Development of high-precision analytical method for lithium and the preliminary investigation on lithium pollution in environmental media in China

At present, lithium-ion battery (LIB) has become the critical technology to support the development of clean energy, e.g., as power battery in new energy automobile and energy storage battery in electricity grid, and it can be predicted that the demand and use of LIB will grow rapidly in future. However, the disposal guidelines for spent LIBs are still lacking and the market of waste LIB recycling is still underdeveloped. Under this background, Li pollution has become an emerging concern globally. However, until now, no work has been conducted to develop the high-precision analytical methods for Li in multiple types of environmental media. Furthermore, the impact of human activities on the occurrence level of Li in multiple types of environmental media is still unclear. In this study, we for the first time established a complete flow scheme for the quantitative analysis of Li in diverse environmental media, including river water, sewage, atmospheric particulate matter, air-borne sand dust, soil, plant, animal, and cathode materials of LIB. In the aspect of pretreatment processes, six common digestion solution systems (including nitric acid, aqua regia, anti aqua regia, nitric acid plus hydrogen peroxide, nitric acid plus hydrofluoric acid, and anti aqua regia plus hydrofluoric acid) can ensure the Li recovery of more than 95% during the whole pretreatment processes of digestion and acid driving. Thus, we can choose the suitable digestion solution based on the chemical characteristics of targeted environmental samples. Then, the residual acid liquor after digestion can be effectively removed at 170℃ in acid driving apparatus. These pretreatment procedures can ensure the best performance of digestion processes and acid driving processes. In the aspect of ICP-MS analysis, when Rh103 and In115 were used as internal standard elements and the normal analytical mode (no gas analytical mode) was used in ICP-MS analysis, the high-precision trace analysis of Li in diverse environmental media was achieved. On the base of the above analytical methods, we further explored the characteristics of Li occurrence in multiple types of environmental media in China, with detailed results as follows: soil and deposit sediment (7.60−66.00 mg/kg), plant (0.03−2.36 mg/(kg dw)), animal (0.02−0.37 mg/(kg dw)), atmospheric particulate matters (0.18−2.71 ng/m3), sand dust (5.18−14.18 ng/m3), natural waters (0.54−92.40 μg/L), industrial and domestic sewage (11.34−36.11 μg/L), cathode materials of Li-ion battery (4.04%−7.70%). These results can provide basic data for the studies of biogeochemical cycle of Li and potential Li pollution caused by the human activities (e.g., industrial activities). In typical regions (such as the Qiantang River Basin), this study has revealed that human activities (such as sewage discharge) can significantly increase Li concentrations in natural water bodies, causing potential lithium pollution issues. It should be noted that the Li content in many important water sources in China (such as the groundwater in the Hetao Plain, surface water and groundwater in the Loess Plateau) has already approached or exceeded the health guidance value for Li level in drinking water (10 μg/L), and even exceeded the recommended upper limit (60 μg/L). In 2021, Li has been included in the fifth list of unregulated pollutants monitoring rules and the fifth draft lists of pollutant candidates set by the U.S. EPA, requiring more basic data on Li occurrence and its potential risks to support the policy-making of administrative departments. In the future, carbon neutrality strategies will rapidly increase global demand for Li resources, thus bringing about more urgent research needs for more severe Li pollution problems in China and globally.