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REMOTE MONITORING OF HEAVY METALS INN IN NATURAL WATER AND EFFLUENTS
Department of Chemistry, NTNU
During the last years an increasing focus has been turned on the quality of water and environmental surveillance. This has also been founded in international agreements and conferences like The Johannesburg Summit and EU Water Framework Directive.
Motivation
Motivation
An extensive activity and interest for the safety and protection of water resources is shown in general from WFD, UN and WHO
Motivation
Additionally the importance of the water security is also shown through the large number of different world-wide organizations which focus on water quality and safety, e.g. GARNET, GESI, GEF, GREEN, GWP, Global Water, IWRN, IAEH, IAWQ, ICWQ, IGRAC, IRC, IWMI, IWRA, WEF, WFP, WQA, WRI etc.
Motivation
There is a strong linkage between the state of environment of freshwater resources in a country and its capacity for poverty eradication and development.
Motivation
Even though water is probably the most important resource and commodity we have, pollution of important water recourses is still a problem. In future it should be focus even more to protect and monitor the water quality
Making low-cost instruments with high sensitivity and reproducibility, which can operate automatically for long time of periods out in the field with little maintenance.
Challenge
Atomic Absorption Spectrometry and Atomic Emission SpectrometryInductive Couple Plasma – Mass Spectroscopy Electrochemical techniques
Ion Chromatography (with a proper detector) Neutron Activation Analysis UV/VIS Spectrometry Classical analytical methods
Methods for trace analyses
Methods for trace analyses
A great number of analytical methods are able for measuring water quality and water pollution. However, all these methods have to be used in laboratories and only a few parameters (e.g. pH, conductivity, nitrate, phosphate) can be monitored out in the field.
This fact represents a large problem in environmental monitoring in general.
Methods for trace analyses
For instance, it is not possible to detect short time pollutions and accidental spills of environmental poisons, and it often takes a long time from sampling to the answer of the analysis is finish.
Methods for trace analyses
A better way to perform environmental monitoring is to combine continuous monitoring in the filed by use of automatic equipment together with manually sampling and analyses in laboratories.
Then a more complete monitoring program can be established, which both can detect short time pollutions, but also the different methods can verify each other.
Methods for trace analyses
Through several years of research within this field, automatic equipment for continuous monitoring of heavy metals and trace metals have now been developed in our research group at NTNU. The scientific interest is large and the commercial potential is worldwide
Methods for trace analyses
Electrochemical techniques offers an interesting group of methods for remote monitoring of heavy metals.
Electrochemical techniques
Good detection limit, possible for use in natural water, moderate price, fast, and simultaneously detection of several metals
Well known and accepted theory
A problem is to find a suitable electrode materials for use in field (avoid liquid mercury)
Properties for electrode materials
High overvoltage towards HER
Wide working window
Non toxic
Slow passivitation
Possible to make nano-dimension
Resistant against fouling of biological material
Low price, easy to produce and cast
Easy to operate in field equipment
Sensor materials
Metal electrodes
Mercury, Gold, Silver, Iridium, Palladium, Platinum
Carbon substrate
Diamond (e.g. Boron doped), Glassy carbon, Graphite (heat treated electrode graphite)
Film electrodes / Meniscus
Bismuth film, Mercury film, Hg-Ag, Hg-Au…
Mixed electrodes
Alloying a metal with high hydrogen overvoltage with a metal with low hydrogen overvoltage.
A significant increase in the hydrogen overvoltage is observed for the alloyed metal, even for small additions.
Silver electrodes added bismuth
Silver electrodes contaminated with 2, 4, 6, 10, 15 % (w/w) bismuth. DPSAV in 0.05 M NH4Ac solution (pH 4,6).
Solid dental amalgam electrodes
Silver electrodes containing 2, 40, and 51 % (w/w) mercury. CV in 0.01 M HNO3 solution, scan rate 100 mV/s.
-2000
-1500
-1000
-500
0
500
-1.60 -1.40 -1.20 -1.00 -0.80 -0.60 -0.40 -0.20 0.00 0.20 0.40
2%Hg
40%Hg
51%Hg
Voltammetric apparatus for use in field
Voltammetric apparatus for use in field, small scale tests
Field Apparatus
Field Apparatus
Sampling
Avoiding contamination
Accuracy in pumping installation
Analyses
Cleaning of the electrodes and the cell system
Field instrument, advantage
Low risk for contamination or changes in the
samples due to time
Speciation studies possible in the field
Possibilities to detect short time pollution and
react immediately
Unique data for biological and / or geological
studies
Polluted river water, Løkken Verk, Norway
Løkken pyrite ore
Løkken Verk is an old mining area in middle part of Norway
Slag heap
Løkken pyrite ore, composition
Placing of the monitoring system
Raubekken, a middle large river passing through the mining area
Instrument mounted in the field.
