Bildiriler Kitabı
TMMOB Metalurji ve Malzeme Mühendisleri Odası
Aysel Şen, Levent Kartal, Gülden Kartal Şireli, Servet Timur
Selective Sulphide Precipitation of Copper, Nickel and
Zinc from Industrial Wastewater
İstanbul Technical University - Türkiye
Abstract
Metal sulphide precipitation is a fast, easy and
environmentally friendly method which provides to work in
wide pH ranges and to reuse/recycle them in metal smelting
processes. In this research, the selective sulphide
precipitations (SSP) of copper, nickel and zinc from
industrial wastewater were investigated by using Na2S as
the sulphur resource. The effects of pH and free sulphide
concentration on the SSP were examined in two types of
solutions; synthetically prepared wastewater and
industrially supplied one from a gold refinery. The highest
precipitation yields of Cu, Ni, and Zn were determined in
the synthetic solution at the pH values of 2.3, 5.3, and 5.3,
respectively. The precipitation efficiencies increased with
increasing Na2S amount and reached its maximum at the
ratio of 1:1.75 (Metal: Na2S in molar ratio). The refining
wastewater, containing 10 g/L Cu2+, 0.3 g/L Ni2+ and 3 g/L
Zn2+ ions, were treated at pH 2.3 and copper was
precipitated as CuS with almost 100% of efficiency. In pH
5.3, the residual nickel and zinc ion concentration in the
solution was decreased to 4 mg/L and 6 mg/L with the 44%
and 52% of precipitation efficiencies, respectively.
1. Introduction
The treatment of wastewater arisen from mining,
electroplating, metal finishing and refining processes is a
very crucial process for the conservation and reuse of
natural resources. Therefore, the separation and recovery of
metals from different kinds of industrial effluents by using
chemical precipitation methods has been becoming more
common application [1]. It is known that industrial
treatment/recovery methods such as electrochemical based
processes are required to make technological investments
which not only cause to spend large amount of capital cost
but lead to adaptation challenges as well [2,3,4]. The
hydroxide precipitation technique, another well-known
basic application, is the one applied in most manufacturing
sectors of Turkey due to its simplicity and hence easy
practicality. However, it creates huge volume of sludge
wastes and consequently related long-term waste
management problems [5].
The metal sulphide precipitation is an alternative way,
which provides the precipitation of metal ions in a wide pH
range and also in a short duration [6, 7].
Furthermore, the obtained metal sulphide precipitates can
be reused as feeding materials to different metal smelting
processes, namely CuS, Cu2S [8]. In the precipitation
methods, very low-priced chemicals such as Na2S and
Thioacetamide utilized which exhibit high solubility
differences at low pH values [9, 10]. These advantages
render the metal sulphide precipitation method more
significant option.
In this study, the selective sulphide precipitations (SSP) of
copper, nickel and zinc were investigated from both
synthetically prepared solutions and industrial wastewater
by using Na2S as the sulphur resource. The effects of pH
and free sulphide concentration on the efficiencies of SSP
were examined in detail.
2. Experimental Procedure
For the investigation of experimental data and the
determination of reaction potentials and pH values at room
temperature, Eh - pH diagrams of Cu-S-H2O, Ni-S-H2O,
Zn-S-H2O, Cu-Ni-S-H2O, Ni-Zn-S-H2O were drawn by
using the FactSage program. In this way, the optimum pH
ranges were determined for the precipitation reactions,
which were performed in the synthetic solution containing
either a single metal ion or mixed metal ions. Afterwards,
the optimized parameters were applied to the industrially
supplied solutions from a gold refinery composing of Cu,
Ni and Zn ions. The experimental studies were categorized
into three groups:
-First two group studies were conducted in the synthetic
solutions (i.e., containing a single metal ion or mixed metal
ions) to optimize pH and Na2S concentrations in order to
reach the highest precipitation efficiencies of copper, nickel
and zinc ions.
- Based on data obtained from first two stages, in last
experiment step were carried out for the selective sulfide
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precipitation of Copper, Nickel and Zinc sulphide from
refinery waste solutions. The precipitation efficiencies of
Copper, Nickel and Zinc sulphide was also determined for
the industrial case.
Proceedings Book
precipitation were additionally analyzed to determine the
concentrations of remained metal ions.
2.1. Single metal precipitations from the single metal ion
containing synthetic solution
The first group of study was conducted in the synthetic
solutions which contain single metal ions such as Copper,
Nickel and Zinc to optimize process conditions, namely pH
and Na2S values. Also the required reaction durations to
complete precipitations were determined experimentally.
Table 1. The synthetically prepared solutions used in the
first two experimental stages
Initial solution metal
Solution
Metal ion
ion concentration
Number
(mg/L)
Cu2+
100
Ni2+
1,200
I
Zn2+
12,500
Cu2+
6,350
2+
Ni
2,935
II
2+
Zn
3,270
100
Cu2+
III
Ni2+
90
Zn2+
100
The followed procedures applied in the experimental
studies were given in Figure 1. During the preparation of
synthetic solutions Merck chemicals, namely CuSO4.5H2O,
NiSO4.6H2O, ZnSO4.7H2O and Na2S were used with
distilled water. The pH values were adjusted with 10%
NaOH and 10% H2SO4 solutions.
