were stirred for 960 minutes. The results are shown in Figure 3.

Claims (14)

CLAIMS:

1. A water treatment product that is a particulate material having an average particle size of at least 5 microns and a specific surface area of at least 10 square meters per gram, or an artifact formed by ligating together this particulate material , and that it has an insoluble hydrated ferric iron oxide coating.

2. The water treatment product of claim 1, wherein the particulate material has an average particle size of 100 microns to 5000 microns.

3. The water treatment product of claim 1 or claim 2, wherein the particulate material is an alumina-based material.

4. The water treatment product of claim 3, wherein the alumina-based material is selected from bauxite, alumina trihydrate and alumina.

5. The water treatment product of claim 3, as in claim 4, wherein the alumina-based material is activated alumina or activated bauxite.

6. The water treatment product of any of claims 1 to 5, wherein the particulate material has a specific surface area of at least 100 square meters per gram. A method for making the water treatment product of any one of claims 1 to 6, which method comprises soaking the particulate material or an artifact formed from the particulate material in a ferrous solution, and recovering and drying the particulate material. coated or the artifact. 8. The water treatment product of any of claims 1 to 6, which is a ferruginous ore having a ferric iron coating precipitated on its surface. 9. The water treatment product of claim 8, wherein the ore is bauxite. 10. The water treatment product of claim 9, wherein the bauxite is activated bauxite. A method for making the water treatment product of any of claims 8 to 10, which method comprises treating a ferrous ore with acidic liquid in order to leach the iron from the ore, and then raising the pH of the liquid in order to form a ferric iron coating precipitated on the surface of the ore. 12. A method of treating water, which method comprises contacting the water to be treated with the water treatment product of any of claims 1 to 6 or 8 to 10, and then recovering the treated water containing a water. reduced concentration of organic materials or cations or anions. The water treatment method of claim 12, wherein the treated water has a reduced concentration of at least one heavy metal such as As or Se or F. 14. The water treatment method of claim 13, wherein the treated water has a reduced As concentration of not more than 10 micrograms per liter.