Key words

Pawełczyk A. - Application of Zeolites ...

APPLICATION OF ZEOLITES IN PROCESSES OF POLLUTANTS REMOVAL FROM LIQUID WASTES ADAM PAWEŁCZYK Institute of Inorganic Technology and Mineral Fertilizers, Wrocław University of Technology Wybrzeże Wyspiańskiego 27 50-370 Wroclaw [email protected] Key words: environment protection, purification, sewage, zeolite

ABSTRACT Waste waters dumped into ground or surface waters have to meet requirements of standards determined by environmental law regulations. Sewages from different technological processes, particularly from copper metallurgy do not meet these standards and have to be treated using physical and chemical processes. The paper presents results of laboratory and industry scale tests of copper works waste waters treatment with the use of natural zeolites. The investigations carried out were focused particularly on ammonium ions present in the waste waters but also heavy metals were analyzed in the examined samples. The scope of the tests was to compare effects of pollutants removal obtained by traditional methods and that with zeolite, not used yet in such a big scale. Preliminary laboratory research carried out with the real industrial sewages proved that zeolites could be effective agents in the process of reducing concentration of ammonium ions and heavy metals in effluents from metallurgical works.

INTRODUCTION Occurrence of nitrogen compounds, heavy metals and other inorganic substances, which are harmful or toxic and pass to waste waters during flotation of ores and manufacture processes is a big problem associated with non-ferrous metallurgy. It is obvious that such

40

Polish Journal of Chemical Technology, 2005, Vol. 7, No. 2

wastes require special and expensive storing or complicated purification systems for reducing concentration of the harmful pollutants to permissible standards. The most troublesome components in the waste waters are ammonium and other ions containing As, Cr, Pb, Cd, Hg, N, P etc. Recent standards for these pollutants in waste waters disposed to surface waters were settled in [1] (table. 1). Such concentration levels are very difficult to maintain in case of metallurgical waste waters. Tab. 1. Allowable values of contaminants for treated waste waters from non-ferrous metallurgy, according to the Polish Ministry of Environment [1]. Parameter

Unit

Average value

Particularly harmful substances 24 hours’ One month’s Hg

mg Hg/dm3

0,1

0,05

Cd

mg Cd/dm3

0,4

0,2

Other contaminants

Highest allowable value

As

mg As/dm3

0,1

Cr

mg Cr/dm3

0,5

Ni

mg Ni/dm3

0,5

Chlorides

mg Cl/dm3

1000

N/NH4

mg NNH4/dm3

30

N tot

mg N/dm3

30

COD

mg O2/dm3

125

BOD

mg O2/dm3

25

Suspensions

mg/dm3

35

pH

-

6,5 – 8,5

41


Different technologies are used for the pollutants removal from the sewages. In case of the heavy metals their precipitation in form of insoluble salts and hydroxides with sodium sulfides, calcium hydroxide or other agents is mostly used. Ammonium and nitrate nitrogen can be eliminated using biological treatment of the sewages or stripping methods. Phosphorus is usually removed from sewages also by biological methods or chemical precipitation. These methods have good points but also shortcomings can be mentioned such as accidental emission of hydrogen sulfide, high cost of chemicals, problems with controlling the processes etc. New trends in waste water treatment focusing on development of more effective and economic methods indicate zeolites as materials, which can replace many chemicals in such technologies.

MATERIALS AND METHODS Investigations on pollutants removal from liquid wastes have been carried out using model sewage and liquid wastes from the copper industry. The tests with zeolites were conducted on both laboratory and industrial scales. The applied zeolite came from Carpathian deposits located in Ukraine [2,3]. Generally the chemical formula of this naturally occurring mineral cannot be expressed precisely, however the approximate empirical simplified formula is (Na,K)6(Al6Si30O72) · nH2O, and its chemical composition is given in tab. 2. When it comes to phase composition clinoptilolite (ca. 70 %), quartz (ca. 10 %) and mica (ca. 5 %) are the basic components of the zeolite. The others are plagioclase and different clayey minerals. Permanent ion and compounds binding capabilities result from internal surfaces, capillaries and pores having ion-exchange properties. Moreover, they are

42


characterized by structure of the so called molecular sieve that permits only specific ions and compounds with diameters not bigger than those of the sieve [5]. Tab. 2. Characteristics of the zeolite used in the investigations [4-6]. Component (as oxides) SiO2 [%] Al2O3 [%] CaO [%] MgO [%] Na2O [%] K2O [%] Fe2O3 [%]