2.3. Wastewater solution precipitation
Figure 1. Applied procedure in the experimental studies
3. Results and Discussion
Experimental studies conducted for the determination the
reaction duration for the single copper precipitation from
the synthetically prepared solution revealed that the
precipitation rates were quite high at the beginning. The
whole metal sulphide precipitation reactions complete at
around 45 min. to 60 min. (please see Figure 2). These
results show that metal sulphide precipitation reactions
occur very fast compared to the other precipitation
reactions, such as metal hydroxide.
700
Cu2+ metal ion concentration(mg/L)
2.2. Metal precipitations from the mixed metal ions
containing synthetic solution
In the second step, the precipitations of three metal ions
(Cu, Ni, Zn) were investigated in the synthetically prepared
solutions according to the obtained results in the previous
single metal ion precipitation studies.
The synthetically prepared solutions used in the first two
experimental stages were given in Table 1 with their initial
metal ions concentrations.
635
600
500
400
300
274 272
234
176
200
163
161
100
0
0
10
20
30
40
50
60
Time (min)
The Last part of studies were carried out in the strong
acidic refinery waste solutions containing 10 g/L Cu2+, 0.3
g/L Ni2+ ve 3 g/L Zn2+ ions. After pH adjustment, Na2S
were added to the main solution to initiate the
precipitations. Afterward, the treated solutions were filtered
and the obtained precipitates were washed with distillated
water, and dried in an oven then send pieces of them for the
chemical analyses. The residual solutions after the
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Figure 2. Variation of Cu2+ ion concentration as a function
of time [25ºC, Cu2+:Na2S=1:1 in mole, pH= 2.3]
The most two significant factors, namely pH and the free
sulphide concentration in the solution, are additionally
studied. During these experiments, the pH values of
solution measured by pH electrode before the addition of
Na2S. However it is strongly recommended that pH
18 th International Metallurgy & Materials Congress
Bildiriler Kitabı
TMMOB Metalurji ve Malzeme Mühendisleri Odası
electrodes be integrated in industrial applications despite
the pH controlling problem in huge volumes. With these
pH measurement attachments in real practices, the pH
variations during the reactions can be prevented, as well as
sulphide ion species can be tracked and so potential
hazardous gas (H2S) formation could be controlled.
Likewise, the usage of mixer is needed to provide the
homogeneity.
The ideal pH values for the highest precipitation yields of
CuS, NiS and ZnS were calculated as 2-2.5, 5.3-5.5 and
5.3-5.5, respectively by FactSage.
The sulphide precipitations from the synthetically prepared
solutions was initially carried out for copper ions and
precipitated as CuS at the pH of 2 -2.5. Then nickel and
zinc ions were precipitated as NiS and ZnS respectively at
pH range of 5.3-5.5.
The effect of Na2S amount added into the solution on the
precipitation efficiencies of Cu2+, Ni2+ and Zn2+ ions were
given in Figure 7. The precipitation efficiencies increased
with Na2S addition. The maximum precipitation yields
were achieved at the ratio of 1:1.75 where the metal ion
(Me2+) molar concentration was 1 and Na2S molar
concentration was 1.75. However, the excess free sulphide
ions were consumed by other metal ions rather than
targeted ions in the wastewater solutions. It should be
emphasized that the ion selectivity in the precipitation
started to disappear when applying the more Na2S than
stoichiometric amount. This observation seen in excess
Na2S addition is also consistence with the synthetically
prepared mixed solution containing different types of metal
ions.
The pH variation experiments showed that the maximum
precipitation efficiency could be obtained by adjusting pH
(Figure 2). However, it was observed that while pH value is
arranged to reach the maximum efficiency, the selectivity
of precipitation decreases. Consequently, the highest
precipitation yields achieved for Cu2+, Ni2+ and Zn2+ ions at
the pH of 2.3, 5.3 and 5.3 respectively.
Precipitation efficiency [%]
Cu2+
Ni2+
Zn2+
100%
80%
Figure 5. XRD diffraction patterns of precipitated particles
in pH 2.3 [Me2+:Na2S 1:1.75 (mole); T=25 ºC, pH 2.3,
duration: 1 hour]
60%
40%
20%
0%
2,3
2.3
pH
5,3
5.3
Figure 3. Precipitation efficiency of Cu2+, Ni2+ and Zn2+
ions from wastewater solutions with respect to adjusted pH
values [Me2+:Na2S 1:1.75 in mole; 25 ºC, 1 hour]
The XRD analyses revealed that the obtained precipitate at
pH 2.3 was composed of CuS and Cu2S (Figure 4). At the
second part, the pH value was increase for the precipitation
of Ni and Zn, the acquired deposit at the pH of 5.3 was in
the composition of mixed Ni- and Zn- sulphur, NiS33.3Zn32.3
(please see Figure 6).
