长江河口及邻近海域表层沉积物中铁溶解和磷释放活性的动力学表征

肖丽; 王迪; 马伟伟; 李文君; 李铁; 朱茂旭

doi:10.3969/j.issn.0253-4193.2019.12.001

长江河口及邻近海域表层沉积物中铁溶解和磷释放活性的动力学表征

doi: 10.3969/j.issn.0253-4193.2019.12.001

1. 中国海洋大学化学化工学院，山东青岛 266100

基金项目: 国家自然科学基金（41576078，41776085）；国家重点研发计划项目（2016YFA0601301）。

详细信息

作者简介:
肖丽（1991—），女，山西省岚县人，主要从事海洋化学研究。E-mail: 464690782@qq.com

通讯作者:
朱茂旭（1967—），男，湖南省澧县人，教授，主要从事海洋化学研究。E-mail: zhumaoxu@ouc.edu.cn

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出版历程
- 收稿日期: 2018-10-20
- 修回日期: 2019-12-17
- 网络出版日期: 2021-04-21
- 刊出日期: 2019-12-25

Kinetic characterization of reactivity of iron dissolution and phosphorus release in surface sediments of the Changjiang (Yangtze) River Estuary and the adjacent East China Sea

College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China

摘要

摘要: 运用溶解动力学实验及活性连续体模型表征了长江河口至东海邻近海域表层沉积物中铁(Fe)和磷(P)的活性。通过动力学数据拟合得到了活性组分的理论含量m₀和表观速率常数k。结果表明，Fe(Ⅱ)普遍存在于表层沉积物中，这应是高活性有机络合态Fe(Ⅲ)絮凝/沉淀到沉积物中后快速还原的结果。沉积物中黏土及总有机碳（TOC）含量对Fe(Ⅱ)的m₀及其k值起重要控制作用。从长江河口至邻近海域沉积物中Fe(Ⅱ)均以FeCO₃形态为主，FeCO₃的溶解及与之相结合磷(主要为交换态P和自生P)的释放导致Fe(Ⅱ)和P具有相似的溶解动力学特征。与吸附于Fe(Ⅱ)矿物相的P相比，与Fe(Ⅱ)矿物相共沉淀的P的m₀较高，但k较低。与TOC含量较低的粗粒沉积物中的Fe(Ⅲ)相比，TOC含量较高的细粒沉积物中Fe(Ⅲ)的m₀值较小，但k值较大。以上特征是Fe不同的氧化还原过程导致的。Fe(Ⅲ)氧化物的含量(m₀)和活性(k)总体上控制着与之相结合P的含量(m₀)及溶解活性(k)。虽然传统活性Fe形态分析未能揭示出长江河口沉积物中活性Fe的富集作用，但溶解动力学表征结果表明，Fe的絮凝/沉淀导致河口沉积物中活性Fe的明显富集，且该过程主要发生在盐度明显增加的低盐度河口区。
- 铁 /
- 磷 /
- 活性 /
- 溶解动力学 /
- 絮凝 /
- 沉淀 /
- 长江河口 /
- 东海
Abstract: Kinetic dissolution and the reactive continuum model were combined to characterize the reactivity of iron (Fe) and phosphorus (P) in surface sediments of the Changjiang (Yangtze) River Estuary and the adjacent East China Sea. Two kinetic parameters, i.e., theoretical amounts (m₀) and apparent rate constant (k) of reactive Fe, were extracted by fitting kinetic dissolution data to the reactive continuum model. Results showed that Fe(Ⅱ) phases occurred in all surface sediments studies, which could be ascribed to rapid reduction of highly reactive organic-bound Fe(Ⅲ) flocculated/precipitated to the sediments. It is inferred that Fe(Ⅱ) occurs mainly as FeCO₃ in both the Changjiang (Yangtze )River Estuarine sediments and the adjacent East China Sea sediments. The m₀ and k values of Fe(Ⅱ) were controlled mainly by total organic carbon (TOC) contents and clay fractions. Simultaneous release of Fe(Ⅱ) and associated P (mainly exchangeable P and authigenic P) resulted in similar pattern of dissolution kinetics. Relative to P adsorbed on surfaces of Fe(Ⅱ) solid phases, coprecipitated P with Fe(Ⅱ) phases has higher m₀ but lower k. In fine-grained sediments with high TOC contents, Fe(Ⅲ) oxides have lower m₀ values but higher k in comparison with those in coarse-grained sediments with lower TOC contents, which is caused by different processes of Fe redox cycling. Overall, the dissolution reactivity of P associated with Fe(Ⅲ) phases is largely controlled by the reductive reactivity of Fe(Ⅲ) phases. Our kinetic characterization indicates that flocculation/precipitation has caused reactive Fe enrichment in the estuarine sediments, occurring mainly in a narrow zone of low salinity, but the enrichment could not be revealed by conventional Fe speciation.
- iron /
- phosphorus /
- reactivity /
- dissolution kinetics /
- flocculation /
- precipitation /
- Changjiang(Yangtze) River Estuary /
- East China Sea

