Adsorption of aqueous Hg2+ and inhibition of Hg0 re-emission from actual seawater flue gas desulfurization wastewater by using sulfurized activated carbon and NaClO
Journal
Science of the Total Environment
Journal Volume
711
Date Issued
2020
Author(s)
Abstract
The potential impacts of seawater flue gas desulfurization (SFGD) process used in coal-fired power plants have been greatly concerned because the wastewater containing Hg is directly discharged into the ocean environment without proper treatment. Furthermore, the re-emission of Hg as Hg0 to the atmosphere from SFGD wastewater caused by the reduction of aqueous Hg2+ has also been observed. This study investigated the dependence of Hg2+ adsorption behavior for sulfurized activated carbon (SAC) in actual SFGD wastewater on various influencing factors, including initial Hg2+ concentration, solution pH, contact time, temperature, and the addition of oxidant (sodium hypochlorite, NaClO). SAC exhibited greater Hg2+ adsorption than raw activated carbon at an initial Hg2+ concentration of more than 4,723 ng L?1. The Hg2+ removal efficiency of SAC was slightly larger at pH 7.0 and 8.0 than that at pH within 2.0–6.0. Hg2+ adsorption on SAC was well correlated with the linear adsorption model. Kinetic analysis results indicate that pseudo-second-order adsorption may serve as the rate-limiting reaction of Hg2+ adsorption on SAC. Thermodynamic analyses confirmed the endothermic and spontaneous adsorption behavior of Hg2+ on SAC in the seawater environment. Notably, the addition of NaClO significantly reduced the Hg2+ removal efficiency when SAC was used as the adsorbent. Nevertheless, NaClO addition also inhibited the reduction reaction of Hg2+ to Hg0 by forming strong Hg[sbnd]Cl complexes, which decreased the risk of Hg0 reemitted into the atmosphere via a SFGD system. ? 2019 Elsevier B.V.
Subjects
Activated carbon; Activated carbon treatment; Adsorption; Chlorine compounds; Coal; Coal fueled furnaces; Desulfurization; Efficiency; Flue gases; Flues; Fossil fuel power plants; Gas plants; Mercury (metal); Seawater; Sodium compounds; Thermoanalysis; Wastewater treatment; Coal-fired power plant; Flue gas desulfurization; Rate-limiting reaction; Re-emission; Removal efficiencies; Sodium hypochlorites; Spontaneous adsorption; Thermo dynamic analysis; Mercury compounds; activated carbon; hypochlorite sodium; mercury; sea water; sulfurized activated carbon; unclassified drug; activated carbon; adsorption; coal-fired power plant; concentration (composition); emission; inhibitor; mercury (element); oxidant; pH; sodium chloride; temperature effect; wastewater; adsorption; air pollution control; aqueous solution; Article; atmosphere; chemical reaction; contact time; controlled study; desulfurization; heavy metal removal; kinetics; pH; priority journal; rate limiting reaction; reemission; seawater flue gas desulfurization; temperature; thermodynamics
Type
journal article