Zeolite for Flue Gas Mercury (Hg) Adsorption & Capture

Q: Does natural zeolite directly adsorb elemental mercury (Hg⁰) from flue gas?

Elemental mercury (Hg⁰) is a non-polar, volatile gas, so it is barely captured by unmodified natural clinoptilolite. The cation-exchange active sites of clinoptilolite work on ionic mercury such as aqueous Hg²⁺, but for chemisorption of gaseous Hg⁰, functionalization that introduces active sites such as silver (Ag), sulfur (S), or halogens is effectively a prerequisite. Therefore, the key to flue gas mercury capture is the design of a modified support.

Q: What kind of modification or loading is used for mercury capture?

Gaseous mercury adsorbents typically introduce active sites that form a stable bond with Hg⁰ (an amalgam or HgS). Representative approaches include silver (Ag) loading to form an Ag–Hg amalgam, or sulfur (S)/sulfide loading to form HgS. With its high specific surface area and thermal/acid resistance, clinoptilolite serves as a support that disperses and immobilizes these active components. Oxidized mercury (Hg²⁺) is separately removed in part by wet flue gas desulfurization (WFGD).

Q: Are elemental mercury and oxidized mercury treated differently?

Yes. Oxidized mercury (Hg²⁺) is water-soluble, so a substantial portion is removed in wet flue gas desulfurization (WFGD), whereas elemental mercury (Hg⁰) is barely soluble in water and requires an adsorbent or an oxidation catalyst. As a result, actual processes are designed either to oxidize Hg⁰ to Hg²⁺, or to capture Hg⁰ directly with an Ag/S-loaded adsorbent. The zeolite support is considered for the latter.

Q: Where in the process is it installed?

Mercury adsorption is generally considered in the low-temperature zones before and after particulate collection (ESP/baghouse) and desulfurization. Options include injecting the adsorbent into the duct (powder) or passing the gas through a fixed-bed adsorption tower (granules). Because the volatilization risk of sulfur-loaded media rises with temperature, confirming the operating temperature window is important. Flue gas composition (SO₂, HCl, moisture, fly ash) strongly affects capture performance through competition and interference.

Q: Can I receive a test sample?

Yes, KMIZEOLITE supports the provision of samples for real-world application review. On the sample request page, please tell us your application purpose (mercury adsorbent support, duct injection, etc.) and your desired particle size.

Why Flue Gas Mercury (Hg) Emissions Are So Difficult to Handle

Mercury is a representative heavy-metal air pollutant that is volatilized as a trace element during combustion in coal-fired power generation, municipal/industrial waste incinerators, and cement kilns, and is emitted in the flue gas. Because mercury travels long distances in the atmosphere and is then deposited, methylated, and bioaccumulated, emission regulations have been strengthened worldwide—including Korea's Clean Air Conservation Act and the U.S. MATS (Mercury and Air Toxics Standards). The problem is that mercury in flue gas does not exist in a single form.

Mercury in combustion flue gas exists largely in three forms. Elemental mercury (Hg⁰) is barely soluble in water and highly volatile, making it the hardest to capture; oxidized mercury (Hg²⁺, mainly HgCl₂) is water-soluble and is largely removed in wet flue gas desulfurization (WFGD); and particulate mercury (Hgₚ) is captured together with fly ash in particulate control devices (ESP/baghouse). Thus, the practical challenge of flue gas mercury control comes down to "how do you capture Hg⁰ or oxidize it to Hg²⁺?" This is a domain whose mechanism differs from ordinary VOC/odor adsorption or liquid-phase heavy-metal removal.

Why Zeolite Is Considered in This Field — The Support and Functionalization Are Key

Here, one key point must be made clear. The cation-exchange capacity (CEC) of 1.6–2.0 meq/g of clinoptilolite originally works to capture ionic cations such as Hg²⁺ in the liquid phase. By contrast, elemental mercury (Hg⁰) in flue gas is an uncharged, non-polar gas, so it is not captured by cation exchange alone. In other words, the explanation that "zeolite captures gaseous mercury because it is a cation exchanger" does not hold, and functionalization (modification) that introduces active sites such as silver (Ag), sulfur (S), or halogens is effectively a prerequisite for gaseous Hg⁰ chemisorption.

