ECOTERRA – Journal of Environmental Research and Protection [611834]

ECOTERRA – Journal of Environmental Research and Protection
www.ecoterra -online.ro
2015, Volume 1 2, Issue 4 95 Passive systems for neutralizing the acid waters by using
limestone
Ioan D . Brăhaița, Călin Baciu , Adina L. Lazăr, Ioan C. Pop,
Roxana M. Tru ță

Babes -Bolyai University, Faculty of Environmental Science and Engineering, Cluj -Napoca,
Romania. Correspond ing author: I. D. Brăhai ța, [anonimizat]

Abstract . In areas with current or previous mining activity, acid mine drainage (AMD) treatment
represents a challenge for the engineers and environmental specialists. Due to very low pH, acidic
waters mobi lize heavy metals found in ore and rocks, transporting them along watercourses. Our study
proposes a passive mine water treatment technology using limestone. Therefore, for the laboratory
experiment, three water samples were used: an acidified water sample (distilled water + HNO 3), a water
sample taken from Adit 714 (Rosia Montana mining area), and a water sample taken from a tailings
storage facility (TSF) (Baia Mare mining area). Two treatment systems have been proposed, in closed
and in open conditions, respectively. The results have shown a higher pH value in case of the acidified
water sample in comparison with the other two water samples. Also the pH from the tailings water
sample increased more than the pH from the Rosia Montana water sample. Comparin g the two systems,
the best results were given by the open system in case of the water sample taken from the TSF and
acidified water. The closed system was more efficient for Rosia Montana sample.
Key Words : acid mine drainage, limestone, close system, op en system .

Introduction . The acid mine drainage (AMD) treatment methods using limestone are
known because of their effectiveness in reducing acidity and decreasing metal
concentration. Another advantage of these methods is the low cost of the system
maintenance . AMD treatment methods using limestone increase pH and heavy metals
precipitation; ferrous iron oxidizes quickly at a high pH and sul phate (SO 42) can be
removed once the solubility of calcium sulphate is exceeded by adding enough calcium
(Akcil & Koldas 2006).
According to the US EPA (2001) , anoxic limestone drains are designed to generate
an increase in alkalinity of acid mine waters, without this being in contact with
atmospheric oxygen. In addition, this anoxic environment prevents iron precipita tion and
also increases the water alkalinity. In case of open limestone drains (oxidizing
environment) Fe2+ oxidize s to Fe3+. Once oxidized, this precipitate s on the surface of the
limestone in the form of iron hydroxide (FeOH 3). Ziemkiewicz et al (1996) h ave shown
that the surface of the limestone, even if it is covered by the iron hydroxide (armo uring
limestone), continues to generate alkalinity.
Silva et al (2012) proved the effectiveness of limestone in neutralizing AMD. The
sulfate concentration in wa ter decreased from 588 mg L-1 to 87 mg L-1 in only 210
minutes. The limestone samples contained 53.7% of calcite and 0.28% of magnesium ,
and the particle size was between 0.42 mm and 0.59 mm (0.77 m2 g-1 surface area) and
< 0.045 μm (2.05 m2 g-1 surface area). The pH was 6.5 and the su lphate concentration
was between 588 -1100 mg L-1.
Another experiment has been conducted in New Zeeland, on the Mangatini river.
On the first 250 meters of the river, the pH value increased from about 3 to 5 -6, but
reached values above 7 after 4 km downstream . Besides the pH increasing, a decrease in
Fe (III) concentration was also observed on the first 10 meters, and in Al concentration
after the first 100 meters. Al and the precipitated Fe were transported as solid
suspension in the area with low flow rate of the river and deposited along its path. Z n
concentration decreased with increasing pH level at 5, but Ni remained dissolved in the
solution during the experiment ( Davies et al 2011).
Experi ments conducted in Malaysia, have shown that the limestone technology
has an efficiency of 90% in heavy metals removal, such as Cd, Pb, Zn, Ni, Cu, Cr (III) ,
and the maximum potential removal was achieved at a pH of 8.5 by adding a certain
amount of lime o f 20 mL, equivalent to 56 g (Hamidi et al 200 8). Zn and Ni precipitation

