Determination of Mercury, Arsenic, Selenium, Bismuth and Antimony in Solid Waste: Analytical Methods

The determination of mercury, arsenic, selenium, bismuth and antimony in solid waste is a critical analytical procedure for hazardous waste identification, pollution control and regulatory compliance. This article provides a comprehensive technical overview of sample preparation, microwave digestion, atomic fluorescence spectrometry and related testing methods in accordance with standards such as HJ 702-2014 and GB 5085.3-2007. It is intended for environmental engineers, laboratory analysts and waste management professionals seeking reliable trace-element characterization of solid waste materials.

Technical Overview

Mercury (Hg), arsenic (As), selenium (Se), bismuth (Bi) and antimony (Sb) are trace elements of major environmental concern in solid waste management. These elements share similar geochemical and analytical behavior: they readily form volatile hydrides, exhibit high toxicity at low concentrations, and can be efficiently measured in a single analytical workflow. Mercury and arsenic in particular are strictly regulated due to their toxicity, bioaccumulation potential and mobility in the environment, while antimony and selenium are increasingly monitored in incineration residues, smelting slag and electronic waste.

In China, the authoritative method for this analysis is the national environmental protection standard HJ 702-2014, "Solid Waste — Determination of Mercury, Arsenic, Selenium, Bismuth and Antimony — Microwave Digestion/Atomic Fluorescence Spectrometry." The method employs closed-vessel microwave acid digestion to completely decompose the waste matrix, followed by hydride generation/cold vapor atomic fluorescence spectrometry (HG-AFS) for highly sensitive quantification. Under the standard conditions of a 0.5 g test portion diluted to 50 mL, typical method detection limits are approximately 0.002 mg/kg for mercury, 0.01 mg/kg for arsenic, and around 0.2 mg/kg for selenium, bismuth and antimony, which is sufficient for most hazardous waste identification and regulatory monitoring purposes.

The analytical results directly support hazardous waste classification under the GB 5085 series standards, leaching toxicity assessment under GB 5085.3-2007, and acceptance decisions for landfill disposal, co-processing in cement kilns and incineration facilities. Internationally, comparable approaches include microwave digestion following US EPA Method 3052 with determination by ICP-MS (US EPA Method 6020B) or hydride generation techniques, ensuring methodological consistency across jurisdictions.

Testing Samples

Industrial Solid Waste and Process Residues

Solid wastes from chemical manufacturing, metal smelting, coal combustion and petrochemical industries frequently contain elevated concentrations of arsenic, antimony and mercury. Typical matrices include fly ash, bottom ash, furnace slag, filter cake, catalyst wastes and scrubber residues. These samples are often heterogeneous and require careful crushing, homogenization and sieving before analysis.

Mining and Metallurgical Waste

Mine tailings, heap leach residues, smelter dust and roasted ores are important sources of arsenic and antimony contamination. Selenium and bismuth are also commonly associated with non-ferrous metallurgical wastes, particularly from copper, lead and zinc processing. Determination of these five elements helps assess environmental risks at legacy mining sites and supports tailings reuse decisions.

Municipal Solid Waste Incineration Residues

Bottom ash and fly ash from municipal and hazardous waste incinerators are routinely tested for mercury, antimony and arsenic. Mercury volatilizes during incineration and concentrates in flue-gas cleaning residues, making accurate low-level determination essential for disposal classification and flue gas emission control verification.

Sludge and Sediment-Type Wastes

Wastewater treatment sludge, river and lake dredged sediment classified as solid waste, and contaminated soils undergoing remediation are analyzed for all five elements. High organic matter and sulfide content in these matrices demands robust oxidative digestion to ensure complete recovery of element species bound to organic and mineral phases.

Electronic Waste and Scrapped Products

Dismantled circuit boards, solder-bearing materials, display glass and battery wastes contain bismuth, antimony and selenium as functional additives. Testing supports environmentally sound recycling, disposal and cross-border waste movement control under the Basel Convention framework.

