Gold (Au) in Water Treatment
Quick Answer
Gold (Au) is a transition metal with atomic number 79. PubChem lists its standard state as solid and its relative atomic mass as 196.96657.
Gold 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
- Gold is so malleable that a tiny mass can be beaten into an extremely thin sheet.
- Gold metal is poorly soluble, but mining chemistry can hold gold in soluble complexes—proof that “the element” and its chemical form are different treatment questions.
- In mine water, recovering a valuable metal and destroying or managing the complexing reagent may both matter.
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
Gold (Au)
1. Basic Information
| Atomic Number | 79 |
| Symbol | Au |
| Atomic Weight | 196.97 g/mol |
| Category | Transition metal |
2. Physical and Chemical Properties
Gold is a yellow-colored metal that is highly malleable and ductile. It is an excellent conductor of electricity and heat. Gold is inert and resistant to most chemical reagents. In colloidal form, gold can be red, purple, or black. Pure gold is very soft so it is usually alloyed with other metals to increase its strength.
Gold has a melting point of 1064°C and a boiling point of 2856°C. Its density is 19.3 g/cm3 at room temperature. Gold does not oxidize in air or water at any temperature, making it one of the most corrosion-resistant metals.
3. Presence in Water and Health Effects
Gold occurs at trace concentrations in most natural water, while mining and metallurgical streams can contain particles or dissolved complexes. Metallic gold, colloids, cyanide complexes, and other gold compounds differ in mobility and hazard; neither the behavior nor the toxicology of one form should be assigned to all of them. Analyze both the gold fraction and any complexing reagent before drawing health or treatment conclusions.
4. Water Treatment Applications and Removal Methods
Although gold is rarely a contaminant of concern in drinking water treatment, there are several methods that can be used to remove gold from water:
- Ion exchange: Specialized anion exchange resins can be used to capture the aurocyanide complex formed during the cyanidation process in gold mining.
- Adsorption: Activated carbon can adsorb gold from solution, especially in the form of complexes.
- Precipitation: Gold can be precipitated from solution using reducing agents such as sodium borohydride or hydrazine.
- Membrane filtration: Membrane technologies such as nanofiltration or reverse osmosis can remove colloidal gold particles or dissolved gold complexes.
- Electrolysis: Gold can be recovered from solution through electrolysis deposition on the cathode.
In industrial wastewater treatment, especially from mining or electroplating operations, gold removal and recovery is becoming more important due to its economic value.
5. Industrial Uses in Water Treatment
Although gold itself is rarely used directly in water treatment, some gold-related applications in the water treatment industry include:
- Gold nanoparticles are used in some emerging water purification technologies due to their unique catalytic properties.
- Gold-plated electrodes are sometimes used in water electrolysis systems for hydrogen production or in water quality sensors due to their high corrosion resistance.
- In gold mining wastewater treatment, specialized water treatment technologies are developed to recover gold and remove associated contaminants such as cyanide.
8. Environmental Impacts and Sustainability Considerations
Although gold itself is considered non-toxic, gold mining and processing can have significant environmental impacts:
- The use of cyanide in gold extraction can contaminate water sources if not properly managed.
- Gold mining is often associated with deforestation and erosion, which can affect surface water quality.
- Mercury, often used in small-scale gold mining, is a highly toxic water contaminant.
Sustainability efforts in the gold industry include:
- Development of more environmentally friendly cyanide-free extraction methods.
- Increased efficiency in water use and recycling at mining operations.
- Implementation of advanced wastewater treatment systems to recover gold and remove contaminants.