Method for Waste Water Purification With the Aid of a Sorption Agent

The present invention relates to a method of purifying waste waters with treated aluminum oxides.

In view of the great emphasis being placed upon waste water purification it is very important that sorbents and the like be used which are effective yet simple and economical to use.

Although activated carbon has been suggested as an adsorption agent for water purification, it has proven to be rather expensive. Furthermore, use of the carbon naturally results in a portion of its activity when thermally regenerated as well as a portion of the carbon being carried away with the purified waste water. Additionally, activated carbon adsorbs higher molecular weight substances to a lesser degree, thus making the purfication more expensive.

Pure aluminum oxide has previously been suggested as a waste water purification agent. These agents are supposed to be relatively effective in purifying water containing organic waste compounds which are strongly polar and which cannot satisfactorily be purfied with activated carbon. In particular, the KMnO.sub.4 active lignin containing products of sulfite cellulose manufacturing waste waters can be adsorptively removed by means of aluminum oxide.

However, pure aluminum oxide, compared with activated carbon has a lesser purification capacity and a less broad spectrum of application. In particular, pure aluminum oxide has proven to be relatively ineffective in adsorbing neutral substances and basic compounds thus presenting a problem because waste waters contain wide varieties of substances. The term "neutral substances" refers to non-polar substances having a p.sub.H of about 7 in aqueous solution.

It is therefore an object of the present invention to provide a method of purifying waste waters containing dissolved and undissolved substances, and especially organic substances which are not easily degradable, thus avoiding the disadvantages of known processes. By undissolved substances are meant those substances and materials which are not dissolved in water but rather are suspended therein in finely divided form and cannot be removed from the water by purely mechanical means.

Another object of the invention is to provide a method of purifying waste waters containing neutral substances and basic compounds.

A further object of the invention is to provide a method of treating waste waters with materials which effectively adsorb materials which are not highly polar.

These and other objects are fulfilled according to the method of the invention which comprises purifying waste water by contacting the waste water with Al.sub.2 O.sub.3 which has been treated with ions which when incorporated in the crystal lattice of the Al.sub.2 O.sub.3 are capable of delaying crystallization of the gamma phase of the Al.sub.2 O.sub.3 or with the salts of the ions.

According to one embodiment of the invention the Al.sub.2 O.sub.3 is such that it has been artificially synthesized. In this instance the treatment comprises incorporation of ions of the type referred to above into the reagents used to synthesize the Al.sub.2 O.sub.3.

The Al.sub.2 O.sub.3 may be treated by incorporating either anions or cations in the reagents. When treating by incorporating cations in the reagents, the cations are added in amounts ranging from about 0.1% to 0.5% by weight based upon the weight of the treated Al.sub.2 O.sub.3.

In an alternative embodiment of the invention the Al.sub.2 O.sub.3 is treated by subjecting it to a surface treatment with salts comprising ions which, when incorporated into the crystal lattice of Al.sub.2 O.sub.3 are capable of delaying crystallization of the gamma phase.

In yet another embodiment, the Al.sub.2 O.sub.3 is treated by doping with CO.sub.2 during the synthesis of the Al.sub.2 O.sub.3 adding CO.sub.2 into the reagents used to synthesize the Al.sub.2 O.sub.3. The CO.sub.2 dopant is preferably present in amounts ranging from about 0.05% to about 2.5% be weight with respect to the so treated and doped Al.sub.2 O.sub.3.

According to the invention, waste waters such as the effluents from commercial processing plants are treated by contacting them with Al.sub.2 O.sub.3 treated with ions which are capable of being incorporated into the crystal lattice of the Al.sub.2 O.sub.3 and of delaying crystallization of the gamma phase of the Al.sub.2 O.sub.3, as well as with CO.sub.2. Alternatively, treatment may be performed by contacting the waste water with Al.sub.2 O.sub.3 which itself has been treated with salts comprising the crystallization impeding ions referred to above.

The effluents may be purified by contacting them with the treated or doped Al.sub.2 O.sub.3 by means of any of the known liquid-solid contacting techniques, as for example stirring reactors, fluidized bed reactors or fixed bed columns.