So what is the role of zeolite? With a porous structure of 40.0 m²/g specific surface area and 4.0–7.0 Å pore diameter, plus high thermal/acid stability, clinoptilolite serves as a support that provides the foundation for evenly dispersing and immobilizing the active components that bind mercury. There are two representative chemisorption pathways: (1) silver (Ag) loading to form an Ag–Hg amalgam with Hg⁰, and (2) sulfur (S)/sulfide loading to form stable mercury sulfide (HgS).

KMIZEOLITE's natural clinoptilolite is 97% pure and is mined and processed at the Amargosa Valley mine in Nevada, USA. With a specific surface area of 40.0 m²/g, pore diameter of 4.0–7.0 Å, pH stability range of 3.0–10.0, hardness of 4.0–5.0 Mohs, and thermal stability of 700°C, it has the physical stability to withstand combustion flue gas environments and loading processes, and is therefore considered as a base material for the mercury adsorption media above or as a support for duct injection.

As for research evidence, Wdowin et al. (2014, Fuel) experimentally evaluated the flue gas mercury removal performance of zeolite-based adsorbents and showed that the degree of functionalization governs Hg⁰ capture (Wdowin, M. et al., 2014, Fuel, doi:10.1016/j.fuel.2014.03.041). Regarding the affinity between mercury and clinoptilolite, a comprehensive review of applying natural clinoptilolite to the remediation of mercury-contaminated environments has been reported (Natural zeolite clinoptilolite for remediation of mercury-contaminated environment, Processes, 2022). The point that surface modification is essential when using natural zeolite for heavy-metal removal is also summarized in a separate review (Modification of natural zeolites for heavy metal removal, Heliyon, 2024).

KMIZEOLITE Key Properties

Item	Value
Clinoptilolite purity	97%
Cation exchange capacity (CEC)	1.6–2.0 meq/g
Specific surface area	40.0 m²/g
Pore diameter	4.0–7.0 Å
pH stability range	3.0–10.0
Hardness	4.0–5.0 Mohs
Thermal stability	700°C
Specific gravity	1.89
Bulk density	45–54 lbs/ft³
Certifications	OMRI KMI-10365, FDA GRAS, TSCA, EN-71-3

Application Examples for Flue Gas Mercury Adsorption & Capture

In the mercury field, the realistic use is not "natural zeolite as is" but rather as a functionalized medium loaded with active components, or as the support for such a medium. The representative scenarios are as follows.

Ag-loaded adsorbent support: Using clinoptilolite as the base material for a medium that loads silver (Ag) to capture Hg⁰ as an Ag–Hg amalgam
Sulfur (S)/sulfide-loaded media: Using it as the support for an adsorbent that loads sulfur to form stable HgS (operating temperature window management required)
In-flight (duct injection) adsorption: Injecting a powder adsorbent into the duct to capture mercury in flight, then recovering it in the downstream particulate collector
Fixed-bed adsorption tower (polishing bed): Passing the flue gas through an adsorption tower packed with granular media to finish-capture residual mercury
Test/pilot application: Pre-verifying the loading method, temperature, and the effect of competing gases (SO₂·HCl) with a small sample

Recommended Particle Size and Product Specifications

For duct injection, Powder (100 mesh or finer, <150μm) with a large specific surface area and rapid dispersion is typical, while for fixed-bed adsorption towers and granular media, Medium Granule (14×40 mesh) to Coarse Granule (8×14 mesh) is considered to balance pressure drop and contact (residence) time. If you intend to carry out Ag/S loading in your own process, the uniform particle size of the base material directly affects loading reproducibility and active-component dispersion, so selecting a single mesh grade is recommended.

Product Group	Mesh	Particle Size	Typical Use
Powder	100 mesh or finer	<150μm	Pozzolan, feed, powder adsorption
Fine Granule	30×50 mesh	0.3–0.6mm	Water treatment, filtration, soil
Medium Granule	14×40 mesh	0.4–1.4mm	Filter beds, bedding, litter
Coarse Granule	8×14 mesh	1.4–2.4mm	Pools, de-icing, large-scale filtration
Extra Coarse	4×8 mesh	2.4–4.8mm	Packed beds, air scrubbers

→ View products by mesh size · Product selection guide by application

Pilot Test and On-Site Review Points

Gaseous mercury behaves very differently in capture depending on its form (Hg⁰/Hg²⁺) and the flue gas composition. Be sure to check the following items together.

