Reference methods for measuring particulate matter and lead emissions from secondary lead smelters: section 2

Section 2: Analysis

• 2.1 Principle
• 2.2 Reliability
• 2.3 Detection Limit of Lead
• 2.4 Interferences
• 2.5 Apparatus
• 2.6 Reagents
• 2.7 Procedures

2.1 Principle

Particulate matter collected in various sections of the sampling train is first weighed and then digested under reflux in aqua regia. The extracted lead is measured by flame atomic absorption spectroscopy at 283 nm.

2.2 Reliability

Accuracy and Precision (Analytical) for Lead Analysis. The accuracy of the method depends to some extent on the quantity of the particulate matter collected, particularly in the case of low mass loadings where filter handling losses of the order of 5 mg may be significant. Otherwise, the estimated analytical accuracy is ± 3% with a precision value of less than 2% coefficient of variation.

2.3 Detection Limit of Lead

For a total sampling volume of 2.8 normal cubic metres (100 normal cubic feet) the detection limit for lead collected on glass fibre filters is approximately 50 μg/m³.

2.4 Interferences

For secondary lead operations the metallic constituents most frequently encountered in addition to lead are antimony, arsenic and tin, with minor quantities of copper and nickel(1). None of these metals interfere with the determination of lead in an air-acetylene flame. A very limited number of inorganic ions (e.g., sulphate and phosphate) which form insoluble lead compounds have been found to interfere when present in large molar excesses over lead. The addition of EDTA has been shown to remove such interferences(2).

2.5 Apparatus

2.5.1 Balance

Mettler H54 or equivalent, 160-g capacity, capable of measurement to within 0.01 mg.

2.5.2 Balance - Top Loading

1200-g capacity, capable of measurement to nearest 0.1 g.

2.5.3 Atomic Absorption Spectrophotomete

with hollow cathode lead lamp and burner for air-acetylene flame.

2.5.4 Extraction Flasks

125 ml with 24/40 ground glass joint.

2.5.5 Reflux Condenser

with 24/40 ground glass joint to fit Erlenmeyer flasks.

2.5.6 Hotplates

2.5.7 Glass Filtering Funnels

55 mm top ID, short stem.

2.5.8 Filter Paper

Whatman 54 l or equivalent.

2.5.9 Graduated Cylinder

100 ml.

2.5.10 Volumetric Flasks

100 ml, 500 ml.

2.5.11 Pipettes

2, 4, 6, 8, 10 ml.

2.6 Reagents

2.6.1 Distilled, Deionized Water

2.6.2 Anti-Bumping Granules

2.6.3 Aqua Regia

Prepare by mixing one part concentrated HNO₃ with three parts concentrated HCl, both reagent-grade. This formula should include one part of water if the aqua regia is to be stored for any length of time. Without water, objectionable quantities of chlorine and other gases are evolved.

2.6.4 Stock Lead Standards

100 μg/ml. Prepare by dissolving 0.1.9 8 g of reagent grade Pb(NO₃)₂ in about 700 ml of distilled water. Add 20 ml of concentrated nitric acid and dilute to 1 litre.

2.6.5 Working Lead Standards

Solution Lead Standards. Pipette aliquots of 2, 4, 6, 8 and 10 ml of the stock lead solution into 100-ml volumetric flasks. Add 2 ml of aqua regia to each and dilute to volume with distilled deionized water. A reagent blank is prepared by diluting 3 ml of aqua regia to volume in a 100-ml volumetric flask.

Filter Sample Standards. Place a glass fibre filter selected from the same lot as that used for the sampling program into each of a series of five 125-ml extraction flasks. Add 25 ml of aqua regia and 20 ml of deionized water. Reflux for 2 hours, rinse the column with a small quantity of deionized water and remove the flask. Filter the contents into a 500-ml volumetric flask and dilute to volume. Pipette one 5-ml aliquot of the filter blank solutions into each of five 100-ml volumetric flasks together with 2, 4, 6, 8 and 10 ml of the 100 μg/ml stock lead standard. To each of the volumetric flasks add 2 ml of aqua regia and dilute to volume.

2.7 Procedures

2.7.1 Nozzle-Probe, Cyclone and Filter Holder Washings

Allow the acetone wash to evaporate in the collection bottle to a volume of approximately 30 ml before transferring the contents with several acetone rinses to a tared 125-ml Erlenmeyer flask. Evaporate to dryness and desiccate to constant weight. Record the weight to the nearest 0.01 mg on the particulate matter analytical data sheet (Figure 4). Add 20 ml of water to the flask and 25 ml of aqua regia. Reflux for 2 hours and rinse the column with distilled water. Filter the contents while hot into a 500-ml volumetric flask. Dilute to volume and prepare such dilutions from this solution as may be required to measure lead in the linear working range of the spectrophotometer. Diluted solutions should be acidified to 2% aqua regia content. Record the weight of lead found on the lead analytical data sheet (Figure 5).

2.7.2 Glass Fibre Filters

Place the filter and loose particulate matter in a tared plastic petri dish. Desiccate to constant weight and record the weight of collected particulate matter to the nearest 0.01 ml (Figure 4). Transfer the filter and particulate matter to a 125-ml Erlenmeyer reflux flask. Rinse the petri dish with 20 ml of distilled water and add the rinse water through a short-stem tunnel to the flask. Add 25 ml of aqua regia and a small quantity of anti-bumping granules. Reflux for 2 hours and rinse the column with distilled water. Filter the flask contents while still hot into a 500-ml volumetric flask and dilute to volume with distilled water.

Figure 4 : Particulate Matter Analytical Data Sheet

In most cases, a 10- to 50-fold dilution of this solution will be required in order to determine lead in the linear working range (1 to 10 μg/ml) of the spectrophotometer. Where such dilutions are made the solution should be acidified to 2% aqua regia content. Record the weight of lead found on the lead analytical data sheet (Figure 5).

Figure 5 : Lead Analytical Data Sheet

2.7.3 Impinger Contents

Weigh to the nearest gram, the spent silica gel taken from the fifth impinger and record the result on the moisture data sheet (Figure 3). The combined first and second impinger contents (container 2) are filtered through a Whatman 541 filter paper. The filtrate is then analyzed directly by flame atomic absorption with the lead solution standards (Section 2.6.5) used to prepare the calibration line.

The filter is transferred to a 125-ml Erlenmeyer reflux flask. Add 20 ml of distilled water and 25 ml of aqua regia and a small quantity of anti-bumping granules. Reflux for 2 hours and rinse the column with distilled water. Filter the flask contents while still hot into a 500-ml volumetric flask and dilute to volume with distilled water. Prepare such dilutions from this solution as may be required to measure lead in the linear working range of the spectrophotometer. Diluted samples should be acidified to 2% aqua regia content.

Record the weight of lead found in the impinger catch on the lead analytical data sheet (Figure 5).