Absorption characteristics of elemental mercury in mercury chloride solutions

Current understanding of the ecological risk of mercury from subsea oil and gas infrastructure to marine ecosystems

Many oil and gas fields are nearing production cessation and will require decommissioning, with the preferred method being complete infrastructure removal in most jurisdictions. However, decommissioning in situ, leaving some disused components in place, is an option that may be agreed to by the regulators and reservoir titleholders in some circumstances. To understand this option's viability, the environmental impacts and risks of any residual contaminants assessed. Mercury, a contaminant of concern, is naturally present in hydrocarbon reservoirs, may contaminate offshore processing and transmission infrastructure, and can biomagnify in marine ecosystems. Mercury's impact is dependent on its speciation, concentration, and the exposure duration. However, research characterising and quantifying the amount of mercury in offshore infrastructure and the efficacy of decontamination is limited. This review describes the formation of mercury-contaminated products within oil and gas infrastructure, expected exposure pathways after environmental release, possible impacts, and key research gaps regarding the ecological risk of in situ decommissioned contaminated infrastructure. Suggestions are made to overcome these gaps, improving the in situ mercury quantification in infrastructure, understanding environmental controls on, and forecasting of, mercury methylation and bioaccumulation, and the cumulative impacts of multiple stressors within decommissioned infrastructures.

Gaseous mercury re-emission from wet flue gas desulfurization wastewater aeration basins: A review

Wet flue gas desulfurization (WFGD) simultaneously removes Hg and SO₂ from coal-fired power plant flue gas streams. Hg⁰ re-emission occurs when the dissolved Hg(II) is converted to a volatile form (i.e., Hg⁰) that can be subsequently emitted into the ambient air from WFGD wastewater aeration basins. Others have shown that Hg⁰ re-emission depends on pH, temperature, ligands (Cl, Br, I, F, SO₃^2-, SO₄^2-, NO₃^-, SCN^-, and ClO^-), O₂, minerals (Se and As), and metals (Fe and Cu) in WFGD wastewater. Still others have shown Hg⁰ re-emission restriction via inhibitor addition (adsorbents and precipitators). This is the first review that summarizes the complex and inconsistently reported Hg⁰ re-emission mechanisms, updates misconceptions related to Hg(II) complexation and reduction, and reviews applications of inhibitors that convert aqueous Hg(II) into stable solid forms to prevent gaseous Hg⁰ formation and release.

Removing and recycling mercury from scrubbing solution produced in wet nonferrous metal smelting flue gas purification process

Wet purification technology for nonferrous metal smelting flue gas is important for mercury removal; however, this technology produces a large amounts of spent scrubbing solution that contain mercury. The mercury in these scrubbing solutions pose a great threat to the environment. Therefore, this research provides a novel strategy for removing and recycling mercury from the scrubbing solution, which is significant for decreasing mercury pollution while also allowing for the safe disposal of wastewater and a stable supply of mercury resources. Some critical parameters for the electrochemical reduction of mercury were studied in detail. Additionally, the electrodeposition dynamics and electroreduction mechanism for mercury were evaluated. Results suggested that over 92.4% of mercury could be removed from the scrubbing solution in the form of a Hg-Cu alloy under optimal conditions within 150 min and with a current efficiency of approximately 75%. Additionally, mercury electrodeposition was a quasi-reversible process, and the controlled step was the mass transport of the reactant. A pre-conversion step from Hg(Tu)₄²⁺ to Hg(Tu)₃²⁺ before mercury electroreduction was necessary. Then, the formed Hg(Tu)₃²⁺ on the cathode surface gained electrons step by step. After electrodeposition, the mercury in the spent cathode could be recycled by thermal desorption. The results of the electrochemical reduction of mercury and subsequent recycling provides a practical and easy-to-adopt alternative for recycling mercury resources and decreasing mercury contamination.