ECOTERRA – Journal of Environmental Research and Protection
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2015, Volume 1 2, Issue 4 96 is closely related to the initial concentration of iron in mine waters, but it is also
influenced by the pH, alkalinity, calcium or sulph ate concentration (Miller et al 2013).
A more extensive study was conducted by Alcolea et al (2012) between 2005 –
2009, in Murcia. They used a limestone chanel , 1986 m in length , and the
parameters they have taken into consideration when analyzing the water
samples were : pH, electrical conductivity (E C), total dissolved solids (T DS), and
the heavy metal concentration s (Al, Fe, Zn, Ni, Cu, As, Cd, Pb). Low values were
recorded in case of EC, T DS, K, Mg, SO 42-, Al, Mn, Fe, Ni, Cu, Zn, As, Cd and Sb.
In Rosia Montana mining area, ore deposits have been ex ploited since pre –
Roman periods, both in the underground and open pit. The underground mining
activities have ceased in 1985. Recent mining operations, combined with historical
mining activities in the area have led to AMD generation, at the surface and al so in
the underground. Disruption from these historical activities is evident in several
places along the Rosia Valley. In addition to the disturbances on the surface, Adit
714 collects and discharges acidic seepage from old underground mines. Adit 714 is
an underground passage way that resurfaces at 714 m elevation above sea level.
Gallery 714 monthly average flows range from 18 to about 63 m3 hour-1 (5 to 17.5 L
s-1), with a recorded average flow of 51 m3 h-1 (14.2 L s-1) (Water Management and
Erosion Control Plan 2006 ).
The Central tailings storage facility is located 2 km eastward of Baia Mare
town, in Tăuții de Sus village, 6 km downstream of Baia Sprie mining area. The
tailings pond is located on the left bank of the Săsar river. The Central tailings pond
stores appro ximately 8.9 million tons of waste resulted from Flotatia Centrala
beneficiation plant in Baia Mare. The gold and base metals ore processed in Baia
Mare mining area (Suior, Cavnic, Herja and Turt) generated waste which was stored
in the Central TSF betwee n 1962 and 1976. After this period, the facility was
inactive (Raport de Securitate 2010).
The aim of our experimental approach is to highlight the potential of using
limestone in a passive system as a water treatment agent in mining areas from
Rosia Monta na and Baia Mare.

Material and Method . The limestone for the tests was c ollected from outcrops on the
left embankment of Somes Valley , upstream from Cluj -Napoca in February 2015 . In
order to remove the moisture, the limestone was dried for 24 hours at a t emperature of
105°C before the experiment . Prior to drying the limestone, it has been crushed and
screened to obtain 5, 10 and 20 mm fractions . An amount of 972 g limestone (6 -10 mm)
was used in a cylindrical 800 m L column.
For the closed system (Figure 1A ) a 800 m L cylinder, filled up with limestone was
used. For the open system (Figure 1B) an open gutter system (PVC) with a length of 100
cm and a diameter of 5 cm , and 5 degrees inclination was used. Five thresholds were
used at a distance of 20 cm for the entire amount of limestone which comes into contact
with the water during the experiment.
In the experiment, 2 litres of water from Adit 714 – Rosia Montana were used, one
sample with the same volume from the Central TSF in Baia Mare, and a control sampl e.
Blank solution had an initial pH of 2.73, a very close value to the water sample from
Rosia Montana (2.81) and Central TSF (3.01). The blank solution was made of distilled
water and nitric acid (HNO 3). The role of the blank solution was to avoid interfe rence that
could affect pH values during the experiment.
A volume of 2 L of water was filtered four times through the limestone column and
the pH value was measured at intervals of 0, 30, 60, 120 and 180 seconds with a WTW
320i multiparameter. During the f iltration process, the volume of water decreased at
1.400 L because the limestone absorbed water and a certain amount was taken as
sample for analysis.

