GB1522410A - Determination of heavy metal ion concentrations - Google Patents

Abstract

1522410 Determining heavy metal ions electro-chemically SIEMENS AG 17 Sept 1976 [25 Sept 1975] 38739/76 Heading G1N Heavy metals in aqueous liquor are determined by conducting the liquor for a predetermined length of time and at a constant flow-rate past a solid electrode maintained at a negative direct voltage to deposit heavy metal thereon, replacing the liquor by an electrolyte and the negative voltage by a positive direct voltage and determining the charge to remove any deposited heavy metal from the electrode. The negative voltage may be - I to -4V preferably - 1À5 to -2À5V, and the predetermined length of time 1-10 minutes. The positive voltage may be 0À5 to 3V preferably 0À8 to 2V. The electrolyte is preferably sodium chloride or sodium sulphate of concentration 10<SP>-1</SP> to 10<SP>-3</SP> mol/litre and pH 1 to 7 preferably 3-4, and is preferably stationary during the dissolution. Apparatus for carrying out the determination comprises a measuring cell 24 with working electrode 25, and counter electrode 26 and gas riser pipe 29. The aqueous liquor is supplied via filter 20, and constant head device 21 and valve 22 and the electrolyte from tank 31 via valve 32. A valve is provided in the cell outlet so that the aqueous liquor can flow through the cell during the deposition period but the electrolyte does not flow during the dissolution. A control circuit for the valves and voltages and means for integrating and displaying or recording the dissolution current and generating an alarm if a predetermined heavy metal concentration is exceeded, are provided. The deposition may be conducted with the working electrode stationary or moving i.e. rotating or vibrating. The liquid in the cell may be mechanically circulated. The electrodes preferably have an area of about 20 mm<SP>2</SP> and are preferably rods and of platinum; graphite, glass-carbon and carbides being alternative materials. The counter electrode is preferably of larger area than the reference electrode. In alternative embodiments the electrodes may be coiled wires; the counter electrode a coiled wire surrounding a rod working electrode, the counter electrode a cylinder surrounding either a cylinder or a rod working electrode or they may both be cylindrical and set in the walls of a ceramic, glass or synthetic plastics tube. The method and apparatus may be used for the automatic monitoring of heavy metal pollution. The method has a detection limit of about 10<SP>-6</SP> equivalent/litre.