Abstract

The creation of a sustainable non-mercury gold processing technology has become a considerable challenge. An efficient gold extraction process with less complicated wastewater treatment to minimize the production cost is the ultimate objective of our Auviola project. Bioleaching based on the cyanide-producing bacterium will be engineered, improving the gold extraction and subsequently degrading the off-process cyanide. The Auviola project utilized an engineered Chromobacterium violaceum. To optimize and design the system, kinetic and genomic scale models were demonstrated in both the extraction process and the cyanide degradation afterward. The bioreactor was also designed as the pilot scale for implementing the engineered gold bioleaching process. In the future, this project has the potential to be implemented as a sustainable low-cost gold bioleaching system for the artisanal and small-scale gold miners to bring achievable and beneficial impacts. Moreover, we also contribute to educating the students for understanding and implementing synthetic biology.

Background

Gold is one of the noble metals which becomes a major economic driver for many countries. Its production requires a gold extraction step to obtain the pure ones from its orebody, for instance a leaching process that aims to separate the gold from other traces. Cyanide is one of these leaching agents that is widely used owing to the effective gold separation.1 However, cyanide waste can result in various harms in our environments, such as the decline of water quality and subsequently cause massive kills of aquatic organisms. Moreover, it also may threaten our health once it exposes our communities.

Up to 20% of the world’s gold comes from Artisanal and small-scale gold mining (ASGM), which is a gold mining community conducted by individuals or small enterprises with limited capital investment and production.2 ASGM becomes a big concern especially in Indonesia as it supports 1 million people’s livelihoods.3 Along with its high effectiveness, cyanide is widely utilized by ASGM as a leaching agent in the hydrometallurgical process.1

However, a study showed that the soil and plants nearby the ASGM has cyanide concentration higher than World and Health Organization (WHO) standard, indicating either the presence of cyanide leakage or improper waste treatment within the practices.4 In addition, a demand of 90 days-treatment of cyanide waste may increase the risk of leakage occurrence.1 Moreover, the limited performance of resources involved in ASGM perplexes people to achieve a proper cyanide waste treatment.5

Other alternatives that may be utilized by ASGM communities; i.e. pyrometallurgy and biohydrometallurgy. Pyrometallurgy as an alternative gold extraction method is unsuitable for ASGM as it needs huge energy sources for the 600oC-heating process.6 Therefore, another approach for gold extraction is needed to achieve a proper implementation among ASGM.

On the other hand, a biohydrometallurgy that involves organism in the gold extraction process becomes a promising alternative as it provides faster waste treatment due to the enzymatic process, resulting in a reduced risk of cyanide leakage. In addition, a bacterium Chromobacterium violaceum has been found to produce cyanide as well as degrade it, therefore may be developed into biohydrometallurgy to a simpler and more applicable leaching process as well as prevent improper waste treatment.7

Approach

With the concepts of synthetic biology, we are developing Auviola–an engineered C. violaceum with an on-off system for cyanide regulation in the gold bioleaching process. Compared to the wild-type, the new C. violaceum is engineered to have more cyanide-regulating genes, resulting in a better gold dissolution and cyanide waste treatment. This engineered bacterium is designed to function in a bioreactor to create the bioleaching system on an industrial scale. Along with this genetic engineering, we hope that this project may help many ASGM communities to create the best yield of gold.

“This Auviola project engineers C. violaceum to have more cyanide-regulating genes, resulting in a better gold dissolution and cyanide waste treatment”

How does this idea come to us?

Indonesia is one of the biggest gold producing countries with more than one hundred tons production in 2020.8 Moreover, there are plenty of ASGM practices directly organized by more than 300,000 inhabitants in Indonesia to give additional incomes.9

The use of gold is not limited to jewelry as it also possesses a lot of financial, electrical, and medicinal purposes. Despite this digital era, gold is still persistent to be used as an investment. Gold is also widely used as a memory chip and conductor for electronics. As for now, gold is broadly developed as diagnostic tools, photothermal therapy agents, drug carriers, and other medicinal uses. Therefore, the development for an environmentally friendly bioleaching model may aid to the improvement of those gold utilizations.

According to plenty of gold producers, this Auviola project has the potential to be developed as a better system of bioleaching process, especially in the ASGM practices. Coming with the merits of gold, we wish that we may create a big impact in reducing cyanide leakage and improving proper cyanide waste treatment through utilizing Auviola within the communities.