Studies on the Transformation Behaviors of Trace Elements in Huainan Coal-fired Power Plants and Antiproliferative Activity of Nitrodoosmium Complexes


Student thesis: Doctoral Thesis

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  • Quan TANG


Awarding Institution
Award date29 Aug 2013


Currently, the topic about trace elements has attracted more and more attention in the world due to the great concern for their toxicological and environmental effects. In this thesis, based on our new data, some important aspects related to geochemistry of trace elements in coals from two coal-fired power plants (CFPPs) in China were reviewed, including the trace elements values, enrichment, human health problems caused by coal combustion and possible recovery of valuable trace elements.

The rapid expansion of CFPPs in China has produced huge volume of toxic elements associated combustion residues, which pose great threat to local environment. In this study, feed coal, fly ash, bottom ash and flue gas desulphurization (FGD) gypsum samples were collected from two pulverized CFPPs at Huainan city, Anhui province, China, both of which burned the bituminous coals. Feed coal and combustion residues were morphologically and mineralogically characterized by scanning electron microscopy equipped with energy-dispersive microanalyser and X-ray diffraction. Concentrations of fifty major and trace elements in these samples were determined by inductively coupled plasma atomic emission spectrometry (Na, Mg, Al, Si, K, Ca, Fe, Ti, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, B, Ba, Be, Bi, Cd, Co, Cr, Cu, Li, Mn, Mo, Ni, P, Pb, Pd, Re, Sn, Sr, Th, V, W and Zn) and atomic fluorescence spectroscopy (As, Hg, Sb and Se). The results showed that As, B, Ba, Be, Ce, Dy, Er, Eu, Gd, Hg, Ho, La, Mn, Mo, Nd, Pr, Sm, Sr, Tb, Y, Yb and Zn were significantly depleted, whereas Bi, Co, Cr, Cu, Ni, Se and V were significantly enriched, when compared with the average values of Chinese coals. Most of the trace elements were concentrated in the fly ash, only ferrum (Fe) and manganese (Mn) were enriched in the bottom ash. The diameters of ash particles removed by the electrostatic precipitator (ESP) were in an inverse relationship with the enrichment factors of most trace elements. To address possible exposure of combustion residues in the environment, laboratory controlled leaching tests were carried out on fly ash and gypsum to understand the environmental behaviors of these elements. Both fly ash and gypsum were identified as not-hazardous wastes.

Environmentally-sensitive elements, such as arsenic (As), mercury (Hg), stibium (Sb) and selenium (Se), are the most toxic metals that have been demonstrated in the USA Clean Air Act Amendments of 1990. The present study has investigated the distribution of As, Hg, Sb and Se in feed coal and its combustion by-products in two different CFPPs. Experimental analysis of simultaneously sampled coal, bottom ash, fly ash and FGD products showed that the concentrations of As, Hg, Sb and Se in coal were in the ranges of typical Chinese power plants reported by others publications. Mercury was found to be the most volatile, whereas Sb was the least volatile. The overall material balances of As, Hg, Sb and Se were established based on the operation parameters of their respective boiler. The average removal efficiencies of As, Hg, Sb and Se by the ESP unit were 83%, 16%, 100%, and 72%, respectively, whereas those by the FGD process were 61%, 80%, 0% and 55%, respectively. The stack emission proportions of As, Hg and Se were 6%, 17% and 13%, respectively. And the total annual emissions of As, Hg and Se from two CFPPs were estimated at 0.46 tons (t), 0.04t and 2.27t, respectively.

Heavy metals are potentially toxic environmental pollutants and have drawn more and more interest throughout the world. The concentrations of heavy metals (As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, V and Zn) in residential area soils (112 stations) in the proximity of the Huainan CFPP were investigated, and the potential ecological risk indices and health risks associated with these concentrations were calculated. Mean concentrations of heavy metals in the downwind direction were relatively higher than those from the upwind direction. Analysis of the potential ecological risk of soil heavy metal concentrations indicated that the studied sample sites presented a relatively low ecological risk. There was a possible risk because of the above average hazard quotient value (1.5) for children downwind. The results of the health risk assessment showed that values of carcinogenic risks were within the range of 1×10-6 and 1×10-4 which would deem them acceptable by most regulatory agencies.

Increasing emission of heavy metals has caused a serious damage to human health. Heavy metals in dust can enter the human body via direct inhalation, ingestion and dermal contact absorption. Then, they affect the central nervous system or act as cofactors in other diseases, which cause adverse health effects, such as carcinogenic effects. Although severe exposure of metals can cause carcinogenic effects, metals can be used as anti-cancer drugs. Metal complexes used as both therapeutic and diagnostic medicine are of growing significance in medicinal inorganic chemistry. Some inorganic compounds have been used as drugs for centuries. A series of osmium(VI) nitrido complexes supported by quinolinolato ligands have been prepared and they exhibit promising in vitro anti-cancer activities. These results establish that OsVI≡N is a versatile and promising platform for the design of a variety of high-valent anti-cancer drugs.

    Research areas

  • Coal-fired power plant, Coal, Combustion residue, Trace element, Soil, Heavy metal, Nitridoosmium complex, Antiproliferative activity