Last part of the experimental study was conducted in the
strong acidic refinery waste solutions. The pH adjustment
step is more challenging in this case due to the industrial
waste water buffer tendency.
Figure 6. XRD diffraction patterns of precipitated particles
in pH 5.3 [Me2+:Na2S 1:1.75 (mole); T=25 ºC, pH 5.3,
duration: 1 hour]
The excess Na2S additions are always consumed by other
ions in the solution with very fast reaction rates. The
18. Uluslararası Metalurji ve Malzeme Kongresi
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IMMC 2016
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UCTEA Chamber of Metallurgical & Materials Engineers
optimized pH values couldn’t be determined in the
industrial wastewater due to the co-precipitation of metal.
For this reason, in industrial wastewater applications, the
measurement of free sulphide ion concentration is required
by using a selective ion electrode.
concentration in the solution decreased to 6 mg/L and
the precipitation yield for zinc was determined as 52 %.
80
x Based on the obtained results, the metal sulphide
precipitation is an alternative way compared to other
wastewater treatment technologies in terms of its fast
reaction rates, easy practicality and reusability of
produces as a feeding material in metallurgical smelting
processes as well as requests of economical raw
materials.
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References
40
[1] H. Shi, Industrial wastewater types, amounts and
effects, “Point sources of pollution, local effects and it’s
control”, 1 Beijing, Çin.
[2] M. Ahmaruzzaman, 2011, “Industrial wastes as lowcost potential adsorbents for the treatment of wastewater
laden with heavy metals.” Adv. Colloid Interface Sci., 166,
no. 1–2, 36–59.
[3] G. Chen., 2004, Electrochemical technologies in
wastewater treatment, Seperation and Purification.
Technology, 38, no. 1, 11–41.
[4] A. Chmielewski, T. UrbaĔski, and W. Migdaá,, (1997).
“Separation technologies for metals recovery from
industrial wastes,” Hydrometallurgy, 45, 333-344.
[5] U.S.E.P.A, (2000). ‘‘Rapor’’ Wastewater Technology
Fact Sheet Chemical Precipitation.
[6] A. E. Lewis,, 2010, Review of metal sulphide
precipitation, Hydrometallurgy, 104, no. 2, 222–234.
[7] D. Bhattacharyya, A. B. Jumawan, R. B. Grieves, 1979,
Separation of Toxic Heavy Metals by Sulfide Precipitation,
Sep. Sci. Technol., 14, no. 5, 441–452.
[8] F. Fu, Q. Wang, (2011). Removal of heavy metal ions
from wastewaters: a review, Journal of Environmental
Management, 92, 407–418.
[9] A. ùen, 2015, Endüstriyel AtÕk Sularda BakÕr, Nikel,
Çinko Sülfür Selektif Çöktürme ùartlarÕnÕn Optimizasyonu,
Istanbul, Turkey.
[10] M. Gharabaghi, M. Irannajad, and Azadmehr, A. R.,
(2012). Selective Sulphide Precipitation of Heavy Metals
from Acidic Polymetallic Aqueous Solution by
Thioacetamide, Ind. Eng. Chem. Res., 51, no. 2, 954–963.
Cu2+
Precipitation efficiency [%]
Proceedings Book
Ni2+
Zn2+
100
20
0
1 ,10 0
11.25
,25
11.50
,50
1,75
1.75
Metal ions [mol]: Na2S [mol]
Figure 7. Precipitation efficiency of industrial wastewater
as a function of Na2S addition [Me2+:Na2S 1:1-1.75 in
mole; 25 ºC, 1 hour].
4. Conclusion
The selective sulphide precipitations (SSP) of copper,
nickel and zinc were investigated from both synthetically
prepared solutions and industrial wastewater by using Na2S
as the sulphur resource and the obtained results of this
research could be summarized as following:
x The single copper precipitation studies from the
synthetically prepared solution revealed that the
precipitation rates were quite high at the beginning.
Total metal sulphide precipitation reactions complete at
around 45 min.
x The highest precipitation yields achieved for Cu2+, Ni2+
and Zn2+ ions were at the pH of 2.3, 5.3 and 5.3
respectively.
x The ion selective precipitation began to disappear when
applying the more Na2S than the stoichiometric amount.
x In last part of the investigation, the SSP was applied to
the refining wastewater containing10 g/L Cu2+, 0.3 g/L
Ni2+ and 3 g/L Zn2+ ions. The copper concentration was
achieved to decrease 40 mg/L by precipitating CuS and
Cu2S at pH=2.3 with almost 100% of efficiency. At the
pH value of 5.3, the nickel ion concentration in the
solution was reduced to 4 mg/L with the 44 % of
precipitation efficiency. When the precipitation
reactions completed in at pH 5.3, the residual zinc ion
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IMMC 2016
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18 th International Metallurgy & Materials Congress