Testing Items

The core testing items cover the total content of five hydride-forming elements in solid waste samples:

• Total mercury (Hg) — determined by cold vapor atomic fluorescence spectrometry following digestion, owing to its volatility and extremely low regulatory thresholds.
• Total arsenic (As) — a priority toxic element with strict limits in hazardous waste identification; requires pre-reduction from pentavalent to trivalent form before hydride generation.
• Total selenium (Se) — an essential yet toxic element at elevated doses; requires reduction of Se(VI) to Se(IV) in concentrated hydrochloric acid medium prior to determination.
• Total antimony (Sb) — regulated in incineration and smelting residues; measured after thiourea–ascorbic acid pre-reduction.
• Total bismuth (Bi) — monitored as a companion element in metallurgical and electronic wastes; determined under the same pre-reduction conditions as antimony.

In addition to total content, leaching behavior can be evaluated using the sulfuric acid/nitric acid extraction procedure of HJ/T 299-2007 or the acetic acid buffer extraction of HJ/T 300-2007, in conjunction with the leaching toxicity identification criteria in GB 5085.3-2007.

Testing Methods

Sample Collection and Preparation

Sampling follows the technical specifications of HJ/T 298-2007 for hazardous waste identification. Representative samples are collected using tools that avoid metal contamination, stored in glass or polyethylene containers, and transported under cool, dark conditions to minimize mercury loss and speciation changes. In the laboratory, samples are air-dried or freeze-dried at low temperature (generally below 40 °C for mercury-bearing samples), crushed, homogenized and sieved, typically to below 0.149 mm (100 mesh). Moisture content is determined separately so that results can be reported on a dry-weight basis.

Microwave Acid Digestion

A weighed test portion of approximately 0.25–0.5 g is transferred to a polytetrafluoroethylene (PTFE) microwave digestion vessel. A mixed acid system of nitric acid, hydrochloric acid and hydrofluoric acid is added to decompose organic matter, sulfides and silicate minerals simultaneously. The sealed vessel is heated in a programmed microwave system, typically ramping to 180–200 °C and held for 20–40 minutes. After cooling, residual hydrofluoric acid is complexed with saturated boric acid solution or removed by evaporation to protect the quartz components of the atomic fluorescence spectrometer. The digest is quantitatively transferred and diluted to a fixed volume with water and hydrochloric acid to establish the required acid medium for hydride generation. Alternative digestion schemes, such as hot-plate aqua regia reflux or US EPA Method 3052 microwave digestion, may be used when validated for the target matrix.

Pre-Reduction and Hydride Generation

Because hydride generation efficiency is highly speciation-dependent, chemical pre-treatment is essential. Arsenic, antimony and bismuth solutions are pre-reduced with a thiourea–ascorbic acid solution to convert pentavalent arsenic and antimony to their trivalent forms and to suppress interference from transition metals. Selenium solutions are heated in concentrated hydrochloric acid medium to reduce Se(VI) to Se(IV). During measurement, potassium borohydride dissolved in dilute sodium hydroxide solution is mixed with the acidified sample stream, generating gaseous hydrides (arsane, selenane, stibane, bismuthane) that are separated from the liquid phase and carried by argon gas into an argon–hydrogen flame. Mercury, measured in cold vapor mode, is reduced to elemental mercury vapor and transported to the excitation source without a flame.

Atomic Fluorescence Spectrometric Determination

The atomized elements are excited by element-specific hollow cathode or high-intensity lamps, and the resulting fluorescence emission is detected by a photomultiplier tube positioned at right angles to the excitation beam. This optical configuration provides extremely low background and picogram-level absolute sensitivity. Quantification is performed using multi-point external calibration curves prepared from certified standard solutions matrix-matched in hydrochloric acid and the same pre-reductant concentration as the samples. Each analytical batch incorporates a reagent blank, calibration verification standards, duplicate samples, matrix spikes and certified reference materials.

Alternative and Complementary Techniques

• Inductively coupled plasma mass spectrometry (ICP-MS) following microwave digestion offers simultaneous multi-element capability and lower detection limits, but requires dilution to control total dissolved solids and careful correction for argon chloride interferences on arsenic and selenium.
• Inductively coupled plasma optical emission spectrometry (ICP-OES) provides higher throughput for wastes containing elevated element concentrations.
• Graphite furnace atomic absorption spectrometry (GFAAS) serves as a confirmatory technique for individual elements at trace levels.
• Direct mercury analyzers based on thermal decomposition, gold amalgamation and atomic absorption permit rapid mercury screening without digestion, subject to matrix validation.

