Hg: one of the most toxic heavy metal in the environment.

1. Effectiveness and mechanisms of mercury sorption by biochars from invasive Brazilian pepperat different temperatures Xiaoling Dong1, Lena Q Ma1*, Yingjia Zhu1, Yuncong Li1, and Binhe Gu2 Soil and Water Science department1University of Florida, Gainesville, FL 32611 South Florida Water Management District, West Palm Beach, FL 33411 Abstract • Mercury and cations analysis • The concentrations of mercury were analyzed by hydride generation atomic fluorescence spectrometry (HG-AFS).The concentrations of Ca2+, Na+, and K+ cations in the filtrate were measured by ICP-AES. Table 2. Effect of modification on Hg(II) removal by BP biochars after reacting with 50 mg/L Hg(II) for 24 h at pH 6.0. Characteristics and mechanisms of mercury sorption by biochars from Brazilian pepper (BP; Schinusterebinthifolius) through pyrolysis at different temperature (300, 450, and 600˚C) were investigated. The surface characteristics of BP biochars before and after Hg(II) sorption were examined with scanning electron microscopy-equipped with energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. The sorption process can be described by the pseudo-second order equation and Langmuir equation. The kinetic data suggested that Hg sorption was rapid initially fast and reaching equilibrium after 24 h. All biochars were effective in Hg sorption, with maximum sorption capacity being 28.6-41.0 mg/g and the sorption capacity decreasing as temperature increased. FTIR and modification results showed that carboxylic and amine groups were responsible for Hg sorption . Release of Ca2+, K+ and Na+cations confirmed the role of ion exchange for Hg(II) removal by BP biochars. Our results suggest that BP biochars can be used as an alternative sorbent to remove Hg from wastewater. Results Table 1. Properties of Brazilian pepper biochar derived from different pyrolysis temperatures (300-600C). (a) (b) (c) Introduction Fig.5.Ca2+, Na+, and K+ concentrations  (a, b, c) in solution before and after Hg(II) sorption onto BP biochars. • Hg: one of the most toxic heavy metal in the environment. • Brazilian pepper: the most aggressive, evergreen shrub-like tree in Florida. • Now it covers more than 700,000 acres in south and central Florida, as well as • many of the islands on the east and west coasts of the state. • Biochar: refers to charcoal produced from carbon-rich biomass, shows • great affinity for heavy metals. • Hg(II) was sorbed onto BP biochars, and after 24 h sorption process reached • equilibrium and the sorption capacity decreased with the pyrolysis temperature • (Fig.2.). • The efficiency of Hg(II) removal increased with the increase of pH (Fig.3). • FTIR analysis suggested that amine and carboxylic groups were involved in Hg(II) removal, and the modification experiment confirmed this result (Fig.3&Table 2). • Ca2+ ,K+ and Na+cations were released during Hg(II) removal by BP biochars and • those cations concentration increased with the increase of Hg(II) concentration • (Fig.5&Table 1). Objectives • Investigate the effectiveness of BP biochars in removing Hg from water via • sorption/desorption studies. • Evaluate the effects of various parameters including pH, initial Hg • concentration, and contact time on its effectiveness. • Determine the mechanisms governing Hg removal by BP biochars. Conclusions Fig.2. Effect of reaction time on Hg(II) removal by BP biochars after reacting with 10 mg/L Hg(II) for 24 h at pH 6.0. Fig.3.Influence of pH on Hg(II) removal by BP biochars after reacting with 20 mg/L  Hg(II) for 24 h. • The Hg(II)sorption by BP biochars was strongly pH-dependent. The higher the pH, the higher the removal efficiency. And the higher the pyrolysis temperature, the lower the removal efficient. • Hg(II) sorption by biochar can be described by the pseudo-second-order model and Langmuir model reasonably well, with sorption capacity being 28.6-41.0 mg/g . • FTIR analysis suggested that amine and carboxylic groups were involved in Hg(II) removal, and the modification experiment confirmed their participation. • Hg(II) removal was probably via ion exchange and complexation mechanisms. (a) Materials and Methods • Biochar preparation and characteristics • Brazilian pepper (BP) biochar was made at specified temperatures 300, 450, and 600˚C in a muffle furnace. The surface morphology, point zero charge and metal composition were measured. • Hg(II) sorption experiment • Batch kinetic study, isotherm study , effect of pH were performed with sorbent dose of 2 g/L at room temperature. • Fourier transform infrared (FTIR) analysis and Modification experiment • FTIR analysis was conducted to identify the function groups involved in Hg(II) removal. Modification experiment was performed to confirm the role of functional groups involved in Hg(II) removal . • Ca 2+, Na+, and K+ after Hg(II) sorption • The concentration of cations released after Hg(II) sorption were analyzed to identify weather ion exchange participate in Hg(II) removal. (b) Reference S.K. Das, A.R. Das, A.K. Guha, A Study on the Adsorption Mechanism of Mercury on Aspergillusversicolor Biomass, Environmental Science & Technology, 41 (2007) 8281-8287. J.-H. Yuan, R.-K. Xu, H. Zhang, The forms of alkalis in the biochar produced from crop residues at different temperatures, Bioresource Technology, 102 (2011) 3488-3497. C. Jeon, K. Ha Park, Adsorption and desorption characteristics of mercury(II) ions using aminatedchitosan bead, Water Research, 39 (2005) 3938-3944. (c) Acknowledgement Fig.4. Fourier transform infrared spectra of BP biochars (a, b, c) before and after reaction with 10 mg/L Hg(II) for 24 h at pH 6.0. • This research is supported in part by TSTAR and University of Florida.