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2015, Volume 1 2, Issue 4 97

Figure 1 . Closed system (A) and open system (B) .

Results . The graphs and tables below show the resu lts of the laboratory experiments
using limestone. The graphs were made using Statistics 8.0 software .

Closed system . Following the laboratory experiment using a closed system method, it
was observed that the limestone neutralizes synthetic water (distil led water + HNO 3)
better than natural acidic water (Table 1). It reaches a pH value of 7.949 compared to
the values of the waters from Rosia Montana (4.93) and the Central TSF (6.33) (Figures
1 and 2) .
Table 2 shows the pH values depending on the number of filtrations for the three
tested water samples (the Blank sample, Rosia Montana sample and the Central TSF
sample).

Table 1
The pH value depending on time and number of filtration for the three water samples

Filtration I II
Time
(s) Blank Rosia
Montana Central
TSF Blank Rosia
Montana Central
TSF
0 2.734 2.817 3.017 6.885 3.29 6.085
30 7.255 3.49 6.24 7.499 4.027 6.205
60 6.303 3.178 5.91 7.417 3.551 6.113
120 6.331 3.19 5.595 7.419 3.512 6.17
180 6.738 4.403 5.43 7.521 3.508 6.206
Time III IV
Time
(s) Blank Rosia
Montana Central
TSF Blank Rosia
Montana Central
TSF
0 7.58 4.165 6.24 7.75 4.581 6.308
30 7.684 4.546 6.278 7.824 4.663 6.327
60 7.65 4.557 6.218 7.818 4.653 6.235
120 7.627 4.458 6.132 7.816 4.651 6.213
180 7.721 4.51 6.316 7.949 4.935 6.333

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2015, Volume 1 2, Issue 4 98
Table 2
The pH value depending on the number of filtration for three water samples

Filtration Blank Rosia Montana Central TSF
0 2.734 2.817 3.017
1 6.885 3.29 6.085
2 7.58 4.165 6.24
3 7.75 4.581 6.308
4 7.801 4.686 6.333

0 30 60 120 180
Time (s)2345678pH Blank Sample
Rosia Montana Sample
Central tailings pond Sample
0 30 60 120 180
Time (s)3.03.54.04.55.05.56.06.57.07.58.0pH
Blank Sample
Rosia Montana Sample
Central tailings pond Sample

0 30 60 120 180
Time (s)4.04.55.05.56.06.57.07.58.0pH
Blank Sample
Rosia Montana Sample
Central tailings pond Sample
0 30 60 120 180
Time (s)4.04.55.05.56.06.57.07.58.08.5pH
Blank Sample
Rosia Montana Sample
Central tailings pond Sample

Figure 2 . The pH value depending on time after – filtration 1 (a), filtration 2 (b), filtration
3 (c), filtration 4 (d) .
0 1 2 3 4
Filtration23456789pH
Blank Sample
Rosia Montana Sample
Central tailings pond Sample

Figure 3 . The pH value depending on the number of filtrations for three water samples . a. b.
c.
d.

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2015, Volume 1 2, Issue 4 99 Open system . For the open system, the analysed parameters were pH and Eh (redox
potential). In the Table s 3-8 and Figure s 4-9, the pH values are pres ented in relation with
the oxidation -reduction potential values for each type of water used. It may be noticed
that these parameters are inversely proportional.