Value 77,9 13,8 3,30 1,07 1,70 3,20 2,06

Parameter Calcination loss [%] Specific density [g/cm3] Bulk density [g/cm3] Diameter of pores [m] Volume of pores [%] Specific surface [m2/g] Hardness [Mohs scale]

Value 14,8 2,16 2,30 4·10 –10 14 30 3,5 - 4

Such properties make the zeolite suitable not only for sewage purification but also for other numerous purposes [7-16]. The zeolite applied both in laboratory and industrial tests was used in a form offered by a commercial deliverer without any additional treatment. Laboratory scale tests The laboratory investigations have been carried out to determine effectiveness of the proposed purification method and optimal doses of the zeolite assuring satisfactory removal of ammonium ions and heavy metals from the sewage. During the laboratory investigations specially prepared model sewage and real industrial sewage were used. Zeolite in different quantities was added to specific samples of the sewages, which were then analyzed for heavy metals and ammonium nitrogen. Heavy metals concentration in the samples was determined by the ICP spectrometry while NH4+ ions using ion selective electrode. In the first stage the laboratory investigations were carried out on clinoptilolite beds of 50 cm3 volume placed in organic glass columns. The model and industrial sewages with the concentration of ammonium nitrogen 50 mg/dm3 and 48,9 mg NH4+/dm3, respectively were fed onto the bed by means of a laboratory pump. The flow direction was from the top to the bottom.

43


Volume of the model and industrial sewages fed to the columns was 800 cm3. The resulting effluents were collected in measuring cylinders in portions of 50 cm3. Subsequently ammonium nitrogen was analyzed in the effluents. In further stage of the research the effect of different zeolite doses introduced directly into the sewage on the reduction of ammonium ions concentration was determined. Different amounts of the zeolite corresponding to 2, 5, 10, 15 and 20 % by weight in relation to the sewage were introduced to conical flasks with the volume of 300 cm3. The flasks were then intensively shaken for the period of 25 minutes and left for 60 minutes for decantation. After shaking the suspension was fixed by adding 0,2 cm3 of the concentrated sulfuric acid. Then the solution was analyzed for ammonium nitrogen. Effect of the sewage pH value on the ion exchange process was investigated for similar conditions as in the case of the above described experiments. The applied pH values controlled by the addition of hydrochloric acid or sodium hydroxide were 4,0, 7,0 and 9,0. Effectiveness of ion exchange process was expressed as the mass ratio of the removed ammonium nitrogen to its initial load in the sewage.

Commercial scale tests Commercial scale tests were carried out at the sewage treatment plant processing industrial waste waters collected from local copper works. The treatment plant consists of two main technological steps: physical and chemical. The physical treatment removes suspension of fine solids carried by both industrial and sanitary sewage streams flowing in through the main collector as well as particles originated after chemical processing of the sewage. Chemical treatment consists in precipitation of heavy metal ions and other pollutants in the form of hydroxides, sulfides and floccules after adding milk of lime, sodium sulfide and flocculating agents [17]. The required parameters of the purified sewage are shown in tab. 3. 44


Tab. 3. Values of parameters of the purified sewages to be met in the industrial scale tests. Parameter pH Cu g/m3 Ni g/m3 Zn g/m3 Pb g/m3 Hg g/m3

Value 8,3 0,17 0,13 0,57 0,01 0,09

Parameter As g/m3 NH4 g/m3 Chlorides g/m3 Sulfates g/m3 Salinity g/m3

Value 0,82 20,0 553 501 2000

Industrial waste waters are blended with sanitary sewage producing the so called blended waste waters subjected then to purification processes. A simplified diagram of the waste water flow and sites of zeolite proportioning during the test are shown in fig. 1. Zeolite

Fig. 1. Simplified waste water flow in the sewage treatment plant and sites of zeolite proportioning was proportioned by weight in two portions. The first one was introduced at the beginning of the treatment plant to a storage reservoir where the sewage contained high charge of pollutants. The agents were then agitated with compressed air. The second portion was introduced in other site, to the sewage stream of high turbulence resulting after blending sanitary and metallurgical process sewages.