Results
Typical voltammetric scan of water sample from the river Raubekken added NH4Cl (0.05 M) . DPASV, scan rate 20 mV/s, modulation pulse 75 mV, deposition time 30 s at – 1450 mV.
Calibration
Calibration by standard addition was performed once or twice a month.
Pb
R2 = 0.9998
0
10
20
30
0 200 400 600 800Conc (g/L)
I (
A)
Cu
R2 = 0.9516
0
10
20
30
40
50
60
0 200 400 600 800Conc (g/L)
I (
A)
Fe
R2 = 0.999
80
100
120
140
160
1000 1200 1400 1600 1800Conc (g/L)
I (
A)
Zn
R2 = 0.9969
20
30
40
50
60
500 700 900 1100 1300 1500Conc (g/L)
I (
A)
Calibration values
Average peak heights for added standards during the period
Zn Cu FeStd.s Conc 250 mg/L 250 mg/L 220 mg/L
I (mA) 21,7 16,0 23,1
Std. Dev 1,3 1,5 1,2
Rel. Std. Dev 6,0 9,6 5,2
Cu
0.0
500.0
1000.0
1500.0
2000.0
2500.0
3000.0
14.1.04 3.2.04 23.2.04 14.3.04 3.4.04 23.4.04 13.5.04
Fe
0.0
500.0
1000.0
1500.0
2000.0
2500.0
3000.0
14.1.04 3.2.04 23.2.04 14.3.04 3.4.04 23.4.04 13.5.04
Continuous measurements from January to May 2004.One measurement every 30 minutes.
Measurements of Zn, Fe, and CuZn
0
500
1000
1500
2000
2500
3000
3500
14.1. 3.2. 23.2. 14.3. 3.4. 23.4. 13.5.Date
Co
nc
(g
/L)
0
2
4
6
8
14.1. 3.2. 23.2. 14.3. 3.4. 23.4.
Date
Tem
p (
C)
-30
-20
-10
0
10
20
4.1. 24.1. 13.2. 4.3. 24.3. 13.4. 3.5.
Date
Tem
p (
C)
A
B
High [Fe]
Low [Zn]
Comparison with ICP-MS
Comparison of voltammetric measurements against ICP-MS
Continuous analyses of zinc, iron, and copper for a time period of four months (middle of January to middle of May, 2004), in polluted river water at Løkken Verk. Sampling performed every 30 minutes, DPASV with 30 s plating time, scan rate was 20 mV/s, and modulation pulse 75 mV. NH4Cl (0.015 M) added to
the sample.
Seawater and brackish water
Costal seawater, Trondheim
Results
Voltammogram of costal seawater. DPASV, scan rate 20 mV/s, modulation pulse 75 mV, deposition time 540 s at – 1450 mV.
Zinc in seawater
Results from continuous measurements of iron in seawater. One measurement every 30 minutes.
Zn conc in costal seawater
0
5
10
15
20
25
30
35
40
45
50
14. jan. 3. feb. 23. feb. 14. mar. 3. apr. 23. apr. 13. mai.
Date
Co
nc
(g
/L)
Avg. [Zn] = 2.3 g/LAvg. [Zn] = 2.3 g/L
Iron in seawater
Results from continuous measurements of iron in seawater. One measurement every 30 minutes.
Fe
0
0.2
0.4
0.6
0.8
1
1.2
1.4
22.1. 22.1. 23.1. 23.1. 24.1. 24.1. 25.1. 25.1. 26.1.
Date
Co
nc
(g
/L)
Falconbridge, Nickel refinery
Waste Incineration Plant
Monitoring of heavy metals in purified scrubbing water at Heimdal varmesentral, Trondheim, Norway.
Waste Incineration Plant
Detection of zinc, cadmium and lead in scrubbing wastewater added NH4Cl (to 0.05M). DPASV, 120 s dep. time at -1300mV, scan rate 15 mV s-1, mod. pulse 50 mV.
Mercury in wastewater, HVS
Concentrations plotted against time
Waste Incineration Plant
Continuous monitoring of mercury in purified scrubbing water at Heimdal incineration plant Trondheim, Norway. DPASV by use of Au-Bi (4%) electrode, deposition time 300 s at 100 mV, scan rate 15 mV/s, modulation pulse 50 mV.
0
5
10
15
20
25
08-aug-03 18-aug-03 28-aug-03 07-sep-03 17-sep-03 27-sep-03 07-okt-03 17-okt-03
Date
Conc
(
g/L)
Boliden, Odda. Zinc refinery, Norway
Field instrument, maintenance
Field instrument, maintenance
Refill of supporting electrolyte solution
Polish of electrode
Cleaning cell and filter systems
Calibration
Maintenance of titanium pump
Continuous measurements have to frequently be
verified by performing manual sampling and detection
with other analytical techniques (e.g. once or twice a
months)
Collaboration with Fugro Oceanor
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