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图 1 沉积物采样站位图

Fig. 1 Stations of sediment sampling

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图 2 表层沉积物组成分类（根据碎屑沉积物分类方法^[27]）

Fig. 2 Classification of surface sediments (according to classification of clastic sediments^[27])

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图 3 pH 3.0盐酸溶液中Fe(Ⅱ)及Fe(Ⅱ)结合态P（Fe(Ⅱ)-P）的溶解动力学曲线，圆点为实测数据，曲线为模型拟合线（a，b）；各站位动力学参数（m₀为酸可溶解释放的理论含量，k为溶解速率常数）、底水盐度、黏土比例及总有机碳含量（c～f）。红色柱状图表示该站位（C3、C4、C6和C7）的动力学参数与其他站位具有明显差异

Fig. 3 Time dependent Fe(Ⅱ) dissolution and simultaneous release of Fe(Ⅱ)-associated phosphorus in HCl solution at pH 3.0, dots: measured results, curves: fitting to the reactive continuum model (a, b). Kinetic parameters (theoretical amounts m₀ and apparent rate constant k) together with bottom-water salinity, clay fraction, and total organic carbon content at each sampling site (c–f). Obvious differences of kinetic parameters at sites C3, C4, C6, and C7 in comparison with other sites are indicated by red color column

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图 4 pH 3.0的盐酸+抗坏血酸溶液中Fe(Ⅲ)还原性溶解及Fe(Ⅲ)结合态P（Fe(Ⅲ)-P）溶解动力学曲线，圆点为实测数据，曲线为模型拟合线（a，b）；各站位动力学参数（酸可溶解释放的理论含量m₀，溶解速率常数k）、底水盐度、黏土比例及总有机碳含量（c～f）。红色柱状图表示该站位（C3、C4、C6和C7）的动力学参数与其他站位具有明显差异

Fig. 4 Time dependent Fe(Ⅲ) reductive dissolution and simultaneous release of Fe(Ⅲ)-associated phosphorus in HCl+ascorbic acid solution at pH 3.0, dots: measured results, curves: fitting to the reactive continuum model (a, b). Kinetic parameters (theoretical amounts m₀ and apparent rate constant k) together with bottom-water salinity, clay fraction and total organic carbon content at each sampling site (c−f). Obvious differences of kinetic parameters at sites C3, C4, C6, and C7 in comparison with other sites are indicated by red color column

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图 5 pH 7.5抗坏血酸缓冲溶液中Fe(Ⅲ)的还原性溶解动力学曲线，圆点为实测数据，曲线为模型拟合线（a）；各站位动力学参数（酸可溶解释放的理论含量m₀，溶解速率常数k）、底水盐度、黏土比例及总有机碳含量（b，c）。红色柱状图表示该站位（C3、C4、C6和C7）的动力学参数与其他站位具有明显差异

Fig. 5 Time dependent Fe(Ⅲ) reductive dissolution in ascorbic acid solution buffered at pH 7.5 (a), dots: measured results, curves: fitting to the reactive continuum model. Kinetic parameters (theoretical amounts m₀ and apparent rate constant k) together with bottom-water salinity, clay fraction, and total organic carbon content at each sampling site (b, c). Obvious differences of kinetic parameters at sites C3, C4, C6, and C7 in comparison with other sites are indicated by red color column

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图 6 Fe(Ⅱ)-m₀及Fe(Ⅱ)-k与总有机碳含量和黏土比例之间的相关性

m₀为酸可溶解释放的理论含量，k为表观溶解速率常数k

Fig. 6 Correlations of Fe(Ⅱ)-m₀ with total organic carbon (a) and clay fraction (b), correlations of Fe(Ⅱ)-k with total organic carbon (c) and clay fraction (d)

m₀ is theoretical amounts, k is apparent rate constant

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图 7 Fe(Ⅱ)和Fe(Ⅱ)结合态P动力学释放量之间的对应关系（a）以及Fe(Ⅱ)-P-m₀与Fe(Ⅱ)-m₀、Ex-P和Au-P之间的相关性（b～d）

m₀为酸可溶解释放的理论含量；Ex-P为交换态或弱吸附态磷P；Au-P为自生磷

Fig. 7 Correlations of kinetic Fe(Ⅱ) dissolution with simultaneous P release (a), and correlations of Fe(Ⅱ)-P-m₀ with Fe(Ⅱ)-m₀, Ex-P and Au-P(b–d)

m₀ is theoretical amounts; Ex-P is exchangeable or weakly adsorbed phosphorus; Au-P is authigenic phosphorus

