Selective removal of heavy metals from metal-bearing wastewater in a cascade line reactor |
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Authors: | Jelena Pavlović Srećko Stopić Bernd Friedrich Željko Kamberović |
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Institution: | (1) Faculty of Technology and Metallurgy, Department of Metallurgical Engineering, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia and Montenegro;(2) IME, Process Metallurgy and Metal Recycling, RWTH Aachen, Intzestrasse 3, 52072 Aachen, Germany |
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Abstract: | Goal, Scope and Background This paper is a part of the research work on ‘Integrated treatment of industrial wastes towards prevention of regional water
resources contamination — INTREAT’ the project. It addresses the environmental pollution problems associated with solid and
liquid waste/effluents produced by sulfide ore mining and metallurgical activities in the Copper Mining and Smelting Complex
Bor (RTB-BOR), Serbia. However, since the minimum solubility for the different metals usually found in the polluted water
occurs at different pH values and the hydroxide precipitates are amphoteric in nature, selective removal of mixed metals could
be achieved as the multiple stage precipitation. For this reason, acid mine water had to be treated in multiple stages in
a continuous precipitation system-cascade line reactor.
Materials and Methods All experiments were performed using synthetic metal-bearing effluent with chemical a composition similar to the effluent
from open pit, Copper Mining and Smelting Complex Bor (RTB-BOR). That effluent is characterized by low pH (1.78) due to the
content of sulfuric acid and heavy metals, such as Cu, Fe, Ni, Mn, Zn with concentrations of 76.680, 26.130, 0.113, 11.490,
1.020 mg/dm3, respectively. The cascade line reactor is equipped with the following components: for feeding of effluents, for injection
of the precipitation agent, for pH measurements and control, and for removal of the process gases. The precipitation agent
was 1M NaOH. In each of the three reactors, a changing of pH and temperature was observed. In order to verify efficiency of
heavy metals removal, chemical analyses of samples taken at different pH was done using AES-ICP.
Results Consumption of NaOH in reactors was 370 cm3, 40 cm3 and 80 cm3, respectively. Total time of the experiment was 4 h including feeding of the first reactor. The time necessary to achieve
the defined pH value was 25 min for the first reactor and 13 min for both second and third reactors. Taking into account the
complete process in the cascade line reactor, the difference between maximum and minimum temperature was as low as 6°C. The
quantity of solid residue in reactors respectively was 0.62 g, 2.05 g and 3.91 g. In the case of copper, minimum achieved
concentration was 0.62 mg/dm3 at pH = 10.4. At pH = 4.50 content of iron has rapidly decreased to < 0.1 mg/dm3 and maintained constant at all higher pH values. That means that precipitation has already ended at pH=4.5 and maximum efficiency
of iron removal was 99.53%. The concentration of manganese was minimum at pH value of 11.0. Minimum obtained concentration
of Zn was 2.18 mg/dm3 at a pH value of 11. If pH value is higher than 11, Zn can be re-dissolved. The maximum efficiency of Ni removal reached
76.30% at a pH value of 10.4.
Discussion Obtained results show that efficiency of copper, iron and manganese removal is very satisfactory (higher than 90%). The obtained
efficiency of Zn and Ni removal is lower (72.30% and 76.31%, respectively). The treated effluent met discharge water standard
according to The Council Directive 76/464/EEC on pollution caused by certain dangerous substances into the aquatic environment
of the Community. Maximum changing of temperature during the whole process was 6°C.
Conclusion This technology, which was based on inducing chemical precipitation of heavy metals is viable for selective removal of heavy
metals from metal-bearing effluents in three reactor systems in a cascade line.
Recommendations and Perspectives The worldwide increasing concern for the environment and guidelines regarding effluent discharge make their treatment necessary
for safe discharge in water receivers. In the case where the effluents contain valuable metals, there is also an additional
economic interest to recover these metals and to recycle them as secondary raw materials in different production routes.
ESS-Submission Editor: PhD Hailong Wang, hailong.wang@ensisjv.com |
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Keywords: | Cascade line reactor chemical precipitation effluent metal-bearing heavy metals removal selective precipitation |
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