Influence of sulfide, chloride and dissolved organic matter on mercury adsorption by activated carbon in aqueous system
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Sustainable Environment Research
(2020) 30:22
RESEARCH
Open Access
Influence of sulfide, chloride and dissolved organic matter on mercury adsorption by activated carbon in aqueous system Chi Chen, Yu Ting, Boon-Lek Ch’ng and Hsing-Cheng Hsi*
Abstract Using activated carbon (AC) as thin layer capping to reduce mercury (Hg) released from contaminated sediment is a feasible and durable remediation approach. However, several aqueous factors could greatly affect the Hg fate in the aquatic system. This study thus intends to clarify the influences on Hg adsorption by AC with the presence of sulfide, dissolved organic matter (DOM), and chloride. The lab-scale batch experiments were divided into two parts, including understanding (1) AC adsorption performance and (2) Hg distribution in different phases by operational definition method. Results showed that the Hg adsorption rate by AC was various with the presence of sulfide, chloride, and DOM (from fast to slow). Hg adsorption might be directly bonded to AC with Hg-Cl and Hg-DOM complexes and the rate was mainly controlled by intraparticle diffusion. In contrast, “Hg + sulfide” result was better described by pseudo-second order kinetics. The Hg removal efficiency was 92–95% with the presence of 0–400 mM chloride and approximately 65–75% in the “Hg + sulfide” condition. Among the removed Hg, 24–29% was formed into aqueous-phase particles and about 30% Hg was adsorbed on AC with 2–20 μM sulfide. Increasing DOM concentration resulted in more dissolved Hg. The proportion of dissolved Hg increased 31% by increasing DOM concentration from 0.25 to 20 mg C L− 1. Simultaneously, the proportion of adsorbed Hg by AC decreased by 47%. Overall, the presence of chloride increases the Hg adsorption by AC. In contrast, the presence of sulfide and DOM causes a negative effect on AC adsorption. Keywords: Mercury, Activated carbon, Chloride, Sulfide, Dissolved organic matter
Introduction Mercury (Hg) has been known as one of the most toxic heavy metals to human beings and living organisms [1–3]. Despite the decreasing industrial use of Hg in the past recent years, human activities including fossil fuel combustions, gold-mining, and manufacturing industries have contributed to the increased Hg levels in the atmosphere and aquatic environments [4]. The released Hg could ultimately transport to aquatic system and accumulate in sediment through wet or dry deposition. Thus, the formation and bioaccumulation of methylmercury (MeHg) formed from inorganic Hg under reducing conditions in sediment could put a serious threat to aquatic ecosystems [5, 6]. * Correspondence: [email protected] Graduate Institute of Environmental Engineering, National Taiwan University, Taipei 10617, Taiwan
Several technical challenges still remain to remediate contaminated sediment, as the traditional approaches could not achieve risk reduction goals for human health and ecosystem protection and may even cause secondary pollution [7–9]. For example, dredging followed by ex-situ approaches has been typically used becau
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