Decide the functionalization method: Unmodified natural zeolite has low Hg⁰ capture capacity. Decide first on the active component and loading method, such as Ag loading or sulfur loading.
Mercury speciation distribution: Determine the Hg⁰/Hg²⁺/Hgₚ ratio in the incoming flue gas. If the Hg²⁺ fraction is high, much is removed in WFGD, changing the adsorption load.
Operating temperature window: Sulfur-loaded media carry a risk of sulfur volatilization/re-emission at high temperatures, so confirm the temperature of the installation zone (the low-temperature section before/after particulate collection and desulfurization).
Competing/interfering gases: SO₂, HCl, moisture, and fly ash can occupy active sites or hinder adsorption, so review the flue gas composition together.
Contact time and pressure drop: For duct injection, the in-flight residence time, and for fixed beds, the EBCT (empty bed contact time) and pressure drop govern capture efficiency.
Field-specific notes: Mercury control is often combined with existing technologies such as activated carbon injection (ACI), oxidation catalysts, and WFGD. The zeolite support is generally considered not as a standalone cure-all but as a loading medium that complements these processes.

→ View TDS (Technical Data Sheet) · View MSDS (Material Safety Data Sheet)

Flue Gas Mercury Adsorption FAQ

Does natural zeolite directly adsorb elemental mercury (Hg⁰) from flue gas?

Elemental mercury (Hg⁰) is a non-polar, volatile gas, so it is barely captured by unmodified natural clinoptilolite. The cation-exchange active sites of clinoptilolite work on ionic mercury such as aqueous Hg²⁺, but for chemisorption of gaseous Hg⁰, functionalization that introduces active sites such as silver (Ag), sulfur (S), or halogens is effectively a prerequisite. Therefore, the key to flue gas mercury capture is the design of a modified support.

What kind of modification or loading is used for mercury capture?

Gaseous mercury adsorbents typically introduce active sites that form a stable bond with Hg⁰ (an amalgam or HgS). Representative approaches include silver (Ag) loading to form an Ag–Hg amalgam, or sulfur (S)/sulfide loading to form HgS. With its high specific surface area and thermal/acid resistance, clinoptilolite serves as a support that disperses and immobilizes these active components. Oxidized mercury (Hg²⁺) is separately removed in part by wet flue gas desulfurization (WFGD).

Are elemental mercury and oxidized mercury treated differently?

Yes. Oxidized mercury (Hg²⁺) is water-soluble, so a substantial portion is removed in wet flue gas desulfurization (WFGD), whereas elemental mercury (Hg⁰) is barely soluble in water and requires an adsorbent or an oxidation catalyst. As a result, actual processes are designed either to oxidize Hg⁰ to Hg²⁺, or to capture Hg⁰ directly with an Ag/S-loaded adsorbent. The zeolite support is considered for the latter.

Where in the process is it installed?

Mercury adsorption is generally considered in the low-temperature zones before and after particulate collection (ESP/baghouse) and desulfurization. Options include injecting the adsorbent into the duct (powder) or passing the gas through a fixed-bed adsorption tower (granules); because the volatilization risk of sulfur-loaded media rises with temperature, confirming the operating temperature window is important. Flue gas composition (SO₂, HCl, moisture, fly ash) strongly affects capture performance through competition and interference.

Which particle size (mesh) is suitable?

For duct injection, Powder (100 mesh or finer, <150μm) is typical, while for fixed-bed adsorption towers and granular media, Medium Granule (14×40 mesh) to Coarse Granule (8×14 mesh) is common. Review pressure drop and contact (residence) time together, and if you carry out Ag/S loading in your own process, a uniform single mesh grade is recommended for loading reproducibility. See the product selection guide by application.

Can I receive a test sample?

Yes, KMIZEOLITE supports the provision of samples for real-world application review. On the sample request page, please leave your application purpose (mercury adsorbent support, duct injection, etc.) and your desired particle size.

Inquiries and Sample Requests

If you are considering applying zeolite to the field of flue gas mercury adsorption and capture, please contact us through the channels below.

Notice

Applicability may vary depending on site conditions, regulations, and test results. Before actual application, a test review suited to the site conditions must be conducted first. The GRAS designation for food/general use follows 21 CFR 182.2729 (clinoptilolite), and the air-emission control use on this page is separate from the food application of that regulation. Zeolite should be understood not as a cure-all in this field, but as a support/material that supplements existing processes (ACI, WFGD, oxidation catalysts, etc.).