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图 8 Fe(Ⅲ)-P-m₀与Fe(Ⅲ)-m₀和Fe-P与Fe(Ⅲ)-P-m₀之间的相关性

Fe(Ⅲ)-P为与Fe(Ⅲ)同时释放的P；Fe-P为Fe结合态P；m₀，酸可溶解释放的理论含量

Fig. 8 Correlations of Fe(Ⅲ)-P-m₀ versus Fe(Ⅲ)-m₀ and Fe-P versus Fe(Ⅲ)-P-m₀

Fe(Ⅲ)-P is phosphorus that is simultaneously released with Fe(III) reductive dissolution ; Fe-P is Fe-associated phosphorus; m₀ is theoretical amounts

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图 9 各站位 [Fe(Ⅱ)-m₀ + Fe(Ⅲ)-m₀]/Fe_HR (a) 或7.5-Fe(Ⅲ)-m₀/Fe_HR (b) 以及底水盐度、黏土比例、总有机碳含量

m₀为酸可溶解释放的理论含量；Fe_HR为总活性铁Fe；7.5-Fe(Ⅲ)-m₀为pH为7.5条件下可还原性溶解的Fe(Ⅲ) ；红色柱状图表示该站位（C3、C4、C6和C7）的[Fe(Ⅱ)-m₀ + Fe(Ⅲ)-m₀]/Fe_HR]或7.5-Fe(Ⅲ)-m₀/Fe_HR比值与其他站位具有明显差异

Fig. 9 [Fe(Ⅱ)-m₀ + Fe(Ⅲ)-m₀]/Fe_HR] ratio (a) or 7.5-Fe(Ⅲ)-m₀/Fe_HR ratio (b) together with bottom-water salinity, clay fraction, and total organic carbon content at each sampling site.

m₀ is theoretical amounts; Fe_HR is total amount of highly reactive Fe; 7.5-Fe(III)-m₀ is Fe(III) that is capable of reductive dissolution at pH 7.5; Obvious differences of [Fe(Ⅱ)-m₀ + Fe(Ⅲ)-m₀]/Fe_HR] ratio (a) or 7.5-Fe(Ⅲ)-m₀/Fe_HR ratios at sites C3, C4, C6, and C7 in comparison with other sites are indicated by red color column

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表 1 采样点及沉积物相关物理和化学参数

Tab. 1 Physical and chemical parameters of sampling sites and sediment samples

参数	C2	C3	C4	C6	C7	C8	A6-1	A6-2	A6-4	A6-6	A6-8	A6-10
底水盐度	0.15	0.14	0.14	0.14	0.15	0.25	4.76	14.41	21.28	31.21	32.17	32.36
TOC/%	0.39	0.12	0.17	0.12	0.15	0.63	0.43	0.73	0.57	0.64	0.39	0.33
黏土/%	19.6	6.07	8.73	5.32	4.41	28.2	19.6	30.1	20.3	23.0	11.6	9.41
粉砂/%	73.4	18.1	23.1	12.5	11.0	71.3	53.6	69.8	73.3	74.7	18.8	17.1
砂/%	7.05	75.8	68.2	82.2	84.6	0.47	26.7	0.09	6.38	2.36	69.6	73.5
Fe_T/%	3.28	2.43	2.48	2.67	3.11	4.31	3.24	4.64	3.74	4.06	2.97	2.60
Fe_HR/μmol·g⁻¹	188	193	202	190	203	205	228	206	212	212	191	146
Ex-P/μmol·g⁻¹	1.13	0.85	0.87	0.87	0.95	1.67	1.21	1.28	1.39	1.66	1.24	1.27
Fe-P/μmol·g⁻¹	3.90	10.8	6.91	8.56	12.4	7.41	4.24	3.94	3.34	2.26	4.00	3.53
Au-P/μmol·g⁻¹	4.22	1.92	2.74	2.49	1.94	5.13	4.09	5.75	4.43	4.66	2.47	2.28
注：Fe_T代表总Fe含量；Fe_HR代表总活性Fe；Ex-P代表交换态或弱吸附态P；Fe-P代表Fe结合态P；Au-P代表自生P。

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