Intergrated HP Introduction
Project Background Investigation
1. Field Survey in Zigui
Under the guidance of Associate professor Jiang Zhou, our team conducted a field survey of the tailings area in Zigui, examining soil samples and the state of local vegetation. We observed that plants such as Miscanthus and Erigeron canadensis, which are found in the tailings area, have the capacity to accumulate heavy metals from the soil. Apart from the role of these plants, tailings can have detrimental effects on local soil and groundwater, which in turn can impact the health of residents in nearby villages. This observation has led the CUG-China team to contemplate more environmentally friendly and resident-focused methods of tailings management. As the mining industry continues to thrive, we are considering whether there are alternative approaches to tailings disposal that are more considerate of the environment and the well-being of local communities, beyond the conventional method of landfilling.
2. An Interview on the Lives of Zigui Residents
The CUG-China team conducted a survey among residents living near the tailings area in Zigui County, Yichang City, Hubei Province. The residents are mostly concerned about the impact of tailings on their lives, including the health effects on crop cultivation and groundwater consumption. As a result, the CUG-China team hopes to achieve more optimized biological treatment methods after effective treatment and utilization of tailings, compared to the current emission standards, and follow up with the attitudes of the residents afterwards.
3. Interview with the Tangshan City Government
The CUG-China team conducted interviews with management personnel from relevant departments in Tangshan City, Hebei Province, China. This city is well-known for its mining industry and well-developed heavy industry,and the purpose of these interviews was to gain insights into the tailings treatment process. We inquired about the level of policy support, existing tailings treatment methods, and the environmental friendliness. According to the management personnel, China's policies strongly support tailings treatment to protect the environment. Tangshan City adopts a tailings-to-brick treatment method, using physical treatment to incorporate tailings into residential construction, achieving reuse of mining slag. However, tailings may contain radioactive and harmful substances, which could potentially harm human health and the environment.
4. Interview with Professor Zhang Lingling on Mineral Leaching
The CUG-China team has observed that, in addition to physical treatment methods, there is a substantial focus on chemical approaches for tailings management. We had the opportunity to interview Professor Zhang Lingling from the School of Materials and Chemistry at China University of Geosciences (Wuhan) to gain insights into various chemical treatment methods. She informed us about several techniques, including: Heap leaching, an effective method for dealing with subeconomic ores, low-grade ores, or waste rocks with minimal metal content from mining operations. It is extensively utilized in the processing of low-grade copper, gold, and uranium ores. This technique is known for its simplicity and cost-effectiveness, albeit it necessitates substantial land and is contingent on specific climatic conditions.
Additionally, we discussed tank leaching and stirred leaching, which are ideal for treating ores that are resistant to decomposition. These processes can enhance metal recovery rates through solid-liquid separation, albeit with higher demands for equipment investment and energy consumption.
Project Optimization
1. Meeting with Associate Professor Hu Yidan
The CUG-China team has observed that there is considerable potential for enhancement in the current management of tailings. The prevailing recycling techniques, which are predominantly physical and chemical methods, are not only costly but also yield suboptimal results. Consequently, we have proposed an innovative approach to our primary Principal Investigator, Associate Professor Hu Yidan, leveraging the resources available in our laboratory. The team intends to employ bioleaching as an alternative method.
Our strategy involves genetically modifying Acidithiobacillus ferrooxidans to enhance its adsorption capacity with minerals and to incorporate gold-specific leaching elements. This would enable the selective leaching of gold from the tailings. The team has engaged in extensive discussions and is confident that this approach could significantly improve the efficiency and cost-effectiveness of tailings treatment.
2. Professor Zhang Lingling Discusses Bioleaching Methods
We had another discussion with Professor Zhang Lingling regarding the selection of microbial strains, and learned that if companies adopt bioleaching for tailings, their specific requirements include three key points: First, the microbial strains used must have efficient leaching capabilities; second, the strains must be versatile, meaning they can adapt to various environmental conditions and characteristics of tailings; and finally, it is essential to ensure that the technology complies with all relevant environmental protection regulations. By meeting these demands, companies can ensure that the implementation of bioleaching technology for tailings will bring the expected environmental and economic benefits.
3. Discussion on Specific Leaching of Gold by Tangshan Municipal Government
We have exchanged ideas with professionals from the Tangshan Municipal Government regarding the design of a specific leaching method for gold. The professional first affirmed the bioleaching method but indicated that it is not practical for the local area of Tangshan. The main considerations are, first, the local tailings brick industry, as a pillar industry, is unshakable; second, the gold content in the local tailings is relatively low, and it might be worth considering production in places like Shandong and Shanxi. After reflection, we believe that we should first inquire about the feasibility of implementing this technology with established tailings treatment enterprises and engage in discussions with regions such as Shanxi and Shandong, where tailings contain gold.
4. Discussion with Sanding Corporation on Bioleaching
We had a project exchange with Mr. Zhan Gang, the Chief Technology Officer of Sanding Corporation. He first affirmed the environmental friendliness of bioleaching but raised concerns that the process has a long cycle and thus consumes a significant economic cost. In response to this, we believe that the efficiency of bioleaching can be increased to some extent by enhancing bacterial contact efficiency, that is, by increasing the concentration of c-di-GMP to strengthen the biofilm formation process. Secondly, he questioned whether potential biological pollution issues should be considered if the treated wastewater is to re-enter nature. This point certainly requires consideration.
