Effect of pH and Grain Size on the Leaching Mechanism of Elements from Recycled Concrete Aggregate
Using recycled concrete aggregate (RCA) as base course in pavement construction also requires the investigation on the potential environmental risk. In this study, leaching characteristics of major elements including aluminum (Al), calcium (Ca), iron (Fe) and magnesium (Mg), trace and minor elements including arsenic (As) and barium (Ba) from RCA under different pH conditions (pH~2–14) were investigated by laboratory batch leaching tests in accordance with the United States Environmental Protection Agency (USEPA) leaching method 1313. Geochemical speciation modelling by Visual Minteq was applied to determine leaching mechanisms of these elements. Results showed that leaching of Fe followed a cationic leaching pattern, where the elemental concentrations leached from RCA decreased with an increase in pH. Leaching of Al present the amphoteric pattern, and leaching behavior of Ca, Mg, As and Ba showed different leaching patterns, which is less pH dependent. Maximum leaching concentrations of the majority elements were measured at extreme acidic (pH ~ 2). The fine particles tended to leach more trace elements than sand and gravel-sized particles at pH > 10. Leaching of Al from all RCA samples are controlled by dissolution/precipitation of (hydr)oxides mineral solid phases. Leaching of Ba is controlled by witherite from pH of 8 to 10, and it seems to be controlled by barite at extremely alkaline pH condition (pH = 13).
KeywordsRecycled concrete aggregate Leaching Grain size pH Geochemical modeling
The National Science Foundation of China (NSF-China, 41701347), Sichuan Science and Technology Project (2016HH0084) and the Fundamental Research Funds for the Central Universities (A0920502051708-89) provided support for Dr. Jian-Nan Chen and Dr. Yi-Bo Zhang. This study was financially supported by the TPF-5 (129) Recycled Unbound Materials Pool Fund administered by The Minnesota Department of Transportation and Federal Highway Administration (FHWA) Recycled Materials Resource Center (RMRC). The findings and opinions in this paper are solely those of the authors. Endorsement by sponsors is not implied and should not be assumed.
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