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REMOTE MONITORING OF HEAVY METALS INN IN NATURAL WATER AND EFFLUENTS. Department of Chemistry, NTNU. Motivation.
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REMOTE MONITORING OF HEAVY METALS INN IN NATURAL WATER AND EFFLUENTS Department of Chemistry, NTNU
Motivation 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 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
Challenge 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.
Methods for trace analyses Atomic Absorption Spectrometry and Atomic Emission Spectrometry Inductive 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 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.
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
TBS HVS Pilot projects in Norway Løkken
Løkken pyrite ore Slag heap Løkken Verk is an old mining area in middle part of Norway
Placing of the monitoring system Raubekken, a middle large river passing through the mining area
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.
Calibration values Average peak heights for added standards during the period
Continuous measurements from January to May 2004. One measurement every 30 minutes. High [Fe] Low [Zn] A B Measurements of Zn, Fe, and Cu
Comparison with 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. Comparison of voltammetric measurements against ICP-MS
Results Voltammogram of costal seawater. DPASV, scan rate 20 mV/s, modulation pulse 75 mV, deposition time 540 s at – 1450 mV.
Avg. [Zn] = 2.3 mg/L Zinc in seawater Results from continuous measurements of iron in seawater. One measurement every 30 minutes.
Iron in seawater Results from continuous measurements of iron in seawater. One measurement every 30 minutes.
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.
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)
