Bismuth (Bi) in Water Treatment
Quick Answer
Bismuth (Bi) is a post-transition metal with atomic number 83. PubChem lists its standard state as solid and its relative atomic mass as 208.98040.
Bismuth is not a common target in ordinary water treatment but may occur in mining or specialized industrial wastewater. Total versus dissolved concentration, oxidation state, pH and complexing agents should be measured before evaluating precipitation, adsorption, ion exchange or membranes.
Interesting Facts
- Bismuth crystals can develop rainbow colours from a very thin oxide layer, not from pigments in the metal.
- Like water, bismuth expands when it freezes—an unusual behaviour among materials.
- It is not a routine drinking-water target; industrial context and dissolved-versus-particulate analysis should justify any treatment.
Water-treatment Design Implications
An element name alone is not enough to select treatment equipment. Confirm chemical form or speciation, total and dissolved concentration, pH, alkalinity, competing ions and the product-water target. Send the water-analysis results to Watermart to identify additional testing and shortlist processes before equipment is specified.
Summary Data Sources
Bismuth (Bi)
1. Basic Information
| Atomic Number | 83 |
| Symbol | Bi |
| Atomic Weight | 208.9804 g/mol |
| Category | Heavy metal |
2. Physical and Chemical Properties
Bismuth is a silvery white metal with slight shades of pink. It is the most diamagnetic metal and has the lowest thermal conductivity among all metals except mercury. Bismuth has high electrical resistance and the greatest Hall effect of all metals. Bismuth is stable to oxygen and water, but soluble in concentrated nitric acid. All bismuth salts form insoluble compounds when put into water.
3. Presence in Water and Health Effects
Bismuth is rarely found in significant amounts in drinking water. However, contamination may occur from mining or industrial activities. Health effects from exposure to bismuth are generally mild compared to other heavy metals. Large doses may cause mild kidney damage. Symptoms of bismuth poisoning may include nausea, loss of appetite, headaches, and discolored gums. Bismuth is considered one of the least industrially toxic heavy metals.
4. Water Treatment Applications and Removal Methods
Although bismuth is rarely a major problem in water treatment, several methods can be used to remove it if needed:
- Ion exchange: Weakly acidic cation exchange resins such as those recommended by DuPont can be used to remove bismuth cations from water at neutral pH.
- Chemical precipitation: Bismuth can be precipitated as hydroxide at high pH.
- Adsorption: Activated carbon or special adsorbents can remove some forms of dissolved bismuth.
- Membrane filtration: Technologies such as nanofiltration or reverse osmosis can remove bismuth ions.
Under acidic conditions, bismuth can form anionic complexes that can be removed with anion exchange resins. Cation exchange resins can also be used to capture bismuth cations in dilute acid solutions.
5. Industrial Use in Water Treatment
Bismuth itself is rarely used directly in water treatment processes. However, some bismuth compounds have limited applications:
- Bismuth subnitrate is sometimes used as a coagulant in wastewater treatment.
- Some bismuth-based catalysts have been investigated for the degradation of organic pollutants in water.
8. Environmental Impact and Sustainability Considerations
Bismuth is generally considered to have a relatively low environmental impact compared to other heavy metals. However, some considerations include:
- Bioaccumulation: Although less than other heavy metals, bismuth can accumulate in aquatic organisms.
- Persistence: Bismuth compounds can persist for a long time in the environment.
- Mining: Extraction of bismuth may cause local environmental impacts.
- Recycling: Efforts to recycle bismuth from electronic and medical products can reduce the need for new mining.