Distribution and Accumulation of Major and Trace Elements in Gypsum Samples from Lignite Combustion Power Plant

Majda Pavlin,Peter Frkal,Milena Horvat,Maja Koblar,Andrej Stergaršek,Radojko Jaćimović

doi:10.4236/ajac.2018.912044

Majda Pavlin, Peter Frkal + Show 4 more

Open Access

https://doi.org/10.4236/ajac.2018.912044

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Abstract

Flue gas containing volatile elements, fine fly ash particulates not retained by particle control devices, and limestone are the most important sources of trace and major elements (TMEs) in wet flue gas desulphurization (WFGD) gypsum. In this study, samples of gypsum slurry were separated into fine and coarse fractions. Multi-elemental analysis of 45 elements in the different size fractions of gypsum, slurry waters and lignite were performed by k0-INAA (k0-instrumental neutron activation analyses). The study found that the volatile elements (Hg, Se and halogens) in the flue gas accumulate in the fine fractions of gypsum. Moreover, the concentrations of most TMEs are considerably higher in the fine fractions compared to the coarse fractions. The exceptions are Ca and Sr that primarily originate from the limestone. Variations of TMEs in the finer fractions are dependent on the presence of CaSO4·2H2O that is the main constituent of the coarse fraction. Consequently, the content of TMEs in the fine fraction is highly dependent on the efficiency of separating the fine fraction from the coarse fraction. Separation of the finer fraction, representing about 10% of the total gypsum, offers the possibility to remove effectively TMEs from WFGD slurry.

Highlights

Coal combustion is the major source of airborne Hg, Mo and Se, and is a significant source of As, Cr, Mn, Sb and Tl [1]
The data obtained for total elemental concentrations and corresponding uncertainties in Lignite samples (LIG) sample, limestone, slurry waters, bulk and various CF and FF of gypsum are presented in Table 1 and Table 2
The presence of trace and major elements (TMEs) in gypsum is primarily related to 1) small size fraction of fly ash not retained by the particle control devices, 2) volatile elements (e.g. Hg, Se and halogens) that are highly accumulated in the wet flue gas desulphurization (WFGD) with respect to coal 3) introduction of limestone as an additional source of TMEs (e.g. Mg, Ca, Sr) associated mostly with CF, 4) and the conditions present in a WFGD scrubber

Summary

Introduction

Coal combustion is the major source of airborne Hg, Mo and Se, and is a significant source of As, Cr, Mn, Sb and Tl [1]. The elements present in coal occur over a wide concentration range that varies according to the geochemical evolution of the coal deposits [3] [4] [5] [6] [7]. Based on their concentrations, chemical elements in coal are classified into three groups [8] with further division of trace elements according to their volatility [8] [9] [10] [11]. The finest fly ash particles contain larger amounts of (trace) elements, due to their greater surface to volume ratio [3] [8] [9] [10] [11] [14]

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