Section 1 : Background
Rare earth elements are one of the most important resources in the world. They can be widely used in civil and military fields[1]. At the same time, rare earths are non-renewable rare natural resources, and the environmental cost of their exploitation is high. Therefore, big importing countries such as the United States, Britain and Japan no longer easily exploit their domestic rare earth resources, but vigorously import them from other countries instead. With the decrease of rare earth exploitation in developed countries and the increase of rare earth exploitation in developing countries, the environmental pollution problem of rare earth exploitation industry is likely to become more and more serious. REE Miner hopes to reduce the adverse effects of environmental problems in rare earth mining on human beings and the earth and recover rare earth elements as a precious resource at the same time.
Fig. 1. Application of rare earth ions
In 2017, our team designed REEBOT to treat acidic industrial wastewater using methods of synthetic biology and extract rare earth elements from it. Since then, we have continued focusing on wastewater treatment technologies in rare earth industry and do more research in this area.
Firstly, a preliminary investigation is conducted: the global total proven rare earth quantity is about 120 million tons, and the annual production is about 210,000 tons[2]. According in 2012, China mined 76,000 tons of rare earth and produced more than 20 million tons of waste water. Based on this, it is estimated that it takes an average of 263 tons of water to mine one ton of rare earths. According to relevant laws and actual sample data, we estimated that the total amount of rare earth elements in the world's annual rare earth wastewater is 21×263×107×0.05g=2760T (in which the rare earth mining wastewater contains about 0.05g of rare earth elements per liter). This will undoubtedly lead to the impact on the environment and the waste of resources. In order to make the existing technology more environmental friendly and efficient, our team designed this year's REE Miner project based on the improved project made in 2017. After Internet searching and enterprise visiting, we learned that the mainstream method of drainage treatment is method of chemical precipitation: the rare earth elements can be collected in the form of compounds by adding chemical reagents in drainage through cooling and precipitation[3]. At present, the mature processing technologies in the industry mainly include: neutralization precipitation method, sulfide precipitation method, and heavy metal capture (chelating) agent treatment method. However, the existing methods still need to be improved. First of all, rare earth elements in wastewater cannot be fully recycled, resulting in economic loss and environmental problems. Secondly, the existing treatment methods include adding a large number of chemical reagents, which cannot achieve zero emission under the existing standards. Prolonged exposure to such environments may affect the health status of staff members.
Fig. 2. The mine wastewater
Therefore, we hope to use synthetic biology methods to recover rare earth elements from acidic wastewater. It can not only protect the environment, but also recover rare earth elements, achieving the goal of zero emissions and realizing the recycling of resources. At the same time, it reduces workers' job risks and reflects humanistic care.
Section 2 : Approach
At present, in the industry, after enterprises use chemical methods to treat rare earth wastewater, some rare earth elements in wastewater still can't be precipitated (about 0.05g/L). If chemical methods are continued being used to treat wastewater, the economic and environmental costs will be huge.
We hope to solve this problem by using the combination of dLBT, OprF, Sitag and LanM proteins. OprF from P. aeruginosa is a membrane ankyrin responsible for anchoring proteins to the membrane, Sitag is responsible for locating engineering bacteria on quartz sand for recycling, and LanM from Methylobacterium extorquens and dLBT from eukaryotes can adsorb rare earth ions.
The content of rare earth elements in rare earth wastewater is low. If only rare earth elements are used as the starting switch for expression of engineering bacteria, the expression efficiency is limited and the amount of protein synthesizing is small.
We modified the Au+ specific sensing protein GolS from Salmonella to become a sensing device activated by Cu2+. Without Cu2+ or Au+ in the environment, protein GolS inhibited the expression of downstream genes. When Cu2+ or Au+ binds to the inhibitory protein, it will interfere with it and make the downstream gene express smoothly. This system also has a precedent of successful expression in E. coli. In our final design, GolS system is parallel to PmrCAB system. We hope to develop a new sensing device and compare its efficiency with PmrCAB sensing device.
Fig. 3. Bacteria miner
Section 3 : Safety
In order to ensure bio-security, we have placed bacterial filter membrane at the hardware entrances and exits while installing sterilization room on the exits, as a result we can guarantee our engineering bacteria not to escape from the device.
Section 4 : Sustainable Development
Rare earth resources are non-renewable and irreplaceable. Our project makes it possible to adsorb and recover large amounts of rare earth elements from wastewater, increasing utilization rate compared with current method. Our project is beneficial to prevent the excessive consumption of rare earth elements and greatly extend the available time of them, making it possible for future generations to find alternative resources without depleting them. As a result, our project could contribute to sustainable development.
