Adsorption-desorption characteristics of typical heavy metal pollutants in submerged zone sediments: a case study of the Jialu section in Zhengzhou, China.

In recent years, the accumulation ability of heavy metals in sediment has become a key indicator for sediment pollution prevention and control. The adsorption-desorption processes of typical heavy metal pollutants in sediments under different conditions were explored and relied in this article. In addition, different binary competitive adsorption systems were designed to study the competitive adsorption properties of heavy metal contaminants, The quasi-secondary kinetic model simulated the adsorption kinetic process. The sediment adsorption rates for heavy metals were (in descending order) Cu, Pb, Cd, Zn. The Elovich equation simulated the desorption kinetics process better, and the sediment desorption rates for heavy metals were (in descending order) Cd, Cu, Zn, Pb. The average free adsorption energy E of heavy metals was within the range of 8-16 kJ∙mol-1. After the removal of organic matter, the ability of the sediment to sequester heavy metals decreases, The binary competitive adsorption results showed that the presence of interfering ions had the greatest effect on Cd and the least effect on Pb. The adsorption and desorption of the four heavy metals by the sediments in the submerged zone increased with the increase of temperature, and the ratio of desorption to adsorption also increased therewith: the adsorptions of heavy metals by the sediments were all spontaneous processes (under heat absorption reactions). The presence of organic matter can increase the ability of the sediment to sequester Cd, Pb, Cu, and Zn. Additionally, heavy metals exhibited significant selective adsorption properties.

Spatial distribution of heavy metal contaminants: The effects of water-sediment regulation in the Henan section of the Yellow River.

Water-sediment regulation (WSR) affects sediment transport in the middle and lower reaches of the Yellow River through periodic interception of sediment by dams and alteration of downstream flow rates, which leads to redistribution and recycling of elements. In this study, based on the evaluation of seven heavy metals (V, Cr, Ni, Co, Cu, Zn, and Cd) in water, sediment and suspended particulate matter (SPM) in the Henan section of the Yellow River, the effects of WSR on the redistribution and risk of release of metals to the downstream aquatic environment were investigated, and the range of impact and pollution sources were determined. Dissolved metals were well below guideline values for water quality, but Cd, Cr, and Cu were enriched in the sediments, especially in the reservoir, and the pollution load index (PLI) results indicated that the contamination in the study area remained very low. The level of contamination was decreased, and metals migrated downstream after WSR. The chemical speciation of metals indicates that anthropogenic input of metals occurs in upstream tributaries, and the risk of release of metals in the sediments increases after WSR, but the spatial distribution of the risk is more homogeneous. The distribution coefficient explains the distribution pattern of pollution, where SPM carries pollutants to the downstream while formed surface sediments through natural deposition during the sand-discharge stage. Based on geological and field investigations, upstream gold mining and downstream riverbank cultivation activities in the study area are potential sources of Cu and Cd pollution. These findings are crucial to the better understanding of patterns of metal release from artificial impoundments in river systems and provide a theoretical basis for ecological development in the Yellow River Basin.