In Vietnam, the Co Dinh mine is the largest chromite mine in the country. Mining, ore dressing and disposal of the tailings provide obvious sources of heavy metal contamination in the mine area. The present study examined the influence of chromite mining activities on the adjacent lowland paddy field by investigating heavy metal and As levels in the mine tailings, sediments, paddy soils and water. At paddy fields located near the mine tailings, the total contents of Cr, Co and Ni were 5,750, 375 and 5,590 mg kg, and the contents of their water-extractable form were 12.7, 1.16 and 32.3 mg kg )1 , respectively. These results revealed severe contamination of lowland paddy soils with Cr, Co and Ni as a result of mining activity, suggesting serious health hazards through agricultural products, including livestock in this area. The principal source of the pollution was sediment inflow owing to the collapse of the dike, which was poorly constructed by heaping up soil. Moreover, water flowing out from the mining area was also polluted with , respectively). This might raise another problem of heavy metal pollution of watercourses in the area, indicating the need for further investigation and monitoring of fluctuations of water quality with seasonal changes.

Levels and chemical forms of heavy metals in forest, paddy, and upland field soils from the Red River Delta, Vietnam were examined. Forest soils contained high Cr and Cu levels that were higher in subsurface than in surface layers. Levels of Cu, Pb, and Zn that exceeded the limits allowed for Vietnamese agricultural soils were found in the surface layer of a paddy field near the wastewater channel of a copper casting village. High amounts of Zn accumulated in the surface soil of paddy fields close to a fertilizer factory and an industrial zone. In these cases, larger proportions of Cu, Pb, and Zn were found in the exchangeable and acid-soluble fractions compared to the low-metal soils. We conclude that no serious, large-scale heavy metal pollution exists in the Red River Delta. However, there are point pollutions caused by industrial activities and natural sources.

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Herein, we reported the composite structure of LiMnO2 and Li2MnO3 as a low-cost and environmentally benign cathode material. This composite with the main phase of LiMnO2 (90%) was synthesized by hydrothermal method at 220°C from LiOH and Mn(CH3COO)2 precursors. The obtained nanosized LiMnO2-LiMnO3 cathode material exhibits a high capacity of 265 mAh g-1 at C/10. The incorporation of Li2MnO3 into the LiMnO2 phase could stabilize the structure, leading to the improved cycle stability of the cathode. The capacity retention of the cathode was 93% after 80 cycles at C/2. Our results facilitate a potential strategy for developing high-performance cathode materials based on the Li-Mn-O system.

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