Background
With the rapid development of industrialization and urbanization, the exploitation and utilization of mineral resources have become an important support for human social development. However, in the traditional mining method of pyrometallurgy, a large amount of energy is needed to reach and maintain high temperatures, which requires the burning of large amounts of fossil fuels, resulting in excessively high operating costs; this process also generates harmful gas and greenhouse gas emissions such as SO2 and CO2, which lead to the formation of acid rain and exacerbate global warming problems, even causing climate change, affecting human living environments and the balance of natural ecosystems. At the same time, a large amount of tailings will be produced during the process, which are solid waste generated in the process of mineral processing and extraction, containing unused precious metal elements such as gold, silver, and platinum, as well as toxic heavy metals such as copper, zinc, nickel, chromium, lead, mercury, and arsenic[1] . These metals can penetrate into soil, surface water, and groundwater through geological movement, weathering, and water erosion [2], posing a major threat to ecosystems over a long period of time. Therefore, tailings treatment not only improves economic benefits, but also protects soil, water, and atmospheric environments. Bioremediation is a technology that uses biological systems (mainly prokaryotic microorganisms) to promote the extraction and recovery of metals from ores and waste [3]. By using this technology to improve the comprehensive utilization level of tailings, valuable resources can be turned into treasure from waste, and the scientific disposal of tailings can effectively alleviate resource pressure and achieve environmental governance and sustainable economic development. In summary, the comprehensive treatment of tailings is of great significance for resource utilization, environmental protection, safe production, and social stability. Through comprehensive treatment, sustainable management and utilization of tailings can be achieved, promoting green economic and social development. With the rapid development of industrialization and urbanization, the extraction and utilization of mineral resources have become an important support for the development of society. However, during the process of mining, a large amount of tailings will be generated. Mine tailings are solid waste generated during ore processing and mining, which contain underutilized precious metal elements such as gold, silver, platinum, as well as toxic heavy metals such as copper, zinc, nickel, chromium, lead, mercury, and arsenic[1]. These metals can penetrate into soil, surface water, and groundwater through geological movements, weathering, and water erosion[2], posing a significant threat to ecosystems over the long term. Therefore, tailings treatment can not only improve economic benefits, but also protect soil, water bodies, and atmospheric environment. By improving the comprehensive utilization level of tailings, valuable resources in tailings can be turned into treasures. Moreover, scientifically disposed of, which can effectively alleviate resource pressure, achieve environmental governance and sustainable economic development. In short, the comprehensive management of tailings is of great significance for resource utilization, environmental protection, safety production, and social stability. Through comprehensive management, sustainable management and utilization of tailings can be achieved, promoting green development of the economy and society.
Existing problem
At present, the popular tailings treatment methods are stacking, landfill, solidification. Storage and landfill occupy a lot of land resources, and it is easy to cause natural disasters such as landslide and debris flow. Toxic supstances, heavy metals and chemicals in tailings may seep into surrounding water sources, causing water pollution and posing a serious threat to surrounding ecosystems and human health. Tailings ponds typically require large amounts of water to dilute and transport waste, which can cause surface and groundwater levels to drop. It has a serious impact on nearby farmland, wetlands and groundwater resources, destroying the ecological balance and biodiversity. Although the curing treatment can reduce the harm of the tailings, it needs to add a lot of lime, cement, etc., which is high in processing cost and difficult to recycle. And the curing process is complex, requiring high input equipment, human resources and other resource costs. Based on current treatment methods, tailings treatment technology is not mature, and the potential utilization value of tailings has not been fully explored. Tailings treatment has become a major problem in economic, social and environmental development[3].
What can biomining do
Biomining is a biotechnology method that utilizes microorganisms to recover metals from ores. Biomining can achieve the recovery and beneficiate of metal elements in mild environment and under lower pressures. Compared to wet metallurgy and pyrometallurgy, which require massive energy and release a large amount of greenhouse gases and harmful chemicals during the process, causing great damage to the environment[4], biomining is a new method that is more economically efficient and environmentally friendly. In addition, many microorganisms used for mining can fix CO2 in the atmosphere, which can alleviate the greenhouse effect. Due to the concerns about environmental issues, depletion of high-grade ore supply, and increasing demand for metals, biomining technology is increasingly being valued. Metals refined from low-grade ores have been extensively utilized[5][6][7]. It has been reported that approximately 20% of copper, 5% of gold, and small amounts of cobalt, nickel, uranium, and zinc are produced worldwide through biomining processes[8][9]. Recently, reports of using microorganisms to extract rare-earth elements on the International Space Station have sparked heated discussions in the scientific community[10], indicating that microbial mining may be used to extract resources from other planets to solve the human resource crisis.
Our project
Biomining is an emerging technology that is sustainable and environmentally friendly, but its long leaching cycle and low efficiency make it difficult to apply in industrial production. Some species are not adapted to treat ores at the speed required for economic metal recovery[11], and these drawbacks are related to the physiological limitations of biomining microorganisms. Therefore, the modification of the chassis cells of biomining to achieve high leaching efficiency and metal extraction productivity has become the focus of current research work.
CUG-China team has designed the Biomining Efficient Specific Treasure (BEST) project to focus on the issues of biomining. The project uses the extreme acidophilic bacterium Acinethiobacillus ferroxidans ATCC23270 isolated under natural acidic conditions to optimize the low efficiency, poor specificity, and difficulty in applying engineering bacteria to mining environments in biomining process. Synthetic biology methods are used for modification.
In the process of biomining, EPS can mediate microbial adsorption onto mineral surfaces, concentrate Fe3+ to enhance the attack on sulfides, and help microbial communities withstand harsh environment[11][12]. In order to improve the metal leaching efficiency of biomining, we focused on the EPS synthesis process and constructed a dynamic synthesis module for cyclic guanosine monophosphate. By excavating the modules of the c-di-GMP efficient synthesis module and dynamically optimizing the construction of the synthesis module, we increased the content of c-di-GMP in bacteria, stimulated the formation of biofilm, enhanced the interaction between bacteria and ore, and improved leaching efficiency.
There is another problem of poor metal leaching specificity in the process of biomining[13], while specific biomining of precious metals can further improve economic benefits. We noticed the gold specific MerR family transcription factors in the Samonella sp. genus bacteria[14]. Using this sequence, we not only designed gene circuits that respond specifically to gold, but also achieved the engineering goal of specific leaching of gold. Moreover, we also added a killing switch for engineering bacteria, allowing them to survive normally and engage in biomining only when the gold concentration is high in the environment, and die when the gold concentration is low. This not only ensures the biological and ethical safety of engineering bacteria, but also provides convenient conditions for supsequent metal leaching and recovery.
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