45


RESULTS A significant reduction of the nitrogen concentration was observed in both model and industrial sewages during the first stage of ion exchange process realized on the zeolite bed (fig. 2). At the beginning of the process, reduction ratio of the ammonium ions concentration was 80 – 90 % for the model sewage and 70 – 85 % for the industrial sewage.

degree of reduction of N-NH

4+ contents [%]

100 90 80 70

60 50 40 30 20 10 0

0

100

200

300

400

500

600

700

800

filtrate volume [cm3]

Fig. 2. Dependence of the reduction degree of the ammonium nitrogen contents in model and industrial sewages on the amount of the sewage passing the zeolite bed ( - model sewage,  - industrial sewage).

At the point corresponding to the sewage-to-zeolite mass ratio equaled to 4:1 a rapid decrease of the ion exchange effectiveness was observed. Almost total depletion of the ion exchange capacity occurred after passing 500 cm3 of the industrial sewage through the zeolite layer. In the case of model sewage the exchange capacity was about 20 % higher than that for the industrial one, mainly due to the lack of other inorganic and organic impurities in the model sewage. The impurities present in the real sewage strongly interfere process of ammonium ions absorption.

46


N-NH4+ contents [mg/dm3]

50

40

30

20

10

0 0

4

10

20

30

40

clinoptilolite dose [g]

Fig. 3. Changes of the ammonium nitrogen contents in the model sewage as an effect of the

N-NH4+ contents [mg/dm3]

zeolite added. 50

40

30

20

10

0 0

4

10

20

30

40

clinoptilolite dose [g] Fig. 4. Changes of the ammonium nitrogen contents in the industrial sewage as an effect of the zeolite added.

47


degree of reduction of NNH4+ contents [%]

100 90 80 70 60 50

40 30 20 10

0

0

5

10

15

20

25

30

35

40

45

clinoptilolite dose [g]

Fig. 5. Dependence of the reduction ratio of the ammonium nitrogen contents in model and industrial sewages on the amount of added zeolite (  - model sewage,  - model sewage).

As one can observe in fig. 3 and 4 the contents of ammonium nitrogen in the sewage decreases with the amount of added zeolite while the effect proceeds faster for the model sewage. The explanation of this phenomenon can be similar to the above described and related to the ion exchange process realized with the use of zeolite beds. Relation between the degree of nitrogen content reduction in both sewages and the amount of added zeolite is shown in fig. 5. With the increase of added zeolite the effectiveness of purification process increases constantly. After adding 2% (4 g) of the zeolite the effectiveness of nitrogen removal for the model and industrial sewage reaches 33,6% and 27,4 %, respectively. The doses of the zeolite exceeding 10% in relation to the sewage did not result in further reduction of the nitrogen contents at the used initial concentrations of ammonium nitrogen. Maximal concentration reduction degree achieved for the zeolite dose of 20% (40 g) for the both sewages was 90,4 and 78,7 %, respectively.

48


50 pH = 4,0

N-NH4+ contents [mg /dm3]

45

pH = 7,0

40

pH = 9,0

35 30 25 20

15 10 5 0 4

10

20 clinoptilolite dose [g]

30

40

Fig. 6. Changes of the ammonium nitrogen contents in the model sewage as a result of the amount of added zeolite at different pH. 50 pH = 4,0 pH = 7,0 pH = 9,0

N-NH4+ contents [mg /dm3]

45 40 35 30 25 20

15 10 5 0 4

10

20

30

40

clinoptilolite dose [g] Fig. 7. Changes of the ammonium nitrogen contents in the industrial sewage as a result of the amount of added zeolite at different pH.

49


The investigations on the effect of sewage pH value on the ion exchange process showed that the most effective removal of ammonium ions from sewage took place at pH=7,0 (fig. 6 and 7). In the case of alkaline sewage the concentration of nitrogen changes insignificantly when growing doses of clinoptilolite are added. At the pH reaction 9,0 considerable decline of the nitrogen removal effectiveness was noticed. It was 50% less efficient than that carried out at pH=7,0. This can be explained by transformation of the ammonium ions into the gaseous ammonia that occurs when pH value exceeds 7,0. This form of nitrogen does not possess electric charge so it cannot undergo the ion exchange process. Decrease of the sewage reaction, that is the increase of hydrogen ions concentration also reflected in a decrease of ammonium nitrogen removal as the H + ions competed with NH4+ in the ion exchange process. Thus, the zeolite absorbed the hydrogen ions more readily from the solution. Laboratory tests on heavy metals removal from waste waters were done with a model sewage prepared from the aqueous solution of heavy metal chlorides (Hg, Cd, Cr) with the concentration 1mg/dm3 of each metal [17]. Additionally sanitary and blended sewage were investigated. Effect of the amount of zeolite added to the model sewage on the mercury concentration is shown in fig. 8.

