『Abstract
The uptake and release of trace metals (Cu, Ni, Zn, Cd, and Co)
in estuaries are studied using river and sea end-member waters
and suspended particulate matter (SPM) collected from the Changjiang
Estuary, China. The kinetics of adsorption and desorption were
studied in terms of environmental factors (pH, SPM loading, and
salinity) and metal concentrations. The uptake of the metals studied
onto SPM occurred mostly within 10 h and reached an asymptotic
value within 40 h in the Changjiang Estuary. As low pH river water
flows into the high pH seawater and the water become more alkaline
as it approaches to the seaside of estuary, metals adsorb more
on SPM in higher pH water, thus, particulate phase transport of
metal become increasingly important in the seaward side of the
estuary. The percentage of adsorption recovery and the distribution
coefficients for trace metals remained to be relatively invariable
and a significant reduction only occurred in very high concentrations
of metals (>0.1 mg L-1). The general effect of salinity
on metal behavior was to decrease the degree of adsorption of
Cu, Zn, Cd, Co, and Ni onto SPM but to increase their adsorption
equilibrium pH. The adsorption-desorption kinetics of trace metals
were further investigated using Kurbatov adsorption model. The
model appears to be most useful for the metals showing the conservative
behavior during mixing of river and seawater in the estuary. Our
work demonstrates that dissolved concentration of trace metals
in estuary can be modeled based on the metal concentration in
SPM, pH and salinity using a Kurbatov adsorption model assuming
the natural SPM as a simple surfaced molecule.
Keywords: Adsorption; Desorption; Trace metals; Distribution coefficient;
The Changjiang Estuary』
『要旨
河口での微量金属(銅・ニッケル・亜鉛・カドミウム・コバルト)の吸収と放出が、中国の長江河口から採取した海水端成分と懸濁物(SPM)を用いて研究されている。吸着と脱着のカイネティックスが環境要因(pHおよびSPM負荷量および塩分)および金属濃度に関して研究された。長江河口でのSPMについて研究した金属の吸収はほとんど10時間以内に生じ、40時間以内に漸近線的な値に達した。低pHの河川水が高pHの海水へ流入し、河口の海側に近づくにつれて水がさらにアルカリ性になると、金属はより高いpHの水中でSPMにさらに吸着し、金属の粒子相輸送が河口の海側でだんだんと重要になる。微量元素に対する吸着回収率の百分率と分配係数は比較的変わらないままであり、非常に高濃度(>0.1
mg/L)の金属でのみ顕著な減少が起こった。金属の挙動に対する塩分の一般的な影響は、SPMへの銅・亜鉛・カドミウム・コバルト・ニッケルの吸着の割合を減少させることであったが、それらの吸着平衡のpHを増加させた。微量金属の吸着−脱着カイネティックスはKurbatov吸着モデルを用いてさらに研究された。このモデルは、河口での河川水と海水の混合時において保存されやすい挙動を示す金属に対してもっとも有用であると思われる。我々の研究は、河口での微量金属の溶存濃度が、単純な表面分子として天然SPMを仮定するKurbatovの吸着モデルを用いることで、SPMの金属濃度とpHと塩分を基にしてモデル化できることを示している。』
Introduction
Sample collection and methods
Sampling and sample characterization
Metal solution preparation
Kinetic equilibrium experiments
Batch sorption experiments
Sample analysis
Results
Kinetic equilibrium time
Adsorption kinetics
Desorption kinetics
Adsorption model of trace metals
Discussion
Effect of pH
Distribution coefficient K and adsorption density
Irreversibility of adsorption-desorption
Application of the model
Conclusion
Acknowledgments
Appendix
References