Transformation Of Trace Elements Research Articles

Migration and transformation of trace elements during sewage sludge and coal slime Co-combustion

Co-combustion of sewage sludge (SS) and coal slime (CS) could improve the combustion properties of the two materials, however, high levels of trace elements (TEs) can be released from the two wastes, resulting in secondary pollution. The migration and transformation behavior of As, Cr, Pb, Zn, and Mn during co-combustion is explored in current research. The results showed co-combustion could inhibit the emission of Zn, As, Pb, and Mn, and the effect was more pronounced for Zn, As and Mn. Meanwhile, minerals like kaolinite and gypsum were found to generated in the ash from co-combustion but not solo-combustion. Model experiments demonstrated that kaolinite captured As, Pb and Mn, while gypsum captured Zn, As and Mn but facilitated the emission of Pb and Cr. This well explained the distinct TEs emission characteristics between co-combustion and solo combustion. As the temperature elevated, kaolinite in co-combustion ash decomposed and the generation of gypsum was promoted. In this way, the emission ratios of Zn, As, and Mn initially increased but subsequently decreased between 700 and 1300 °C, whereas Pb and Cr emission ratios increased by twofold within the same temperature range. Leaching characteristics and risk assessment code on co-combustion ashes were also conducted in this study. The results indicated a marginal elevation in the risk associated with trace elements (TEs) following co-combustion, provided that all five TEs remained within the limits of national standards.

Effect of humic acid on Se and Fe transformations in soil during waterlogged incubation

Humic acid (HA) serves as electron donor and acceptor in the biogeochemical cycle of Fe and Se in soil. In anoxic condition, a series of redox reactions occur, including reductive dissolution of Fe oxides, decomposition of organic matters, and transformation of trace elements. Thus, this study demonstrates the effect of HA on Se and Fe transformations in soil during waterlogged incubation. Soils were incubated under anoxic condition for 56 days, and pH, redox potential (Eh), and Fe and Se concentrations were measured at specific reaction times (days 2, 4, 8, 15, 28, and 56 of incubation). Moreover, sequential extraction and X-ray photoelectron spectroscopy (XPS) were used to obtain Se and Fe transformations, respectively. High resolution transmission electron microscopy (HR-TEM) was used to observe the morphology properties of soil. Results indicated that 4% HA addition decreased the pH and inhibited Eh decline continuously, and HA addition inhibited the Fe and Se release from soil. The Se concentration in soil solution without and with 4% HA addition at the day 15 of incubation were 1.05 mg L−1 and 0.30 mg L−1, respectively. Moreover, the residual Se fraction in soil with HA addition was evidently more than that in soil without HA addition. XPS of Se3d and Fe2p revealed that the binding energy of the main peak shifted to low values and the peak shape varied with the increase in HA addition. XPS2p3/2 and HR-TEM data indicated that the surface structure of Fe oxides in soil varied with the variations in anoxic incubation time and HA addition amount. HA addition would negatively influence Se and Fe release in soil solution and then reduce their bioavailability. This study aids in understanding the environmental behavior changes of Se and Fe when high HA concentrations enter the soils, especially wetland or paddy soil.

Process study of biogeochemical cycling of dissolved inorganic arsenic during spring phytoplankton bloom, southern Yellow Sea

Previous studies in the southern Yellow Sea (SYS) suggest that large spring phytoplankton blooms (SPBs) have occurred in recent decades. Elevated primary production in the water column can lead to the accumulation and transformation of trace elements. Two field study cruises (including two drifting anchor surveys) were conducted on 12–19 February and from 24 March to 15 April 2009, to investigate the impact of different SPB development periods on the concentrations of total dissolved inorganic arsenic (TDIAs: [TDIAs]=[As(V)]+[As(III)]) and As(III) (arsenite) in the SYS. The distribution of TDIAs in the study area was similar between the two field studies, with concentrations increasing from coastal to offshore areas. High arsenite concentrations and As(III)/TDIAs ratios were found in areas having high concentrations of chlorophyll-a, particularly in the subsurface waters of the central SYS during the drifting surveys, where a significant SPB occurred. Results show that the integrated arsenite concentrations increased at an average transformation rate of 0.53±0.24nmol/L/d within the 15days during the bloom, and data from the anchor drifting surveys indicated that approximately 15.1% of the arsenate in the euphotic zone (~30m depth) was converted to arsenite. In addition, 7.1% of TDIAs was scavenged from the water column by phytoplankton forming the blooms (a factor of 5 higher than expected). A preliminary box model was established to estimate the budget for TDIAs in the SYS in early spring (February to April). This showed that biological scavenging is an important sink for TDIAs, which may promote the transformation and migration of inorganic arsenic species, and thus have a substantial impact on the biogeochemical cycling of this element in the SYS. Depletion of arsenate in the upper waters could lead to arsenate stress, potentially damaging fisheries and the ecosystem.

Trace Element Transformation during the Development of an Estuarine Algal Bloom

Copper and arsenic underwent large changes in chemical form during the development and senescence of natural phytoplankton blooms in the Patuxent River, a subestuary of Chesapeake Bay in Maryland. Arsenate was rapidly reduced to arsenite and methylated species. At a total arsenic concentration of 20 nmol l−1, arsenate reduction rates ranged from 50 amol cell−1 d−1 to >230 amol cell−1 d−1, with the rate and extent of reduction dependent upon the concentration of arsenic, the dominant phytoplankton present, the season, and the degree of decline in phosphorus concentrations during bloom development. In general, the percentage of organically-associated copper was lowest (20–40% of total copper) during periods of rapid cell growth and highest (60–100% of total copper) during periods of cell decline or periods of dominance by red tide-forming dinoflagellates, a pattern associated with periods of high release of organic compounds during either bloom senescence or dense algal blooms. The end result of biological mediation was to increase the proportion of each element present in a less toxic form, thus affecting the potential toxicity to a natural ecosystem.