Blank
Table 3
The pH value and redox potential depending on the time and the number of filtrat ions

0 30 60 120 180
Time (s)23456789pH
-100-50050100150200250
Eh (mV) pH(L)
Eh(R)
0 30 60 120 180
Time (s)8.258.308.358.408.458.508.558.608.65pH
-100-98-96-94-92-90-88-86-84-82-80
Eh (mV) pH(L)
Eh(R)

0 30 60 120 180
Time (s)8.508.518.528.538.548.558.568.578.58pH
-97.5-97.0-96.5-96.0-95.5-95.0-94.5-94.0-93.5
Eh (mV) pH(L)
Eh(R)
0 30 60 120 180
Time (s)8.5168.5188.5208.5228.5248.5268.5288.5308.5328.5348.5368.5388.5408.5428.544pH
-95.6-95.4-95.2-95.0-94.8-94.6-94.4-94.2-94.0
Eh (mV) pH(L)
Eh(R)

Figure 4 . The pH and redox potential depending on the time after – filtration 1 (a),
filtration 2 (b), filtration 3 (c), filtration 4 (d) .

Table 4
The pH and redox potential depending on the number of filtrations
Filtration I II III IV
t(s) pH Eh (mV) pH Eh (mV) pH Eh (mV) pH Eh (mV)
0 2.749 196.1 8.276 -82 8.508 -93.7 8.537 -95
30 8.388 -87.4 8.598 -98.1 8.573 -96.9 8.542 -95.4
60 8.074 -71.6 8.521 -94.5 8.511 -93.8 8.518 -94.1
120 7.525 -43.5 8.494 -92.8 8.562 -96.4 8.52 -94.3
180 7.463 -40.6 8.498 -93.2 8.558 -96.2 8.521 -94.3
Filtration pH Eh
0 2.749 196.1
1 8.276 -82
2 8.508 -93.7
3 8.537 -95
4 8.67 -101.5 a. b.
c. d.

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2015, Volume 1 2, Issue 4 100 0 1 2 3 4
Filtration23456789pH
-150-100-50050100150200250
Eh (mV) pH(L)
Eh(R)

Figure 5. The pH and redox potential depending on the number of filtrations .

Rosia Montana water s ample

Table 5
The pH value and redox potential depending on the time and the number of filtrations

0 30 60 120 180
Time (s)1.92.02.12.22.32.42.5pH
210212214216218220222224226228230232234236238
Eh (mV) pH(L)
Eh(R)
0 30 60 120 180
Time (s)2.32.42.52.62.72.82.93.03.13.2pH
175180185190195200205210215220
Eh (mV) pH(L)
Eh(R)

0 30 60 120 180
Time (s)3.13.23.33.43.53.63.73.83.9pH
140145150155160165170175180
Eh (mV) pH(L)
Eh(R)
0 30 60 120 180
Time (s)3.743.763.783.803.823.843.863.883.903.923.943.963.984.004.024.04pH
132134136138140142144146148
Eh (mV) pH(L)
Eh(R)

Figure 6. The pH and redox potential depending on the time after – filtra tion 1 (a),
filtration 2 (b), filtration 3 (c), filtration 4 (d) . Filtration I II III IV
t(s) pH Eh (mV) pH Eh (mV) pH Eh (mV) pH Eh (mV)
0 1.95 236.1 2.385 216.2 3.174 176.4 3.763 146.7
30 2.471 211.6 3.157 177 3.817 143.7 3.936 137.9
60 2.289 220.8 2.973 186.2 3.702 149.5 3.911 139.2
120 2.241 223.3 2.892 190.5 3.703 149.6 3.927 138.4
180 2.29 220.8 2.988 185.7 3.808 144.3 4.012 134
a. b.
c. d.

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2015, Volume 1 2, Issue 4 101 Table 6
The pH and redox potential depending on the number of filtrations

0 1 2 3 4
Filtration1.82.02.22.42.62.83.03.23.43.63.84.04.2pH
120140160180200220240260
Eh (mV) pH(L)
Eh(R)

Figure 7. The pH and redox potential depending on the number of filtrations .