After contact, the waste water is separated from the Al.sub.2 O.sub.3 leaving the sorbed and separated impurities adhering to the Al.sub.2 O.sub.3. In one embodiment of the invention, the Al.sub.2 O.sub.3 employed has been treated by incorporating cations of at least one of the alkali earth metals or one of the metals, iron and chromium during the synthesis of the Al.sub.2 O.sub.3. The cations are present in amounts ranging from about 0.1% by weight to about 10% by weight with respect to the treated Al.sub.2 O.sub.3. The cations can be present in amounts ranging from about 0.5% to about 10% by weight with respect to the treated Al.sub.2 O.sub.3, but lower concentrations of about 0.1% to 0.5% can also be used with good effect.

In yet another embodiment of the invention, the Al.sub.2 O.sub.3 is surface treated with anions of at least one species from the group including chloride, nitrate, sulfate and hydrogen phosphate ions, preferably an Al.sub.2 O.sub.3 into whose surface anions have been introduced in the range from about 0.5% by weight to about 10% by weight with respect to the treated Al.sub.2 O.sub.3 end product.

According to the invention, an Al.sub.2 O.sub.3 can also be used which has been surface treated with at least one cation from the group including the alkali earth metal ions, iron ions and chromium ions. The cations introduced into the surface then are also present in the Al.sub.2 O.sub.3 in quantities in the range from about 0.5% by weight to about 10% by weight.

By treating the aluminum oxide with ions or doping with CO.sub.2 while it is being synthesized, the following phenomena occur:

1. The inner surface area of the Al.sub.2 O.sub.3 particles is noticeably enlarged. For example, when incorporating 5 weight percent Ca.sup.++ ions in the Al.sub.2 O.sub.3 there occurs an increase from about 80 m.sup.2 /g to about 230 m.sup.2 /g.

2. The Al.sub.2 O.sub.3 crystal lattice configuration is stabilized with the result of better sorption properties, if there were no treating or doping during synthesizing the Al.sub.2 O.sub.3, the Al.sub.2 O.sub.3 powder would be converted at the high temperatures necessary for thermal regeneration of about 500.degree. C. to 600.degree. C. to a sorption mass which would be much less effective for the sorption process; and

3. In the course of the curve showing the pore size distribution there occurs a significant peak at about 20 A; larger pores, as they can be found in undoped, pure Al.sub.2 O.sub.3 are almost nonexistent.

Treating the surface of an undoped, that is, pure Al.sub.2 O.sub.3 after its manufacture with suitable salts, salt solutions or oxide suspensions as in Example XXXIII, where the salts or oxides, respectively, are fixed in the surface of the Al.sub.2 O.sub.3 particles also produces an increase in surface area and also an additional purification effect with respect to the substances to be removed from the waste water.

The method according to the invention in which the treated or doped Al.sub.2 O.sub.3 is employed, not only avoids the drawbacks of the prior art but also permits charges containing larger quantities of the substances to be removed from the waste water. By using the treated Al.sub.2 O.sub.3 the following can be removed with good success:

(a) Dispersion dyes such as low molecular azo dyes dispersed with surface active agents, used with cellulose esters, e.g., cellulose genuine yellow G ##STR1##

(b) Reactive dyes containing cyanuric chloride: ##STR2##

(c) Cationic dyes such as methylene blue: ##STR3##

(d) Anionic dyes such as phtaleine: ##STR4## and

(e) Substantive dyes containing acid and basic groups such as Congo red: ##STR5##

In a particularly advantageous embodiment of the invention, the Al.sub.2 O.sub.3 is doped with carbon dioxide. Preferably, the Al.sub.2 O.sub.3 is doped with CO.sub.2 in amounts ranging from about 0.05% by weight to about 2.5% by weight with respect to the doped Al.sub.2 O.sub.3.

The Al.sub.2 O.sub.3 materials suitable for the method of the present invention can be easily manufactured and examples for the manufacture of doped Al.sub.2 O.sub.3 by treating with ions during synthesis of the Al.sub.2 O.sub.3 as well as for the manufacture of physicochemically surface treated Al.sub.2 O.sub.3 and Al.sub.2 O.sub.3 doped with CO.sub.2 will now be set forth, respectively, for purposes of illustration and are in no way to be construed as a limitation.

A treated Al.sub.2 O.sub.3 is synthesized by adding 5 liters of an aqueous solution containing 1 kg aluminum nitrate to 100 g calcium nitrate and bringing the pH of the mixture to 9 with an ammonium hydroxide solution. The resulting precipitate is filtered off after having aged for two hours and is rinsed with pure water. The treated hydroxide gel is then activated at temperatures between 500.degree. and 800.degree. C. for a period of 10 to 24 hours. When preparing Al.sub.2 O.sub.3 which is to comprise lower concentrations of cations in amounts of between about 0.1% and 0.5%, activation temperatures of about 500.degree. C. to 1000.degree. C. are used.

