Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Exchange of heavy metal (Cd) at the sediment-water interface affected by salinity, pH, andhydrodynamic based on one-dimensional soil column experiments
Zhirui Zhang 1, Sha Lou *12, Shuguang Liu *12, Larisa Dorzhievna Radnaeva3，Elena Nikitina3

1. Department of Hydraulic Engineering, Tongji University, Shanghai, China2. Key Laboratory of Yangtze River Water Environment and Ministry of Education, Tongji University, Shanghai, China
3. Laboratory of chemistry of natural systems, Baikal Institute of Nature Management of Siberian branch of the Russian Academy of sciences,
Ulan-Ude, Republic of Buryatia, Russia.

ABSTRACT

frequent recently due to the density of population and the increase ofhuman activities, which lead to the degradation of wetland resources
and cause serious damage to the ecological environment(Fan 2021).
Since 1979, the area of natural wetlands in the Yangtze River Estuary
in China has decreased by a total of 163km2(Sun et al. 2017; Zhang
2018). In addition, a large amount of industrial and municipal sewage isdischarged into the inshore area of the Yangtze River Estuary every
year, especially heavy metal pollutants including Hg, Cd, Pb, Cr, Cu
and metal-like As. These heavy metals have high biological toxicity
and strong accumulation, which are harmful to the ecologicalenvironment of the Yangtze Estuary wetland(Adugna 2020) and theregional environment(Zhang, 1999; Fan et al. 2020;Li et al. 2020).
According to the field investigations, Cd is the main contributor topotential ecological risks in the Yangtze Estuary wetlands (Uthe et al.
1971;Wang et al. 2015; Han et al. 2017; Sun et al. 2018;He et al. 2018;
Li et al. 2020; Wang et al. 2021; Zhanget al. 2021).
Heavy metals in the wetland water environment usuallyaccumulate and enrich in sediments accompanied by the complex
migration and biochemical processes(Wang et al. 2015). Under certain
conditions, especially when the environment is disturbed, heavy metals
will be desorbed again from the sediment and released into the watercolumn, resulting in the "secondary pollution"(Ampofo 2018; Zhang etal. 2020). Hassimi (Hassimi et al. 2019)found that the oxidation ofsulfides caused by the increase of oxygen content in water can cause
heavy metals to be desorbed from sediments to the water, which
aggravated the risk of heavy metals in the area. During flood, thesurface sediment at the bottom of river was suspended with the releaseof heavy metals, which caused abnormal heavy metal content in thelower reaches in a short time(Haag et al. 2001). Huang et al.(Huang etal. 2012) used annular flume to reproduce the resuspension
phenomenon of heavy metals in the sediments of Liangshui River, andsummarized the change law of flow velocity-suspended particulatematter-heavy metals. Hao (Hao 2012) used indoor flume to study theadsorption and desorption of heavy metals under the influence of wave
and current, and pointed out that the chemical oxidation process of
reduced sediments during resuspension was an important inducement topromote the transformation of heavy metals to dissolved state. Bi andZhao(Bi et al. 2011;Zhao et al. 2011) used particle entrainment
simulator (PES) to study the resuspension law of heavy metals under
different disturbance intensity and different water quality, andThe migration and enrichment of heavy metals have great influence on
environment and ecosystem due to the increasing biological toxicity,
resulting in serious environmental risk. This paper focuses on thevertical distribution of heavy metals in the water environment systemand the migration of heavy metals at the sediment-water interface. It
aims to reveal the law of adsorption and desorption of heavy metals atthe interface of different media under the influence of water quality
factors and to propose an improvement method to describe theisothermal adsorption at the interface including time factor. Based onfield investigation results in the Yangtze River Estuary, a series of soilcolumn experiments were setup to analyze the distribution of heavy
metal cadmium (Cd) affected by multi-water hydraulic factors (salinity,pH and hydrodynamic) and the adsorption and desorption mechanism
at the sediment-water interface. The experimental results were fitted by
two-constant rate model, Elovich model the pseudo-first-order kinetic
model and the pseudo-second-order kinetic model to reproduce theisothermal desorption at the interface. Moreover, pseudo-first-orderkinetic model and pseudo-second-order kinetic model were used todescribe the adsorption and desorption of Cd under the influence ofhydrodynamics, and the hysteresis mechanism of heavy metal
desorption sequence under the influence of hydrodynamics is proposed.
Finally, the hydrodynamic processes of adsorption and desorption of
Cd at the sediment-water interface under the influence of salinity, pHand hydrodynamic factors were discussed, and a prediction curve wasproposed. Results in this paper can be used as the verification andcorrection of desorption kinetics model, which can also provide
effective information for the research of heavy metal migration,
adsorption and desorption under complex conditions.

KEY WORDS: heavy metals, soil column experiments, sedimentwater interface, adsorption and desorption

INTRODUCTION
Wetland is the transitional area between terrestrial ecosystem andaquatic ecosystem, which is important for the environment andecosystem. However, environmental pollution occurs more and more

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