Search

Abstract: Chloride in fly ash from municipal solid waste incinerators (MSWIs) is one of the obstructive substances in recycling fly ash as building materials. As a result, we have to understand the behavior of chlorides in recycling process, such as washing. In this study, we used X-ray absorption near edge structure (XANES) and X-ray diffraction (XRD) to study the chloride behavior in washed residue of raw fly ash (RFA). We found that a combination of XRD and XANES, which is to use XRD to identify the situation of some compounds first and then process XANES data, was an effective way to explain the chlorides behavior in washing process. Approximately 15% of the chlorine in RFA was in the form of NaCl, 10% was in the form of KCl, 51% was CaCl2, and the remainder was in the form of Friedel''s salt. In washing experiments not only the mole percentage but also the amount of soluble chlorides including NaCl, KCl and CaCl2 decreases quickly with the increase of liquid to solid (L/S) ratio or washing frequency. However, those of insoluble chlorides decrease slower. Moreover, Friedel''s salt and its related compound (11CaO·7Al2O3·CaCl2) were reliable standards for the insoluble chlorides in RFA, which are strongly related to CaCl2. Washing of RFA promoted the release of insoluble chlorides, most of which were in the form of CaCl2. [Copyright &y& Elsevier]

To efficiently reduce and reuse fly ash from incinerators, we suggest trying a new alkaline reagent to neutralize the acid compounds in discharged gas from incinerators and reuse fly ash as the raw material in the cement industry. Normally the washing process includes a pretreatment method to remove chlorides to comply with the strict standards for cement. We examined chloride behavior in washing experiments by X-ray absorption near edge structure (XANES) and X-ray diffraction (XRD) for two kinds of fly ash: (1) fly ash collected in a bag filter with the injection of calcium hydroxide (Ca(OH)2) for acid gas removal (CaFA), and (2) fly ash collected in a bag filter with the injection of sodium bicarbonate (NaHCO3) for acid gas removal (NaFA). We found that the insoluble chlorides in both CaFA and NaFA combined calcium chloride (CaCl2), with some sodium chloride (NaCl) also possibly combined. Under some conditions, the combined CaCl2 and NaCl were released. In particular, when the liquid/solid ratio was greater than 3 or the washing frequency was doubled, less chlorine, insoluble chlorine, and CaCl2 were left in the residues of NaFA than in the residues of CaFA. As a result, it is desirable to use NaHCO3 as the alkaline reagent instead of Ca(OH)2 in the air pollution control system of incinerators for recycling fly ash as a raw material in the cement industry. [ABSTRACT FROM AUTHOR]