Bismuth Hydroxide and Organic Matter Interactions

Bismuth hydroxide is a non-toxic bismuth compound used in many pharmaceuticals and in bacterial resistance studies. It is widely used in antidiarrheal medications, especially for oral use. It also is used as an adjuvant for chemotherapy in a range of cancers.

Biologically, bismuth is a highly stable and non-toxic metal that is next to lead in the periodic table. It has a low melting point and is resistant to the toxic effects of chlorine and iodine.

It is a hard, brittle, reddish-colored metal that is in oxidation state +3 when in solid form. It dissolves in nitric acid and in hot sulfuric acid. It can be reacted with halogens to form bismuthine, BiH3, which is an endothermic compound that has a low boiling point of 17@C (62.6@F).

Bismuth oxidizes to bismuth subnitrate in acidic medium (H2SO4), but it does not dissolve in the neutral pH of water and should be dissolved with an acid such as citrate buffer solution or NaOH. It does not bind to natural organic matter and is generally inert.

We investigated the interactions of bismuth and natural organic soil material using a combination of batch equilibration experiments and EXAFS spectroscopy. The results indicate that the equilibration of bismuth with organic matter is a complexation reaction and involves a cationic ion competing with the metal for the complexation sites in the aqueous phase. Our data support the use of geochemical models such as WHAM-Model VII, NICA-Donnan and SHM to predict metal binding kinetics in organic soils.

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