科研之友
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摘要
A simple, but reliable mercury free method to analyse chemical oxygen demand is introduced. The method is based on international standard procedures but avoids the highly toxic mercury. In the procedure the oxidation temperature is brought clown from 148 degrees C to 120 degrees C. At this temperature the chloride interference is reduced to a large extent, whereas the oxidation of most compounds is still complete. Chloride interference is further reduced by addition of silver ions and practically absent at a molar ratio Ag(+)/Cl(-) over 1.7. Compounds that Lire difficult to oxidise even at 148 degrees C oil only in the presence of silver ions are investigated at 120 degrees C. A slight reduction in recovery of 20-35%, is observed for compounds like acetic acid, ethanol or lauryl sulfate in the absence of chloride. In the presence of 3000 mg L(-1) chloride only the reduction for acetic acid is more pronounced due to the low availability of silver ions. The other compounds Studied showed no further decrease in recovery. The interference of bromide is about 50%, less at 120 degrees C than at 148 degrees C. The interference of ammonium in the presence of chloride is not confirmed in this method. The recovery of the method Lit high chloride and low COD concentration, i.e., at 3000 mg Cl(-) L(-1) and 25 mg COD L(-1), is acceptable (122%) whereas Lit 2000 mg Cl(-) L(-1) and 25 mg COD L(-1) it is better (110%). Precision is good: Relative standard deviations Lire 5.6% respectively 2.6%, The results Of 99 wastewater samples over a wide range of chloride concentrations Lire similar compared to analyses based on ISO 15705 (cuvette) or ISO 6060. With the addition of 20 mL silver sulfate-sulfuric acid solution. the chloride in sample,, Lip to 3000 me L (1) chloride is largely precipitated. More Volume silver sulfate-sulfuric acid solution or a hi, her concentration of silver sulfate increases the range of samples that can effectively be analysed. The believed favourable effect of addition of Cr(3+) 10 samples has not been confirmed. In the Netherlands 95% of about 100 000 wastewater samples that are analysed for COD each year have chloride concentrations below 3000 mg L(-1) and Could be analysed without the use of mercury. This may save as Much as 10 kg mercury per annum. It will however require the additional use of about 0.5 kg of silver.
- 出版日期2009-11
