Long, and two co-authors, reported in 2018 that Neogene lignite was widely used for enterprise’s electric power generation, local residents’ warming and cooking, and crops’ fertilizer in South China. But there is still no report about the elemental variations in Neogene lignite from the Zhaotong Basin, South China. Understanding the elemental concentrations in lignite is of great importance to comprehensive utilization and to evaluation of environmental impacts of the Neogene lignite. The authors studied the variation patterns of 34 elements in lignite samples collected from the Neogene Zhaotong Formation at Zhaotong Basin, Yunnan Province, China.
The arithmetic average of Cr, V, Ga, As, Cu, Rb, Co, Mo, and Cd in studied lignite samples is higher than those of China coals, while the content of Li and Bi are lower. Contents of As, Rb, La, Ni, Cd, Mo, Co, Ga, and V in northeastern Yunnan lignite are higher than the corresponding elements in common American Texas lignite, while contents of Li and Bi are lower.
Elements are classified into four groups (Si−K−Zn−Rb−Ba−Pb, Co−Cd−Na−Al, Ni−Ti−Bi−Cr−Cu−In−Mn−Mg-Ga−Fe−Tl, and V− U−Cs−Sc−La−Sr−L−Se−Ca−As−Mo-S) based on their correlation coefficient with ash yield. Elements, including Al, K, Na, Si, Ti, Ba, Bi, Cd, Cr, Cu, Cs, Co, Ga, Ni, Sc, Zn, and Pb, decrease from bottom to top of the Neogene Zhaotong Formation, whereas Ca, Mg, As, Se, Mo, Fe, and S increase. In addition, in M2 and M3 coal-bearing beds, Ga has potential applications after recycling and Se could be re-utilized as a kind of Se-containing fertilizer, and their reserves estimations are approximately 98 × 104 (Ga) tons and 7.8 × 104 tons (Se). Chromium and Cadmium in Neogene lignite have potential risk for local natural environments and the health of human beings
The authors concluded that arithmetic average concentrations of Se, As, Mo, and Cd in Neogene lignite from Zhaotong Basin, northeastern Yunnan Province, China are higher than those of upper continental crust. Meanwhile, contents of Zn, Fe, Co, Ti, Ba, Ca, Sc, Si, Ni, P, Rb, Sr, Al, In, Mg, K, Na, and Mn in Neogene lignite are lower than those of the upper continental crust. Contents of Cr, V, Ga, As, Cu, Rb, Co, Mo, and Cd in northeastern Yunnan lignite are over those of China coals, while concentrations of Li and Bi are lower.
As, P, Rb, La, Ni, Cd, Mo, Co, Ga, and V are enriched in the northeastern Yunnan lignite, compared to the American Texas lignite, while Bi, Mn, and Se are depleted. Four groups of elements from the studied samples can be divided, as follows:
1. Si−K−Zn−Rb−Ba−Pb,
2. Co−Cd−Na−Al,
3. Ni−Ti− Bi−Cr−Cu−In−Mn−Mg−Ga−Fe−Tl, and
4. V−U−Cs −Sc− La−Sr−L−Se−Ca−As−Mo−S.
The authors calculated the coefficients between the concentrations of elements from first and second groups,and its ash yield was positive. There exist no negative or lower positive correlation coefficients of those in the third and fourth groups.
Three types of element distribution patterns in ascending order of the Zhaotong coal-bearing bed are recognized:
1) elements including Al, K, Na, Si, Ti, Ba, Bi, Cr, Cd, Co, Cu, Cs, Ga, Ni, Sc, Pb, and Zn decrease from bottom to top,
2) whereas Ca, Mg, As, Se, Mo, Fe, and S increase from bottom to top;
3) the rest of the elements, including V, U, Tl, Sr, Sc, Rb, Li, La, In, P, and Mn, have irregular distribution patterns.
Contents of Ga and Se in Neogene lignite from Zhaotong Basin are transported with the lignite to the industrial index and could be utilized, with crude reserves estimations of 976,000 tons and 78,000 tons, respectively. Contents of Cr and Cd in Neogene lignite are slightly higher than the safety threshold recovery and could cause damage to the environment and human health when disposed in holding ponds, pits, or lagoons, which calls for further pollution management.
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