Central TSF water sample

Table 7
The pH value and redox potential depending on the time and the number of filtrations

Filtration I II III IV
t(s) pH Eh (mV) pH Eh (mV) pH Eh (mV) pH Eh (mV)
0 2.36 217.8 6.385 14.1 6.748 -4.3 6.999 -17.2
30 6.03 31.6 6.586 3.7 6.863 -10.3 7.055 -20.3
60 5.352 66.6 6.463 10.2 6.834 -8.9 7.004 -17.5
120 4.759 96.7 6.448 10.8 6.864 -10.3 7.008 -17.6
180 5.613 53.3 6.524 7.1 6.856 -10 7.032 -19

Table 8
The pH and redox potential depending on the number of filtrations

Filtrari pH Eh
0 1.95 236.1
1 2.385 216.2
2 3.174 176.4
3 3.763 146.7
4 3.942 137.7
Filtration pH Eh
0 2.36 217.8
1 6.385 14.1
2 6.748 -4.3
3 6.99 -17.2
4 7.108 -22.7

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2015, Volume 1 2, Issue 4 102 0 30 60 120 180
Time (s)2.02.53.03.54.04.55.05.56.06.5pH
20406080100120140160180200220240
Eh (mV) pH(L)
Eh(R)
0 30 60 120 180
Time (s)6.366.386.406.426.446.466.486.506.526.546.566.586.60pH
246810121416
Eh (mV) pH(L)
Eh(R)

0 30 60 120 180
Time (s)6.726.746.766.786.806.826.846.866.88pH
-11-10-9-8-7-6-5-4
Eh (mV) pH(L)
Eh(R)
0 30 60 120 180
Time (s)6.997.007.017.027.037.047.057.06pH
-20.5-20.0-19.5-19.0-18.5-18.0-17.5-17.0
Eh (mV) pH(L)
Eh(R)

Figure 8. The pH and redox potential depending on the time after – filtration 1 (a),
filtration 2 (b), filtration 3 (c), filtration 4 (d) .

0 1 2 3 4
Filtration2345678pH
-40-20020406080100120140160180200220240
Eh (mV) pH(L)
Eh(R)

Figure 9. The pH and redo x potential depending on the number of filtrations .

Table 9 presents the pH values for the open system for the three water samples: the
Blank sample, the Rosia Montana sample, and the Central TSF respectively . As previously
seen when using a closed system , the limestone efficiency is much higher for synthetic
water when compared to the other samples. This is better evidenced in Figure 10.

d c
. b a

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2015, Volume 1 2, Issue 4 103 Table 9
The pH value depending on the number of filtration for three water samples

Filtration Blank sample Rosia Montana Central TSF
0 2.749 1.95 2.36
1 8.276 2.385 6.385
2 8.508 3.174 6.748
3 8.537 3.763 6.99
4 8.67 3.942 7.108
0 1 2 3 4
Filtration123456789pH
Blank Sample
Rosia Montana Sample
Central tailings pond Sample

Figure 10. The pH value depending on the number of filtrations for three water samples .

The o pen sy stem compared to the closed system – blank sample. Starting with almost
the same pH levels, it was observed that the open system is more efficient compared
with the closed system in case of the Blank sample (Table 10 , Figure 11 ).

Table 10
The pH value depending on the number of filtration s for two systems

Filtration Closed Open
0 2.734 2.749
1 6.885 8.276
2 7.58 8.508
3 7.75 8.537
4 7.801 8.67

0 1 2 3 4
Filtration23456789pH
Closed System
Open System

Figure 11. The pH value depending on the number o f filtrations for two systems .

ECOTERRA – Journal of Environmental Research and Protection
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2015, Volume 1 2, Issue 4 104 The o pen system compared to the closed system – Rosia Montana sample. On the other
hand, the closed system was proved effective for the Rosia Montana water sample.
However it must be taken into consideration that there is o nly a small difference between
the pH levels (Table 11, Figure 1 2).

Table 11
The pH value depending on the number of filtrations for three water samples

0 1 2 3 4
Filtration1.52.02.53.03.54.04.55.0pH
Closed System
Open System

Figure 12. The pH value depending on the number of filtration for two systems .