1,0

3

contents of Hg [mg/dm ]

0,9

0,8

0,7

0,6

0,5

0,4 0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

3

dose of zeolite [g/dm ]

Fig. 8. Changes of mercury contents in model sewage as an effect of the amount of the added zeolite.

50


In fig. 9. dependency of the reduction of Hg concentration in sanitary and blended sewage on the amount of the added zeolite is presented. The laboratory investigations show that using zeolites for heavy metals removal from the sewage is much more effective than in the case of ammonium nitrogen. Even very small doses of about 1% of zeolite in relation to the sewage reflect in a rapid decrease of heavy metals content in both model and in industrial sewages.

degree of Hg content reduction [%]

100 90 80 70 60 50 40 30 20 0,0

0,5

1,0

1,5

2,0

3

dose of zeolite [g/dm ]

Fig. 9. Degree of mercury contents reduction in sanitary and blended sewages as an effect of the dose of the added zeolite (- sanitary sewage,  - blended sewage).

The industrial test realized on the basis of previously determined laboratory assumptions lasted 5 subsequent days. During the normal operation, sodium sulfide is used at the industrial plant for precipitating heavy metals ions, particularly for mercury removal. When the test was carried out, proportioning of sodium sulfide had been stopped and zeolite started instead. Samples of the industrial, sanitary and purified sewages were continuously collected and analyzed for heavy metals, ammonium nitrogen, chemical oxygen demand, suspension concentration, soluble matter content and pH value [18].

51


Results of analyses of pollutants content in the industrial, blended (industrial + sanitary) and treated sewages during the industrial scale tests are shown in table 4. In the first period, after stopping sodium sulfide metering into the sewage a slight increase of mercury ions content in the treated sewage was observed. After the zeolite introduction had started concentration of heavy metals begun to drop to a low level, which was maintained until zeolite proportioning was held in the 96-th hour of the test. Rapid increase of heavy metals concentration in the blended and in treated sewages was noticed again in the third period of the test, when neither zeolite nor sodium sulfide was added to the system. Tab. 4. Changes of the selected parameters of sewages during the industrial scale test. Parameter Hg mg/dm3 N/NH4 mg/dm3 Fe mg/dm3 As mg/dm3 Soluble matter mg/dm3 Suspension mg/dm3 COD mgO2/dm3 Conductivity mS/cm

Type of sewage Industrial Blended Purified Industrial Blended Purified Industrial Blended Purified Industrial Blended Purified Industrial Blended Purified Industrial Blended Purified Industrial Blended Purified Industrial Blended Purified

25.11 0,14 0,03 0 1,22 0,19 0,09 14,95 9,97 0,35 1640 2060 2030 55 40 3 161 175 168 2,43 2,88 2,7

26.11 0,15 0,04 0 40,6 35 31,3 1,48 9,43 0,05 16,9 8,6 3,38 2180 2150 2100 83 75 5 198 176 175 3,08 2,87 2,87

52

27.11 0,19 0,07 0,02 18,1 29,9 21 2,59 0,93 0,04 15,11 5,65 1,78 1410 1710 1580 71 42 1 163 155 156 2,06 2,22 2,08

28.11 0,07 0,04 0,02 12,6 25,5 24,4 4,13 0,39 0 9,91 5,65 2,09 1440 2090 2060 120 48 1 193 142 143 1,97 2,61 2,65

29.11 0,09 0,03 0,01 17,5 29,3 24,6 4,91 0,83 0,02 21,2 8,62 5,37 1660 2260 1960 23 25 2 147 162 159 3,23 2,99 2,56


