DE2537754A1 - PROCESS FOR THE REMOVAL OF PHOSPHATES FROM AQUATIC SOLUTIONS - Google Patents

Abstract

Dissolved phosphates are removed from aqueous solutions by metal-impregnated activated charcoal. After treatment with phosphate, the activated charcoal is itself treated with metal salt solution and thus regenerated. The metal used is in particular iron and/or aluminium.

Description

Process for removing phosphates from aqueous solutions Subject The present invention is a method for removing dissolved phosphates from aqueous solutions.

To date, phosphates have been almost exclusively obtained from aqueous solution by chemical precipitation with the help of salts of calcium, aluminum or iron removed. Various other processes are also known in which phosphates e.g. be eliminated by plants or microorganisms, but these are in not often used in practice.

The usual chemical precipitation processes are usually continuous carried out, which has the disadvantage that a relatively accurate Adjustment of the metal salt dosage to the currently flowing phosphate amount is necessary is. In the case of precipitation processes that ensure thorough mixing of what has already been treated Bring the amount of water with the freshly flowing and # the ChemikSlien, so e.g. in phosphate precipitation in the activated sludge stage of a biological sewage treatment plant, Although short-term deviations from the correct dosage are not serious, however, interruptions of longer duration lead here too - i.e. in the grade 3 classification an hour and longer - inevitably leads to an increase in the phosphate content in the Drain.

In addition, it is generally difficult to use them in, for example, water treatment plants The phosphate elimination methods mentioned, the phosphorus concentration significantly below 1 mg P / 1 in the run to lower, which, however, to avoid eutrophication in particular of lakes would be desirable.

Basically there would be the possibility to bypass this -difficulty, by using anion exchangers to eliminate the phosphate, the rate of their recovery would be high enough to be one at the highest inflowing amounts and concentrations to ensure a sufficient degree of elimination. The currently known, technically However, the anion exchangers that can be used are relatively complex and expensive and also not selective for phosphates. If unselective exchangers are used, then take these not only, as desired, the phosphates, but also other anions and become therefore exhausted more quickly as soon as such anions in addition to the phosphates in considerable amounts Concentration. This makes the process expensive, since regeneration is more frequent and larger systems are required.

It is known that certain inorganic compounds - such as metal oxides such as aluminum oxide - preferentially adsorb phosphate ions. A technical one However, the use of such products for the elimination of phosphate from water is still available either their insufficient capacity or their difficult regenerability. These main disadvantages do not apply if the phosphates are impregnated with metal for adsorption Activated carbons can be used as described below.

It has now been found according to the invention that commercially available activated carbons, how they are normally used for water treatment and wastewater treatment, have the ability to adsorb phosphates from neutral, aqueous B6 solutions, when using solutions of metal salts, especially iron or liuminmalzen treated and then washed neutral. Though owns Activated carbon that is not impregnated with metal also has a certain adsorption capacity for phosphates, but this is compared to that with metal salt solution treated activated carbon low.

The application of iron or aluminum to the activated carbon is on various ways possible, but is preferably done by treatment the coal with the moderately concentrated solution of a salt of the metals concerned.

Depending on the type of metal and the anion, the metal ion concentration, During the washing process, a certain amount of the metal remains in the pH and type of activated carbon on the coal and then largely determines the phosphate adsorption capacity. Depending on the choice of conditions, metal can be in the order of magnitude of per thousand up to several percent (based on the weight of the dry charcoal) on the activated charcoal raise. The content of metal on the coal can optionally be determined by chemical Increase the neutralization of the activated carbon soaked with metal salt.

After the phosphate uptake until its capacity can be exhausted the carbon can be completely reactivated by treatment with a metal salt solution. The adsorbed phosphate goes into solution. With multiple activation / I # osphat loading cycles, especially in the case of iron, the amount of metal adsorbed on the coal increases initially something with each cycle in order to strive for a certain maximum value. The phosphate adsorption capacity improves simultaneously, but not directly proportional to the metal content of the coal. -Ideal with the examples below the principle of the process can be illustrated: Example 1 50 g each of dry activated carbon "Hydraffin BR Supran resp. LS Supra "(both company lurgi) that during 30 minutes at room temperature with a 0.2 molar solution of iron (III) sulfate treated, then filtered and washed with tap water for so long were until the washing water was neutral and no iron ions were detectable in it, were wet in portions of 2.5 g each (corresponds to dry substance) in 200 ml of tap water with an initial phosphorus concentration of 10 mg P / 1 (as orthophosphate in solution) stirred for 3 hours. After the experiment was the residual concentration of phosphorus 1.95 mg Pjl for the Fe-treated coal "BR-Supra" resp. 5.15 mg P / 1 for "TS Supra" with a pH of 7.5 and an iron content of Coal from 18.7 resp. 9.2 mg Fe / g dry substance. The phosphate-laden coals were then, as described above, for regeneration again with a Solution of iron (III) activated, reloaded with phosphate, etc. With exactly the same The procedure was repeated for the 7th cycle (activation / loading) after loading starting from a phosphorus solution with 10 mg P / 1 residual phosphorus concentrations from 1.4 resp. 1.35 mg P / 1 at a pH of 6.5 resp. 6.8 and an iron content of 48.5 resp. 30 mg Fe / g dry substance measured.