The open system compared to the closed system – the Central TSF. For the Central
tailings pond sample, the open system is more effective compar ed to the closed system
(Table 12, Figure 1 3).

0 1 2 3 4
Filtration2345678pH
Closed System
Open System

Figure 13. The pH value depending on the number of filtration for two systems .

Filtration Closed Open
0 2.817 1.95
1 3.29 2.385
2 4.165 3.174
3 4.581 3.763
4 4.686 3.942

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2015, Volume 1 2, Issue 4 105 Table 12
The pH value depending on the number of filtrations for thre e water samples

Conclusions . Acid mine drainage is a global problem due to high costs of treating them
with active technology. Following the preliminary resul ts presented above , it can be
concluded that limestone methods are suitable for neutralizing acid mine drainage. Also,
the experiment showed that limestone is more efficient for synthetic water than natural
water. The difference in efficiency of limestone for the types of water used is given by
their chemistry.
The results have shown a higher pH value obtained by reaction with the limestone
in case of the acidified water sample , in comparison with the other two water samples.
Also the pH of the tailings wa ter sample increased more than the pH from the sample
taken from Rosia Montana mining area. Comparing the two systems, the best results
were given by the open system in case of water samples taken from the tailings pond
and acidified water. The closed syst em was more efficient for Rosia Montana water
sample.
Consequent to the preliminary results obtained in this experiment, the research
will be focused on testing different limestone types, in order to assess their efficiency in
neutralizing acid water and r emove heavy metals. We will try to better understand what
are the key parameters that control the neutralization and metals precipitation in our
specific mine water types.

Acknowledgements . The present contribution was financially supported by a grant of
the Romanian National Authority for Scientific Research, CCCDI – UEFISCDI, project 3 –
005 Tools for sustainable gold mining in EU (SUSMIN).

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Accessed: December, 2015 [in Romanian]. Filtration Closed Open
0 3.017 2.36
1 6.085 6.385
2 6.24 6.748
3 6.308 6.99
4 6.333 7.108

ECOTERRA – Journal of Environmental Research and Protection
www.ecoterra -online.ro
2015, Volume 1 2, Issue 4 106 Water Management and Erosion Control Plan , 2006 – RMGC . Available at:
http://en.rmgc.ro/rosia -montana -project/environment/water.html . Accessed:
December, 2015.

Received: 03 August 2015. Accepted: 20 December 2015. Published online: 30 December 2015.
Authors:
Ioan Dorian Brăhaita, Babes -Bolyai University, Faculty of Environmental Science and Engineering, Fântânele
str., no. 30, 400327 Cluj -Napoca, Romania, e -mail: doryan_89@yahoo.com
Călin Baciu, Babes -Bolyai University, Faculty of Environmental Science and Eng ineering, Fântânele str., no. 30,
400327 Cluj -Napoca, Romania, e -mail: calin.baciu@ubbcluj.ro
Adina -Laura Lazăr, Babes -Bolyai University, Faculty of Environmental Science and Engineering, Fântânele str.,
no. 30, 400327 Cluj -Napoca, Romania, e -mail: marika_ laura@yahoo.co.uk
Ioan Cristian Pop, Babes -Bolyai University, Faculty of Environmental Science and Engineering, Fântânele str.,
no. 30, 400327 Cluj -Napoca, Romania, e -mail: cristitzu@yahoo.com
Roxana Maria Tru ță, Babes -Bolyai University, Faculty of Environmental Science and Engineering, Fântânele str.,
no. 30, 400327 Cluj -Napoca, Romania, e -mail: truta.roxanamaria@yahoo.ro
This is an open -access article distributed under the terms of the Creative Commons Attributio n License, which
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are credited.
How to cite this article:
Brăhaita I. D., Baciu C., Lazăr A. L., Pop I. C., Truță R. M., 2015 Passive systems for neutralizing the acid
waters by using limestone . Ecoterra 12(4): 95-106.