Exploring potential opportunities for the efficient development of the cobalt industry in China by quantitatively tracking cobalt flows during the entire life cycle from 2000 to 2021.

Owing to its key role in high-tech industry and clean energy technology, cobalt has been regarded as a critical material in many countries. In this paper, material flow analysis was used to quantitatively track cobalt material flows in China throughout the entire life cycle from 2000 to 2021. Based on data pertaining to cobalt commodity trade, cobalt loss during raw material processing, and recovered cobalt, we analysed the actual cobalt consumption in China. During the study period from 2000 to 2021, the main findings were as follows: (1) China's cobalt raw material imports accounted for 84.7% of the total raw materials acquired, while the export of cobalt-containing end products amounted to 32.6% of the total production. (2) China's cumulative net import of all cobalt commodities reached 561 kt, and battery products accounted for 73.3% of the total cobalt consumption. (3) China recovered 77 kt of cobalt from end-of-life products, while 327 kt of cobalt was not recovered. (4) The cumulative cobalt loss during raw material processing reached 288 kt, with the highest loss occurring in refining (51.0%), followed by manufacturing and fabrication (26.5%), beneficiation (12.3%), and ore mining (10.2%). The overall utilization efficiency of cobalt was 73.8% throughout the entire life cycle. (5) China's actual cobalt consumption reached 497 kt, accounting for 51.9% of the apparent cobalt consumption. Moreover, 61.1% of the cobalt products produced in China was consumed domestically, while 38.9% was exported. The massive export of cobalt commodities resulted in China bearing a disproportionate responsibility for carbon emission reduction. The research results can provide a scientific reference for the reasonable adjustment of the trade structure of cobalt commodities and realization of the economic and efficient utilization of cobalt resources in China.

How C: N: P stoichiometry in soils and carbon distribution in plants respond to forest age in a Pinus tabuliformis plantation in the mountainous area of eastern Liaoning Province, China.

Carbon distribution in plants and ecological stoichiometry in soils are important indicators of element cycling and ecosystem stability. In this study, five forest ages, young forest (YF), middle-aged forest (MAF), near-mature forest (NMF), mature forest (MF), and over-mature forest (OMF) in a Pinus tabuliformis plantation were chosen to illustrate interactions among the C: N: P stoichiometry in soils and carbon distribution in plants, in the mountainous area of eastern Liaoning, China. Carbon content was highest in the leaves of MAF (505.90 g⋅kg-1) and NMF (509.00 g⋅kg-1) and the trunks of YF (503.72 g⋅kg-1), MF (509.73 g⋅kg-1), and OMF (504.90 g⋅kg-1), and was lowest in the branches over the entire life cycle of the aboveground components (335.00 g⋅kg-1). The carbon content of the fine roots decreased with soil layer depth. In YF, MAF, and NMF carbon content of fine roots at 0.5 m was always higher than that of fine roots at 1 m; however, it was the opposite in MF and OMF. The carbon content of the leaves changed with forest age; however, carbon content of branches, trunks and fine roots did not change significantly. Soil total carbon (TC), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) content was highest in the OMF. Soil TC, TN and AP content, and TC: TN, TC: TP and TN: TP ratio decreased with increasing soil depth. Soil TC, TN, and TP content had a significant effect on the carbon content of fine roots (p < 0.05). The leaf carbon content and soil element content changed obviously with forest age, and the soil TN, TP and AP increased, which might reduce the carbon content allocation of fine roots.