POLISH JOURNAL OF CHEMICAL TECHNOLOGY, 2005, VOL. 7, NO 2, PP. 40-45
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
adam.pawelczyk@pwr.wroc.pl
fax: 071 320 34 69
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 an 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
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processes is a big problem associated with non-ferrous metallurgy. It is obvious that such
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
2
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
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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) Value Parameter Value
SiO2 [%] 77,9 Calcination loss [%] 14,8
Al2O3 [%] 13,8 Specific density [g/cm3] 2,16
CaO [%] 3,30 Bulk density [g/cm3] 2,30
MgO [%] 1,07 Diameter of pores [m] 4·10 –10
Na2O [%] 1,70 Volume of pores [%] 14
K2O [%] 3,20 Specific surface [m2/g] 30
Fe2O3 [%] 2,06 Hardness [Mohs scale] 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.
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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.
5
Tab. 3. Values of parameters of the purified sewages to be met in the industrial scale tests.
Parameter Value Parameter Value
pH 8,3 As g/m3 0,82
Cu g/m3 0,17 NH4 g/m3 20,0
Ni g/m3 0,13 Chlorides g/m3 553
Zn g/m3 0,57 Sulfates g/m3 501
Pb g/m3 0,01 Salinity g/m3 2000
Hg g/m3 0,09
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 a
sanitary and metallurgical process sewages.
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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.
100
contents [%]
90
80
70
+
4
degree of reduction of N-NH
60
50
40
30
20
10
0
0 100 200 300 400 500 600 700 800
filtrate volume [cm 3]
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.
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50
N-NH4+ contents [mg/dm 3]
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
zeolite added.
50
N-NH4+ contents [mg/dm]
40
3
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.
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contents [%] 100
90
80
70
+
4
degree of reduction of N-NH
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.
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50
pH = 4,0
45
pH = 7,0
N-NH4+ contents [mg /dm]
40 pH = 9,0
3
35
30
25
20
15
10
5
0
4 10 20 30 40
clinoptilolite dose [g]
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
45 pH = 7,0
pH = 9,0
N-NH4+ contents [mg /dm]
40
3
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.
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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
0,9
contents of Hg [mg/dm ]
3
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.
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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.
100
degree of Hg content reduction [%]
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].
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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 Type of sewage 25.11 26.11 27.11 28.11 29.11
Industrial 0,14 0,15 0,19 0,07 0,09
Hg
Blended 0,03 0,04 0,07 0,04 0,03
mg/dm3
Purified 0 0 0,02 0,02 0,01
Industrial - 40,6 18,1 12,6 17,5
N/NH4
Blended - 35 29,9 25,5 29,3
mg/dm3
Purified - 31,3 21 24,4 24,6
Industrial 1,22 1,48 2,59 4,13 4,91
Fe
Blended 0,19 9,43 0,93 0,39 0,83
mg/dm3
Purified 0,09 0,05 0,04 0 0,02
Industrial 14,95 16,9 15,11 9,91 21,2
As
Blended 9,97 8,6 5,65 5,65 8,62
mg/dm3
Purified 0,35 3,38 1,78 2,09 5,37
Soluble Industrial 1640 2180 1410 1440 1660
matter Blended 2060 2150 1710 2090 2260
mg/dm3 Purified 2030 2100 1580 2060 1960
Industrial 55 83 71 120 23
Suspension
Blended 40 75 42 48 25
mg/dm3
Purified 3 5 1 1 2
Industrial 161 198 163 193 147
COD
Blended 175 176 155 142 162
mgO2/dm3
Purified 168 175 156 143 159
Industrial 2,43 3,08 2,06 1,97 3,23
Conductivity
Blended 2,88 2,87 2,22 2,61 2,99
mS/cm
Purified 2,7 2,87 2,08 2,65 2,56
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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
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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”
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