Surface Chemical Characteristics of Coal Fly Ash Particles after Interaction with Seawater under Natural Deep Sea Conditions YANIV BRAMI, † BARAK HERUT,* ,‡ ALDO SHEMESH, † AND HAGAI COHEN § Departm ent of Environm ental Sciences and Energy Research, Weizm ann Institute of Science, Rehovot 76100, Israel, Israel Oceanographic & Lim nological Research, National Institute of Oceanography, Tel-Shikm ona, P.O. Box 8030, Haifa 31080, Israel, and Chemical Services Unit, Weizmann Institute of Science, Rehovot 76100, Israel The surface (0.2-0.5 nm) chemical characteristics of coal fly ash (CFA) before and after interaction with Mediter- ranean deep seawater was studied by X-ray photoelectron spectroscopy (XPS). Significantly lower values of Si, Ca, and S and higher values of Mg and Cl were found in the retrieved CFA as compared to fresh CFA. It is suggested that hydrolysis of the oxide matrixes results in an alkaline environment which rapidly leads to several chemical reactions. The two most important are (a) dissolution of the amorphous silicate and the calcium phases and (b) precipitation of Mg(OH) 2 -brucite. A depth profile of the retrieved CFA was measured by both line-shape analysis of the XPS spectra and by consecutive cycle of sputtering. The thickness of the brucite layer is estimated to be 1.3 nm. Introduction Power plants, which rely on coal as an energy source, have led to a management problem related to the storage and disposalofcoalflyash (CFA).The option ofdeep sea disposal wasrecognized asan attractive opportunityforcoastalpower plants (1, 2). However, an environmental concern may rise due to the potential availability of toxic elements (Cd, Pb, Zn, Cu, As, Se, and Cr) released from CFA to the marine environment. The leaching of elements from CFA into seawateriscontrolled bysolubilityprocesses(3, 4);therefore, identification of mechanisms governing the leaching pro- cesses is an important step for comprehending the role of CFAinteractions with seawater. To present, leaching ofCFA in seawater and in freshwater was studied under different conditions, such as pH, solid-to-liquid ratio, and exposure time (5-7). Many laboratory experiments and field mea- surements were performed to investigate bulk chemical variations due to the interaction between CFAand seawater (1, 2, 4, 7-9). These laboratory experiments had short duration and could not account for the effects of long-term aging and weathering processes that might occur under natural deep sea conditions. The comprehension of long- term aging and weathering processes that might occur to CFA is facilitated by utilizing surface sensitive techniques such as XPS (10, 11). Extensive studies using XPS for surface characterization of fresh CFA were conducted in the past (12-16). These studies suggested that volatilization -condensation mech- anisms may result in the enrichment of the elements Ca, P, S, and Mg on the CFAparticle surfaces. To the best of our knowledge, no studies have been carried out on changes in the surface chemical composition ofCFAparticles retrieved after a long duration under natural deep sea conditions. In the present study, CFA dumped to the southeastern Medi- terranean since 1982 was retrieved and its surface charac- teristics, chemical composition, and morphology were compared with the originalfresh CFAproduced at the power plant. XPS was used to characterize the surface chemical composition of the CFA particles. Scanning electron mi- croscopycoupled with energydispersive spectroscopy(SEM/ EDS)were used to identifyparticle morphologyand elemental composition of discrete particles. Experimental Section Since 1982,more than one million tons ofCFAwere disposed into a deep (1400 m) dump site located 70 km off the Israeli Mediterranean coast (7).CFAsamples were retrieved (RCFA) from the dump site during January 1995 on board of R/V Shikmona (Stations Aand P9). The temperature and salinity monitored at the sampling station were 13.70 ( 0.10 °Cand 38.68 ( 0.04 ‰ , respectively. Sediment samples containing CFA were sampled using a BX 700AL box corer and CFA pebbleswere retrieved usinga beam trawl.The exact exposure time of these samples to seawater is not known and is probably in the range of 1-3 years. The upper layer of the sediment (approximately1 cm)was mostlyfine grained CFA particles and aggregates which were picked up and stored with the pebbles in 4 °C prior analysis. The CFA physical characteristics are given in ref 7. Twenty RCFA aggregates (<2 cm diameter) were thoroughly washed with double distilled water.Their outer 2-3 mm was removed and sieved through 45 μm. Representative fresh CFA (FCFA) samples from the Hadera Electricity Power Station were used for comparison.These composite samplesrepresent an average of a period of a six-month period of production and were treated similarly to the RCFA samples. A further size fractionation to particles smaller than 25 and 5 μm was conducted for the representative FCFAand RCFAsamples by a conventional method using cylinders of 5 cm diameter and 80 cm long. The suspension was centrifuged at 2000 rpm, and <5 μm particles were separated from the suspen- sion. As given hereafter, to assess possible affect of this pretreatment on differential dissolution of certain phases we used Al as a conservative element. The particle size of each group was also confirmed by scanning electron microscopy (SEM) screening. X-ray powder diffraction (XRD) was used for the miner- alogical analyses. Particle morphology and bulk chemical composition were studied by Philips 505 SEM/EDX. Kratos Analytical AXIS-HS XPS was used to study the surface chemical composition of the particles. Atypical 0.5-0.2 n m surface layer was analyzed bya 2-mm-diameter beam which encompasseshundredsofparticlesand therefore represents an average composition of the surface layer. In the present study, a new sample holder was designed to solve the problems associated with the particles suspension. The sample holder was constructed ofgold-coated stainless steel *Corresponding author telephone: +972-4-8515202; fax: +972- 4-8511911; e-mail address: barak@ocean.org.il. † Department of Environmental Sciences and Energy Research, Weizmann Institute of Science. ‡ National Institute of Oceanography. § Chemical Services Unit, Weizmann Institute of Science. Environ. Sci. Technol. 1999, 33, 276-281 276 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 2, 1999 10.1021/es9805573 CCC: $18.00  1999 American Chemical Society Published on Web 12/10/1998