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Highlights: [•] Hg was mainly distributed in strong complex phase in FGD gypsum. [•] Chlorine content in coal might influence water soluble Hg in FGD gypsum. [•] Hg release ability from FGD gypsum was related to its speciation. [•] Water soluble Hg was easily to release, while residual Hg was relatively stable. [•] Hg emission from FGD gypsum during its disposal in Zhejiang province was estimated. [Copyright &y& Elsevier]

Abstract: With the extensive utilization and disposal of flue gas desulfurization (FGD) gypsum, Hg0 re-emission and Hg2+ dissolution could cause severe atmospheric and groundwater contaminations. The present study employed two precipitating agents: sodium dithiocarbamate (DTCR) and 2,4,6-trimercaptotiazine, trisodium salt monohydrate (TMT) to prevent mercury in FGD gypsum from releasing into the environment as Hg0 and Hg2+. The results indicated that in the presence of DTCR and TMT, Hg2+ in leachate decreased to nearly 10%, while the amount of released Hg0 declined by over 2/3. Hence, it demonstrated an apparent effect of precipitants on the inhibition of Hg2+ dissolution and Hg0 re-emission. However, precipitation efficiencies represented better inhibitive performance of DTCR than that of TMT. Further increase of initial pH value and the precipitant dosage had an outstanding effect on the decline of total dissolved Hg2+, released Hg0 and Hg2+ remaining in leachate. Thus, in some severe conditions such as acid rain prone areas, the stabilization of mercury in FGD gypsum from dissolving and releasing could be extraordinarily controlled by the addition of DTCR and TMT, which is highly promising for future applications. [Copyright &y& Elsevier]

Abstract: Several heavy metals, including Cu2+, Ni2+, Pb2+, and Zn2+, were investigated in simulated desulfurization solutions to evaluate their interferences with Hg2+ during the reaction with dithiocarbamate type chelating resin (DTCR). Appropriate DTCR dosage and the effect of pH were also explored with respect to restoration of high Hg2+ precipitation efficiency and reduction of mercury concentrations. The experimental results suggested that increasing heavy metal concentration inhibited Hg2+ precipitation efficiency to a considerable extent and the inhibition order of the four heavy metals was Cu2+ >Ni2+ >Pb2+ >Zn2+. However, the coordination ability was closely related to the configuration and the orbital hybridization of each metal. In the cases of Cu2+ and Pb2+, increased DTCR dosage was beneficial to Hg2+ precipitation, which could lay the foundation of practical applications of DTCR dosage for industrial wastewater treatment. The enhanced Hg2+ precipitation performance seen for increasing pH might have come from the deprotonation of sulfur atoms on the DTCR functional groups and the formation of metal hydroxides (M(OH)2, M=Cu, Pb, Hg). [Copyright &y& Elsevier]

Abstract: Mercury (II) (Hg2+) ion can be reduced by aqueous S(IV) (sulfite and/or bisulfite) species, which leads to elemental mercury (Hg0) emissions in wet flue gas desulfurization (FGD) systems. Numerous reports have demonstrated the high trapping efficiency of sodium dithiocarbamate over heavy metals. In this paper, a novel sodium dithiocarbamate, DTCR, was utilized as a precipitator to control Hg2+ reduction and Hg0 emission against S(IV) in FGD solutions. Results indicated that Hg2+ reduction efficiency decreased dramatically while precipitation rate peaked at around 91.0% in consistence with the increment of DTCR dosage. Initial pH and temperature had great inhibitory effects on Hg2+ reduction: the Hg2+ removal rate gradually increased and reached a plateau along with the increment of temperature and initial pH value. Chloride played a key role in Hg2+ reduction and precipitation reactions. When Cl− concentration increased from 0 to 150mM, Hg2+ removal rate dropped from 93.84% to 86.05%, and the Hg2+ reduction rate remained at a low level (<7.8%). SO4 2−, NO3 − and other common metal ions would affect the efficiency of Hg2+ reduction and precipitation reactions in the simulated desulfurization solutions: Hg2+ removal rate could always be above 90%, while Hg2+ reduction rate was maintained at below 10%. The predominance of DTCR over aqueous S(IV), indicated by the results above, has wide industrial applications in FGD systems. [Copyright &y& Elsevier]