CONCLUSIONS 1. Laboratory investigations proved that the clinoptilolite zeolite could be a good agent for metallurgical sewage treatment. 2. The effectiveness of the pollutants removal in the industrial tests was lower than that obtained during laboratory investigations. 3. Zeolite examined in the industrial scale tests can be successfully used for removal of particular heavy metals and other pollutants from the sewages. This concerns the following elements: Cu, Zn, Sb, Ag, Ce, Sn, Fe. Concentration of P, Re, Rh, W and some other pollutants was not reduced significantly after sewage treatment process. 4. In spite of exclusion of sodium sulfide proportioning commonly used for heavy metals precipitation, the permissible standards of heavy metals contents in sewage obtained after treatment with zeolite were not exceeded during the commercial scale tests. 5. Observations made during preliminary laboratory research and industrial scale tests proved that it is possible to reduce the zeolite consumption by 50 – 80 % but this would involve additional optimization investigations and changes in equipment as well as in some technological settings of the treatment plant. 6. Laboratory investigations on ammonium nitrogen removal from model and industrial sewages showed that zeolite is a good agent for the sewage treatment. On the other hand no significant effect of the zeolite used on content of ammonium ions was observed during the commercial scale tests. It could be because of a very high concentration of inorganic and organic pollutants in the treated sewage originating in the metallurgical processes and in sanitary sewage system and different hydrodynamic conditions existing in the big scale system. Thus, a removal of nitrogen compounds should be considered at source, not at the end of the metallurgical process. The second solution of the problem

53


could be a separate treatment of sanitary sewages, before introducing them to the industrial sewage. ACKNOWLEDGEMENTS

This work was supported by the Polish Scientific Committee in the framework of a grant no 4T09B 027 25 entitled “Application of natural zeolites for manufacture of slow release fertilizers” REFERENCES (1) Decree of Ministry of Environment from 29. Nov.2002, Dz. U. 02.212.1799 from 16 Dec. 2002 r. (2) Vasylechko V., Lebedynets L., Gryshchouk G., Leboda Skubiszewska-Zieba J., Ivestigations of Usefulness of Transcarpathian Zeolites in Trace Analysis of Waters Application of Mordenite for the Preconcentration of Trace Amounts of Copper and Cadmium, Chemia Analityczna, Volume 44, No 6 (November – December), 1999 (3) Kallo D., Sherry H., Occurrence, Properties, and Utilization of Natural Zeolites, Akademiai Kiado, Budapest, 858 pp. 1988 (4) Armbruster T., Clinoptilolite-heulandite: applications and basic research, Elsvier Science B.V., 2001 (5) Cool W.M., Willard J.M., Hayhorst D.T., Prepriuts of International Conference on Molecular Sieves, University of Chicago, 1977. (6) Mumpton F., Uses of natural zeolites in agriculture and industry, Proc. Natl. Acad. Sci. USA, vol. 96, pp. 3463-3470, March 1999 (7) Munszpton F.A., Natural Zeolites, Properties, Use, Pergamon Press, 1978. (8) Kiss J., Process for preparing an agricultural fertilizer from sewage, Pat. USA No 4772307, 20.09.1988 (9) Chang H., Method of preparing a slow release fertilizer, Pat. USA No 5695542, 9/12/1997 (10) Goto I., Horticultural medium consisting essentially of natural zeolite particles, Pat. USA No 5106405, 21/04/1992 (11) Ming D., Golden D., Slow-release fertilizer, Pat. USA No 5433766, 27/02/2001 (12) Anderson D., Coated particles, methods of making and using, Pat. USA No 6482517, 19/11/2002 (13) Lefroy R., David B., Fertilizer coating process, Pat. USA No 5766302, 16/06/1998 (14) Sower L., Methods for producing fertilizers and feed supplements from agricultural and industrial wastes, Pat. USA No 6409788, 25/06/2002

54


(15) Waldman D., Polyansky E., Controlled release chemicals, Pat. USA No 6284278, 4/09/2001 (16) Princz P.,“Improvement of the biological degradability of wastewaters using activated zeolites”, NATO SfP Project SfP-972494, July 1999 (17) A. Pawełczyk, H. Górecki, J. Hoffmann, H. Górecka, A. Chojnacki, Commercial scale test on mercury removal from industrial waste waters with the use of natural zeolite, Chemistry for Agriculture., Ed. By H. Górecki, Z. Dobrzański & P. Kafarski, CZECH-POL TRADE, Prague-Bruxelles-Stockholm, vol.4, 404, 2003 (18) Górecki H., Pawełczyk A., Hoffmann J., Górecka H., Utilization of mercury from sewages at a commercial waste waters treatment plant. Report No D – 169/2002 from commercial scale tests, Wroclaw 2003,

55