Interference Control and Quality Assurance

Principal interferences include hydride generation suppression by high concentrations of copper, nickel, cobalt and other transition metals, which is mitigated by dilution, masking with thiourea–ascorbic acid, or the method of standard additions. Memory effects of mercury are controlled by rinsing with dilute potassium permanganate or hydrochloric acid solutions. Quality control criteria typically require calibration correlation coefficients of at least 0.995, blank values below the method detection limit, duplicate relative deviations within 20–30 percent, and spike recoveries in the range of 70–130 percent. Certified reference materials of soil, sediment or fly ash matrices are analyzed to verify method accuracy, and all analytical work should be performed by accredited third-party laboratories operating under ISO/IEC 17025 quality management systems.

Applications

Determination of mercury, arsenic, selenium, bismuth and antimony in solid waste serves a wide range of regulatory and industrial purposes:

• Hazardous waste identification and classification under the GB 5085 series, including attribute judgment based on leaching toxicity thresholds in GB 5085.3-2007 and supporting criteria in GB 5085.7.
• Disposal acceptance testing for hazardous waste landfills, municipal solid waste landfills and monofills, ensuring compliance with storage and disposal pollution control standards.
• Co-processing assessments for cement kilns and incineration facilities, where feedstock limits on mercury, arsenic and antimony protect product quality and air emissions compliance.
• Site contamination investigation and remediation verification at industrial relocation sites, mining areas and accidental spill locations.
• Environmental impact assessment and pollution source apportionment studies supporting waste generation unit supervision and discharge permitting.
• Verification of resource recovery and recycling processes, including metallurgical recovery of bismuth and antimony from secondary materials.
• Import and export waste verification and transboundary movement control under international environmental conventions.

FAQ

Why are mercury, arsenic, selenium, bismuth and antimony determined together?

These five elements share similar analytical chemistry: they form volatile hydrides (or, for mercury, atomic vapor) under potassium borohydride reduction and can be measured with exceptional sensitivity by atomic fluorescence spectrometry. HJ 702-2014 integrates them into one digestion and one instrumental platform, improving efficiency, reducing sample consumption and ensuring consistent data quality across elements that frequently co-occur in metallurgical, incineration and chemical wastes.

What is the difference between total content and leaching toxicity determination?

Total content determination measures the entire quantity of an element contained in the waste matrix after complete digestion, reflecting the maximum potential reservoir of the pollutant. Leaching toxicity determination, by contrast, simulates the release of elements under specified acidic extraction conditions defined in HJ/T 299-2007 or HJ/T 300-2007 and is compared against the identification thresholds in GB 5085.3-2007 to judge whether the waste exhibits hazardous characteristics. Both measurements are complementary in comprehensive waste evaluation.

What detection limits can be achieved?

Using HJ 702-2014 with a 0.5 g test portion diluted to 50 mL, typical method detection limits are approximately 0.002 mg/kg for mercury, 0.01 mg/kg for arsenic, and 0.2 mg/kg for selenium, bismuth and antimony. Actual achievable limits vary with instrument sensitivity, reagent purity, blank levels and matrix dilution factors. ICP-MS can extend detection capability to sub-µg/kg levels when required.

How should samples be preserved before testing?

Samples should be collected with non-metallic tools, stored in glass or polyethylene containers with minimal headspace, kept cool and dark during transport, and analyzed promptly. Because mercury and selenium species can volatilize, transform or adsorb to container walls, drying at low temperature, homogenization under dust-free conditions and avoidance of strong oxidants during storage are essential for maintaining sample integrity.

Can the method handle high-silicate or sulfide-rich wastes?

Yes. The nitric–hydrochloric–hydrofluoric acid microwave digestion system in HJ 702-2014 is specifically designed to decompose silicate and refractory matrices, while nitric acid oxidizes sulfides and organic matter. For extreme matrices such as high-carbon wastes or slags, extended holding times, repeated digestion cycles or pre-oxidation steps may be required and must be validated through spike recovery and certified reference material studies.

Which quality documents should a testing report include?

A complete report should state the sampling basis, sample pretreatment and digestion procedure, instrumental method and standard reference, dry-weight basis of results, method detection limits, quality control data including blanks, duplicates, spike recoveries and certified reference material results, measurement uncertainty where applicable, and accreditation status of the testing laboratory under ISO/IEC 17025.