One Step Interface Activation of ZnS Using Cupric Ions for Mercury Recovery from Nonferrous Smelting Flue Gas

The flue gases with high concentration of mercury are often encountered in the nonferrous smelting industries and the treatment of mercury-containing wastes. To recover mercury from such flue gases, sorbents with enough large adsorption capacity are required to capture and enrich mercury. ZnS is a cheap and readily prepared material, and even can be obtained from its natural ores. In this work, a simple controllable oxidation method-soaking in cupric solution-was developed to improve the interfacial activity of ZnS and its natural ores for Hg⁰ adsorption. The gaseous Hg⁰ adsorption capacity of ZnS was enhanced from 0.3 to 3.6 mg·g^-1 after such treatment. Further analysis indicated that a new interface rich in S^1- ions was formed and provided sufficient active sites for the chemical adsorption of Hg⁰. In addition, the cyclic Hg⁰ adsorption and recovery experiments demonstrated that the adsorption performance of spent activated-ZnS was recovered after reactivating sorbents with Cu²⁺, indicating the recovery of activated interface. Meanwhile, the high concentration of adsorbed mercury at the surface can be collected using a thermal treatment method. Utilization of raw materials from a zinc production process provides a promising and cost-effective method for removing and recovering mercury from nonferrous smelting flue gas.

Mercury adsorption and re-emission inhibition from actual WFGD wastewater using sulfur-containing activated carbon

A series of batch experiments were conducted to obtain the optimal adsorption condition for removing aqueous Hg from actual lime-based wet flue gas desulfurization (WFGD) wastewater with sulfur-containing activated carbon (SAC). The experimental results showed that SAC1 had an average 0.32 μg mg^-1 larger aqueous Hg adsorption capacity and 21% larger Hg removal than the CS₂-treated SAC1 (i.e., SAC2) in all tested pH values, confirming that greater sulfur content associated with effective sulfur functional group (i.e., elemental S) caused the larger Hg adsorption capacity. Furthermore, as increasing pH from 4 to 7, the Hg adsorption capacity of SAC1 decreased by 22% (i.e., 0.27 μg mg^-1). The equilibrium Hg adsorption capacity was well fitted with linear and Freundlich adsorption isotherms. Kinetic simulations showed that both pseudo-second order and Elovich equations could well describe the chemisorption behavior of Hg to SAC1. Thermodynamic parameter calculation confirmed that Hg adsorption by SAC1 was thermodynamically spontaneous and exothermic. Re-emission of gaseous Hg markedly decreased by 88% as SO₃^2- addition increased from 0 to 0.01 mM. Notably, by the addition of SAC1, zero re-emission of gaseous Hg was achieved. These experimental results confirm that the capture of aqueous Hg²⁺ and the inhibition of gaseous Hg⁰ re-emission can be successfully and simultaneously achieved in actual WFGD wastewater via the addition of SAC.

Transport and transformation of mercury during wet flue gas cleaning process of nonferrous metal smelting

Reducing mercury emission is hot topic for international society. The first step for controlling mercury in fuel gas is to investigate mercury distribution and during the flue gas treatment process. The mercury transport and transformation in wet flue gas cleaning process of nonferrous smelting industry was studied in the paper with critical important parameters, such as the solution temperature, Hg⁰ concentration, SO₂ concentration, and Hg²⁺ concentration at the laboratory scale. The mass ratio of the mercury distribution in the solution, flue gas, sludge, and acid fog from the simulated flue gas containing Hg²⁺ and Hg⁰ was 49.12~65.54, 18.34~35.42, 11.89~14.47, and 1.74~3.54%, respectively. The primary mercury species in the flue gas and acid fog were gaseous Hg⁰ and dissolved Hg²⁺. The mercury species in the cleaning solution were dissolved Hg²⁺ and colloidal mercury, which accounted for 56.56 and 7.34% of the total mercury, respectively. Various mercury compounds, including Hg₂Cl₂, HgS, HgCl₂, HgSO₄, and HgO, existed in the sludge. These results for mercury distribution and speciation are highly useful in understanding mercury transport and transformation during the wet flue gas cleaning process. This research is conducive for controlling mercury emissions from nonferrous smelting flue gas and by-products.