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(1) Scope of application
It is suitable for the determination of mercury, arsenic, selenium, bismuth and antimony in solid waste and solid waste leachate
(2) Method principle
After microwave digestion of solid waste and leachate samples, they enter the atomic fluorescence spectrometer.
(3) Reagents and materials
(1) Ultrapure water: resistivity greater than 18.
(2) Nitric acid , hydrochloric acid , sulfuric acid : top grade pure
(3) Thiourea, sodium hydroxide : analytically pure
(4) Potassium borohydride : pure superior grade
(5) Potassium borohydride solution A, p=2g/L: Weigh 0.
(6) Potassium borohydride solution B, p=20g/L: Weigh 0.
(7) Thiourea solution, p=100g/L: Take 10g of thiourea , dissolve it with pure water, and dilute to 100ml
(8) Standard solutions of mercury, arsenic, selenium, antimony, and bismuth (1000ug/L), produced by AccuStandard, USA
(4) Instruments and equipment
(1) The performance index of the atomic fluorescence spectrometer should meet the requirements of GB/T21191
(2) Microwave digestion instrument: The model is ETHOS TC
(3) Balance: the accuracy is 0.
(4) Analytical balance: the accuracy is 0.
(5) Commonly used instruments and equipment in general laboratories
(5) Sample preparation
1.
According to the "Technical Specifications for Sampling and Preparation of Industrial Solid Wastes" (HJ/T20-1998), solid waste samples are naturally air-dried or freeze-dried, ground, all are passed through a 100-mesh sieve and their dry matter content is determined
.
Use an analytical balance to weigh 0.
5000 g of the sieved sample into a microwave digestion tank, and add a small amount of water to moisten it
.
Add 6 mL of hydrochloric acid and 2 mL of nitric acid in a fume hood to fully contact the sample with the digestion solution.
After the reaction is complete, put it in a microwave digestion apparatus and perform microwave digestion according to the heating program in Table 5-49
.
After the digestion, when the temperature in the tank drops to room temperature, take it out, vent and open it in a fume hood
.
Use filter paper to filter the digested solution into a 50mL volumetric flask, dilute to volume, and mix well
.
Table 5-49 Heating program for microwave digestion of solid waste
2.
Preparation of solid waste leachate
The samples were leached in accordance with the "Solid waste leaching toxicity leaching method, sulfuric acid and nitric acid method" (HJ/T299-2007)
.
Add a mixture of concentrated sulfuric acid and concentrated nitric acid with a mass ratio of 2:1 to pure water (about 2 drops of 1L water) to make the pH 3.
20±0.
05
.
After the sample is crushed and sieved, according to the moisture content of the sample, calculate and add the volume of the required extract at a liquid-to-solid ratio of 10:1 (L/kg), adjust the speed to 30±2r/min, at 23℃± Shake at 2℃ for 18h±2h
.
After the above steps are completed, let it stand still after filtering
.
Measure 20 mL of solid waste extract into a 50 mL microwave digestion tank, add 1.
5 mL of hydrochloric acid and 0.
5 mL of nitric acid , and place it in a microwave digestion apparatus after the reaction is complete, and perform microwave digestion according to the temperature setting program in Table 5-50
.
After digestion, transfer to a 50mL volumetric flask
.
Table 5-50 Microwave digestion heating program of solid waste leachate