5. Communicate with FUDAN and BIT teams on similar topics
We engaged in a discussion with the FUDAN and BIT teams, who are also working on bioleaching. We shared insights on safety and efficiency improvements. While each project has its merits and demerits in terms of efficiency, the safety aspect was a common concern. Both teams' experiments are confined to specific areas or equipment. After our discussion, we agreed on the necessity of enhancing safety measures in our design, although the specifics of these enhancements require further contemplation.
6. Safety Design
After conducting research, our team took note of the self-killing module utilized by the XMU2020 team to ensure that potential leakage issues were addressed. Drawing inspiration from this, we have incorporated a killing switch module into our design. We introduce the inverter into our kill switch systems which consist of a cI repressor and a pR promoter from E. coli λ phage, where cI repressor can inhibit pR promoter. In this case, activation of the upstream promoter of cI repressor will lead to high expression of it, thereby reducing the expression efficiency of downstream pR promoter. By using an inverter, inducible promoters can obtain two-way uses, while reducing the complexity of circuit construction and eliminating the need of precise control of steady state. It is a basis of our kill switches design.
7. Visit and Study Tour at the Datong Coal Industry Group in Shanxi
During a study visit to the Datong Coal Industry Group in Shanxi, our team gained a preliminary understanding of the coal mining process and the development path of the enterprise. It was observed that there are indeed numerous issues with tailings treatment in Shanxi's tailings areas. While the coal industry is thriving, tailings treatment has not been elevated as a main industry. Moreover, the mines contain a variety of minerals, and the bioleaching of gold with specificity is feasible, hence considering the possibility of setting up production in Shanxi.
Post-Project Development Discussion
1. Zigui County Government Development Discussion
We returned to the Zigui area and communicated with the relevant village committees, understanding that policies encourage the improvement of resource utilization efficiency. For instance, the 'Guiding Opinions on the Comprehensive Utilization of Bulk Solid Waste during the 14th Five-Year Plan' proposes that by 2025, the comprehensive utilization rate of tailings and other bulk solid waste will reach 60%. This policy emphasizes the comprehensive use of resources and promotes mining enterprises to adopt bioleaching technology for tailings to improve the utilization rate of mineral resources. The policy highlights the construction of green mines. For example, the 'Notice on Further Strengthening the Construction of Green Mines' proposes that by the end of 2028, 90% of large mines and 80% of medium-sized mines should meet the green mine standards. This policy sets higher requirements for environmental protection, encouraging enterprises to adopt more environmentally friendly tailings treatment methods, such as bioleaching technology, to reduce environmental pollution. The policy strengthens the supervision of mine safety production, such as the 'Opinions on Further Strengthening Mine Safety Production Work', which proposes the implementation of a safety production responsibility system for coal mines, metal non-metal underground mines, and tailings dams led by leaders of municipal and county-level governments. This policy strengthens the supervision of mine safety production and ecological restoration. Bioleaching technology for tailings is more environmentally friendly and more in line with new safety and environmental protection standards. Meeting the needs of policies, the future development prospects of bioleaching are broad.
2. Development Discussion with Residents of Zigui
We engaged in discussions with residents from Datong, Zigui, and other places, sharing with them the differences between bioleaching and traditional leaching methods. Compared to physical and chemical approaches, bioleaching is supported by many for its superior safety. The residents also believe in its better economic benefits. Some residents inquired whether it is possible to absorb all the waste in the tailings so that safer water can be discharged, thus avoiding environmental pollution. We also indicated that this is just our first step, and we will strive to develop methods to leach a variety of metals from tailings wastewater in the future, making life safer for residents.
3. Development Discussion with San Ding Technology Company
In our follow-up discussion with San Ding Technology, we identified potential areas for enhancement, which include: Firstly, the possibility of leaching multiple metals simultaneously, but it remains to be determined whether to use the same microbial strain or multiple strains; Secondly, the exploration of integrating biological and chemical methods to achieve a balance between economic efficiency, speed, effectiveness, and environmental friendliness. Further refinement of these aspects can be pursued to advance the project.
4. Development Discussion with Professor Zhang Lingling
We once again interviewed Professor Zhang Lingling to discuss the potential development of our project. Professor Zhang pointed out that the current academic research on bioleaching of tailings is mainly focused on the screening and optimization of microorganisms and the exploration of leaching mechanisms. Different microorganisms play different roles during the leaching process. For example, A.ferrooxidans and the moderately thermophilic Siberian thermophilic bacteria play roles in acidolysis, complex decomposition, as well as oxidation-reduction and bio-enrichment. The performance of microorganisms can generally be improved through mutation breeding, mixed culture of microorganisms, and genetic improvements.
Currently, there are two noteworthy findings that merit attention: first,the interaction between microorganisms and plants, Leguminous plants and other remediation plants can work synergistically with beneficial microorganisms during the tailings leaching process; Second, the incorporation of biochar and surfactants has been shown to effectively control leaching system parameters and eliminate passivation films, serving as valuable methods for enhancing tailings leaching. Additionally, research on bioleaching of tailings should focus on the combination of bioleaching technology with other technologies, such as chemical leaching, physical methods, or electrochemical methods, to enhance leaching efficiency. These have all provided us with new ideas for development.