Abstract: Acid treatment is a routine demineralization process to obtain black carbon (BC), but there has been little systematic research about its influence on BC’s characteristics. In this study, elemental analysis, SEM, FTIR, and Boehm titration were used to investigate that effect. Our results showed that the acid treatment had little influence on the sorption of fly ash and soot to pentachlorophenol (PCP), but it greatly increased the sorption of rice chars to PCP. There were two competing effects of acid demineralization on the adsorption capacity of BC. On one hand, it increased the amount of the acidic functional groups, which decreased the adsorption capacity. On the other hand, it increased the surface and pore volume of BC and caused the emergence of hidden carbon enclosed by minerals, which in turn increased the sorptivity significantly. Especially for rice chars (600°C), after acid treatment, their surface area increased from 3.52 to 235m2 g−1 and the sorption capacity coefficient increased from 2.12 to 4.10. [Copyright &y& Elsevier]

Abstract: The widely existing fly ash and soot produced during the process of combustion, which are often known as waste but also an important source of black carbon (BC) in the environment, were treated by HCl and HF solution for this study, and recorded as FC and SC, respectively. A series of experiments were carried out to investigate the toxicity of pentachlorophenol (PCP) in sediment, influence of various BCs in sediment with different contents (0%, 0.5%, 1%, 2%, 5% and 10%) on the extractability and toxicity of PCP (50mg/kg), and toxicity of various BC in sediment. The results demonstrated that the PCP exposure to wheat seed exhibited a dose-dependent behavior, and the extractability and toxicity of PCP decreased with the increasing content of BC in sediment. The PCP extractable rate was significantly (P <0.01) influenced by the higher content of BCs. Noticeably, each BC had no toxic but stimulative effect on root elongation and early seedling growth. Furthermore, it was found that the inhibitive effect on the extractability and toxicity of PCP and the stimulative effect on root elongation and early seedling growth caused by SC were more evident than FC. [Copyright &y& Elsevier]

Abstract: To investigate the feasibility of using biochar to control organic pollutants in sediments, we extracted biochar from rice-straw combustion residues (RBC) and studied its adsorption ability and effect on seed germination ecotoxicity of pentachlorophenol (PCP). The results showed that the Freundlich and dual-mode models could describe all the sorption isotherm data well, and the log KOC values increased with increasing RBC content. With 50mgkg−1 PCP in the sediment, a significant seed growth inhibition (P <0.01) was observed. The addition of 2.0% RBC lowered the PCP concentration in the extraction liquid from 4.53 to 0.17mgL−1 and increased the germination rate and root length significantly. Furthermore, it was found that the addition of RBC had no toxic but stimulative effect on root elongation. Consequently, RBC could serve as a potential supersorbent for the remediation of organic pollution in situ. [Copyright &y& Elsevier]

Abstract: Rice straw charcoal, soot and fly ash (collectively termed “black carbon” or BC), which were found to widely exist in the environment and exhibit strong sorption of many organic compounds, were prepared for this study, and recorded as RC, SC, and FC, respectively. The characterization, sorption isotherm, and the effect of pH (from 3.0 to 9.0) on sorption capacity of each BC were investigated. It is demonstrated that RC possessed the largest surface area (234.9m2/g), the highest porosity (0.4392mL/g), and the largest amount of functional groups (2.995mmol/g) of all. All the Freundlich, Langmuir and Dual-mode model can fit the sorption data of each BC well. The pH value could apparently affect the sorption capacity of pentachlorophenol (PCP) to BCs, which reached maximum value at pH 4.0. Furthermore, in order to validate the effect of pH on desorption capacity, we designed sorption–desorption cycle experiments at pH 9.0 and then pH 7.0, and found that the effect of pH on irreversible sorption and hysteresis effects were significant. As pH value decreasing from 9.0 to 7.0, the irreversible sorption capacities for RC, FC, and SC increased, and the desorption hysteresis index (H) values of PCP increased approximately 3 times for each BC. [ABSTRACT FROM AUTHOR]