The preferential retention of VIZn over IVZn on birnessite during dissolution/desorption

Publication date: 1 September 2018
Source:Applied Clay Science, Volume 161
Author(s): Zhangjie Qin, Hui Yin, Xiaoming Wang, Qin Zhang, Shuai Lan, Luuk K. Koopal, Lirong Zheng, Xionghan Feng, Fan Liu
Zn is a common heavy metal in soils and sediments. In this study, the release behaviors of octahedral (^VIZn) and tetrahedral (^IVZn) Zn complexes on synthesized hexagonal birnessite were explored by solution chemistry method in combination with spectroscopic analysis. In acidic dissolution processes, the release of adsorbed Zn²⁺ from birnessite occurred into two stages: in the first stage, ~60% of Zn²⁺ was desorbed rapidly, with only 8% of Mn being released, and the ratio of ^VIZn/^IVZn increased with time; in the second stage, the residual Zn²⁺ was mostly ^VIZn and released slowly at a nearly constant rate until complete dissolution of the matrix mineral was observed. During desorption of Zn²⁺ by Pb²⁺, the ratio of ^VIZn/^IVZn on birnessite also increased, while the residual percentage of ^VIZn remained nearly constant. However, it is known that ^IVZn-triple corner-sharing (TCS) is more stable than ^VIZn-TCS, suggesting that part of the remaining ^IVZn-TCS on birnessite might transform to ^VIZn-TCS immediately when ^VIZn-TCS is replaced by H⁺ or Pb²⁺. Additionally, the possible distribution of Mn³⁺ and ^IVZn or the partial charge compensation by protons can lead to the preferential retention of ^VIZn on birnessite or the preferential re-adsorption of ^VIZn at the new edge sites. These results can provide new insights into the geochemical behavior of Zn²⁺ contaminant in soil and aquatic environments.

Graphical abstract

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