# In situ gold adsorption experiment at an acidic hot spring using a blue-green algal sheet

## TL;DR

A blue-green algal sheet was used to recover gold from acidic hot spring water, achieving high efficiency with minimal environmental impact.

## Contribution

A novel method for gold recovery using blue-green algae in situ, achieving ultra-high enrichment from low-concentration solutions.

## Key findings

- The algal sheet adsorbed up to 30 ppm of gold after 7 months in hot spring water.
- Gold concentration in the water was below detection, showing a 3×10⁷ enrichment factor.
- The method is effective for low-impact recovery of gold from Au-poor solutions.

## Abstract

Gold (Au), as one of the most precious metal resources that is used for both industrial products and private ornaments, is a global investment target, and mining companies are making huge investments to discover new Au deposits. Here, we report in situ Au adsorption in an acidic hot spring by a unique adsorption sheet made from blue-green algae with a high preferential adsorption ability for Au. The results of in situ Au adsorption experiments conducted for various reaction times ranging from 0.2 h to 7 months showed that a maximum Au concentration of 30 ppm was adsorbed onto the blue-green algal sheet after a reaction time of 7 months. The Au concentration in the hot spring water was below the detection limit (< 1 ppt); therefore, Au was enriched by preferential adsorption onto the blue-green algal sheet by a factor of more than ~ 3 × 107. Thus, our gold recovery method has a high potential to recover Au even from an Au-poor solution such as hot spring water or mine wastewater with a low impact on the environment.