Mercury in plants

In an official method [33] for the determination of mercury in plant material, the sample is digested at 150 °C with 70% m/v concentrated nitric acid in a pressure vessel. Potassium permanganate is added to prevent loss of mercury and remove nitrogen oxides, and the concentration of mercury was determined either by flameless AAS at 253 nm or by flameless atomic fluorescence. 

Wang and Wai [43] showed that bioaccumulated mercury in plants can be recovered using a methanol-modified supercritical-fluid carbon dioxide containing a dichromate liquid. 

Shaw BP, Sahu A, Panigrahy AK. 1986. Mercury in plants, soil, and water from a caustic chlorine industry. Bull Environ Contam Toxicol 36 299-305. 

Dumarey, R., Van Ryckeghem, M. and Dams, R. (1987) Comparison of wet-digestion methods for the determination of mercury in plant samples by cold vapour atomic absorption spectrometry (CVAAS). J. Trace Microprobe Techniques, 5, 229-242. 

Maserti BE, Ferrara R (1991) Mercury in plants, soil and atmosphere near a chlor-alkali complex. Water Air Soil Pollut 56(1) 15-20. doi 10.1007/bf00342257... 

Problems of removal of mercury from aqueous effluents are more comphcated in plants that manufacture a variety of inorganic and organic mercury compounds it is generally best to separate the effluent streams of inorganic and organic mercurials. When phenyhnercuric acetate is precipitated from its solution in acetic acid by addition of water, the filtrate is collected and reused for the next precipitation. This type of recycling is necessary not only for economic reasons but also to minimise recovery operations. 

In the profiles of the core from the industrial area, mercury displays the highest accumulation. Mercury in this area, close to the industrial district, has probably derived from a large chloralkali plant which has employed mercury cathodes since the fifties. Whereas, at present, very severe measures are taken to prevent mercury spills into the Lagoon, in the past, polluted waters and solid materials were discharged almost untreated. In the most superficial strata a marked decrease in the accumulations is, in fact, recorded. Lead and Cd accumulations are lower here by a factor of 5-10. The presence of cadmium in the sediments of the Lagoon has been referred to sphalerite (ZnS) processing on the basis of a strict concomitant... 

Standards imposed to the industrial waste streams charged in heavy metals are more and more drastic in accordance with the updated knowledges of the toxicity of mercury, cadmium, lead, chromium... when they enter the human food chain after accumulating in plants and animals (Forster Wittmann, 1983). Nowadays, the use of biosorbents (Volesky, 1990) is more and more considered to complete conventional (physical and chemical) methods of removal that have shown their limits and/or are prohibitively expensive for metal concentrations typically below 100 mg.l-i. 

The zone elution method has been used for quantitative estimation or recovery of heavy metals in plants and vegetable juices [29], mercury (11) in river and waste waters [52], zinc in different environmental samples [46], nickel and copper in alloys [53], zirconium in Mg-Al alloys [22], cobalt, zinc, nickel, and copper in natural water and alloy samples [54], thiocyanate in spiked photogenic waste water [55], and aluminum in bauxite ores [42],... 

Drum Top Crushers (DTCs) are available in the market for crushing the lamps and capturing the mercury in a safe and contained manner. The full and sealed drums along with filters need to be transported onward to a recycling plant. The cost of the DTC is about 7,300, whereas the operational costs (for replacement of filters, drums, etc.) are in the range of 0.01-0.03 per lamp. The DTCs have a capacity of about 3,000 crushed CFLs or 1,000 crushed FTLs per drum. 

Finally, it should be mentioned that three out of the eight Spanish chlor-alkali plants operating with the mercury process are located in the Ebro River basin in the cities of Sabinanigo and Monzon - along the tributaries Gallego and Cinca Rivers, respectively - and Flix along the Ebro River (Fig. 1). Indeed, mercury emissions from the Hix and Monzon have already been reported [28]. Therefore, the mid-low Ebro River watershed might be considered as a hot spot of aquatic pollution of mercury in Spain. 

Biester H, Muller G, Scholer HF (2002) Estimating distribution and retention of mercury in three different soils contaminated by emissions from chlor-alkali plants part I. Sci Total Environ 284 177-189... 

Jenkins, D.W. 1980. Biological monitoring of toxic trace metals. Volume 2. Toxic trace metals in plants and animals of the world. Part II. Mercury. U.S. Environ. Protection Agen. Rep. 600/3-80-091 779-982. 

Leonard, T.L., G.E. Taylor, Jr., M.S. Gustin, and G.C.J. Fernandez. 1998a. Mercury and plants in contaminated soils 1. Uptake, partitioning, and emission to the atmosphere. Environ. Toxicol. Chem. 17 2063-2071. 

Accumulation in plant and structures - a considerable amount of mercury accumulates, e.g. in pipework, and can only be recovered and accounted for at the time of plant decommissioning (or possibly, in part, during maintenance and/ or replacement of individual plant items such as pumps) studies suggest that over 90% of this mercury can eventually be recovered. 

Orica Australia Pty Ltd, formerly ICI Australia, is the largest manufacturer of chlorine and caustic soda in Australia. In December 1998, the Orica Board sanctioned a project to replace two mercury cell plants with new membrane plants. The plants are due to be commissioned sequentially at the end of 2000/mid-2001 at a total capital cost of US 100 million. 

This chapter gives an overview of the chlor-alkali industry in Australia and examines the background to the decision to replace the mercury cell plants. It then describes the new plants, their technical and safety features and the process used to arrive at the selection of the technology supplier. 

Orica is the largest producer of chlorine in Australia and currently operates three chlor-alkali plants on the east coast. Two of these plants (in Melbourne and Sydney) are mercury cell plants dating back over 50 years while the third plant is a small, modern membrane cell plant in the central Queensland town of Gladstone. The mercury cell plants have both reached the end of their useful economic lives. 

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