MERCURY INVENTORY IN ELECTROLYTIC CELLS

  INTRODUCTION

The circulating mercury acts as cathode of the cel1 and a cell may contain 1000-2500 Kg mercury. Production losses of mercury are accountab1e. However losses in the form of leakage, pilferage etc cannot be accounted for. Hence in order to make periodical overall balance of circulating mercury by weighing requires plant shut down involving loss of production and considerable labour every time.

The technique developed has the advantage that it can be employed on line hence no loss of production. About 50 cells can be assayed in a period of 2 days.

  THEORY

This technique is based on Isotope Dilution Technique. The technique involves introduction of a known amount ¹⁹⁷Hg, radiotracer (mass M and concentration A) into the cell and the measurement of resultant tracer concentration after homogenisation. Specific activity of representative cell sample when compared with the reference standard of known specific activity gives amount of mercury circulating in the cell. The reference standard is prepared by diluting a sample from original, active tracer injected by a factor say 'N' such that the diluted sample have approximately, the same specific activity , as expected in the cell sample.

  EQUIPMENTS & ACCESSORIES

The equipments & accessories required are following:

• Portable gamma ray spectrometer consisting of High Voltage Unit, Linear Amplifier, Preset Timer, Counter.
• Well type scintillation detector (well size : 15mm f X 50 mm,
                                                       crystal size : 76mm f X 76mm)
• Contamination monitor
• Microbalance
• Accessories :

 TRACER

Radiotracer ¹⁹⁷Hg will be supplied in sealed vials by Isotope Division, BARC, Bombay-400 085 on advance payment. Each tracer vial will contain 5 mCi ¹⁹⁷Hg diluted in 100 gm virgin mercury. Virgin mercury will be supplied by customer. The packing note will give all the details of tracer.

 PROCEDURE

• Back ground samples from each cell are drawn in counting vials using Mercury Sampling Pipette.
• The tracer vial is opened using decapping tool and tracer is poured into the cell using vial holder. This is repeated for all cells.
• A small tracer sample is removed from one of the vials by a micro pipette.
• After homogenisation cell samples are drawn, following the procedure ( 1 ) .
• Standard preparation: The already removed tracer sample(3) is successively diluted by desired dilution factor using virgin mercury such that the diluted sample have approximately the same specific activity as expected in cell samples.
• The back ground samples, cell samples and standard are counted in gamma ray spectrometer.
• Net cell counts (C*) and net standard counts (C) are determined and using formula W is determined for each cell.

 MANPOWER

Manpower required is following:

• One person having qualification B.Sc. (with Physics or Chemistry as one of the, subject) or a Diploma in Engineering for handling ¹⁹⁷Hg .
• One person having qualification secondary or Hr. secondary (with science background) for assistance.
• One typist for office work etc.

 TRAINING

The training of staff who will be handling ¹⁹⁷Hg will be provided by Isotope Division, BARC.

 FORMALITIES FOR OBTAINING RADIOTRACER

The following forms are to be filled by customer for procuring and using tracer:

• A-1 Form (available from Sales & Marketing Section, Isotope Division, BARC, Bombay - 400 085) in triplicate for supply of tracer.
• Application for permission from Division of Radiological Protection BARC for to procurement and use of ¹⁹⁷Hg for mercury inventory in electrolytic cells.

 OVER VIEW

This technique is advantages to electrolytic plants for carrying out mercury inventory without any production loss. The agencies who will be offering such services will also get a handsome profit on their investments. It has good potential and market in the country.