This chapter provides an example of the 3-D TOPOS visualization approach to a real-world application of metal-ligand complexation. It utilizes the Multi TOPOS software, an extension of Complexation TOPOS to include multi-metal/multi-ligand mixtures. It examines the impact of toxic chromium and manganese in effluents from Bangladesh leather tanneries before completion of a water treatment plant. Effluents were collected from a newly established leather processing district in the Savar suburb of Dhaka, Bangladesh. Trace metal concentrations were determined by both atomic absorption spectroscopy (AAS) and inductively coupled plasma spectroscopy (ICP). The concentrations of both metal ions dropped quickly from the highest value at the discharge point to ever decreasing values with distance from their initial release. Thinking that naturally occurring humic substances might be responsible for the attenuation, we extracted and purified humic acid from the effluent. It was compared with humic acid from rural soils in NE Bangladesh. Spectral shifts in FTIR and EDX spectra supported the incorporation of metals into humic acid’s organic framework. Mathematical modeling was performed on a system comprised of Cr3+, Mn2+, and a mixture of six organic ligands that mimic humic acid binding sites. At the effluent’s ambient pH of 8.5, essentially all of the Cr was precipitated as Cr(OH)3(s). Under the same conditions, Mn was bound predominantly to the phthalate (36.7%) and 1,10-phenanthroline (57.9%) components of the humic acid mimic mixture. These results suggest that agglomeration took place between Cr(OH)3(s) and colloidal humic acid. Because Mn2+ was bound to humic sites, it became incorporated in the coagulated assemblies. The sandy bed of the drainage channel subsequently acted as a filter. Levels of Cr and Mn present in the discharge channel were attenuated to near drinking water standards by the time the receiving river was reached.
© 2021 Ayesha Sharmin, Md Mainul Huda, Mahabub Islam, Md Mainul Hossain, Garon C. Smith, Sohidul Islam, Mohammad Moshiur Rahman, Mohammad Hossain Shahriare, Mohsin Kazi, Mohammad Jakariya
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Sharmin, Ayesha; Huda, Md Mainul; Islam, Mahabub; Hossain, Md Mainul; Smith, Garon C.; Islam, Sohidul; Rahman, Mohammad Moshiur; Shahriare, Mohammad Hossain; Kazi, Mohsin; and Jakariya, Mohammad, "Chapter 2.3: Natural Attenuation of Chromium and Manganese from a Bangladesh Tannery Effluent Via Humic Substance Complexation: Field, Laboratory and Modeling Studies" (2021). Water Topos: A 3-D Trend Surface Approach to Viewing and Teaching Aqueous Equilibrium Chemistry. 7.