Al.sub.2 O.sub.3 is surface treated by evaporating a suspension of a commercially available aluminum oxide from a calcium nitrate solution until it is dry and the dry residue is then heat treated at 500.degree. C. for 12 to 24 hours.

Al.sub.2 O.sub.3 which is treated with other ion containing substances during synthesis is manufactured in an analogous manner.

Al.sub.2 O.sub.3 doped with CO.sub.2 is produced by slowly bringing 5 liters of an aqueous solution containing 1 kg of aluminum nitrate to a pH of 9 with an ammonium hydroxide solution. At the same time, CO.sub.2 is slowly introduced into the solution for 6 hours. The resulting hydroxide gel precipitate is then filtered out and rinsed with clean water. The hydroxide gel is then heat treated to activate it at a temperature of 500.degree. C. for a period of 12 to 24 hours.

The following examples are given below for illustrating eliminating previously only incompletely or difficultly removable substances from waste waters.

50 ml of the waste waters listed in the table below or 50 ml of a solution of the substances listed in the table below, respectively, were each mixed by shaking with 1 g of treated Al.sub.2 O.sub.3 (treated by incorporating the ions during synthesis) which contained 5% by weight Ca.sup.++ ions and their elimination effectiveness was examined. For comparison, 50 ml samples of the same waste waters and solutions were treated with Al.sub.2 O.sub.3 produced in a corresponding manner but without treatment (i.e. pure Al.sub.2 O.sub.3) and were likewise examined. The values obtained on the basis of analysis results for the respective elimination of the substances to be removed, in terms of the percent of the starting concentration, as well as in terms of the charge of the sorption agents in percent carbon or phosphorus, respectively (in the case of orthophosphate) or CrO.sub.3, respectively (in the case of chromic acid) are compiled in the table and examples below:

The two waste waters I and II (examples IV and V) are genuine effluents from a factory producing mainly anthraquinone and azo-dye-stuffs. The different compounds in these effluents were not identified.

The procedure was the same as was described for Examples IV-XII with the exception that the treated Al.sub.2 O.sub.3 (treated by incorporation during syntiesis) contained only 0.5 percent by weight Ca.sup.++.

The test followed the same procedure as described for Example IV-XII with the difference that the treated Al.sub.2 O.sub.3 [treated by incorporation during synthesis] contained 5 percent by weight Ba.sup.++.

The purification method was the same as described for Examples IV-XII with the exception that the treated Al.sub.2 O.sub.3 (treated by incorporation during synthesis) contained 5% by weight Fe.sup.+++.

The elimination of methylene blue and p-nitrophenol was effected as described for Examples IV-XII, but with treated Al.sub.2 O.sub.3 (treated by incorporation during synthesis) which contained 5% by weight Cr.sup.+++ and produced the following results.

The following examples relating to the removal of sodium dihydrogen phosphate and chromic acid from aqueous solutions illustrate the advantages of the invention even when the aluminum oxide has been treated during synthesis with ions in amounts of between 0.1% to 0.3%.

The substantially improved elimination of lignin sulfonic acid (LS) from waste waters with the aid of the process of the present invention is demonstrated by the examples shown in the table below. The procedure was the same each time as described for Examples IV-XII with the exception that instead of using an Al.sub.2 O.sub.3 which was treated furing synthesis, Al.sub.2 O.sub.3 was used which had been subsequently physiochemically surface treated with suitable substances.

In view of the advantages of the process according to the invention as described above, costs for waste water treatment can be reduced since fewer adsorbents are required to produce the desired degree of elimination and better quality of the discharged water is realized. The specific adsorbent consumption for the elimination of 1 g of organic carbon or LS in the waste waters or solutions, respectively, under examination is listed below.

The Al.sub.2 O.sub.3 employed in Examples XXXVIII to XLIII was prepared by incorporation during synthesis (doping) and the waste waters I and II (Examples XXXVIII and XXXIX) are the same as in Examples IV and V.

The desirable properties of Al.sub.2 O.sub.3 which has been doped with CO.sub.2 are illustrated by the data below relating to the removal of sodium dihydrogen phosphate from an aqueous solution.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.