With an activated carbon of the type "Pittsburgh Filtrasorb 400" (Chemviron / Calgon) With the same experimental set-up, a residual phosphorus concentration resulted in the first cycle of 6.4 mg P / 1 (pH = 7.7, 4.4 mgFe), in the 7th cycle a rate of 0.65 mg P / 1 (pH = 7.3, 41.8 mg Fe).

Example 2 Treated with Fe (III) solution and then with tap water washed commercial activated carbon ~ Norit ROW 0.8 "(Norit N.V., Amsterdam) stirred in neutral, aqueous solutions, the ortho- resp. Pyro, resp. Tripolyphosphate contained, where 1.25re3pfi 1.45 or 35 mg P based on 1 gram of the dry, impregnated charcoal were adsorbed at corresponding residual phosphorus concentrations in the solution of 2.60 resp. 3.05 resp. 2.7 mg P / 1 and pH values between 6.45 and 7.10. 1 gram of the dry, impregnated charcoal contained 16 mg of iron.

Example 3 "Norit ROW 0.8" activated carbon was mixed with 0.2 molar iron (III! Chloride resp. Treated iron (III) chloride sulfate solution and then with tap water neutral washed.

2.5 g wet, impregnated coal (equivalent to 1.1 g rock substance) adsorbed from a neutral aqueous solution 0.95 resp. 1.1 mg P (as orthophosphate in solution) resp. 1.3 resp. 1.6 mg P after 10 consecutive activation and Loading cycles at residual concentrations in solution of 5.3 resp. 4.4 and 3.55 resp. 2.3 mg P / l. The iron content of the coal used was 8.8, respectively. 13 mg Fe / l, l g dry substance in the first cycle respectively. 47.6 resp. 54.8 mg Fe on the 10th cycle. Activated carbon "Norit RGW 0.8" not treated with iron solution merely adsorbed C. 9 mg mg g dry charcoal at a concentration in solution of 5.5 mg Pjl.

Example 4 700 g of dry activated carbon "Norit ROW 0.8" in granulated form were placed in a column of 6 cm through which the flow was from bottom to top. Inside diameter treated with 2 liters of 0.5 molar solution of iron (III) sulfate and then washed until the wash water was neutral and iron-free. The column was charged with a neutral aqueous solution with 10 mg P / 1 as orthophosphate and pH 7 → 8 at a flow rate of 2 liters / h. For the P concentration respectively. the pH of the solution treated in this way, the following values were measured as a function of the volume of the treated solution: Volume of the residual concentration pH treated on orthophosphate Solution (t) (mg P / 2) 5 0.0 6.2 64 0.0 7.2 93 0.1 7.6 100 0.3 7.4 136 1.6 7.9 The column was then regenerated again by treatment with iron (II1) solution and neutral washing. After loading and regenerating three times, the following leakage values were recorded in the 4th loading test under analogous conditions. Volume of the residual concentration pH treated on orthophosphate Solution (#) (mg P / e) 30 0.0 6.2 89 0.0 7.0 122 0.0 7.2 138 0.05 6.9 160 0.5 7.2 163 0.6 165 ~ 1.25 Example 5 Commercially available, granulated activated carbon Norit ROW 0.8 "was impregnated with aluminum by treatment with a 10% solution of aluminum sulfate in water and subsequent extensive washing with distilled water and adsorbed 4.1 mg P as orthophosphate, based on 4.2 g dry, in a loading test at equilibrium , impregnated activated carbon with a residual phosphate concentration in solution of 1.9 mg P / 1 and a pH of 7.35 compared with an adsorption of 1.3 mg P based on 4.2 g dry, untreated activated carbon Norit with a residual concentration of 7.35 mg P / 1.

Example 6 Activated charcoal orit ROW 0.8 ", which lasts for thirty minutes stirred in a 1.5 molar solution of iron (II) sulfate at room temperature and then washed with tap water. until no more iron can be detected in the washing water was, adsorbed in a loading test from neutral, wetter, orthophosphate solution containing 0.4 mg P / g dry substance with a residual concentration in Solution of 0.2 mg respectively. 0.9 mg P / g at 1.3 mg P / 1 benz. 1.5 mg P / g at 5-7 mg P / 1. The pH values of the aqueous solution after the loading experiment were between 7.6 and 7.7. The carbon impregnated with iron (II) contained 18 mg Fe / g dry substance.

Claims (4)

Patent claims 1. Process for removing dissolved phosphates from aqueous Solutions, characterized in that these liii metal-impregnated activated carbon Be brought into contact, which in turn after the loading with phosphate by Treatment with metal salt solution is regenerated again. 2. The method according to claim 1, characterized in that the metal Iron (II), iron (III), aluminum (III) or combinations thereof can be used. 3. The method according to claim 1, characterized in that the activated carbon impregnated or regenerated by treatment with a solution of a metal salt will. 4. The method according to claim 1, characterized in that the activated carbon by treatment with a solution of a salt of iron (II), iron (III), aluminum (III) or combinations thereof is impregnated or regenerated.